腹板开槽冷弯薄壁卷边槽钢抗火性能有限元分析模型

位于冷弯薄壁型钢构件腹板的槽孔,可延长构件两边的热量传递路线,减弱冷弯薄壁钢构件作为墙板龙骨引起的冷桥效应。常温下冷弯薄壁构件的屈曲破坏模态已非常复杂,包括整体屈曲、局部屈曲和畸变屈曲等,且不同的屈曲破坏模态可能会相互影响。火灾下冷弯薄壁构件的破坏机理将更为复杂,根据常规的稳定理论难以求解其火灾下的临界荷载。本文利用有限元方法对火灾下腹板开槽冷弯薄壁卷边槽钢的受力性能进行了模拟,研究了单元类型、材料模型、初始几何缺陷以及求解方法等因素对分析结果的影响,为同类构件抗火性能的有限元模拟分析提供了建模依据。     

钢筋-沥青隔震层非线性震动特性研究

为了研究钢筋-沥青隔震层的材料与几何非线性震动特性,对钢筋-沥青隔震结构进行了振动台试验,分析了结构在不同加速度幅值输入时的隔震性能。同时,在钢材的应力-应变关系基础上,考虑构件竖向力的二次矩效应,提出了钢筋-沥青隔震层骨架曲线的计算方法,并结合双线型恢复力模型的滞回规则,建立了相应的恢复力模型。利用建立的恢复力模型,编制程序进行了弹塑性时程分析,并与试验结果作对比。结果表明:当钢筋-沥青隔震层的受力钢筋进入弹塑性阶段时,隔震层能够吸收大部分地震能量,显著降低上部结构的地震反应;弹塑性时程分析结果与试验结果吻合较好,由此建立的恢复力模型准确并且适用,可为钢筋-沥青隔震层的工程设计与非线性地震反应分析提供参考。     

考虑轴-弯-剪耦合效应的钢筋混凝土柱滞回性能研究

试验研究及震害调查发现:由于配箍不足或箍筋间距过大,地震作用下钢筋混凝土柱易发生剪切破坏,继而发生轴向破坏。采用纤维截面的钢筋混凝土梁柱单元及与之串联的剪切弹簧以及轴向弹簧考虑钢筋混凝土柱的轴-弯-剪耦合效应,其中纤维梁柱单元用于模拟柱的弯曲机制,与梁柱单元串联的剪切弹簧和轴向弹簧用于模拟剪切机制和轴向机制,并利用单轴材料模型中的Limit State Material及其相应的Shear Limit Curve和Axial Limit Curve确定材料的剪切破坏与轴向破坏失效点,最终从单元层次上定义轴-弯-剪耦合效应。为验证该数值模型的合理性,选取不同破坏形式、轴向力与水平循环往复荷载共同作用下拟静力试验的钢筋混凝土柱,借助Open Sees分析软件模拟其滞回性能。模拟结果与试验结果的对比分析表明:考虑轴-弯-剪耦合的串联模型能较好地模拟钢筋混凝土柱的强度、刚度退化及捏拢效应等,且能够反映钢筋混凝土构件在复杂应力条件下的受力性能。     

足尺RC剪力墙倒塌试验和数值模拟研究

钢筋混凝土(RC)剪力墙是我国工程结构中的重要抗震抗倒塌构件,其抗倒塌性能是研究结构抗震抗倒塌性能的关键。以一足尺RC剪力墙试件作为研究对象,对其进行了拟静力倒塌试验,基于损伤特征,提出了适用于该类构件的组合建模模拟方法。结果表明：剪力墙试件的破坏模式为弯曲破坏,当试件位移角达到1/39时,试件底部有5根纵筋和1根箍筋发生断裂,底部混凝土被压溃,试件水平承载力下降至峰值承载力的12.5%,构件发生倒塌;基于组合建模方法,对该试件进行模拟,该方法可以较好地模拟试件的受力特征、变形能力和滞回行为,数值模拟所得的屈服、峰值和极限承载力与试验结果的相对误差不超过2.71%。     

一种钢筋混凝土非线性宏观单元--筒体墙单元

高层结构一般都要设置复杂的钢筋混凝土抗震墙,如何模拟这些复杂墙体的力学性能就成为高层结构弹塑性分析的关键.本文在梁柱单元、单片墙单元的基础上提出了一种简体墙单元,并将此单元应用于高层混凝土结构推覆分析中.单元考虑了材料非线性,并采用较为精确的方法考虑了结构的二阶效应.理论与试验结果对比分析表明,简体墙单元具有精度高、计算稳定和自由度少等特点,为复杂体型高层结构的弹塑性分析提供了有力保证.     

一种钢筋混凝土非线性宏观单元——简体墙单元

高层结构一般都要设置复杂的钢筋混凝土抗震墙，如何模拟这些复杂墙体的力学性能就成为高层结构弹塑性分析的关键。本文在粱柱单元、单片墙单元的基础上提出了一种简体墙单元，并将此单元应用于高层混凝土结构推覆分析中。单元考虑了材料非线性，并采用较为精确的方法考虑了结构的二阶效应。理论与试验结果对比分析表明，简体墙单元具有精度高。计算稳定和自由度少等特点，为复杂体型高层结构的弹塑性分析提供了有力保证。     

基于MIDAS的钢板桩支护结构水平位移数值模拟分析

根据厚德明挖段钢板桩支护结构的实测数据的情况,结合GTS有限元模拟分析,对钢板桩支护结构的实测值和计算值进行对比。得出以下两个问题:①钢板桩单独受力和整体紧扣受力相对位移变形比较;②围檩和支撑构件对钢板桩受力变形的贡献,并且为钢板桩的预警值提供参考值。在进行MIDAS有限元分析时,采用莫尔-库伦破坏准则的理想弹塑性本构模型考虑土的弹塑性性质。     

立面开大洞复杂高层结构的整体抗震性能评价

本文针对某平面不规则、立面开大洞、带高位转换层的超限复杂高层结构,首先建立了整体模型结构的非线性计算模型,根据振动台试验结果选择了材料非线性参数,进行了弹塑性时程分析,并对模型结构及参数进行了验证。用验证过的模型和参数对原型结构进行了弹塑性时程分析,并对该结构作出整体抗震性能评价。通过本文分析表明,按照试验微粒混凝土材性试验数据,考虑附加质量建立的计算模型,能较好地捕捉到整体结构初始时的频率、振型等动力特性;选择现有的软件确定构件的本构关系,将其输入通用程序进行弹塑性时程分析,能够获得结构的非线性动力反应;通过模型乃至原型结构的弹塑性时程分析,可以对该立面开大洞复杂结构整体抗震性能作出合理评价。     

连梁可更换构件及连接的试验和模拟分析

结构可更换构件通过可更换连接与主体结构相连,共同工作并集中塑性损伤,震后更换损伤构件即可恢复结构功能。为了研究一种连梁可更换构件及连接的性能,对可更换构件及连接试件进行反复加载试验,并对低屈服点耗能钢材进行单向拉伸试验。采用ABAQUS软件对该可更换构件及连接进行有限元模拟分析,比较了壳单元和实体单元模拟的计算效率和精度,并提出合理可行的材料参数取值方法,采用非线性接触对模拟可更换螺栓端板连接,模拟结果与试验结果吻合良好。试验分析可用于研究该类可更换构件及连接的实际性能,模拟分析可为该类可更换构件及连接提供性能预测方法,并验证了可更换构件实际屈服力与设计屈服力的吻合度和超强系数,验证连接螺栓不产生滑移。在此基础上,给出了该可更换构件及连接在工程中的应用方法。     

集中塑性铰在网壳弹塑性地震响应中的应用

运用SAP2000分析设计软件和集中塑性铰理论,对现有振动台试验模型进行弹塑性时程模拟分析,通过试验与模拟分析对比,验证集中塑性铰理论在空间网格结构弹塑性地震响应分析中的适用性。分析中考虑几何和材料双重非线性影响,获得了节点位移响应、杆件塑性铰的分布特征、结构的整体变形及失效形态。振动台试验与模拟分析均表明:单层网壳试验模型在地震作用下的破坏始于支座附近及靠近肋杆的斜杆杆件端部,最终破坏是由网壳模型底部第一圈、第二圈结构杆件动力失稳破坏引起的,模型底部第一圈、第二圈大部分杆件经历了失稳或较大塑性变形,部分杆件达到极限强度与节点拉脱,使结构整体向下凹陷;采用集中塑性铰方法模拟杆系结构的动力弹塑性性能与振动台试验结果基本吻合,较适用于空间杆系结构地震下的弹塑性性能评定,且易被工程师掌握。     

基于Radon变换的CT图像杯状伪影校正

目的:目前的射束硬化校正算法大多需要能谱、检测器特性等信息。针对硬化校正的复杂性,提出一种基于图像后处理的硬化校正方法。方法:首先将带有杯状伪影的水模体CT图像中水的部分分割出来并对其做Radon变换以获取水的投影信息,以此信息构建带有未知系数的校正模型;然后将校正模型与理想图像对比,当它们之间的差异最小时,确定出校正模型的未知系数。利用确定出来的系数和预校正图像软组织的投影信息组合成的校正模型校正实际CT图像,以此消除实际CT图像中的硬化杯状伪影。结果:通过模拟数据验证表明,该方法能去除医用CT中由于射束硬化而引起的杯状伪影。结论:本文提出的方法在不需要能谱信息及投影数据的情况下就能进行杯状伪影的校正,提高了硬化校正的灵活性。      

Buckling of a pervasively faulted lithosphere

We investigated the buckling response of a faulted elastic plate under horizontal compression using the finite element technique to better understand the effect of faults on the elastic behavior of a plate. We studied the effect of changes in fault spacing, depth and dip on the effective Young's modulus, buckling stress and wavelength. Our model consists of a thick elastic plate whose entire upper surface is cut by evenly spaced faults. We impose either an initial sinusoidal deformation with a fixed wavelength or a random deformation to the grid. A fault is represented as a free surface with no resolved shear stress and is allowed to slip in a specified direction using the method of slippery nodes. With the assumption of free slip on the faults, our model results represent an end member case in which the buckling wavelength and buckling stress are minimized by the presence of the faults.In our models, fault depth was varied from 0 to 75% of the plate thickness. As strain increases, the grid deforms by antisymmetric flexural folding and the initial imposed wavelength of deformation is modified such that the new buckling wavelength emerges. Our results show that the effective Young's modulus is a decreasing function of fault depth and an increasing function of fault spacing. In addition, buckling of the plate occurs at a lower stress for greater fault depths. Buckling wavelength is independent of the initial deformation wavelength however, it is modified by the presence of faults. For a plate with closely spaced faults extending through at least 75% of the plate, buckling occurs at a wavelength one half as large as that for a continuous plate. Buckling stress is not independent of the intial deformation wavelength, rather it increases slightly with increasing difference between the initial deformation wavelength and the buckling wavelength.Analytical models that approximate or ignore the effect of faulting can have large errors in calculation of the buckling stress. More importantly, modeling the observed wavelength of deformation in a faulted region with analytical solutions for continuous plates may result in a significant underestimate of elastic thickness. Fault dip does not strongly affect either the effective Young's modulus or the buckling wavelength. Thus, the buckling response should be the same for a plate cut by a low angle fault or a high angle fault.     

Modeling RC column flexural failure modes under intensive seismic loading

The aim of this work is to model beam‐column behavior in a computationally effective manner, revealing reliably the overall response of reinforced concrete members subjected to intensive seismic loading. In this respect, plasticity and damage are considered in the predominant longitudinal direction, allowing for fiber finite element modeling, while in addition the effect of inelastic buckling of longitudinal rebars, which becomes essential at later stages of intensive cyclic loading, is incorporated. Α smooth plasticity‐damage model is developed for concrete, accounting for unilateral compressive and tensile behavior, nonlinear unloading and crack closure phenomena. This is used to address concrete core crushing and spalling, which triggers the inelastic buckling of longitudinal rebars. For this reason, a uniaxial local stress‐strain constitutive relation for steel rebars is developed, which is based on a combined nonlinear kinematic and isotropic hardening law. The proposed constitutive model is validated on the basis of existing experimental data and the formulation of the buckling model for a single rebar is developed. The cross section of rebar is discretized into fibers, each one following the derived stress‐strain uniaxial law. The buckling curve is determined analytically, while equilibrium is imposed at the deformed configuration. The proposed models for concrete and rebars are embedded into a properly adjusted fiber beam‐column element of reinforced concrete members and the proposed formulation is verified with existing experimental data under intensive cyclic loading.     

用二相介质有限元方法对共和7.0级地震前兆的数值模拟

利用固液二相介质平面应变问题的有限元程序对共和７．０级地震的前兆现象的时空分布进行了数值模拟．研究中不仅考虑了固相的非线性、硬化及膨胀等效应，也充分考虑了水对前兆的影响，因此模拟结果与实际的前兆分布特征符合较好．     

圆钢管混凝土压弯构件荷载一位移滞回性能分析

在空钢管中填充混凝土可以避免或延缓钢管过早地发生局部屈曲，并有效地提高构件的延性，从而增强构件的抗震性能，本文在对圆钢管混凝土构件弯矩－曲率关系分析的基础上，分析了圆钢管混凝土压弯构件P－△滞回关系曲线，理论计算结果得到国内外大量结果的验证，基于理论分析模型，分析了各参，如构件轴压比，长细比，截面含钢率和材料强度等因素对圆钢管混凝土压变变构件P－△滞回关系曲线的影响，最后，确定了圆钢管混凝土压弯构件P－△恢复力学模型和延性系数的简化计算方法。     

Mathematical modeling and full-scale shaking table tests for multi-curve buckling restrained braces

Buckling restrained braces(BRBs)have been widely applied in seismic mitigation since they were introduced in the 1970s.However,traditional BRBs have several disadvantages caused by using a steel tube to envelope the mortar to prevent the core plate from buckling,such as;complex interfaces between the materials used,uncertain precision,and time consumption during the manufacturing processes.In this study,a new device called the multi-curve buckling restrained brace (MC-BRB) is proposed to overcome these d...     

插桩过程对临近平台桩基础的影响研究

由于大型自升式钻井船的插桩位置通常距离海上钻井与采油平台较近,桩靴的插入过程可能会对临近平台的桩基础承载力和稳定性产生不利影响。以实际工程为背景,运用球孔扩张理论推导挤土效应产生的水平附加应力大小及其范围;提出一种近似考虑动力挤土效应的拟静力数值模拟方法,分析桩靴下沉到不同深度处时的桩基承载力、桩身应力和最大水平位移,并与静力分析结果进行对比。研究表明,桩靴插入过程对周围土体产生巨大的挤压和扰动作用,使得桩基承载力降低,桩身应力变大,最大水平位移增加;与静力法计算数值相比,由挤土效应导致的单桩承载力下降6%~8%,桩身应力增大30%~80%,桩身最大变形量增长1倍。     

An experimental study on steel‐encased buckling‐restrained brace hysteretic dampers

This paper describes a seismic test program performed on 12 steel‐encased buckling‐restrained braces (BRBs). The use of rolled or built‐up buckling‐restraining mechanisms with welded or bolted attachments was examined. In addition, the effects of bolt pretension, core‐to‐encasing attachment details, aspect ratio of core segment and imperfections due to manufacturing on the brace response were investigated. All specimens were subjected to a stepwise incremental quasi‐static testing protocol with a maximum axial strain amplitude of 2%. All specimens except one showed satisfactory performance with stable hysteretic response and sustained cumulative inelastic deformations in excess of 200 times the yield deformation. Based on the experimental results, the compression strength adjustment factor, and the strain hardening adjustment factor for each excursion were quantified. Test results revealed that these two factors are significantly influenced by the parameters investigated in the experimental program. BRB details were also found to influence the buckling and the yielding patterns of the core segment. Copyright © 2009 John Wiley & Sons, Ltd.     

一种改进的基于原始投影数据的CT硬化校正方法

在X射线CT（Computed Tomography）技术中,X射线能谱的多色性将导致重建图像出现杯状伪迹,降低成像图像的质量。为提高重建图像的质量,本文研究了一种校正X射线多色性产生硬化现象的方法。针对噪声多集中在高频部分的特点,先将投影数据分成高低频段,然后基于射线硬化的物理属性,采用本文研究的硬化校正方法对低频部分作校正,再和高频部分进行相加,并采用实验系统对其验证。实验结果表明该方法能够有效地提高重建图像的质量。