Control of Cracking on the Side Faces of Large Reinforced Concrete Bridges

Several large reinforced concrete highway bent cap girders, designed according to ACI and AASHTO provisions, were found to have very wide cracks near middepth on the side faces. Although the crack width at the level of main reinforcement was acceptable, the side face cracks near middepth were up to three times as wide. This indicated potential durability problems. A 3/8 scale laboratory model using deformed bars and reduced maximum size aggregate accurately reproduced the crack pattern and crack widths of the full size bent caps. A simplified test specimen was developed to accurately simulate the behavior of a portion of a beam under constant moment loading. A series of 44 specimens investigated the variables affecting side face cracking: amount and distribution of side face reinforcement, cover, web width, and beam depth. A relatively simple two-dimensional finite element analysis generally confirmed the laboratory results. A new design procedure was developed to control side face crack widths and was simlified for code use. To verify the new design procedure, the original model bent cap with the serious side face cracking problem was redesigned and tested. The procedure worked very well. Although the new procedure requires substantially more side face reinforcement for large beams than present provisions do, it appears that the side face cracking problem can be controlled at little or no additional cost by considering the flexural strength contribution of the side face reinforcement.