竖向荷载差作用下多层砌体房屋顶层裂缝行为研究

构建了能够反映实际情况的U型砌体结构实体研究模型,实时测定并分析了U型砌体结构实体模型在竖向荷载差作用下纵横墙(即非承重与承重墙)的变形,以及裂缝的产生和发展行为．结果表明,纵横墙变形大小随荷载增加而增大,并且当荷载增加至一定值时,纵横墙相交部位将出现变形骤增,反映出竖向荷载差的累积作用效应,同时伴有裂缝的产生和扩展．对于多层砌体结构房屋而言,竖向荷载差是除温度差等因素外导致项层裂缝产生和发展的又一重要影响因素．还首次建立了U型多层砌体结构足尺模型在竖向荷载差作用下的最大剪应力计算分析模型和计算方法,为《砌体结构设计规范》的进一步完善和扩展提供了有价值的理论参考．

带构造柱和圈梁的多层砌体结构在竖向荷载差下的力学性能

为研究带构造柱和圈梁的多层砌体结构在竖向差异荷载作用下的力学性能,对1个按1/4缩尺比例建造的6层试验墙体模型进行试验和非线性有限元分析,获得了模型墙体在竖向差异荷载作用下整体强度和变形的试验参数,以及墙体顶部的裂缝反应,并将模拟结果与试验结果进行了对比,结果比较吻合。同时,研究了均匀竖向差异荷载作用下不同因素如结构高度、构造柱间距、砌体弹性模量及抗剪强度等对多层砌体结构整体强度和变形的影响,提出了该种荷载作用下带构造柱墙体剪应力的计算公式,给出了竖向阻力系数工程推荐值。

竖向荷载差作用下的砌体顶部裂缝特征研究

通常情况下认为,墙体的干缩以及混凝土屋盖的温度变形是砌体结构房屋顶部裂缝产生的主要原因。但是根据对一些房屋的裂缝研究,一定数量的此种裂缝存在的房屋(楼板采用预制板或者是单向板的房屋),保温隔热措施也做得较为合理,且温度缝的处理符合规范也要求。由于承重墙与非承重墙的荷载差,在房屋的顶部两种墙体的压缩变形不同,有时会沿两墙体相交的墙角处产生斜裂缝。裂缝的产生则是两墙体之间的累积变形差在顶部的反映。关于墙体开裂与变形差两者之间的关系是课题研究的主要内容。

竖向荷载差作用下多层砌体房屋顶层裂缝的理论和试验研究

本研究构建了能够真实反映多层砌体结构的H型实体研究模型,从试验和理论两方面研究了竖向荷载差作用下纵横墙(即非承重与承重墙)变形位移大小,以及裂缝的产生和发展行为。结果表明:纵横墙变形差大小随荷载增加而增大,并且当荷载增加至一定值时,顶部伴有裂缝的产生和扩展。另一方面,本研究建立了竖向荷载差作用下多层砌体房屋顶层最大剪应力计算分析模型,提出并确定了顶层最大剪应力计算公式和相关参数确定方法。理论分析指出荷载差引起的纵横墙交界处的剪力在Y=H时最大(τmax),房屋的顶层最易开裂。

竖向荷载差引起砌体顶部开裂有限元分析

墙体顶部斜裂缝问题一直是困扰设计和施工人员的重要课题,以往的研究往往将这种斜裂缝的形成归结于温度变化、地基不均匀沉降等因素。从竖向荷载差的角度,采用有限元方法,对竖向荷载差作用下砌体墙体模型进行模拟分析,得到的裂缝位置、形态特征与理论分析以及试验结果吻合较好,证实了竖向荷载差理论是正确的,为研究此类问题提供了一种合理有效的方法。同时,对带构造措施和不带构造措施的砌体进行对比模拟,探讨防止竖向荷载差裂缝的有效方法。

中远场振动有限元分析中微差爆破荷载的等效施加方法研究

建立了微差爆破荷载等效施加方式的关系式,首次提出了中远场振动有限元分析中的微差爆破荷载的等效施加方法。结合新城金矿采场中深孔微差爆破回采项目,基于动力有限元软件ANSYS/LS-DYNA,应用微差爆破荷载等效施加方法模拟距爆源不同距离的中远场巷道围岩质点振动速度,通过对数值模拟和现场数据的分析比较,证明了微差爆破荷载等效施加方法的有效性和可行性。该方法显著提高了爆破荷载下中远场岩体振动特性数值模拟的效率。

多层砌体1/4比例模型墙体顶部裂缝试验研究

为了研究多层砌体结构房屋顶端裂缝问题,根据简单相似性原理构建了一1∶4比例、每层均布有构造柱和圈梁的H型六层混凝土小型空心砌块砌体结构墙体模型.通过对墙体模型进行竖向加载的拟静力试验,模拟了纵横墙荷载差,深入研究了在竖向荷载差作用下砌体房屋顶端裂缝的产生行为和发展规律.研究结果表明:随着承重墙上竖向荷载的增加,承重墙与非承重墙之间的荷载差所引起墙体的竖向变形差增大,同时承重墙中部变形相对承重墙和非承重墙交界处变形较大.当荷载增加到一定值时,由于承重墙对非承重墙产生的拉应力进一步加大,承重墙上靠近非承重墙一端顶部出现裂缝.随着荷载的继续增加,承重墙上裂缝宽度增大并扩展,并有新的裂缝出现.由于构造柱-圈梁体系的约束作用,有效地控制了承重墙与非承重墙之间的竖向变形差的增大.

Mechanical behaviors of cross roller bearings with raceway roundness error

Taking the raceway roundness error into account,mechanical characteristics of cross roller bearings(CRBs)were investigated.A static analysis model of CRBs considering the raceway roundness error was established.Based on this model,the rotational accuracy and load distribution of CRBs under constraints of geometry and external loads were derived.The fatigue life of CRBs with roundness error was calculated by applying Palmgren-Miner linear cumulative damage theory.The influence of inner and outer raceway roundness error on the performance of the CRBs,such as rotational accuracy,load distribution,and fatigue life,was studied through the analysis of examples.The results indicate that the influence of roundness error on the rotating inner raceway is more significant than that of roundness error on the nonrotating outer raceway.The roundness error on the rotating inner raceway always degrades the performance of CRBs.However,a proper roundness error on the nonrotating outer raceway can reduce the loads acting on the rollers and thus improve the fatigue life of CRBs.The effect of the roundness error amplitude on the bearing performance is ordinal,whereas the effect of the roundness order on the bearing performance is not in order.

Optimization of friction and wear behaviour of Al-Si_3N_4 nano composite and Al-Gr-Si_3N_4 hybrid composite under dry sliding conditions

The tribological behaviour of gravity die stir cast LM6alloy with graphite(Gr)and silicon nitride nanoparticles was investigated.Al?Gr?Si3N4hybrid composite,Al?Si3N4nanocomposite and Al?Gr nanocomposites were separately fabricated to investigate their frictional and wear characteristics under dry sliding conditions.EDS was used to ensure the uniform presence of nano Si3N4and graphite in the cast.L9orthogonal array method was chosen to conduct the experiments to study the effect of different applied loads(20,30and40N)and sliding distances(1,2and3km).The results showed that the respective wear rate and coefficient of friction(COF)decreased by25%and15%for hybrid composite when compared with those of Al?Si3N4nanocomposite whereas the wear rate and COF of Al?Gr was found to be very minimal.The micro Vickers hardness of the hybrid composite was14%more than that of the simple nanocomposite and there was not much notable variation for Al?Gr and Al?Si3N4nanocomposite materials.Scanning electron microscope was used to analyze the worn surface and subsurface,from which it was noted that the predominant wear mechanisms observed were abrasive for nanocomposite and both abrasive and adhesive mechanism for hybrid composite.Analysis of variance(ANOVA)and F-test were used to check the validity model and to determine the significant parameters affecting the wear rates.

An Experimental Study on the Response of Model Footings Resting on Reinforced Flyash Beds under Repeated Load

In the present, investigation an attempt has been made to study the behavior of reinforced flyash beds under repeated loads by conducting carefully designed experiments. The main objective of the experiments conducted is to evaluate the beneficial effects of using flyash as a backfill material in the reinforced beds to resist the repeated loads. As no unique standard equipment is available for the application of repeated loads and to measure the response, different researchers have designed and fabricated different types of equipments for the testing. The repeated load of known intensity with waveform type and frequency is applied on the surface and embedded footing in unreinforced and reinforced flyash beds. The response of the flyash beds, in the form of settlement is measured using linear variable differential transducers. The experimental results clearly demonstrated that the provision of reinforcement in the flyash beds is effective in improving the performance of both surface and embedded footing under repeated loads.

广州某超高层结构几个关键设计分析

某塔楼地上69层,屋面高度306m,带4层裙房,采用带伸臂桁架及环桁架的钢管混凝土柱钢梁框架-钢筋混凝土核心筒体系,文中对设置伸臂桁架、环桁架的位置做了敏感性研究,并对结构设计中几个关键问题做了深入的设计分析,如斜柱水平分力对钢框梁的拉、压作用,局部穿层柱的屈曲分析,核心筒墙肢在竖向荷载下变形差导致抗剪截面不足的处理措施,从而确保整体结构设计的安全可靠和经济合理。