Post-fire performance of glulam panels after real fire exposure and strain-rate effects in a multi-hazard scenario

Fire safety design is critical for timber elements, and predicting effective post-fire resistance is essential for safety, reuse, and retrofitting. This aspect has become increasingly important with the growing use of mass timber in mid- and high-rise construction, where structural elements may be exposed to multi-hazard scenarios, such as fire followed by blast loading. This study investigates the post-fire performance of glued-laminated timber panels exposed to real fire, with a focus on char depth, charring rate, equivalent zero-strength layer (ZSL) and post-fire assessment under static and dynamic loading. The panels were extracted from the Mass Timber Demonstration Fire Test Program in Ottawa. The average char depth and charring rate were 20.0 mm and 0.78 mm/min, respectively, exceeding the values in current design standards. Static tests showed a post-fire equivalent ZSL thickness of 23.8 mm, which is significantly larger than the code-based in-fire ZSL values used for fire design calculations. As the specimens were tested after cooling, this equivalent ZSL represents a post-fire residual strength-loss depth rather than the in-fire ZSL defined in design standards. These results highlight the need to potentially revise post-fire assessment approaches to account for larger residual strength-loss depth and higher charring rates. Under high strain rate loading, the equivalent ZSL increased further, indicating that multi-hazard scenarios may require dedicated design approaches.