Safety and Serviceability of Reinforced Concrete Beam-Column Joints Supported by Shores and Reshores during Construction

Abstract

Reshoring makes a floor support its own weight and decreases the construction load in the lower levels. However, a significant concern regarding reshoring lies in its safety and serviceability when shores are replaced while the construction load of the upper levels is applied. To investigate this concern and compare the construction load in shores and reshores, reinforced concrete (RC) beam-column joints at early ages were tested in the laboratory and were also monitored at a construction site. The specimens at ages of 2 and 3 days showed a shear-compression failure, and the specimens at ages of 7 or more days showed sufficient flexural behaviors. The test also found that the beam-column joints have sufficient stiffness even at the earliest ages that the joint can be safely assumed to be fully restrained regardless of the concrete age. Analysis of the test results showed that reshoring at 5 days of concrete age is 55% safer than keeping the shores until the age of 28 days, and no serviceability problems were identified, such as deflection, deformation, or cracks under the expected construction loads. The safety and serviceability concerns were also addressed by the field monitoring of beam deflections and the strain of the longitudinal rebar in the beams. The maximum beam deflection was only L/5,000, and the maximum rebar strain was only 3.6% of the yield strain. Field monitoring of the construction load showed that the load on the shores decreased by 50% after reshoring and was also 35% lower than the load on shores that have been kept. This result coincides well with the predicted values based on the simplified analysis recommended by code provisions.