Water Efficient Suppression Material Fire Behaviour and AI Driven Safety in Future Fire Protection Research

There is difficulty in accurately modelling adhesive influence in structural performance of cross laminated timber (CLT), due to a lack of available knowledge on the heat performance of adhesives. Therefore, the main aim of this research was to evaluate the thermal and mechanical properties of adhesives used in production of engineered wood products like CLT. The properties of the timber species and the adhesive types used in the simulation were derived from published literature and handbooks. ANSYS mechanical 2020 R1 was employed because it has a provision for inserting the thermal condition and the temperature of the system set to the required one for analysis. The simulations were conducted for temperatures 20, 100, 140, 180, 220, and 260 °C, within which Zelinka et al. conducted their experiments, which have been the basis for the current study. The main findings were, the adhesive layer had little influence on the thermal properties of CLT composite (solid wood had the same thermal properties as CLT), but had a significant effect on the structural properties of CLT composite, the stresses and strains of the simulated wood species reduced with increase in temperature, the adhesives strengths at room temperature were greater than for solid wood at the same temperature and finally, the stresses and strains of the simulated wood adhesives reduced with increase in temperature. It is also important to note that computations for temperature distribution from the char layer were lower than computed using heat transfer equation, and the simulated values from steady state model. All in all, the objectives of this research were met and more research in thermal structural modelling using ANSYS should be conducted in the future.

Cross-laminated solid timber panels represent an interesting technical and economical product for modern timber structures. The use of large prefabricated cross-laminated solid timber panels for load-bearing wall and floor assemblies has become increasingly popular in particular for residential timber buildings. The fire behaviour of cross-laminated solid timber panels has been experimentally and numerically studied during two different ongoing research projects carried out at the Institute of Structural Engineering of ETH Zurich, Switzerland and the Trees and Timber Institute CNR-IVALSA in Trento, Italy. The paper presents the main results of the experimental and numerical analyses. Particular attention is given to the comparison of the fire behaviour of cross-laminated solid timber panels with homogeneous timber panels. The results of the analysis have shown that the fire behaviour of cross-laminated solid timber panels depends on the behaviour of the single layers. If the charred layers fall off, an increased charring rate needs to be taken into account. The same effect is observed for initially protected timber members after the fire protection has fallen off. Thus the fire behaviour of cross-laminated solid timber panels can be strongly influenced by the thickness and the number of layers. Further vertical structural members (walls) may show a better fire behaviour in comparison to horizontal members (slabs).

Fire represents a serious challenge to the safety and integrity of buildings, especially timber structures exposed to high temperatures and intense heat radiation. The combustibility of timber is one of the main reasons why regulations strictly limit timber as a building material, especially in multi-storey structures. This investigation seeks to assess the fire behaviour of cross-laminated timber (CLT) edifices and examine the ramifications for structural integrity and fire protection. Utilising computational fluid dynamics (CFD) simulations, critical variables including charring rate, heat emission, and smoke generation were analysed across two scenarios: one featuring exposed CLT and another incorporating protected CLT. The outcomes indicated that protective layers markedly diminish charring rates and heat emission, thereby augmenting fire resistance and constraining smoke dissemination. These revelations imply that CFD-based methodologies can proficiently inform fire protection design paradigms for CLT structures, presenting potential cost efficiencies by optimising material utilisation and minimising structural impairment.

Construction fires are a big threat to worker safety and property safety. Mass timber buildings under construction are largely unprotected as they are not yet equipped with active fire protection systems. With the addition of Types IVA, B, and C, the 2021 International Building Code adopted stricter requirements for mass timber buildings that are under construction. Cross‐laminated timber (CLT) is used as the primary structural element for high‐rise mass timber buildings. However, to date, limited number of research studies investigated the impact of passive fire protection for CLT buildings that are under construction. To facilitate a better understanding of construction fires and their consequences, it is necessary to develop a numerical modeling solution for the early phases of a CLT construction project, which can be achieved by using building information models together with fire dynamics simulation (FDS). However, the numerical modeling technique must be benchmarked against experimental data first to then extrapolate the modeling technique to explore other parameters and conduct FDS analysis. Therefore, this paper develops and benchmarks a numerical modeling solution against a mid‐scale CLT compartment fire test by applying the FDS tool to simulate the fire behavior within the CLT compartment. The FDS analysis results are expected to validate the practicality of simulating the fire behavior in CLT structures using the numerical model proposed in this study. The overarching goal of this study is therefore to develop a comprehensive numerical modeling solution to simulate and assess passive fire protection sequencing in CLT buildings that are under construction.

Observations and impact of char layer formation and loss for engineered timber

Timber panel construction using Cross-Laminated Timber (CLT) or Laminated Veneer Lumber (LVL) panels have been developed for cost and construction efficiencies in the building industry. The increased use of timber as a sustainable construction material in buildings is expected to expand the forest industry and increase carbon stock. Heavy timber structural elements with sufficient load bearing capacity could be used in tall buildings. However, sufficient data are not yet available to understand the structural and thermal behaviors of domestic timber panel elements with cross laminations/layers when they are exposed to fire. In this study, fire testing data for timber panels are obtained and the charring characteristics and failure modes of structural elements under standard fire exposure are investigated to develop a simple method for estimating the fire resistance of timber panels. Toward this end, a series of experiments consisting of heating tests and load bearing tests for walls in furnaces with various experimental parameters was conducted. The experimental parameters considered include the adhesive type, thicknesses of laminations and panels, wood species, fire protection, and applied loads of the panels. Experiments without loading showed that CLT and LVL panels and joints of panels with 135 mm thickness showed sufficient thermal insulation and integrity over 90 min in standard fire tests. Smoke leakage from the joints of the timber panels was observed in the early stage of the fire tests because of a lack of air-tightness. Delamination of almost all charred layers glued with an API adhesive was observed in fire tests of CLT panels; however, delamination of LVL and CLT panels with a RPF adhesive was limited. The estimated charring rates of a Japanese cedar CLT panel with API and RPF adhesives were 0.78 mm/min and 0.66 mm/min at 260°C, respectively. The charring rate of LVL panels was ∼0.6 mm/min at 260°C, less than that of CLT panels. The load bearing capacity of timber walls subjected to one-sided fire exposure depended on the buckling strength under the eccentric load caused by asymmetric charring. A prediction method based on the Secant formula was presented to estimate the buckling strength in fire tests. An equation that considered the effect of the degradation of elasticity at high temperatures and eccentricity of loading provided the approximate buckling strength of the timber panel specimens in the fire tests.

Structural health monitoring data collected during construction of a mass-timber building with a data platform for analysis

Application of European design principles to cross laminated timber

The embodied carbon of timber buildings is often miscalculated at early design stages. Primary materials in mass timber developments typically include glulam and cross-laminated timber, the volume of which is estimated and used to quantify upfront carbon emissions. However, to ensure like-for-like comparisons, the impact of metallic connections and, where needed, fire protection (boarding or treatment) and acoustic insulation should also be considered, even at early stages. This is particularly relevant when comparing timber against concrete schemes, which normally do not require additional allowances for connections, fire protection and soundproofing. This study suggests the upfront embodied carbon of a timber superstructure may increase by up to 60% in residential developments and 30% in commercial buildings when considering secondary components critical to the structure. Note that this is an initial study and that more real-world data should be collated to improve the accuracy of these findings, especially for residential buildings.

The European market for cross-laminated timber (CLT) is rapidly growing in the field of multi-story residential buildings. However, water leaks repeatedly lead to severe moisture damage in timber buildings. Undetected moisture damage may result in biological degradation of the CLT structure, is difficult to repair, and incurs high costs. Currently, there is a lack of awareness of the fact that timber buildings require different mechanical, electrical and plumbing (MEP) installation methods than buildings made with mineral construction materials. In addition, too little attention is given to protecting the wooden structure by applying appropriate sealing measures that actually work in practice. Lack of planning and uncoordinated construction work exacerbate this problem. Presenting 2D drawings and 3D BIM models, the paper illustrates concepts that can be used to optimally design and safely integrate MEP installations in bathrooms in multi-story residential timber buildings. A special focus is placed on a holistic view of the topics structure, pipe installation, sealing, and fire protection. The concepts presented are based on an analysis and classification of over 1100 bathroom layouts. Therefore, they are applicable to a wide range of bathrooms in practice. The presented results were developed in the research project CLT_Plumbing_Design. They contribute to the development of standardized, timber-specific solutions for pipe installation and sealing in bathrooms, and can help reduce moisture damage in timber construction. In addition, these concepts form a basis for a new automated planning process in the area of bathroom planning, for which a brief outlook is given.

The European market for cross-laminated timber (CLT) is rapidly growing in the field of multi-story residential buildings. However, water leaks repeatedly lead to severe moisture damage in timber buildings. Undetected moisture damage may result in biological degradation of the CLT structure, is difficult to repair, and incurs high costs. Currently, there is a lack of awareness of the fact that timber buildings require different mechanical, electrical and plumbing (MEP) installation methods than buildings made with mineral construction materials. In addition, too little attention is given to protecting the wooden structure by applying appropriate sealing measures that actually work in practice. Lack of planning and uncoordinated construction work exacerbate this problem. Presenting 2D drawings and 3D BIM models, the paper illustrates concepts that can be used to optimally design and safely integrate MEP installations in bathrooms in multi-story residential timber buildings. A special focus is placed on a holistic view of the topics structure, pipe installation, sealing, and fire protection. The concepts presented are based on an analysis and classification of over 1100 bathroom layouts. Therefore, they are applicable to a wide range of bathrooms in practice. The presented results were developed in the research project CLT_Plumbing_Design. They contribute to the development of standardized, timber-specific solutions for pipe installation and sealing in bathrooms, and can help reduce moisture damage in timber construction. In addition, these concepts form a basis for a new automated planning process in the area of bathroom planning, for which a brief outlook is given.

Critical heat flux and mass loss rate for extinction of flaming combustion of timber

Slim-floor-type of steel-timber hybrid floor systems which use steel beams contained within the depth of the cross-laminated timber (CLT) floor slab offer many benefits, but there is still very little research available on the fire resistance performance of these systems. In the study presented in this paper two furnace tests and numerical simulations have been conducted to investigate the thermal profiles of the steel member and CLT slabs and to obtain information on the temperature development and charring of the hybrid beam section when it is exposed to standard fire conditions. Also, the effects of intumescent fire protection on temperatures and charring performance were investigated. Numerical 2D thermal simulations for unprotected and protected cases were conducted using SAFIR software, and the agreement between experiments and numerical-analysis predictions were in general very good. The results show that intumescent protection reduces the temperatures of the steel and CLT components as well as charring depth significantly, and the start of charring at CLT slab support may be delayed if intumescent paint protection thicker than that required for the load bearing steel member is used. The result also showed that CLT temperatures exceed 100°C already in the early stages of the fire which decrease the strength and stiffness properties of CLT much before the start of charring. Therefore, the fire design of the CLT slab support should not only consider the char depth and residual cross-section analysis but also the reduction in strength.

The purpose of this paper is to investigate the fire performance in a multi-storey cross-laminated timber (CLT) structure by the computational fluid dynamics (CFD) technique using the Fire Dynamics Simulator (FDS v.6.7). The study investigates fire temperature, heat release rate (HRR), and gas concentration (O2, CO2). The importance of this research is to ensure that the fire performance of timber buildings is adequate for occupant safety and property protection. Moreover, the proposed technique provides safety measures in advance for engineers when designing buildings with sufficient fire protection by predicting the fire temperature, time to flashover and fire behaviour. The present numerical modelling is designed to represent a 10-storey CLT residential building where each floor has an apartment with 9.14 m length by 9.14 width dimensions. The pyrolysis model was performed with thermal and kinetic parameters where the furniture, wood cribs and CLT were allowed to burn by themselves in simulation. This research is based on a full-scale experiment of a two-storey CLT building. The present results were validated by comparing them with the experimental data. Numerical simulation of CLT building models show a very close accuracy to the experiment performed in the benchmark paper. The results show that the CFD tools such as FDS can be used for predicting fire scenarios in multi-storey CLT buildings.

Buildings constructed from engineered timber are becoming more prevalent globally as building designers, owners and architects realize the sustainability opportunities with timber construction and the overall aesthetic of a completed timber building. As timber buildings are planned to be taller than many model codes permit, the National Fire Protection Association (NFPA) Fire Protection Foundation commissioned research entitled “Fire Safety Challenges of Tall Wood Buildings”, with the aim of understanding where the current gaps in knowledge are and how the research agenda should be prioritized. With new engineered timber products such as cross-laminated timber becoming more prevalent, this study evaluated the current knowledge of tall timber construction to identify gaps in knowledge, and where if fulfilled, will provide a better understanding of the potential fire safety performance of tall timber buildings. The study identified a number of knowledge gaps, of which most were related directly to the new technology of engineered timber products that have resulted from the use of CLT. These included system-level fire testing, use of composite assemblies, CLT char fall-off and construction fire safety. The study concluded that the priority for future research should target three areas of research, being the contribution of exposed timber to room fires; connections between timber components and timber composite assemblies; and penetrations for building services.