Proof load testing and shear assessment of kishwaukee I-39-river bridge using the modified compression field theory

The questions raised about bridge performance are carried out by conducting physical bridge load testing and rating. The outcomes of bridge load testing are widely used to ensure bridge safety for the public when theoretical analysis cannot provide a sufficient conclusion of in-service performance. The research illustrates the load ratings and shear assessment of a 1976-built I-39 Kishwaukee bridge over the Kishwaukee River in Winnebago County, District 1, Illinois. Load ratings of the Kishwaukee twin post-tensioned concrete box girder bridges are governed mainly by the shear stresses located near the piers in combination with visible shear cracks exhibited at the joints around the shear key due to the inception of the cracks at the time of construction in single key joints. Proof of four different trucks loading weights of 76 tons (167 k), 90 tons (200 k), 122 tons (268 k), and 136 tons (300 k) were conducted on the bridge. Nine testing scenarios were successfully completed with a maximum of two testing trucks of approximately 136 tons (300 k). Half of the bridge was instrumented using vibrating wire strain gauges to measure the strains near the pier, where shear and negative moment are critical, and at midspan, where the positive moment is crucial. Furthermore, crackmeters were placed along the cracks near the shear key region to measure the crack opening during testing. Linear variable differential transducers (LVDTs) were placed at the critical Sect. (0.40L) of Span #5 to measure the deflection. The modified compression field theory (MCFT) is used to calculate the shear capacity along the joints considering the contributions of vertical and horizontal reinforcing steel, the prestressing Dywidag bars, and the effect of the external post-tension tendons. This paper illustrates a detailed procedure for Kishwaukee Bridge load rating, field operation, instrumentation, and interpretation of the test results to determine the bridge load rating based on the 2018 AASHTO Manual for Bridge Evaluation. Findings from this study demonstrated that there is no crack slippage across the web-cracked section, and the bridge’s concrete shear capacity remains strong and contributes to the bridge’s total shear capacity. This study also showed that the shear capacity of the bridge is 1.8 times stronger than the total applied shear force, concluding that the Kishwaukee I-39 bridge remains safe for future traffic load increases or higher truck loads.