焊接工字形截面钢支撑低周疲劳性能试验研究

通过21根铰支焊接工字形截面支撑在6倍试件的受拉屈服位移幅值下的对称循环轴向加载试验,研究了具有不同几何特性的该类支撑构件的低周疲劳和耗能性能。研究发现,支撑翼缘直到断裂的疲劳损伤发展过程可分为可见裂纹萌生,穿透裂纹形成和穿透裂纹扩展3个阶段,并根据试验数据提出了估算支撑构件疲劳寿命和循环耗能能力的经验公式。统计分析表明,裂纹萌生疲劳寿命与弹塑性局部屈曲密切相关,当支撑翼缘的宽厚比越小,支撑的长细比越大时,其裂纹萌生疲劳寿命就越长。试验还表明,低周疲劳性能较优的支撑构件亦具有较高的耗能能力。为了防止框架-中心支撑结构中的支撑构件在强震下过早发生断裂破坏,在实际设计中除要限制板件的宽厚比之外,还应适当放宽现行规范对支撑构件长细比的限制。     

部分填充混凝土箱形截面钢桥墩的超低周疲劳裂纹萌生寿命预测

为研究部分填充混凝土箱形截面钢桥墩的超低周疲劳裂纹萌生寿命,通过与既有试验结果对比,确定所采用的钢材混合强化模型和混凝土损伤塑性模型的准确性,并且验证了Ge模型(基于塑性应变幅的累积损伤模型)非局部法在预测部分填充混凝土钢桥墩超低周疲劳寿命时的有效性。针对50%填充率的部分填充混凝土钢桥墩试件,利用Ge模型的非局部法,在3种不同加载形式的往复荷载作用下,研究翼缘宽厚比、正则化长细比等参数对超低周疲劳裂纹萌生寿命的影响,并基于参数化分析结果,拟合了预测该类钢桥墩超低周疲劳寿命的计算式。结果表明:钢材的混合强化模型和混凝土的损伤塑性模型能准确预测部分填充混凝土钢桥墩的滞回性能; Ge模型中的非局部法同样适用于部分填充混凝土钢桥墩的裂纹萌生寿命预测,基于参数化分析结果,提出了预测部分填充混凝土钢桥墩超低周疲劳裂纹萌生寿命的经验式。     

频率效应对Q345钢疲劳行为的影响

本文对结构用钢Q345的低周、超低周以及高频试验疲劳行为进行了研究。实验在常温下岛津电液伺服疲劳试验机和QBG-100高频疲劳试验机上进行。低周疲劳试验采用轴向应变控制方法,恒定应变速率为0.005 s~(-1),应变比为-1。超低周疲劳试验采用加载频率控制。高频试验通过增减砝码质量(激励质量)的数目来改变系统的谐振频率,应用共振原理测试高频下试件的载荷-周期(S-N)试验数据。实验结果表明,在同一应力水平下,加载频率更高的高频试验条件下的试件寿命总体上比低频率的低周疲劳试验试件的寿命长。超低周疲劳试验中,随着加载应力的提高,试件寿命曲线逐渐下降,通过频率-寿命(f-N)图可以看出,随着加载频率的增加,试件寿命有所提高。通过SEM扫描电镜对三种试件断口进行观察,可以发现低周及超低周疲劳试验试件的裂纹多从表面起源,高频试验既有表面起源的裂纹也有从内部萌生的裂纹,破坏形式主要取决于加载应力和材料性质,与加载频率无太大关系。     

循环荷载作用下含缺陷岩石破坏特征试验研究

 采用水泥砂浆材料和充填材料模拟含缺陷岩石,分别对含孔洞、柔性充填物及刚性充填物试样进行低周疲劳试验,观察含缺陷试样的疲劳破坏特征,得出含缺陷试样的轴向不可逆变形阶段性规律,研究不同缺陷对岩石类材料的疲劳寿命、疲劳裂纹萌生及其扩展的影响。试验结果表明：循环荷载作用下含缺陷岩石试样的轴向不可逆变形经历初始变形、等速变形以及加速变形3个阶段;含缺陷试样疲劳裂纹首先在有较大应力集中的缺陷与基体材料界面边缘处萌生及扩展;在相同循环加卸载条件下,预制孔洞直径越大,对应的孔洞试样疲劳寿命越短;刚性充填物试样最容易发生疲劳破坏,孔洞试样次之,柔性充填物试样疲劳寿命最长。     

630MPa超高强钢筋低周疲劳性能试验研究

630MPa超高强钢筋已应用于实际工程,而目前针对国产630MPa超高强钢筋的低周疲劳性能研究尚未见报道。为此,以我国国产630MPa超高强钢筋为研究对象,对其进行了静力拉伸试验,得到其静拉力学性能参数。通过恒应变幅加载低周疲劳试验,得到疲劳寿命、循环响应特征及应力-应变滞回曲线等指标,研究了630MPa超高强钢筋的疲劳性能,进行了低周疲劳特性评价。在试验研究的基础上,得到了630MPa超高强钢筋疲劳性能参数,建立了其疲劳寿命预测公式。采用OpenSees软件进行了630MPa超高强钢筋材料低周疲劳试验数值模拟,分析表明利用得到的超高强钢筋疲劳性能参数可以较精确地进行630MPa超高强钢筋低周疲劳数值模拟。     

钢筋混凝土柱低周疲劳全过程累积损伤性能简化分析方法

为了有效预测地震作用下钢筋混凝土柱的低周疲劳损伤累积程度与损伤后的剩余承载能力,提出了一种 基于单调荷载-位移关系并考虑低周疲劳效应的钢筋混凝土柱损伤承载能力简化分析方法。首先,根据自洽方法 并假设裂纹符合Weibull分布,提出了基于细观机理的混凝土损伤模型,给出了混凝土损伤指标与有效模量、应 变的定量表达式,并通过非线性数值分析得到了钢筋混凝土柱的单调荷载-变形曲线;然后,通过分析纵筋的塑 性低周疲劳损伤,建立了基于割线刚度的钢筋混凝土柱低周疲劳变形性能损伤计算模型,模型参数根据试验研究 获得,推导了柱割线刚度和抗力的衰减规律计算公式;最后,在以上工作的基础上,分析低周疲劳作用对钢筋混 凝土柱底截面混凝土和纵筋应变的累积增大效应,得到混凝土损伤后的有效弹性模量,提出了考虑低周疲劳损伤 后的钢筋混凝土柱承载能力和变形能力计算方法。编制非线性损伤分析程序,对损伤后试验柱进行了计算分析。 结果表明,该方法得到的计算值与试验值的相对误差处于合理范围之内,验证了该方法的可靠性和实用性。     

低屈服点钢低周疲劳性能研究

近年来,低屈服点钢因其优越的耗能能力而广泛应用于结构抗震中。为了对国产低屈服点钢的低周疲劳性能进行研究,本文对牌号为LY100、LY160及LY225的低屈服点钢进行了大塑性变形下的低周疲劳试验,试验采用应变控制的等幅循环加载,分析了其破坏现象、循环应力响应特征、循环骨架曲线、滞回曲线特点等性能,并基于不同的模型对其低周疲劳寿命进行了预测。结果表明：国产低屈服点钢具有良好的抗低周疲劳能力;Ramberg-Osgood模型可以很好地拟合钢材循环应力-应变曲线;Manson-Coffin模型及Kuroda模型均可有效拟合低屈服点钢的低周疲劳寿命曲线,其中Manson-Coffin模型的拟合精度较好,而Kuroda模型更适用于大应变下疲劳寿命预测。     

E319全铸铝合金材料低周疲劳试验研究

针对汽车发动机零部件工作中的低周疲劳效应,影响发动机寿命的情况。对E319全铸铝合金材料在不同温度下进行拉伸试验和低周疲劳试验,分析试验结果,得到了疲劳寿命受到应变幅的影响,并且温度与材料的疲劳寿命呈反比趋势。通过试验得到材料寿命及寿命均值数据,并对数据进行拟合数值曲线,得到E319铸铝合金材料的过渡疲劳寿命,当实际寿命小于计算得到的过渡疲劳寿命时,材料的弹性变形损伤将大于塑形变形损伤。     

基于延性破坏准则的钢管混凝土圆柱低周疲劳寿命研究

将钢筋混凝土结构的等效延性破坏准则应用于钢管混凝土圆柱的低周疲劳寿命分析,提出了钢管混凝土圆柱的低周疲劳寿命计算方法,综合考虑了结构的首超破坏和累积损伤.建立了钢管混凝土圆柱的低周疲劳寿命拟合曲线,拟合公式的相关系数为0.971;通过23根钢管混凝土圆柱的低周疲劳试验结果对提出的计算方法进行了验证.结果表明:建议计算模型能够较好地反映钢管混凝土圆柱在不同位移延性水平下的疲劳寿命.     

非对称位移循环下钢筋混凝土柱的低周疲劳性能

为了利用屈服后位移幅值与低周疲劳寿命之间的关系，建立抗震钢筋混凝土结构的更为合理的破坏准则，在完成了对称位移循环下钢筋混凝土柱低周疲劳性能的第一个试验系列后，着重介绍六根非对称位移循环下钢筋混凝土柱的累积损伤发育特点及其低周疲劳寿命随位移幅值和正负位移幅值比的变化规律，并在此基础上给出了低周疲劳寿命与不同位移水平下正负位移幅值比之间关系的表达式。     

考虑屈曲效应的混凝土柱纵筋低周疲劳性能和变形能力研究

屈曲导致的局部塑性应变集中将使钢筋损伤加重,并提前断裂.传统低周疲劳损伤模型(如Coffin-Manson模型,简称C-M模型)中未考虑屈曲效应的影响,这将高估屈曲钢筋的低周疲劳寿命.为研究屈曲对钢筋疲劳寿命的影响,完成了30个原状钢筋试件考虑屈曲的循环加载试验,得到了钢筋断裂时的极限塑性平均应变的测量结果,分析了局部...     

考虑低周疲劳效应的圆管截面钢支撑现象滞回模型

通过ABAQUS分析软件对一系列不同长细比、径厚比圆管截面钢支撑的压屈承载力、非线性屈曲平衡路径、卸载 再加载路径及损伤进行计算和统计，并选取典型构件计算结果与现有试验结果进行了对比，证明了有限元模型的准确性。通过统计的数值数据及现有的试验数据，拟合了简单、有效的圆管截面钢支撑现象滞回模型。该模型采用Coffin-Manson公式和Miner线性累积法则进行支撑低周疲劳损伤预测，建立了材料强度折减与疲劳损伤的相关公式，可以考虑支撑在滞回过程中的一些复杂非线性行为，如受拉屈服、受压非线性屈曲、包辛格效应及低周疲劳效应引起的材料强度折减和断裂等。该模型预测的支撑滞回曲线和累积能量耗散曲线与现有试验和校正的有限元模型的计算结果吻合较好，且计算耗时大幅缩减，适用于圆管截面钢支撑结构的非线性分析。     

Inelastic seismic response of steel bracing members

A survey of past experimental studies on the inelastic response of diagonal steel bracing members subjected to cyclic inelastic loading was carried out to collect data for the seismic design of concentrically braced steel frames for which a ductile response is required under earthquakes. The parameters that were examined are the buckling strength of the bracing members, the brace post-buckling compressive resistance at various ductility levels, the brace maximum tensile strength including strain hardening effects, and the lateral deformations of the braces upon buckling. Equations are proposed for each of these parameters. In addition, the maximum ductility that can be achieved by rectangular hollow bracing members is examined.     

Intermediate HSS bracing members during seismic excitations: modeling,design, and behavior

Concentric hollow structural section (HSS) bracing members are used frequently in steel framed structural systems to resist seismic excitations. Finite element modeling of the HSS braces that utilizes the true stress-strain curves produces hysteresis responses that are reasonable matches to the experimental response. True stress-strain curves are obtained from coupon tests or stub-column tests while utilizing an exponential function or strain hardening rule with a trial and error procedure to obtain the hysteresis behavior. In the current study, the true stress-strain curves are directly obtained from tests on stub-columns extracted from the full scale HSS bracing members away from the mid-length plastic hinge after cyclic testing. Two experimental tests (Shaback 2001 and Haddad 2004) were used to validate the model. Results indicate that the stress-strain curves for these braces are not unique. A refined damage accumulation model for ultra-low-cycle fatigue is implemented to predict fracture of the brace tests. The refined damage model is then used in the finite element modeling to predict fracture of braces in a chevron braced frame of an eight-storey building subjected to selected ground motions analyzed using OpenSees program. Results indicate that all braces could sustain the selected earthquake records without fracture.     

Cyclic behavior studies on I-section inverted V-braces and their gusset plate connections

Inverted V-braces and their central gusset plate connections are popular patterns of brace arrangements for special concentrically braced frames (SCBF). To improve the understanding of their seismic performances and promote their applications in seismic designs, the hysteretic behavior of nine I-section inverted V-braces and their gusset plate connections subject to inelastic cyclic loading is examined through experiments and analytical simulations. It is found that the clearance at the brace end on the gusset plate, the locations of the intersection point of bracing members, and the ratio of the free edge length to the gusset plate thickness are the key parameters. The loading capacities of braced frames show no decrease before the brace low-cycle fatigue fracture, but a longer plateau at a lower load level exists in the hysteretic loops. Although specimens with a linear clearance exhibit better seismic behaviors, a negative clearance is also acceptable as long as the gusset plate does not fracture prior to the braces. A brace intersection point with moderate eccentricity is preferable for its better behavior and its economical dimension of the gusset plate, but the brace point location in the gusset plate could induce out-of-plane deformations in the gusset plate and cause the system ductility to deteriorate. Based upon test results, a suggested limitation of the ratio of the free edge length to thickness for the gusset plates is presented.     

横梁加强型人字撑结构的弹塑性滞回性能

人字形支撑是多高层钢结构建筑的一种常用支撑形式。在侧向荷载作用下,由于受压支撑发生屈曲,承载能力快速下降,支撑架的横梁会受到拉压支撑间的竖向不平衡力的作用,JGJ 99—98《高层民用建筑钢结构技术规程》规定需加强支撑架横梁来承受这一不平衡力的作用。静力弹塑性推覆分析的结果显示,在加载后期横梁受拉支撑屈服荷载对加强型人字撑结构抗侧能力有很大的贡献。但是,在强烈地震作用下,由于每一支撑均处于拉压交替的受力状态,因此支撑架的受力性能要复杂得多。通过对横梁加强型支撑结构在往复荷载和地震荷载作用下的抗侧性能进行研究,以更好地了解这种支撑结构的抗震性能。     

循环非弹性应变下低碳钢对接焊缝的性能

评估钢结构构件的材质和细部构造在极限荷载作用下的无弹性需求范围。描述了对非弹性有要求部位(屈服应力相对较低的钢板和接头全部焊透的对接焊缝细部构造)的循环响应和低周循环疲劳寿命,对不同的基底材质和对接试样进行大振幅循环应变试验,设计了多种焊接方式来缓和焊接试样的应力集中现象、降低其残余应力、改善焊趾外观。采用单轴材料模型和低周疲劳模型描述试样的循环应力-应变响应和低周循环疲劳寿命。研究表明,线性累积损伤模型也适用于预测不同应变历史下试样的破坏情况。对接焊缝仅略微降低试样的低周循环疲劳寿命,不同的焊接方式对低周循环疲劳寿命的影响最小。     

有平面外支撑的工形截面圆弧钢拱弹性稳定性能及支撑刚度设计

采用有限元特征值屈曲数值方法，对平面外支撑工形截面圆弧拱弹性屈曲荷载及其刚度取值进行研究。在考虑各种荷载条件与拱脚条件下，研究了支撑刚度，约束类型、数量以及作用位置对钢拱平面外屈曲性能的影响，对于设置等间距侧向支撑的情况，给出了侧向支撑弹性门槛刚度的拟合式，并提出了支撑点间拱段不发生平面外弹性失稳的条件。研究结果表明：平面外支撑越靠近拱顶，其防止平面外失稳的工作效率越高；设置侧向支撑的钢拱屈曲时，随着支撑刚度的增大其屈曲半波数逐渐增加，而仅在拱顶设置扭转约束时始终呈现1个半波失稳模式；从均匀受压圆弧拱的情况获得的等间距侧向支撑门槛刚度，应用在其他组合荷载作用下，同样可以获得足够的支承刚度；当工形截面钢拱的支撑点间拱段长度满足所提出的要求时，钢拱平面外失稳不先于平面内反对称整体失稳。     

Steel concentrically braced frames using tubular structural sections as bracing members: Design,full-scale testing and numerical simulation

This paper presents the results of experimental and analytical studies carried out on two full-scale, one-bay, two-story steel concentrically braced frames. Square hollow and round hollow structural sections were used for the bracing components. The specimens were designed and detailed according to the 2005 AISC Seismic Provisions, and tested cyclically under displacement control but with a fixed lateral load distribution over height. Numerical computational models including the brace components, gusset plate details and frame members were implemented in OpenSees. Numerical simulations were then performed to investigate the cyclic behavior of brace components, brace failure mechanisms and overall system response. Satisfactory agreement was obtained in comparisons of experimental and numerical results. Premature failures observed suggest that beamto-gusset plate connections could be pinned to accommodate large rotational demands at this location without the need to form plastic hinges. Test results also showed that for the braced frames having the same configuration, designed for similar base shear capacities, and subjected to the same roof level displacement history, the braced frame specimen using round tubular sections as diagonal braces was able to sustain larger story drifts without brace fracture than the specimen employing square tubular sections. Fracture of the column base in the second specimen, although inconclusive from a single test, suggests more study is needed of design requirements for column to base plate connections where large variations of axial, bending and shear load are expected.