Laminated Solid Timber Slab with Transverse Prestressing Using the Strategy of Interleaved Vertical Displacement of Lamellae

This article presents a study on the structural behavior of transversely prestressed laminated timber slabs,focusing on an innovative approach:vertically misaligned lamellae.This misalignment,achieved by sliding vertically the wooden lamellae rather than aligning them,enhances the slab’s cross-section moment of inertia,thereby improving load-bearing capacity and stiffness.Testing involved two groups of structural size specimens:one with vertically aligned lamellae(control group)and the other with misaligned lamellae(study group).Results showed the study group exhibited 42%superior stiffness and 10%less load capacity compared to the control.Failures typically occurred individually in the lamellae,particularly in those with defects or lower modulus of elasticity,concentrated in the middle third of the slabs’free span where tensile stresses peak.Despite a higher number of failed lamellae,the study group demonstrated promising performance.Analysis of prestressing bar indicated no damage at all in the thread,suggesting potential for reducing bar diameter.These findings offer crucial insights into applying these slabs in timber construction as well as to any kind of construction.

Poroelastodynamic responses and elastic moduli of a transversely isotropic porous cylinder under forced deformation test

Existing transversely isotropic poroelastodynamics solutions are limited to infinite domains and without experimental validation. Furthermore, there is a lack of analytical simulations for the elastic moduli dispersion of fluid-saturated porous cylinders. To address these three limitations and investigate the mechanisms of moduli dispersion, we present the analytical solutions of the poromechanical responses and the elastic moduli dispersion of a transversely isotropic, fluid-saturated, finite porous cylinder subjected to a forced deformation test. Through an example, we demonstrate the effects of loading frequency, boundary conditions, and material's anisotropy, dimension, and permeability on the responses of pore pressure,force, displacement, and dynamic elastic moduli of the cylinder. The specimen's responses are significantly influenced by the frequency of the applied load, resulting in a drained state at low frequencies and an undrained state at high frequencies. At high frequencies, the sample behaves identically for an open or a closed lateral boundary, and permeability has insignificant effects. The dynamic elastic moduli are mainly controlled by the loading frequency and the ratio of the sample's radius to its height. Lastly,we show excellent matches between the newly derived analytical solution and laboratory measurements on one clay and two shale samples from Mont Terri.

Effects of 3D deformation and nonlinear stress–strain relationship on the Brazilian test for a transversely isotropic rock

To improve the accuracy of indirect tensile strength for a transversely isotropic rock in the Brazilian test, this study considered the three-dimensional (3D) deformation and the nonlinear stress–strain relationship. A parametric study of a numerical Brazilian test was performed for a general range of elastic constants, revealing that the 3D modeling evaluated the indirect tensile strength up to 40% higher than the plane stress modeling. For the actual Asan gneiss, the 3D model evaluated the indirect tensile strength up to 10% higher and slightly enhanced the accuracy of deformation estimation compared with the plane stress model. The nonlinearity in stress–strain curve of Asan gneiss under uniaxial compression was then considered, such that the evaluated indirect tensile strength was affected by up to 10% and its anisotropy agreed well with the physical intuition. The estimation of deformation was significantly enhanced. The further validation on the nonlinear model is expected as future research.

Analysis of stresses at the center of transversely isotropic Brazilian disk

This article presents the stresses at the center of a Brazilian disk(BD)for transversely isotropic rocks.It is shown that the solution of stresses at the center of an anisotropic disk is a function of the disk radius and the magnitude of applied load,as well as the material orientation with respect to the load axis and two dimensionless ratios with specific physical meanings and limitations.These two dimensionless parameters are the ratios of Young’s modulus and apparent shear modulus,although the ratio of apparent shear modulus will be eliminated if the Saint-Venant assumption is considered.Considerable finite element simulations are carried out to find the stresses at the disk center concerning the material orientation and the two dimensionless parameters.Also,an approximate formula obtained from analytical results,previously proposed in the literature for solving the tensile and compressive stresses at the disk center,is re-written and simplified based on these new definitions.The results of the approximate formula fitted to the analytical results are compared to those obtained from numerical solutions,suggesting a good agreement between the numerical and analytical methods.An approximate equation for the shear stress at the disk center is also formulated based on the numerical results.Finally,the influence of the assumptions for simplification of the proposed formula for the tensile,compressive,and shear stresses at the disk center is discussed,and simple and practical equations are proposed as estimations for the stresses at the center of the BD specimen for low to moderate anisotropic rocks.For highly anisotropic rocks,the reference plots can be used for more accuracy.

Uncertainty analysis of ship model vertical center of gravity and transverse moment of inertia test

The usability of test results of ship model vertical center of gravity and transverse moment of inertia is generally depends on its uncertainty. Referring to the guidelines for uncertainty analysis in examination of liquid dynamic recommended by International Towing Tank Conference （ ITTC）, the results were analyzed, bias limits and precision limits were calculated and total uncertainty was estimated. The total uncertainty of six tests on ship model vertical center of gravity is is 0. 16% of the mean value, and the total uncertainty of six tests on ship model transverse moment of inertia is 5.66% of the mean value. The test results show that the total uncertainty of both the multiple tests and the single test is from the precision limits of ship model vertical center of gravity and transverse moment of inertia tests. Thus, the improved measurement system stability can enormously decrease the total uncertainty of multiple tests and the single test.

A modified failure criterion for transversely isotropic rocks

A modified failure criterion is proposed to determine the strength of transversely isotropic rocks. Me-chanical properties of some metamorphic and sedimentary rocks including gneiss, slate, marble, schist, shale, sandstone and limestone, which show transversely isotropic behavior, were taken into consider-ation. Afterward, introduced triaxial rock strength criterion was modified for transversely isotropic rocks. Through modification process an index was obtained that can be considered as a strength reduction parameter due to rock strength anisotropy. Comparison of the parameter with previous anisotropy in-dexes in literature showed reasonable results for the studied rock samples. The modified criterion was compared to modified Hoek-Brown and Ramamurthy criteria for different transversely isotropic rocks. It can be concluded that the modified failure criterion proposed in this study can be used for predicting the strength of transversely isotropic rocks.

Stress Distribution in the Cruciform Specimen under Transverse Tension Stress for SiC/Ti-6Al-4V Composites

The cruciform specimen was selected to obtain the transverse tensile behavior of SiC fiber reinforced titanium matrix composites. Moreover, the means of combining the unilaterally coupled finite element method with the transverse tensile test was developed to evaluate the interfacial normal bond strength of composites. The results showed that the initial non-linearity in the transverse stress-strain curve of SiC/Ti-6Al-4V occurs at the stress of 350 MPa. The means of combining the unilaterally coupled finite element method with the transverse tensile test is an effective method to predict the interfacial normal bond strength of composites. In addition, the interface failure mechanism of composites was analyzed in detail.

Effects of Microstructure on Quasi⁃Static Transverse Loading Behavior of 3D Circular Braided Composite Tubes

The effects of microstructure on quasi-static transverse loading behavior of 3D circular braided composite tubes were studied. Transverse loading tests were conducted. Transverse load-deflection curves were obtained to analyze the effects of braiding parameters including the braiding angle, the wall thickness, and the diameter on the transverse loading of 3D circular braided composite tubes. Breaking loads, moduli and strengths had also been used to describe the transverse loading behaviors. The failure morphologies were shown to reveal damage mechanisms. From the results, the increase in braiding angle, wall thickness and diameter increases the ability of anti-deformation and breaking load of braided tubes. The breaking load of specimen with a braiding angle of 45° is about 1.68 times that of specimen with a braiding angle of 15°. The breaking load of specimen with 4 layers of yarns is about 2.15 times that of specimen with 2 layers of yarns. The breaking load of the tube with a diameter of 25.5 mm is about 2.39 times that of the tube with a diameter of 20.5 mm.

扣件系统横向刚度及抗倾翻试验研究:以WJ-8型扣件为例

为了对扣件系统横向刚度及抗倾翻性能进行研究,首先借鉴等间隔弹性点支承梁模型分析钢轨横向力学行为;然后,考虑钢轨自身截面特性,推导扣件系统横向刚度及抗倾翻系数计算公式;最后,设计并进行1组及3组WJ-8型扣件横向加载试验,验证分析及推导的合理性。试验结果表明:当钢轨整体扭转中心为轨底中心点时,钢轨自身扭转不可忽略,钢轨横向力及扭矩的传递过程都是非线性过程;1组及3组扣件试验得到的位移相对误差不超过6.8%,转角相对误差不超过9.5%;3组扣件试验允许加载范围更大,且更适用于非对称式扣件;WJ-8型扣件钢轨横移过程可按扣件横向反力的组成划分为钢轨滑移、线性变形和非线性变形3个阶段,钢轨倾翻过程可按钢轨轨底与轨下垫板接触形式划分为钢轨脱离和整体倾翻2个阶段。扣件横向刚度及抗倾翻系数可通过横向力-位移曲线、扭矩-转角曲线确定。

基于实车路试的高速公路减速标线运行效果研究

为探寻高速公路减速标线设置对小客车的纵向运行特性的影响,明确减速标线的减速效果,以G50沪渝高速重庆段的3处减速标线区段为对象,开展了实车驾驶试验,采集了自然驾驶状态下的车辆速度、加速度和轨迹等数据,对比分析了车辆经过3处减速标线区段时的速度整体特征、幅值分布和变化模式;同时分析了纵向减速度变化特征;根据速度与加速度的组合示意图和纵向减速标线设置区段内速度的最大降幅、起止点的速度差异性,评价了减速标线的实施效果。结果表明:由于道路线形条件不同,3处减速标线区段的车辆行驶速度整体特征和变化模式存在差异,其中弯坡组合路段车辆速度存在波动,分为“近匀速—减速—加速—稳定—加速”的五阶段变化模式;减速度中位值和85%位值分别为0.123 m/s^(2)、0.225 m/s^(2)、0.185 m/s^(2)和0.346 m/s^(2)、0.513 m/s^(2)、0.489 m/s^(2)。减速标线主要有两方面作用效果:能够使车辆运行车速显著降低,或能够抑制车辆速度增加的趋势。研究成果为高速公路减速标线有效性评价及安全改善提供了基础数据支持。

碳纤维增强复合材料黏结型锚固体系弯拉性能试验研究

为了研究碳纤维增强复合材料(CFRP)黏结型锚固体系的弯拉性能,对设计的锚固体系试件进行了10组轴向拉伸试验与12组弯拉试验。在锚固体系优化基础上研究了CFRP筋直径、弯曲半径改变下试件的极限承载力、破坏模式、锚固效率及CFRP筋荷载‒应变关系。结果表明,锚固体系的弯拉承载力折减量系数随CFRP筋弯曲半径的增大而减小,CFRP筋直径越大试件承载力折减量系数越大,并且CFRP筋横向约束有利于弯拉极限承载力的提高。此外,CFRP筋荷载‒应变曲线的非线性变化是试件失效前的典型特征。弯曲半径和CFRP筋直径的比值与锚固效率系数为线性关系,比值在2.4‰以下时试件的弯拉锚固效率系数小于80%,试件呈不均匀断裂和剪切的破坏形式。

碳纤维增强热塑性树脂基复合材料界面性能研究

采用宏观力学性能测试(0°压缩测试、90°拉伸测试、层间剪切测试、弯曲测试)、微观力学性能测试(微脱粘测试)、扫描电镜(SEM)以及偏光显微镜观察,对不同碳纤维/热塑性树脂复合材料界面性能进行了多维度的研究。

无损检测指标与木材横纹局部抗压强度和密度的相关性

【目的】探索不同类型和数量的无损检测(NDT)指标与木材横纹局部抗压强度和密度的相关性差异,确定最优NDT指标组合,为基于无损检测手段评估木材横纹局部抗压强度和密度的研究提供参考。【方法】以某典型藏式古建筑木结构梁构件为研究对象,锯解得到横纹局部抗压无疵试样。通过物理力学试验和NDT试验,获得无疵试样的密度ρ、横纹局部抗压强度f_(lc),以及顺纹应力波速v_(l)、横纹应力波速v和微钻阻力F,计算不同NDT指标或指标组合与ρ、f_(lc)的线性相关系数,进而对比讨论。【结果】(1)使用单一NDT指标预测ρ时,v_(l)效果较好,两者相关系数绝对值为0.662,补充微钻阻力均值Fm后可提高15.56%,达到0.765;使用单一NDT指标预测f_(lc)时,Fm效果较好,两者相关系数为0.526,在此基础上补充横纹应力波速均值v_(m),二者相关系数提升26.80%,达到0.667,进一步补充v_(l)后相关系数继续提升7.20%,达到0.715。(2)当两组NDT指标中的基本指标构成一致时,即便基本指标的形式存在差异,两组NDT指标与被预测参数的相关系数也近似。(3)当两个与被预测参数相关性较好的NDT指标组合时,相关系数可能进一步提高;当相关性较好的指标与较差的指标组合时,相关系数接近于前者;当相关性较差的指标与不相关指标组合时,相关系数可能大幅提升,也可能仍然较低;当两个均不显著相关的指标组合时,指标组合与被预测参数仍不具有显著相关性。【结论】确定合理的NDT指标比一味增加指标数量对相关系数的提高影响更大。综合考虑相关系数提升效果以及由此可能增加的测试工作量,预测木材密度和横纹局部抗压强度时建议分别使用“v_(l),F_(m)”和“F_(m),v_(m)”的NDT指标组合。

超声波检测法辨别焊缝中微细裂纹

超声波检测法在检测海洋工程钢结构焊缝时发现一种难于辨别的缺陷反射波,难点在于此反射波的波型特征像横向裂纹,但波幅很低,横向扫查有反射波,纵向扫查反射波时有时无,且横向扫查波幅高于纵向扫查,在骑缝扫查移动探头过程中,超声波显示屏中出现此起彼伏的波形,按照经验判断,此反射波应是缺陷,且应是横向裂纹,但气刨和打磨到指定位置,未见缺陷。为解决这一难题,超声波检测法主要利用GE USM35超声波探伤仪和45°、60°、70°探头对此批焊缝进行换角度多方向扫查,经过1∶1作图,精确定位缺陷反射波水平位置和垂直深度,而后气刨到距指定深度一定距离处,再逐步进行打磨加磁粉检测,最终发现和验证了横向微细裂纹和微小气孔,总结了区分两种缺陷的方法,形成了超声波检测法辨别焊缝中微细裂纹的方法。

港珠澳大桥人工岛横截沟篦子截水能力验证研究

港珠澳大桥人工岛项目位置常年易受如热带气旋和台风等极端气象事件的侵扰,且台风过境时往往伴随历时长的强降雨。为降低极端恶劣条件下隧道的运营期风险,针对人工岛敞开段横截沟篦子开展截水能力验证局部物理模型试验,分别研究栅条角度、开孔比率、路面坡度、比尺效应以及横截沟数量对篦子截水能力的影响规律。研究结果表明,0°栅条设计方案的篦子截水能力优于90°栅条,同时设置2道横截沟的方案具有显著的截水效果。本次研究成果对人工岛横截沟篦子的设计布置准确性、排水隐患的消除、防范风险、保障运营安全具有重大意义。

A Comprehensive Investigation on Shear Performance of Improved Perfobond Connector

This paper presents an easily installed improved perfobond connector (PBL) designed to reduce the shearconcentration of PBL. The improvement of PBL lies in changing the straight penetrating rebar to the Z-typepenetrating rebar. To study the shear performance of improved PBL, two PBL test specimens which containstraight penetrating rebar and six improved PBL test specimens which contain Z-type penetrating rebars weredesigned and fabricated, and push-out tests of these eight test specimens were carried out to investigate andcompare the shear behavior of PBL. Additionally, Finite Element Analysis (FEA) models of the PBL specimenswere established and validated against the test results. Through FEA, the effects of concrete grade, perforatedplate’s aperture, Z-type penetrating rebar’s diameter, Z-type penetrating rebar’s bending angle, and bending lengthon shear behaviors were discussed. The results indicate that (1) Compared with PBL specimens with straightpenetrating rebars, Z-type penetrating rebar can significantly improve the shear resistance and shear stiffnessof the specimens. This enhanced performance can be mainly attributed to the increased adhesion of the transverserebar. (2) By comparing the load-slip curve, the slip of PBL test specimens which contain straight penetratingrebar increases rapidly and the bearing capacity decreases rapidly after concrete craking, while the bearingcapacity of Z-type penetrating rebar specimens decreases first and then increases gradually, showing betterductility. (3) The stress of the PBL shear connector with Z-type penetrating rebar is more uniform than thePBL shear connector with straight penetrating rebar, and the overall deformation is more uniform. (4) The higherthe concrete grade, the higher the shear bearing capacity and the better ductility of the new PBL. Increasing theaperture of the perforated plate or the diameter of the rebar has a very limited effect on the improvement of theshear capacity of PBL. Through the systematic analysis of the mechanical properties of Z-type penetrating rebarPBL specimen, the experimental reference is provided for improving the structure and design of new type PBL.

锅炉水冷壁壁面高温腐蚀及壁管横向裂纹泄漏试验研究

考虑到锅炉水冷壁壁面高温腐蚀会导致壁管产生裂纹而出现泄漏事故,为了得到影响锅炉水冷壁壁面高温腐蚀的因素,提出锅炉水冷壁壁面高温腐蚀及壁管横向裂纹泄漏试验研究。针对锅炉水冷壁高温腐蚀区存在的横向裂纹进行失效分析,通过宏观观察,材质分析和无损检测,研究分析锅炉水冷壁管横向裂纹的产生原因,再根据锅炉水冷壁壁面高温腐蚀实验原理,确定气氛条件,通过试样块的制备,设计了锅炉水冷壁壁面高温腐蚀实验方案,测试了气氛条件和温度对锅炉水冷壁壁面高温腐蚀的影响。结果表明,锅炉烟气的H_(2)S含量越多、温度越高,壁温波动导致的热疲劳应力和高温的共同作用下,锅炉水冷壁的壁面腐蚀越严重,从而使壁管产生横向裂纹而发生泄漏。

基于热点应力法的钢箱梁横隔板焊接节点疲劳性能研究

在运营活载作用下,正交异性钢桥面板的破坏往往体现为各板件焊缝的疲劳破坏。尤其纵肋与横隔板焊接细节的焊址是疲劳裂纹最容易萌生的部位。为了研究该焊接细节的疲劳性能,以苏通大桥为工程案例,建立钢箱梁纵肋与横隔板焊接细节有限元模型。通过采用热点应力法对纵肋与横隔板焊接细节焊缝周围的热点应力进行详尽的数值模拟,在全面分析单元类型与单元尺寸对数值计算结果的影响的基础上,通过现场试验测试对数值计算结果进行对比验证。最后采用热点应力法与名义应力法分别预测该焊接细节的疲劳寿命,并与纵肋与顶板焊接细节对比,结果表明采用热点应力法FAT90计算结果更准确,且该焊接细节相对于其他焊接细节更容易发生疲劳破坏。

基于广义梁格法的整体化铺装加固空心板桥荷载横向分布系数计算方法

由于整体化铺装加固后的空心板桥的铺装层较厚、横向整体性更突出,因此荷载横向分布系数的计算必须考虑整体化铺装层的影响。基于此提出采用广义梁格法考虑整体化铺装层的影响,在足尺模型试验和有限元计算的基础上,对基于广义梁格法的整体化铺装层加固后的空心板桥荷载横向分布系数计算方法进行验证。结果表明,广义梁格法的计算结果可以准确考虑采用整体化铺装层加固空心板桥的荷载横向分布规律。不同宽度、不同跨径的空心板桥,铺装层的高度折减系数取值在0.5~0.8之间时,计算结果更加精确。桥越宽则折减系数取值越大,跨径越大则折减系数取值越小。

低应变同条件下桩型实测波速差异大研究探讨

在工程实践中,有时会出现在设计强度、成桩工艺、养护条件以及龄期相同的桩型,实测低应变波速差异大的情况。这一现象不符合同条件下的桩型,实测波速在某一范围内分布这个常规认知。甚至曾经有过相关专家以实测波速偏差过大为由,质疑检测数据的真实性。通过研究发现,这个波速差异大,并不是检测数据不真实导致的,也不是同条件下的桩型这一条件不满足,更不是同条件下的桩型实测波速在某一范围内这个常规认知不对,而是因为横向尺寸效应引起的。横向尺寸效应能够引起基桩实测波速产生差异,在桩径较大,桩长较短的时候,尤其明显。论本结合实例,对横向尺寸效应影响低应变实测波速进行了分析。