共查询到20条相似文献,搜索用时 171 毫秒
1.
AbstractThis study examined the performance of mechanically graded timber in bending when exposed to fire at various load
ratios. The test specimens were 150 pieces, each with the dimensions of 60 × 120 × 3500mm. The modulus of elasticity (MOE)
of 150 specimens was measured, and 60 among them were selected to formulate the prediction equation for MOE and modulus of
rupture (MOR), which was used to predict the remaining 90 specimens. These were tested under fire exposure in bending using
three-point loading at 11.1%, 16.7%, 33.3%, 66.7%, and 83.3% of the ultimate load. Using mechanically graded timber, which
means acknowledging the actual strength of the bending member, permits fairly precise application to the targeted design load.
This research confirmed that mechanically graded timber under fire exposure has the following tendencies: under the same load
ratio, time to failure is independent of strength class, and, at any load ratio, the critical strength is dependent on the
timber strength class. The obtained design bending strength under fire exposure using the reduced cross section method and
the reduced strength method conformed to those calculated based on Eurocode 5. Following those findings, mechanically graded
timber can be applied to obtain the design bending strength when taking into account the fire attack. 相似文献
2.
Strength grading of Norway spruce structural timber: revisiting property relationships used in EN 338 classification system 总被引:1,自引:0,他引:1
Solid timber for structural applications has to be strength graded prior to its use. In order to remain economic the grading process usually focuses on the most important physical and mechanical properties: density, modulus of elasticity (MOE) and bending strength. Based on respective limits given in standards, the timber is assigned to strength classes. Additional mechanical properties such as tensile and compression strength parallel to the grain are derived from the basic property values by empirical relationships. The objective of this study was to review some of these property relationships based on recently compiled large data sets as a contribution for a future revision of the grading standards. Based on mechanical tests of Norway spruce structural timber with different cross-sections, the following characteristic values and property relationships were evaluated: (a) strength and MOE in bending, (b) in-grade characteristic values of bending strength, bending MOE and density, (c) relationship of characteristic values of tension and compression strength parallel to the grain with respect to the corresponding characteristic value of bending strength, (d) ratio of fifth percentiles and mean values of density and MOE, as well as (e) the ratio of MOE in bending, tension and compression. Mechanical tests were accompanied by measurements of density and ultrasonic wave speed. Resulting dynamic MOE was partly used as an indicator of timber quality. 相似文献
3.
《Scandinavian Journal of Forest Research》2012,27(2):185-195
Abstract To enable use of round Scots pine timber in structural frameworks it is necessary to estimate the mechanical properties of the material. This paper presents data on density, bending strength and modulus of elasticity (MOE) of 533 debarked Scots pine logs with diameter from 75 mm to 250 mm sampled from 10 sites in southern Norway. The results show that round timber can have high values of bending strength and MOE, depending on the sites from which the trees have been collected. Some of the variation in bending properties can be explained by visual characteristics, but since a significant proportion of the residual variance is related to sites, criteria for visual strength grading have to be conservative to be valid across all sites. The potential for machine grading based on measuring MOE is better since this model is more accurate and the random effect of site is smaller. 相似文献
4.
This study focused on the relationship between stress level and the fire resistance of structural lumber. The 210 samples were prepared from 15-year-old trees of Acacia mangium from the Forest Estate Plantation, Indonesia. Specimens were 20 ® × 20 (T) × 500mm (L) and were air-dried. Sixty samples were tested under four-point bending stress to obtain the modulus of elasticity (MOE) and the modulus of rupture (MOR) for classifying the stress grades of the remaining 150 samples. The tests were performed using a four-point load bending position at various stress level while the specimens were exposed to fire along the shear-free region. Time to failure was affected by the stress levels in an exponential trend. Despite changes in stress level, charring rate, and time to failure, the critical stress of a member from the same species was similar. The fire performance under applied load could be predicted by using simplified fire-testing methods. The developed testing apparatus is valid for evaluating the small-scale fire resistant behavior of structural lumber in bending. 相似文献
5.
John Moore Alexis Achim Andrew Lyon Shaun Mochan Barry Gardiner 《Forest Ecology and Management》2009,258(7):1174-1180
The effects of early re-spacing on the physical and mechanical properties of Sitka spruce (Picea sitchensis [Bong.] Carr.) structural-dimensioned timber were studied using material from a fully replicated 57-year-old trial located in Northern Ireland, which had been thinned at age 11 years. Basic density, distortion (spring, twist and bow), modulus of elasticity (MOE) and modulus of rupture (MOR) in bending of structural timber from four different re-spacing treatments (1.83 m × 3.66 m, 3.66 m × 3.66 m, 3.66 m × 5.49 m and 5.49 m × 5.49 m) were compared with those of timber from a control (1.83 m × 1.83 m). Re-spacing intensity had a significant effect on both modulus of elasticity (p = 0.006) and modulus of rupture (p = 0.009), but not on basic density (p = 0.379) or distortion (p > 0.200). Timber from the two widest re-spacing treatments failed to meet the requirements for the C14 strength class, while timber from the control met the requirements for the C16 strength class. Both MOE and MOR were significantly and negatively associated with knot size and frequency, which in turn increased with re-spacing intensity. Overall, re-spacing intensity only explained approximately 10% of the total amount of variation in both MOE and MOR, with most of the variation due to inter- and intra-tree differences within a treatment. Based on these results, re-spacing of Sitka spruce to a residual stand density of less than 900 trees/ha (3.33 m × 3.33 m) is not recommended if the goal of management is to produce C16 structural timber. 相似文献
6.
H. Heräjärvi 《Wood Science and Technology》2004,37(6):523-530
The purpose of this study was to determine the modulus of elasticity (MOE) and the modulus of rupture (MOR) in the radial bending test for small, clear specimens of Finnish birch (Betula pendula Roth and B. pubescens Ehrh) wood originating from mature trees. The dependency of MOE and MOR on the specific gravity of birch wood was studied, and the relationship between MOE and MOR was modelled at the different heights and at the different distances from the pith of the tree. For B. pendula, the mean values for MOE and MOR were 14.5 GPa and 114 MPa, whereas B. pubescens had means of 13.2 GPa and 104 MPa, respectively. At the corresponding specific gravity, the bending stiffness and strength values did not differ between the two species. The results indicated a linear relationship between the MOE and MOR, irrespective of the birch species or the within-stem location. Both MOE and MOR increased clearly from the pith towards the surface of the tree and decreased slightly from the base to the top of the tree. It seems that if products with as high stiffness and bending strength as possible are wanted, sorting of raw materials into different grades according to their within-tree origin can be of value. 相似文献
7.
The objective of this study was to investigate the physical and mechanical performance of flakeboard reinforced with bamboo strips. The study investigated three different bamboo strip alignment patterns and an experimental control. All panels were tested in static bending both along parallel and perpendicular to the lengths of the bamboo strips. Internal bond strength (IB), thickness swelling (TS), linear expansion (LE), and water absorption (WA) were also examined. As expected, modulus of rupture (MOR) and modulus of elasticity (MOE) were substantially greater for all three experimental panel types as compared to the control group. LE was also improved for all three experimental panel groups. The bamboo strip alignment patterns had no significant effect on TS, WA and IB. The sample means for MOR, MOE and LE tested perpendicular to the bamboo strip lengths yielded slightly lower mean values than corresponding samples tested parallel to the bamboo strips lengths. This difference in mechanical properties is largely attributed to low panel density in the failure zones. 相似文献
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Sudijono Dwianto Wahyu Yusuf Sulaeman Iida Ikuho Furuta Yuzo Minato Kazuya 《Journal of Wood Science》2004,50(4):371-374
Mechanical property changes due to the moisture content (MC) and/or temperature changes were examined for 15 Indonesian wood species. A static bending test was carried out at 20°C, 65% relative humidity (air-dry), and water-saturated at 20°C (wet-20) and 80°C (wet-80). For individual test conditions, modulus of elasticity (MOE) and modulus of rupture (MOR) increased linearly with specific gravity regardless of wood species; however, maximum deflection did not correlate with specific gravity for any MC or temperature conditions. The relative values of MOE and MOR measured in wet-20 to air-dry conditions were variously affected from slightly to strongly depending on the wood species. However, the relative values always decreased markedly when saturated in water at 80°C, regardless of wood species. The relative MOE, MOR, and maximum deflection values due to the change in MC or MC and temperature combined were independent of specific gravity but may be dependent on wood type: softwood or hardwood. 相似文献
10.
Thirty types of three-ply parallel- and cross-laminated woods were prepared from five species, and their static bending strength performance were investigated. The modulus of elasticity (MOE), proportional limit stress, and modulus of rupture (MOR) perpendicular to the grain were increased by cross-laminating, and the extent of the increase increased with decreasing density of the species. The measured values of MOE parallel and perpendi-cular to the grain of parallel-laminated woods and perpendicular to the grain of face laminae of cross-laminated woods were approximately equal to those calculated from true MOEs of individual laminae. However, the MOE parallel to the grain of face laminae of cross-laminated woods was much lower than the calculated MOE owing to the effect of the deflection caused by shear force on the MOE. The percentage of deflection caused by shear force versus total deflection (Y
s) showed high values, from 16.1% (buna) to 40.5% (sugi), and it decreased linearly with increasing shear modulus in the cross section of the core. In addition, there was an extremely high positive correlation between the MOR and the measured MOE parallel to the grain of face laminae of cross-laminated woods. The MOR was also highly dependent on the shear modulus in cross section of the core.Part of this paper was presented at the 50th Annual Meeting of the Japan Wood Research Society, Kyoto, April 2000 相似文献
11.
CHANG Liang WANG Zheng GAO LiResearch Institute of Wood Industry Chinese Academy of Forestry Beijing P.R.China 《中国林业科技(英文版)》2004,3(4):81-87
In this paper, the physical and mechanical properties of laminated bamboo lumber were studied by testing moisture content, delamination ratio, horizontal shear strength, MOE and MOR of the structure-use material, in the same time, these subjects of finger-joint were tested too. The results showed that, the horizontal shear strength, MOR, MOE of laminated bamboo were superior to the ordinary structure-use timber in architecture, such as Pinus. The performance of aging test was not extraordinary, although the physical and mechanical properties of laminated bamboo lumber decreased after aging test, these properties were beyond Pinus yet. 相似文献
12.
Md. Qumruzzaman Chowdhury Swapan Kumar Sarker Jiban Chandra Deb Sanjay Saha Sonet 《Wood Science and Technology》2013,47(4):797-813
Timber species grouping (TSG) is essential for meaningful and cost-optimal use of wood. Bangladesh forests are exceedingly diverse and comprise many woody species which are potentially suitable for versatile uses including structural materials. Traditionally, widely known tree species are used for structural timber because technological properties of most of the species are poorly known. In this study, a hierarchical agglomerative cluster analysis based on three selected wood properties [i.e., wood density, modulus of elasticity (MOE) and modulus of rupture (MOR)] of seventy-nine timber species was done. The clustering process led to the formation of four distinct species groups [i.e., very low (TSG1), low (TSG2), medium (TSG3) and high (TSG4)]. However, the species grouping patterns also varied from trait to trait. This might be due to moderate relationship between density and MOE (r 2 = 0.46) or MOR (r 2 = 0.52). Species of the TSG1 group are mainly characterized by extremely low trait values, while the TSG4 group consists of species having exceedingly high trait values. The TSG2 and TSG3 groups are characterized by low and medium trait values. Hence, it is suggested to select suitable species from these groups, particularly the lesser known high-quality species in afforestation and reforestation programs to meet future timber demand in Bangladesh. 相似文献
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14.
Song-Yung Wang Cheng-Jung Lin Chih-Ming Chiu Jin-Hau Chen Te-Hsin Yung 《Journal of Wood Science》2005,51(1):1-6
The effects of different thinning and pruning methods on the bending strength and dynamic modulus of elasticity (DMOE) of young Taiwania (Taiwania cryptomerioides Hay) were investigated. The average DMOE, modulus of elasticity (MOE), and modulus of rupture (MOR) in the thinning treatments showed the following trend: no thinning > medium thinning > heavy thinning. This indicates that thinning reduces average bending properties. The average DMOE, MOE, and MOR in the pruning treatments showed the following trend: medium pruning > no pruning > heavy pruning. According to this tendency, better average qualities of lumber and specimens were from wood subjected to no-thinning and medium-pruning treatments according to an ultrasonic wave technique and static bending tests. However, most results showed no statistically significant differences among thinning, pruning, and thinning and pruning treatments. The average values of DMOE, MOE, and MOR of visually graded construction-grade lumber were significantly greater than those of below-grade lumber. Moreover, there were very significant positive relationships between density, ultrasonic velocity, DMOE, MOE, and MOR, although the determination coefficients were small. 相似文献
15.
The bending and growth characteristics of large fresh stems from four silver fir (Abies alba Mill.) and three Norway spruce (Picea abies (L.) Karst.) trees were studied. Twenty logs taken from different stem heights were subjected to four-point bending tests. From the bending test records, we calculated stress-strain curves, which accounted for detailed log taper, shear deformation and self weight. From these curves we determined, among other parameters, the modulus of elasticity (MOE), the modulus of rupture (MOR) and the work absorbed in bending (W). No significant differences were found between species for the wood properties examined. Values of MOE, MOR and W generally decreased with stem height, with MOR in the range of 43 to 59 MPa and MOE ranging from 10.6 to 15.6 GPa. These MOE values are twice or more those reported for stems of young Sitka spruce (Picea sitchensis (Bong.) Carr.) trees. Based on the radial growth properties measured in discs from the logs, we calculated predicted values of MOE and MOR for the stem cross section. The predictions of MOE were precise, whereas those of MOR were approximate because of a complex combination of different failure mechanisms. Methods to test and calculate MOE, MOR and W for the stems of living trees are discussed with the aim of improving analyses of tree biomechanics and assessments of forest stability protection. 相似文献
16.
The objectives of this study were to establish the method of evaluating wood mechanical properties by acoustic nondestructive
testing at standing trees and at logs of a Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) plantation, and to compare three acoustic nondestructive methods for evaluating the static bending modulus
of elasticity (MOE), modulus of rupture (MOR), and compressive strength parallel-to-grain (σc) of plantation wood as well. Fifteen Chinese fir plantation trees at 36 years of age were selected. Each tree was cut into
four logs, for which three values of dynamic modulus of elasticity, i.e., E
sw, of the north and south face based on stress waves to assume the measuring state of the standing tree, E
fr, longitudinal vibration, and E
us, ultrasonic wave, were measured in the green condition. After log measurements, small specimens were cut and air-dried to
12% moisture content (MC). Static bending tests were then performed to determine the bending MOE and MOR, and compressive
tests parallel-to-grain were made to determine σc. The bending MOE of small clear specimens was about 7.1% and 15.4% less than E
sw and E
us, respectively, and 11.3% greater than E
fr. The differences between the bending MOE and dynamic MOE of logs as determined by the three acoustic methods were statistically
significant (P < 0.001). Good correlation (R = 0.77, 0.57, and 0.45) between E
sw, E
fr, and E
us and static MOE, respectively, were obtained (P < 0.001). It can be concluded that longitudinal vibration may be the most precise and reliable technique to evaluate the
mechanical properties of logs among these three acoustic nondestructive methods. Moreover, the results indicate that stress
wave technology would be effective to evaluate wood mechanical properties both from logs and from the standing tree. 相似文献
17.
Influence of Ammoniacal Copper Quaternary treatments on mechanical properties of blue-stained Lodgepole Pine wood 总被引:1,自引:0,他引:1
Three concentrations (2.8%, 2.0%, 1.2%) of Ammoniacal Copper Quaternary (ACQ) was selected to treat Lodgepole pine wood for evaluating ACQ treatment on mechanical properties of blue-stained wood. The bending modules of elasticity (MOE), modules of rupture (MOR), toughness and shearing strength parallel to grain on tangential surface, are tested according to the criteria GB1927-1943-91. Non-treated sample were also tested according to the same procedure. The results showed that the three groups specimen impregnated by different concentrations of ACQ solution met the AWPA standard 2003 of America (UC4A 6.4g/cm^3). There were significant difference of toughness between treated wood and non-treated wood (p=0.01), but there were no statistically significant differences among three concentrations in terms of toughness, and toughness of treated wood was approximately 20% lower than non-treated. MOR, MOE as well as sheafing strength parallel to grain were found to be not significantly different between treated wood and non-treated one, and there were no statistically significant difference among three concentrations of ACQ too. Toughness, MOR, MOE and sheafing strength parallel to grain increased with decrease of concentration of ACQ, but they were hardly affected by ACQ preservatives. 相似文献
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20.
Takaaki Fujimoto Hisashi Akutsu Miki Nei Kazuhito Kita Makoto Kuromaru Kazuyuki Oda 《Journal of Forest Research》2006,11(5):343-349
Genetic parameters for wood stiffness and strength properties were estimated in a 29-year-old hybrid larch stand (Larix gmelinii var. japonica × Larix kaempferi). The study included 19 full-sib larch families from Hokkaido, northern Japan. Implications of these genetic parameters in
wood quality improvement are subsequently discussed. Traits included in the analyses were the dynamic modulus of elasticity
of green logs (E
log), the modulus of elasticity (MOE), the modulus of rupture (MOR), compression strength parallel to the grain (CS) in small
clear specimens, wood density (DEN), and diameter at breast height (DBH). DEN had the lowest coefficients of variation and
MOE the highest. The narrow-sense heritability estimates of E
log, MOE, MOR, and CS were 0.61, 0.44, 0.60, and 0.43, respectively, and those of DEN and all mechanical properties increased
from an inner to outer position within the stem. E
log and DEN had high positive phenotypic (0.52–0.83) and genetic (0.70–0.92) correlations with MOE, MOR, and CS. The mechanical
properties of the inner position of the stem had rather high phenotypic and genetic correlations with those of the outer position
and overall mean. The predicted gains in wood stiffness (E
log and MOE) were higher than those of the strength properties (MOR and CS). The predicted correlated responses in MOE, MOR,
and CS when selecting for E
log and DEN were 72.6%–97.8% of a gain achievable from direct selection of these traits. DBH showed an insignificant correlation
with all mechanical properties, although selection of this trait had a slightly negative effect on the mechanical properties. 相似文献