Design Of Wood Structures Research Articles

Experimental investigations on the bearing properties of bamboo scrimber joints by a bolted bamboo-steel-bamboo connection

ABSTRACT In this study, a total of forty-two joint specimens were designed to explore the properties of the bolted bamboo-steel-bamboo connection under axial tension. Key design parameters were selected as variables, including the bolt end distance, diameter, and number. Failure modes and mechanical properties were analyzed from the aspects of both bolts and joints. Finally, modified from calculation formula for the bearing capacity of bolted joints in wood structures, the design method for the tested bamboo scrimber connection joint was proposed for the bearing capacity while considering the influence of bolt diameter and bolt number. According to the experimental results, the joint failure was mainly controlled by the bamboo scrimber bearing capacity and bolt bending. Within the design scope, the influence of bolt end distance on the bearing capacity of the joint can be ignored. The bearing capacity of the joint increases with the increase of the bolt diameter. For single-row bolt connection, the bearing capacity of the joint increases with the increase of the number of bolts. The modified formula of single-bolt bearing capacity in the Chinese design codes and multi-bolt bearing capacity in the European code for design of wood structures are in best agreement with the test results.

СOMPARATIVE ANALYSIS OF DOMESTIC AND FOREIGN STANDARDS FOR THE CALCULATION OF JOINTS OF WOODEN ELEMENTS OF THE NAGEL TYPE

The article presents the chronology of the development of regulatory documentation for the calculation and design of wooden structures in the Republic of Belarus. The analysis of the methodology for calculating symmetrical double-cut joints of wooden elements on metal nagels according to the construction rules of SP 5.05.01-2021 and the norms of foreign countries that have harmonized building codes with the Eurocode 5 standard, taking into account national applications. The differences in the provisions for the calculation of compounds on metal nagels in terms of assigning the value of the partial coefficient of the properties of the compound materials are revealed. A different approach to the assignment of technological parameters in the manufacture of building structures using metal nagels is noted. A comparative calculation of the joint of the lower belt of the truss with double-sided wooden plates on bolts is performed. The calculation results were evaluated according to the construction standards of the Republic of Belarus, China, Poland, Ukraine and Lithuania. It is established that the introduction of national applications established by national standardization bodies affects the results of the calculation of the joints of wooden elements on the nagels.

Research on the Charring Rate of Cross Laminated Timber Structural

<p>本研究透過蒐集歐洲、北美、日本等地有關直交集成板CLT之構造防火法規與規範，以直交集成板CLT之構造耐火試驗及防火特性進行探討研究，並針對木構造建築物設計及施工技術規範〔1〕提出有關直交集成板CLT構造增修建議。預計進行2組CLT樓板及2組CLT牆板之耐火實驗，探討做為驗證所需。實驗試體使用5層15cm日本扁柏CLT(符合JAS規定)〔2〕及5層12cm日本扁柏加柳杉(符合JAS規定)〔2〕分別進行樓板與牆各1小時及2小時之耐火實驗。CLT實驗試體經耐火試驗後，進行炭化層之刮除以確認炭化深度及炭化速率。 CLT實驗試體加熱面經清除炭化層後所殘留之結構斷面，以每100mm距離量測其縱向及橫向炭化深度值，將量測之炭化深度及炭化速率結果，以日本木材炭化率預估模式〔3〕，藉由公式之計算與實際實驗後所得到之炭化深度交叉比對分析，利用實驗數據與預估模式之相關係數討論公式預估之準確性，提出炭化深度防火規定建議值，以作為木構造結構設計之依據。</p> <p> </p><p>This research is collecting about the fire regulations and codes for the construction of Cross Laminated Timber of CLT in Europe, North America, Japan, and discussion and research on the structural fire resistance test and fire characteristic execute of the Cross Laminated Timber CLT, and according to the reference manual for fire design and construction of wooden structures, suggestions on the addition and repair of the CLT structure of the Cross Laminated Timber are proposed. It is expected to execute the fire resistance test of 2 sets of CLT floor and 2 sets of CLT wall to discuss for verification. The test specimens used 5 layers of 15cm Japanese cypress CLT (in compliance with JAS regulations) and 5 layers of 12cm Japanese cypress and Cryptomeria (in compliance with JAS regulations) to execute fire resistance tests for the floor and wall for 1 hour and 2 hours. After the CLT test specimen to the fire resistance test, the charring layer is scraped to confirm the charring depth and the charring rate. After the charring layer has been clearing for structural section of the CLT specimens heating surface, and the longitudinal and transverse charring depth values are measured every 10cm. The charring depth and charring measurement rate results are by the Japanese wood charring rate prediction model, it is calculated by the formula and cross-compared analyzed with the charring depth obtained after the practical experiment. Use the correlation coefficients of test data and estimation models to discuss the accuracy of the predictions, and serve as a reference for the design of wooden structures for future reference revisions.</p> <p> </p>

Full-scale shake table tests of P&B type of Japanese three-story wood dwellings for the collapse characterization

The 2009 test program of E-Defense aims to investigate the new design concept compliant with high-performance expectations and long-span service life for wood structures under the act of quality assurance. This study describes the full-scale shake table test program of three-story Post and Beam (P&B) Grade-1 and Grade-2 index wood structures in the Japanese building taxonomy. Input ground motions of the test program are generated to represent a frequent, rare, and very rare level of earthquake ground motion using a random process with an envelope function. Design and analysis of test specimens were carried out following the Japanese seismic design code, where the component tests of structural elements were performed before the shake table test program. A sequence of spectrally matched artificial ground motions was used in the test program to assess the progressive collapse mechanism of both test specimens. Wall to plan ratio is a critical indicator in the structural design of wood structures to determine the minimum required amount of wall and proper plan layout on each floor. Simplified N value method and allowable stress design approach are conducted for configuring and proportioning the structural elements during the design process. Special attention is given to connection details and foundation anchorages to ensure a continuous load transfer path. The first mode-dominated response characteristics of the structure are derived from the test data. Progressive damage mechanism has yielded to cyclic strength and stiffness deterioration. The global drift angle of the test structure has exceeded the 5% drift ratio. The capability of the versatile hysteretic model for wood structures is well-justified through the comparison of the numerical model and the physical test data for collapse characterization under gradually increased earthquake demands. Accumulation of damage at the last phase of the test program is led to the loss of dynamic stability in the Grade-1 building and total collapse of Grade-2 wood-dwelling, respectively. Test results have provided valuable data to overview and improve the response characteristics of code-conforming wood structures with an extended service life towards earthquake resilience of cities.

Structural performance and charring of loaded wood under fire

Wood has been widely used in construction and infrastructures due to its great environmental and economic benefits. However, wood structures are highly vulnerable to fire because of its flammability. The effect of unavoidable service load on the structural performance and charring characteristics of wood structures is still unclear, posing serious safety risk under fire hazard. In this study, the fire behavior of wood components under different service loads was experimentally evaluated. To assess the fire performance in detail, the structural response and charring characteristics, including charring depth and charring rate were provided and compared. The results highlight that service load can accelerate the charring rate and increase the charring depth, aggravating the thermal degradation of wood element under fire exposure. An influential mechanism of service loading condition on the fire behavior of wood is proposed and a more accurate approach to predict charring rate is recommended. The findings from this study can advance the understanding on structural behavior of wood under fire and contribute to the trustworthy charring predictions as well as to reliable fire design of wood structures.

Comparison of reliability evaluation methods between China and Canada standards for wood structures featuring duration of load

Duration of load (DOL) is a key factor in design of wood structures, which makes the reliability analysis of wood structures more complicated. The importance of DOL is widely recognized, yet the methods and models through which it is incorporated into design codes vary substantially by country/region. Few investigations of the effect of different model assumptions of DOL and other random variables on the results of reliability analysis of wood structures can be found. In this paper, comparisons are made on the reliability analysis methods that underlie the China and the Canada standards for design of wood structures. Main characteristics of these two methods, especially the way how DOL is treated are investigated. Reliability analysis was carried out with the two methods employing the same set of material properties and load parameters. The resulted relationships between reliability index β and resistance partial factor γR* (the β–γR* curves) for four load combinations are compared to study the safety level indicated by the two methods. The comparison shows that the damage accumulation model (Foschi–Yao model) in the Canada analysis method is highly dependent on the type and duration of load, resulting in more conservative design than the China analysis method in loading cases dominated by dead load, but less conservative design in cases of high level of live loads. The characteristics of the load effect term of the performance function are also found to make considerable difference in reliability levels between the two methods. This study aims to provide references for researchers and standard developers in the field of wood structures.

Influence Of New Design Characteristics Of Wood On Determining The Longitudinal Bending Coefficient

The standard methodology for calculating the stability of wooden rods, in which the longitudinal bending coefficient depends on the ratio of the elastic modulus to the design resistance is implemented in a linear formulation. The use of this linear method for calculating wooden structures that have a creep in time is due to studies conducted in the last century, in which it was found that this ratio for wood is constant, both during short-term loading and long-term loading. Since then, this characteristic for wood, used in calculations for the design of wooden structures, has not changed practically and the method of calculating the stability has not lost its relevance. But in the latest version of the design standards for wooden structures, the design resistances and elastic modulus for lumber, glued wood and new material made of unidirectional veneer differ depending on the strength classes, and the ratio of the elastic modulus to the design resistance becomes variable. Therefore, the formula for calculating the longitudinal bending coefficient for wooden rods with a flexibility of more than 70, left unchanged in the latest version of the norms, requires adjustment. It is proposed to change this formula taking into account the new values of the calculated strength and deformation characteristics for solid and glued wood elements. At the same time, the method of assigning calculated values of the modulus of wood elasticity is being questioned.

Особенности проектирования и контроля качества деревянных конструкций с учетом класса древесины по прочности

The transition to strength classes in the design of wooden structures allows correctly assessing the level of reliability of the designed constructions. The article presents a comparison analysis of the safety factor values in the Russian regulative standards and those previously in force and assesses their impact on the reliability level. The influence of the transition to probabilistic normalization of the strength properties of elements and structures made of wood in general using strength classes is substantiated. The development of the approach will significantly improve the reliability and safety of wooden structures, especially large-span structures and multi-storey buildings.

Evaluation of the Potential Use of Oiticica-Amarela Wood for Structural Applications

In relation to other materials such as concrete, plastic, steel and aluminum, wood has a number of advantages, such as beauty, high mechanical resistance to mass, good thermal insulation and easy workability. Still, wood presents environmental advantages when compared to other building materials (cement, concrete, steel and aluminum), beause it is recyclable, renewable, biodegradable and requires low energy needs for its processing. Taking so many advantages of the wooden use, it’s necessary to aim a rational use for this raw material, as an example, there are the physical and mechanical properties, which are important for the structural use of the species in the design of wood structures. This work aimed to characterize the wood species Clarisia racemosa (Oiticica-Amarela), objectifying its viable use for structural purposes. The tests to obtain the physical and mechanical properties were carried out according to the recommended established by Brazilian Standard ABNT NBR 7190 (1997), allowing the classification of such species in strength class C60 (hardwoods), as well as evaluating the possibility of estimation (linear, exponential, geometric and logarithmic models) of the physical and mechanical properties in function of the apparent density. The results obtained from the regression models implied the possibility of estimating only the mechanical property of compressive strength parallel to the fibers (fc0) as a function of the apparent density (ρap, 12%).

Issues of further development and improvement of design standards for wood structures

The current state of design of wooden structures against the background of the historical development of design standards is analyzed, the tasks of their further development are formulated. The strength criteria ensuring progress in the design of unique and spatial wooden structures are considered. Examples of unique large-span coatings, principles of their design with providing a spatial scheme are presented. In addition, the methodology for the nonlinear analysis of such systems with due regard for the duration of action of the load and of redistribution of internal stresses, especially under unsymmetrical loads, including with due regard for the coverings between the ribs experiencing a complex stress state is proposed. The application of the calculation method considered provides material savings and at the same time increases the reliability and survivability of the structure. Some possible additions and proposals on the structure and content of the new version of the norms are proposed. Taking into account continuity and achievements of the technical progress the necessity of development of new standards on the basis of advanced technologies of production, design and calculation of designs on the computer is proved.

Species, grading, and mechanical properties of locally sourced timber in the Joyabaj region of Guatemala

The purpose of this project was to research the timber used by Engineers without Borders (EWB) groups in the Joyabaj region of Guatemala. This project aimed to investigate the species of wood, evaluate the quality by assessing the distribution of timber grades, and determine mechanical properties. The results will aid EWB groups in the design of wood structures in the Joyabaj region of Guatemala.Samples were collected for species investigation and mechanical testing. Species investigation was triangulated from interviews with the sawmill owner, construction foreman, testing by the USDA Forest Products Laboratory, and comparisons to literature. The results were inconclusive and indicated multiple species were intermixed at the sawmill with no distinction made when purchased. Timber quality was evaluated by using a visual grading guide developed by the authors to assess the distribution of grades within a large order of lumber. Static bending and compression parallel to grain tests were conducted to obtain modulus of rupture, compression parallel to grain, and modulus of elasticity. Specific gravity was also obtained.The results indicate that three different species were collected. Ninety per cent (90%) of the timber was No. 3 or better and 50% to 80% was No. 2 or better depending on the size. Clear wood testing values were similar to those of Eastern White Pine. Structural design should be performed based on National Design Specification (NDS) design values for a No. 3 or No. 2 Eastern White Pine, depending on the degree of wood selection in the construction process.

Theoretical predictions on the influence of moisture on movements of wooden construction elements

The paper presents a method for determining the creep function of wood. A key feature of this method is a constitutive relation which includes the continuous effect of wood moisture on creep. The method can be applied to improve the precision of design of wooden structures as well to assess the safety of biodegraded (biologically corroded) structural elements fabricated from wood. Keywords: construction, wooden constructions, rheology, constitutive relation, creep function

Determination of the elasto-plastic material characteristics of Norway spruce and European beech wood by experimental and numerical analyses

Abstract Experimental and numerical analyses are presented concerning of compression tests parallel and perpendicular to the grain, three-point bending, and double-shear joints in compliance with the relevant test standards (ASTM D2395, BS 373, EN 383 and EN 26891). Woods of Norway spruce (Picea abies L. Karst.) and European beech (Fagus sylvatica L.) were tested to describe their non-linear behavior. Elasto-plastic material models were the basis for the finite-element (FE) analyses with the input of own experimental data and those of the literature. The elasto-plastic material model with non-linear isotropic hardening was applied based on the Hill yield criterion in regions of uniaxial compression. The material characteristics were first optimized and validated by means of basic 3D FE models under the same conditions as applied for the experiments. Afterwards, the validated material models were implemented into the solver with more complex numerical analyses of wooden dowel joints. Concurrently, the digital image correlation (DIC) served for verification of the numerical wooden joint models. A good agreement (with a relative error up to 16%) was found between numerically predicted and experimentally measured data. The differences may be mainly attributed to some natural characteristics of wood which were not considered in the proposed material models. The proposed elasto-plastic material models are capable of predicting the wood’s ultimate strength, and therefore could contribute to a more reliable design of wood structures and their performance.

Influence of the angle between applied force and wood grain direction on shear strength

Wood is an anisotropic material and its resistance characteristics vary with the angle between the effort and the fiber direction (α). The Brazilian Code NBR 7190 – Design of Wooden Structures, foresees the strength correction to the normal stress, whenever α > 6o, and it recommends to apply Hankinson’s expression to design values. However, this referred code is omitted about this correction to the tangential stress. Besides, there is not experimental confirmation about the validity of using this expression on design values, originating from characteristic values. The objectives of this work were: to search in the bibliography other used expressions; to verify the validity of these expressions, to represent the variation of the shear strength, with the α angle; and, to verify the validity of application of these expressions in characteristic values. For this, a sample formed by twelve boards was used. From each board, specimens to shear tests were retired, with different fibers inclinations, which were tested in agreement with current NBR 7190, supplying the shear strength, for different α values. Four models (Hankinson, Sin, Karlsen and Keylwerth) were evaluated, using the pairing and deviation tests. The model that best represented the phenomenon, in both cases, was Keylwerth’s.

Numerical analysis of flexural strengthening of timber beams reinforced with CFRP strips

Near-surface mounted (NSM) laminate strips of carbon fibre-reinforced polymer (CFRP) is a promising technique for increasing the load-carrying capacity of timber beams in bending. The aim of this study is to develop a numerical procedure to simulate the flexural behaviour until failure of CFRP-strengthened timber beams. A local approach based on the coupling between anisotropic elasto-plasticity with non-linear isotropic hardening and an isotropic ductile damage is presented to model this behaviour, and implemented into Abaqus/Explicit using the Vumat user subroutine. The numerical model proposed predicted all aspects observed experimentally, and can be used to assess relevant information in the design of wooden structures strengthened by NSM method.

Metodologia para o cálculo dos módulos de elasticidade longitudinal e transversal em vigas de madeira de dimensões estruturais

Este trabalhou objetiva apresentar uma metodologia analítica para o cálculo dos módulos de elasticidade longitudinal (E) e transversal (G) em vigas de madeira de dimensões estruturais, segundo o emprego das teorias de vigas de Euler Bernoulli e Timoshenko, sendo utilizado o ensaio de flexão estática a três pontos. As madeiras testadas foram o Pinus elliottii e a Corymbia citriodora. Os resultados encontrados relevaram ser o módulo de elasticidade longitudinal 18,70 vezes superior ao módulo transversal do Pinus elliottii e 21,2 superior ao módulo transversal do Corymbia citriodora, sendo estes compatíveis quando comparada a relação entre E e G estabelecida pela norma Brasileira ABNT NBR 7190:1997 (Projeto de Estruturas de Madeira), que define ser o módulo de elasticidade longitudinal vinte vezes superior ao transversal.

Numerical Evaluation of Longitudinal Modulus of Elasticity of <i>Eucalyptus </i><i>g</i><i>randis</i> Timber Beams

Currently, the standard NBR 7190:1997 (Design of Wood Structures) makes no reference to any test aimed to determine the stiffness and strength of structural-sized lumber components, restricting this analysis to small and clear specimens. Methodologies proposed by international standard do not include optimum criteria in their calculation models. This study presents an alternative methodology to determine the longitudinal modulus of elasticity in Eucalyptus grandis timber beams, based on a combination between the Finite Element and the Least Square Methods. Besides the use of nu- merical methods, the modulus of elasticity was also analytically obtained by the equation presented in NBR 7190:1997, concerning the static three-point bending test, adapted to a non-destructive testing condition. Results found for the elastic modulus for the Eucalyptus grandis species showed statistical equivalence between the methodologies, which implies the reliability of using Brazilian standard for the characterization of structural components subjected to bending. However, these results cannot be extended for other woods from the same species or different species, justifying the use of the numerical calculation approach discussed in this paper.

Material properties and external factors influencing the charring rate of solid wood and glue‐laminated timber

AbstractIn fire design of timber structures the charring rate of the material is a very important property, but the charring rate varies with the conditions in the fire compartment and the characteristics of the wood. Many experiments have been carried out through the years, trying to determine the effect of various properties on the charring rate of wood. This paper gives a summary of the material properties and external factors found in the literature to have the largest influence on the charring rate of exposed wood, i.e. the density, moisture content, chemical composition, grain orientation, permeability, scale effect, thermal exposure, char contraction, char oxidation, oxygen concentration and opening factor, resulting from experiments found in the literature. It has not been possible to determine which properties or factors have the most significant influence on the charring rate of wood, due to large differences between the test conditions and methods, wood species and measurement methods. There is a great need for further testing to determine the relative effect of these properties and factors, and international test methods need to be developed to enable comparison of results from research all over the world. More information about the most important properties and factors can help standardise the calculation of charring of wood, and improve the input to computer models for fire safety design. This will result in more economic fire design of wooden structures, as the calculated residual cross sections will be closer to reality. Copyright © 2010 John Wiley & Sons, Ltd.

A Review of Models for the Charring Rate of Solid Wood, Nail- and Glue- Laminated Structural Members

Simple calculation models for charring rate of solid wood, nail- and glue-laminated structural elements for use in fire design of wooden structures have been compared with test results from the literature. The applicability to these structural elements, and the accuracy of the models, have been evaluated based on parameters influencing the charring rate, which include species, density, moisture content, char contraction factor, external heat flux, oxygen concentration and duration of the fire. The models evaluated in this article are applicable to one- or two-dimensional charring under standard fire exposure.

Uniform hazard versus uniform risk bases for performance‐based earthquake engineering of light‐frame wood construction

AbstractThis paper investigates the implications of designing for uniform hazard versus uniform risk for light‐frame wood residential construction subjected to earthquakes in the United States. Using simple structural models of one‐story residences with typical lateral force‐resisting systems (shear walls) found in buildings in western, eastern and central regions of the United States as illustrations, the seismic demands are determined using nonlinear dynamic time‐history analyses, whereas the collapse capacities are determined using incremental dynamic analyses. The probabilities of collapse, conditioned on the occurrence of the maximum considered earthquakes and design earthquakes stipulated in ASCE Standard 7‐05, and the collapse margins of these typical residential structures are compared for typical construction practices in different regions in the United States. The calculated collapse inter‐story drifts are compared with the limits stipulated in FEMA 356/ASCE Standard 41‐06 and observed in the recent experimental testing. The results of this study provide insights into residential building risk assessment and the relation between building seismic performance implied by the current earthquake‐resistant design and construction practices and performance levels in performance‐based engineering of light‐frame wood construction being considered by the SEI/ASCE committee on reliability‐based design of wood structures. Further code developments are necessary to achieve the goal of uniform risk in earthquake‐resistant residential construction. Copyright © 2010 John Wiley & Sons, Ltd.