Fire Resistance of In-Plane Compressed Log-House Timber Walls with Partial Thermal Insulation

Chiara Bedon,Massimo Fragiacomo

doi:10.3390/buildings8100131

Abstract

This paper presents the full-scale experimental assessment of a log-house timber wall with partial thermal insulation under in-plane compression and exposed to fire on one side. A key aspect of the current design application for log-house systems is represented by geometrical details, like cross-sectional properties of logs (typically characterised by high depth-to-width ratios) and outriggers. The latter provides restraint condition for the examined walls and hence markedly affects their overall load-carrying capacity. As a result, careful consideration should be given to the choice of these details, compared to fully monolithic timber walls (i.e., made from cross-laminated timber), due to the possible occurrence of local structural and/or thermo-mechanical mechanisms. This is the case of exceptional loading conditions like fire load, as the fire resistance of these systems could be affected by a multitude of variables, including the presence (even though limited to few surfaces only) of thermal insulation panels. To this aim, the results of a full-scale furnace test are discussed in the paper for a log-wall with partial thermal insulation, namely thermal insulation applied on the outriggers only, under the effects of EN/ISO standard fire conditions. The results of Finite Element (FE) numerical studies are also reported, to further explore the load-carrying performance of the reference log-house specimen and compare it with the experimental observations. Several thermal insulation configurations are finally numerically investigated, showing their effects on the overall fire resistance of the assembly. In accordance with literature, the test shows that the log house’s timber wall is suitable to obtain a fire resistance of about 60 min under relevant loading. The FE results are in rather close agreement with the temperature measurements within the section of logs, as well as a qualitative correlation with respect to the mechanical behaviour observed in the full-scale furnace experiment. The key role of outriggers and their thermo-mechanical boundaries, finally, is emphasised.

Highlights

Introduction andState-of-the-ArtThe fire resistance of timber structures and building systems is an open issue for designers, especially when novel technologies, materials and methods are used
Since the reference temperature of 300 ◦ C is considered to detect the charred section of logs, the numerical simulation gave evidence of a progressive reduction of the actual resisting section, with half charred depth after ≈50 min of fire exposure, suggesting a further correlation with the experimental load-carrying capacity of the full-scale specimen
At the 60th min of fire exposure, the timber logs are expected to offer less than 50% of residual section, giving evidence of large deflection increase and possible buckling phenomena

Summary

Introduction

Introduction andState-of-the-ArtThe fire resistance of timber structures and building systems is an open issue for designers, especially when novel technologies, materials and methods are used. Full-scale tests and specific investigations are frequently required to assess their response under fire exposure conditions (see for example [3,4,5]), loading configurations, as well as to explore the reliability and potential of simplified design methods [6,7,8,9], novel timber-composite systems [10,11], modified material treatments [12], or thermal insulation methods [13,14]. Buildings 2018, 8, 131 in this regard, can offer robust support to full-scale testing, at least for preliminary fire resistance considerations [15,16,17,18,19] This is the case of traditional structural solutions like log-house (or log-haus, or Blockhaus) systems that are not considered by design codes (see for example [20,21]), in fire conditions [22]. Research studies have been focused on their structural performance under various loading configurations, including seismic events [23,24,25,26,27], buckling [28] and thermal exposure [29]

Methods

Results

Discussion

Conclusion