Timber-glass shear wall stabilised timber modules

Abstract

Currently, most of the modular building can be fabricated off-site, except for the stability system. Therefore, the question arises: Could modules be designed such that there is no need for an additional stability system? As modules are typically built in a rectangular shape, incorporating stability elements such as bracings along the longer side of the module is not the problem. The main challenge lies in the limited length available for stability elements on the shorter side of the module, combined with the fact that this shorter side is commonly used for windows and openings for door frames. This introduces a conflicting interest between structural capacity and daylight within the module. This conflicting interest becomes more and more prominent as the building height goes up. A possible solution to this problem can be found in the use of a load-bearing window frame with glass infill as a stability element, often referred to in literature as a timber-glass shear wall (TGSW).

Therefore, this thesis will answer the main research question: 'To what extent can the structural performance of a timber-glass shear wall as a stability element in a timber module be used to accommodate for the stability of a mid-rise modular timber building?'

The approach to answering the main research question consists of several steps. First, a literature study was conducted on modular buildings and TGSW's. The outcome of the study has provided insight into how modular buildings are constructed in general and how relevant aspects such as progressive collapse, fire safety design, and foundation design influence structural design. The study also resulted in an analytical prediction model for the load-bearing capacity and stiffness of the TGSW. Through this prediction model, it became clear how the properties of individual components relate to the load-bearing capacity and stiffness of the total TGSW-system.

The second step was to propose a design for a modular timber building composed of timber modules. To save on computational time, the stability elements of the building are modelled using steel diagonals as an equivalent system for the TGSW. The cross-sectional area of the steel diagonals is directly related to the properties of the TGSW. Therefore, the steel diagonals have identical stability properties as the TGSW. In this study, varying the type of adhesive and the spacing of the screws was found to have the most significant impact on the overall structural properties of the TGSW. The horizontal connections are made of steel plates fastened with screws. The vertical connections are realised by shear plate connectors. The entire building was modelled in a 3D FEM programme to assess the structural behaviour of the building and its compliance with building regulations. Several building configurations ranging from 1:1 to 1:3 height-to-width ratio were investigated. For each building configuration, the cross-sectional area of the steel diagonals was adjusted within a specified range. This range corresponds to variations in adhesive type or screw spacing. As a result, design graphs were produced, which present the requirements for the load-bearing capacity and stiffness of the stability system. These can be compared to the load-bearing capacity and stiffness of the TGSW. This comparison can be used as a validation method to determine the viability of the TGSW stability element in a modular building.

The results of this study indicate that a modular building can be stabilised by a TGSW up to six stories within the height-to-width ratio of 1:1 to 1:3. The minimum building configurations per story height are: 3 modules high by 5 modules wide, 4 by 8 modules, 5 by 12 modules, and 6 by 18 modules. These slenderness ratios were governed by the strength of the TGSW. The limiting factor in the load-bearing capacity is the shear strength of the adhesive. These slenderness ratios could only be reached with elastic adhesives such as silicones.

The next step is to create a more extensive FEM model that could predict the load-bearing capacity and stiffness of the TGSW in a more accurate way compared to an analytical model. Furthermore, exploring the performance of the TGSW under different horizontal loads, such as earthquakes, would give valuable insight.