Seismic Response of Slab Column Connection with Pyramid Shaped Drop Panel

Abstract

Both experimental and finite element analysis (FEA) was used to study the seismic response of reinforced concrete (RC) interior slab-column connection made with pyramid-shaped drop panel subjected to vertical and horizontal loads. The dimensions of the models at “¼ ” linear scale for laboratory testing and FE Analysis (FEA) are derived from rules for dimensions of column drops, given a prototype “9.60m” grid and a slab thickness of “320mm”. Lab specimens were tested with the drops (flat slab, rectangular and pyramid-shaped) facing up, with loadings (vertical down and horizontal in grid direction) applied by jacks towards the top of a central projecting “150mm” square column. One flat slab (“80mm” thick no drop), tested to failure under vertical load (80kN), provided values for setting variables used in the FEA. The remaining 5 lab specimens (1 flat and 1 each rectangular and pyramid-shaped 40mm and 30mm drop thicknesses), under a fixed vertical load (40kN), were tested to failure by increasing a moment at the column slab junction applied by a horizontal load to the column “500mm” above the slab. FEA results for the same conditions compared closely with experimental results. The pyramid-shaped drop models, with equal thickness to the rectangular drop models at the column faces (drops of “40mm” and “30mm”), exhibit similar maximum force resistances to the rectangular drop models. However, these resistances were achieved in the pyramid drops at higher maximum deflections – deflections being measured downwards at column centerline one half of slab thickness away from the face. A parametric study was conducted by FEA, at constant load, in vertical steps (10kN; 25kN 55kN), calculating deflections under increasing horizontal load. Calculations were made on the following definitions: Energy absorption is represented by the area under the deflection vs horizontal load curves; Ductility is the ratio of deflection at maximum to deflection at yield, and Stiffness and Overstrength factors are the slopes of the deflection load diagrams in the elastic and plastic zones respectively. Both drop type models exhibit significantly improved performance compared to the models without drops. The pyramid-shaped drop models exhibited improved energy absorption, ductility, and stiffness and overstrength compared to the rectangular drop models of the same column face thickness.