On August 7, a total of 16 strain gages, seven linear variable differential transformers (LVDTs), and three thermocouples were installed to monitor the bridge. Seven electrical resistance strain gages (i.e. WFLM-60-11-2 LT) were glued to the bottom of the beams in the longitudinal direction at mid-span to measure the strain from truck loading.
Seven vibrating wire strain gages (i.e. KM- 100B), were installed in gage brackets that had been epoxied to the beam bottoms. They were placed in the longitudinal direction at mid-span to measure the strain from temperature loading; two were also epoxied on two columns of the frame in the vertical direction to measure the strain frame from temperature.
A total of three thermocouples were used, one on the left column of the frame, one on the right column of the frame, and one on the bottom of Beam 4.
The seven LVDTs were affixed to the frame using brackets. The frame was used as a reference surface from which the bridge response was measured. Figure 18 shows the LVDT mounted to the frame along with a KM-100B mounted in a bracket (temporarily held in place with duct tape as the epoxy sets), and the electrical resistance strain gage (white).
Bridge testing
On August 8, two loaded trucks were used to load-test the bridge. The weights of the trucks were 249.5 and 237.5 kN (56.1 and 53.4 kip). Four static load configurations were used in the tests, and the trucks were positioned to obtain the maximum moment at mid-span. The first and second load configurations consisted of a single truck placed in the left and right lanes, respectively. The third load configuration consisted of two trucks placed side-by-side, and the forth load configuration consisted of both trucks placed back-to-back in the left lane (Figure 19).
Data was collected using two data-acquisition systems. The exterior instrumentation, which included seven WFLM-60-11-2 LT gages and seven LVDTs, was connected to Acquisition System 1. All embedded instrumentation, KM-100Bs, and thermocouples were connected to Acquisition System 2, which was programed to take readings every 15 minutes. (Acquisition System 1 took readings during the time the trucks were stopped on the bridge.)
After finishing the static truck testing, dynamic testing was conducted by driving one truck at speeds of 8, 16, 24, 40, and 48 km/h (5, 10, 15, 25, and 30 mph), and data was collected. After finishing the dynamic truck test, the seven LVDTs were connected to Acquisition System 2 for long-term monitoring.
On December 15, five LVDTs and three thermocouples were added to the bridge. Joints 4, 5, and 6 were instrumented with three LVDTs. Two brackets were used to install the LVDTs across the joints in the transverse direction at mid-span. Two LVDTs were installed at the two ends of Beam 7 to monitor the girder movement during temperature changes. One thermocouple was installed on Beam 1 and another on Beam 7 to monitor the temperature on both sides of the bridge. One thermocouple was installed on the bottom of Beam 3 to monitor the temperature at this location, in addition to the four thermocouples already embedded in the beam.
Conclusion
The construction process started with prior bridge removal on May 28, 2014. The new bridge was opened to traffic on August 13, less than three months from closing the road (which included performing research on the new shear key design). The relative rapid reopening of the bridge emphasizes the reason for preferring the adjacent box beam bridge for local owners. Longitudinal cracks did not appear in the longitudinal shear key joints for this bridge, which have been observed in the early age of some non-shrinkage grout shear keys in other bridges. The superior mechanical properties and durability of UHPC appear to make it suitable to use as grout material in the shear keys of adjacent prestressed concrete box beam bridges. The bridge continues to be monitored with instrumentation and data is being processed for further evaluation on bridge performance.
If the joints on this bridge continue to perform well, designs containing larger dowel spacing may be able to be utilized for cost savings without hindering performance. The overall improved joint performance may lead to renewed use and longer design lives for adjacent prestressed concrete box beam bridges.
Eric Steinberg, PhD, PE, is a professor in civil engineering at Ohio University. He served as assistant chair from 1997 to 2005 and is a registered engineer in the State of Ohio. A member of the American Concrete Institute (ACI), American Society of Civil Engineers (ASCE), and Precast/Prestressed Concrete Institute (PCI), he is a board member of Ohio’s Research Initiative for Locals, and has served as an expert witness in the field of structural engineering. Steinberg is an active member of PCI’s Student Education and Bridge Committees, and has been faculty advisor for student organizations of ASCE and Structural Engineers Association of Ohio (SEAO). He can be reached via e-mail at steinber@ohio.edu.
Ali Semendary, MS, is a graduate research assistant at Ohio University and a PhD candidate in its Department of Civil Engineering. He obtained his bachelor’s and master’s degrees from Babylon University in Iraq. Semendary’s research interests are in the area of structural engineering. He can be reached via e-mail at as295111@ohio.edu.
Kenneth Walsh, PhD, is an assistant professor at Ohio University’s Department of Civil Engineering and the director of the school’s Experimental Engineering Mechanics Laboratory. His research interests are in the area of structural engineering with emphasis on computational methods of analysis. Walsh has published multiple research articles in academic journals including Structural Engineering, Journal of Earthquake Engineering, and Engineering Vibration. A member of the American Society of Civil Engineers (ASCE) and the American Institute of Steel Construction (AISC), he can be reached via email at walshk@ohio.edu.
