历经循环荷载历史混凝土动态受压试验研究

为了研究历经不同循环加载历史和不同应变速率对混凝土的动态峰值应力、峰值应变和弹性模量的变化规律的影响,进行了混凝土圆柱体试件历经循环加载历史后,在应变速率为10-5、10-4、10-3/s时的单轴受压特性试验。试验结果表明:随着应变速率的提高,混凝土的动态单轴抗压强度明显增加;在相同的应变速率和循环振幅情况下,混凝土的峰值应力随着循环荷载频率的增加而降低;在相同循环加载历史的条件下,混凝土的峰值应变随应变速率的提高总体上有增加的趋势;在相同循环加载历史条件下,混凝土的弹性模量随应变速率和循环加载历史振动频率的变化规律总体上并不明显。     

珊瑚砂动剪切模量预测的应变-损伤状态耦合模型

对南海饱和珊瑚砂进行了4类不同加载模式的不排水动三轴试验,研究了不同相对密度Dr和平均有效围压σ'0下加载第一周的动剪切模量比G1st/G0与剪应变幅值γa的关系,G1st/G0受Dr的影响很小,随σ'0的增大而增大。由于分级加载过程中土体结构与相对密度发生改变,在γa3×10-4时,应变控制的分级循环加载获得的G1st/G0-γa曲线位于等应变幅值循环加载获得的G1st/G0-γa曲线的上方。结合两类试验结果,给出了饱和珊瑚砂的G1st/G0-γa模型。基于弹性应变能理论,提出了可以描述土体损伤状态的状态参数Pd(damage parameter),探究了不同加载模式下动剪切模量比G/G0随土体损伤状态参数Pd的发展规律。在双对数坐标中,同一应变幅值下的(1-G/G0)-Pd可用直线表示,其斜率与应变幅值γa和历史加载过程中的最大应变幅值γa,max有关。结合G1st/G0-γa和G/G0-Pd关系,给出了可以同时反映应变幅值和破坏状态影响的珊瑚砂动剪切模量预测模型。     

Q460D高强度结构钢材循环加载试验研究

高强度结构钢材在实际钢结构工程中已经得到广泛应用,国内外学者已经进行了一些研究,但对于循环荷载下高强度钢材本构关系的研究还很缺乏。通过对17个Q460D高强度结构钢材试件进行14种不同加载制度的单调和循环加载试验,得到不同加载制度下的应力-应变关系,探讨不同加载历史对其本构关系的影响,研究其材料本构模型、力学性能、破坏模式、变形和延性特征以及损伤退化特性。基于Ramberg-Osgood模型,拟合得到Q460D高强度结构钢材在循环荷载下的应力-应变关系骨架曲线;在Chaboche钢材塑性本构模型的基础上,通过试验标定Q460D高强度结构钢材的循环加载本构模型参数,并结合有限元程序ABAQUS对上述试验进行准确模拟。研究结果可为准确分析计算高强度钢材钢结构在地震作用下的受力性能提供基本前提。     

高强耐蚀钢材料力学特性试验研究

海洋钢结构的腐蚀劣化是导致结构失效的关键因素,应用耐蚀钢材可以显著提升结构服役寿命。通过对高强耐蚀钢的力学特性开展研究,进行了一系列单调和循环加载力学性能试验,分析了高强耐蚀钢在单调和循环荷载作用下的破坏形态、应力-应变关系、延伸率等性能,研究了循环加载历史、应变幅值和应变增量等参数对材料力学性能的影响。结果表明:高强耐蚀钢在单调加载下无明显屈服平台,断后伸长率在16%~19%之间;循环加载下,钢材循环应力-应变关系随加载圈数增加表现为先强化、后软化、最终逐渐趋于稳定;不同应变幅值软化因子呈近似线性变化,其值较小且加载后期幅值影响不显著;单次循环的能量耗散值随着应变幅值增大而显著增大,但其增大倍率呈近似线性下降趋势,变幅应变加载造成材料损伤程度较常幅应变加载更严重;可采用Rasmussen模型和Ramberg-Osgood模型分别描述高强耐蚀钢单调加载力学行为和循环加载力学行为。     

由宏观滞回曲线分析岩石的微细观损伤

在MTS上进行超过砂岩屈服强度的正弦波（频率为5～15Hz）加载实验，通过对σ-ε滞回曲线和滞回曲线的面积，体应变随轴向应变的变化，探讨了岩石在循环载荷作用下微损伤的演化，通过轴向应变随时间的变化，探讨了循环载荷作用下的应变硬化和软化以及饱和液体对应变随时间变化曲线的影响。     

基于R-N非线性疲劳损伤累积模型的砂土震陷计算方法

构造不同加载次序的阶跃荷载进行应变控制循环单剪试验,并基于R-N模型与传统P-M模型进行土体材料损伤计算,对比分析计算值与试验值,验证R-N模型的有效性;基于R-N模型既能考虑荷载幅值和加载次序的特征,根据R-N非线性疲劳累积损伤理论推导并建立砂土震陷计算方法;利用GCTS测试系统对美国Filter净砂展开研究,进行404组剪应变控制动循环单剪试验,考虑荷载幅值、上覆荷载、砂土特性及地震动特性等影响,测定模型参数,并建立模型参数回归模型;同时,进行202组不同特性的真实地震荷载输入剪应变控制动循环单剪试验,测定不同工况下的砂土试样在地震荷载作用下引起的竖向变形;最后,将基于本文方法预测的砂土震陷时程曲线和累积值与试验值对比分析,验证了该方法的正确性。     

循环荷载作用下结构钢材本构关系试验研究

为准确模拟结构的地震响应,寻找在循环荷载下钢材的本构关系,采用工程常用Q235B及Q345B钢材共50个试件,施加多种加载制度,分析其单调性能、滞回性能、宏观微观破坏形态、延性特征以及损伤退化特性,并采用Ramberg-Osgood模型对循环加载骨架曲线进行拟合,进而得到Q235B及Q345B钢材在循环荷载下的一维应力应变关系骨架曲线;在Chaboche钢材塑性本构模型的基础上,通过试验标定,确定了两种等级钢材本构模型的关键材料参数,并结合通用有限元程序ABAQUS对试验结果进行有效模拟,为今后准确计算结构在地震荷载下的反应提供重要依据.结果表明:钢材在循环荷载下的反应与在单调荷载下的本构关系有很大差别,循环荷载下的骨架曲线对于准确的数值模拟起到重要作用;循环的圈数以及幅值会严重影响构件的断裂延性,钢材在循环荷载下的破坏应变不能按照单调荷载来确定.     

真三轴循环载荷作用下煤岩力学及损伤特征试验研究

为了研究煤矿采掘过程中真三轴循环扰动应力对煤岩力学特征的影响,利用GCTS真三轴力学试验系统,开展分级循环中间主应力σ_2下的煤岩力学试验研究,分析分级循环σ_2对煤岩变形、能耗及损伤特征的影响,揭示真三轴循环过程中的中间主应力效应。研究结果表明:分级循环σ_2对中间主应变ε_2和最小主应变ε_3的影响明显大于最大主应变ε_1。随着最小主应力σ_3值增加,分级循环σ_2引起地ε_1和ε_3都明显降低。循环加或卸载σ_2都可引起煤岩的失稳破坏,且当σ_3较小时,煤岩倾向于在σ_2卸载至靠近σ_3的过程中发生破坏,而当σ_3较大时,煤岩倾向于在σ_2加载至靠近最大主应力σ_1的过程中发生破坏,但破坏时对应的σ_2逼近率相近都在70%左右。σ_2的加载和卸载作用对煤岩的残余变形甚至破坏具有等效性。随着分级循环σ_2幅度的增加,煤岩的总耗散能呈"指数型"增加,煤岩的损伤变量呈现明显的"减速→加速→再减速"的S型变化趋势。分级循环σ_2过程中的煤岩平均安全损伤变量阈值为D_c=0.9。     

循环加卸载下塑性混凝土强度及变形特性

通过塑性混凝土在单调和循环加卸载下的试验,对不同加卸载作用下塑性混凝土的强度和变形性能进行研究。结果表明,经过循环加载后塑性混凝土的强度与单调直接加载相比有所降低,变化幅度均在10%以内;当循环加卸载最大荷载为单轴强度的60%时,塑性混凝土峰值应力大于其余循环水平下的峰值应力。塑性混凝土在循环荷载作用下的加载曲线与卸载曲线不重合,卸载曲线总是滞后于加载曲线,加载曲线和卸载曲线形成了封闭的塑性滞回环。滞回环面积的大小与循环加载最大荷载密切相关,与循环加卸载的次数无关,随着循环加卸载最大荷载的增大,滞回环面积相应增大,但滞回环的斜率保持不变,即变形模量保持不变。循环加卸载影响了塑性混凝土峰值应变,单调直接加载峰值应变大于循环加卸载作用后峰值应变。     

玻璃纤维复材筋损伤力学性能试验研究

对直径16 mm玻璃纤维增强复合材料(GFRP)筋单调一次拉伸及在应力上限水平为0. 3σ_b、0. 6σ_b(σ_b为筋体的极限抗拉强度)的9次循环加载拉伸损伤后的一次拉伸进行破坏试验,分析GFRP筋体损伤前后的力学性能变化规律。结果表明:筋材的极限抗拉强度随循环拉伸应力的增加呈下降趋势,折点处强度随循环拉伸应力的增加呈上升趋势。0. 6σ_b循环拉伸损伤后筋体纵向应力-应变曲线呈线性关系,随着荷载重复次数的增加,残余变形逐渐减小。0. 3σ_b循环拉伸后GFRP筋的纵向应力-应变曲线呈双折线。简化计算出0. 3σ_b、0. 6σ_b循环拉伸后的筋材损伤程度为0、0. 135。     

反复荷载作用下方钢管混凝土柱与钢梁连接节点非线性有限元分析

本文首先选择合适的本构模型作为约束混凝土循环本构模型的骨架曲线,提出了考虑局部屈曲和开裂的钢材循环本构关系;进而建立两类方钢管混凝土柱与钢梁连接节点———缀板焊接连接节点和穿芯螺栓-端板连接节点的空间非线性分析模型,对其在低周反复荷载作用下的滞回性能进行了非线性分析计算。结果表明:由有限元模型所得的单调荷载-位移曲线与试验所得的低周反复荷载作用下的骨架曲线极为相似,但在峰值荷载后差异较大;由有限元模型所得的在低周反复荷载作用下滞回曲线也与在反复荷载作用下试验所得的相一致。有限元模型能准确地预测上述两类节点的弹塑性行为和整体抗震性能,可用于节点滞回性能的非线性参数分析研究。     

高强度钢材在±10%大应变下的循环加载试验

为实现高强度结构钢材拉压大应变循环加载试验,避免受压失稳,采用了标距与直径比为1.13的特小标距试件。有限元分析结果表明,在此标距范围内,钢材屈服后应力、应变仍是均匀的。标准尺寸试件与特小标距试件的单调拉伸试验结果对比表明,为去除大应变范围内试件面积变化影响而采用真实应力 真实应变表达钢材力学行为是必要和有效的。针对屈服强度达到510MPa的国产高强度结构钢材,采用了循环拉伸、等幅升幅、等幅降幅和等幅交替4种不同的循环加载制度,使最大循环应变幅达到了±10%。试验获得了大应变范围内钢材的应力-应变关系及滞回特性,结果显示,大应变范围内循环加载时钢材的应力强化将有显著趋缓现象,与常用的双折线模型有显著不同。     

Complete nonlinear response of reinforced concrete beams under cyclic loading

Complete nonlinear analysis is carried out for cyclically loaded reinforced concrete (RC) beams made of normal‐ and high‐strength concrete. The loading stage covers not only the pre‐peak stage but also the post‐peak stage in particular. The analysis is based on a numerical method that employs the actual stress–strain curves and takes into account the stress‐path dependence of concrete and steel reinforcement. The complete nonlinear behavior of RC beams under both non‐reversed and reversed cyclic loading is studied based on the moment–curvature relationship obtained. Generally, the response under cyclic loading is found to be dependent on the loading path in bending. The variation of neutral axis depth is different for under‐ and over‐reinforced sections during cyclic loading. The Bauschinger effect of steel reinforcement is insignificant for non‐reversed cyclic loading but notable for reversed cyclic loading, especially when the loading extends into the post‐peak stage. The beneficial effects of concrete tension stiffening are only observed at the service stage and are more significant for under‐reinforced RC beams than over‐reinforced ones. Copyright © 2007 John Wiley & Sons, Ltd.     

低屈服点钢LYP100单调与循环拉伸试验研究

对47个LYP100低屈服点钢焊接试件进行单向拉伸和反复拉伸加载试验,研究其在不同加载制度下的应力-应变曲线、荷载-位移曲线、骨架曲线、破坏机理和延性特征.结果表明:试件横截面厚度是影响其耗能能力的重要因素,12mm试件的耗能能力明显优于6mm试件;焊接接头对试件的破坏有不利影响,带焊接接头的试件在循环加载作用下疲劳损伤累积效应显著,容易发生脆性破坏,延性变差;LYP100低屈服点钢与Q345钢、Q460钢焊接后,试件的强度提高,循环荷载作用下强度硬化现象明显,但是其延性变差.     

双向加载路径下型钢-混凝土组合柱抗震性能试验研究

通过8根型钢-混凝土组合柱在低周往复荷载作用下的加载试验,研究配钢形式、加载路径对该类组合柱破坏过程、滞回性能、刚度退化、延性性能及累积耗能的影响,分析纵筋及型钢的应变发展。结果表明：在相同含钢率下,配置方钢管的型钢混凝土柱的变形能力比十字形截面型钢的型钢混凝土柱的大,破坏位移角增大了约24%;加载路径对组合柱滞回特性影响显著,在非对称路径加载下,滞回特性亦表现出明显的非对称性;与单向循环加载组合柱相比,双向循环加载组合柱的峰值荷载小、刚度退化快、屈服位移小、延性差、破坏位移角小,但其累积滞回耗能明显大于单向循环加载时的情况;纵筋屈服发生在峰值荷载前,而型钢一般在达到峰值荷载时才屈服;在位移加载后期,双向循环加载组合柱纵筋及型钢应变增长明显较单向加载组合柱的快。因此,双向加载路径对型钢-混凝土组合柱承载能力、变形性能及累积耗能等抗震性能的影响显著,在设计时应予以考虑。     

Behavior of butt-welds and treatments using low-carbon steel under cyclic inelastic strains

The materials and details used to construct sacrificial structural steel components must be evaluated for the full range of inelastic demands imposed by extreme loading events. This study characterizes the cyclic response and low-cycle fatigue life of a plate steel material designed to have a relatively low yield stress and various complete joint penetration butt-weld details considered for use in applications where inelastic behavior is expected. Large amplitude cyclic strain tests were performed on the base material and butt-welded specimens. The welded specimens utilized several different weld treatment details designed to mitigate stress concentrations, reduce tensile residual stresses, and improve weld-toe geometry. Uniaxial material models and a low-cycle fatigue model were used to characterize the cyclic stress–strain response and low-cycle fatigue life of the specimens. A linear damage accumulation model was also applied and found to adequately predict the failure of specimens subjected to more arbitrary strain histories. The presence of butt-welds were found to only slightly decrease the low-cycle fatigue life and the various weld treatments were found to have minimal impact.     

循环荷载作用下锈蚀钢材滞回性能与本构模型

为研究循环荷载作用下锈蚀钢材的滞回性能,采用人工加速腐蚀及自然暴露腐蚀的方法获取了17组锈蚀试件,并对其开展单调拉伸及循环加载试验,分析了单调拉伸曲线、滞回曲线和骨架曲线等的差异性,得到了锈蚀钢材单调拉伸与滞回性能退化规律,基于混合强化模型提出了材料参数随腐蚀程度、等效塑性应变的退化表达式,进而建立了锈蚀钢材塑性本构模型。研究结果表明：单调拉伸作用下,锈蚀导致钢材屈服平台缩短、抗拉强度和断裂伸长率降低;锈蚀钢材单调曲线和滞回曲线存在显著差别,锈蚀加剧钢材循环强化,循环损伤累积则进一步加剧锈蚀钢材延性退化,造成峰值点应变、断裂应变和滞回耗能大幅降低,但对抗拉强度的影响较小。通过锈蚀钢材塑性本构模型应力 应变模拟曲线与试验曲线的对比,验证了所提模型的可靠性。     

Cyclic behavior of shear walls with HPFRCCs in the inelastic deformation critical region

This study presents a structural application of high‐performance fiber‐reinforced cement composites in the inelastic deformation critical region of the shear wall to improve the performance and reduce the disadvantages of conventional reinforced concrete members. Six small‐scale wall specimens with the same aspect ratio and various configurations were tested under reversed cyclic loading, and their cyclic behaviors were evaluated and compared. The fiber cementitious material examined in this study exhibited excellent pseudo strain‐hardening behavior in tension and high tensile ductility. The results of the quasi‐static cyclic tests revealed that the deformation compatibility between the steel reinforcements and high‐performance fiber‐reinforced cement composite (HPFRCC) matrix could maintain composite integrity. Accordingly, the damage tolerance of the wall specimens for high inelastic deformation could be improved. Furthermore, the ultimate deformation and energy dissipation capacities of the wall specimens were dominated by the ductility and stability of the longitudinal reinforcements. Consequently, the combination of highly ductile mixture material and buckling‐restrained measures of steel reinforcement, such as the steel sleeve presented in this paper, was proposed for use in shear walls under moderate or even higher axial loads. Copyright © 2016 John Wiley & Sons, Ltd.     

Experimental study on the constitutive relation of austenitic stainless steel S31608 under monotonic and cyclic loading

In order to study the constitutive relation of Chinese-made austenitic stainless steel S31608 (EN 1.4401, AISI 316) under monotonic and cyclic loading, different types of coupons were tested. Based on the Ramberg–Osgood model, modified by Gardner and Nethercot, parameters that described stress–strain relationship under monotonic loading were obtained. Comparison between data obtained using different types of coupons was made and the influences of welding and rolling directions were reviewed. Parameters of the hardening model of cyclic plasticity were calibrated from cyclic test data and the tests were simulated using ABAQUS finite element analysis software. The results show that stainless steel exhibits remarkable nonlinearity, and the stress–strain relationship may vary from different rolling directions. Under cyclic loading, with the increase of cyclic loops and change in strain amplitudes, stainless steel exhibits cyclic hardening behavior, and the simulated curves agree fairly well with the test curves. It is therefore recommended that the influences of welding and rolling directions on the stress–strain relationship should be taken into consideration and the constitutive relation under cyclic loading should be used if the component is subjected to cyclic loads.