Irregular Flat Slabs Designed According to Structural Membrane Approach

Flat slabs are less labour intensive, simplify the installation of services and can accommodate more floors within restricted heights. However, the span influencing their design is the longest and they require more steel compared to two-way slabs. Other drawbacks of flat slabs are vulnerability to punching shear failure and higher deflections. To avoid punching shear failure drop panels, column heads or shear reinforcement are used. If span in flat slabs is reduced then both deflection and punching shear problems can be avoided. However, architects prefer to have few exposed columns in usable areas. This inevitably leads to columns in an irregular layout, hidden inside partitions or walls [1]. Flat slab construction with columns in an irregular layout is a viable solution in constructing buildings that satisfy their functional requirements in urban environments. The purpose of this paper is three fold. One is to encourage the application of the structural membrane approach to design flat slabs on non-rectangular column grid by providing experimental evidence [2,3]. Second is to encourage more research on bimoment concepts. Third is to leave some carefully performed experimental evidence for the research community to be used in validating structural assessment tools like nonlinear finite element or yield line analysis. In the next section, existing approaches to design flat slabs on non-rectangular column layout are briefly reviewed. Methods involving trial and error, like yield line design (considering the slab with an assumed steel distribution and assessing the load capacity for possible yield line patterns) or elastic finite element analysis (which results in peaky moments above columns and needs experience to perform redistribution) are not considered. This is followed by a simplified introduction to structural membrane approach applied to flat slabs. When applied to flat slabs, twisting moments along particular directions are assumed negligible in the structural membrane approach. This assumption is checked by using Gurley’s bimoment concepts applied to flat slabs on square column layout [4]. In the following sections experimental method, details of specimens and their behaviour at ultimate load and service load are discussed before concluding the paper.