This paper describes fire tests on loaded glued laminated timber columns in which the structural response was measured during the heating and cooling phases. Identical columns with 280 × 280 mm2 ...cross‐section and 3.7 m length were tested under various heating durations in a standard furnace to investigate integrity to full burnout. Two of the columns were subjected to ISO 834 heating until failure and their measured fire resistance was 55 and 58 min, respectively. Two columns were subjected to 15 min of ISO 834 heating followed by controlled cooling; these columns failed during the cooling phase, respectively after 98 and 153 min. Flame self‐extinction occurred after approximately 40 min while smoldering continued locally. Two columns tested under 10 min of ISO 834 heating both survived the defined heating–cooling exposure. Thermocouples inside the columns show sustained temperature increases for hours after the end of the heating phase. These full‐scale furnace experiments show that timber columns may fail during the cooling phase after exposure to standard heating for about 25% of the standard fire resistance duration. These results, in line with previous numerical predictions, highlight the need for further investigation into fire safety until full burnout for timber structures.
•Various single and ensemble-based ML models were developed and compared to predict the fire resistance of timber columns based on geometry and material-related parameters.•Different explainability ...methods are examined to understand the physical relationship between fire resistance, column geometry, and timber properties.•Random forest models provide accurate and balanced predictions of fire resistance.•Column capacity at ambient feature is the most important parameter to predict fire resistance.
The global attention to using timber products as sustainable construction material urges careful assessment of their performance against different hazards, particularly fire. However, the current methods prescribed by design codes for evaluating the fire resistance of timber components tend to underpredict the outcomes of standard fire resistance tests, and lack interpretability due to the use of semi-empirical equations. This study develops explainable data-driven models to predict fire resistance of timber columns using geometry- and material-related properties based on a comprehensive experimental database. Nine different single and ensemble-based machine learning algorithms were trained, and their performance was optimized through rigorous hyperparameter tuning and feature selection. The best models were then interpreted using partial dependence and Shapley plots to infer the underlying relationship between fire resistance and column properties. Lastly, the models’ predictive capabilities were compared to available prescriptive equations. The results show that a random forest-based model provides the best performance with an average ratio of predicted to observed fire resistance of 1.03 on the test set. The random forest prediction is mainly governed by column capacity at ambient temperature, and to a lesser degree, columns’ cross-section dimension. In addition, the partial dependence plots indicate that the effect of density, modulus of elasticity, length, and compressive strength on fire resistance was not notable. Finally, while the considered prescriptive equations consistently underpredict fire resistance, the random forest model provides a consistently accurate and balanced prediction.
The paper presents a newly developed steel‐timber composite column, called “STIMBER‐COL”, which is made of an inner hollow section wrapped by several veneer layers glued together. In addition to the ...well‐known environmental benefits, the potential advantages at mechanical level are thoroughly discussed in consideration of the literature available. In view of the promising experimental results on steel‐timber composite columns reported in recent studies, a foreseen experimental campaign of 5 stub and 3 slender columns is described along with the setup and instrumentation. Special emphasis is given to the manufacturing process which represents a challenging step in this feasibility study. The test results confirm that the veneer layers lead to a significant increase in stiffness and strength. The work is conducted in the frame of an applied research project to support more advanced research and the implementation of the market in the future.
This study presents the first ever investigation aimed at accurate numerical modelling of the behavior of hybrid fibre reinforced polymer (FRP)-timber laminated (HFT) Cee section columns under axial ...compression. Existing numerical modelling approaches for modelling thin-walled structural members, such as modelling using composite laminate shell elements, orthotropic laminate shell elements with experimentally obtained properties, were found to either over-predict or under-predict the stiffness and capacity depending on the approach used. Existing modelling approaches fail to accurately capture the effects of possible interlaminar slips under combined flexural and axial loading. A new modelling approach using ABAQUS subroutine UGENS was proposed incorporating both in-plane stiffness matrix and bending stiffness matrix simultaneously, forming the general section stiffness matrix. Failure initiation criteria and a damage evolution law were incorporated in the subroutine to derive the damaged section stiffness matrix. The predictions from the proposed numerical model showed much improved agreement with the test results.
•Existing numerical approaches for modelling laminated structures were found to be inadequate for modelling HFT Cee sections columns.•Both axial and bending properties are important in modelling the behaviour of HFT Cee section columns.•A numerical model considering different membrane and bending stiffnesses was developed to predict the behaviour of the HFT Cee section columns.•Proposed numerical model was found to accurately capture the behaviour of HFT Cee section columns.
For any construction material, failure during or after the decay phase of a fire is possible, notably due to delayed temperature increase and material properties degradation. As mass timber ...construction is increasingly proposed for large buildings, there is a need to better understand the susceptibility of timber members to fire decay phases. This paper investigates the resistance to full burnout of timber columns. First, a dataset of glulam columns tested under standard fire is analyzed using finite element modeling, showing conservative agreement. Then, the numerical model is used to analyze the columns under ‘standardized’ natural fires comprising a cooling phase. Adopting a systematic procedure based on the minimum Duration of Heating Phase (DHP) that leads to failure, the burnout resistance of the columns is found to range from 20 to 50% of their standard fire resistance. These results indicate significant susceptibility to failure during the cooling phase, which is due to the combined effect of delayed heating and loss of mechanical properties at relatively low temperatures for timber. Based on heat transfer and structural mechanics, it is thus shown that guaranteeing resistance to full burnout with timber structures presents important challenges, even when setting aside the question of combustibility and auto-extinction.
•Numerical modeling of standard fire resistance tests on timber columns shows conservative agreement.•The columns are then analyzed under natural fires to quantify resistance to full burnout.•The burnout resistance (DHP) varies between 20% and 50% of the standard fire resistance time.•Delayed heat transfer in timber sections is critical given the material strength loss at moderate temperature.•Designing for burnout requires explicit consideration beyond the issue of auto-extinction.
Prefabricated glass fibre reinforced polymer (GFRP) wrapping systems have been established as an attractive retrofitting technique for structural columns in various applications. Further exploration ...is needed to evaluate their contribution to the flexural performance of timber columns due to their inevitable exposure to bending under different loads, such as wave actions, wind, and earthquake, among the others. This study investigates the contribution of GFRP wrapping systems to the capacity of timber columns tested under three-point bending. Eight unwrapped and GFRP-wrapped circular timber columns with annular space filled by grout or epoxy materials were tested. The inclusion of carbon FRP (CFRP) straps within the epoxy infill was also investigated. The flexural load-midspan deflection, longitudinal strain responses, and failure modes were carefully studied. Finite element modelling (FEM) and theoretical analyses were performed and compared with the experimental results. The results revealed that GFRP-wrapped columns with epoxy infills exhibited a significant increase in flexural capacity by up to 95% compared with unwrapped columns. The results also showed that the provision of epoxy infill along with CFRP straps within the wrapping system can substantially improve the energy absorption of timber columns whilst, those with grout infills revealed a remarkable increase in ductility compared with unwrapped columns. The results predicted by FEM and theoretical analyses were in good agreement with experiments. This study demonstrated that the studied GFRP wrapping system is an adequate strengthening technique that can improve the flexural performance of circular timber columns.
Traditional Chinese timber columns are prone to rocking and sliding because the column feet are directly placed on foundation stones. Determining the motion of columns under horizontal accelerations ...is essential to preventing the collapse of traditional Chinese timber structures during earthquakes. This paper divides the states of motion of traditional Chinese timber columns into static and dynamic. For the static state, a coefficient describing the compression height is proposed based on the variation of the compressive zone at the column foot, and the moment-rotation relationship of the column foot is then established. For the dynamic state, the rocking and slide-rocking dynamic equations are proposed by considering the contribution of the column foot and the mortise-tenon joint to the lateral force of the timber columns. Finite element models of timber frames are constructed and validated through existing timber frame shaking table tests. Based on numerical simulation, this paper analyzed 125 groups of timber column models and 98 groups of timber frame models to validate the proposed static and dynamic equations. The results reveal that the proposed moment-rotation relationship of the column foot agreed with the simulated results at the initial stiffness and bearing capacity. Hence, the proposed dynamic equations reflect the timber columns' slide and rocking characteristics under horizontal acceleration. This investigation provides a theoretical base for the reinforcement and protection of traditional Chinese timber structures during earthquakes.
•Adhesive bonding of wooden tubes by injection.•Real-scale tensile tests on thin-walled moulded wooden tubes.•Probabilistic prediction of ultimate load capacity.
Moulded wooden tubes combine the ...advantages of the sustainable building material wood with the material efficiency that can be found in the field of steel and composite construction. They are particularly suitable for lightweight constructions and cantilevered structures under dynamic loads. The objective of ongoing research is the design of a joining solution that is appropriate for the material and structure of the tubes. This paper describes an adhesive approach for connecting thin-walled timber elements to tubular steel connectors. The presented solution will be applied for the fabrication of connections within a truss tower segment used in small wind power turbines. In addition to experimental investigations, numerical approaches to determine the load carrying capacity of such joints are presented. The experimental investigations include both compression and tensile tests on specimens of different sizes. For the numerical determination of the joint capacity a probabilistic approach is used which takes into account specific properties of brittle failure modes and allows for the determination of a characteristic strength value used by engineers in the design of structures. The numerical results are verified by the experimental data and show good accordance for both load cases.
Summary
Timber buildings are becoming increasingly sought after for their aesthetic and environmental appeal. Commonly, timber elements are encapsulated using multi‐layered fire rated gypsum board in ...order to prevent the timber from contributing additional fuel load to the fire or to be approved by authorities. In recent studies performed in the last 5 years where non‐standard fire exposures have been utilised, there have been concerns as to whether encapsulation successfully can improve the fire performance of the assembly due to board fall off or heat penetration between layers in the full duration of a non‐standard fire scenario (which includes cooling phases and burn out). There has been a dearth of attention in understanding the underlying mechanisms to these documented behaviours. To address this research gap, a two‐stage research program studying multi‐layered and fire‐rated gypsum clad stand‐alone columns was undertaken by the authors in both a field and controlled laboratory study. These experiments were conducted with the purpose of understanding timber column multi‐layered encapsulation performance in non‐standard fires that include a natural cooling phase. In the field study, a stand‐alone timber column within a large, open farm structure was encapsulated in three layers fire rated gypsum board. The fire was spot‐ignited and allowed to burn until the building and the column collapsed. That experiment provided evidence that the fire rated gypsum board was not sufficient to protect this timber column, as the temperature increases under the layers of gypsum board were equivalent to the temperature increases on the exterior of the column. The second stage of the research involved four, encapsulated timber columns with localised non‐standard fires (methanol pool fires exposing one face only) in controlled laboratory conditions. These tests used novel narrow‐band spectrum illumination to document the underlying breakdown of the gypsum board with non‐standard fire exposure and cooling phases. Results of these experiments imply that timber elements can be adequately protected from fire exposure providing that the screw spacing is strictly adhered to and redundant layers are utilised. The article concludes with a listing of priority research areas that will advance knowledge of the performance of gypsum boards on timber in fire.
In order to check out the effects of the method how the FRP sheets wrapped on the axial behavior of timber columns confined by CFRP sheet, 6 short columns were confined with CFRP sheets in different ...wrapped ways, i.e. toroidal, single helix, double helix and cross helix. Another column in the same size was prepared as contrast. The ultimate carrying capacity of the specimens was analyzed as well as the load-displacement curves and strain-stress relationships. The comparison of the ultimate carrying capacity showed significant enhancement when the specimens were confined in any ways, and the way wrapping FRP sheets in the toroidal direction was more efficient than other ways in which the FRP sheets wrapped in the experiment. The analysis of the load-displacement curves indicate that the stiffness of the specimens was improved by the reinforcement with FRP sheets in any ways, however, the improvement of the ultimate carrying capacity and the stiffness was in the cost of the ductility. The comparison of the FRPs train between the specimens with toroidal wrapping method and the helix ones can clearly explain the lower efficiency in the enhancement of ultimate carrying capacity of the specimens with helix wrapping methods.
