Impact of Combustible Linings in the Simulated Fluid Dynamics of a Compartment Fire

The modern building industry is continually seeking materials and products that are less pollutant, stronger, more aesthetically appealing and easier to construct with. As a response to these drivers, Engineered Wood Products (EWP) have entered the construction market as an evolution of very well-known conventional products such as plywood. However, contrary to plywood, EWP consist of much thicker layers and contemporary glues. New manufacturing technologies enable the use of EWP on an entirely different scale. Today, wooden high-rise buildings, bridges, and other macro-structures can effectively be designed.Despite the multiple benefits of timber construction, new fire safety hazards have sparked with the arrival of EWP. These hazards correspond to increased fuel load density and the potential for structural collapse since timber structures are combustible. These changes challenge the fire safety strategy for timber buildings.The purpose of any fire safety strategy is to ensure a safe evacuation and operation of a building during and after a fire event. Most fire strategies rely on compartmentalisation (physical boundaries that restrict fire spread to other parts of the building) and on a robust structure that maintains its integrity after all the fuel has burned out. Compartment fire dynamics and external flaming are key to understanding how compartmentalisation can be achieved in timber buildings. To ensure compartmentalisation and structural integrity, it is fundamental that the timber walls and floors stop burning, i.e. self-extinguish. Charring materials such as timber have the ability to self-extinguish without external intervention under certain circumstances.This research aims at investigating the effect of exposed timber on the compartment fire dynamics and the external flaming with respect to the current fire dynamics’ theory for buildings with non-combustible structures. This thesis also aims to study the mechanisms that lead to self-extinguishment of timber in compartments with a geometry representative of residential construction. For this purpose, three experimental campaigns using Cross Laminated Timber (CLT) were conducted. The first consisted of medium-scale compartment fires with varying configurations of exposed CLT with a kerosene pool fire as the fire source. The use of kerosene as the fuel facilitated the characterisation of the fire dynamics. The second consisted of medium-scale compartment fires with two exposed CLT walls and different densities of wood cribs as the fire source. The use of wood cribs as the fuel allowed for a progressive and long decay phase to be achieved. The third consisted of a large-scale demonstration test to enable a scaling analysis and validation of the results from the medium-scale tests.The most novel finding from this research is that the burning of the internal CLT surfaces induces additional momentum-driven flows, thus altering the energy balance in the compartment. As a result, it was found that the commonly-used compartment fire framework developed by Thomas et al., which relates temperatures and fire regimes to the compartment geometry only, is not applicable. The location of the exposed timber surfaces is shown to be relevant for the fire behaviour; an exposed CLT ceiling always presents a lower burning rate than any other vertical wall.As in any under-ventilated fire, the excess of pyrolysis gases produced by the CLT walls is found to be unable to combust inside the compartment due to a lack of oxygen. These gases are forced to flow outside, producing a much larger external flame than those obtained in fires with non-combustible boundaries. This thesis proposes new models to predict the projection and thermal exposure of external flaming as a function of exposed CLT inside the compartment.Finally, design criteria are proposed to achieve self-extinguishment of timber in the context of compartment fires. These criteria are a function of the amount of exposed timber and its location within the compartment.To conclude, this thesis provides an insight into a new framework for compartment fires with exposed timber walls. This framework serves as input to engineering new fire safety strategies for this type of structures. The outcomes from this research indicate that by adding additional exposed timber surfaces the fire dynamics within the compartment experience a change in regime, the external flaming is more severe and self-extinguishment may or may not occur in time depending on the ratio of exposed timber and its configuration.

The use of mass timber in construction is becoming a compelling option when faced with the high carbon footprint of traditional concrete and steel production. However, fire safety standards are yet to evolve to support these designs. Encapsulation is commonly used to protect all, or some, of the timber surfaces and reduce the risks introduced. This paper presents the results fromCodeRed #04, the final experiment of theCodeRedexperimental campaign. This experiment was carried out inside a purpose‐built facility to capture fire dynamics in large compartments with exposed timber.CodeRed #04had identical characteristics toCodeRed #01with the exception that ~50% of the cross‐laminated timber (CLT) ceiling was encapsulated. The experiments were intentionally similar to the traveling fire experiments,x‐ONEandx‐TWO, which had a non‐combustible ceiling to enable a direct comparison. The overall fire dynamics experienced inCodeRed #04, intersect the characteristics observed inCodeRed #01andx‐ONEandx‐TWO.1. InCodeRed #04, there was a delay in the ignition of the CLT ceiling as the CLT directly above the crib was encapsulated. Once the CLT ceiling ignited, the fire spread rapidly throughout the compartment. The peak heat release rate (HRR) was estimated to be approximately 100 MW, a 17% decrease fromCodeRed #01. Following CLT ignition the resulting fire duration, maximum temperatures, and heat fluxes were broadly similar toCodeRed #01. Flame heights of approximately 1.5 m were observed from the windows while flame heights of 2.5–3 m were observed inCodeRed #01. Therefore, flame heights were found to be comparable tox‐TWO.1, though over a greater number of windows, reflecting the greater extent of simultaneous burning within the compartment. The average charring depth of the exposed CLT panels was ~25 mm, which is similar to that measured inCodeRed #01‐suggesting that the fire severity near the ceiling was not strongly impacted by the 50% encapsulation of timber. No charring was observed where the ceiling was encapsulated and loaded service fixings installed through the encapsulation were found to be less likely to fail than when attached directly to the exposed timber. Smoldering was observed after the cessation of flaming and, in a few locations, was observed to progress through the thickness of the CLT panel and continue behind the encapsulation. This illustrates that, while encapsulation can succcessfully prevent flaming, it cannot be completely relied on to avoid smouldering. The findings fromCodeRed #04contribute to the development of evidence‐based fire safety design methodologies for exposed mass timber buildings.

As concerns about climate change and its extensive impacts continue to grow, the construction industry has become focus of attention due to its substantial role in contributing to carbon dioxide emissions and resource depletion. This research thesis delves into the potential of timber structures, particularly cross-laminated timber (CLT), to offer sustainable alternatives to traditional construction materials. The study is structured into two main parts: an examination of the long-term performance of CLT and an evaluation of its environmental impacts through life cycle assessment (LCA). The initial section of the study focuses on the durability and mechanical integrity of CLT structures, emphasizing their capacity for long-term serviceability. This includes an in-depth analysis of the fatigue behavior of self-tapping screws used in CLT, which are pivotal for the structural reliability of timber buildings. The research identifies optimal angles and depths for screw insertion, which significantly enhance the load-bearing capabilities of these connections, thus contributing to the overall durability and safety of timber constructions. In the second part, the environmental credentials of CLT are rigorously assessed through a comprehensive LCA. This analysis quantitatively compares the carbon footprints of a building constructed with CLT versus one built with the conventional material, concrete. The findings reveal that CLT reduces upfront carbon emissions due to its lower energy-intensive production processes and serves as a carbon sink, thus offsetting emissions throughout the building’s lifecycle. Additionally, the LCA highlights the benefits of using sustainably sourced CLT to reduce the overall environmental impact of construction activities. By integrating detailed experimental research with environmental evaluation, this thesis substantiates the role of mass timber, particularly CLT, as a sustainable construction material that aligns with global efforts to mitigate climate change. It offers architects, builders, and policy-makers valuable insights into the advantages of incorporating timber in modern construction, paving the way for more sustainable building practices that significantly lessen the construction industry’s environmental footprint.

The contribution of exposed mass timber to compartment fire dynamics is often framed by prescribed fuel load density, implicitly assuming fuel-agnostic thermal feedback. This paper interrogates that assumption experimentally using full-scale cross-laminated timber (CLT) compartments with two exposed surfaces (ceiling and side wall) and a movable fuel; either a kerosene pool or a wood crib. High-resolution measurements of heat flux, in-depth timber temperatures, burning rates, opening flows, and gas species demonstrate that fuel chemistry and geometry strongly modulate oxidizer delivery and residence time, thereby governing radiative feedback, CLT burning rates, and external flaming. The pool fire exhibited pronounced radiative enhancement and transient oxidizer starvation near the timber until pool decay. In contrast, the crib burning rate was inhibited, while the CLT burned efficiently. Analysis of the Global Equivalence Ratio (GER) and air bypass ratio revealed significant excess oxygen in the outflow, indicating that entrained air did not permeate the crib but instead oxidized the CLT, leaving unreacted air due to short mixing timescales. Despite unchoked doorway conditions, the crib fire produced bypass ratios and external flaming fractions comparable to the pool fire. The work shows that fuel load and ventilation factors alone are insufficient to describe the mass timber compartment fire dynamics and the CLT performance (e.g. charring). The fuel chemistry, geometry and placement have significant levels of interaction with the compartment geometry. Therefore, the role of the moveable fuel is fundamental, and care must be employed when extrapolating demonstrator experiment results to the fire safety design of mass timber buildings. • Burning rates of pools, wood cribs and exposed timber in large compartment fires • Mass balance in a large timber compartment fire quantified • Entrained air can bypass the fuel leaving unreacted oxygen in the outflow • Exposed timber burning rates are dependent on local flow and oxidizer field • Fuel load density alone is insufficient to characterize timber compartment fires

The use of cross laminated timber (CLT) for construction has increased greatly in recent years and the large volumes of wood used for CLT means that it is important to optimize the use of the material. This requires relevant grading of lamellas and knowledge of relationships between lamella and CLT properties. In the present study, the relationship between dynamic axial modulus of elasticity (MoE) of lamellas and the quasi-static out of plane bending stiffness of CLT is investigated. By means of four-point bending test, it is shown that the effective quasi-static MoE of lamellas in CLT is only 2–6% lower than the average axial dynamic MoE of the individual lamellas. With this knowledge, producers of CLT can easily predict and control the important out of plane bending stiffness of the produced CLT. Moreover, it is shown that effective rolling shear stiffness of layers in CLT can be accurately determined by means of digital image correlation performed in connection to four-point bending of CLT, even for long test spans. For layers of lamellas of Scots pine of size 40 × 190 mm2 the average apparent or effective rolling shear modulus was determined to be 159 MPa. The average rolling shear modulus of the same material was determined to be 56 MPa.

SummaryStandard fire resistance tests have been used in the design of structural building elements for more than a century. Originally developed to provide comparative measures of the level of fire safety of noncombustible products and elements, the recent resurgence in engineered timber construction raises important questions regarding the suitability of standard fire resistance tests for combustible structural elements. Three standard fire resistance floor tests (5.9 m × 3.9 m in plan), one on a concrete slab and two on cross‐laminated timber (CLT) slabs, were undertaken to explore some of the relevant issues. The fuel consumption rate within the furnace was recorded during these tests, and the energy supplied from this was determined. An external fuel supply (from natural gas supplied to the furnace) equating to approximately 3 MW was recorded throughout the concrete test, whereas this was about 1.25 MW throughout the CLT tests. The total heat release rate was calculated using carbon dioxide generation calorimetry; this yielded values of approximately 1.75 MW during the CLT tests (ie, an additional energy contribution of approximately 0.5 MW from the timber). This demonstrates that considerably more energy input (by about 1.25 MW) was needed to heat the system when the test sample was noncombustible. A further series of six large‐scale compartment fire experiments (6 m × 4 m × 2.52 m) was undertaken to further explore comparative performance of combustible versus noncombustible construction when the external fuel load is kept constant and is governed by more realistic compartment fire dynamics. For a fuel‐controlled case, the peak temperatures in the compartment with an unprotected CLT ceiling were approximately 200°C higher than in the compartments with a concrete ceiling, whereas for a ventilation‐controlled case, the compartment with a CLT slab ceiling displayed a burning duration that increased by approximately 15 minutes. Potential implications for standard fire resistance testing of combustible specimens are discussed.

Multistory buildings using mass timber and cross-laminated timber (CLT) as the primary structural elements are being planned and constructed globally, with interest starting to gather momentum in the United States. Model building codes in the United States limit timber construction to a building height of 85 ft (25.9 m) because of concerns over fire safety and structural performance. Up to 85 ft, the mass timber can be exposed. Architects and developers in the United States are pushing boundaries, requesting mass timber structures are constructed as high-rises and that load-bearing mass timber such as CLT be exposed and not fully protected. This provides an opportunity for the application of recent fire research and fire testing on exposed CLT to be applied, and existing methods of analyzing the impact of fire on engineered timber structures to be developed further. Fire testing has shown that exposing large areas of CLT significantly impacts the heat release rate and fire duration. This article provides an overview of the code requirements for timber construction in the United States, provides methods for building approval for a high-rise timber structure, and summarizes recent CLT compartment fire testing that is informing the fire engineering process. Methods for solutions are also discussed.

Cross-laminated timber (CLT) construction is gaining momentum in the US because it offers multiple advantages over traditional construction methods. Benefits that have received the most attention focus on constructability, the environment, and protection (e.g., blast resistance), although CLT construction is likely to offer other benefits, as well. Still, these have not been studied at length because such evaluations are costly, requiring long-term assessments in an actual building and specialized technical knowledge. Among the possible benefits, CLT construction likely provides a higher-performing building envelope. Using CLT panels to enclose a building means fewer joints in the opaque envelope than what is required in traditional stick-framed construction. Fewer joints mean fewer locations where the air- and water-resistive barrier (WRB) could be compromised; thus, a CLT building enclosure may require less maintenance and have a longer lifespan than a traditionally built structure because of fewer air and water leaks. In addition, CLT’s thermal mass moderates indoor temperatures, allowing the heating, ventilation, and air conditioning (HVAC) system to operate more efficiently during peak hours, reducing operational energy consumption throughout the lifetime of the CLT building (Salonvaara et al., 2022). Furthermore, more stable indoor temperatures can increase occupant comfort. The CLT’s thermal mass can also reduce energy costs by adjusting to utility time-of-use pricing without affecting occupant comfort. The ability of CLT buildings to bridge periods without HVAC operation prepares them for future grid interaction and provides a certain level of resilience against power outages. Researchers have attempted to quantify these benefits; however, their work is based on simplified simulations with numerous assumptions. To correctly understand the benefits, an actual building must be monitored. Therefore, information needs to be gathered on indoor and outdoor temperatures, HVAC energy consumption, thermostat setpoints, temperatures, and thermal transport in CLT components to comprehend how these parameters are affected by the CLT’s thermal mass. These data are needed to reduce the number of assumptions and calibrate simulation models to optimize HVAC controls to minimize overall energy consumption, reduce energy use and higher fees during peak demand, and maintain occupant comfort. Additionally, the calibrated simulation model allows the optimization exercise to be repeated in various US climates. Potential benefits can be tailored to buildings in various locations, and decisions can be made on where CLT construction could be most advantageous. Furthermore, monitoring and simulation results are needed to evaluate the durability of the CLT structures in different climates. This project’s researchers gathered information to help understand and quantify the benefits of CLT buildings concerning operational energy, moderated indoor temperatures, and comfort; the dynamic operation to provide grid services; and resilience in times of power outage. Through the corroboration of simulation models with real-world measurements, this study paves the way for extrapolating findings to other climatic zones and building typologies, thereby broadening the understanding of CLT’s multifaceted benefits and reinforcing its position as a material of choice in sustainable construction.

Cross-laminated timber (CLT) is an innovative wood product that is increasingly used in both residential and non-residential construction projects, since it offers a range of advantages, such as light carbon footprint, quick erection time, good thermal and sound insulation characteristics. CLT members have the potential to provide excellent fire resistance characteristics, often comparable to typical massive, non-combustible construction assemblies. However, the fire performance of CLT can be affected by a large variety of material and design parameters, such as physical properties (e.g. density, grain orientation), member thickness, number of plies, adhesive type, connector type, protection panels. In this context, this work presents a thorough review of recent experimental studies, aimed at determining the fire behaviour of CLT members. A large number of test results obtained in a broad range of setups, spanning multiple scales, such as cone calorimeter (50 tests), standard fire resistance furnace (90 tests) and fire compartment (20 tests), are comparatively assessed. The impact of the main material and design parameters on several important fire performance factors is investigated. Analysis of the reported experimental results allows the determination of certain global trends that are observed in the majority of cases.

Cross Laminated Timber (CLT) construction is now considered a viable and sustainable alternative to traditional building techniques within the multi-storey building sector. This is primarily due to the high level of prefabrication possible with CLT construction, its high strength-to-weight ratio and its potential as a carbon negative building material. As a result, an increasing number of developers and architects are requesting a CLT design option for multi-storey buildings using CLT wall and floor panels. The latter, especially long span floors, provides a challenge for engineers. Long span CLT floors have a lower natural frequency and are light in weight, which can cause noticeable vibrations. This paper examines existing analytical design procedures available to calculate floor vibrations and provides a preliminary design for floors spanning 9 m. Innovations in CLT panels are introduced, including increased connection rigidity and the use of hardwood timber species, resulting in increased panel stiffness and reduced floor vibrations. Whilst CLT has been extensively researched and tested in Europe and Canada, only limited research has occurred within Australia and New Zealand. This paper also discusses Australian and New Zealand standards and codes and the use of locally grown soft and hardwood timber species for CLT panels.

A total of 50 healthy volunteers aged between 18 and 54 years underwent phase-contrast cine MRI to assess cerebrospinal fluid flow characteristics in different regions of the vertebral canal. The results revealed that the cerebrospinal fluid peak flow velocity and peak flow rate in the systolic phase were significantly greater than those in the diastolic phase at the same level in the subarachnoid space of the cervical spinal canal. The ventral peak flow velocity and peak flow rate were significantly greater than the post-lateral peak flow velocity and flow rate, while there were no differences between left and right post-lateral subarachnoid peak velocity and flow rate. Moreover, there were no significant differences in peak flow velocity and peak flow rate between the systolic and diastolic phases, ventral, right post-lateral or left post-lateral peak flow velocity and peak flow rate at the same level in the subarachnoid space of the cervical spinal canal among different age groups (18-24, 25-34, 35-44, ≥ 45 years).

<p>In a climate where standard methods of construction are being challenged, developments in engineered timbers are allowing mass timber construction to be explored as a sustainable alternative to traditional building methods. Cross- laminated timber (CLT) is at the forefront of this evolution and, with the advancement in computational design and digital fabrication tools, there lies an opportunity to redefine standard construction. This project explores how digital modelling and advance digital fabrication can be combined to generate a connection system for CLT panels. The advantages of CLT and mass timber construction are numerous and range from environmental and aesthetic benefits to site safety and cost reduction benefits. There are, however, issues that remain surrounding the connections between CLT panels. Steurer (2006, p.136) stated that, “Progress in engineered timber construction is directly related to developments in connector technology.” This thesis creates connections inspired by traditional Japanese joinery that have been adapted to be used for the panel construction of CLT structures. Using CLT offcuts as a primary connection material, the system not only reduces waste but also mitigates thermal bridging and lowers the number of connection points whilst increasing the ease of building and fabrication. The connections are first considered at a detail scale. They use the literature review and case studies as a base for design before being tested using digitally fabricated prototypes. These prototypes are evaluated against a framework created in line with the aforementioned criteria. Within this framework, the connections are analysed against existing connection systems as well as previous designs to establish a successful system. The connections are then evaluated within the context of a building scale and considers large-scale fabrication and on- site assembly whilst continuing to focus on the reduction of waste. This research found that the simplicity of the connections is key to a successful system as this allows for faster and cheaper fabrication and installation. However, there is still further research needed surrounding large-scale fabrication and the structural capacity of timber connection systems.</p>

<p>In a climate where standard methods of construction are being challenged, developments in engineered timbers are allowing mass timber construction to be explored as a sustainable alternative to traditional building methods. Cross- laminated timber (CLT) is at the forefront of this evolution and, with the advancement in computational design and digital fabrication tools, there lies an opportunity to redefine standard construction. This project explores how digital modelling and advance digital fabrication can be combined to generate a connection system for CLT panels. The advantages of CLT and mass timber construction are numerous and range from environmental and aesthetic benefits to site safety and cost reduction benefits. There are, however, issues that remain surrounding the connections between CLT panels. Steurer (2006, p.136) stated that, “Progress in engineered timber construction is directly related to developments in connector technology.” This thesis creates connections inspired by traditional Japanese joinery that have been adapted to be used for the panel construction of CLT structures. Using CLT offcuts as a primary connection material, the system not only reduces waste but also mitigates thermal bridging and lowers the number of connection points whilst increasing the ease of building and fabrication. The connections are first considered at a detail scale. They use the literature review and case studies as a base for design before being tested using digitally fabricated prototypes. These prototypes are evaluated against a framework created in line with the aforementioned criteria. Within this framework, the connections are analysed against existing connection systems as well as previous designs to establish a successful system. The connections are then evaluated within the context of a building scale and considers large-scale fabrication and on- site assembly whilst continuing to focus on the reduction of waste. This research found that the simplicity of the connections is key to a successful system as this allows for faster and cheaper fabrication and installation. However, there is still further research needed surrounding large-scale fabrication and the structural capacity of timber connection systems.</p>

Cross-laminated timber (CLT) has been widely discussed as a relevant industrialized construction solution. Numerous publications have considered CLT as a structural wood-based panel, but other documents have mentioned it as a building or even a construction system. Many authors address its application in multistory buildings, although single-family houses and lower building applications have become desirable topics as well. Given these gaps, this review study addresses a systematic method to evince the functions of cross-laminated timber in construction. The elucidation and discussion were led by technical and scientific contents through publications present in scientific websites and the Google web search engine. Intricate perceptions about the knowledge and reference of CLT functions were identified. From prospections, it was possible to state that CLT is a timber-forest product created in Europe, whose function acts as a structural composite panel of the engineered wood product category. However, CLT has been mentioned by many publications as a building or a construction system. Suggestions were raised to clarify to all readers with respect to misconceptions, and elucidate the construction systems capable of using it as the main resource. Discussions evinced the characteristics and potentials of this wood product. Even with its increasing application in tall buildings, the commercial application of CLT in low-rise buildings may be boosted by the possibility of large-scale production of industrialized houses.

Comparative life cycle assessment of a reinforced concrete residential building with equivalent cross laminated timber alternatives in China