Seismic Tensile Force on Steel Girder-Concrete Wall Connections in High-Rise Composite Building Structures

Abstract

Composite steel frame – reinforced concrete (RC) core wall structures are often used in high-rise buildings. It is commonly assumed that reinforced concrete walls carry lateral loads such as earthquake loads, while steel frames carry gravity loads. As a result, lateral loads are directly applied to wall elements during a typical structural analysis. This design based on this simplification can be adequate for most structural members except the connections between steel girders and RC walls. This study focuses on the tensile loads on girder-wall connections for composite building structures in earthquakes. Computer models were created for a 28-story composite structures recently built in Chongqing China. SAP2000 was used because detailed finite element models are available for RC shear walls and slabs without high computational costs, and a variety of earthquake analyses are available such as effective lateral load analyses and time history analyses. Different from typical analyses for design, floor slabs are modeled using shell elements such that the earthquake induced inertia force are properly positioned in the structure model. In addition, a gap is created between floor slabs and RC walls to better represent the slab-wall interfaces created by stage construction. The analysis results indicated that 1) a significant amount (more than 50 percent) of floor inertia forces is transferred to core walls through steel girders and girder-wall connections; 2) the total floor inertia force is directly related to the acceleration responses at floor levels; 3) the tensile forces on girder-wall connections also include that created by incompatible deformations between RC core walls and steel frames, especially at lower levels. All previous studies on the girder-wall connections are on their load resisting capacity. This study is a demand analysis and critical step towards a reasonable safe design for composite structures. Future studies must include realistic models of the connections and other components such as embedded reinforcements. Shake table tests of building models are also critical in order to verify the demand analyses. The demand analyses will result in a set of reasonable design loads for engineers to safely design composite build structures in seismic regions.