New Methods in Efficient Post-Tensioned Slab Design Using Topology Optimization

Post-tensioned (PT) flat-plate gravity framing systems are highly efficient and reduce embodied carbon when compared to conventional reinforced concrete framing systems. Efficiency is especially apparent in multi-span applications with regular orthogonal support arrangements. Even though PT flat-plate gravity framing systems are less efficient in single-span or irregular support applications, they are is still useful in reducing slab thickness, improving construction efficiency, and reducing seismic mass. A novel approach to determining PT tendon arrangements has been applied to several buildings informed by topology optimization results. Topology optimization is an optimization method which determines optimal load paths in a finite element continuum. Thus, by orienting PT tendons along the optimal load paths suggested by topology optimization, it has been shown that 25% or more of PT quantities can be reduced while maintaining the same mild steel reinforcement. Many of the observed arrangements do not follow traditional uniform/banded arrangements. Also, the deflection performance is significantly more consistent since tendons are resisting load in a manner consistent with the load demands. This can help alleviate common issues with thin flat-plate gravity systems such as irregular floor flatness due to warping incited by PT systems and inconsistent deflection at the exterior wall. This new design method has been applied to three buildings and coordinated with construction teams for efficient application. This presentation will discuss the entire design procedure from initial concepts through complete construction documents as applied to three buildings. This presentation will be of interest to academics and practicing structural engineers.