Exploration of design strategies and optimization for efficient mass timber structures as a function of column position

Abstract

The building sector is responsible for a large share in global carbon emissions. As the load bearing structure is particularly material-intensive, a decisive shift can be achieved by improving its design and decreasing its volume. This thesis examines how structural mass timber floor systems can be designed in an efficient, low-waste manner through a design-oriented approach that is immediately applicable within the context of conventional construction techniques and building practices. Reducing material in timber structures has economical and ecological benefits. Reduced timber demand entails significant cost savings and decreased building weight which considerably cuts embodied carbon. Since common floor systems mainly act in bending, this work focuses on the reduction of moment forces in standard setups comprised of timber slabs, beams, and columns. In principle, bending forces in beams and slabs can be reduced by moving the supports inwards, leading to overhanging structural elements. The original method presented in this thesis shows how this approach applies to conventional mass timber floor systems. This work provides an understanding of how informed column positioning can take advantage of this behavior and allows for material and embodied carbon reduction trough design. The consequent architectural implications of the resulting irregular column grid are explored in a floor plan design suggestion Material demand and embodied carbon are evaluated as a function of column position through finite element analysis and optimization as part of a computational model. By consulting a mass timber manufacturer’s catalogue to assign appropriate products to structural members, this approach enables material reduction in the design process rather than in the production. Bypassing slow-changing, inert fabrication procedures, this method can be realized instantaneously. This work identifies the optimal support position to reduce bending forces in beams and slabs to be at 41% of the distance from the element’s edge to its midspan. Furthermore, this research finds that the impact of ideal column position on material efficiency depends on required minimum effective spans. While being negligible in the absence of constraints, informed column positioning can reduce timber demand by 20% and embodied carbon by 16% when subjected to a minimum effective span requirement of 6 m – a common span in timber construction – in a building of 30x30 m and five floors. Building dimensions are found to have an insignificant impact on these results. This thesis illustrates the potential for architects and engineers to enhance structural efficiency of mass timber floor systems merely by deviating from the usual, regular column grid and taking advantage of straightforward structural principles through design.