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The effective width of cross-laminated timber rib panels is analysed. The floor system consists of cross-laminated timber plates rigidly bonded to glued-laminated timber ribs by means of screw-press gluing. Ultimate-load tests were performed on four different cross-sections. Digital image correlation was used to visualize and monitor the strain distribution on top of the cross-laminated timber plates at midspan. The longitudinal strain distributions along the cross-laminated timber width were obtained for the determination of the effective width. The experimental results are compared to numerical results of a finite element model and to Eurocode 5 estimations. The longitudinal strain distributions show good agreement and confirm digital image correlation as a suitable measurement technique.

In the frame of a research project, the structural behaviour in fire and the fire resistance of cross-laminated timber rib panels were studied based on experimental and numerical investigations. The floor system consists of cross-laminated timber plates rigidly bonded to glued-laminated timber ribs. The full composite action between the composite components is provided by means of screw-press gluing. The results of the reference tests showed 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 [1]. The fire resistance tests resulted in fire resistances up to 120 min and confirmed the assumption that the effect of the composite action was maintained in fire. In this paper, the numerical investigations cover thermal, and uncoupled thermo-mechanical simulations using a 2D FE model of a linear beam system for discussion of the mechanical behaviour under fire exposure. The numerical results of the tested cross-sections are compared with the experimental results of the fire resistance tests. Depending on the modelled crosssection, the influence of the effective width on the numerical results is investigated.

Cross-laminated timber rib panels are floor systems consisting of cross-laminated timber plates rigidly bonded to glued-laminated timber ribs. The composite action is achieved by screw-press gluing 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.

The composite structure of cross‐laminated timber rib panels consists of cross‐laminated timber (CLT) plates connected to glued‐laminated timber (glulam) ribs. Full composite action is provided by a rigid connection between the composite components by means of screw‐press gluing. For ribbed cross‐sections, the assumption that the cross‐section remains plane is incorrect. The simple beam theory according to Euler‐Bernoulli is not applicable because the strains in the flange vary according to the distance from the rib due to the in‐plane shear flexibility of the flange, leading to a non‐uniform distribution of the longitudinal strains along the flange width. For simplified structural analysis, the effective width defines an equivalent cross‐section that provides the same maximum bending stress and effective bending stiffness as the actual cross‐section. Simplified formulae are proposed as basis for the final document of CLT design for a revised version of Eurocode to determine the effective width at normal temperature for ribbed plates build up from cross‐laminated timber plates. In an ongoing research project, fire resistance of cross‐laminated timber rib panels (CLT rib panels) is studied with experimental and numerical analysis. The experimental results of a series of full‐scale fire tests showed more than 90 and 120 min of fire resistance and confirmed the assumption that the effect of the composite action was maintained in fire. The proposed paper focuses on the numerical simulation of the structural behaviour of CLT rib panels exposed to ISO‐standard fire and loaded out of plane for the discussion of the effective width in fire., INTER Proceedings - Meeting 55

In the frame of a research project, the structural behaviour in fire and the fire resistance of cross-laminated timber rib panels were studied based on experimental and numerical investigations. The floor system consists of cross-laminated timber plates rigidly bonded to glued-laminated timber ribs. The full composite action between the composite components is provided by means of screw-press gluing. The results of the reference tests showed 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 [1]. The fire resistance tests resulted in fire resistances up to 120 min and confirmed the assumption that the effect of the composite action was maintained in fire. In this paper, the numerical investigations cover thermal, and uncoupled thermo-mechanical simulations using a 2D FE model of a linear beam system for discussion of the mechanical behaviour under fire exposure. The numerical results of the tested cross-sections are compared with the experimental results of the fire resistance tests. Depending on the modelled cross-section, the influence of the effective width on the numerical results is investigated., Proceedings of the 12th International Conference on Structures in Fire, ISBN:978-962-367-869-8

In the draft of the Eurocode 5‐1‐2 revision (2020), the charred depth of CLT is modelled using a simplified model, which takes into account two different scenarios: linear charring when the bond line integrity is maintained and stepwise bilinear charring when the bond line integrity is not maintained. That means that fall‐off of charred CLT layers is taken into account when during fire exposure the bond line integrity is not maintained. Numerical simulations based on FE heat transfer models are usually conducted based on the temperature‐dependent thermal properties for wood and the char layer according to the current Eurocode 5‐1‐2 (2004). König and Walleij (1999) proposed these thermal properties for initially unprotected and protected timber members. Thus, fall‐off has been considered as single incident in the case of fall‐off of the fire protection system. However, it is questionable if the thermal properties according to the current Eurocode 5‐1‐2 (2004) can be used for CLT plates showing multiple fall‐off of charred layers. In the frame of an ongoing research project the fire behaviour and fire resistance of cross‐laminated timber rib panels (CLT rib panels) is studied with experimental and numerical analysis. The floor system consists of cross‐laminated timber plates rigidly bonded to glued‐laminated timber ribs by means of screw‐press gluing. Two different types of cross‐section are studied. The experimental results of a series of full‐scale fire tests recently concluded showed more than 90 and 120 min of fire resistance and confirmed the assumption of fall‐off of single or multiple charred CLT layers. The proposed paper focuses on the numerical simulation of the charring behaviour of the CLT plates exposed to ISO‐standard fire on one side, taking into account multiple fall‐off of CLT layers. The proposed paper provides the results of numerical simulations, which were conducted for the analysis of the development and distribution of the temperature within the four tested cross‐sections, in comparison with the experimental results and the estimated results according to the simplified design method of Eurocode 5‐1‐2 revision (2020). For this objective, FE 2D heat transfer models were generated modelling the cross‐section of a T‐section or box‐section. Fall‐off of charred CLT layers were defined as time steps of the thermal simulation when the average temperature between CLT layers exceeded 300°C. In a further step, the FE model was re‐created omitting the fallen‐off layer and the calculation was continued until the next layer has fallen off. Using the temperature‐dependent thermal properties according to Eurocode 5‐1‐2 (2004), the thermal simulations predicted a significantly earlier fall‐off of the charred CLT layers in comparison with the experimental results. The proposed paper presents a new set of thermal properties calibrated to the experimental results of the tested cross‐sections of the CLT plates. The validation of the calibrated data is made by comparing additional thermal simulations with further experimental results (mostly single CLT plates). This leads to the proposal to use the new set of temperature‐dependent thermal properties for cross‐laminated timber to consider the effect of multiple fall‐off of charred layers.

Ein Begrenzungsfaktor für den Holzbau ist oftmals die Nachfrage nach weitspannenden Deckensystemen. Diese Anforderung wird insbesondere für Gebäudetypen mit flexiblem Grundrissaufbau wie gewerbliche Bürogebäude, Wohngebäude, Schulen und Industriegebäude benötigt. Zusammen mit einem Industriepartner wird an der ETH Zürich ein Deckensystem für Spannweiten über 6 m diskutiert. Der obere Flansch besteht aus Brettsperrholz, welcher mittels Schraubpressverklebung mit einer Rippe aus Brettschichtholz (BSH) zu einem Verbundquerschnitt schubsteif verbunden wird. Im Rahmen einer Doktorarbeit ist es das Ziel Bemessungsregeln von CLT-Rippendecken für die außergewöhnliche Situation einer Brandbeanspruchung zu entwickeln, welche derzeit nicht durch den Eurocode abgedeckt werden. Innerhalb einer ersten Versuchsreihe wurden vier Querschnitte in Grossbrandversuchen auf ihre Feuerwiderstandsdauer sowie in Referenzversuchen unter Normaltemperatur auf ihre Bruchlast untersucht. Die Ausführung und Erkenntnisse dieser Versuchsreihe werden in dieser Publikation beschrieben und diskutiert.