Light Timber Research Articles

Proposal of a new typology of structures using timber elements

The paper proposes a new typology of structures using timber elements, divided into homogenous and hybrid, considering the materials from which they were made, along with presenting classification criteria and an example of use. In addition, previously insufficiently specified terms were defined, such as massive timber and light timber frame.

Prefab Light Clay-Timber Elements for Net Zero Whole-Life Carbon Buildings

"Net zero whole life carbon" is an ambitious climate target that refers to neutralizing and offsetting the entire LCA-based carbon footprint of a building, including both operational and embodied greenhouse gas emissions. Especially in the Northern climate, viable building envelope structures must, therefore, provide good thermal insulation and low embodied emissions. Carbon offset is typically based on excess on-site renewable energy or purchased carbon offsets disconnected from the building and the site. Viable strategies for carbon neutrality start by minimizing material-related and energy-related CO2e emissions. As a result, new kinds of building envelope structures have been recently introduced in the academic literature and experimental building projects. Traditional construction materials, such as timber and clay, have been sourced locally and processed manually, providing good results for the embodied emissions in life cycle assessment. Recent studies on clay-based construction materials have concluded that more research on clay as a construction material is needed, in particular considering its environmental performance. One specific concern in the Northern climate is that the weather conditions limit clay construction outdoors and prevent industrial-scale application of these solutions. The methods of prefabrication can address these issues. This study introduces the critical technical and environmental properties of a new prefabricated wall element based on a combination of light timber frame and light clay. In a hybrid light clay-timber structure, a mixture of clay and hemp shives is cast between the timber studs. On the one hand, the novelty of this wall structure is the prefabrication that enables industrial applications and upscaling without the limitations of weather conditions. On the other hand, the study assesses the climate impact of a light clay-timber wall element : cradle-to-gate emissions, thermal insulation, and the climate benefits outside the system boundary (carbon handprint) reported in the D-module of the LCA framework. The study also shows that natural materials require a different approach than synthetic materials from industrial processes. There may be variations in the properties of hemp and clay, especially when local sourcing is prioritized for better environmental performance. Moreover, the mixing and installation processes have a significant impact on the final properties and the performance. We show that constructing a light clay wall is a knowledge-intensive process that may result in very different technical properties.

Building Paper arrives in New Zealand

Building paper, invented in Beloit, Wisconsin in 1869, arrived in New Zealand in the late 1880s. In 1891 it was used under the corrugated iron roof and walls in the four-bed Tasman Glacier Hut where it would have provided relief from condensation on the inside of the corrugated iron as well as reducing the ability of the wind to blow through the hut. Building paper quickly became common place, with advertising from English and American manufacturers appearing daily newspapers as well as trade journals. The paper traces the first decades of building paper use in New Zealand as it evolved from a novelty to a common building product – hidden under the cladding but improving on the comfort of the occupants. It ends with a brief foray into the twentieth century, with examples of its use and eventual inclusion in building controls starting with NZSS 95 Part IX: Light Timber Construction:1944.

Experimental Study of the Charring of I-Joists and Recession of Combustible Insulation in Light Timber Frame Assemblies with Comparison to Eurocode 5

Design models are commonly used in fire safety design of light timber frame assemblies. Parameters for use in the models are available for rectangular members with mineral wool, wood fibre or cellulose insulation and for assemblies with I-joists and mineral wool. For assemblies where I-joists and combustible insulations are combined, design parameters are missing. Five fire experiments with two I-joist types and four combustible insulation products have been conducted. The aim was to study charring of I-joist flanges and recession rates of combustible insulations and in addition, to compare their behaviour to the new and existing models of Eurocode 5. Charring rates for the flanges were 0.40–0.76 mm/min and 0.54–1.72 mm/min for the protected and post-protected phase, respectively. Rates decreased with increasing flange size. Charring rates for flanges of solid wood and LVL were comparable. The results show that lateral charring of I-joist flanges can be significant in the protected phase. The tested insulation products showed a lower recession rate than values reported for glass wool insulation, with a more pronounced difference for wood fibre and cellulose insulations. The low recession rates compared to previously reported generic values can possibly be explained by better product-specific properties, negligible shrinking and slightly different test set-up. The insulation stayed well in place after gypsum board fall-off and best-practice for keeping the insulation in place is given. The results, completed with future loaded full-scale tests, can give basis for further development of design models for assemblies with I-joists and combustible insulations.

Light timber framed wall under fire: Effect of the load and cladding

Light Timber Frame Walls are made of solid timber elements and are usually protected by cladding materials (gypsum). This investigation finds the effect of different load levels and cladding systems on the fire resistance. The timber frame structure is made with three studs and two rails, and will be analysed with two different protection levels. The computational model includes the thermal analysis under standard fire and a sequential mechanical analysis with time increments. Both, thermal and thermo-mechanical models are validated against experimental results developed in the reduced scale and full scale. The timber frame structure is deemed to have failed when it is no longer supporting the test load. The results are also compared with the failure criteria used for the experimental tests. The timber frame is deformed and all simulated models attained the global bucking instability mode, with studs moving to the outside of the furnace, due to the effect of load and charred layer. The fire resistance of a double-layered light timber frame wall is higher than a single-layered, and both decrease with the load level. This ability is reduced by 46%, on average for all load levels, when using only one gypsum layer. A new formula is proposed to determine the fire resistance, based on the load level and cladding systems. The fire resistance of the specimens with two layers of gypsum plates decreases faster than the specimens with one layer of gypsum, with respect to the increase of the load level.

Analysis and enhancement of the new Eurocode 5 formulations for the lateral elastic deformation of LTF and CLT walls

This paper analyses the analytical formulations for the lateral elastic deformation of Light Timber Framed (LTF) and Cross-Laminated Timber (CLT) shear walls according to the new Eurocode 5 (EC5) proposal. Finite Element (FE) models and the Standard predictions are compared by emphasizing the role of each deformation contribution. A total of 1830 comparisons between analytical and numerical estimations are carried out by exploiting the Application Programming Interface of SAP2000 to modify the FE model parameters automatically. The parametric analyses proved that the numerical and analytical predictions are pretty consistent. Furthermore, in both LTF and CLT shear walls, the estimates for in-plane shear and rigid body sliding are in excellent agreement. Conversely, the analytical formulas for kinematic rocking are generally conservative for LTF and monolithic CLT shear walls, with an approximate 18%–19% discrepancy. The analytical expressions of the upcoming EC5 perfectly match the numerical model for segmented CLT shear walls under lateral forces and no vertical load. However, the presence of the vertical load determines a significant bias. Additionally, the predictions for bending deformations are not in good agreement. Therefore, the paper discusses possible enhancements for the equations proposed in the next generation of Eurocodes for the rocking deformation of segmented CLT walls to better conform with FE predictions.

From Dysfunction to Functionalism: The Evolution of Military Construction in the Interwar Period Poland

The purpose of the article is the general characteristics of military residential architecture built in the 1920s and 1930s in the 2nd Polish Republic. In the newly restored Poland the most pressing problem was the improvement of the housing conditions of the population. The military, who contributed the most to the reinstating of independence held special privilege with the state officials. Therefore, the problem of their quartering was resolved with utmost preference. After an unsuccessful period of trial and error with traditional and light timber frame construction the government addressed this problem systemically establishing the Military Accommodations Fund with a dedicated budget for creating typified, repeatable solutions. The MAF commissioned specific designers, held open as well as limited competitions and hired a cadre of architects and engineers to come up with designs that could rapidly and cost effectively replenish the housing base with functional, hygienic solutions. Because the MAF was well funded, the most prominent polish modernist architects readily cooperated with the organization making Polish interwar <i>architectura militaris</i> an engine of modernization.

Mechanical performance of poplar laminated veneer lumber truss joints

ABSTRACT Poplar laminated veneer lumber (LVL) offers many advantages such as high strength and small variability. This study explored the application of poplar LVL for making light timber trusses in China. A total of 12 poplar LVL truss joint specimens were designed and constructed, including truss support joints and ridge joints connected by bolts and tooth plates. The mechanical properties of the poplar LVL truss joints were experimentally tested and theoretically calculated. It was found that (1) the average bearing capacity of 10-mm bolted joints was 12.98%–22.62% higher than that of 8- or 12-mm bolted ones; (2) the average bearing capacity of ridge joints with 133 mm × 75 mm tooth plates was 23.03% and 28.22% higher than those with 152 mm × 75 mm and 152 mm × 50 mm tooth-plate connected ones; (3) the average bearing capacity of the bolted joints was higher than that of the tooth-plate connected ones when the shape of both joints were the same; (4) The damage of LVL dowel grooves and pull-out of tooth-plates from LVL were observed in the bolted and tooth-plate connected joints, respectively; and (5) The calculated values were, in comparation with the experimental results, were conservative for bolted joints and were in good agreement with the tooth-plate connected ones.

Performance of reversible timber connections in Australian light timber framed panelised construction

This paper provides a novel insight into using reversible mass timber connectors in light-timber framed (LTF) construction to create dismountable, panelised LTF construction systems that enable adaptable building design and panel reuse in the context of a circular economy. The study presented in this paper focused on Australian LTF panelised construction:. A total of 10 IdeFix 304 connectors by SIHGA GmbH, and 20 M20 connectors by SHERPA Connection Systems GmbH were installed in Australian machine graded pine and subjected to monotonic tensile and shear loads to assess their feasibility in the given application. Two strength prediction models were evaluated in comparison to experimental results: Formulae given in the manufacturers’ European Technical Assessments (ETAs) and a prediction model adapted from literature. On average, the latter was more accurate in the given configuration. Considering the set goal of repeated assembly and disassembly, the connectors with a tight fit faced tolerance issues due to moisture fluctuations. Furthermore, rupture of the connector was observed in some instances, owed to higher screw withdrawal capacity in Australian timber. A reduction of the number of screws or their length is suggested to achieve a more ductile response with screw withdrawal. Finally, following comparative analysis of experimental tests and prediction models, recommendations were made for future design of novel LTF panel connectors in the context of disassembly and reuse.

Development and validation of a numerical strategy for the seismic assessment of a timber retrofitting solution for URM cavity-wall buildings

ABSTRACT This work presents the results of a numerical investigation on the effect of light timber retrofit systems on the global response of URM cavity-wall buildings. The building object of the study is a two-storey cavity-wall terraced house, retrofitted with OSB panels and timber frames. The Applied Element Method, was chosen for the numerical analyses. Numerical models, calibrated on experimental data of both retrofitted and non-retrofitted walls, were validated through the simulation of a shake-table test of a full-scale retrofitted specimen. A parametric study was then conducted to investigate the influence of different retrofit layouts on the building’s global seismic response.

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.

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.

Seismic performance of single-storey light timber-framed buildings braced by gypsum plasterboards considering rigidity of ceiling diaphragms

Light timber framed (LTF) structures provide a cost-effective and structurally efficient solution for low-rise residential buildings. This paper studies seismic performance of single-storey LTF buildings sheathed by gypsum-plasterboards (GPBs) that are a typical lining product in New Zealand houses. Compared with wood-based structural panels, GPBs tend to be more susceptible to damage when they are used in bracing walls to resist earthquake loads. This study aims to provide insights on how the bracing wall irregularity allowed by the current New Zealand standard NZS 3604 and the in-plane rigidity of ceiling diaphragms affect the overall seismic performance of these GPB-braced LTF buildings. Nonlinear time-history analyses were conducted on a series of single-storey baseline buildings with different levels of bracing wall irregularities and ceiling diaphragm rigidity. The results showed significant torsional effect caused by the eccentric bracing wall layout with semi-rigid/rigid ceiling diaphragms. On average, bracing wall drift demand caused by the extreme bracing wall irregularities was three times of that in the regular bracing wall layout under the rigid diaphragm assumption. This finding agreed well with the house survey after the 2011 Canterbury Earthquake in which significantly more damage was observed in the houses with irregular bracing wall layouts and relatively rigid diaphragms. Therefore, it is recommended to limit the level of bracing wall eccentricity and ensure the sufficiently rigid diaphragms to avoid excessive damage in these LTF buildings in future events.

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.

A Comparative Study on the Life Cycle Assessment of New Zealand Residential Buildings

In New Zealand, housing is typically low density, with light timber framing being the dominant form of construction with more than 90% of the market. From 2020, as a result of the global pandemic, there was a shortage of timber in New Zealand, resulting in increased popularity for light steel framing, the main alternative to timber for housing. At the same time, the New Zealand government is committed to sustainability practises through legislation and frameworks, such as the reduction of whole-of-life carbon emissions for the building industry. New Zealand recently announced reducing its net greenhouse gas emissions by 50% within 2030. Life cycle assessment (LCA) is a technique for assessing the environmental aspects associated with a product over its life cycle. Despite the popularity of LCA in the construction industry of New Zealand, prior research results seem varied. There is no unified NZ context database to perform an LCA for buildings. Therefore, in this paper, a comprehensive study using LCA was conducted to quantify and compare the quantity of carbon emissions from two commonly designed houses in the Auckland region, one built from light timber and the other from light steel, both designed for a lifespan of 90 years. The cradle-to-cradle system boundary was used for the LCA. From the results of this study, it was found that the light steel house had 12.3% more carbon in total (including embodied and operational carbons) when compared to the light timber house, of which the manufacturing of two houses had a difference of 50.4% in terms of carbon emissions. However, when the end-of-life (EOL) analysis was included, it was found that the extra carbon could be offset due to the steel’s recyclability, reducing the amount of embodied carbon in the manufacturing process. Therefore, there was no significant difference in carbon emissions between the light steel and the light timber building, with the difference being only 12.3%.

Acoustics Performance Research and Analysis of Light Timber Construction Wall Elements Based on Helmholtz Metasurface

Based on the efficient sound absorption characteristics of Helmholtz resonance structures in the range of medium and low frequency acoustic waves, this paper investigates an effective solution for light timber construction walls with acoustic problems. This study takes the light timber construction wall structure as the research object. Based on the Helmholtz resonance principle, the structure design of the wall unit, impedance tube experiment and COMSOL MULTIPHYSICS simulation calculation were carried out to obtain the change rule of acoustic performance of the Helmholtz resonance wall unit structure. The research results show that the overall stability of sound insulation of the structure is improved, and the frequency range with sound transmission loss more than 50 dB in the experimental group is 640–1600 Hz, while in the control group is 500–906 Hz and 1238–1600 Hz; the sound absorption performance of the structure is obviously better than that of the ordinary structure, especially in the low frequency acoustic wave range of 100–320 Hz, the sound absorption coefficient of the experimental group is more than 0.49, while the sound absorption coefficient of the control group is less than 0.1. It is expected that these results will contribute to the optimization of the acoustic performance of light timber construction walls and have high application and popularization value.

Network arch timber bridges with light timber decks and spoked configuration of hangers – Parametric study

The paper presents the results of a parametric study performed on FEM models of network arch timber bridges with inclined and spoked configuration of hangers. The study focuses on performance and instability of the arches depending on the geometry of the bridge. The parameters taken into account are the bridge span, the arch rise and the in-plane and out-ofplane hanger configuration. The parametric study was performed by use of the Abaqus software and an adapted Python framework, which generates complete 3D geometry models inclusive loading, where the geometrical parameters are defined by the user. The findings show that double inclination of hangers is beneficial both for arch stability and structural performance of the bridge.

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...