HBM-General Instrumentation, Testing Experience

Below are a few examples of typical projects in which Dr. Moussa A. Issa was the Principal Investigator at the Florida Department of Transportation(FDOT) in Tallahassee, FL

Field Instrumentation, Testing, Monitoring and Load Rating of In-Service Bridges Florida DOT, 1989-2000

Experimental investigation/testing of structuresusingNon-Destructive Testing (NDT)methodsis more important now than ever beforeinevaluation of a structure’sload-carrying capacity. Suchtests are also usedto rate existing structures,calibrate/evaluate standard codes and computer models,and diagnose the structure’sbehavior under static/dynamic loading.Several components are required for successful experimental/field testsincluding: 1) Instrumentation(i.e. strain gages, LVDT’s, crack gages, Vibrating Wire Strain Gages, accelerometers, thermocouple, etc.) to measure deflection,crack width, strain, temperature and acceleration, 2)Data Acquisition Systemsand3) Loading Conditions

Generally,two typesof field load testingare utilized. In the first type of test,called proof load testing,the bridge is loaded to a required load to establish a target rating providedthe bridge doesnot show any sign of structural distress. This method does not rely on bridge analysisbut rather relies on field testing data to prove the loading capacity of the bridge. The second type of test is called diagnostic testing. In diagnostic testing, the loadis lower than used in proof load testingand the relationship between analysis and field testing is established by comparing the predicted bridge performance to measured values.

The application of field testing and load rating eliminates some unnecessary retrofitting/demolishing of structures and identifies the safety ofbridges for the motoring public.

Static and Dynamic Load Tests of Prestressed Concrete Girder BridgesFlorida DOT, 1995

Full-scale static and dynamic tests were performed on two prestressed concrete bridges. Both bridges containeda variety of AASHTO-type girders and were designed to carry two lanes of HS20 loading. The critical spans were instrumented at quarter span (L/4) and midspan (L/2) with accelerometers, strain gages anddeflection transducers. The bridge load testing apparatus consistedof a mobile data acquisition system and two load testing vehicleswhich weredesigned to deliver the ultimate live load specified by the AASHTO Code. For the static testing, the bridge was incrementally loaded up to the full ultimate design live loadwith test vehicles loaded to simulateHS-20 truck loads. At each load step,the instruments were monitored,and the results were subsequently compared to the analytical model,before proceeding with the next load step. The dynamic load tests were performed with the two testing vehicles traveling at 55 MPH, 45 MPH, and 35 MPH.

Experimental and Analytical Investigation of the Florida Bulb-Tee Girders, Ft. Myers Florida DOT, 1996

An experimental investigation was conducted to investigate cracking in the Edison Bridge. Unit Two South was the last unit to be constructed in the southbound portion of the Edison BridgeandGirders Four and Five of Span Two South were chosen for the experimental program. In addition, it wasdecided to investigate Girder Four of Span Six South whichhad cracked during the first stage of post-tensioningin Unit Three South. Crack development during the construction process was also monitored,along with the crack width and propagation with time,after the first stage of post-tensioning.The objectives of this experimental program were to study the effect of grouting pressure and evaluate the bursting stress in the bulb-tee web during post-tensioning.

Embedded vibrating wire and electric resistance strain gauges were used to monitor strain and temperature changes, and consequentlythe state of stress in the web,during the first and second stages of post-tensioning and grouting of the ducts. In addition tothese gauges, surface strain gauges were used across the crack to measure the cracks during the remaining stages of construction. A data acquisition system continuously monitoredand storedthe collected data from the vibrating wire gauges at a preset timeanda High-Speed Data Acquisition System was used to collect the data obtained from the embedded electric resistance strain gauges.