Progressive Collapse (Robustness) Resistance of Tall Frame Timber Buildings with Cross Laminated Timber Floors

Project Description

This project aimed to advance industry knowledge about the performance of engineered wood products (EWP) mass timber products such as Cross Laminated Timber (CLT) and Laminated Veneer Lumber (LVL) used in mid-rise to tall timber buildings which are becoming internationally popular. With increased building height, these buildings must be designed for progressive collapse, as specified in the National Construction Code. Progressive collapse is essentially a dynamic process, and the dynamic response of mass timber frame buildings under a sudden column removal scenario is still unknown. In addition, internationally recognised progressive collapse design guidelines, developed from studies performed on steel and concrete buildings, unsatisfactorily lead to design “guesses” and uneconomical conservatism or unsafe designs.

This project will fill this gap in knowledge by experimentally and numerically quantifying the dynamic responses and resistance demands of mass timber frame buildings subjected to a sudden column loss. The ultimate outcome of this project will be a scientifically-based collapse-resistant capacity prediction model replicating the true dynamic nature of progressive collapse of mass timber frame buildings. This will result in safe, economical and efficient designs, thereby preventing injury and the loss of life.

Project Personnel and Beneficiaries

The world is witnessing an increasing number of mid-rise mass timber buildings because they provide significant benefits to communities. Using timber in building constructions enables less resources and less energy to be consumed when compared to traditional concrete and steel buildings, thereby minimising adverse environmental impacts. Timber buildings require less time and less specialised workers to be constructed, thus saving time and money for both domestic and commercial property owners.

The research outcomes will help to effectively mitigate the seriousness, or prevent the occurrence, of progressive collapses through gaining new knowledge and fundamental understanding of the behaviour of mass timber buildings. The project outcomes will also benefit Australian consulting engineers and the building sector by providing advanced expertise in progressive collapse, thereby improving the structural integrity of the next generation of mid-rise mass timber buildings.

Outcomes to Date

A total of 11 static and 25 dynamic tests were conducted on 2-bay planar post-and-beam mass-timber frames. The ability of commonly used beam-to-column connections to develop catenary action was evaluated and an understanding of the dynamic responses of such systems was gained. Additional five 2×2-bay 3D post-and-beam mass-timber substructures were also tested to large deformation stages. Results showed that continuous CLT floors, by creating alternative load paths, are important design elements to robust mass timber buildings. 2D and 3D high-fidelity finite element models were also established to capture both the compressive arch and catenary actions in 2D frames and to accurately replicate the experimentally recorded ultimate loads, failure modes, load redistributions, and strain developments of 3D substructures under various column removal scenarios.