Effect of laminate configuration on the modulus of elasticity of glulam evaluated using a strain gauge method

The purpose of this study was to measure the strain of glulam laminae by affixing a strain gauge at the central axis of the lateral face in order to determine the effect of the configuration of the glulam. Japanese cedar and southern pine were used in the study. The strain and stress of the laminae during the bending test were recorded, and the modulus of elasticity (MOE) was calculated. The influence of the MOE of the adhesive layers was also considered. Results showed that the MOE of the laminated elements increased as its specific gravity increased, although the specific gravity was not the only factor evaluated. The MOE of glulam (E _bsg) measured by the strain gauge method was very close to the observed MOE of glulam (E _b) and a significant linear relationship was identified. The MOE (e) of laminae measured by the strain gauge method was very close to that determined (E) under the “free condition” before bonding. The difference between the modified MOE (E _bsa) and E _bsg was not significant. The MOE of glulams made of heterogeneously graded lumbers were about 23% and 31% larger than the average MOE of their laminae for Japanese cedar and southern pine, respectively. The actual neutral axis was just below the longitudinal center line. It shifted slightly within the proportional limit range and moved downward when the load increased.     

Classification study for using acoustic-ultrasonics to detect internal decay in glulam beams

Bayes, k-nearest neighbor (KNN), and neural network classifiers were used to study the decay detection efficiency of acousto-ultrasonics (AU). Brown-rotted Douglas-fir glulam beams removed from service were measured by using through-transmission AU. Single and multiple sets of AU signal features included velocity, attenuation, shape, and frequency content. Although all of the AU signal features were sensitive to decay, they were also affected by natural characteristics of wood. However, it was possible to improve the detection efficiency by using multiple signal feature sets in classification analysis. A 79% efficiency was achieved with the neural network classifier for detecting small levels of decay (10% of the cross section) and a 68% overall correct classification for different degrees of decay when using three or four signal features as inputs. The results of the Bayes and KNN classifiers were quite similar, with 79% KNN and 75% Bayes detection efficiency for small levels of decay, and 67% overall. Received 22 January 1999     

SPF胶合木植筋抗拔性能研究

采用“拉-拉”荷载模式研究SPF(云杉-松木-冷杉)胶合木植筋抗拔性能,探讨了边距、胶层厚度以及长径比等对胶合木植筋连接抗拔强度和破坏模式的影响.结果表明:边距对植筋连接抗拔强度有显著影响,胶层厚度对植筋抗拔强度有极显著影响,长径比是影响植筋连接抗拔强度的重要因子;植筋连接抗拔强度随长径比的增大而增大,当长径比达到一定值时植筋抗拔强度取决于植筋杆的屈服强度;胶合木开裂、植筋杆拔出和植筋杆屈服是试验中的3种主要破坏模式.     

Investigation of the structural performance of glulam beam connections using self-tapping screws

The characteristic strength properties of structural glulam connections assembled with self-tapping screws were examined following the ASTM testing procedure in the study. Four screw types with various numbers were designated at each connection of the beam–girder structure with different nailing schedules. The results indicated that the maximum load capacity and dissipated energy of a connection fastened with 10-mm self-tapping screws were higher than those with 8-mm screws. And, the screws with both double-threaded sections and fully threaded shanks were higher than those of single-threaded screws. An improvement on the initial stiffness of a connection was found when the number of self-tapping screws increased. The connections assembled with the toe-nailing approach from the beam’s bottom surface provided higher maximum loading capacity, medium initial stiffness, and a larger ductility factor, resulting in higher dissipated energy with less fragile failure. The derived allowable loading values for a beam–girder connection fastened with self-tapping screws using the face-nailing approach were close to the code values for bolted and pinned connections. And, a toe-nailing approach provided higher allowable loads for connections than using a face-nail approach.     

An experimental approach to determine pull-out strength of single and multiple axially loaded steel rods bonded in glulam parallel to the grain

ABSTRACT

A glued-in rods' connection is generally constituted by a group of steel bars bonded by an adhesive into timber elements. In the past, most of the research focused on single-rod connections, in order to exploit the maximum resistance of the connection without accounting for interaction among bars or splitting failure in the timber member due to close edge distances or spacing between bars. Such interaction problems arise when dealing with multiple rods, thus requiring specific investigation to fully understand the behavior of the connection as a whole and to determine its capacity. In both cases, existing test procedures determine bond strength in specific geometrical configuration. The paper aims to determine the pull-out strength of single and multiple axially loaded steel rods bonded in glulam parallel to the grain differentiating the adhesive failure from the other failure modes. After an initial review of typical applications and existing design procedures, test results on single rod with confined or unconfined test setup on single rod at different embedment depths are presented and discussed, indicating that the confinement has a negligible influence on the pull-out capacity. Subsequently, interaction between bars is investigated by a specific unconfined configuration. The accounted parameters are the embedment depth of the bars, the dimensions of the timber section, and the spacing between bars. Results are discussed and compared with three-dimensional numerical simulations. Both experimental and numerical results suggest that the critical value at which the transition from pull-out to timber-related failure is observed depends on the mechanical properties of the timber and on the properties of the adhesive, such that a single value of spacing should not be provided in design standard if the full capacity of the adhesive is to be exploited.     

Comparisons of bearing properties for various oriented glulam using digital image correlation

The goal of this study was to analyze the bearing properties of the differently oriented glulam using digital image correlation (DIC). Six differently oriented specimens associated with three anatomical directions including longitudinal (L), radial (R), and tangential (T), and 12-mm drift pins were used to analyze the bearing properties, including yield load and bearing strength. The highest bearing strength of 22.57 MPa from RL was found, whereas the lowest bearing strength of 6.47 MPa from LR was found. Different strain distributions were observed from the differently oriented bearing specimens using DIC. Different failure ratios of the differently oriented specimens were highly related to the strain distributions. Although the bearing properties were found to be different between the differently oriented specimens, for the connection design aspect, the bearing properties of glulam could be grouped as RL and TL specimens, RT and TR specimens, and LR and LT specimens.     

Mechanical analysis of glulam beams exposed to changing humidity

This study deals with the mechanical analysis of glulam beams during changing relative humidity of the surrounding air. The computational part of the article includes two separate numerical procedures. First, the diffusion equation is solved to determine the temporal and spatial distribution of water content in the cross-section of the beam. The results of the first computational stage are used as the input data for the numerical analysis of mechanical response of the beam. The displacements and stress distribution at some characteristic cross-sections are presented. In the article some experimentally determined values of vertical displacements in the middle of span are shown and compared to the results of numerical analysis.     

Size effect of glulam beams in tension perpendicular to grain

The strength of wood is reduced when the stressed volume is increased. The phenomenon is termed size effect and is often explained as being stochastic in the sense that the probability of weak locations occurring in the wood increases with increased volume. This paper presents the hypothesis that the lower strength is caused by stress concentrations. The stress concentrations arise from the anisotropic structure of wood, and are therefore deterministic. The hypothesis is substantiated through extensive FEM-calculations and experiments. A reasonable agreement between ultimate stresses determined experimentally and in FEM-computations was found.     

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.     

Prediction of bending properties for structural glulam using optimized distributions of knot characteristics and laminar MOE

This study established a prediction model for bending properties of glued-laminated timber (glulam) using optimized knot and modulus of elasticity (MOE) distributions of lumber laminate as the main input variables. For this purpose, knot and MOE data were investigated for all pieces of lumber that were prepared for glulam manufacturing, and statistical distributions of knot size, knot number in one lumber, and MOE of each laminate were optimized as distribution functions. These knot and MOE data were used as input variables in the prediction model for bending properties, and were also used in generating virtual glulam using the inverse transform method. Prediction of bending properties for glulam was carried out using the transformed section method, which is partially provided in ASTM D 3737 (Annex A4). Predicted values were compared with those from full-scale four-point bending tests for 60 six-layered glulams with 10 different laminar combinations. Finally, the allowable bending properties of glulam for each specific laminate combination were determined by calculating the fifth percentile of the modulus of rupture and the average modulus of elasticity from virtual test results of more than 1000 virtual glulams. From the results of this study, predicted bending properties for glulam and their distributions could be used for structural design in both allowable stress design and limit state design.     

Height-diameter models with random coefficients and site variables for tree species of Central Maine

Height-diameter models were developed for nine tree species common to the northeastern United States: Abies balsamea, Acer rubrum, Betula papyrifera, B. populifolia, Picea rubens, P. mariana, Pinus strobus, Populus tremuloides, and Tsuga canadensis. Stem heights and diameters were collected from 6 146 trees (between 136 and 2615 trees per species) on 50 plots within 10 structurally diverse stands that are part of a long-term silvicultural experiment in central Maine. The models were developed using both generalized nonlinear least squares (GNLS) and multi-level, mixed-effects approaches. Mixed-effects approaches were superior to GNLS, with inclusion of site covariates (tree density and basal area) accounting for some of the variability explained by the random coefficients in the full mixed-effect models. Analysis of plot-level parameter estimates suggested that differences in stand structure (even-aged vs. uneven-aged silvicultural practices) had a significant influence on the height-diameter relationships.     

A decision support tool approach based on the Electre TRI-B method for the valorisation of tropical timbers from the Congo Basin: an application for glulam products

An alternative approach to the formal management strategy of tropical timber species from the Congo Basin was investigated. It focused on the development of glulam, with an aim to specify a decision support model for the valorisation of tropical timber species considered for use in these products. There were 76 forest species analysed regarding ecological, engineering and social criteria according to their major uses. The Electre TRI-B multicriteria sorting method was used. The main result was a new and robust classification tool of timber species from the Congo Basin, corresponding to their multicriteria consensus degree. The potentials of the new grouping system were analysed. Species that meet a great majority of criteria were identified. They were highly suitable for sustaining the market position of glulam products. Implementing this strategy may significantly improve the management and increase the value of the timber species from the Congo Basin, while preserving endangered species.     

A method to estimate the structural parameters of windbreaks using remote sensing

Windbreaks are a major component of agroforestry practices and play an important role in agroforestry ecosystems. They can reduce wind velocity and protect shelter crops from wind damage and soil from wind erosion. Porosity is one of the most important structural parameters that affect wind speed and is widely used in the study of wind protection provided by windbreaks. In this paper, a method to estimate porosity using high-resolution satellite imagery is represented. Porosity was difficult to estimate through the direct use of remote sensing data due to the poor relationship with vegetation indices. Thus, two intermediate variables, that is, CL ² × LAI and CL × LAI × W, which were highly related to porosity, were selected. Leaf area index (LAI) and average tree crown length (CL) were estimated using vegetation indices, and W, which refers to the width of a windbreak, was identified using object-based image analysis. Porosity was estimated using a statistical relationship between porosity and intermediate variables. The average prediction accuracy of the estimated porosity value was 76.104 %. Based on the estimated porosity value, the windbreaks were grouped into three types, and their efficiency of wind protection was evaluated. The evaluation result indicated that the windbreaks have a very good protective structure in the study area and they can effectively shelter crops from wind damage and erosion. This study can provide a useful guide for studying the wind protection provided by windbreaks on spatial and temporal scales using remote sensing.     

Modelling the site index of Pinus pinaster plantations in Turkey using ecological variables

The determination of site productivity in forest ecosystems plays a crucial role in resource management.This study was carried out to identify relationships between site characteristics and height growth of Corsican maritime pine(Pinus pinaster Ait.) plantations in Turkey.Sixty-nine sample plots 20 years of age were selected from locations with different inclinations,aspects,elevations,slope positions and site class.Soil samples were taken at various depths.Height and age were measured on a dominant tree after felling in each plot.Physical and chemical properties of the soil were determined.Relationships between site index(SI_(25)) and physiographic factors,climatic attributes as well as soil properties were evaluated using correlation analysis and multiple regression analysis.Site index was significantly related with annual precipitation,mean spring rainfall,rainfall June to September,rainfall of the driest month,length of the dry period,mean maximum temperature,mean temperature of the warmest month,stoniness of the soil,sand,silt,clay,pH,electrical conductivity,and available water capacity.Multiple regression accounted for 57.9% of variations in height growth.The models obtained can be used to determine the site index of potential areas in Turkey for maritime pine.It can be said that the productivity of maritime pine may decline in the future due to global climate change.     

Estimation of taper curve using stand variables and sample tree measurements

The aim of the study was to develop methods for estimating the taper curves for trees tallied in a forest inventory. The average stem form in a stand was described by the principal components of the stand effects in the stem dimensions measured in the polar coordinate system. Measurements of diameter at breast height, diameter at a height of 6 meters, and height taken from trees on the sample tree plots were used for determining the first four principal components. Regression models were derived to predict the principal components from the site and growing stock variables. These models were used to estimate the taper curves of the tallied trees. Use of the principal components estimated by the regression models gave less reliable results than use of the principal component estimates based on measurement of the height of one randomly chosen tree on the sample plot. The best result was found with combined use of the principal component estimates and one height measurement per sample plot.     

Application of the SB distribution to the simulation of correlated lumber properties data

Summary With the emergence of probabilistic design procedures, the need for precise knowledge of the entire probability distributions of load effects and material resistance has never been greater. In order to evaluate these distributions, simulation techniques have provided a reliable and cost and time effective alternative to large scale destructive testing. With the use of the Johnson's S_B probability distribution, a closed-form, analytic procedure has been developed to model the inherent variability in strength, given some nondestructively evaluated parameter. This modeling procedure serves as the basis of a verified simulation process to predict a strength distribution, given a probability distribution of the NDE parameter. The approach presented here, represents a closed-form, analytic solution to a problem which has heretofore been treated in a more subjective fashion. This simulation procedure is complemented by a stratified sampling scheme.The author wishes to recognize Engineering Data Management, Inc. for the use of their computer software, STADMAN, and the Mc Intire-Stennis Research Program for the financial support of this study     

Exploring visitors' willingness to pay to generate revenues for managing the National Elephant Conservation Center in Malaysia

Financial sustainability of protected areas is one of the main challenges of management. Financial self-sufficiency is an important element in improving conservation effort in these areas. This study seeks to review best practices in recreational fee systems in different countries and to find a relevant entry fee for a wildlife sanctuary in Malaysia. The revenue of the National Elephant Conservation Center (NECC) in Kuala Gandah, Malaysia, comes from several sources, including the national government, but all these budgetary sources are strained by tighter public budgets and greater demands. The present study investigates the introduction of visitor entrance fees to supplement an otherwise inadequate budget for supporting the operational costs of the sanctuary. Factor analysis and a double-bounded contingent valuation method were combined to estimate tourists' willingness to pay (WTP) the proposed entrance fee. Factor analysis showed that respondents' motivation to support the NECC with user fees is conditioned by their direct experiences with elephants, their satisfaction with NECC's educational programs and services, and other experiences it gives to users. The WTP model considered respondents' four motivation factors with their sociodemographic characteristics. Since NECC visitors arrive from both within and outside the country, this study suggests to center managers a two-tier fee structure (residents vs. nonresidents of Malaysia), based upon mean WTP estimates. This study further suggests that revenue from such an entrance fee for NECC could support the Center's management and development costs.     

Species variables or environmental variables as indicators of forest biodiversity: a case study using saproxylic beetles in Maritime pine plantations

? To assess the sustainability of plantation forest management we compare two types of biodiversity indicators. We used the species richness of saproxylic beetles as a case study to test the “species” and “environmental” indicator approaches. We compared single species abundance or occurrence and deadwood volume or diversity as predictor variables.

? Beetles were sampled with flight interception traps in 40 Maritime pine plantation stands. The volume and diversity of deadwood was estimated with line intersect and plot sampling in the same stands. Predictive models of species richness were built with simple linear or Partial Least Square regressions.

? Deadwood variables appeared to be good predictors of saproxylic beetle richness at the stand-scale with at least 75% of variance explained. Deadwood diversity variables consistently provided better predictive models than volume variables. The best environmental indicator was the diversity of deadwood elements larger than 15 cm in diameter.

? By contrast, the use of “species variables” appeared to be less relevant. To reach the quality of prediction obtained with “environmental variables”, the abundance or occurrence of 6 to 7 species — some of which are difficult to identify — had to be used to build the indicator.