Light Timber Frame Research Articles

Collapse processes and associated loading of square light-frame timber structures due to bore-type waves

Extreme hydrodynamic events such as hurricanes or tsunamis threaten coastal regions in particular. Such hazards must be assessed and appropriately incorporated into building codes to mitigate casualties and damages to coastal structures. Guidelines are often developed through experimental investigations that assume buildings remain rigid during hydrodynamic loading. To challenge this ‘rigid building paradigm’, test specimens were designed to replicate the deformation characteristics of an idealized light-frame timber structure using Froude-Cauchy similarity. Subsequently, a large-scale experimental study was conducted at the Large Wave Flume of the Coastal Research Center in Hannover. Hydrodynamic loads and load gradients were investigated to describe both the influence of an elasto-plastically modeled test specimen compared to a rigid reference model and the effect of load history on the structural loads. Finally, the collapse sequences of elasto-plastic specimens were extracted from high-speed photographs and classified into three failure mechanisms. In this study, data analyses are presented with the intention to not only inform local authorities for future development of guidelines but also serve as calibration and validation data for improving numerical methods. • A new methodology to replicate light-frame wood structures is provided. • Realistic tsunami on land conditions are resembled in large-scale experiments. • Structural loads due to bore-like flows differ for rigid and non-rigid structures. • Collapse processes are disseminated and categorized in three failure mechanisms. • Failure mechanisms of idealized light-frame wood structures vary significantly.

Seismic performance of glulam timber post and beam structures with and without light frame timber shear wall infill

Timber post and beam structure is typical frame construction with a simple structural system and clear force transmission path. This work studies the seismic performance of glued-laminated timber (glulam) post and beam structures under cyclic loading, as well as the effect of light frame timber shear walls on their seismic performance. Experimental investigation on two types of full-scale glulam post and beam structures was carried out to compare the failure modes, mechanical properties, and energy dissipation. According to the test results, simplified models whose nonlinearity was assumed to be concentrated plasticity in the springs were developed. The comparison between test data and model prediction has a good agreement in terms of evaluation from backbone curves and strength degradation ratio. This calibrated model was then adopted as a benchmark model for further parametric analysis. Eight different configurations considering various aspect ratios were modeled to assess the influence of elastic stiffness and the maximum load-carrying capacity using the pushover analysis. The test investigation and numerical analysis of the glulam post and beam structures with and without light frame timber shear walls help comprehensively understand the seismic performance, providing some valuable guidance for further studies and structural design in engineering practice.

Numerical Analysis of the Seismic Performance of Light-Frame Timber Buildings Using a Detailed Model

Timber structures have gained interest for the construction of mid-rise buildings, but their seismic performance is still a matter under development. In this study, a numerical analysis of the seismic performance of light-frame timber buildings is developed through a highly detailed model using parallel computing tools. All of the lateral-load-resisting system components and connections are modeled. Combinations of lateral load capacity distributions in structures of one, three, and five stories are studied in order to assess the effects on the global performance of different triggered failure modes through nonlinear static and dynamic analyses. The results suggest that shear bracket connections and sheathing-to-framing connections control the buildings’ responses, as well as the failure mode. For a ductile response, the lateral displacement must be dominated by the in-plane wall distortion (racking); therefore, the system must be provided with a story shear sliding stiffness and load capacity at least twice that of the walls. Furthermore, based on the pushover capacity curves, the performance limits are proposed by evaluating the stiffness degradation. Finally, the effect of the mobilized failure mode on the structural fragility is analyzed. Even though standard desktop PCs are used in this research, significant reductions in the computation effort are achieved.

COMPARATIVE CARBON-FOOTPRINT ANALYSIS OF RESIDENTIAL BUILDINGS WITH DIFFERENT STRUCTURAL MATERIALS

An important step towards achieving sustainability goals in the construction sector is taken by developing solutions that adopt ‘greener’ structural materials for buildings. This paper establishes a comparison among four existing residential buildings in Sweden, that utilize different structural solutions, in terms of their global warming potential (GWP). The structural solutions compared are prefabricated reinforced concrete (RC), light timber frame, cross-laminated timber (CLT) panels, and CLT modular construction. For each building, a life cycle assessment (LCA) was performed to estimate the greenhouse gas (GHG) emissions attributable to material production. In general, the results of this study revealed climate benefits associated with timber-based construction, with approximately 50% savings on average in the GHG emissions per unit floor area of the buildings as compared to prefabricated RC construction. Finally, this effort demonstrates the significance of the structural material choice on the overall carbon footprint of a building, especially at the production stage.

Integration of energy and seismic-structural design variables through the optimization of a multi-story residential light-frame timber building with different seismic lateral connectors and building stories

The structural and energy performance of the light-frame buildings is intrinsically linked, but the design process of both domains is not. Light-frame timber buildings are subjected to overheating due to the lack of thermal mass. A solution to eliminate or mitigate overheating is adding thermal mass, but the main drawback is increasing the seismic forces the building needs to withstand. Furthermore, the length of exterior shearwalls, fenestration openings, and studs spacing affect both the energy and structural performances. This paper aims to analyze and integrate energy and seismic-structural design variables for a light-frame residential timber building with different lateral seismic connectors and building stories. An Energy and Structural Timber Building Optimization (ESTIBO) methodology is proposed to integrate energy and seismic-structural design variables by optimizing the building energy performance. ESTIBO is based on GenOpt optimization software using a hybrid multidimensional optimization algorithm, while the energy simulations are performed on EnergyPlus using the Rhino's Grasshopper plugin. A structural model is implemented in Matlab under a modal response analysis of the building structure. The main results show that integrating critical design variables achieves different optimal values considering feasible structural solutions with reduced heating and cooling loads. It was found the four main variables that primarily reflect the link between energy and seismic-structural performances are stud spacing, wall insulation thickness, wall insulation type (high or low specific heat capacity), and floor concrete layer thickness. This paper contributes to improving the understanding of light-frame timber buildings' performance regarding the interaction of energy and structural-seismic design variables. Moreover, ESTIBO demonstrated to be able to provide optimal energy and seismic-structural solutions. Thus, it can support the early design stage of light-frame timber buildings.

Potresna otpornost postojećih zgrada s dodatnim katovima od laganih drvenih konstrukcija

In the presented paper, the problem of vertical expansions is treated in terms of seismic resistance of structures with added storeys. A large parametric study has been performed, confirming the impact of different number of added storeys, and the change of their stiffness, on the seismic response of structures. The paper shows examples of how stiffness in light timber frame and cross laminated timber structures can be easily altered just by changing the type and distribution of fasteners. Known procedures are used to calculate the stiffness of the wall elements of a light timber frame system, and a new procedure is developed for determining the stiffness of cross laminated timber wall elements. The study shows how changing the stiffness of the vertical expansion can have a significant impact on the seismic response and that, in some cases, vertical expansion can have a favourable effect on seismic resistance, despite a minor increase in the mass of the structure.

COMPARATIVE CARBON-FOOTPRINT ANALYSIS OF RESIDENTIAL BUILDINGS WITH DIFFERENT STRUCTURAL MATERIALS

An important step towards achieving sustainability goals in the construction sector is taken by developing solutions that adopt ‘greener’ structural materials for buildings. This paper establishes a comparison among four existing residential buildings in Sweden, that utilize different structural solutions, in terms of their global warming potential (GWP). The structural solutions compared are prefabricated reinforced concrete (RC), light timber frame, cross-laminated timber (CLT) panels, and CLT modular construction. For each building, a life cycle assessment (LCA) was performed to estimate the greenhouse gas (GHG) emissions attributable to material production. In general, the results of this study revealed climate benefits associated with timber-based construction, with approximately 50% savings on average in the GHG emissions per unit floor area of the buildings as compared to prefabricated RC construction. Finally, this effort demonstrates the significance of the structural material choice on the overall carbon footprint of a building, especially at the production stage.

Blast resistance of timber structural elements: A state-of-the-art review

The response of structures subject to impulsive loads remains a field of intense research. Whilst traditional construction materials, such as steel and concrete/masonry, have been the focus of most studies, further research on the performance of alternative materials for blast-resistant applications has been driven by their growing use in sustainable construction. Over the last years, engineers have been re-evaluating the use of timber as a prime construction material for a range of building types, from small office to high-rise residential buildings. As a result, there is now a growing need to study the blast resistance of timber structures, as they may become potential targets of terrorist attacks or being placed in the blast-radius of other critical buildings. A review of existing research on the blast resistance of timber structures is presented and key factors on the blast analysis and design of such structures are discussed. Most of the research has been conducted on light-frame wood stud walls, glued- and cross-laminated timber, and addresses material properties under high strain rates, typical failure modes, behaviour of structural connections and retrofitting solutions. Failure modes are reported to be highly dependent on the element layout and manufacturing aspects, and dynamic increase factors for the modulus of elasticity and maximum strength in the ranges of [1.05, 1.43] and [1.14, 1.60], respectively, have been proposed for different timber elements. Mechanical connectors play a significant role in dissipating energy through plastic deformation, as the brittle nature of timber elements compromises the development of their full capacity. Regardless the element type, SDOF models can accurately predict the dynamic response as long as idealised boundary conditions can be considered. Overall, although a good amount of research is available, more extensive research is needed to guide the design and engineering practice and contribute to the development of design codes and testing standards for timber structures under blast loading.

Sound absorption performance of light-frame timber construction wall based on Helmholtz resonator

In order to improve the sound absorption performance of the light-frame timber construction wall, this paper combined the aperture embedded wall unit structure with the actual building wall structure based on the Helmholtz resonance structure principle to design and fabricate two sets of wall structures: a new aperture embedded Helmholtz resonance structure (experimental group) and a conventional structure (control group). The sound absorption coefficients of the two wall structures were measured by the reverberation chamber test, and related analysis was carried out. The results showed that the aperture embedded Helmholtz resonance wall structure exhibited good sound absorption performance in the low frequency range; in particular, a perfect sound absorption effect was basically achieved at a frequency of 100 Hz. Compared with the conventional wall structure, the sound absorption performance of the aperture embedded Helmholtz resonance wall structure in the test frequency range was enhanced greatly. While the value of the sound absorption coefficient was increased in the low frequency range, the bandwidth of sound absorption frequency was expanded to a certain extent, and the average sound absorption coefficient and noise reduction coefficient were both improved. This paper explored the applicability of Helmholtz resonance structure in practical wall structure. The research results could provide reference for reducing indoor noise pollution and creating a better living environment.

Effect of pinching on structural resilience: performance of reinforced concrete and timber structures under repeated cycles

This article attempts to define pinching of two structural joints, reinforced concrete (RC) and wood ones. In particular, the research outlines differences and analogies between pinching of an RC portal and a Light Timber Frame (LTF) wall. This is done by focusing on the concavity of pinching in their response under repeated cycles, which produces differences in the energy dissipation. The response of the two structural archetypes under pseudo-static and dynamic simulations is analysed using the Atan hysteresis model modification. The truncated incremental dynamic analysis (TIDA) of the two systems modelled as single-degree-of-freedom (SDOF) oscillators yielded the fragility curves, approximated by a lognormal cumulative distribution (CDF). The stability of RC under repeated cycles reveals its significant resilience compared to LTF structures. The examination of the fragility functions supports a discussion about the relation between the pinching concavity and the notion of structural resilience by introducing a robustness index ranging from 0 to 1. Ultimately, a parametric analysis of a fictitious structural system derived from the timber one by varying the concavity of the pinching path leads to the estimation of the robustness index as a function of the pinching concavity.

Load Bearing Capacity of Light Timber Frame Walls Under Fire

Light Timer Frame Walls are made of solid timber elements and are usually fire protected by other materials. This investigation determines the residual load bearing capacity of Light Timber Frame Walls for fire rating periods of 30, 60, 90 and 120 min. The timber frame is made with 3 studs and 2 tracks, using two different fire protection levels (one and two gypsum layers). The computational model includes the thermal analysis under standard fire, including all types of materials and a sequential mechanical analysis with incremental load applied for each fire rating periods, applied just for the load bearing material. Nonlinear solution methods are used with small tolerance values for solution convergence, to determine the correct temperature and displacement fields. The thermal and the mechanical properties are considered temperature dependent. The mechanical analysis considers large displacement behaviour, and the charring effect of wood is included by the reduction of the stiffness and strength of the timber. The results show that the load bearing capacity decreases with the fire exposure time. A new proposal is presented between the load bearing capacity and the fire rating and finally the char layer is compared with the current and future version of Eurocode 5, part 1.2.

Thermal Behavior of a Light Timber-Frame Wall vs. a Theoretical Simulation with Various Insulation Materials

The objective of this paper is to compare the thermal behavior of a light frame timber wall by measuring 15 test samples with various insulation materials versus a theoretical simulation with the use of a software. This work establishes the variance between the two different methods to measure the thermal transmittance coefficient of timber walls. It is verified that the mean percentage alteration between the two methods is 4.25%. Furthermore, this approach proved that with the use of a simulation software, additional readings (humidity, vapor flux, heat flux, and vapor pressure) can also be considered and measured, enhancing the overall development of a timber wall. This can provide additional information regarding to the characteristics of the masonry’s elements assisting in an improved design of a timber wall with upgraded performance.

Improved seismic response of light-frame-timber panels with cement-particle-board sheathing of various thicknesses and different configurations of fasteners

Due to their comparable fire characteristics and surface preparation, light-frame timber panels using cement-particle boards (CPB) as a sheathing material present a potential alternative to gypsum-fibre boards. An experimental campaign was conducted to evaluate the behaviour of CPB light-frame-timber panels under in-plane lateral loading. Monotonic and cyclic in-plane shear tests were conducted on full-size panels, following preceding tests on the stapled sheathing-to-timber connections used in the panels. The influence of the boards’ thickness and staple geometry on the response of connections and panels was studied, also on panels with an asymmetrical CPB layout, which proved not to have a negative influence on the panels’ lateral load-bearing capacity. Furthermore, in order to improve the seismic response, panels, which had almost twice the number of staples compared to the basic panel, were tested; one variation with two rows of staples, and the other with the staples spaced closer together, such that the spacing distance was halved. The tests revealed a significant, though not proportional, increase in lateral resistance in the strengthened panels. Fastening the CPB with two rows of staples proved the better option, since subsequent failure of the CPB along the connections, as opposed to ductile failure of the staples in the basic panels, proved not to reduce the panels’ deformation capacity. The paper also compares the test results of the connections and panels to analytical results according to Eurocode 5 (EC5), the European code provision for the design of timber structures.

A numerical and experimental investigation of non-linear deformation behaviours in light-frame timber walls

In recent decades, there is a trend in Scandinavian countries to build multi-storey residential houses using prefabricated timber modules. It is a highly efficient construction process with less environmental impact and less material waste. A significant building element in the timber modules is the light-frame timber wall, which has to be carefully analysed and optimized in this process. This paper presents a new parametric Finite Element (FE) model that can simulate both in-plane and out-of-plane deformations in the light-frame walls. A new and flexible (Eurocode based) approach to define the properties of the mechanical connections is introduced. A numerical model is presented through simulations of several walls that were verified with full-scale experiments. The results indicate that the numerical model could achieve fairly reasonable accuracy with the new approach. Furthermore, several parametric studies are presented and discussed from global and local points of view, to investigate the effects of certain parameters that are not considered in the design method according to Eurocode 5.

Reliability-Based Assessment of LTF and CLT Shear Walls under In-Plane Seismic Loading Using a Modified Bouc-Wen Hysteresis Model

AbstractThis paper reports on the reliability-based assessment of light timber frame (LTF) and cross-laminated timber (CLT) shear walls. The outcomes of cyclic tests on 17 timber shear wall specime...

Experimental study of compartment fire development and ejected flame thermal behavior for a large-scale light timber frame construction

Most of the previous work focused on fire behavior of non-combustible construction. However, few investigations have systematically addressed fire development and window ejected flame based on large-scale light timber frame construction (LTFC). This paper conducted a large-scale natural fire experiment to explore the fire development of wooden buildings and the ejected flame behavior by a two-layer light timber frame construction (LTFC). The experimental LTFC included two compartments, with four façade walls consisted of external and internal linings, within 5.1 m height, 3.6 m long and 2.4 m width, and weight of 1480.1 kg. The room temperature, mass variation in burning, radical temperature profiles outside the openings-façade wall, and ejected flame dimension were measured and analyzed. The results were summarized as follows: In LTFC, the room temperature and heat release rate (HRR) would show a second rapid rise, as if “twice flashover” occurred in fully burning stage. This phenomenon is obviously different from the traditional compartment fire development of buildings. Besides, after flashover, the ejected flame height continuously increased until the fire turned into decay stage, whereas the horizontal ejection distance would maintain a steady stage and increased as the openings broken extremely. Furthermore, the region outside the openings façade wall could be divided into three regions, ejected flame region (including continuous and intermittent flame) (Tr > 180 °C), buoyant plume region(150 °C > Tr > 60 °C) and heated air region(60 °C > Tr > T∞). A modified function was proposed to predict the temperature profile at different heights for the openings-ejected flame. The data of this paper will enhance the comprehension for fire development of timber buildings and provide some useful information to assess the thermal behavior of window-ejected flame of façade wall.

The role of the hold-down in the capacity model of LTF and CLT shear walls based on the experimental lateral response

Cross Laminated Timber (CLT) and Light Timber Frame (LTF) shear walls are widespread constructive technologies in timber engineering. Despite the intrinsic differences, the lateral response of the two structural systems may be quite similar under specific connection layouts, boundary constraints, and size of the shear walls. This paper compares the experimental cyclic responses of CLT and LTF shear walls characterized by the same size 250×250cm, and loaded according to the EN 12512 protocol. The rigid-body rotation of the shear walls prevails over the deformation and rigid-body translation in the post-elastic displacement range. As a consequence, a capacity model of the two systems based on the sole hold-down response accurately seizes the observed cyclic response, despite ignoring the other resisting contributions. The authors examine the differences exhibited by the CLT and LTF shear walls and the related error corresponding to a capacity model based on the sole hold down restraints. Additionally, it is assessed the overstrength of the CLT panel and LTF sheathing to the shear walls collapse due to the hold-down failure. The estimated overstrength factor is the most meaningful difference between the two structural systems in the considered experimental layouts.

Damped Timber Shear Wall: Shake-Table Tests and Analytical Models

Light-timber frames, using plywood (PW), exhibit a pinched hysteresis response, and their energy absorption capacity is limited. The energy-dissipation capacity can be enhanced using energy-dissipation mechanisms. In this paper, two wood-friction-based connectors, with wood-plywood-wood (WPW) and wood-steel-wood (WSW), are utilized. Reverse-cyclic static load tests have shown that the WPW and WSW wall systems have nondegrading and stable hysteretic curves. In this paper, through shake-table tests, performance of WPW, WSW, PW, and WSW-PW coupled wall systems are investigated. As expected, the shake-table results indeed showed nondegrading hysteretic curve responses of WPW and WSW wall systems. Furthermore, a phenomenological model, where nonlinear behavior of the shear wall is reduced to a single spring element, is proposed for the wall systems. The nondegrading wall system (WPW, WSW) is modeled using the Bouc-Wen hysteretic model and the PW is modeled using the Pinching4 hysteretic model. Overall, there is good agreement between the test and analytical models. Results of the experimental test indeed show the utility of the new wall systems.

An empirical transcendental hysteresis model for structural systems with pinching and degradation

AbstractThe authors present a novel transcendental hysteresis model based on the piecewise definition of arctangent functions. The definition of the shape parameters of the arctangent functions originates from the features of the experimental hysteresis curves directly. In the first step, the authors present this model's application to the experimental cyclic response of cross‐laminated timber (CLT), light‐timber frame (LTF) shear walls, and a steel angle bracket. Then, the response of a plywood‐coupled laminated‐veneer lumber (LVL) shear wall is used for validation purposes. The paper introduces the arctangent‐based model, labeled Atan model, by illustrating some possible shortcomings of hysteresis models with pinching. The paper concludes with a simple demonstration of these issues in the case of a Bouc‐Wen class hysteresis model, the extended energy‐dependent generalized Bouc‐Wen (eegbw) model. The numerical instabilities of the eegbw model are used to endorse the advantages of the proposed formulation in modeling complex structural arrangements, like wood joints and structural systems. The proposed model originates from the analysis of the experimental response of wood joints. However, it can be of more general application, and the particular reference to wood joints does not preclude other application fields.

Experimental and numerical study on the deflection of multi-storey light-frame timber shear walls

This study aims at investigating the deflection behavior of multi-storey shear walls, including the effect of the diaphragm out of plane stiffness. Two-storey half-scale light-frame shear walls were investigated experimentally and numerically. Each level was loaded separately in order to isolate the effect of load transfer and deformation from one level on the other. The study shows that the deflection estimated based on the cumulative effect assumption was reasonably close to that observed in the experimental study, when no consideration for the floor diaphragm’s out of plane stiffness was included. It was observed that the majority of the cumulative effect stems from the rigid body rotation due to deformation in the hold-down devices. Results from a numerical model showed that the assumption of cumulative effects due to rigid body rotation is valid for stacked shear walls when consideration for the floor diaphragm’s out-of-plane stiffness is not included. The design expression showed a slight tendency to over-estimate the deflection especially at higher storey levels. The results of investigating the effect of the diaphragm’s out of plane stiffness showed that a significant reduction in the shear wall deflection. Diaphragm supported on multiple wall panels was found to further reduce the deflection of the shearwalls.