Effect of vertical load difference on cracking behaviors in multistory masonry buildings and numerical simulation

To investigate the causes qf cracks in multistory masonry buildings, the effect of vertical load difference on cracking behaviors was investigated experimentally by testing and measuring the displacements at the testing points of a large sized real masonry U-shaped model. Additionally, the cracking behaviors in U-shaped model were analyzed with shear stress and numerical simulated with ANSYS software. The experimental results show that the deformation increases with the increase of the vertical load. The vertical load results in different deformation between the bearing wall and non-bearing wall, which leads to cracking on the non-beating wall. The rapid deformation happens at 160 kN and cracks occur firstly at the top section of non-bearing wall near to the bearing wall. New cracks are observed and the previous cracks are enlarged and developed with the increase of vertical load. The maximum crack opening reaches 12 mm, and the non-bearing wall is about to collapse when the vertical load arrives at 380 kN. Theoretical analysis indicates that the shear stress reaches the maximum value at the top section of the non-bearing wall, and thus cracks tend to happen at the top section of the non-bearing wall. Numerical simulation results about the cracking behaviors are in good agreement with experiments results.

Finite-difference model of land subsidence caused by cluster loads in Zhengzhou,China

Groundwater exploitation has been regarded as the main reason for land subsidence in China and thus receives considerable attention from the government and the academic community.Recently,building loads have been identified as another important factor of land subsidence,but researches in this sector have lagged.The effect of a single building load on land subsidence was neglected in many cases owing to the narrow scope and the limited depth of the additional stress in stratum.However,due to the superposition of stresses between buildings,the additional stress of cluster loads is greater than that of a single building load under the same condition,so that the land subsidence caused by cluster loads cannot be neglected.Taking Shamen village in the north of Zhengzhou,China,as an example,a finite-difference model based on the Biot consolidation theory to calculate the land subsidence caused by cluster loads was established in this paper.Cluster loads present the characteristics of large-area loads,and the land subsidence caused by cluster loads can have multiple primary consolidation processes due to the stress superposition of different buildings was shown by the simulation results.Pore water migration distances are longer when the cluster loads with high plot ratio are imposed,so that consolidation takes longer time.The higher the plot ratio is,the deeper the effective deformation is,and thus the greater the land subsidence is.A higher plot ratio also increases the contribution that the deeper stratigraphic layers make to land subsidence.Contrary to the calculated results of land subsidence caused by cluster loads and groundwater recession,the percentage of settlement caused by cluster loads in the total settlement was 49.43%and 55.06%at two simulated monitoring points,respectively.These data suggest that the cluster loads can be one of the main causes of land subsidence.

Dynamic caustics test of blast load impact on neighboring different cross-section roadways

Using digital laser dynamic caustics experimental system and conducting simulation experiment researched the influence rule of blasting excavation of a new roadway on neighboring existed different cross-section roadways. The experimental results show that the influence of blast load on adjacent roadway has a good relationship with the cross-section of roadway. The expansion distance of precrack existed in circular, arch-wall, rectangular roadway is respectively 1.76, 1.61 and 0 cm under blast load.At the same time, the direct-blast side of rectangular roadway has more obvious damage compared with circular and arch-wall roadway. It explains that plane reflects more stress wave than arc, so that it exerts more tensile failure in the direct-blast side, which leads to less stress wave diffracting to the precrack in the back-blast side. When the precrack extends, higher value dynamic stress intensity factor in circular roadway works longer than that of arch-wall roadway. Indirectly, it explains that plane's weakening function on stress wave is significantly stronger than arc. Stress wave brings about self-evident influence on the upper and bottom endpoints of the rectangular roadway, and it respectively extends 1.03, 2.06 cm along the line link direction of the center of the blasthole and the upper and bottom endpoints on the right wall.

FRP Retrofitted RC Slabs Using Finite Difference Model

Current guidelines recommend using single-degree-of-freedom(SDOF) method for dynamic analysis of reinforced concretec (RC) structures against blast loads, which is not suitable for retrofitted members. Thus, a finite difference procedure developed in another study was used to accurately and efficiently analyze the dynamic response of fibre reinforced polymer (FRP) plated members under blast loads. It can accommodate changes in the mechanical properties of a member's cross section along its length and through its depth in each time step, making it possible to directly incorporate both strain rate effects (which will vary along the length and depth of a member) and non-uniform member loading to solve the partial differential equation of motion. The accuracy of the proposed method was validated in part using data from field blast testing. The finite difference procedure is implemented easily and enables accurate predictions of FRP-plated-member response.

Influence of vertical loads on lateral response of pile foundations in sands and clays

Although the load applied to pile foundations is usually a combination of vertical and lateral components,there have been few investigations on the behavior of piles subjected to combined loadings.Those few studies led to inconsistent results with regard to the effects of vertical loads on the lateral response of piles.A series of three-dimensional(3D) finite differences analyses is conducted to evaluate the influence of vertical loads on the lateral performance of pile foundations.Three idealized sandy and clayey soil profiles are considered:a homogeneous soil layer,a layer with modulus proportional to depth,and two-layered strata.The pile material is modeled as linearly elastic,while the soil is idealized using the Mohr-Coulomb constitutive model with a non-associated flow rule.In order to confirm the findings of this study,soils in some cases are further modeled using more sophisticated models(i.e.CYsoil model for sandy soils and modified Cam-Clay(MCC) model for clayey soils).Numerical results showed that the lateral resistance of the piles does not appear to vary considerably with the vertical load in sandy soil especially at the loosest state.However,the presence of a vertical load on a pile embedded in homogeneous or inhomogeneous clay is detrimental to its lateral capacity,and it is unconservative to design piles in clays assuming that there is no interaction between vertical and lateral loads.Moreover,the current results indicate that the effect of vertical loads on the lateral response of piles embedded in twolayered strata depends on the characteristics of soil not only surrounding the piles but also located beneath their tips.

The critical loading for lateral buckling of continuous welded rail

The most significant differences between continuous welded rails （CWRs） and general split-type connectors are axial compression in the longitudinal direction, buckling stability and other issues generated under the influence of thermal effect. Under thermal effect, a dynamical behavior similar to that of a beam fixed on two sides occurs in the central locked area of the welded rail, as there is axial compression but no possibility of sliding. Continuous welded rails do not contract or expand, and are supported by the dynamical system made up of ballasts and rail clips. The rail-support system mentioned above has the features of non-uniform material distribution and uncertainty of construction quality. Due to these facts, the dynamics method based on the linear elastic hypothesis cannot correctly evaluate the rail＇s buckling conditions. This study is aimed at applying Finite Difference Method （FDM） and Monte Carlo Random Normal Variables Method to the analysis of welded rail＇s buckling behavior during the train＇s acceleration and deceleration, under thermal effect and uncertain factors of ballast and rail clips. The analysis result showed that buckling occurs under the combined effect of thermal effect and the train＇s deceleration force co-effect and the variance ratio of ballast and rail clips is over 0.85, or under the combined effect of thermal effect and the train＇s acceleration force when the ariance ratio is over 0.88.

Elastic solutions for partially embedded single piles subjected to simultaneous axial and lateral loading

In order to improve the design level of partially embedded single piles under simultaneous axial and lateral loads, the differential solutions were deduced, in which the soil was treated as an ideal, elastic, homogeneous, semi-infinite isotropic medium. A comparison was made between model test results and the obtained solutions to show their validity. The calculation results indicate that the horizontal displacement and bending moment of the pile increase with increases of the axial and lateral loads. The maximum horizontal displacement and bending moment decrease by 37.9% and 13.9%, respectively, when the elastic modulus of soil increases from 4 MPa to 20 MPa. The Poisson ratio of soil plays a marginal role in pile responses. There is a critical pile length under the ground, beyond which the pile behaves as though it was infinitely long. The presented solutions can make allowance for the continuous nature of soil, and if condition permits, they can approach exact ones.

Dynamic Response Analysis of Semi-Submersible Floating Wind Turbine with Different Wave Conditions

To address the problem of poor wave resistance of existing offshore floating wind turbines,a new type of semisubmersible platform with truncated-cone-type upper pontoons is proposed by combining the characteristics of offshore wind turbine semi-submersible floating platforms.Based on the coupled hydrodynamic,aerodynamic,and mooring force physical fields of FAST,the surge,heave,pitch,and yaw motions responses of the floating wind turbine under different wave heights and periods are obtained,and the mooring line tension responses are also obtained;and compare the dynamic response of the new semi-submersible platform with the OC4-DeepCwind platformat six degrees of freedom.The results show that different wave conditions have obvious effects on the heave and pitch motions of the new floating wind turbine,and fewer effects on the surge and yaw motions;the tensegrity response of the mooring system is more affected by the wave conditions;compared with the OC4-DeepCwind floating wind turbine,the pitch and roll response of the new floating wind turbine has been significantly reduced and has good stability.

Study on the subgrade deformation under high-speed train loading and water–soil interaction

It is important to study the subgrade characteristics of high-speed railways in consideration of the water–soil coupling dynamic problem,especially when high-speed trains operate in rainy regions.This study develops a nonlinear water–soil interaction dynamic model of slab track coupling with subgrade under high-speed train loading based on vehicle–track coupling dynamics.By using this model,the basic dynamic characteristics,including water–soil interaction and without water induced by the high-speed train loading,are studied.The main factors-the permeability coefficien and the porosity-influencin the subgrade deformation are investigated.The developed model can characterize the soil dynamic behaviour more realistically,especially when considering the influenc of water-rich soil.

Analysis of Critical Load of the Orthotropic Plate Structures

Advanced design based on the concept of orthotropic structure includes better use of materials, less weight compared to the equivalent isotropic construction and controlled effectively reserve resistance in all its segments. In this case a calculation of critical load is exposed using the FDM （Finite Difference Method） concept of thin plates subjected to complex loads due to forces in the middle-plane. Results of calculation model, discussed in this paper, are given in graphic form. Presented results should serve as an indicator of the expansion of theoretical base of similar models, which can be reasonably use by researchers and engineers in their practices, and by students for educational purposes.

Slope Stability Considering the Top Building Load

Slope stability is one of the most important subjects of geotechnics. The slope top-loading plays a key role in the stability of slopes in hill slope areas. When the building load is too large or the point of action from the shoulder is too close, the shear stress of the slope will be significantly greater than its shear strength, resulting in reduced slope stability. Therefore, it is of great importance to study the relationship between the building load and the stability of the slope. This study aims to analyze the influence of different building loads applied at different distances on the top of the slope and deduces their effects on the slope stability. For this purpose, a three-dimensional slope model under different building loads with different distances to the slope shoulder was established using the finite-difference analysis software Flac3D. The results show that the loads applied at different distances on the top of the slope have different effects on the slope stability. The slope factor of safety (FOS) increases with the increase of the distance between the top-loading and the slope shoulder;it varies from 1.37 to 1.53 for the load P = 120 KPa, 1.27 to 1.53 for the load P = 200 KPa, and from 1.18 to 1.44 for P = 300 KPa, resulting in the decrease of the coincidence area between the load-deformation and the potential sliding surface. The slope is no longer affected by the potential risk of sliding at approximately 20 m away from the slope shoulder.

Comparisons and Analysis between English and Chinese Culture-loaded Vocabulary

Language is the carrier of culture while culture is the connotation of language.English vocabulary contains many cultureloaded words and expressions that carry certain cultural information.These words and expressions seem simple literally but the comprehension of this type of vocabulary requires knowledge of relevant cultural background information.This article adopts some cases to make comparative studies of culture-loaded vocabulary between Chinese and English and discuss its classifications and translation strategies.

多电压等级配电系统智能软开关协同配置

配电网逐步发展成为光伏、电动汽车等新型源荷的主要承载平台,面临的电压越限和线路过载等问题逐步加剧。柔性配电装置具有良好的调控能力,成为提高配电网运行灵活性的有效手段。已有的柔性化升级主要面向中压或低压配电网,多电压等级配电网柔性互联的潜力被忽视。因此,该文开展多电压等级配电系统智能软开关协同配置方法研究。首先,提出多电压等级配电系统智能软开关协同配置策略;其次,在计及源荷不确定性影响下,考虑源荷典型场景的概率化波动,建立多电压等级配电系统智能软开关协同配置模型。最后,为实现大规模优化配置模型的可靠收敛,采用凸差规划算法进行求解。选取实际配电网算例对优化配置模型和求解算法进行验证,结果表明,所提方法可以有效解决多电压等级配电系统智能软开关协同配置问题,支撑配电网承载高比例新型源荷,在提高系统运行安全性的同时具有更好的经济效益。

多执行器载荷差异储能均衡系统特性

针对阀控多执行器复合作业系统节流损失大、动势能浪费严重等问题,提出一种多执行器载荷差异储能均衡原理。首先对多执行器系统功率分配特性进行分析,明确了载荷差异产生节流损失的原因是动力源压力与最大负载相匹配,导致其他执行器控制阀产生过大的压力损失。然后建立了载荷储能均衡液压挖掘机联合仿真模型。并设计电液储能单元控制各执行器进油腔的压力相等,从而消除执行器载荷差异造成的节流损失。在动臂、铲斗同时动作时,与流量匹配系统相比,所提系统节流损失降低达75%,系统效率提升39%;同时,电液储能单元实现了传统压力补偿器的压差调控功能,显著提升了系统运行平稳性。

基于热平衡法生成同时发生设计日的方法研究

提出了基于热平衡法生成同时发生设计日的方法.首先基于热平衡法计算某城市的历年逐时动态冷负荷,以历年平均不保证50 h为依据确定理论设计负荷,采用综合聚类法挑选同时发生设计日.用热平衡法计算同时发生设计日、传统设计日的峰值负荷,确定为同时发生设计负荷和传统设计负荷.分别对比了哈尔滨、北京、长沙和广州样本房间的同时发生设计负荷、传统设计负荷与理论设计负荷的差异率.结果显示,各城市同时发生设计负荷与理论设计负荷的差异率偏差范围都远小于传统设计负荷与理论设计负荷的差异率.说明依据同时发生设计日的气象参数进行空调系统设计负荷计算是更加合理、准确的,基于热平衡法可以准确生成适合工程应用的同时发生设计日.

多道撑式深基坑垮塌事故连续破坏机理研究

随着城市地铁建设不断发展,多道撑式深基坑应用日益广泛,然而目前对于内撑式深基坑局部破坏引发连续破坏在空间上的传递规律仍缺乏系统研究。文章依托新加坡地铁Nicoll Highway基坑事故,建立三维有限差分模型,提出内支撑荷载传递百分比S1,i和荷载增量承担百分比S2,i两种支撑荷载(轴力)传递评价指标。对比分析了单位厚度平面应变模型与三维模型的模拟结果,探究了不同初始破坏支撑数量在不同位置发生初始破坏所引发的荷载重分布规律,同时还研究了围护结构体系刚度和强度对于连续破坏发展的影响。结果表明,三维模型可以避免平面应变模型传力路径单一的局限性,更好地反映出连续破坏在三维空间中的传递现象;初始破坏支撑所释放的荷载主要作用在紧邻层支撑;当失效荷载存在向下的传递路径时,紧邻初始破坏的上层和同层支撑承担的荷载增量明显减少;底层支撑的安全系数提高会减缓连续破坏在水平方向的发展;支撑刚度越大,在初始破坏后所承担的荷载增量越多;当墙体间无有效连接时,支撑连续破坏沿竖直方向发展的趋势更加显著。

考虑蠕变影响的堆载作用下被动排桩受力变形分析

为分析堆载作用下被动桩受力变形的时间效应,首先引入分数阶Merchant模型描述土体的蠕变特性,然后根据对应性原理和Laplace变换推导Boussinesq黏弹性解,计算堆载引发水平附加应力,并通过Terzaghi土拱模型将附加应力传递到桩上,得到堆载作用在桩上的被动荷载.其次,将桩简化为黏弹性Pasternak地基上的欧拉梁,建立桩身挠曲微分方程,并采用有限差分法及Laplace逆变换求解,随后通过与已有试验结果的对比分析,验证了本文方法的可行性.最后,对分数阶Merchant模型参数(虎克体的弹性模量Eh、Kelvin体的弹性模量Ek及黏滞系数η、分数阶阶次α)、堆载-桩身水平距离以及堆载荷载对桩身水平位移的影响进行了分析,分析结果表明:Eh越大,桩身初始水平位移越小;Ek越大,桩身水平位移随时间的增量越小;η越大,桩身到达最终变形量的时间越长;α越大,Kelvin体的黏滞性越大;堆载-桩身水平距离越小、堆载荷载越大,桩身水平位移越大;且随时间的增加,桩身水平位移对Eh的敏感度降低,对堆载-桩身水平距离和堆载荷载的敏感度会增大.

矩差分析理论及其在配电网最小弃光决策中的应用

高比例分布式光伏接入配电网会导致潮流返送和电压越限等一系列问题,严重威胁到配电网的安全运行。文中提出了含分布式光伏配电网的矩差分析理论,将配电网对分布式光伏的消纳问题转化成恢复和维持矩差方程的平衡问题。对一个给定的配电网,当最高节点电压等于规定的电压上限时,光伏矩减去负荷矩的矩差近似为一个常数,称为临界矩差。临界矩差代表了配电网对分布式光伏消纳能力的极限,光伏矩才是配电网需要消纳的对象,而负荷矩是消纳光伏矩的资源。基于矩差分析理论提出了配电网分布式光伏的最小弃光决策,并应用于某10 kV单分支配电线路以及12.66 kV的IEEE 33节点多分支配电网的分析计算。算例表明,所提的最小弃光决策在误差不大于1.2%条件下,寻优速度提高了2877倍,验证了该方法的正确性和快速性。

光伏微网储能系统用电峰谷差自适应控制技术

光伏微网储能系统(PMESS)用电峰谷差的增大会导致电网负荷波动增大,影响电网的稳定性。为了有效降低电网的峰谷差,提出一种光伏微网储能系统用电峰谷差自适应控制技术。通过估计光伏微网发电系统的负荷,计算光伏微网储能系统的充电功率和电量,并根据该计算结果计算光伏微网储能系统的额定容量。设置用电峰谷差自适应控制约束条件,并结合二轮迭代的方式实现光伏微网储能系统用电峰谷差自适应控制。实验结果表明,所提技术可以准确估计光伏微网发电系统负荷,并将用电峰谷差控制在200 kW左右,同时,可以有效提升光伏微网储能系统的有功功率,具有良好的实际应用效果。

不同加载速率下蒸养混凝土单轴压缩声发射特性研究

为研究加载速率对蒸养混凝土受压破坏过程中声发射特性的影响,针对蒸养混凝土试件开展3种加载速率工况单轴压缩试验,并利用声发射技术对试验全过程进行动态监测,分析了不同加载速率下蒸养混凝土内部声发射特征参数的变化特征。结果表明:不同加载速率下蒸养混凝土受压破坏过程的声发射振铃计数变化呈现接触期、平静期、陡增期的三阶段变化规律,随加载速率增加,振铃计数率和能量计数率峰值逐渐增大,累计振铃计数和累计能量计数逐渐减小。低加载速率下,声发射幅度分布较为稀疏,内部损伤信号多而分散;高加载速率下,声发射幅度分布较为密集,内部损伤信号少而集中。声发射Ib值随加载进程呈现上升、波动和下降的演化过程,随加载速率的增加,混凝土试件破裂模式由剪切破坏向拉伸破坏的趋势演变。