Effects of logs steaming,veneer drying and aging on the mechanical properties of laminated veneer lumber (LVL)

In this study the effects of steaming and drying condition on the mechanical properties and durability of laminated veneer lumber (LVL) and solid sawn lumber were investigated in a comparative way. Steamed beech and steamed and non-steamed spruce logs were used and two different veneer drying temperatures (20 and 110 °C) were selected for this aim. Aging test was applied according to EN 321 to determine the durability of LVL and solid wood samples. Steaming decreased considerably all investigated strength properties of LVL panels and the least affected was the compression strength. The compression strength and the static bending strength values of both beech and spruce LVL panels were higher than those of the solid wood groups obtained from the same logs. The impact strength values of LVL panels, unlike the static bending strength and the compression strength, were lower than those of the solid samples, which were not steamed and aged.     

简支T梁制架与购架方案的技术经济比选

详细讨论了应用于铁路简支T梁桥的预应力钢筋混凝土T梁的预制架设与购买架设两种施工方案,并以某铁路项目为例,探讨了在该项目中如何对两种施工方案进行比选,最终确定出技术经济合理的施工方案。     

Effects of scarf joints on bending strength and modulus of elasticity to laminated veneer lumber (LVL)

The role of geometry on the mechanical performance of scarf joints in laminated veneer lumber (LVL) bonded with phenol formaldehyde and melamine formaldehyde (MF) adhesives was investigated. Model joints consists of 3, 4 and 5 mm veneer thicknesses at 30°, 45° and 60° of varying scarf joints for LVL produced from brutia pine (Pinus brutia Ten) and elm (Ulmus compestris l.) woods. However, there is little information available concerning the bending strength and modulus of elasticity for LVL, and in particular, scarf joints in these field. In this study, it was aimed to determine the bending strength and modulus of elasticity for LVL. For this purpose, samples were tested according to TS EN 310 standard. It was observed that the highest bending strength (291.5 N/mm²) and modulus of elasticity (28 101 N/mm²) were obtained in control (solid wood) samples having three layered LVL, jointed with 30° angle and bonded with MF adhesive. As a result of the effects scarf joints on bending strength and modulus elasticity test, if the scarf angle decreases, the properties of LVL increase.     

Effects of moisture content on formaldehyde emission and mechanical properties of plywood

Wood is a hygroscopic material and has ability to exchange its moisture content with air. Many mechanical properties are affected by changes in moisture content below the fiber saturation point of wood. This study evaluates the formaldehyde emission and some mechanical properties of poplar and spruce plywood panels manufactured from rotary cut veneers having different moisture content by using urea–formaldehyde (UF) and modified urea formaldehyde by melamine (M+UF). Rotary cut veneers obtained from poplar and spruce logs were classified into three groups and veneers in each group were then conditioned in a climate chamber to either 4–6%, 10–12% or 16–18% moisture content. Plywood panels with three plies and in 6 mm thickness were manufactured for each group. Formaldehyde emission, shear strength, bending strength and modulus of elasticity values of plywood panels were determined. Best bonding results were obtained in plywood panels with veneers having 4–6% moisture content. Lowest mechanical properties were found for plywood panels manufactured from veneers conditioned to 16–18% moisture content. Formaldehyde emission values of poplar and spruce plywood panels decreased with increasing veneer moisture content for both glue types. Formaldehyde emission content of panels decreased with melamine addition into the urea formaldehyde glue mixture.     

The impact of digital technology usage on economic growth in Africa

This study analyses the impact of the use of digital technology on economic growth for 39 African countries from 2012 to 2016. This analysis applies a system GMM estimator to understand the extent to which the usage of digital technology facilitates growth using a measure of digitalisation from the Networked Readiness Index. Unlike previous research, we distinguish between the impact of individual, business, and government ICT usage on growth and show that only individual usage has a positive impact. Furthermore, a disaggregated analysis of the types of usage reveals that two indicators, social media and the importance of ICTs to government vision, are significant for growth.     

Impacts of impregnation chemicals on combustion properties of the laminated wood materials produced combination of beech and poplar veneers

The aim of this study was to investigate the effects of impregnation with boron compounds Borax (B_X), Boric acid (B_A), B_X + B_A, Imersol-Aqua (I_AQUA) and Timbercare-Aqua (T_AQUA) on combustion properties of the laminated wood materials produced combination of Oriental beech and poplar veneers bonded with Desmodur-VTKA (D_V) and Poly(vinyl acetate) (P_VAc) adhesives. The test samples, prepared from beech (Fagus orientalis Lipsky) and poplar (Populus nigra Lipsky) woods, were impregnated boron compounds by vacuum, I_AQUA by dipping and T_AQUA by brushing methods according to ASTM D 1413-76-99 and directions of the manufacturer. The laminated wood materials were prepared in the form of five layers, 4 mm thickness from the impregnated beech and poplar veneers according to TS EN 386. Combustion properties of samples after laminated and impregnated process were determined according to ASTM E 160-50. Considering the interaction of combustion type and impregnation materials, combustion temperature was found the highest in flame source combustion (F_SC) + T_AQUA (528.150 °C) but the lowest in without flame source combustion (WF_SC) + B_A (391.333 °C). Consequently, boron compounds and I_AQUA showed a decreasing impact on combustion properties of the laminated wood materials, produced combination of beech and poplar veneers, bonded with D_V. In consequence, impregnation with boron compounds and Imersol-Aqua of the laminated wood materials, bonded with Desmodur-VTKA, provides security for the usage of having high risk of fire.     

A cost analysis of the lumber and plywood industries in two Pacific Northwest sub-regions

Translog cost models are used to represent production technologies for the Pacific Northwest lumber and plywood industries. Expressions for cost elasticities are obtained along with measures for derived demand, factor substitution, and biased technological change. Emphasis is placed on the behavior of costs over output, the derived demand and substitutability of inputs due to changes in factor prices and technology, and the resulting effects on product prices. Estimation results over the 1950–79 sample period suggest the presence of output economies in specific industries, a potential impact of reduced factor prices, and the lack of a consistent trend in technological change across products and regional industries.This work was partially supported by the USDA Forest Service and Wichita State University. The authors wish to thank Gerald McDougall, Dong Cho, and David Poynter for their assistance in this project.     

Effects of layered structure on the physical and mechanical properties of laminated moso bamboo (Phyllosachys edulis) flooring

The physical and mechanical properties of five different layered structure types of laminated moso bamboo (Phyllosachys edulis) flooring (LBF) were investigated in this study. In addition, the dynamic modulus of elasticity (DMOE) calculated from ultrasonic wave velocity was also investigated. A good correlation between the DMOE and modulus of rupture (MOR) values of the LBF was found (R² = 0.92, p < 0.01). Results indicated that the DMOE can be a predictor of the bending properties of LBF. The mean linear length expansion value of the cross-laminated layered structure type LBF (group V) was higher than those of the other types. Overall, the mean thickness swelling, water absorption, linear width, and thickness expansion values obtained from group V were smaller than those from the other groups. Thus, group V should be of a better quality than the other groups from the viewpoint of its dimensional stability. The cross-laminated type (group V) of a layered structural design affected the MOE and MOR values significantly less than those of the other groups. However, the mean bending strength (87.5 MPa) of group V was suitable for flooring purposes, in addition, concerned to the orthotropic bending properties of group V, defined as the ratio of bending properties parallel to fiber direction (MOE_(para), MOR_(para)) to those perpendicular to fiber direction (MOE_(perp), MOR_(perp)) were 1.28 for MOE_(para) to MOE_(perp) and 1.20 for MOR_(para) to MOR_(perp), respectively.The results suggest that it is feasible to evaluate the bending properties of LBF using the DMOE, and group V should be a better choice than the other groups to meet the basic necessities for flooring purposes.     

The effects of ply organization and loading direction on bending strength and modulus of elasticity in laminated veneer lumber (LVL) obtained from beech (Fagus orientalis L.) and lombardy poplar (Populus nigra L.)

The effects of ply organization and loading direction on bending strength and modulus of elasticity in laminated wood materials produced from 3 mm thick veneers, of beech (Fagus orientalis L.) and lombardy poplar (Populus nigra L.) placed one on top of the other in various arrangements were examined in this study. Kleiberit 303 (PVAc), a vinyl (polyvinyl acetate – PVAc) based glue was used in lamination. Eight hundred samples were prepared in order to measure oven-dry specific gravity, bending strength and modulus of elasticity values perpendicular and parallel to the glue line of a total of 10 different arrangements, eight of which have different laminated ply organizations, namely (AAAAAAA) (7A), (BBBBBBB) (7B), (ABBBBBA), (ABABABA), (AABBBAA), (AABABAA), (ABBABBA), (BABABAB), in which (A) represents beech wood and (B) represents poplar wood and the other two, which consist of solid beech and solid poplar wood in same dimensions as control samples. The samples were subjected to tests perpendicular and parallel to the glue line in accordance with the ISO 16978 standard. As a result of statistical analysis of the data obtained from the tests, the bending strength and modulus of elasticity values of solid woods both perpendicular and parallel to the glue line were observed to be smaller than those values of laminated woods made of the same species of woods. It was also observed that as contribution rate of beech in lamination increases, the bending strength and modulus of elasticity values increase.     

预应力积成材力学性能试验研究与有限元分析

通过木材单板叠加试验和预应力积成材参数化分析试验及相应的有限元分析验证,研究了单板及预应力积成材在跨中集中荷载作用下受力模式、变形形态、承载力以及破坏模式的变化规律,并探讨了预应力的大小,螺杆的布置方式、直径、纵向间距及上下边距对构件承载力的影响规律。结果表明：随着板材积成数量的增加,预应力积成材的破坏模式由弯扭变形导致的强度破坏逐渐转变为由面内弯曲导致的强度破坏,承载力大幅度提升;预应力过大、螺杆直径过大和间距过小导致木材承压破坏或产生贯通裂缝,而预应力过小、螺杆直径过小和螺杆间距过大均不足以限制板材的侧向扭转变形,导致材料强度无法充分发挥;木节等木材初始缺陷严重削弱板材的承载力。最后针对本文研究的板材规格,提出了能够应用于工程实际的预应力施加建议。     

高层钢筋混凝土框架/混合框架—核心筒体系技术经济比较

选择高度为118,150,177m的三个工程实例,分别采用钢筋混凝土框架-核心筒结构体系和混合框架-钢筋混凝土核心筒混合结构体系进行设计和计算,对两种结构体系进行了技术和经济两方面的对比和分析。探讨了两种结构体系随高度增加显现出的规律和经验。对比结果显示:混合结构体系的结构质量减小20%,风载效应增大10%,地震效应减小15%～25%,工程总造价增加10%～12%,有效使用面积和楼层净高度增加、施工速度更快、抗震性能好,综合而言,混合框架-核心筒结构体系具有一定优势。     

The effects of some manufacturing factors on surface roughness of sliced Makoré (Tieghemella heckelii Pierre Ex A.Chev.) and rotary-cut beech (Fagus orientalis L.) Veneers

In this study, the effects of veneer thickness, cutting speed, knife bevel, vertical and horizontal opening, and drying temperature on surface roughness of sliced Makore veneer and rotary-cut beech veneer were evaluated. Makore logs for sliced veneers and beech logs were used for rotary-cut veneers manufacturing. Before veneer manufacturing, the Makore and beech logs were steamed indirectly at 80 °C for 50 and 36 h, respectively. Roughness measurements were conducted according to DIN standard 4768 by using stylus profilometer. The sliced radial and tangential veneers were grouped and evaluated separately. Results showed that veneer thickness, cutting speed and knife bevel had a significant effect on surface roughness for the sliced veneers, but veneer drying temperature did not affect significantly the surface roughness. In general, surface roughness of the veneer increases with increasing veneer thickness. However, increases in cutting speed decreased the surface roughness. The most suitable knife bevel was 17.5° for manufacturing sliced veneers from Makore. For rotary-cut veneers, vertical and horizontal opening had a significant effect on the surface roughness. The results indicated that vertical opening should be about 50% and horizontal opening about 80–90% of veneer thickness to minimize the surface roughness in manufacturing rotary cut veneer from oriental beech.     

Effects of stream acidification on fungal biomass in decaying beech leaves and leaf palatability

We examined the effect of surface water acidification on rates of decomposition, ergosterol concentrations (as a measure of fungal biomass), and palatability to shredders of common beech leaves (Fagus sylvatica L.) in five mountain streams (pH 4.7-7.1). Leaf decomposition was significantly faster in the circumneutral streams (pH 6.4-7.1; k > or = 0.00175 d(-1)), when compared to acidic streams (pH 4.7-4.9; k < or = 0.00100 d(-1)). Fungal biomass showed no particular trend along the acidification gradient except that it peaked earlier in the stream closest to neutrality. Leaf palatability, measured as the feeding activity of the leaf-shredding amphipod Gammarus fossarum Koch, varied with the exposure time in the streams. Except for the higher palatability of leaves exposed during 6 weeks at the highest pH, patterns among streams were mostly similar. These results suggest that reduced processing rates in the most acidic streams were not related to differences in fungal biomass associated with decomposing leaves and that microbial conditioning was only slightly delayed by acidification. Possible effects of low pH and related variables (Ca, Al) on microbial decomposition and detritivorous macroinvertebrates are discussed to clarify the inhibition of beech leaf decomposition in the studied systems.     

某地库工程地基基础设计方案分析与经济比较

针对某地库工程,通过计算分析提出了三种不同的地基基础设计方案,经过经济性对比,得出了最优设计方案,为该工程地基基础选型提供了理论依据。     

地下室防水板采用平板式与梁板式经济性比较

鉴于人们对梁板式和平板式两种防水板的认识和实际工程结果上的反差,结合某工程实例,从设计角度详细分析了防水板之间的差别,简述了其原因,对各方案进行了经济性比较,最终确定了最优方案。     

几种能源供暖方式的技术经济比较

分析了几种能源供暖方式的初投资和经营费用，给出了费用年值的计算公式。采用费用年值法对几种能源供暖方式的经济性和使用过程的技术性进行了比较。     

The effects of heat treatment on some technological properties in Uludağ fir (Abies bornmuellerinana Mattf.) wood

Heat treatment is often applied to improve the dimensional stability of woods. In this study, the effect of heat treatment on some mechanical properties of Uluda? fir wood (Abies bornmuellerinana Mattf.) having industrially high usage potential and large plantations in Turkey was evaluated. Samples collected from Bolu Forest Enterprises, Turkey were subjected to heat treatment for varying temperatures and durations. Then, the treated and control samples were tested for some mechanical properties; compression strength, bending strength, modulus of elasticity in bending, janka-hardness, impact bending strength and tension strength perpendicular to grain. The results indicated that treated samples had lower mechanical properties compared to the control samples. In addition, increase in temperature and durations decreased the mechanical properties.     

The housing and economic development debate revisited: economic significance of housing in developing countries

Should housing improvement be part of economic development strategies? Must housing improvement wait until high-economic growth is attained? How much priority should be given to housing in view of the limited resources in less-developed countries? What are housing benefits in economic development vis-à-vis other economic investments? These questions have generated heated debates, both in the literature on development problems and in planning and practice in the 1950s and 1960s. This paper draws on the accumulated body of knowledge resulting from past experiences in research and policy to revisit the earlier debates, survey the main lines of argument and reassess the economic potential of housing. It then attempts to generate broad policy considerations. The main contention of this paper is that in light of past and present evidence, the housing sector needs to be given serious consideration in economic growth strategies.     

建筑施工企业项目经济效益管理与控制

本文从工程招投标、施工准备、施工实施以及工程竣工结算等过程,来阐述建筑施工企业项目经济效益管理与控制。     

A comparison of kraft and kraft-sodium borohydrate brutia pine pulps

Although the reaction of borohydrate with lignin is well-known, limited literature is available regarding the effect of borohydrate on kraft pulp yield and pulp and fiber properties. Therefore, the objective of this study was to study the effects of borohydrate on kraft pulps for Burita pine. First, the optimal cooking conditions for kraft method were determined by varying the active alkali (16% and 18%) and cooking time (60, 90, and 120 min). Then, kraft-sodium borohydrate cooks were done at optimal kraft condition by adding sodium borohydrate to the cooking liquor at the amount of 1%, 2%, and 3% (o.d. wood). The results indicated that adding sodium borohydrate in kraft cook not only increases the pulp yield but also significantly decreases the amount of rejects leading to improved selectivity of the lignin removal and delignification rate. Also, kraft-sodium-borohydrate pulps gave higher pulp viscosity and brightness; however, the strength properties were little lower compared to the kraft method.