Cross-laminated timber rib panels in fire


Kleinhenz, Miriam

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Cross-laminated timber rib panels are floor systems consisting of cross-laminated timber platesrigidly bonded to glued-laminated timber ribs. The composite action is achieved by screw-pressgluing using a one-component polyurethane adhesive. The structural behaviour, fire behaviour, and fire resistance were studied using experimental, numerical, and analytical investigations.
The overall aim of the thesis was the development of design rules for cross-laminated timber rib panels in fire. The experimental investigations cover ultimate-load tests at normal temperature as reference tests, and fire resistance tests under standard fire exposure on four cross-section types. In addition, shear tests of the glue line between cross-laminated timber plate and glued-laminated timber rib were performed at normal and elevated temperatures for analysis of the cross-sections’ composite action. The results of the reference tests show good agreement with results based on the method of rigidly bonded components and the effective width according to the final European draft of cross-laminated timber design prEN 1995-1-1. The shear tests and the fire resistance tests confirm the assumptions that the glue line remains intact and the effect of the composite action is maintained in fire. The screws remaining after screw-press gluing have negligible influence on the fire behaviour of the floor system. The fire resistance tests show results on the safe side compared to predictions of the fire behaviour according to EN 1995-1-2 and its final draft prEN 1995-1-2. However, the fire resistance is underestimated due to the conservative assumption that the effective width is limited to the rib width in case of fire. The numerical investigations cover thermal, mechanical, and thermo-mechanical simulations using finite-element models. All finite-element models are validated against the experimental results. A new set of temperature-dependent thermal properties for timber exposed to standard fire is proposed to take into account the post-fall-off behaviour in fire. The thermo-mechanical models give good approximations of the cross-sections’ structural behaviour in fire and their fire resistance. A parametric study analyses the structural behaviour in fire, and thus the effective width in fire for a parameter range expected in practice. Design rules are presented for the design of cross-laminated timber rib panels in fire. The effective width in fire is defined depending on the effective width at normal temperature according to prEN 1995-1-1. The analytical investigations are discussed in comparison to the experimental and numerical results using the method of rigidly bonded components for the design in fire. The developed design rules are shown to give safe estimates of the fire resistance.