DESIGN ASPECT OF INCLUDING INFILL WALL IN REINFORCED CONCRETE FRAME DESIGN FOR SEISMIC REGION
Contribution of infill wall to the lateral stiffness of structure has been acknowledged by many researchers but its analysis and design method is not yet adopted in most building codes. This study compares analysis and design of a 4 story infill frame with open basement structures, modeled as open frame (MOF) and infill frames (MIFs). The reason of modeling walls as structural is to satisfy requirement of column thickness not to exceed wall thickness. The reinforced concrete (RC) frames in the basement are made bigger to avoid soft story effect using 20 MPa concrete and 400 MPa rebar. In the first infill model (MIFStrut), infill wall of 4 MPa was modeled using 6 compression only diagonal strut. The second infill model (MIF-Strut-Mod) was developed by modifying dimensions of column in MIF-Strut to satisfy the code’s steel ratio criteria. The 3rd infill model is MIF-Shell, in which the wall was modeled as shell element, with gap element at the interface between frames and wall. Finally, a full wall model (MIF-Full) was made by adding walls at basement level of MIF-Strut. All five 3D models are loaded with vertical and quake load appropriate for south Bali region. Results show that the infill models are more than twice stiffer than MOF in the wall direction. Perpendicular to the wall, however, the lateral stiffnesses of all models are similar. MOF also require 29 percent more steel and 2 percent more concrete than MIFs for the columns. Compared to the shell model, the strut model is slightly more flexible and consequently, produces more conservative design. Interestingly enough, the soft storey mechanism cannot be avoided in the absence of wall at basement level, regardless of the bigger column dimensions.