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Remote Monitoring Systems For Substructural Health Monitoring by Jonathan D. Collins A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Civil Engineering Department of Civil and Environmental Engineering College of Engineering University of South Florida Major Professor: Austin G. Mullins, Ph.D. Rajan Sen, Ph.D. William C. Carpenter, Ph.D. Date of Approval: June 26, 2008 Keywords: thermal, stra in, wireless, shm, sshm Copyright 2008 Jonathan D. Collins
Acknowledgements I would like to thank the Geotechnical and Structural Research Team at the University of South Florida, including Julio Aguilar, Dr. Mike Stokes, Danny Winters, and Dr. Gray Mullins. Without this team of extraordinary men, this would never have been possible. I would especially like to thank Mr. Carl Ealy and Dr. Gray Mullins for their help and guidance and th e opportunity to be inside the columns of the St. Anthony Falls Bridge in Minnesota. Honorable mention must be paid to th e iron-worker crews on the southbound pier of the St. Anthony Falls Bridge. Without their banter, working in sub-zero temperatures would not have been tolerable. Finally, the people in my life who always believed I could do something great: My parents, Alice and David Collins, my grandparents, Warren and Dorothy Slack, and most of all, my wife, Abby.
i Table of Contents List of Tables iii List of Figures iv Abstract ix Chapter 1 Introduction 1 1.1 Problem Statement 2 1.2 Research Scope 2 1.3 Thesis Organization 3 Chapter 2 State of the Practice 4 2.1 General Monitoring Systems 4 2.2 Case Study 6 2.3 Wireless Sensors for Health Monitoring 9 2.4 Fiber Optic Sensors for Health Monitoring 13 2.5 Current and Future Possibilities for H ealth Monitoring 16 Chapter 3 Voided Shaft Thermal Monitoring 32 3.1 Test Specimen Instrumentation 33 3.2 Test Specimen Construction 34 3.3 Monitoring System Instrumentation and Procedure 35 3.4 Results and Conclusions 36 Chapter 4 St. Anthony Falls Bridge Founda tion Monitoring 51 4.1 Phase I Thermal Monitoring 52 4.1.1 Construction and Instrumentation 53 4.1.2 Monitoring Setup and Procedure 55 4.1.3 System Results and Conclusions 56 4.2 Phase II Construction Load Monitoring 58 4.2.1 Construction and Instrumentation 59 4.2.2 Monitoring Setup and Procedure 61 4.2.3 System Results and Conclusions 65 4.3 Phase III Long Term Health Monitoring 67 4.3.1 Instrumentation 68 4.3.2 Monitoring Setup and Procedure 69 4.3.3 System Results and Conclusions 70
ii Chapter 5 Conclusions 104 5.1 Conclusions from Tested Systems 104 5.2 Future Work for I-35W Bridge Study 105 5.3 Possibilities for Remote Substructural Health Monitoring Systems 106 References 108
iii List of Tables Table 4-1: Overview of Monitoring System s for I-35W Bridge Study 63
iv List of Figures Figure 2-1: Standard Rotary Dial Gages 18 Figure 2-2: Pier EA-31 Site Map 19 Figure 2-3: Pier EA-31 Pile Instrume ntation Layout 20 Figure 2-4: Pier EA-31 Gage Failure Summary 21 Figure 2-5: Pier EA-31 Av erage Pile Tip Load Piles 1,7,10 22 Figure 2-6: Pier EA-31 Average Strain Change Pile 1 23 Figure 2-7: Pier EA-31 Average Strain Change Pile 7 24 Figure 2-8: Pier EA-31 Average Strain Change Pile 10 25 Figure 2-9: Wireless Data Collection and Transmit Setup 26 Figure 2-10: Train Crossing Br idge Causes a Strain Event 26 Figure 2-11: Bascule Bridge on SR-401N, Port Canaveral, FL 27 Figure 2-12: Locations and Types of Sensor s on Bascule Bridge 28 Figure 2-13: FRP Wrap Installation on Bri dge Superstructure 28 Figure 2-14: FOS Installation Beneath FRP Layers 29 Figure 2-15: FOS Installation Above FR P Layers 29 Figure 2-16: Measured Strain Induced on Bridge from Events 30 Figure 2-17: East 12 th Street Bridge, Des Moines, Iowa 30 Figure 2-18: Dedicated Host Computer near Bridge Site 31 Figure 3-1: Map of Voided Shaft Testing Site 38
v Figure 3-2: Voided Shaft Reinforcement Cage Instrumentation 38 Figure 3-3: Voided Shaft Central Casing Ce nter Tube Supports 39 Figure 3-4: Voided Shaft Thermocouples Inst alled in Central Casing 39 Figure 3-5: Voided Shaft Thermocouples on Outside of Central Casing 40 Figure 3-6: Voided Shaft Ground Monitoring Tube Installation 40 Figure 3-7: Excavation for Voided Shaft 41 Figure 3-8: Picking of Reinforcement Cage for Voided Shaft 41 Figure 3-9: Placement of Reinforcement Cage for Voided Shaft 42 Figure 3-10: Hanging of Reinforcement Cage for Voided Shaft 42 Figure 3-11: Picking of Central Casing for Voided Shaft 43 Figure 3-12: Placement of Central Casing for Voided Shaft 43 Figure 3-13: Voided Shaft Central Casing Stabilization 44 Figure 3-14: Double Tremie Concrete Placement 44 Figure 3-15: Outer Steel Casing Removal 45 Figure 3-16: Final Voided Shaft at Ground Level 45 Figure 3-17: Campbell Scientific CR1000 Data Logger 46 Figure 3-18: AM25T 25-Channel Multiplexer 46 Figure 3-19: Raven100 CDMA AirLink Ce llular Modem 46 Figure 3-20: PS100 12V Power Supply with R echargeable Battery 46 Figure 3-21: ENC12x14 Environmental En closure 46 Figure 3-22: Thermocouple Wire Connection to AM25T to CR1000 47 Figure 3-23: Remote Thermal Monitoring System for Voided Shaft 47 Figure 3-24: Battery Voltage as of 10/8/07 48
vi Figure 3-25: Battery Voltage as of 12/14/07 48 Figure 3-26: Thermocouple Data as of 11/12/07 49 Figure 3-27: Final Average Thermocouple Data for All Locations 50 Figure 4-1: Artists Rendering of I-35W Bri dge over Mississippi River 71 Figure 4-2: Event Schedule and Overlap of I-3 5W Bridge Project Phases 71 Figure 4-3: I-35W Bridge Shaft Reinforcem ent Cage Construction 72 Figure 4-4: I-35W Bridge Gage Levels on Drilled Shafts 72 Figure 4-5: Cable Bundles in Reinforcement Cage for I-35W Bridge 73 Figure 4-6: Top Section of Drilled Shaft for I-35W Bridge 73 Figure 4-7: Placement of Reinforcement Cage for I-35W Bridge Shaft 74 Figure 4-8: Conduits Running from Shafts to DAS Boxes 74 Figure 4-9: Lower Layer of Pier Footing Rein forcement for I-35W Bridge 75 Figure 4-10: Upper Layer of Pier Footing Reinforcement for I-35W Bridge 75 Figure 4-11: Thermal Monitoring DAS for I35W Bridge Shafts 76 Figure 4-12: 35 Watt Solar Cell Panel for I-35W Bridge Monitoring System 76 Figure 4-13: CC640 Jobsite Camera with Perspective Outlines 77 Figure 4-14: Sample Camera Shot from Close-Up Cam on I-35W Bridge 77 Figure 4-15: Data Logger Battery Voltage from I-35W Monitoring System 78 Figure 4-16: Concrete Mix Design for Drilled Shafts on I-35W Bridge 79 Figure 4-17: I-35W Bridge Southbound Pier 2 Shaft 1 Thermal Data 80 Figure 4-18: I-35W Bridge Southbound Pier 2 Shaft 2 Thermal Data 81 Figure 4-19: I-35W Bridge Shaft 1 Thermal Data from TCs and Thermistors 82 Figure 4-20: I-35W Bridge Shaft 2 Thermal Data from TCs and Thermistors 82
vii Figure 4-21: Pier 2 Southbound Footing Thermal Data from Thermocouples 83 Figure 4-22: Detail of Geokon 4911 Sister Ba r Strain Gage 83 Figure 4-23: VW Gage Instal led in Shaft Reinforcement Cage 84 Figure 4-24: Coupled VW and RT Gages 84 Figure 4-25: Reinforcement for 1 st Column Pour for I-35W Bridge Columns 85 Figure 4-26: Reinforcement at Mid-Section of Columns for I-35W Bridge 85 Figure 4-27: Longitudinal and Horizontal Column Reinforcement 86 Figure 4-28: Coupled Gage Installed in Corner of Column 86 Figure 4-29: Gage Wires Tied and Secured 87 Figure 4-30: Gage Wires Exiting Through Conduit 87 Figure 4-31: Gage Wires Connection to System 2 88 Figure 4-32: Construction Load Monitoring Systems 88 Figure 4-33: Annotated Graph of Shaft Construction Loads and Events 89 Figure 4-34: I-35W Bridge Southbound Pier Footing Concrete Placement 90 Figure 4-35: I-35W Bridge Lift 1 Column Concrete Placement 90 Figure 4-36: I-35W Bridge Interior Column Lift 2 Formwork Placement 91 Figure 4-37: I-35W Bridge Exte rior Column Lift 2 Formwork Placement 91 Figure 4-38: I-35W Bridge South Perspective CC640 Field Camera 92 Figure 4-39: I-35W System 1 Battery Voltage over Time 92 Figure 4-40: I-35W System 2 Battery Voltage over Time 93 Figure 4-41: I-35W System 2 Battery Voltage Compared to System 3 93 Figure 4-42: Main Page of St. Anthony Falls Bridge Study Website 94 Figure 4-43: Secondary Page of St. Anthony Fa lls Bridge Study Website 94
viii Figure 4-44: I-35W Bridge Pier 2 Interior Column Strain Data with Links 95 Figure 4-45: I-35W Bridge Pier 2 Exterior Column Strain Data with Links 95 Figure 4-46: I-35W Bridge Pier 2 Shaft 1 All Le vels Strain Data with Links 96 Figure 4-47: I-35W Bridge Pier 2 Shaft 2 All Le vels Strain Data with Links 96 Figure 4-48: I-35W Bridge Pier 2 Interior Column Strain Data 97 Figure 4-49: I-35W Bridge Pier 2 Exterior Column Strain Data 98 Figure 4-50: I-35W Bridge Pier 2 Shaft 1 A ll Levels Strain Data 99 Figure 4-51: I-35W Bridge Pier 2 Shaft 2 All Levels Strain Data 100 Figure 4-52: Superstructure Gage Locations I 101 Figure 4-53: Superstructure Gage Locations II 102 Figure 4-54: Superstructure Gage Locations III 103
ix Remote Monitoring Systems for Substructural Health Monitoring Jonathan D. Collins ABSTRACT Remote Wireless Monitoring Systems have made a large impact in the area of Structural Health Monitoring (SHM). Ho wever in the specialized sub-field of Substructural Health Monitoring (SSHM), remo te monitoring techniques have not made as much headway. First, monitoring system s are often retrofitted onto a structure. Therefore it is much harder to retrofit the substructure of a bri dge or building. Second, many foundation elements such as driven piles or auger-cast piles are constructed in a way that makes installation difficult or can severely damage the sensing materials. This thesis presents two case stud ies of Remote Monitoring Systems for Substructural Health Monitoring applications that were carried out by the Geotechnical Research Department of The University of South Florida. The first is a thermal monitoring system for a Voided Shaft study. Th e second is a thermal, construction load, and ongoing health monitoring system of the St. Anthony Falls Br idge in Minnesota. Results show that the systems that were used provide adequate data collection, data storage, and data transmission. Furtherm ore, this data is easily analyzed and provided for public or private use on a de dicated website, which provides a fully automated and remote Substructural Health Monitoring System.
1 Chapter 1 Introduction As a Civil Engineering application, remo te monitoring has not yet made a great breakthrough into the field. However as a res earch and development tool, its benefits are finally coming to a realization. In all walks of life there is a push for our society to become wireless. Therefore it increasingly be comes a necessity for the Civil Engineering profession to lead the way in wireless. This will come in the area of remote structural health monitoring. Remote monitoring, at its most basic, provi des the user with a way to collect data from an event of particular interest, such as a foundation capacity test or ongoing thermal recording, and then transmit that collected data to another lo cation, such as a database or spreadsheet file on a computer. This concept can be taken one step further by introducing limits on the data collector for alerting us ers or programming triggers on the data collector to initiate retroactive data collection and transmitting. Remote monitoring can be used for many different Civil Engineering applications, from quality assurance in cons truction to ongoing health verification and much more. Remote monitoring can and will pr ovide assurance to engineers and society as a whole that the infrastructure that we a ll rely on will carry us safely into the next generation. Furthermore, as new technology continues to upgrade daily, the cost and
2 effectiveness benefits of remote monitoring continue to increase. Many times, yesterdays technology is more than sufficient for the needs of the project, providing us with exceptional technology at yester days prices. This is a la rge reason why the move to remote monitoring is making such progress. 1.1 Problem Statement As a civil engineering tool, remote mon itoring is a priceless benefit for health monitoring of structural members. As of now, the most common monitoring technique for inspection bridges is by visual inspec tion. By FDOT and FHWA standards, every bridge is required to undergo a visual inspection once every two years. While this method is satisfactory for structurally sufficient, non-critical structures, it does not provide a reliable way to determine the actual hea lth of a structure. By providing a remote monitoring system, a bridge can be monitored in real-time at a remote location. This is a way to reduce man hours, as well as provide more accurate results and up-to-date data that can assess the structural integrity of a member, not just its visual appearance. 1.2 Research Scope This research proposes the use of wire less communication an d internet systems technologies as a means of providing remote monitoring capabili ties for structural members or systems for agencies such as state DOTs and the FHWA. However, the use of these technologies as descri bed herein would not be limited to the use as needed by these agencies. The original intent of th e research was not to determine the best technology to carry out the project, but ra ther to provide examples of monitoring
3 procedures and providing data from a variet y of tests which were monitored using this system. Another focus of this res earch was to provide a numb er of different monitoring techniques that could be applied to a stru ctural member to be monitored throughout its life. This included sensors and devices to provi de data related to temperature, load, and strain as well as video recordings. All of these parameters are considered vital for the determination of structural he alth of a member or system. 1.3 Thesis Organization This thesis consists of 5 chapters. Chapter 2 is a summary of the state of the practice of Structural Health Monitoring in general, with an emphasis placed on Substructural Health Monitoring, and the ability to convert current wired systems into wireless. Chapter 3 is an in-depth look at a case study that was carried out on an innovative type of drilled shaft. This was where the original Remote Monitoring System was first implemented. It summarizes the successes and learning experience s gained from this project. Chapter 4 is a look at the culmination of all the work on th is project. It reviews the shortand longterm monitoring procedures implemented on a bridge in Minnesota. This section will explain in detail the constr uction, setup and instrumenta tion, and monitoring procedure and results for a full-scale Remote Structur al Health Monitoring System. Chapter 5 will summarize the main discoveries made throughout the project and will present conclusions and recommendations fo r future work in this area.
4 Chapter 2 State of the Practice From an investigation into the state of th e practice of structural health monitoring (SHM), it is seen that there are a number of different monitoring systems and techniques. All of them have their pros and cons, but each can be useful to a certain degree. At the moment, most of the advances in SHM ha ve been made in the monitoring of the superstructure elements of bridges and ot her structures. However the importance of substructure health monitoring ( SSHM) can not be underestimated. Since a great deal of the modern technology of SHM is already widely used and documented as it pertains to superstructure monitoring, this review of the state of the practice will primarily focus on common t echnology and its practicality for use in a SSHM system. 2.1 General Monitoring Systems Monitoring systems range widely in thei r functionality, cost applied technology and monitoring approach. A system generally contains three components: a measuring device, a method of reading that device, and a method of storing the measurements taken. Depending on the complexity of the measurem ent being taken, the measuring device and readout component may be one and the same such as dial gages or pressure gages
5 (Figure 2-1). These devices convert a meas urement parameter into mechanical gage movement. These devices can be considered the most basic of transducers as they transfer one physical aspect into another. Virtually all types of measuremen ts have specialized devices to read that particular occurrence (i.e. time, displacement, velocity, acceleration, load, pressure, frequency, EMF, light inte nsity, strain, sound inte nsity, x-rays, voltage, inductance, capacitance, and more). For most measurement types, there are numerous ways to take that measurement which in turn dictate the capabilities and/or limitations of a monitoring system. The most basic systems use fully manual devices and readouts (e.g. dial gages, proving rings, pressure gages, etc) coupled with manual record keeping. The limitations imposed on this method by requiring physical on-site personnel (reco rding/storage rate, man-hours, and travel) is in some ways o ffset by the unforeseen observations and the ability to react to and record unplanned sec ondary happenings. The most exotic systems use complex measurement devices requiring s ophisticated readout units coupled with multifunction data acquisition systems capable of sending the recorded data via cellular or satellite communications. These systems are often enabled to accept remote configuration/scheme changes, are self-powered or self contained, and require little to no site visits. The most extreme cases of this type of system would likely be used by NASA for space exploration, as it is impossible to access the unit during use. Aside from the obvious cost, these systems are rarely adaptable to unforeseen occurrences. For SHM and SSHM applications, some mid-range systems can be selected to provide a balance between equipment cost and required on-site man-hours, which will allow most projects to be affordable.
6 2.2 Case Study A study was done by Shannon & Wilson, Inc. along with the Federal Highway Administration (FHWA), the Washington State Department of Transportation (WSDOT), the City of Seattle, and the Bridge Desi gn Team on the West Seattle Freeway Bridge (Shannon & Wilson, 1982). It presents a good example of SSHM for the structural elements of a bridge pier during construction of the bridge as well as data collection over time. The West Seattle Freeway Bridge wa s built between 1981 and 1984. The original bridge was struck by a freighter in 1978 and was deemed inoperable as a result of the incident. The goal was to advance the state-of -the-art of pile group design and analysis, and the information collected would be us ed in increasing pile group efficiency. The City of Seattle author ized the use of instrumentat ion on Pier EA-31, which is a single column pier that s upports the eastbound approach ramp from Spokane Street near the East Waterway and the Duwamish River (Figure 2-2). Shannon & Wilson, Inc. designed, specified and installed the instrume ntation that was reviewed by the FHWA, the City of Seattle and the Bridge Design Team. As stated above, the purpose of the project was to improve the state-of-the-art of pile group design and analysis. This would be done by collecting information regarding the load distribution amongst the pile group, the load transfer from the piles to the soil, the portion of the load transferred from the pier footing to the piles, and the settlement of the pier footing. Furthermore, the results gathered from this data were compared with theoretical predictions that w ould either validate the theoretical models or allow for the modification of those models.
7 In order to provide measurements for th e above mentioned data collection criteria, measurements were selected as follows: First, pile tip load was measured, as wells as the load at six elevations along the pile, to dete rmine the individual pi le load distribution. A load cell placed at the pile tip permitted direct measurement of the load. Second, six telltale rods were in stalled on each pile to determine th e pile tip displacement. The pile deformation as measured by the rods was conve rted to strain and used as a check. Third, strain gages were installed at the top of the piles which provided information of the load transferred from the pier footing to the individual piles. Fourth, settlement of the pier footing was measured by using a precise surv eying measurement at the four corners of the footing. Fifth, soil settlement below the pi er footing and within the pile group was measured to determine the soils reaction to th e loading and the subse quent deformation of the piles. In total, three of the 12 piles were instru mented with a load cell at the pile tip, six elevations of strain gage pair s, and a five position telltale extensometer (Figure 2-3). Data from the instrumentation was collected in the field using portable manual readout units and recorded on field sheets. During construction, the measurements were made at irregular intervals dependent on accessibility and other constraints du e to the construction progress. The instruments were monitored as each significant phase of construction was completed as well to provide realistic data fr om the construction process. Instrumentation monitoring was conducted by Shannon & Wils on engineers throughout construction and continued through 1987, five years after start of construction. Data was again collected in 09/1988, 09/1999, and 10/1993. Two additional sets of data were taken in 1999 and 2002, which extended the period of monitoring to 20 years. The report by Shannon & Wilson
8 presents a summary of the existing working ga ges, as well as the date at which failed gages were considered to be no longer working (Figure 2-4). As reported, all pile tip load cells are functioning after 20 year s of service, with the exception of one transdu cer from pile 7, which was damaged during pile driving. From the data collected in 2002, the average lo ad for all three piles was 100 tons with a maximum deviation of approximately 11% (Figur e 2-5). This suggests that all 12 piles in the pile group are carry ing approximately the same load, wh ich is assumed in typical pile group design. During the instrumentation phase, pairs of strain gages were installed into the three monitored piles at six different levels along the pile. This provided 12 gages in each pile for a total of 36 strain gages. All of these gages were located beneath the groundwater level, and 17 of these gages were no longer functioni ng after 20 years of service. However, all the gages were reported to have worked at least until October of 1987, which provided 4 years of data collecti on. Since all of the gages were installed below the groundwater level, it is suggested that their failure was due to the water resistance of the system. The data from the strain gages that were still in commission were plotted over time (Figures 2-6 through 2-8). For piles 1 and 10, the average strain change in the pile was between -300 and -500 micro strain, with pile 1 being on the higher end of that range. However for pile 7 the average strain change in the pile was approximately -225 micro strain. This suggests th at the piles farther aw ay from the center of the pile cap, where the column is sitting, experienced more strain change, likely due to bending. The gages installed at th e top of the other piles as we ll as the strain gages in the column were all still functioning after 20 years.
9 The conclusions of this study show that SSHM using wired gages is extremely useful. With the advances in th e durability of data collecti on and monitoring systems, it is likely that this same system, if installe d today, would not have the number of failed gages. While this study required a worker to be on-site to record the data, the usefulness of the instrumentation far outweighed the cost of the man-hours required. While the technology used in this study is somewhat out dated, the information gleaned from this study is highly useful in t odays monitoring systems. 2.3 Wireless Sensors for Health Monitoring Wireless systems use basically the same m easurement devices (or transducers) as wired systems, but replace the lead wires w ith a transmitter and receiver system. Wire costs range between $0.4/ft to $1.0/ft per ga ge installed. Transmitters, like data logging equipment, are limited by their sampling and transmission rates, meaning higher reading rates come at higher costs with an up per rate limit in the range of 5-10k samples/sec/channel. Transmitter/receiver systems can cost thousands of dollars per channel depending on the required transmission/ sampling rate. The cost comparison of wireless to wired systems is generally site specific, but leans towards wired systems. However, in the case of moveable structures or mechanical devices, slip rings or other features which allow the movements of the wi res are required which tend to tip the scales in favor of wireless systems. Wireless sensors for SHM systems are being used more frequently as the technology becomes more widely available. Since no wires are required between the gages and the data acquisition system, instal lation time and those costs associated are
10 reduced as compared to traditional wired systems. Typically, wireless sensors are installed over an entire structure to get a full mapping of the desired measurement (i.e. stress, strain, displacement, temperature, ve locity, etc.) across the entire structure. A wireless data acquisition system collects the data sent back from these sensors and either stores the collected data to a data logger or is sends it wirelessly using a modem to a remote site. A study by Arms et al. introduced the idea of a SHM system in which even the data acquisition software could be reprogram med remotely. The goal is that one should be able to alter the operating parameters of a monitoring system, such as sampling rate, triggering parameters, downloading intervals, etc., from a remote location and therefore never have to go back to the site after initial in stallation. This provides a fully remote monitoring system in which all the parameters of the data logging and collection can be altered from a separate location (Arms et al., 2004). The wireless transmittable gages were installed on the existing structure at main points of interest. Wireless sensors received transmitted data and the data was uploaded to an on-site laptop (Figure 2-9). The laptop transmitted the data through a cellular uplink to the base station. From this base station, the software that was running on the laptop could be altered to change the data collection parameters. The software could also be altered with trigger parameters so that the system could be sleeping, but would wake up when an event occurred, such as a train cros sing the bridge, that in creased the change in strain levels (Figure 2-10). While this provides for a completely wireless system, its use as a SSHM system is not as probable. For installa tion in the deep foundation sy stem, wireless sensors would
11 have to be extremely powerful to transm it data wirelessly th rough surrounding soil, sometimes at depths upwards of 100 feet. Sensors capable of this would most likely be expensive enough to negate th e cost savings from not dealing with wired sensors. Furthermore, sensors used for reinforced concrete structural elements can provide much better data when installed within the concrete member where the reinforcement is located. Once again, a typical wireless sensor would not have the capability to transmit signals through hardened concrete. However the wireless data acquisition system could still be used with no obstructions. A second study by Susoy et al. researched the development of a standardized SHM system for the movable bridges in Flor ida. The assumption was that due to the multitude of elements, movable bridges are more prone to damage and deterioration and that the typical visual inspection as re quired by FHWA is not adequate. The study detailed the SHM system that was instal led on the SR-401N Bascule Bridge over the Barge Canal in Port Canaveral (Figure 2-11). A detailed finite element analysis was run to determine the probable locations for stress concentrations on the bridge. Once this was complete, wireless transmitting strain gages were mounted on the bridge in these locations (Figure 2-12). The st rain sensors transmitted their data wirelessly to the installed data acquisition system and the data was logged on a field computer also installed on-site (Susoy et al., 2006). For this study, the wireless sensors were almost a necessity, due to the type of project. Installing wired sensor s on a movable bridge could pr ove to be quite difficult and could cause damage to the wires. No menti on was made concerning the accessibility of the data once it was collected, so it is assume d that the data was downloaded by a worker
12 sent to the site. However once again, this st udy was based on the idea of wireless sensors for the monitoring system, and therefore woul d have the same difficulty translating to SSHM as the Arms 2004 study. A final study by Watters et al. introdu ces the idea of a special design for a wireless sensor capable of de tecting threshold levels. The se nsor is coupled with radiofrequency identification (RFID) chip. The sensor is read by scanning the system with a radio-frequency (RF) transceiver. The RF tr ansceiver awakens the RFID chip to power the sensor to collect data. Once the data is collected, the RFID chip transmits the data back to the transceiver to be read (Watters et al., 2001). This study focuses on the use of the sensor to determine whether certain data may have crossed a threshold, namely chloride ingr ess into reinforced c oncrete structures. A particular threshold is set and then the system will read the data and determine if the threshold has been met. This system is extrem ely useful for data that does not need to be streamed. For chloride intrusion into reinforced concrete structures, the critical point at which the chloride concentration is reached c ould take years to be met. Therefore, a DAS capable of collecting and logging data at a high rate is not needed. In typical concrete inspection, a core sample of the concrete deck must be taken and then analyzed in a lab. With this technology, a sensor can be embedded into a structure and then routinely checked at a predetermined interval. Furthermore, the trends can be plotted over time to help owners and engineers predict when the ch lorine intrusion will reach a critical level. The capability to send an alert when a certa in threshold level is reached would be extremely useful in bridge monitoring. If an alert was programmed into the transducer that would react when a certain level is met, it would allow authorities to react and make
13 a decision about keeping a bridge open or closing it down depending on the severity of the event, possibly saving lives. While this is a useful system for data that need only be monitored over long intervals, from a strict SHM point of view the system would not be beneficial for structures loaded with highly irregular or dynamic loading, su ch as a bridge. The sensors for a bridge SHM system would need to be read and have the data collected and stored at a relatively high rate in order fo r the owner or engineer to de termine what is happening to the structure during its service life. 2.4 Fiber Optic Sensors for Health Monitoring With the recent advances in the teleco mmunications field with fiber optics, the interest in fiber optic sensors (FOS) has increased and has made way for extremely powerful new sensors to be used for SHM. FOSs are used by sending light beams through the fiber optic cable at regular intervals a nd measuring the return time. When the crosssectional area of the cable changes, the retu rn time changes, and this change in return time can be related to engineering parameters (i.e., strain, displacement) of the structural member to which they are attached. They are co nsidered to be beneficial because they are relatively immune to interference from radio fr equencies, electric or magnetic fields, and even temperature differences. A study by Udd et al. introduced the use of FOS in existing structures. The paper introduces the use of single axis fiber grati ng strain gages for the use of non-destructive evaluation of existing structures. The benefits of these are said to include a long service life and can be installed in long gage lengths providing more accurate results. There was
14 nothing in the study that related to remote or wireless monitoring. The study was instead focused on the sensitivity of the gages as well as the installation requ irements of working on an existing structure. In this case, the bridge required structur al strengthening in order to accommodate increased loads on the structures that were not expected at the time of construction. The bridge was strengthened using FRP composites th at would not alter the look of the bridge while still providing increased st rength (Figure 2-13). The fiber grating strain gages were installed embedded into saw cuts in the botto m of the bridge girders, as well as on the outside of the adhered FRP coating (Udd et al., 1999) (Figures 2-14, 2-15). This study, again, focused primarily on the monitoring of the bridge superstructure, but the FOS could have been in stalled just as easily to the pile foundation of the bridge. This would have provided data to show how the bridge foundation reacts to the same loads that are visible in the data from the superstructure. The sensors proved to be extremely sensitive. The gages were able to detect not only small cars crossing the bridge, but also, on one occasion, the effect of a single person running out to the center of the bridge, jumping up and down 5 times, and th en walking back off the bridge (Figure 216). Furthermore, gages could easily be installed embedded w ithin the structure as well as applied to the exterior of the structure with adequate results from each installation. FOS would be helpful in a SSHM system because of their relative immunity to temperature effects. Typically, bridge f oundations are designed with mass concrete elements, such as drilled shafts or piles fo r the subsurface foundation, a shaft or pile cap, and large concrete columns. The temperature changes that can take place inside these mass concrete elements are quite large. Typi cal resistance type or vibrating wire gages
15 can show large amounts of strain on a mass c oncrete element just due to temperature when the element is otherwise unloaded. Therefor e, if a sensor were able to be unaffected by these temperature changes, it would greatly aid in the simplification of the conversion from strain to load. A second study by Hemphill studies the marriage of wireless technology with Fiber-Optic sensors. It proposed and tested the idea of a fully integrated, continuous wireless SHM system for the East 12 th Street Bridge in Des Moines, Iowa (Figure 2-17). Fiber Bragg Grating (FBG) strain sensors were installed at 40 diffe rent locations on the bridge. The data collector scans the FBG sensors, and then transmits the data wirelessly to a dedicated computer in a secure facility close to the site (Figure 2-18). The data was stored as a data file and automatically upl oaded to an FTP site. When this site was accessed, the data file was downloaded and deleted from the FTP site to make room for the next data file. This data was compiled a nd processed and then pos ted to a website that allowed users to view real-time strain data along with real-time streaming video of the bridge (Hemphill, 2004). This system is useful because it can provide the end user with simple, easy to follow data viewing that can easily be mon itored. With the addition of the real-time streaming video, a data monitor can simply l ook at the data and compare it with the live traffic on the bridge and make the needed corr elations to the loadi ng on the structure. The wireless transmitting of the data is also usef ul because it cuts down on the man-hours that are required to go to the site and download th e data from the collection system, which can be time consuming and expensive. As stated ab ove, this system is very efficient and has very few drawbacks, if any. The fiber optic strain gages could be installed in the
16 substructure as well as on the superstructure, and there are really no limiting factors to the system. 2.5 Current and Future Possibilities for Health Monitoring A report by Weyl studies the proposal for a full-scale Structural Health Monitoring system for the Indian River Inlet Bridge in Delaware. The design of the SHM system was fully integrated throughout the design phase of the project so that it would fit seamlessly with the construction phase. The following types of gages will be installed throughout the bridge: Vibrating wire strain gages, weld able foil strain gages, accelerometers, GPS sensors, load cells, line ar potentiometers, corrosion monitors and more. This combines for a total of 240 sensors, 11 DASs, and 39 Data Loggers (Weyl, 2005). The project will be carried out in thr ee phases. Phase 1 will take place during construction to determine live construction loads. Phase 2 will take place immediately after bridge construction to dete rmine the initial response of the bridge to traffic, thermal, and wind loading. Phase 3 will take place during the intended service life of the bridge to compare against the data collected during Phase 2 (Weyl, 2005). Finally, a web-based user interface will be programmed to present data in an easy to read and understand format that will be accessible to Delaware DOT and those that worked on the project. At the time of this re port, there is no data to report from this project. It is currently in th e preliminary construction phase. This project is a very good example of the future possibilities that Structural Health Monitoring holds for the sustainabi lity of the nations infrastructure. While
17 integrating the monitoring system fully in the design phase of the project, the construction is not held-up, nor is the monitori ng system held back. The data that will be collected from this system can be archived as useful data for the history of the bridge and will most likely be very useful in the determination of any possible problems that might take place in the distant future. This particular study involved a very high number of sensors, gages, and data acquisition systems for the full SHM system, but it is still very similar to the proposed monitoring for the I-35W St. Anthony Falls Bri dge monitoring system that is studied in this report. The use of common everyday tec hnology, such as the dedicated website that provides certain users with real-time data from the bridge, coupled with the advanced technology of resistance and vi brating wire strain gages wi ll propel Structural Health Monitoring and Substructure Health Monitoring into the next phase.
Figure 2-1: Standard Rotary Dial Gages. 18
Figure 2-2: Pier EA-31 Site Map. (Shannon & Wilson 2002) 19
Figure 2-3: Pier EA-31 Pile Instrumentation Layout. (Shannon & Wilson, 2002) 20
Figure 2-4: Pier EA-31 Gage Failure Summary. 21
Figure 2-5: Pier EA-31 Average Pile Tip Load Piles 1,7,10. (Shannon & Wilson, 2002) 22
Figure 2-6: Pier EA-31 Average Strain Change Pile 1. (Shannon & Wilson, 2002) 23
Figure 2-7: Pier EA-31 Average Strain Change Pile 7. (Shannon & Wilson, 2002) 24
Figure 2-8: Pier EA-31 Average Strain Change Pile 10. (Shannon & Wilson, 2002) 25
Figure 2-9: Wireless Data Collection and Transmit Setup. (Arms et al., 2004) Figure 2-10: Train Crossing Bridge Causes a Strain Event. (Arms et al., 2004) 26
Figure 2-11: Bascule Bridge on SR-401N, Port Canaveral, FL. (Susoy et al., 2006) 27
Figure 2-12: Locations and Types of Sensors on Bascule Bridge. (Susoy et al., 2006) Figure 2-13: FRP Wrap Installation on Bridge Superstructure. (Udd et al., 1999) 28
Figure 2-14: FOS Installation Beneath FRP Layers. (Udd et al., 1999) Figure 2-15: FOS Installation Above FRP Layers. (Udd et al., 1999) 29
Figure 2-16: Measured Strain Induced on Bridge from Events. (Udd et al., 1999) Figure 2-17: East 12 th Street Bridge, Des Moines, Iowa. (Hemphill, 2004) 30
Figure 2-18: Dedicated Host Computer near Bridge Site. (Hemphill, 2004) 31
32 Chapter 3 Voided Shaft Thermal Monitoring The first study conducted during the period of this research involved the thermal monitoring of a drilled shaft. Floridas brid ge substructures have continually grown in size due to the high demand of larger and larger bridges to accom modate the growing population. Typically, drilled shaf ts were not considered to behave as a mass concrete element due to their smaller size (usually no gr eater than 4 ft. in diameter). However with the increase in size of today s bridges, drilled shafts are more and more acting as mass concrete elements (such as the 9ft. diameter shafts for the Ringling Causeway Bridge in Sarasota, FL), yet are slipping through the mass concrete specificat ions without special review. One of the problems associated with mass concrete elements is the extremely high temperatures that occur during the conc rete curing process. Due to the high heat experienced due to hydration reactions, cracking can occur in the concrete shaft. This, in turn, could translate to a loss in the stre ngth of the foundation, potentially creating a hazard to human life. Therefore, the Civil Engineering Research department at the University of South Florida proposed the idea of construction of dr illed shaft with a full length centralized void to mitigate the mass concrete effects exhibited by the foundation element.
33 This section of the report will focus on the remote thermal monitoring procedure that was used for the research done on th e USF Voided Shaft Research project. Of particular interest will be the installation and instrumentation of the drilled shaft, the thermal monitoring procedure and a review of its efficacy, and th e results from the remote thermal monitoring system and its indi vidual parts. More emphasis will be placed on the actual monitoring procedure than the results from th e voided shaft; however these thermal results will be presented in a summary. 3.1 Test Specimen Instrumentation The testing site for the thermal monitoring of the voided shaft will take place at R.W. Harris, Inc. in Clearwate r, FL (Figure 3-1). Prior to the construction of the drilled shaft, the instrumentation for the thermal m onitoring was put into place. The first step was the instrumentation of the rebar cage wh ich would be installed in the shaft. The reinforcement cage was built using 36 longitudina l bars with 26 #5 stirrups at 12 inches on center. The cage was equipped with 9 26 ft long, 2 inch Schedule 80 PVC pipe for thermal testing (Figure 3-2). On three of these tubes, at 120 degree spacing from each other, thermocouples (TCs) were placed at the top, middle, and bottom of the tubes to provide readings from all around the shaft. Th e inner steel casing (needed to provide the central void in the shaft) was outfitted with 3 cross-bar support s welded to the interior of the casing which allowed for a central tube to be run thr ough the center of the void for thermal integrity testing (Fi gure 3-3). TCs were also placed at the top, middle, and bottom of each side of the inner casing, sp aced 120 degrees away on the cross-bars, as well as attached to the top, middle, and bottom of the central tube (Figure 3-4). More TCs
34 were placed at the top, middle, and bottom of the outside of the inner casing (Figure 3-5). In the surrounding soil, ground monitoring tube s were installed at Shaft Diameters (Ds), D, 1D and 2Ds away from the edge of the shaft (Figure 3-6). TCs were also installed with the tubes at these locations. 3.2 Test Specimen Construction The voided shaft was constructed at the R.W. Harris test site on September 25, 2007. The entire process was broadcast via we bcam from the USF geotechnical webpage for those who were unable to visit the cons truction site. Records of the construction sequence, thermal testing, and long-term thermal monitoring were posted and updated every 15 minutes to http://geotech.eng.usf.edu/voided.html A 9ft diameter drilled shaft with a 4 ft diameter central void was constr ucted. The first step was the excavation. An oversized surface casing of 10 ft in diameter and 8 ft in length was embedded 7 ft into the soil. Excavation was carried out in the dry c ondition with a 9 ft diameter auger for the first several feet. After that polymer slurry was introdu ced into the excavation for stabilization. The excavation proceeded without issue do a depth of 25 ft (Figure 3-7). A clean out bucket was used to scrape the bo ttom of the excavation of debris immediately after the auger and then agai n after a 30 minute wait period. The reinforcement cage was picked at two locations to avoid excess bending (Figure 3-8). Locking wheel cage spacers we re placed at the top and bottom of the reinforcement cage to maintain 6 inches of clear cover (Figure 3-9). The reinforcement cage was hung in-place during the pour so that the finished concrete would be level with the top of the cage (Figure 3-10).
35 The central casing to create the fu ll length void was actually 46 inch outer diameter steel casing that was 30.5 ft long. It was set into the center of the excavation with a crane (Figures 3-11 and 3-12). The self -weight of the steel casing penetrated the soil to about 3 to 6 inches. This prevented the concrete from entering the void area. To prevent the top of the inner casing from shifting during the initial concrete pour, a backhoe bucket was used to hold the top of th e casing steady (Figure 3-13). A double tremie system was used to place the concrete on oppos ite sides of the excavation (Figure 3-14). Concrete specifications were a standard 4000 psi, 8 inch slump, #57 stone mix design. During the concrete placement, concrete level at three points around the shaft was measured to ensure concrete was flowi ng around the void and through the reinforcement cage. The temporary surface casing was removed after final concrete placement (Figures 3-15 and 3-16). 3.3 Monitoring System Instrumentation and Procedure Once the construction of the voided shaft was complete, all the thermocouple (TC) wires were accesses through the tubes so they could be attached to the data collection system. The entire remote monitoring system is made of a number of parts: A Campbell Scientific CR1000 data logger, an AM25T 25-channel multiplexer, a Raven100 CDMA AirLink Cellular Modem, PS100 12V power supply and 7Ahr rechargeable battery, a 12W solar cell panel from Unidata, and a large environmental enclosure to protect all the materials from the elements (Figures 3-17 through 3-21) The total cost of the system, including all equipment and ongoing services was approximately $4,500. The TC wires were connected to the multiplexer as there were not enough channels on the
36 CR1000 to read all of the TCs. The multip lexer was then connected to the CR1000 (Figure 3-22). Loggernet, the data collecti on software, was pre-installed into the CR1000 and setup to monitor the system. The data co llection system was e quipped with the solar panel to help sustain the battery voltage (Figure 3-23). The system was programmed to wake up every 15 minutes, take a temperature re ading and record it, and then go back to sleep. The Raven modem was programmed to wake up once every 60 minutes and transmit the collected data back to the host computer, which was stationed in the Geotechnical Research Departme nt at USF, where the data could be processed. Due to the high number of TCs that were being m onitored, two TCs were not attached to the remote monitoring system. The TCs that were located at 1D and 2Ds away from the shaft were attached to an OMEGA OM-220 data logger that collected data at the same rate as the CR1000, however the data was simply stored and a site visit wa s required to collect that data. The battery voltage was also m onitored and sent to the host computer along with the thermal data so that the power consumption could be tracked. 3.4 Results and Conclusions Overall the system worked extremely we ll. At one point during the monitoring period, there was a cellular timeout and the modem stopped transmitting the data to the host computer. This was fixed by a site visit to reset the modem and the problem did not occur again. However the main problem that was encountered was an issue with power usage. At the beginning of the monitoring procedure, the Raven modem was left on and would send back its data every hour. However this used an extremely large amount of power and the system lost power after ju st a few hours (Figure 3-24). The monitoring
37 procedure was revised so that the modem would go to sleep and only wake up once every hour to transmit the collected data. Even with this alteration, the ba ttery was still losing an ongoing battle with the pow er consumption of the Raven modem. Once the battery voltage dropped below 11.6V, the data collec tion system has approximately 8 hours of life before it quits. Due to this large amount of power usage, three site visits were required to get to the system and recharge th e battery. These three vi sits can clearly be seen in the plot of the batt ery voltage over time (Figure 325). In order to provide a completely remote unit, a larger solar cel l is recommended/require d as the 12W did not gain enough power to make the system fully remote. Originally, the data collec tion period was supposed to last until it was seen that the temperatures in the shaft had reached so mewhat equilibrium. However, in reviewing the data, the temperatures recorded from the soil surrounding the shaft were increasing while the temperatures within the shaft had reached equilibrium (Figure 3-26). Therefore data collection was continued as a result. Th e data was collected for another period of time until it was determined that the temperat ures both in the shaft and in the surrounding soil had reached equilibrium. From the final temperature plot, it can be seen that the temperature in the soil at 1D away from th e shaft was the last to eventually reach equilibrium. It can also be seen that the temp erature in the soil at 2D s away from the shaft was affected only slightly by the immense heat coming from the shaft (Figure 3-27).
Figure 3-1: Map of Voided Shaft Testing Site. Figure 3-2: Voided Shaft Reinforcement Cage Instrumentation. 38
Figure 3-3: Voided Shaft Central Casing Center Tube Supports. Figure 3-4: Voided Shaft Thermocouples Installed in Central Casing. 39
Figure 3-5: Voided Shaft Thermocouples on Outside of Central Casing. Figure 3-6: Voided Shaft Ground Monitoring Tube Installation. 40
Figure 3-7: Excavation for Voided Shaft. Figure 3-8: Picking of Reinforcement Cage for Voided Shaft. 41
Figure 3-9: Placement of Reinforcement Cage for Voided Shaft. Figure 3-10: Hanging of Reinforcement Cage for Voided Shaft. 42
Figure 3-11: Picking of Central Casing for Voided Shaft. Figure 3-12: Placement of Central Casing for Voided Shaft. 43
Figure 3-13: Voided Shaft Central Casing Stabilization. Figure 3-14: Double Tremie Concrete Placement. 44
Figure 3-15: Outer Steel Casing Removal. Figure 3-16: Final Voided Shaft at Ground Level. 45
Figure 3-17: Campbell Scientific CR1000 Data Logger. Figure 3-18: AM25T 25-Channel Multiplexer. Figure 3-19: Raven100 CDMA AirLink Cellular Modem. Figure 3-20: PS100 12V Power Supply with Rechargeable Battery. Figure 3-21: ENC12x14 Environmental Enclosure. 46
Figure 3-22: Thermocouple Wire Connection to AM25T to CR1000. Figure 3-23: Remote Thermal Monitoring System for Voided Shaft. 47
Figure 3-24: Battery Voltage as of 10/8/07. Figure 3-25: Battery Voltage as of 12/14/07. 48
Figure 3-26: Thermocouple Data as of 11/12/07. 49
Figure 3-27: Final Average Thermocouple Data for All Locations. 50
51 Chapter 4 St. Anthony Falls Bridge Foundation Monitoring On August 1 st 2007, a portion of the Interstate 35 Westbound Bridge over the Mississippi River collapsed in the middle of rush hour. The collapse killed 13 people and opened the eyes of engineers across the country to Americas failing infrastructure. Part of this research is proposing that a catastr ophe such as this coul d be prevented through the use of remote monitoring systems with the capability to alert users when certain structural members reach a predetermined level of stress. In order to fully understand the forced induced into a structure such as a bridge, the Minnesota Department of Transportation (MnDOT), the Federal Highway Administration (FHWA) and USF Geotechnical Research Department are worki ng together on a remote monitoring system that will provide such much needed information. As the MnDOT is re-building I-35 Westbound, USF will be instrumenting a number of structural members to provide realtime information about the stresses be ing felt by the bridge (Figure 4-1). This study was broken into three phas es. The first phase was during the construction of the concrete drilled shafts or caissons and the pier footing that ties the drilled shafts together. Thermocouples were pl aced in the re-bar cag es of the shafts as well as throughout the pier foo ting and used to determine the core temperatures of the
52 mass concrete elements. This part of the st udy was similar to the Voided Shaft study that was discussed in Chapter 3. The second phase of the study slightly overlapped the first phase in that it involved the drilled shafts, but it also branched upwards to the columns. Two different types of strain gages were placed in the re-bar cages of the shafts and at the center height of the columns. These were used to more accurately determine the load induced in the shafts by the pier footing, columns and s uperstructure, and the loads induced in the columns by the bridge superstructure during the bridge construction. Furthermore, as each new section of the concrete box-girder su perstructure is added to the columns, the added weights of the sections can be correlate d to the strain in the columns measured by the installed gages. This will provide more accu rate calibrations to be used in the ongoing health monitoring of the bridge, which is phase three of the project. At the time of completion of this report the final phase of the study has not yet started. It will use the same strain gages that are embedded in the shafts and columns, as well as strain gages that will be installed in the superstruc ture components of the bridge by the University of Minnesota. The final pha se of the project will monitor the loads on the bridge throughout its service life, which can be used to determine the Structural Health of the bridge, and can provide MnDOT and FHWA w ith real-time strain and load data from the bridge (Figure 4-2). 4.1 Phase I Thermal Monitoring As stated above, the first phase of this project was to monitor the internal temperatures of the mass concrete elements (drilled shafts and pier footing). While the
53 overall procedure of the thermal monitoring wa s very similar to the R.W. Harris Voided Shaft study, there were some major differences First, the shafts are solid, not voided. Voided shafts have not been tested for their strength capabilities, so therefore would not be used in a bridges substructure. Secondly, the ambient temperature at the site is much different. As seen from Figures 3-26 a nd 3-27, in the Tampa Bay area during the monitoring period, the air temperatur e ranges from approximately 100 F down to 65 F. In Minnesota during the construction and thermal monitoring period, the temperature ranges from approximately 35 F down to -10 F. This should be expected to have a significant effect on the temperatures reached by the mass concrete elements. 4.1.1 Construction and Instrumentation Prior to construction and inst allation of the drilled shafts, the instrumentation for the thermal monitoring was put into place. The first step was the instrumentation of the reinforcement cage for the drilled shafts. The reinforcement cage was built using high strength longitudinal steel and mild stirrup steel. The cage has 20-63mm threaded longitudinal bars with #6 ba r circular ties at 5 inches on center. Locking wheel cage spacers were placed along the reinforcement cag e to maintain 6 inches of clear cover (Figure 4-3). After the reinforcement cages were asse mbled, they were instrumented with thermocouples (TCs) and strain gages. The stra in gages will be disc ussed in the section on Phase II. The TCs were installed in pairs at 4 levels along the shafts, later named GL1, GL2, GL3 and GL4, for a total of 10 TCs per sh aft. GL4 was located at the bottom of the shaft, GL3 at the level of competent roc k, GL2 at the bottom of the permanent casing,
54 and GL1 at the top of the shaft (Figure 4-4) The wires from the TCs were bundled with the wires from the strain gages and run to the top of the shafts in tw o groups (Figure 4-5). After the cages were fully instrumented, th e excavations for the shafts were made. The shafts were drilled with two distinct sections. The top section is 7-0 in diameter with a thick permanent steel casing surroundi ng the shaft (Figure 4-6). This section is surrounded by dirt all around and needs the casi ng to keep the excavation clear. The casing runs down approximately 3-0 below th e level of bedrock. The lower section is 6-6 in diameter with no steel casing. This section is placed in a bedrock socket and therefore has no need for a casing. GL2, GL3, and GL4 are all in this lower section of the shaft. After the excavation was made, the re inforcement cages were lifted and lowered into the excavation (Figure 4-7). After reinfo rcement cage placement, the concrete for the shafts were poured with a single tremie. U pon removal of the tremie after concrete placement, a rebar instrumented with two mo re TCs was inserted down the center of the shaft. The wires from all the TCs and strain gages were run out through a 1 diameter schedule 40 PVC conduit that was placed running out through the top of the shaft, underneath the future pier footing that woul d be constructed, and out to the temporary Data Acquisition Systems (DASs) that were installed on s ite (Figure 4-8). Two of the eight shafts were instrumented, (these can be seen in Figure 4-8) and when all eight shafts were finished, time was a llowed for the concrete to cure, as well as the formwork and reinforcement for the pier footing. The pier footing is a large mass of concrete that sits above the dr illed shafts. It suppor ts the columns as well as ties the tops of the drilled shafts together. The pier foo ting for this project is 81-2 long by 34-0 wide by 14-0 tall (Figure 4-9). It is reinforced with 3 layers of #18 bars at the bottom of
55 the footing and 3 layers of #18 bars at the top. Along the top, steel W-Shapes were used to support the reinforcing bars to prevent excess bending. TCs were installed at the base of the footing, the center of the footing, and the top of the footing. These TC wires were run out through a 1 diameter schedule 40 PV C conduit down and out of the footing out to the DAS boxes alongside the conduits fr om the shafts. The MnDOT also ran PVC cooling tubes that were cast into the footing. Water was run through the tubes to help mitigate the mass concrete effects (Figure 4-10). 4.1.2 Monitoring Setup and Procedure For this first phase of the study, the data collection was actuall y split into two sub phases. The first was the thermal monitoring of the shaft, and the second was the thermal monitoring of the pier footing. The two pha ses were done similarly, however, and the setup for the thermal monitoring system was very similar to the setup used in the Voided Shaft study discussed in Chapter 3. The syst em was made up of the following pieces: A Campbell Scientific CR1000 data logger, an AM25T 25-channel multiplexer, a Raven100 CDMA AirLink Cellular Modem, PS100 12V power supply and 7Ahr rechargeable battery, and a large environmenta l enclosure to protect all the materials from the elements (Figure 4-11). From the Voided Shaft study, it was learned that a larger solar panel would be needed to provide power to the system, and so a 35W solar cell panel was utilized (Figure 4-12). The Thermal Monitoring procedure was id entical to that of the Voided Shaft study. A thermal data sample was taken every 15 minutes and stored to the data logger at the same interval. Every 60 minutes, the Raven modem sent the collected data to the host
56 computer at USF for data analysis. Once th is data was received, it was reviewed and plotted for use on the USF Geotechnical Resear ch website. This thermal data from the shafts was collected from 1/9/08 until 1/21/08. At this time, the TC wires from the shaft were disconnected, however the vibrating wire strain gages (discussed in Phase II) come with a thermistor. This thermistor was used to continue the thermal data from the shafts. The thermal data from the pier footing was co llected from 2/6/08 until 2/25/08. No strain gages were installed in the pier footing, so the only thermal data collected was stopped after this date. As with the Voided Shaft study, the battery vol tage for the data logger was also monitored, so that the logger would not lose power. Along with the thermal monitoring setup, a CC640 camera was set up to take hourly photographs of the construction site (F igure 4-13 and 4-14). It was powered by the same solar panel as the thermal monitoring system. The photos taken by the camera were sent back with the data collected from the TCs by the CR1000. The camera was useful for the thermal monitoring phase, but it was rea lly installed as an aid in the construction load monitoring phase, which will be discussed later. 4.1.3 System Results and Conclusions The thermal monitoring procedure fared extremely well. From the information gathered from the Voided Shaft study about the power consumption, the 35 watt solar cell panel worked much better and the ba ttery voltage never dipped below 12 volts (Figure 4-15). Twice during the thermal monitoring phase, the system lost and then regained cellular communication with the hos t server. These occurrences seemed to correspond to the use of a large electric pow er plant directly adjacent the systems
57 cellular modem. This type of EMF is known to adversely affect such systems and is therefore a reasonable explanat ion. Other than these interfer ences, the thermal monitoring system worked as planned. The concrete mix that was used was self consolidating concrete that was designed to have a lower heat of hydrat ion (Figure 4-16). Therefore, the temperature traces were expected to be lower than that of the Void ed Shaft study. The thermal data from Shaft 1 shows that the general averag e heat attained in the c oncrete was approximately 90 F, however there are two TCs that record a higher temperature of approximately 126 F, a 36 difference (Figure 4-17). Similarly in Shaft 2, the most of the TCs recorded a temperature of approximately 85 F, however there are two TCs that record a higher temperature of approximately 110 F, a 25 difference (Figure 4-18). This was not the result of a bad TC level. In reality, the shaf ts were poured one level at a time, alternating between shafts. When the trucks were comp lete, the shafts were not fully concreted. Therefore, extra trucks of concrete were requi red. It is assumed that the extra trucks did not use the same concrete mix as the first se ctions, and therefore th is second batch had a higher heat of hydration, causing an elevated temperature readi ng in the top of the shafts. As discussed in the monitoring procedure, the TC wires from the shafts were cut on 1/21/08 and the thermal data was no l onger collected. Upon connection of the vibrating wire gages from the shafts the ther mistors again started collection thermal data. This thermal data was analyzed and compiled with the data from the TCs and the continuation of the thermal curves were plotted (Figures 4-19 and 4-20). As stated above, the thermal data from th e pier footing was collected from 2/6/08 until 2/25/08 (Figure 4-21). As seen on the plot of the temperature over time, the TC in
58 the extreme center of the footing recorded a maximum temperature of approximately 140 F, while the TC at the center bottom of the footing only reached a temperature of approximately 90 F. The same concrete mix was used throughout the pier footing, so it should all be roughly the same temperature, however the ambient temperature, which ranged from 40 F down to -10 F, caused the temperatures to drop drastically closer to the outside edges of the footing. 4.2 Phase II Construction Load Monitoring This phase of the study expands above and beyond what was done in the Voided Shaft study. In Phase II, the loads placed on th e shafts by the pier footing, columns, and superstructure, and the loads placed on the columns by just the superstructure will be monitored. As shown in Figure 4-2, this phase ac tually begins at the start of the footing construction, but no real data was expect ed until the footing concrete was poured. For the section on construction and instru mentation, there is obviously an overlap with the construction sequence. Therefore, th is section of the report will not go into the details of the construction of the drilled sh afts nor of the pier footing. However more emphasis will be placed on the strain gages that were installed in the drilled shafts. For the pier columns however, the construc tion will be explained as well as the instrumentation. Furthermore, focus will be pa id to the phases of th e construction of the column and how it affected the construc tion loads placed on the drilled shafts.
59 4.2.1 Construction and Instrumentation For the instrumentation of the drilled sh afts, some information will overlap, but it is necessary to explain the strain gages and their placement within the shaft. The strain gages used in this study were provided by Geokon, Inc. They are Model 4911 Sister Bars and are specifically made for ease of in stallation (Figure 4-22). They come with the strain gage pre-installed on a 54.25 length of #4 bar. This bar is then tied to the existing reinforcement in the shaft or column. Since the gage is on a #4 bar, it does not provide enough extra steel area that the cross-section of the element would be altered (providing the element is quite large) and therefore doe s not affect the calculations of converting strain to load. The strain gages in the shafts were installed at the same four levels as the TCs: GL1, GL2, GL3, and GL4 (Figure 4-4). Ho wever, two types of strain gages were used. At each level, 4 vibrating wire (VW) strain gages and 2 resistance (RT) strain gages were installed, which makes for a total of 16 VW gages and 8 RT gages. The VW gages were installed at 90 separation (Figure 4-23), with the RT gages at 180 separation, coupled with the VW gages. The VW gages, as explained in Phase I, come equipped with a thermistor. These gages are not capable of recording strains at extremely high rates, which is why RT gages were also installed. At each main pier, two reinforced concre te columns sit on top of the shaft cap to support the superstructure for one direction of traffic. The co lumns were constructed with a varying cross-section (Figure 41). The critical crosssection is at the mid-height of the columns. This is where the strain gages we re placed. The columns were cast in three separate pours to get the full length of the columns.
60 First, the longitudinal bars running up through the columns were spliced to the longitudinal bars embedded in the pier footi ng (Figure 4-25). Then the formwork for the lower half of the column was set in place. The first pour was a small 200 yd 3 pour to get the column started. After that, the horizontal reinforcement was set in place inside the formwork up to the mid-height of the column. After the horizontal steel was in place, the next level of longitudinal steel was spliced to the first level so that the bottom of the bars would be embedded in the lower half of th e column. After the reinforcement up to mid height was installed, the second pour took place. This finish ed the concrete up to midheight of the column (Figure 4-26). The ne xt phase of construction was to place the formwork for the top half of the column, a nd then install the horizontal steel in the column. This was when the gage installati on took place. The critical section of the column is 8-0 by 16-0 with reinforcement that consists of 44 #18 bars with 8 on the short sides and 16 on the l ong sides (Figure 4-27). The total instrumentation for each column consists of 4 vibrating wire strain gages and 4 resistance type strain gages. The same coupled gages that were installed in the shafts were used in the columns (one VW gage and one RT gage). One installation unit was installed at each corner of the column in the critical section (Figure 4-28). By placing the gages in the corners of the cross-section, the strain at th e extreme fiber of the column could be measured. Once the gage installation units were tied and secured in place (Figure 4-29), the wires were run out of th e top of the column formwork so that the cables could be bundled together. Then the wires were brought back down to the midsection of the column and were run ou t through the 1 Sch. 40 PVC conduit that reached up through to the mid-height of the columns (Figure 4-30). The wires ran
61 through the conduit down through the column a nd the shaft cap and then out to the temporary DAS that was installed on site. In addition to these strain gages, the University of Minnesota Civil Engineering department also placed 5 strain gages in each column. These strain gages were instal led in the same locations as those done by USF, but with an additional gage located in the center of th e column. The wires for these gages were bundled with the wires from the USF gages a nd drawn out to the DAS at the same time. These cables are grey in color (as opposed to the blue and green used by USF) and can be seen clearly in Figure 4-30. 4.2.2 Monitoring Setup and Procedure For this second phase of th e study, the data collection wa s actually split into two sub phases. The first was the load monitoring of the shaft, and the second was the load monitoring of the columns. The reason for this is that a large amount of dead load on the shaft comes from the construction of the pier footing and the columns. Furthermore, if the loads on the shafts are monitored first, then checking that the measured loads are correct is much easier as the load is simply the dead load of the footing and columns. Each phase of monitoring was carried out in the same way. The monitoring setup and procedure will be explained by discussing the th ree different systems that we re installed and used during this phase of the study. System 1 was the same thermal monitoring system that was used in the first phase of the study as well as the Vo ided Shaft study discussed in Chapter 3. It was re-used during this phase of the st udy as the monitoring and tran smission system for the CC640 field camera. The camera was set up to take a picture every hour and then transmit that
62 picture back to the host computer via the cellular modem. During the thermal monitoring phase of the study, System 1 was powered by th e installed solar cell panel with a back-up deep cycle battery. During the 2 nd phase of the study the system was moved to A/C power, but with a deep cycle battery still in reserve shoul d the A/C power be disrupted. This A/C power was provided by the Army Corps of Engineers who had an A/C power source at the site. The second and third systems were installe d at almost the same time but have different capabilities/assignments. System 2 was designated to collect data from the vibrating wire gages installed in shafts 1 and 2 as well as those in the interior and exterior columns. This system also recorded the gage temperatures via changes in thermistor resistance. In all, 50 vibrating wire gages and 50 thermistors were connected to this logger via two AVW-200 two channel spectrum analyzers. Each channel of the AVW200 units is connected to a MUX 16/32B multiplexe r (four in all). MUX 1 was connected to shaft 2 (16 gages), MUX 2 was connected to shaft 1 (16 gages), MUX 3 was connected to the interior column (10 gages), and MUX 4 was connected to the exterior column (10 gages) (Figure 4-31). The true value of the AVW200 data is at pres ent unclear as many pieces of data quality is recorded along with the raw strain and temperature values of interest. These additional measur es of data quality (e.g. signal to noise ratio, etc.; four in all) are intended to provide insight into th e health of the gage, but triple the required storage space and therein significantly reduc e the overall duration of monitoring without remote intervention. The system monitoring the VW gages (System 2) used a Campbell Scientific CR1000 data logger, while the sy stem monitoring the RT gages (System 3) used a Campbell Scientific CR9000 data logg er. System 2 worked similarly to the
thermal monitoring system. A sample was taken by and stored to the data logger every 15 minutes. Every hour, this stored information was sent back to the host computer at USF to be compiled and analyzed. System 3, using the CR9000, took a sample at a rate of 100 Hz (100 samples per second). However, all of this data was not stored. Rather, the mean, maximum, and standard deviation of these samples was stored every 15 minutes. Then, every hour, the stored data points were sent back to the host computer along with the data from System 2. This provided the user with a better idea of the strain in the system because of the high sampling rate; however it used a large amount of power, which will be discussed in an upcoming section. The monitoring system sampling and storage rates and other information are given in Table 4-1. Between the two systems were a shared Raven100 CDMA AirLink Cellular Modem, PS100 12V power supply and 7Ahr rechargeable battery, and three large environmental enclosures to protect all the materials from the elements (Figure 4-32). Table 4-1 Overview of Monitoring Systems for I-35W Bridge Study System 1System 2Gage TypeThermocouplesVW Strain GagesThermistorsData LoggerCR1000CR1000Sampling Rate15 Min15 MinStorage Rate15 Min15 MinTransmit Rate1 Hr1 HrCR9000System 3RT Strain Gages(Sample Mean,1 Hr15 Min100 HzSample Max,Std. Deviation) Both System 1 and System 2 are powered by the A/C power source as provided by the Army Corps of Engineers, however each are connected to a deep-cycle battery and a solar cell panel as a backup. For System 3, it was known that a large amount of power would be consumed by the monitoring system. Therefore it was necessary to provide the 63
64 system with enough back-up power so there would be no power problems as there were with the Voided Shaft study. The CR1000 could only be run from either the A/C source on site or the solar panel, not both. Therefore, if the A/C were ever to cut out, there would not be the back-up of the sola r cell panel to run the system Therefore a battery manager was set in place to bypass this limitation. The CR1000 was hooked up to run off the A/C source. The battery manager was hooked up to the solar cell panel a nd the back-up Deep Cell battery as well as the external ba ttery pin on the CR1000. The battery manager allowed the Deep Cell battery to be charged by the solar cell pane l, and kept the A/C power from back feeding the solar cell panel when it received little power (such as at night). As with the thermal data from the sh afts, once this data was received and reviewed it was plotted for us e on the USF Geotechnical Research website. The strain in the shafts at the four different levels was monitored begi nning on 2/6/08 with the pier footing concrete placement. Back in the Geotechnical Research department at USF, the strain data from the shafts was computed in to construction loads a nd an annotated graph was updated to the USF Geotechnical Research website (Figure 4-33). Along with this graph, using the CC640 field camera, pictures fr om these events were captured and they can be related to the points of interest on the graph. This aids in verifying the loading event, as well as verifying the amount of load that is calculated in the shaft (Figures 4-34 through 4-37). At the time of the report cons truction is still in progress, therefore the construction loads on the shafts are still being monitored. As seen in Figure 4-37, the column foundation quickly became too large to be seen in its entirety by the close-up camera location. Therefore the CC640 field camera
65 was moved to a new location atop the Univer sity of Minnesota Bob Main building on the south west bank of the river. This new position affords oversight of the entire project from end bent to end bent and can now be used to dovetail recorded strains to construction events (Figure 4-38). 4.2.3 System Results and Conclusions The three monitoring systems used duri ng the construction lo ad monitoring phase fared very well. System 1 twice lost and then regained communication with the host server. These occurrences seemed to correspond to the use of a large electric power plant directly adjacent the sy stems cellular modem. This type of EMF is known to adversely affect such systems and is therefore a reasona ble explanation. As st ated in the monitoring procedure, the system as repositioned in early March. This system worked without issues from Mar 5th to March 19th when communication between the camera and logger failed. Review of the system revealed the camera was still recording images to its internal compact flash card, but images were not tr ansferred to the logger for scheduled collection. Cellular communication with the logger has not faltered since its repositioning atop of the University of Minnesota BOBMAIN building. As stated in the monitoring procedure, power consumption was a large concern for this phase of monitoring. The power of Syst em 1 was stable throughout this phase. As stated earlier, the System was originally pow ered by completely via solar energy while a deep cycle battery was used as a back-up. In early March, the power source was switched to constant A/C and provided the system with more stabil e voltage (Figure 4-39). At no time did the voltage approach the critical l ogger shut down voltage. Results of both the
66 close-up pictures and the overv iew pictures are shown in the previously documented figures. The results of System 2 were a little less desirable. The cellular communication with this system became somewhat of a con cern with regards to reliability. This system, which was similar to System 1, logged data th at was collected without issue from Feb 5 th until March 26 th For a short period following this time frame, no collections were possible. It was unclear whet her the system was still powered and logging although up until the last collection the power cycles were regular (Figure 4-40). Since the critical threshold voltage of 11.2 volts was not approa ched at any time, it is unlikely that power interruption was the cause of the communicati on errors. The concern with the intermittent communication was resolved, but the data collected from one of the four multiplexing units responsible for monitoring nine of the vibrating wire gages wa s unintelligible. This is thought to be a total failure due to a cut wire or a bad connection between that device and the data logger. The results of System 3 were much better than those of System 2. To date, System 3 communication has not faltered. The primary difference between this system and the other two is the logger type CR9000 vs. CR1000. The latter of which has not been consistent. The battery voltage of System 3 va ries much less than the battery voltage of System 2, yet neither system seems to ha ve had a power interruption (Figure 4-41). Along with the results from the gages, th e website hosted by the University of South Florida host computer was drastica lly changed. The main page now has hover points associated with pathways to videos or data locations (Figure 4-42). The link to the South Camera Perspective takes the user to a page that shows a video made of time lapse
67 photos taken by the CC640 Field Camera in its altered position atop the University of Minnesota Building. The link to the West Camera takes the user to a page that shows a video made of time lapse photos taken from the web camera set up by the Minnesota DOT. The Pier 2 Close-up Camera link takes the user to a page that shows a video made of time lapse photos taken by the CC640 Field Camera in its original close-up position. All of these videos provide a quick look at the construction progress of the bridge from different vantage points and were used to rela te the strain data to specific construction events. The FHWA Substructure Health Monito ring Site link takes the user to a separate page with a close-up view of the site with more hover points (Figure 4-43). Each of the texts is a link that will take th e user to a plot of the strain of that subject over time (Figures 4-44 through 4-47). These graphs we re broken down into daily increments as shown by the dotted lines running vertical on the graphs. The space between these dotted lines is a link that takes the user to th e pages with the web cameras showing the construction progress up to that date. This way the strain data can be more accurately related to construction events. The graphs s hown show the strain data up to 5/2/08. These graphs are provided just to show the capab ilities of the updated website. Figures 4-48 through 4-51 provide the latest strain data from the shafts and columns as of 6/25/08. In these graphs it is easier to s ee the tremendous increase in load that the columns and shafts are experiencing due to the cons truction of the superstructure. 4.3 Phase III Long Term Health Monitoring The third and final phase of the St. An thony Falls Bridge Monitoring Project is the long term health monitoring of the substructu re as well as the superstructure. In Phase
68 III the loads induced on the enti re bridge by the ongoing daily use of the bridge will be monitored. As shown in Figure 4-2, this phase will actually begin once the bridge is fully constructed and open to the public. At the time of this report, the bridge is still being constructed and is set to be completed n ear the end of December, 2008. Therefore this phase of monitoring will not be started until that time. For the section on instrumentation, focus will be placed on the planned added instrumentation that will be required for this phase of monitoring, but there will obviously be no final information that can be provided. For the monitoring setup and procedure, once again focus will be placed on the planned monitoring procedure. This phase will utilize the information gleaned fr om the first two phases of the study to provide more accurate data collection and anal ysis, as well as the steps necessary to guarantee the full automation of the monitoring systems. 4.3.1 Instrumentation Upon completion of construction of the br idge superstructure, the entire group of 64 wires from the substructure strain gages will be disconnected from the temporary DAS boxes at the base of the pier foundation. Thes e wires will require hermetically sealed splices, and then will be run back up through the pier footing, co lumns, and into the bridge superstructure. Here the wires will be re-connected, along with the wires from the superstructure gages, to the permanent DAS boxes. The type of box and location is yet to be determined, but similarly to the tem porary DAS boxes, they should be generally resistant to rodent-induced damage, environm ental damage, and vandalism. There will be no added gages from the substructure used in the long term health monitoring phase.
69 The University of Minnesota will be responsible for the determination and location of the gages that will be installed on th e bridge superstructure. At the time of this report, the planned gages for the superstruc ture include the following: vibrating wire strain gages with temperature gages (therm istors), chloride pe netration sensors, accelerometers, and acoustic monitors. Figure 4-48 through 4-50 show the planned locations for the superstructure gages. These gage locations have not been finalized and are subject to change if the pr oposed locations are not accessible. 4.3.2 Monitoring Setup and Procedure The substructure gages are planned to be continually monitored with the same monitoring procedure that was used during the construction lo ad monitoring phase of the study. It is expected that the resistance type gages will be very useful during this phase because the sampling rate of resistance t ype gages is basically only limited by the sampling rate of the DAS. However it is impor tant for the vibrating wire gages because the resistance gages are more susceptible to signal decay from long lead wires than the vibrating wire gages. The monitoring procedure for the superstructure gages will be determined by the University of Minnesota research team, and has not been determined at the time of this report. It is expected that the CC640 field camera will stay installed atop the University of Minnesota BOBMAIN buildin g and it will continue to take pictures every hour. This will be useful in relating strain events to act ual traffic conditions that are visible on the bridge.
70 4.3.3 System Results and Conclusions As stated previously, at the time of this report th e long term health monitoring phase of this project is not underway and is not expected to begin until December 2008. Therefore at this time there are no results or conclusions to be made based on the long term health monitoring procedure. Howeve r it is expected that the substructure monitoring procedure will be completely fina lized and that therefore once the gages are permanently installed to the DAS boxes, no work will need to be done on them.
Figure 4-1: Artists Rendering of I-35W Bridge over Mississippi River. Event ScheduleProject Phase IProject Phase IIProject Phase IIIFooting Concrete CuringFooting InstrumentationFooting ConstructionShaft InstrumentationShaft ConstructionShaft Concrete CuringLong-Term Health MonitoringBridge CompletionSuperstructure ConstructionColumn Lift 3Column InstrumentationColumn Lift 2Column Lift 1 Figure 4-2: Event Schedule and Overlap of I-35W Bridge Project Phases. 71
Figure 4-3: I-35W Bridge Shaft Reinforcement Cage Construction. Figure 4-4: I-35W Bridge Gage Levels on Drilled Shafts. 72
Figure 4-5: Cable Bundles in Reinforcement Cage for I-35W Bridge. 73 Figure 4-6: Top Section of Drilled Shaft for I-35W Bridge.
Figure 4-7: Placement of Reinforcement Cage for I-35W Bridge Shaft. Figure 4-8: Conduits Running from Shafts to DAS Boxes. 74
Figure 4-9: Lower Layer of Pier Footing Reinforcement for I-35W Bridge. Figure 4-10: Upper Layer of Pier Footing Reinforcement for I-35W Bridge. 75
Figure 4-11: Thermal Monitoring DAS for I-35W Bridge Shafts. Figure 4-12: 35 Watt Solar Cell Panel for I-35W Bridge Monitoring System. 76
Figure 4-13: CC640 Jobsite Camera with Perspective Outlines. Figure 4-14: Sample Camera Shot from Close-Up Cam on I-35W Bridge. 77
Figure 4-15: Data Logger Battery Voltage from I-35W Monitoring System. 78
Figure 4-16: Concrete Mix Design for Drilled Shafts on I-35W Bridge. 79
Figure 4-17: I-35W Bridge Southbound Pier 2 Shaft 1 Thermal Data. 80
Figure 4-18: I-35W Bridge Southbound Pier 2 Shaft 2 Thermal Data. 81
Figure 4-19: I-35W Bridge Shaft 1 Thermal Data from TCs and Thermistors. 82 Figure 4-20: I-35W Bridge Shaft 2 Thermal Data from TCs and Thermistors.
Figure 4-21: Pier 2 Southbound Footing Thermal Data from Thermocouples. Figure 4-22: Detail of Geokon 4911 Sister Bar Strain Gage. 83
Figure 4-23: VW Gage Installed in Shaft Reinforcement Cage. Figure 4-24: Coupled VW and RT Gages. (VW Blue Cable, RT Green Cable) 84
Figure 4-25: Reinforcement for 1 st Column Pour for I-35W Bridge Columns. Figure 4-26: Reinforcement at Mid-Section of Columns for I-35W Bridge. 85
Figure 4-27: Longitudinal and Horizontal Column Reinforcement. Figure 4-28: Coupled Gage Installed in Corner of Column. 86
Figure 4-29: Gage Wires Tied and Secured. Figure 4-30: Gage Wires Exiting Through Conduit. 87
Figure 4-31: Gage Wires Connection to System 2. Figure 4-32: Construction Load Monitoring Systems. (VW Blue, RT Green) 88
Figure 4-33: Annotated Graph of Shaft Construction Loads and Events. 89
Figure 4-34: I-35W Bridge Southbound Pier Footing Concrete Placement. 90 Figure 4-35: I-35W Bridge Lift 1 Column Concrete Placement.
Figure 4-36: I-35W Bridge Interior Column Lift 2 Formwork Placement. 91 Figure 4-37: I-35W Bridge Exterior Column Lift 2 Formwork Placement.
Figure 4-38: I-35W Bridge South Perspective CC640 Field Camera. 92 Figure 4-39: I-35W System 1 Battery Voltage over Time. Battery Voltage 15 14.5 System 1 14 13.5 13 12.5 12 11.5 1/3/200 1/13/20 3/23/20 4/2/200 1/23/20 2/2/200 2/12/20 2/22/20 3/3/200 3/13/20 4/12/20 8 0:00 08 0:00 08 0:00 8 0:00 08 0:00 8 0:00 08 0:00 08 0:00 8 0:00 08 0:00 08 0:00 Time / Date
93 Figure 4-40: I-35W System 2 Battery Voltage over Time. 15.4 Battery Voltage 15.2 15 14.8 14.6 14.4 14.2 14 13.8 13.6 13.4 3/3/2008 3/28/2008 2/27/2008 3/8/2008 3/13/2008 3/18/2008 3/23/2008 4/2/2008 0:00 0:00 0:00 0:00 0:00 0:00 0:00 0:00 Time / Date Figure 4-41: I-35W System 2 Battery Voltage Compared to System 3. 15.6 Battery Voltage 15.4 System 3 CR9000 15.2 System 2 CR1000 15 14.8 14.6 14.4 14.2 14 13.8 13.6 13.4 2/27/2008 3/3/2008 4/2/2008 3/8/2008 3/13/2008 3/18/2008 3/23/2008 3/28/2008 4/7/2008 0:00 0:00 0:00 0:00 0:00 0:00 0:00 0:00 0:00 Time / Date
Figure 4-42: Main Page of St. Anthony Falls Bridge Study Website. Figure 4-43: Secondary Page of St. Anthony Falls Bridge Study Website. 94
Figure 4-44: I-35W Bridge Pier 2 Interior Column Strain Data with Links. 95 Figure 4-45: I-35W Bridge Pier 2 Exterior Column Strain Data with Links.
Figure 4-46: I-35W Bridge Pier 2 Shaft 1 All Levels Strain Data with Links. 96 Figure 4-47: I-35W Bridge Pier 2 Shaft 2 All Levels Strain Data with Links.
Figure 4-48: I-35W Bridge Pier 2 Interior Column Strain Data. 97
Figure 4-49: I-35W Bridge Pier 2 Exterior Column Strain Data. 98
Figure 4-50: I-35W Bridge Pier 2 Shaft 1 All Levels Strain Data. 99
Figure 4-51: I-35W Bridge Pier 2 Shaft 2 All Levels Strain Data. 100
Figure 4-52: Superstructure Gage Locations I. (Courtesy of Smart-Bridge Concepts) 101
Figure 4-53: Superstructure Gage Locations II. (Courtesy of Smart-Bridge Concepts) 102
Figure 4-54: Superstructure Gage Locations III. (Courtesy of Smart-Bridge Concepts) 103
104 Chapter 5 Conclusions The research in this thesis has shown th at a reliable, remote Substructure Health Monitoring (SSHM) system can be implem ented on any number of structures. The available options for data logging and strain ga ge installation, as we ll as the advancement of wireless technologies for cellular uplink and data transmission, have made remote monitoring systems a viable alternative to the typical monitoring system that is generally used on most structures. Generally speaking, there were no great problems encountered throughout both the Voided Shaft study and the I-35W Bridge study. There is one important aspect in the implementation of a remote monitoring system for any project: Power. How to get power, how to maintain power, and how to verify that if power is lost, back-up power will be accessible and is ready to take over for th e system. Without this verification, the monitoring system becomes fragile and cannot be relied upon. 5.1 Conclusions from Tested Systems From the Voided Shaft study, it was learned th at it is necessary to determine, prior to system installation and start-up, how mu ch power all of the instruments in the monitoring system will require. It was l earned early on that the Raven 100 CDMA
105 Airlink Modem required an extremely large amount of power. However if it is allowed to fall asleep and only awake when transmitting data, that power consumption is greatly reduced. Second, the back-up power source in the form of a solar cell panel, while capable of providing some back-up power, was not strong enough to combat the power consumption of the modem. From the I-35W Bridge study, it was lear ned that the power source, even if provided on site, may not be sufficient to run the system. It was learned that the PS100 Power Supply could only receive power from either an A/C power source or a solar cell panel, but not both. This means that this lim itation had to be circumvented with extra equipment (and therefore extra money) in or der to provide for a fully remote system. 5.2 Future Work for I-35W Bridge Study At the time of this report, the Univers ity of South Florida Geotechnical Research Department has been granted a 2 year extens ion on its involvement in the I-35W project. In the short term, this will include the installation and wiring of th e gages that will be installed in the bridge supe rstructure as well as the full wiring of the installed substructure gages to the permanent data acquisition system (DAS). This system is planned to be located at a monitoring site that is located on the north bank of the Mississippi river that is a pproximately1500 feet away from the temporary DAS at the base of the southbound pier as described in this report. This will be the instrumentation of Phase III of the study (Figure 4-2). In the long term, all of the substruc ture and superstructure gages will be monitored for the proposed exte nsion of 2 years. The monitoring of these gages will
106 include the general data collecti on and data analysis that has been described in this report. In addition, it will involve the process of making the analyzed data available to select parties by means of the USF Ge otechnical Research website ( http://geotech.eng.usf.edu ). This will include the strain and load data from the instrumented shafts, columns, and superstructure as well as the other data collected from the superstructure gages. It will also include up-to-date images from the bridge site as well as a reference that will relate strain and load events to real-time traffic and bridge loading events. 5.3 Possibilities for Remote Substructu ral Health Monitoring Systems Obviously, while the study of remote data collection and analysis is a complete study in itself, there are no limits to where this type of project can lead. The data provided by this instrumentation can be us ed by governmental institutions or by engineering societies for furthering the profession. For agencies such as state departments of transportation (DOTs) and the Federal Highway Administration (FHWA) the data will most likely be used as an early warning or protection system. Threshold limits can be placed on the data collection or monitoring system and can be used to alert the user when certain limits are met, such as a percentage of capacity or an extreme event. For engineeri ng societies, this information could be used for increased information for future analysis This can include a back-check of future bridge designs to determine the design assump tions of the engineers of record. It could also be used as a verification of the statistical loads that are used in bridge design, such as the HL93 Truck. This is a specified loading th at is denoted by the American Association of State Highway and Transporta tion Officials (AASHTO) and is not actually a truck that
107 exists. From 2 years worth of data collected fr om a bridge, this loadi ng can be verified to be a worst case scenario that is experienced by an actual structure. Finally, the analyzed data could be used to propose a possible increa se in the specified re sistance factors that are used in bridge design. The more that is learned about what forces an actual bridge experiences, the more streamlined the design approach can become. This can result in a decrease in the amount of materials used and therefore a more cost effective and efficient design.
108 References  Arms et al. (2004). Remotely Programmable Sensors for Structural Health Monitoring. Structural Materials Technology: NDE/NDT for Highways and Bridges. Buffalo, NY.  Udd et al. (2000). Single and Multi-axis Fiber Grating Strain Sensor Systems for Bridge Monitoring. Internati onal Conference in Optical NDE.  Susoy et al. (2006). Development of a Structural Health Monitoring Framework for the Movable Bridges in Florida. Submitted for Transportation and Research Boards 86 th Meeting. Washington, D.C.  Weyl, Laura Isa (2005). Developing a Web-based Management System for the Indian River Inlet Monitori ng Plan. Research Experiences for Undergraduates in Bridge Engineering, University of Delaware, Newark, DE.  Watters et al. (2001). Design and Perfor mance of Wireless Sensors for Structural Health Monitoring. SRI Inte rnational, Menlo Park, CA.  Hemphill, Derek (2004). Structural H ealth Monitoring System for the East 12 th Street Bridge. Iowa State University, Ames, IA.  Shannon & Wilson (2002). Continued Mon itoring of Pier EA-31, West Seattle Freeway Bridge, Seattle, Washington Order Number DTFH61-02-P-00197. Seattle, WA.
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Collins, Jonathan D.
Remote monitoring systems for substructural health monitoring
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by Jonathan D. Collins.
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Thesis (M.S.C.E.)--University of South Florida, 2008.
Includes bibliographical references.
Text (Electronic thesis) in PDF format.
ABSTRACT: Remote Wireless Monitoring Systems have made a large impact in the area of Structural Health Monitoring. However in the specialized sub-field of Substructural Health Monitoring, remote monitoring techniques have not made as much headway. First, monitoring systems are often retrofitted onto a structure. Therefore it is much harder to retrofit the substructure of a bridge or building. Second, many foundation elements such as driven piles or auger-cast piles are constructed in a way that makes installation difficult or can severely damage the sensing materials. This thesis presents two case studies of Remote Monitoring Systems for Substructural Health Monitoring applications that were carried out by the Geotechnical Research Department of The University of South Florida. The first is a thermal monitoring system for a Voided Shaft study. The second is a thermal, construction load, and ongoing health monitoring system of the St. Anthony Falls Bridge in Minnesota. Results show that the systems that were used provide adequate data collection, data storage, and data transmission. Furthermore, this data is easily analyzed and provided for public or private use on a dedicated website, which provides a fully automated and remote Substructural Health Monitoring System.
Mode of access: World Wide Web.
System requirements: World Wide Web browser and PDF reader.
Advisor: Austin G. Mullins, Ph.D.
x Civil Engineering
t USF Electronic Theses and Dissertations.