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Tagungsband Von der Forschung zur Praxis Erweiterung der Möglichkeiten im modernen Holzbau – Erdbebensicherheit und Brettsperrholz Mai 2021, ISBN:978-906703-57-2

In Switzerland, the advantages of timber buildings for the climate are broadly discussed. In the following paper, a comparative sustainability assessment of four building alternatives is presented. Especially the contribution of implementing Swiss timber versus the implementation of imported timber is highlighted. Additionally, the timber-hybrid building structures are compared to a pure reinforced concrete structure. The timber-hybrid structure, with Swiss timber, has clear ecological advantages with only half the greenhouse gas emissions and half the non-renewable energy consumption compared to the reinforced concrete alternative. Comparing the Swiss timber alternative to the imported timber alternative, there are clear ecological advantages, as well. In terms of economic and social sustainability assessment criteria, the reinforced concrete alternative has the lowest production costs and the lowest labor intensity (measured in terms of full-time equivalents). Additionally, the paper includes an analysis of biogenic CO2 emissions and CO2 storage within the timber building alternatives. Finally, an up-scaling to the national level is attempted, showcasing the ecological and economic advantages of promoting the use of locally produced timber., Sustainability, 13 (3), ISSN:2071-1050

With the increasing number of complex and tall timber buildings with a significant share of unprotected timber surfaces, questions arise about the contribution of the combustible structural elements to the fire development (fire dynamics) as well as on the robustness of these buildings. In recent building projects, measures for robustness have been implemented on ad-hoc basis in agreement between the designer and the authorities. This paper discusses some more general approaches to achieve structural robustness with regard to fire design and evaluates these approaches to give guidance for timber structures., World Conference on Timber Engineering (WCTE 2021), ISBN:978-1-7138-4111-1, ISBN:978-1-7138-4097-8

Mass timber is an increasingly popular material for large and tall buildings. Such buildings typically have higher consequence classes than buildings of traditional timber construction and have higher fire resistance requirements. Architectural demands pushing towards having large surface areas of visible and exposed wood lead to additional fire safety challenges. Previous research has shown that some mass timber products can exhibit glue line integrity failure when exposed to fire, while other mass timber products are not prone to this phenomenon. In practice, it is important to know whether glue line integrity failure occurs, to be able to suitably perform fire resistance calculations (for example using the upcoming version of Eurocode 5) and to be able to predict the fire exposure and duration of fires in real buildings (needed for a performance-based approach). The research presented in this report studies the suitability of a furnace test for determining whether products exhibit glue line integrity failure or not. The study includes the determination of a conservative test duration, by comparisons with conditions of a statistically severe compartment fire. Furthermore, a round robin study with twelve fire tests in furnaces of different labs at different scales, fired with different fuel types has been performed. For all tests, the specimens were made of a mass timber material that does not exhibit glue line integrity failure. The average mass loss rate per unit of exposed area and the average charring rate were determined and assessment criteria were evaluated. Comparisons of the round robin study results have been made, against those of a specific CLT product that has been shown to maintain glue line integrity in numerous furnace and compartment fire tests and a recommendation of a pass/fail criterion is given for a future classification standard.

The fire dynamics of fire compartments when structural timber is left fire exposed has been a major obstacle when more complex timber buildings have been designed in the past. Available models use strong simplifications or require parameter studies to estimate the contribution of the structural timber to the fire development, determine the compartment temperature, the fire duration and assess burnout. To address the shortcomings of available methods, at ETH Zürich, a large experimental campaign was launched to deliver input for an innovative design approach. The approach distinguishes between the source material and the thermally modified material, which acts as temporary storage for energy during the fire event. Consequently, it was possible to assess the variable energy contribution to the compartment and, thus, the fire development. The model results show good agreement with compartment experiments available in the literature. In the future, it is expected that the model can be used to develop simplified design rules for design fires in timber structures., World Conference on Timber Engineering (WCTE 2021), ISBN:978-1-7138-4111-1, ISBN:978-1-7138-4097-8

A common approach to assess the performance of fire insulation panels is the component additive method (CAM). The parameters of the CAM are based on the temperature-dependent thermal material properties of the panels. These material properties can be derived by calibrating finite element heat transfer models using experimentally measured temperature records. In the past, the calibration of the material properties was done manually by trial and error approaches, which was inefficient and prone to error. In this contribution, the calibration problem is reformulated in a probabilistic setting and solved using the Bayesian model calibration framework. This not only gives a set of best-fit parameters but also confidence bounds on the latter. To make this framework feasible, the procedure is accelerated through the use of advanced surrogate modelling techniques: polynomial chaos expansions combined with principal component analysis. This surrogate modelling technique additionally allows one to conduct a variance-based sensitivity analysis at no additional cost by giving access to the Sobol' indices. The calibration is finally validated by using the calibrated material properties to predict the temperature development in different experimental setups., Engineering Structures, 205, ISSN:0141-0296

The structural behaviour of Timber‐Concrete Composite (TCC) slabs, as known, is mainly governed by the shear connection between timber and concrete components. There, a key role is assigned to possible changes in stiffness and strength, especially for TCC systems exposed to fire loading. In the last years, several studies have been spent for the assessment of the fire performance of TCC systems in fire loading, including experimental, analytical and Finite Element (FE) numerical modelling, see for example [1–5]. In desire to describe the behaviour of TCC elements in fire conditions, effects of temperature on the mechanical properties of timber, concrete, and connection components should be properly taken into account. In this paper, a final activity report is proposed from the WG2‐TG2 members. First, experimental methods and results are discussed. Then, an insight on the Finite Element numerical modelling of TCC structures in fire is presented.

In the setting of structural design for fire hazards the simulation of thermal transport in insulation panels is of great interest. The use of such simulation tools initially requires the calibration of the underlying heat transport models and the temperature-dependent specific heat capacity, conductivity and density. We herein outline an approach for the calibration of a finite element model (FEM), describing heat transfer in insulation panels when exposed to fire, by using a Markov chain Monte Carlo (MCMC) based Bayesian inference approach. The procedure is enhanced by employing a surrogate modelling technique that couples polynomial chaos expansion (PCE) with principal component analysis (PCA). This allows the model parameters in question to be inferred in an efficient way. We showcase the adequacy of this approach by calibrating the temperature-dependent effective material parameters for a set of real measurements. We further show the superiority of the presented approach to a widely used conventional manual calibration method in timber engineering., Reliability and Optimization of Structural Systems: Proceedings of the 19th IFIP WG-7.5 conference on Reliability and Optimization of Structural Systems, ISBN:978–3–906916–56–9

This paper summarizes the background of fire design of timber, as it is available to-day for an audience interested in interactions with various fields of science. The inten-tion is to give a broad overview for structural engineers together with available solu-tions but also existing limitations and outlook for the future. The paper addresses (1) the background of the legal design framework to achieve fire safety and (2) thoughts about fire safety in general and in particular for timber structures. The authors point out inconsistencies where further research is needed and also show where political actions are required. Further, the article summarizes the fire resistance design for var-ious members and gives an outlook to the changes in Eurocode 5 (EN 1995-1-2) ex-pected to be implemented in national laws in the year 2025., ISBN:978-3-906226-25-5

We outline an approach for the calibration of a finite element model (FEM) by using a full Bayesian inference approach. The considered FEM describes the heat transfer in insulation when exposed to fire, it uses so-called temperature dependent effective material parameters. These parameters are required for applying the improved component additive method to determine the fire resistance of e.g. timber frame assemblies. After setting up the Bayesian inference problem, we distinguish two approaches to compute the posterior distribution and thus calibrate the sought effective material parameters. The first approach is standard Markov chain Monte Carlo (MCMC) based parameter estimation. In order to alleviate the computational burden typically associated with MCMC computations, we initially construct a surrogate model to be used instead of the computationally expensive FEM code. This model combines a dimensionality reduction technique (principal component analysis), with a sampling-free uncertainty propagation technique (polynomial chaos expansion). A second, novel approach is spectral likelihood expansion (SLE). In this procedure, the likelihood function of the posed Bayesian problem is projected onto an orthogonal basis. Following this projection, the computation of posterior quantities of interest (mean, covariance matrix,...) can be done analytically by post-processing the SLE coefficients. We compare these two posterior computation approaches and showcase their ability to calibrate the sought effective material parameters.

An accurate measurement of the temperature during fire tests is of utmost importance. The measuring device used therefore (1) shall indicate the exact temperatures in the specimen and (2) shall not disturb its temperature field. For timber as a low conductive material this is particularly difficult. The paper presents five standard fire tests (four cross laminated timber panels and one solid timber panel), in which eight different thermocouple designs and installations were investigated. The tests showed that any thermocouple design installed in boreholes perpendicular to the isotherms leads to considerably lower measurements than wire thermocouples placed parallel to the isotherms. Referring to the time when the measurement indicates 300°C the difference is between 10 and 35 min. An installation parallel to the isotherms is found to be accurate, while perpendicular to them suffers from significant heat loss through conduction in the thermocouple. Additionally, missing contact pressure between the thermocouple and the sample increases the temperature discrepancy. Convection in the tight gaps between the thermocouple and the borehole does not happen in usual configuration and hence has no effect on the measured temperature. For proper temperature measurements in timber, it is thus recommended to install thermocouples parallel to the isotherms, to use thermocouples with fewest possible conductive material and a high contact pressure., Structures in Fire SiF'2018 : 10th International Conference on Structures in Fire, Belfast, United Kingdom, 6-8 June 2018, ISBN:978-1-85923-274-3

Karlsruher Tage 2016 - Holzbau : Forschung für die Praxis, Karlsruhe, 06. Oktober - 07. Oktober 2016, ISBN:3-7315-0577-0, ISBN:978-3-7315-0577-8