Efficient seismic analysis of high-rise building structures with the effects of floor slabs

Box system structures, composed of only reinforced concrete walls and slabs, have been recently adopted for many high-rise apartment buildings. Commercial software such as ETABS, commonly used for the analysis of high-rise apartment buildings, assumes a rigid diaphragm for floor slabs. The flexural stiffness of slabs is generally ignored in the analysis. This assumption may be reasonable for the analysis of framed structures. In box system structures like apartment buildings, however, the floor slabs may have a significant influence on the lateral response of the structures. If the flexural stiffness of slabs in a box system structure is totally ignored, the lateral stiffness may be significantly underestimated. In reality, the cracked section property of a slab will determine the amount of its flexural stiffness that will be included in the analysis. In order to include the flexural stiffness of slabs, the slab needs to be modeled with plate elements. If the slab is subdivided into many plate elements while keeping each shear wall with a large element (as generally modeled with commercial software), the compatibility condition will not be satisfied at the interface of the slab and the shear wall. To enforce the compatibility condition at the interface, a fictitious beam is introduced. It would cost a significant amount of analysis time and computer memory to model the floor slab with many subdivided plate elements in every floor of a high-rise building. In this study, an efficient method is proposed to analyze high-rise box system structures considering the effects of floor slabs. The proposed method will reduce computational time and memory in the analysis by using the substructuring technique and matrix condensation.