Seismic performance of post-and-beam timber buildings II: reliability evaluations

This paper presents an approach to evaluate the performance reliability of post-and-beam timber buildings under seismic excitation. The uncertainties considered include those associated with the earthquake ground motions, the structural mass and shear wall characteristics. The approach uses a verified structural model called “PB3D” for the creation of a database of seismic responses, which are then represented by appropriate response surfaces. These, in turn, are used to formulate explicit performance functions for the reliability analysis. Performance is studied in terms of peak inter-story drift, and polynomial functions are used to represent the seismic response surfaces. Non-performance probabilities are evaluated with respect to different performance expectations, using FORM and importance sampling methods. Case studies for two multi-story post-and-beam buildings are also presented.     

Pseudodynamic tests and earthquake response analysis of timber structures III: three-dimensional conventional wooden structures with plywood-sheathed shear walls

Pseudodynamic (PSD) tests were conducted on plywood-sheathed conventional Japanese three-dimensional (3D) wooden structures. Lateral load was applied to the edge beam of specimen structures to generate eccentricity loading. Specimens were based on a combination of shear walls with openings in the loading direction and horizontal diaphragms with different shear stiffness. The principle deformation of the horizontal diaphragm was torsion for rigid diaphragms and shear deformation for flexible diaphragms. Lumped-mass time-history earthquake response analysis was conducted on the tested structures, and additional calculations were conducted on structures with different eccentricity rates. Dynamic analyses were conducted by varying the masses and the resistance of the walls in the loading direction. The simulated peak displacement response in the loading plane agreed comparatively well with the PSD test results. The maximum displacement response on changing the wall resistant ratio showed almost the same tendency as that obtained by changing the mass ratio up to an eccentricity rate of 0.3; however, the maximum displacement response increased markedly beyond an eccentricity rate of 0.4. It was proved that the lumped-mass 3D model proposed in this study was appropriate for conducting a parameter study on the 3D dynamic behavior of timber structures.     

Conservation and restoration of degraded ecosystems in arid and semi-arid areas of northwest China

In “West Development” of China, one of the most important activities is the Natural Forest Protection Program, designed to swiftly convert the focus of management and utilization of the natural forests from a timber orientation towards forest conservation, sustainable management and environmental protection. The project covered almost all the arid and semi-arid regions in Northwest region. Accompanying this great campaign this paper studied the conservation and restoration model of degraded ecosystems in arid and semi-arid lands in Northwest China. The past practices have resulted in considerably natural forest degradation and loss through land conversion (primarily for agriculture), over-harvesting, inadequate reforestation and lack of protection. The consequences have been the loss of soil and water resources, diminished timber production capacity on a sustainable basis, and environmental losses. This paper applied Aronson’s restoration model and proposed the conservation, restoration, re-allocation and preservation program for the implementation of environmental improvement and natural forest conservation.     

Rotational performance of traditional Nuki joints with gap I: theory and verification

The Nuki joints in Taiwan and Japan are similar in appearance; however, due to lack of wedges used in Nuki joints in Taiwan, the gap between the column and beam increases the complexity of timber joints. In this article, the rotational performance of traditional timber joints is reported. A theoretical model considering Hook’s law and Hankinson’s formula was developed for predicting the rotational performance of Nuki joints with gaps. A total of 24 specimens was tested and used to verify the rotational performance of timber joints. The proposed model not only predicts the rotational stiffness of Nuki joints, but can also estimate the initial slip of these joints. Good agreement was found between predicted and experimental data.     

Performance evaluation of multi-storey cross-laminated timber structures under different earthquake hazard levels

The inter-storey drift limitations are meaningful reference values for structural seismic performance evaluation. This paper presents an analytical investigation into the seismic performance of multi-storey cross-laminated timber (CLT) structures to obtain the drift limitations under different earthquake hazard levels reasonably. The Pinching4 model was used to simulate the nonlinear mechanical behavior of three types of connections used in CLT structures, and a numerical model was further developed to capture the lateral load-resisting properties of CLT shear walls. Moreover, three benchmark multi-storey CLT apartment buildings were designed using the Equivalent Static Force Procedure according to National Building Code of Canada (NBCC), and simplified structural models were developed for these buildings. Depending on the results from numerous time-history dynamic analyses, the empirical cumulative distribution functions (CDFs) of the maximum inter-storey drifts were constructed for the three benchmark buildings. The probability of non-exceedance (PNE) of inter-storey drift thresholds under different earthquake hazard levels was proposed and validated. It is recommended that for low-rise CLT buildings within three stories, values of 0.30%, 0.75%, and 1.40% can be considered as the drift limitations for frequent, medium, and rare seismic hazard levels, respectively. For mid-rise or high-rise buildings without three stories, 0.25%, 0.70%, and 1.30% can be considered as drift limitations.     

Pseudodynamic tests and earthquake response analysis of timber structures I: plywood-sheathed conventional wooden walls with opening

Pseudodynamic (PSD) lateral loading tests were conducted on conventional post and beam timber frames with plywood-sheathed shear walls to validate the dynamic model of wall panels, each with an opening of a different configuration. The lateral forces were applied step by step at the top of the wooden frames by the computer-controlled actuator, and the displacement response for the next step was computed on the basis of the input accelerogram of the 1940 El Centro earthquake scaled up to 0.4g. The test results were compared with those of the lumped mass time-history earthquake response analysis using the hysteresis model with pinching. The results of the dynamic analysis with this global model consisting of the envelope curves, unloading and reloading with pinching agreed well with the experimental results of the PSD tests of this type of earthquake record. Some parametric studies may be necessary, however, to validate the model with different earthquake records. The hysteretical parameters obtained in this study showed similar values for each of the wall panels with different opening configurations. This makes it possible to use the model and parameters for the plywood-sheathed shear walls to estimate the dynamic behavior of entire structures without conducting expensive PSD tests or shaking table tests.     

Determining Young’s modulus of timber on the basis of a strength database and stress wave propagation velocity I: an estimation method for Young’s modulus employing Monte Carlo simulation

In this article, we report on an estimation method for Young’s modulus that entails measuring only the stress wave propagation velocity of timber built into structures such as wooden buildings. Methods of estimating Young’s modulus that use the stress wave propagation velocity and characteristic frequency of timber in conjunction with timber density have long been used. In this article, we propose a method of easily and accurately estimating Young’s modulus from the stress wave propagation velocity without knowing the timber density. This method is based on a database of wood strength performance and density accumulated from a variety of research data and the method estimates Young’s modulus by a simulation method. We compared the Young’s moduli estimated by this method with those obtained by the bending test and by the measurement of the stress wave propagation velocity and density, and found similar results. This coincidence suggests that the method of estimating Young’s modulus presented in this article is valid. For example, the method is effective for convenient evaluation on site when determining whether a wooden building’s structural components should be reused or replaced when repairing or remodeling a building.     

Effective lateral resistance of timber–plywood–timber joints connected with nails

In this study, an experimental study was conducted on the nailed timber–plywood–timber joints extended from the standard wall–floor joints of wooden light frame constructions, where the bottom plates of shear walls are nailed to the floors consisting of joists and floor sheathings nailed to them. The principal conclusions are as follows: The allowable lateral resistance of the nailed timber–plywood–timber joints can roundly be estimated by neglecting the plywood panels if their densities are higher than those of the timber main-members and they are fastened effectively onto the timber main-members. The stiffness of the timber–plywood–timber joints is less than that of the control timber–timber joints, which is improved by increasing the number of nails used to fasten the plywood panels onto the timber main-members. The stiffness of the joints whose floor sheathings are glued onto the joists is equivalent to the control timber–timber joints. The timber–plywood–timber joints with appropriate specifications have greater energy capacity until the failure than that of the control timber–timber joints. This ensures their energy capacity, which is important in dynamic resistance, to be equivalent to the control timber–timber joints.     

A new proposal to reinforce planked timber shear walls

Timber is one of the most common materials used in traditional buildings worldwide. Our previous research has suggested that timber shear walls play an important role in resisting external loadings, such as earthquakes. Thus, improving the structural performance of in-filled shear walls can also improve that of the entire structure. In the traditional Taiwanese timber shear wall system, the embedment strength of beams and friction between wooden planks and beams significantly affect the strength of the shear wall. This article proposes a new method of reinforcing traditional timber shear walls in Taiwan by inserting teak and padauk strips into the grooves between wooden planks and beams to increase the embedment strength of beams and the friction between wooden planks and the hardwood strips. A total of 18 full-scale specimens were tested under reversed cyclic loading. The results revealed that the strength and energy dissipation capacities of a wooden shear wall can be significantly increased by inserting teak and padauk strips into the grooves between planks and beams. Furthermore, the simplified calculation method proposed in this study can be used to calculate the strength of both reinforced and unreinforced wooden shear walls with satisfactory agreement.     

Prediction of seismic behavior of wood-framed shear walls with openings by pseudodynamic test and FE model

 This article summarizes an experimental and numerical study on seismic behavior of wood-framed shear walls with an opening. The objectives of this study were to compare the results of static and pseudodynamic tests of plywood-sheathed shear walls with numerical simulation by the Finite Element (FE) model and to validate a finite element code EFICOBOIS for such an application. This software is based on a macroelement approach to limit the number of degrees of freedom for the whole system. Nonlinear laws for connections such as nails and hold-down connections, among others, are applied through macroelements that link plate elements to beam elements. Numerical results obtained for the various loading conditions showed good agreement with the experiments. Both static and dynamic computations are presented here. Received: February 15, 2002 / Accepted: April 25, 2002 Correspondence to:M. Yasumura     

Experimental evaluations of material damping in timber beams of structural dimensions

Understanding the inherent damping mechanisms of floor vibrations has become a matter of increasing importance following the development of new composite floor layouts and increased span. The present study focuses on the evaluation of material damping in timber beam specimens with dimensions that are typical of common timber floor structures. Using the impact test method, 11 solid wood beams and 11 glulam beams made out of Norway Spruce (Picea abies) were subjected to flexural vibrations. The tests involved different spans and orientations. A total of 420 material damping evaluations were performed, and the results are presented as mean values for each configuration along with important statistical indicators to quantify their reliability. The consistency of the experimental method was validated with respect to repeatability and reproducibility. General trends found an increasing damping ratio for higher modes, shorter spans, and edgewise orientations. It is concluded from the results that material damping of timber beams of structural dimensions is governed by shear deformation, which can be expressed more conveniently with respect to the specific mode shape and its derivatives.     

Work environment of processor operators

Seven processor operations were investigated to examine the work environment of the processor operator. The invisible objects in the visual field of four processors were the jib, head, instrument for measuring logs, wiper, and cabin. The operator looked mostly at “the head of the processor” during delimbing, bucking and arranging; “the delimbed tree-length log for bucking” during delimbing and bucking; “the bucked log” during bucking and arranging; and “the sides of the road” during moving and skidding. From the frequency of fixation for each fixated object, the instrument for measuring logs and the head was found to require the most attention. The height of three processors’ steps for “mounting and alighting” were higher than the optimum value (58 cm), obtained from an anthropometric investigation of forest machine operators. The levers and pedals of four processors were arranged at suitable positions, according to JIS guidelines.     

On mechanical behavior of traditional timber shear wall in Taiwan II: simplified calculation and experimental verification

In the previous report of this ongoing study, results of an extensive field survey were collated and a theoretical model was proposed to predict the mechanical behavior of timber shear walls of traditional design in Taiwan. The initial objective of the present report was to propose a simplified calculation method for estimating the initial stiffness and yield strength of traditional timber shear walls. Based on the results of the field survey, a total of 15 full-scale specimens were tested to verify the theoretical model and simplified calculation proposed previously. Good agreement was found from comparison of analytical and experimental results. The results of this study show that the friction behavior between board units and beams plays the major role in resisting the lateral force applied on the timber shear wall, followed by the resistance supplied by embedment. The resistance provided by bamboo nails is minor due to the small section. Another trend found was that for set dimensions of a timber shear wall, the board width can be increased to obtain higher stiffness and strength of the shear wall.     

明清时期木结构建筑风格分析及其保护

我国木结构建筑历史悠久。分析了明清时期建筑物类型以及木结构建筑的规模、构造特点等,阐述了明清木结构建筑文化元素,并结合这些分析对当代建筑以及古建筑保护等方面提出了建议,旨在为木结构建筑的保护和相关设计提供参考。     

Shear tests of timber joints composed of sugi composite glulam beams using newly developed steel connectors

A research project supported by the Japan Wood Working Machinery Association has been conducted since 1999 to examine the feasibility of sugi (Cryptomeria japonica D. Don) composite glulam beams reinforced with Douglas fir (Pseudotsuga menziesii Franco) lamination. This study, part of the project, was concerned with the strength properties of timber joints composed of composite glulams using newly developed structural steel connectors. Two types of beam were prepared: 10 plies (inner 6 plies sugi, outer 4 plies Douglas fir) and 8 plies (inner 4 plies sugi, outer 4 plies Douglas fir). Two types of structural steel connector, Haratec and Standard, were used for joining the beam with a post or a girder. The relation between load and deformation of the joints was represented as a typical nonlinear curve. Initial stiffness and maximum load of the joint composed of the composite glulam were in the range between those of sugi and Douglas fir. Strength properties of the joints varied with three variables: type of connector, depth of the glulams, and the type of joint. Thus, the allowable loads for the connectors should be determined for each combination of these variables.     

国外木结构建筑的抗震性能研究

根据国外的有关文献资料，论述了影响木框架结构抗震性能的主要因素以及木框架建筑的震害调查结果，介绍了目前木框架建筑抗震研究的最新成果。     

Landowner Willingness to Engage in Long-Term Timber Leases in West Virginia,USA

As global competition increases for wood-based products, the need for more efficient supply chains becomes increasingly important. In the forest products sector, these supply chains involve individuals and firms ranging from private forestland owners with standing timber to factories producing final finished products. Long-term timber leases are one mechanism that can be used to develop access to timber supplies for companies unable or unwilling to purchase land outright for growing timber. To investigate private forest owner opinions and attitudes regarding long-term timber leases, we conducted a survey of landowners from Wetzel county, West Virginia. No long-term leases were reported by respondents, but 24% claimed they would enter a lease under certain conditions. The most frequently listed concern related to long-term timber leases was for the “loss of control”. Results of this survey are discussed in the light of forest management efforts that might be used to improve the social, financial, and environmental benefits for private forest owners.     

Challenges of Organizing Private Forest Owners in Serbia

Small-scale forestry in Serbia is characterized by high fragmentation of properties, a large number of parcels and forest owners. Numerous activities for private forest owners in Serbia supported by the State, FAO and CEPF have resulted in an increased interest of owners in forming private forest owners’ associations (PFOA). The goal of this paper is to explore preconditions that are necessary for organizing private forest owners in Serbia into effective associations. In order to reach this goal, results of PRIFORT project were used. The over-arching research questions of this paper are: “What is the level of interest among forest owners in forming owners’ associations?”; “Why has forest owner interest in organizing developed so slowly?” and “What are the necessary preconditions for the development of private forest owners’ organizations in the country?” In order to answer these questions, quantitative survey with 42 close, open and Likert scale questions was conducted. Sample size was determined following Malhotra’s proportion method and, in total, 350 private forest owners, from nine municipalities were interviewed. Results of this paper show that majority of respondents are very little or not at all aware of existing legislation. Almost half of respondents consider that their interests are not represented well. Although about 50% of interviewed forest owners miss interest organization, only 0,3% are members of PFOA. More than 70% are ready to join association, if it would provide some economic advantages.     

The Faustmann model as a model for a forestry of prices

The relation between the Faustmann model and “a forestry of prices” as a concept of thought was examined. At first, the meaning of the Faustmann model in economic sciences is the explanation of allocation and distribution by prices. The rotation age determination plays a secondary role only. Secondly, “a forestry of prices” as an application of the “free to choose” way of thinking is explained. The concept allows us to understand how individuals of anonymous groups achieve forest sustainability and provide forest environmental goods. Thirdly, the relation between the Faustmann model and “a forestry of prices” is discussed. For this purpose, the Faustmann model is described as a scientific laboratory. It helps us to observe how equilibrium arises as a non-intended result of individual welfare maximization in anonymous interactions. And conversely with the help of “a forestry of prices”, we understand also that the individual maximization approach of the Faustmann model re-enacts the unintended interaction situations in anonymous group. With help of the Faustmann model, we can understand deep aspects of “a forestry of prices”. Vice versa, “a forestry of prices” shows the meaning of the formal solutions of the Faustmann model.