爆炸荷载作用下钢柱的动力响应与影响因素分析

采用有限元软件ANSYS/LS-DYNA,建立钢柱有限元模型,模拟爆炸荷载作用下钢柱的动力响应,并对影响钢柱动力响应的主要因素进行数值分析。考虑了不同爆炸荷载、材料失效应变、单元网格密度、柱高、柱截面尺寸和柱承担的轴向压力等参数的影响。通过对钢柱动力响应时程曲线进行分析,研究爆炸荷载作用下钢柱响应特性及其破坏机理;通过分析,得到各参数对其动力响应的影响规律。分析结果表明：增大柱的截面尺寸,能够降低柱跨中水平位移;增大柱截面高度,能有效地提高钢框架柱的抗爆承载力;在钢柱抗爆设计中,应控制其所承受的轴向压力大小,轴压比值不宜超过0.3。     

地震荷载作用下加筋土挡墙动力特性分析

利用有限元软件对加筋土挡墙在地震荷载作用下的动力特性进行模拟分析,重点分析其在不同加筋长度、加筋间距以及峰值加速度条件下的动力响应特性。通过有限元分析一个高6m、底部为基础土的加筋土挡墙在地震荷载作用下的行为,针对理想化墙体研究加筋土挡墙的某些动力特性。模拟计算结果表明加筋土挡墙的加筋长度、加筋间距以及峰值加速度的变化对其水平位移、沉降及受力有较大影响。采用长度大的加筋材料可以有效减小加筋土挡墙的水平位移,但这样将导致加筋拉伸荷载的增大,同时也将导致加筋土挡墙的隆起增大。峰值加速度的大小对加筋土挡墙的水平位移有很大影响,当峰值加速度增大时水平位移也随之增大,但并不呈线性增长关系。减小加筋间距会有效地限制加筋土挡墙面板整体的水平位移,但在一定范围内减小加筋间距也会使加筋区域内土体底部挡墙的水平位移出现相对增大的现象,因此通过减小加筋间距来限制加筋土挡墙的位移在一定程度上具有局限性。     

门式钢框架结构非线性爆炸响应

采用ALE多物质流固耦合方法模拟爆炸荷载,对门式钢框架结构在内部爆炸荷载作用下的动力响应全过程进行了计算分析。分析中考虑了爆炸源的水平爆距和放置高度对框架结构动力响应的影响。研究结果表明,当爆炸源的放置高度较低时,水平爆距对框架柱的动力响应影响较大,而对框架梁响应影响较小;当爆炸源的水平爆距一定时,框架梁的动力响应随着爆炸高度的提高而增大。通过计算结果的分析对比得到使框架结构发生最大响应的最不利爆炸位置。     

冲击荷载作用下混凝土破坏强度的确定及CT验证

从细观结构出发,把混凝土看作由骨料、界面和砂浆组成的非均质复合材料,建立随机骨料模型,应用损伤塑性本构,对试件进行了冲击荷载作用下的数值模拟,通过施加不同的加载方式,研究材料的损伤破坏过程,最终以位移加载得出荷载-位移曲线的峰值强度作为细观混凝土试样的破坏强度.通过对混凝土进行冲击荷载作用下的实时CT扫描,得出试件的荷载位移曲线及各个应力阶段的CT图像,发现数值模拟所得混凝土强度及破坏过程与CT观测到的结果有较好的相似性.结果表明,利用该方法研究混凝土在冲击荷载作用下的损伤破坏过程是合适的,以荷载-位移曲线的峰值点作为混凝土破坏强度点是合理的.     

爆炸荷载作用下方钢管混凝土柱的动力响应及破坏机理

方钢管混凝土柱是被广泛采用的组合构件之一。爆炸发生时产生的爆炸冲击波可能会对框架结构内部的方钢管混凝土柱造成严重破坏,然而目前对其动力响应及破坏机理的研究成果相对较少。本文采用有限元分析软件ANSYS/LS-DYNA对爆炸荷载作用下方钢管混凝土柱的动力响应和破坏机理进行了研究分析。建立了方钢管混凝土柱实体有限元模型,其中混凝土采用HJC模型,方钢管采用考虑应变率的塑性随动强化模型,爆炸荷载施加在柱子一侧表面。通过对方钢管混凝土柱的破坏过程的模拟,比较分析了其在不同＂比例距离＂下的动力响应和破坏形式,进而得出方钢管混凝土柱的破坏机理。在爆炸荷载作用下,方钢管对其核心混凝土有一定的约束作用,使其处于复杂应力状态之下,从而使混凝土强度得以提高,塑性和韧性同时得到改善;同时,由于混凝土的存在,延缓了方钢管柱底和柱顶过早地发生局部屈曲。随着＂比例距离＂的增大,柱中水平位移逐渐减小。结果表明,方钢管混凝土柱具有良好的延性、优越的抗爆性能,所提出的破坏机理可供结构抗爆设计的进一步研究参考。     

强震作用下风电塔损伤特征与振动台试验研究

基于某轮毂高度为86 m的海上风电塔结构,考虑"叶片-轮毂-塔筒-桩"的精细化有限元模型,研究了考虑桩土作用时近远场地震动和不同加速度峰值对风电塔结构的非线性动力响应影响规律。为了验证有限元模拟的正确性进行了室内模型振动台试验研究,验证所建模型和数值模拟方法的正确性。研究结果表明:远场地震动对风电塔这种高耸柔性结构的动力响应影响最大,对其塑性极限状态极限值起着控制作用;由于受到偏心荷载作用,结构最薄弱部位位于结构的7/8左右高度处,此截面处应力和加速度随着地震动加速度峰值的增大而增大,首先进入塑性阶段;在弹性范围内,结构各部位的加速度响应峰值成几何倍数增长,与振动台实验得到的结果相吻合,验证了所建模型和数值模拟方法的正确性。     

压电陶瓷传感器的埋地长输管道动力响应监测

为监测埋地长输管道在冲击荷载作用下的动力响应,制作土箱-管道缩尺模型,将标定好的压电陶瓷传感器粘贴在管道上进行冲击试验。根据压电陶瓷传感器输出的加速度值,得到埋地管道在冲击荷载作用下的动力响应规律,并分析管道壁厚、管径、埋深、冲击高度等参数对管道动力响应的影响。利用有限元分析软件ABAQUS对该过程进行非线性有限元模拟,将有限元分析结果与试验结果进行对比,二者吻合程度较好。结果表明:在冲击荷载作用下,冲击高度增加,管道振动加速度峰值增大;相同工况下,大管径和薄壁管道振动加速度峰值较大,管道覆土越深,管道振动加速度峰值越小;压电陶瓷能够有效监测埋地管道的动力响应,为管道工程抗震设计和安全性评估提供参考依据。     

SV波斜入射下Nam Ngum 5拱坝-库水-地基系统的地震响应分析

基于黏弹性人工边界与相应地震动输入方法,推导了任意角度下三维SV波斜入射时的等效节点荷载,构建了考虑地震波斜入射的三维黏弹性静-动力统一人工边界,探究了三维情况下混凝土拱坝在地震波斜入射时的地震动响应,应用于Nam Ngum 5重力拱坝-库水-地基系统的地震响应分析中。研究结果表明：当SV波斜入射角度逐渐增大时,坝体关键点的顺河向位移、主应力以及动水压力峰值均呈现逐渐增大的趋势,横河向位移呈现逐渐减小的趋势;其中25°与0°入射相比,坝顶点顺河向位移从0增加至0.15 m,横河向位移影响较小仅减小0.011 m;坝踵点、坝趾点主应力与斜入射角度存在明显差异,当入射角度为25°时,主拉应力与主压应力峰值相较于垂直入射分别增加了1.41 MPa与3 MPa;坝踵处动水压力峰值也在入射角度为25°时达到最大为0.33 MPa与-0.29 MPa;需要在类似实际工程设计中应考虑地震波斜入射的影响。     

冲击荷载对埋地管道影响的试验与数值模拟研究

为了研究冲击荷载作用下埋地管道的动力响应,自制管道及土箱缩尺模型,开展埋地管道落锤冲击试验,并建立管道冲击模型对冲击荷载作用下埋地管道的动力响应过程进行数值模拟分析,探讨管道距振源水平距离、冲击能量以及管道埋深等参数对埋地管道动力响应的影响。试验测量得到管道纵向和环向的应变分布特性,同时对比冲击荷载作用下埋地管道数值模拟所得的结果与试验结果,二者较为吻合。研究结果表明：在冲击荷载作用下,管道受土压力的影响随管道距振源水平距离的增加而减小,并且管道受影响最大的位置因距振源水平距离的增加而发生偏移;随着冲击能量的增加,管道距离冲击中心点较近区域受到的影响随之明显增大,管道两端距离冲击中心点较远的区域受到的影响较小;管道覆土深度增加,土体缓冲作用随之增强,管道的应变峰值明显减小。研究结论可为埋地管道抗冲击设计规范制订、管道敷设及管道维护提供参考。     

季节冻土区土钉支护边坡地震反应动力特性分析

为了更科学地评价地震荷载作用下土钉支护季节冻土边坡的抗震性能，基于热-动力理论控制方程，应用大型非线性有限元软件ABAQUS，建立带有黏弹性人工边界的地震荷载作用下土钉支护季节冻土边坡的数值模型，对比分析夏季和冬季这两个典型季节时的加速度响应、位移响应以及土钉轴力响应。结果表明：无论是夏季还是冬季，加速度峰值随着季节冻土边坡高程以及激振加速度峰值增加而增加，在夏季时刻的季节冻土边坡坡顶位置处达到最大。此外，在不同地震波峰值加速度作用下，相同位置处的位移响应峰值却有明显的不同，同一地震烈度地震波激震时，夏季的季节冻土边坡坡顶位移最大，表明地震荷载对夏季的季节冻土边坡坡顶破坏效应最为明显，土钉轴力具有高程放大效应和坡面放大效应，季节冻土边坡坡底至坡顶的土钉端部轴力峰值逐渐增大。文中数值模拟模型及结论可为制定地震荷载作用下土钉支护季节冻土边坡抗震设计提供一定的参考。     

地震作用下黄土边坡动力响应的时频特征分析

地震作用下黄土边坡的动力响应特征与变形失稳机制是具有重要理论与实践意义的课题,但从动力响应频谱特性方面开展的研究还相对较少。以大型振动台模型试验获得的黄土边坡地震动峰值加速度数据为基础,通过分析其变化规律,着重从频谱特性的角度分析,讨论黄土边坡的动力失稳机制。进一步通过对坡面不同高程测点、边坡内部垂直方向以及水平方向上测点的加速度时程进行绝对加速度反应谱分析,从频谱变化角度提出黄土边坡的动力失稳机制。研究表明,黄土边坡在地震动作用下的响应过程可以分为三个阶段：弹性阶段、塑性阶段与破坏阶段;黄土边坡进入破坏阶段时均会伴随反应谱峰值的增幅或者主周期的变化,在弹性阶段反应谱加速度峰值增幅与输入地震动幅值增幅一致,进入塑性阶段后反应谱峰值增幅比输入地震动幅值增幅小;研究提出将反应谱首峰的凸显情况作为坡体破坏程度的判断依据之一。     

卵石土场地地震反应特征振动台试验研究

为研究卵石土场地地震反应特征,基于四川成都典型卵石土场地,通过振动台模型试验研究卵石土场地在不同地震波、不同地震强度激励下的加速度峰值放大系数、加速度频谱反应及动土压力反应,并且对其场地地震反应非线性效应及土体动剪应力-动剪应变关系进行分析。结果表明：卵石土场地表层土层对地震波具有明显的放大效应,加速度峰值放大系数介于1～1.4之间,下部土层放大效应较小,加速度峰值放大系数介于0.9～1.2之间。卵石土场地对地震波具有低频放大,高频滤波的作用,滤波频率上、下限随激励强度的增大逐渐向低频方向移动。激励强度较小时,土体尚未破坏,动土压力在地震过程中逐渐增大;随着激励强度的增大,动土压力反应明显增大,表现出骤减后逐渐增大的现象。在激励强度较小时(SN1),中部土体最先进入非线性反应阶段,地震波在中部土层能量损耗最大;激励强度较大时(EL3),土体均发生了较大变形,土体最大动剪应变达到1.7%,此时卵石土场地对地震波的放大作用明显减弱。     

Analysis of Russian Hydroacoustic Data for CTBT Monitoring

—?As part of a collaborative research program for the purpose of monitoring the Comprehensive Nuclear-Test-Ban Treaty (CTBT), we are in the process of examining and analyzing hydroacoustic data from underwater explosions conducted in the former Soviet Union. We are using these data as constraints on modeling the hydroacoustic source as a function of depth below the water surface. This is of interest to the CTBT because although even small explosions at depth generate signals easily observable at large distances, the hydroacoustic source amplitude decreases as the source approaches the surface. Consequently, explosions in the ocean will be more difficult to identify if they are on or near the ocean surface. We are particularly interested in records featuring various combinations of depths of explosion, and distances and depths of recording.¶Unique historical Russian data sets have now become available from test explosions of 100-kg TNT cast spherical charges in a shallow reservoir (87?m length, 25?m to 55?m width, and 3?m depth) with a low-velocity air-saturated layer of sand on the bottom. A number of tests were conducted with varying water level and charge depths. Pressure measurements were taken at varying depths and horizontal distances in the water. The available data include measurements of peak pressures from all explosions and digitized pressure-time histories from some of them. A reduction of peak pressure by about 60–70% is observed in these measurements for half-immersed charges as compared with deeper explosions. In addition, several peak-pressure measurements are also available from a 1957 underwater nuclear explosion (yield <10?kt and depth 30?m) in the Bay of Chernaya (Novaya Zemlya).¶The 100-kg TNT data were compared with model predictions. Shockwave modeling is based on spherical wave propagation and finite element calculations, constrained by empirical data from US underwater chemical and nuclear tests. Modeling was performed for digitized pressure-time histories from two fully-immersed explosions and one explosion of a half-immersed charge, as well as for the peak-pressure measurements from all explosions carried out in the reservoir with water level at its maximum (3?m). We found that the model predictions match the Russian data well.¶Peak-pressure measurements and pressure-time histories were simulated at 10?km distance from hypothetical 1-kt and 10-kt nuclear explosions conducted at various depths in the ocean. The ocean water was characterized by a realistic sound velocity profile featuring a velocity minimum at 700?m depth. Simulated measurements at that same depth predict at least a tenfold increase in peak pressures from explosions in the SOFAR channel as compared with very shallow explosions (e.g., ～3?m depth).¶ The observations and the modeling results were also compared with predictions calculated at the Lawrence Livermore National Laboratory using a different modeling approach. All results suggest that although the coupling is reduced for very shallow explosions, a shallow 1-kt explosion should be detectable by the IMS hydroacoustic network.     

辽宁台安砂土液化特性动三轴试验研究

为探讨台安砂土液化相关特性及发展规律,针对辽宁台安砂土进行一系列不排水动三轴试验,研究台安砂土在动荷载作用下动孔压及动应变变化规律,分析影响台安砂土发生液化的主控因素,揭示动载作用次数下台安砂土动力响应特征。结果表明：动应力水平不同的各相对密度试样u_d曲线可分为后期陡增和匀速增长两种类型,动应力幅值较大时,u_d始终以较快速度增长,呈现匀速增长特征,动应力幅值较小时,u_d曲线则呈现初期缓增后期陡增的特点;相对密度D_r和动应力幅值CSR是决定砂土液化的主控因素,在同一里氏震级等效动载作用次数下,随着D_r持续发展,液化所需CSR增长逐渐加快,当D_r足够大时,砂土基本处于密实状态,此时难以发生液化;循环荷载作用下,台安砂土呈现出初期整体受压、中期拉压平衡、后期受拉凸显的动力响应特征,到后期试样拉应变迅速增大,试样易发生受拉破坏。研究成果可为辽宁台安地区建筑物抗震设计提供参考依据。     

STUDY ON DYNAMIC RESPONSE AND INSTABILITY OF SOIL-ROCK MIXTURE DEPOSIT WITH DIFFERENT STONE CONTENTS AND SLOPE GRADIENTS

Soil-rock mixture deposit is an extremely heterogeneous loose rock-soil deposit formed since Quaternary, which is composed of blocks, fine-grained soil and pore with a certain engineering scale and high strength and has a certain stone content. These soil-rock mixtures accumulated on slopes have been completely destroyed and their mechanical strength is very low. They are widely distributed in the mountainous areas of Southwest China, which poses a great threat to the engineering. Earthquakes occur frequently in Southwest China, and the instability of soil-rock mixture deposit under seismic load is one of the important factors causing the damage to this type of deposit. The dynamic response of soil-rock mixture deposit under seismic load is an important index to study its instability mechanism under seismic load. Based on indoor shaking table model test, the influence of rock content and slope gradient on dynamic response characteristics of soil-rock mixture deposit was studied. In model tests, rock content is 30%, 40% and 50%respectively, and slope gradient varies from 20°, 30° and 40°. Two different seismic loading frequencies and three different excitation strengths were given. The peak acceleration(PGA)amplification coefficients in horizontal and vertical directions of soil-rock mixture deposit were analyzed under the change of rock content and slope gradient. The permanent displacement and deformation law of the top and foot of the slope of soil-rock mixture deposit were analyzed by model test. The experimental results show that the dynamic acceleration response characteristics of the soil-rock mixture deposits at the top and foot of the slope are different under different slope gradients and rock content conditions, and the horizontal PGA amplification coefficients of the soil-rock mixture deposits are also different. With the same seismic frequency and excitation intensity, the horizontal PGA amplification coefficient increases with increased slope gradient, and the rate gets faster. With the increase of stone content, the magnification coefficient of horizontal PGA decreases, and the higher the stone content, the slower the decrease rate of horizontal PGA magnification coefficient. When the slope gradient of soil-rock mixture deposit increases, the corresponding horizontal and vertical PGA amplification coefficients increase with the same seismic frequency and excitation intensity. The amplification coefficients of PGA in the vertical direction are different, but the overall magnification is weaker than that in the horizontal direction. The vertical PGA amplification coefficients of the foot, middle and lower parts of the slope are larger, while the vertical PGA amplification coefficients of the upper and middle parts of the slope tend to decrease. The higher the frequency of seismic wave is, the smaller the vertical PGA amplification coefficient corresponding to the same elevation will be, which indicates that the vertical PGA amplification coefficient is negatively correlated with the elevation. The variation trend of PGA magnification coefficient of soil-rock mixed deposit in vertical direction is different with the change of stone content. Under the same excitation intensity, the larger the slope gradient is, the larger the permanent displacement at the top of the slope will be, and the larger the rock content, the smaller the corresponding displacement at the top of the slope. The permanent displacement of the top of the slope is obviously larger than that of the foot of the slope, which indicates that the magnification effect of the top of the slope is obvious. After the vibration process and sliding of the landslide, the large-sized particles in the soil-rock mixture deposit move downward faster and slip on the surface of the deposit body. There was a very obvious phenomenon of particle sorting in the pile-up at the foot of the landslide body. The results of this study are of practical significance for the analysis of the dynamic response law of soil-rock mixture deposit under seismic load due to the change of rock content and slope gradient.     

交通荷载及其对紧邻基坑支护结构影响的现场实测分析

目前对交通荷载对深基坑围护结构的影响研究尚处于起步阶段。本文通过对某深基坑工程交通荷载以及交通荷载作用下深基坑围护结构振动加速度及桩后动土压力的现场实测研究,给出了坑边车辆荷载计算经验公式,并分析了车辆荷载大小、行驶速度等因素对基坑围护结构振动特性及动土压力的影响规律。结果表明:在地表面处,车辆荷载产生的振动以竖直向为主;车辆荷载的大小将直接影响围护结构振动加速度幅值及动土压力大小;车辆行驶速度不同,车辆振动产生的峰值加速度和土体惯性力也不同,从而使得基坑围护结构桩后动土压力也不同,车辆行驶速度越大,基坑围护结构振动峰值加速度及动土压力也越大;车辆交通荷载对基坑围护结构的影响将随着距离的增加而衰减。研究所得结果可供相关基坑工程设计施工参考。     

地震动入射角度对地下结构地震响应的影响

考虑土-结构接触面效应和场地初始静应力影响,基于大型商用有限元软件ANSYS和粘弹性人工边界条件,采用动力松弛法的分析思路,建立了一种地震动斜入射条件下地下结构的接触非线性动力反应分析模型和方法,并讨论了地震动入射角度对地下结构动力反应的影响。结果表明：地震波斜入射使得结构的整体反应发生明显变化;随着入射角度的增加,节点的水平向应力反应明显增大,竖向应力峰值较小,增大程度也相对较小;节点的位移峰值随输入加速度峰值的增大也有一定的变化。因此,在分析近源地震作用下的地下结构动力响应时,需要考虑地震动的非一致输入问题。     

Influence of confining pressure and impact loading on mechanical properties of amphibolite and sericite-quartz schist

In order to investigate the dynamic mechanical properties of amphibolite and sericite-quartz schist under confi ning pressure, two rocks are subjected to impact loadings with different strain rates and confi ning pressures by using split Hopkinson pressure bar equipment with a confi ning pressure device. Based on the experimental results, the stress-strain curves are analyzed and the effects of confi ning pressure and strain rates on the dynamic compressive strength, peak strain and failure mode are summarized. The results show that:(1) The characteristics of two rocks in the ascent stage of the stressstrain curve are basically the same, but in the descent stage, the rocks gradually show plastic deformation characteristics as the confi ning pressure increases.(2) The dynamic compressive strength and peak strain of two rocks increase as the strain rate increases and the confi ning pressure effects are obvious.(3) Due to the effect of confi ning pressure, the normal stress on the damage surface of the rock increases correspondingly, the bearing capacity of the crack friction exceeds the material cohesion and the slippage of the fractured rock is controlled, which all lead to the compression and shear failure mode of rock. The theoretical analysis and experimental methods to study the dynamic failure mode and other related characteristics of rock are useful in developing standards for engineering practice.     

爆炸波在地铁车站中的传播规律研究

应用LS-DYNA软件建立了北京比较典型的2层地铁车站有限元模型,通过数值模拟方法分析地铁车站发生内部爆炸时,爆炸波在地铁车站内部的传播规律。研究表明：①在0.3m/kg~（1/3）〈Z〈1.6m/kg~（1/3）范围内,车站内部超压峰值可用Henrych经验公式估算;②爆炸波在地铁车站的封闭空间不断出现反射、绕射现象,使得结构构件遭受多次冲击作用;③楼梯口起到了一定的泄爆作用。本文研究结果可供地铁车站的抗爆设计与安全分析参考。     

地震作用下高填减载明洞土压力研究

针对西北黄土高原地区高填方减载明洞工程,明洞顶部铺设EPS板可以有效减小明洞周围土压力,保证结构安全。然而,由于填土的动力高敏感性,地震作用将会对已经稳定的回填土体产生扰动,导致明洞结构周围土压力发生较大变动,对明洞结构造成不利影响。因此,采用数值模拟方式,对地震作用下的高填减载明洞周围土压力变化特性及土拱效应进行研究。研究结果表明:地震作用下,由于减载作用产生的土拱效应始终存在,使得土拱高度降低和效应减弱;明洞顶部竖向动土压力时程曲线在距明洞中央0~5 m范围内变化趋势一致,在距中央5~7 m范围内变化趋势相反,当明洞顶竖向动土压力达到峰值时,平均竖向动土压力为平均竖向静土压力的1.14倍;明洞两侧水平动土压力时程曲线变化趋势呈“此消彼长”状态,当水平动土压力达到峰值时,平均水平动土压力为平均水平静土压力的2.89倍。