Deterioration Process and Evaluation of Strengthening Methods for Reinforced Concrete Bridge Deck

The heavier the traffic becomes, the more cases of damaged bridge deck slabs are reported year by year. It is basically important to clarify the mechanism of punching shear failure. In addition, various strengthening methods for damaged bridge deck slabs have been proposed and they can be divided into two. One is so-called surface strengthening method. SFRC surfacing and D-RAP method are included in this category. The other is so-called bottom surface strengthening method. In this case, steel plates or carbon-fiber sheets (CFRP) are glued on the lower face of slab by epoxy resin. Experimental studies were made to clarify the mechanism of punching shear failure and to evaluate the strengthening methods stated the above. Principal conclusions derived are as follows ; 1) During loading tests, surface compression strain of slabs in radial direction near loading position increased at first and it turned to decrease fairly before punching shear failure occurred and even became tension at final stage, though strain in circumferential direction increased monotonously. The fact suggests that the changing of stress flow occurred in the internal structure of slab near loading position during loading. 2) Punching shear cracking spread abruptly irrespective to the existing bending cracks at final stage. 3) The effectiveness of surface strengthening method showed just as the same level as the slabs with same depth. 4) In case of bottom surface strengthening flexural rigidity increased largely. The increase is caused by the arresting effect of crack re-opening with the glued materials.