Experimental Investigations On Eccentrically Loaded RC Interior Slab-column Connections

Reinforced concrete slabs on columns were initially dev eloped in the U.S. and Europe at the beginning of the 20 th century. Thanks to the simple structure form, reduced building story heights, convenient for construction and good economic efficiency, they have become very common for residential and office build ings as well as for parking garages. To increase the lateral stiffness and strength of the structure, shear walls are added in the actual engineerings. Inevitably, slab-column connections are usually subject to both gravity loads and unbalanced moment simu ltaneously due to the factors such as lateral load, the unequal spans of slab-column structure itself and the others, which prones to occur brittle punching shear failure. This subject therefore still attracts attention by code writers and researchers.In this paper, gravity shear ratio and slab reinforcement ratio were adopted as the two test variables of competitive experiment to study the failure process of eccentrically loaded interior slab-column connection by means of 7 specimens. Test data including the load-deflection curves and deflected shape of slabs, strains of the concrete and longitudinal reinforcedments, cracking pattern at the bottom of slab, the cracking load and limited strength were obtained, and the formation and development of inner shear crack were monitored by using a special strain measuring rod during the experiment. The test results showed that the failure pattern of specimens was related to both gravity shear ratio and slab reinforcement ratio; unbalanced moment bearing capacity of the same gravity shear ratio specimens can be improved effectively by increasing reinforcement ratio; the inner shear crack has been generated before punching shear failure happens, and develops from the middle or the upper area of slab to the compression zone near the column and the tension zone locating at the bottom of specimen.Based on the test results and historical test data, the accuracy of punching shear capacity formulas for square section interior slab-column connections were compared, which were propsed or adopted by Ying Tian, Kyoung-Kyu Choi, Zhaofa SHU, code GB50010-2010, ACI318-11 and Eurocode2-04. For the conservative calculation on the critical shear stress and the unreasonable criterion of slab-column connection failure, the discrete degree of calculation results are pretty high by using GB50010-2010 and ACI318-11 based on eccentric shear stress model for the high gravity shear ratio connections. A suggestion was put forward that the influence of gravity shear ratio should be considered when calculate the unbalanced moment distribution coefficient 0?, and the calculation accuracy was inproved by modifying original code formula according to the advice.