Seismic stability of reinforced soil walls under bearing capacity failure by pseudo-dynamic method

In order to evaluate the seismic stability of reinforced soil walls against bearing capacity failure,the seismic safety factor of reinforced soil walls was determined by using pseudo-dynamic method,and calculated by considering different parameters,such as horizontal and vertical seismic acceleration coefficients,ratio of reinforcement length to wall height,back fill friction angle,foundation soil friction angle,soil reinforcement interface friction angle and surcharge.The parametric study shows that the seismic safety factor increases by 24-fold when the foundation soil friction angle varies from 25°to 45°,and increases by 2-fold when the soil reinforcement interface friction angle varies from 0 to 30°.That is to say,the bigger values the foundation soil and/or soil reinforcement interface friction angles have,the safer the reinforced soil walls become in the seismic design.The results were also compared with those obtained from pseudo-static method.It is found that there is a higher value of the safety factor by the present work.

EXPERIMENT OF SHORT WAVE COMMUNICATION AND THE INVESTIGATION OF THE PROPAGATION BEARINGS BETWEEN THE GREAT WALL STATION AND XINXIANG

The distance from the Great Wall Station (62.2°S, 58.9°W) to Xinxiang (35.3°N, 113.8°E) is 16981 km. The path passes through the polar cap absorption region and the auroral absorption zone, and it is across the equator.In this paper firstly the effects of short wave communication and usable time blocks and frequency ranges between the Antarctic Great Wall Station and Xinxiang from December 1985 to March 1986 are introduced. The comparison between the usable frequency ranges with the estimated MUF is made. The upper limit of frequency ranges of communication along the short great circle path basically agrees with the MUF but there is difference between them along the long great circle path.Secondly, the result of the propagation bearings experiment in January to February 1986 is introduced in more detail, The propagation along the great circle path from the Great Wall Station to Xinxiang is the main propagation mode. But the propagation along non great circle paths occurs at times between Great Wall Station and Xinxiang. The non great circle path propagation varies with time because the ionospheric absorption and other conditions which support the non great circle path propagation are the function of the time. So the courses of the non great circle path propagation may be different in the different time. The mechanism of the constructing non great circle path propagation has been analysed. We preliminarily think the main cause of propagation along non great circle path is the ground scatter. The stronger radialization of the side lobes of the antenna and the less absorption of the ionosphere contribute to forming non great circle path propagation.

Progressive collapse resisting capacity of reinforced concrete load bearing wall structures

Reinforced concrete(RC) load bearing wall is widely used in high-rise and mid-rise buildings. Due to the number of walls in plan and reduction in lateral force portion, this system is not only stronger against earthquakes, but also more economical. The effect of progressive collapse caused by removal of load bearing elements, in various positions in plan and stories of the RC load bearing wall system was evaluated by nonlinear dynamic and static analyses. For this purpose, three-dimensional model of 10-story structure was selected. The analysis results indicated stability, strength and stiffness of the RC load-bearing wall system against progressive collapse. It was observed that the most critical condition for removal of load bearing walls was the instantaneous removal of the surrounding walls located at the corners of the building where the sections of the load bearing elements were changed. In this case, the maximum vertical displacement was limited to 6.3 mm and the structure failed after applying the load of 10 times the axial load bored by removed elements. Comparison between the results of the nonlinear dynamic and static analyses demonstrated that the "load factor" parameter was a reasonable criterion to evaluate the progressive collapse potential of the structure.

Research on the Influence of Cutting Condition on the Surface Microstruct ure of Ultra-thin Wall Parts in Ultrasonic Vibration Cutting

In many fields of high-tech industry the ultra-t hi n wall parts are employed. In this paper the experiments were carried out to dis cuss the surface microstructure of the camera’s guided drawtube by applying ult rasonic vibration cutting device to the traditional lathe. The influence rule of the cutting condition on the surface roughness was put forward, which was drawn by comparing the ultrasonic cutting with the common cutting by use of the cemen ted carbide tool and the polycrystalline diamond (PCD) tool. The test results sh owed that the ultrasonic cutting performs better than the common cutting in the same condition. According to the test results analyzing, the surface characteriz ation is influenced clearly by the rigidity of the acoustic system and the machi ne tool, as well the setting height of the tool tip. Otherwise, the dense regula r low frequency vibration ripples will be scraped on the machined surface. When the tool tip is set higher than the rotating center of the work piece by three t imes of the amplitude of ultrasonic vibration, the vibration ripples behave alig ht; they turn light and shade alternatively when the tool tip is lower than the rotating center of the work piece by three times of the amplitude of ultrasonic vibration. According to the test result analyzing, the following conclusions are put forward: 1) The surface roughness in ultrasonic cutting is better than that in common cutting. Under a one third critical cutting velocity, the value of th e surface roughness in ultrasonic cutting rise slightly along with the cutting v elocity, while in common cutting it decreases contrast to the cutting velocity; the curves of the surface roughness in ultrasonic cutting and common cutting see m to be alike, both increase along with the feed rate and the cutting depth, but the value in ultrasonic cutting is smaller in the same condition.2) The influen ce of the coolant on the surface roughness cannot be ignored. The kerosene can b e employed to improve the surface roughness in ultrasonic machining.3) In ultras onic cutting process of aluminum alloy ultra-thin wall work piece, the PCD tool performs better than the cemented carbide tools.4) The vibration ripples result from the not enough rigidity of the acoustic system and the improper setting he ight of the tool tip. The departure of the tool tip from the rotating center of the work piece to some extent causes the vibration ripples on the machined surfa ce.

Research on Influence of Cutting Conditions on Roundness of Ultra-thin Wall Parts in Ultrasonic Vibration Cutting

In the paper, the experimental researches were carr ie d out to discuss the roundness forming rule and the influence of cutting paramet ers on roundness by ultrasonic vibration cutting of the camera’s guiding drawtu be with 47.75 mm diameter and 0.6～1.5 mm wall thickness. The research results s h ow that the roundness error of ultra-thin wall parts in ultrasonic vibration cu tting is only one third of that in common cutting. The relations between the rou ndness error and the cutting parameters behave as: (1) The roundness error in co mmon cutting decreases gradually with the rise of cutting speed, while in ultras onic cutting, the roundness changes not obviously till the cutting speed is up t o a value, which is nearly equal to one third of the critical velocity. Then the roundness of workpiece will begin to increase slowly. (2) The roundness error i ncreases along with the feed rate both in common cutting and ultrasonic cutting. (3) Within the range of cutting depth in experiment, the influence of cutting d epth on the roundness error is more obvious in common cutting than that in ultra sonic vibration cutting. The conclusions are useful in machining such precise ul tra-thin wall parts. According to the tests, the following conclusions can be o btained: 1) Compared with common cutting, ultrasonic cutting can decrease effect ively roundness error of the workpiece. Under the same condition, the roundness error of the ultra-thin wall part in ultrasonic turning is about one third of t hat in common cutting. 2) In common cutting, cutting depth and feed rate have mu ch influence on the roundness and the influence of cutting velocity is little. W hile in ultrasonic cutting, the roundness was influenced heavily only when feed rate is more than 0.1 mm/r and cutting speed is more than 1/3 of the critical ro tation speed, cutting depth has little influence on the roundness in the experim ent. 3) Kerosene-oil is an optimum cutting fluid in machining ultra-thin wall workpiece. 4) To machine the ultra-thin wall precision part, ultrasonic cutting is the perfect method which can decrease the roundness error effectively an d ensure high quality of the surface.

Effect of Optimum Plastic Depth on Stresses and Load-bearing Capacity of Autofrettaged Cylinder

Autofrettage is an effective measure to even distribution of stresses and raise load-bearing capacity for （ultra-）high pressure apparatus. Currently, the research on autofrettage has focused mostly on specific engineering problems, while general theoretical study is rarely done. To discover the general law contained in autofrettage theory, by the aid of the authors’ previous work and according to the third strength theory, theoretical problems about autofrettage are studied including residual stresses and their equivalent stress, total stresses and their equivalent stress, etc. Because of the equation of optimum depth of plastic zone which is presented in the authors’ previous work, the equations for the residual stresses and their equivalent stress as well as the total stress and their equivalent stress are simplified greatly. Thus the law of distribution of the residual stresses and their equivalent stress as well as the total stress and their equivalent stress and the varying tendency of these stresses are discovered. The relation among various parameters are revealed. The safe and optimum load-bearing conditions for cylinders are obtained. According to the results obtained by theoretical analysis, it is shown that if the two parameters, namely ratio of outside to inside radius, k, and depth of plastic zone, kj, meet the equation of optimum depth of plastic zone, when the pressure contained in an autofrettaged cylinder is lower than two times the initial yield pressure of the unautofrettaged cylinder, the equivalent residual stress and the equivalent total stress at the inside surface as well as the elastic-plastic juncture of a cylinder are lower than yield strength. When an autofrettaged cylinder is subjected to just two times the initial yield pressure of the unautofrettaged cylinder, the equivalent total stress within the whole plastic zone is just identically equal to the yield strength, or it is a constant. The proposed research theoretically depicts the stress state of ultra-）high pressure autofrettaged cylinder more accurately and more reasonably and provides the reference for design of （ultra-）high pressure apparatus.

轻钢格栅混凝土组合墙体抗压性能研究

轻钢格栅混凝土组合墙体的抗压性能研究是该种新型结构应用和发展的关键问题。为此对3个足尺轻钢格栅混凝土组合墙体试件进行了轴压、偏压试验,探究轻钢骨架、水泥纤维板和混凝土的协同工作状态,分析试件的抗压承载力和破坏模式,提出轴压承载力的计算方法。结果表明:相比于无混凝土填充试件,填充混凝土试件的抗压承载力和稳定性均有明显提高;在偏压状态下,试件所受拉力主要由轻钢骨架承担,试件表现出良好的延性特性;增大立柱根数、立柱腹板高度、水泥纤维板厚度以及混凝土强度均可以提高该种组合墙体的抗压承载力,其中对于轴压试件,提高混凝土强度最有效;对于偏压试件,立柱腹板高度、水泥纤维板厚对其抗压承载力影响较大。最后,采用强度叠加方法计算了该种组合墙体轴压承载力,计算结果试验结果吻合良好。

基于振动信号的柔性薄壁轴承故障特征提取综述

由于高柔性和薄壁特性,柔性薄壁轴承产生的振动信号相较于普通滚动轴承更加微弱,并具有高度非线性和非平稳性的特点。此外,在柔性薄壁轴承的工作过程中,大尺寸径向变形会使其套圈形状变为椭圆形,从而产生周期性结构冲击,这些特点极大地增加了柔性薄壁轴承故障特征提取的难度。简述了柔性薄壁轴承的结构特点以及故障特征提取的流程和难点,详细介绍了柔性薄壁轴承振动信号的预处理及故障特征提取方法并对比分析了不同方法的原理及优缺点,最后对柔性薄壁轴承故障特征提取与状态监测技术的发展趋势进行了展望。

主轴承柔性及润滑特性对RV减速器传动误差影响分析

【目的】RV减速器因具有减速比大、传动误差低、结构紧凑等优点被广泛应用于工业机器人关节当中。由于其主轴承为薄壁轴承,工作时套圈易发生较大形变,柔性支撑变形引起的传动误差不可忽略。为此,有必要研究主轴承柔性及润滑特性对减速器传动误差的影响。【方法】以角接触球轴承为研究对象,分别建立主轴承和减速器参数化三维模型,构建主轴承刚柔耦合多体动力学模型、考虑套圈柔性变形的主轴承弹流润滑模型与RV减速器动力学模型;在研究减速器关键零部件动态响应、主轴承接触特性的基础上,进一步探究了主轴承柔性特性对RV减速器传动误差的影响。【结果】结果表明,不考虑主轴承柔性特性时,传动误差范围为-25.2″~21.6″,考虑主轴承柔性特性后,传动误差范围增大至-43.2″~45″;随着套圈变形量的不断增加,减速器传动误差不断增大;随着油膜厚度的不断增加,减速器传动误差先减小后增大;随着油膜压力的不断增加,减速器传动误差也是先减小后增大;主轴承柔性特性对减速器传动误差的影响不可忽略;适当提高主轴承的支承刚度,对减小RV减速器传动误差具有重要意义。所提方法对RV减速器及主轴承精密设计具有一定借鉴意义。

夹板剪力墙中U型抗拔锚固节点的承载性能

夹板剪力墙抗侧力性能优异,其抗侧刚度和承载力是普通轻木剪力墙的2~3倍。然而,夹板剪力墙中常用的三角形抗拔锚固件(hold⁃down)会使端部墙骨柱偏心受拉,并易在顶部螺栓孔处发生断裂,严重制约墙体抗侧承载能力。采用U型锚固连接件能很好解决该不利破坏。对采用了不同紧固件形式和数量的4组U型锚固件节点进行单调和低周往复加载试验,分析其破坏模式、荷载⁃位移曲线、初始刚度、极限承载力和延性系数,并基于GB 50005—2017《木结构设计标准》对其承载力和屈服模式进行理论计算和预测。研究结果表明,采用螺钉连接的U型hold⁃down节点(6SH、10SH)均表现为螺钉弯曲和拔出破坏,而采用3根和5根螺栓连接(3BH和5BH)的U型hold⁃down节点则分别表现为螺栓弯曲和墙骨断裂破坏。采用螺栓连接的U型hold⁃down节点刚度和极限承载力分别比采用螺钉连接的节点高81.5%和62.0%以上,但延性较后者低23.2%以上。采用3根螺栓连接的U型hold⁃down节点(3BH)充分利用了螺栓的屈服强度和弹塑性变形能力,综合性能表现最佳。基于GB 50005—2017能准确预测采用螺钉连接U型hold⁃down节点的屈服模式和承载力,但会低估32%~43%的螺栓连接U型hold⁃down节点承载力。研究得到的U型hold⁃down节点荷载⁃位移关系和力学性能指标可为后续的夹板剪力墙数值模拟研究提供关键数据。

保温叠合剪力墙FRP连接件力学性能

以夹心保温叠合剪力墙为研究对象,研究螺纹型、矩形和六芒星状3种纤维增强复合材料连接件(FRP)在施工阶段和使用阶段下的抗剪力学性能,并且对三种FRP连接件在两个阶段下的破坏形态、抗拔承载力和荷载-位移曲线进行分析,结果表明:试件的破坏形态主要有混凝土锚固破坏,层间剪切破坏和断裂破坏。施工阶段下单根FRP连接件最终抗剪承载力在1.41~3.91 kN之间,使用阶段下单根FRP连接件最终的抗剪承载力在3.19~6.02 kN之间,根据理论公式得到的计算值与试验值对比可知,在两个阶段情况下3种连接件的安全系数均大于1,均有较大的安全储备,可以应用到实际工程中。

Experimental investigation on the lateral bearing behavior of lattice-shaped diaphragm wall with double-layer configuration

This paper delves into the lateral load-bearing behavior of lattice-shaped diaphragm wall(LSDW),a novel type of diaphragm wall foundation with many engineering advantages.By employing a double-layer wall structure for the first time in laboratory settings,the research presents an innovative testing methodology,complete with novel computational formulas,to accurately measure the responses of LSDW’s inner and outer walls under varying loads.It is found that the Q-s curves of LSDWs exhibit a continuous,progressive deformation and failure characteristic without any abrupt drops,and the standard for judging the horizontal bearing capacity of LSDW foundations should be based on the allowable displacement of the superstructure.The bearing capacity for the double-chamber LSDWs was found to be approximately 1.68 times that of the single-chamber structure,pointing to a complex interplay between chamber number and structural capacity that extends beyond a linear relationship and incorporates the group wall effect.The study also reveals that LSDWs act as rigid bodies with minimal angular displacement and a consistent tilting deformation,peaking in bending moment at about 0.87 of wall depth from the mud surface,across different chamber configurations.Furthermore,it can be found that using the p-y curve method for analyzing the horizontal behavior of LSDW foundations is feasible,and the hyperbolic p-y curve method offers higher accuracy in calculations.These insights offer valuable guidance for both field and laboratory testing of LSDWs and aid in the design and calculation of foundations under horizontal loads.

存在施工偏差的空心薄壁桥墩安全性验算分析

空心薄壁桥墩具有结构刚度好、自重轻、截面惯性矩大等特点,是跨越深沟峡谷的常选桥墩型式。空心薄壁桥墩在采用节段施工成形的过程中容易出现一定的施工偏差。以实际工程为例,结合现场测量的实际施工偏差情况,建立了考虑桥墩施工偏差的有限元计算模型,计算得到了不同荷载组合下结构的内力,进行了最不利内力下桥墩的不同承载能力和结构抗裂与抗扭验算。验算结果表明本实际工程出现偏差桥墩的抗压承载力、抗扭承载力及结构抗裂均能满足现行规范的要求。

钢筒仓环板环梁稳定承载力的中外规范比较

钢筒仓在仓壁、仓裙及漏斗相交处容易发生平面外屈曲破坏,通常在相交处设置一道环梁来抵抗破坏,相交处环梁稳定对钢筒仓安全运行起着至关重要的作用。环梁通常分T型环梁与环板环梁2种。环板环梁宽度、环板环梁厚度是环板环梁的2个主要参数,为进一步研究其对环板环梁稳定承载力的影响,以某项目钢筒仓环板环梁为例,分别依据中国规范、欧洲规范的计算方法,深入研究环板环梁宽度、环板环梁厚度与环板环梁稳定承载力的关系,比较分析中国规范与欧洲规范计算值之间的差异,提出合理化建议,为类似工程提供参考。

附加纵向加劲肋火灾后冷弯型钢背对背拼合柱弯曲屈曲性能研究

冷弯薄壁型钢结构在道路桥梁建设方面得到了广泛应用。为了研究温度对带附加纵向加劲肋的冷弯型钢背对背拼合柱(CFS-BBC-∑)屈曲承载力的影响,利用ABAQUS软件建立了有限元模型,与试验数据结果进行比较,验证了模型的可靠性,并通过改变试件长度、螺钉间距和温度等条件进行参数分析。结果表明:当螺钉间距增大时(50~300mm),极限承载力呈下降趋势,最低下降至81.7%;温度对试件的极限承载力变化具有显著影响,当20≤T<500℃时,极限承载力下降趋势较平缓,当500≤T<800℃时,极限承载力下降趋势较陡,最低下降至74.7%。同时提出了火灾后CFS-BBC-∑承载力折减系数ηT的预测公式。最后,对直接强度法定义的CFS弯曲屈曲承载能力公式进行评估,分析其准确性与适用性。

含气油井采出液低温集输工艺界限研究

老油田因开发时间较长,存在产液量低、含水率高、能耗大等问题。为降低老油田高含水区块的运行能耗,针对低含气油井和高含气油井开展了降温实验,根据井口回压和进站温度随时间的变化规律,获取了含气油井采出液的低温集输工艺界限。结果显示:低含气油井在降温过程中出现了两个压力突变点,高含气油井在降温过程中压力呈不规则变化,但也出现压力突变区域;产液量越大、含水率越高、气液比越大,越有利于油井进行低温集输。推广区块内有55口油井从双管掺水工艺转为低温集输工艺,实施后全年可节约运行费用235.9万元,减少CO_(2)排放量为2650 t,节能减排效果明显。

Numerical simulation on the seismic performance of retrofitted masonry walls based on the combined finite-discrete element method

Due to the long construction life,improper design methods,brittle material properties and poor construction techniques,most existing masonry structures do not perform well during earthquakes.The retrofitting method using an external steel-meshed mortar layer is widely used to retrofit existing masonry buildings.Assessing the seismic performance of masonry walls reinforced by an external steel-meshed mortar layer reasonably and effectively is a difficult subject in the research field of masonry structures.Based on the combined finite-discrete elements method,the numerical models of retrofitted brick walls with four different masonry mortar strengths by an external mortar layer are established.The shear strength of mortar and the contact between the retrofitted mortar layer and the brick blocks are discussed in detail.The failure patterns and load-displacement curves of the retrofitted brick walls were obtained by applying low cycle reciprocating loads to the numerical model,and the bearing capacity and the failure mechanism of the retrofitted walls were obtained by comparing the failure patterns,ultimate bearing capacity,deformability and other aspects with the tests.This study provides a basis for improving the seismic strengthening design method of masonry structures and helps to better assess the seismic performance of masonry structures after retrofitting.

L形内置钢板混凝土组合剪力墙抗剪性能分析

为揭示L形内置钢板混凝土组合剪力墙的工作机理并提出其抗剪承载力计算公式,首先建立了非线性有限元模型,并通过试验结果进行了验证。在此基础上研究了高宽比、轴压比、钢板厚度、混凝土强度、翼缘长度等参数对剪力墙抗剪性能的影响。最后,提出了剪力墙的抗剪承载力计算公式。结果表明:剪力墙在受力过程中,腹板是主要受力构件;随着高宽比的减小,剪力墙的抗剪承载力和初始抗侧刚度增大;随着轴压比的增大,剪力墙的抗剪承载力增大,但当轴压比超过0.5时,抗剪承载力开始降低;将所提出的剪力墙抗剪承载力计算公式与现有的计算公式相比,计算结果误差较小,可以为工程应用提供参考。

加气混凝土复合保温外墙板连接节点试验研究

通过对钢管锚节点、套筒节点和新型F型节点进行的6组加气混凝土板四分点加载节点极限承载力试验,分析不同板厚下3种节点的节点强度、节点刚度等性能指标。研究表明:新型F型节点力学性能良好,连接可靠,节点极限承载力随板厚增加而增大。新型F型节点可较好地适用在加气混凝土复合保温外墙板体系中。

十字形钢管束自密实混凝土短肢剪力墙轴压性能研究

为研究十字形钢管束自密实混凝土短肢剪力墙的轴压受力性能,通过模型试验研究和ABAQUS数值模拟相结合的方法,对不同腔体数十字形钢管束自密实混凝土短肢剪力墙的轴压性能进行分析。首先,根据轴压试验结果对剪力墙的破坏形态和轴向荷载-应变曲线等轴压受力性能进行分析,提出轴压承载力计算公式。其次,建立剪力墙轴压有限元计算模型,将试验结果和模型计算结果进行对比以验证有限元模型的准确性。最后,根据有限元参数化分析结果验证并修正剪力墙轴压承载力计算公式。研究发现,剪力墙的轴向荷载-应变曲线在不同腔体数下具有相似的特征,表明其变形能力良好。在破坏过程中,钢管束对核心混凝土的约束作用显著,提高了试件的延性和承载能力,其中钢管束的破坏主要表现为多波鼓曲和焊缝开裂,尤其是在钢管束中部的1/4区域。此外,随着腔体数增加,剪力墙极限承载力提升,但其延性系数有所下降。本研究提出的简化公式与有限元分析结果的误差控制在10%以内,该公式可为工程设计应用提供理论借鉴。