古砖塔子结构压剪复合受力性能分析

为研究古塔子结构的受力性能,设计制作了3件不同楼层的子结构缩尺模型试件,进行低周反复加载试验,观察试件的开裂、变形及破坏现象;建立数值模型进行计算,得到了试验荷载作用下各试件的等效塑性应变、荷载?位移曲线,将计算结果与试验结果进行对比,分析竖向压应力对古塔砌体抗震性能的影响。结果表明,特征荷载的计算值相对试验值的误差均小于21%,等效塑性应变的分布与试件开裂破坏区域一致;当竖向压力保持恒定时,随着水平荷载的增大,塔体沿砌筑缝逐渐开裂破坏,裂缝宽度亦随之增大,在塔体洞口周围的破坏更为明显,且试件残余变形增大;随着压剪比的增大,古塔砌体开裂破坏的范围减小,抗剪承载力、刚度以及耗能能力均有所提高,但延性和变形能力略有降低。研究结果为砖石古塔建筑结构损伤及抗震能力评定提供参考。      

轻质混凝土拼装墙板填充钢框架协同抗震性能试验研究

为了研究墙板与钢框架结构之间的协同抗震性能,对采用不同墙框连接节点的轻质混凝土拼装墙板填充钢框架进行了低周往复荷载试验。通过对比试件的承载力、滞回性能、刚度、耗能以及延性性能,探讨了轻质混凝土拼装墙板及其整体性对结构抗震性能的影响。结果表明:填充墙板钢框架结构的最终破坏形态以墙板挤压开裂,框架梁柱端部翼缘屈曲为主;轻质混凝土拼装墙板与钢框架协同工作,有利于提高结构整体的承载力和变形能力,减轻钢框架在平面内的屈曲破坏;与刚性节点相比,采用柔性节点连接墙板与钢框架对结构的承载力、层间刚度和耗能能力更为有利;增强拼装墙板的整体性,有助于提高结构整体刚度、变形和耗能能力。研究结果可为轻质混凝土拼装墙板填充钢框架结构的抗震设计提供参考。      

冷弯薄壁C型钢节点的抗震性能试验研究

通过4个冷弯薄壁C型钢梁柱节点的低周反复荷载试验,以节点板螺栓间距与节点板厚度为参数,研究分析了该种节点的滞回曲线、延性与承载能力、刚度退化、耗能能力及其破坏特征。结论表明,冷弯薄壁C型钢梁柱节点的滞回曲线呈纺锤形,延性系数在2.38～3.56之间,达到极限荷载后刚度退化较快,耗能能力较强。由于节点最终的破坏为冷弯薄壁C型钢梁受弯破坏,所以螺栓间距与节点板厚度对节点的受力性能和抗震性能影响不大。     

新型三重钢管防屈曲耗能支撑的力学性能

基于在大跨网架结构中的应用,对目前的三重钢管防屈曲耗能支撑进行改进,设计了一种新型支撑,并对该支撑考虑初始缺陷下的力学性能进行了理论分析.根据理论分析,设计了四组不同的支撑,利用ABAQUS有限元软件模拟分析了在拉压循环荷载作用下支撑强度比对其力学性能的影响,包括连接段应力状态、滞回耗能能力和核心管屈曲破坏模式.研究结果表明:该新型耗能支撑结构布置可行,设计方法合理,强度比是影响支撑力学性能的重要参数,在强度比合理范围内,支撑具有良好的滞回耗能性能;在轴向循环荷载作用下,内外套管约束作用明显,核心管破坏模式为多波小幅屈曲破坏,变形稳定,满足防屈曲支撑设计要求.      

钢骨混凝土偏压长柱受力性能试验研究

为了研究细长钢骨混凝土柱在偏心荷载作用下的性能,文章进行了10根钢骨混凝土偏心受压长柱的试验,主要变化参数为混凝土强度、试件长细比和荷载作用偏心距。主要研究了柱子的长细比、荷载作用的偏心距及混凝土强度对柱子承载力的影响。     

一种新型装配式钢骨混凝土节点的抗震性能研究

为了避免装配式钢骨混凝土节点核心区的破坏,提出一种可实现损伤部位转移的新型节点形式.以框架边节点为研究对象,建立7组节点数值模型,开展低周反复荷载试验.从混凝土等效塑性应变、钢筋骨架Mises应力、节点滞回曲线和骨架曲线等方面计算分析,探究混凝土强度等级、柱轴压比、焊接位置、梁柱强度比等参数的影响.结果表明:装配式节点可将损伤位置从核心区转移到梁端;增加混凝土强度等级,可提高节点承载能力,但节点耗能能力和延性会下降;调整柱轴压比,可减小等效塑性应变,但对钢筋骨架应力、耗能能力、承载能力等影响极小;增加焊接位置至柱边距离,可使节点损伤部位外移,屈服后刚度和承载力有所提高,但耗能能力有所下降;增加梁柱强度比能够改善节点的耗能能力和承载力,但当强度比超过0.6时,梁端与节点核心区应力差变小.     

一种新型装配式钢骨混凝土节点的抗震性能研究

为了避免装配式钢骨混凝土节点核心区的破坏,提出一种可实现损伤部位转移的新型节点形式.以框架边节点为研究对象,建立7组节点数值模型,开展低周反复荷载试验.从混凝土等效塑性应变、钢筋骨架Mises应力、节点滞回曲线和骨架曲线等方面计算分析,探究混凝土强度等级、柱轴压比、焊接位置、梁柱强度比等参数的影响.结果表明:装配式节点可将损伤位置从核心区转移到梁端;增加混凝土强度等级,可提高节点承载能力,但节点耗能能力和延性会下降;调整柱轴压比,可减小等效塑性应变,但对钢筋骨架应力、耗能能力、承载能力等影响极小;增加焊接位置至柱边距离,可使节点损伤部位外移,屈服后刚度和承载力有所提高,但耗能能力有所下降;增加梁柱强度比能够改善节点的耗能能力和承载力,但当强度比超过0.6时,梁端与节点核心区应力差变小.     

抗弯刚度比对加劲板屈曲性能的影响

以一大型薄壁钢结构的加劲板为研究对象,采用有限元方法,考虑了13种不同的刚度比、多种不同的加劲肋布置方式以及边界条件等因素,分析了加劲板线性屈曲和非线性屈曲性能.抗弯刚度比对加劲板的屈曲性能影响显著,加劲板最佳抗弯刚度比将其线性屈曲模态划分为整体屈曲和局部屈曲,其值为10~20.加劲板非线性屈曲荷载随抗弯刚度比增大而提高.另外,在加载方向增加加劲肋布置可以提高加劲板局部屈曲荷载,在非加载方向增加加劲肋布置对加劲板的局部屈曲性能影响较小.      

装配式桥墩连接部位构造参数对抗震性能的影响分析

为研究装配式桥墩连接部位构造参数对抗震性能的影响,利用有限元软件ABAQUS针对灌浆套筒连接的装配式桥墩进行了模拟分析,通过改变套筒长度、套筒厚度和配箍率建立7组有限元模型.在往复荷载作用下,分析比较了不同构造参数下装配式桥墩的滞回曲线等抗震性能,并对比了墩柱塑性铰区的应力应变.研究表明:在规范允许范围内改变套筒尺寸,对结构的抗震性能影响不大.增大配箍率,可以提高一定的承载力,但对结构刚度影响较小,配箍率宜保持在1.28％-2.56％间.     

正交胶合木填充墙-钢框架体系受力性能

采用开源地震工程模拟系统（OpenSees）对以正交胶合木作填充墙的钢框架结构进行探索性数值研究,主要研究该填充墙钢框架单元在单调和循环加载作用下的受力性能,墙体与钢框架之间的协同工作性能以及连接个数对整体结构受力性能的影响.结果表明:正交胶合木填充墙能够提高钢框架的抗侧刚度和水平承载力;柔性连接的设置使整体结构耗能性能良好;工作缝的设置减缓墙体的开裂,更大程度上发挥连接件的耗能和变形能力;连接个数对构件的抗侧能力影响较大,可以通过调整连接数量和连接间距设计出具有多种刚度和耗能能力的框架单元.      

面内双轴循环载荷下304不锈钢的力学行为

为研究面内双轴载荷下304不锈钢材料的力学行为,运用有限元方法对十字形试样尺寸进行了设计与优化,在自主设计的面内双轴疲劳试验系统上对304不锈钢进行了单轴拉伸、双轴比例加载和非比例圆路径下的力学试验。结果表明,比例加载条件下304不锈钢的棘轮应变累积最小,圆路径下材料的棘轮应变最大,而单轴加载的棘轮应变累积介于比例载荷与圆路径之间。进入棘轮应变稳定增长阶段,圆路径对应的棘轮应变率高于单轴与比例加载,说明圆路径使304不锈钢的损伤失效进程加速。     

Experimental Testing of Pile-to-Cap Connections for Embedded Pipe Piles

For bridges supported by piles, acceptable system performance under seismic loading depends on effective pile-to-cap connections. A fixed pile-to-cap connection is often desirable to help control deflections during lateral loading when soft soils are present. While reinforcement bar cages that extend from the pile into the cap are effective in providing a fixed pile-to-cap connection, it is more economical to rely on pile embedment to provide fixity and moment resistance. This study investigated embedded pile-to-cap connections for concrete-filled pipe piles. Four full-scale specimens, each consisting of a cap with two piles, were investigated in the field under cyclic loading. The specimens had minimal reinforcement and varying amounts of pile embedment. Results show that the moment resistance of pile-to-cap connections can be significantly greater than what is typically calculated based on the flexural reinforcement and embedment bearing. Excess moment capacity may be explained by friction between the pile and the cap at the connection. This friction mechanism is described and discussed in the context of experimental results from other studies.     

Fabrication and Testing of Cuff Connections for GFRP Box Sections

A new type of connection between beams and columns has been designed and fabricated specifically for use with glass fiber reinforced plastic (GFRP) pultruded box members. The work is built on previous efforts in the area of GFRP connections, which demonstrated that innovative connections between box sections are superior to connections based on concepts from steel construction for connecting I-beams. The new connection element is designed as a monolithic connection for frame members and is fabricated using a vacuum assisted resin transfer molding process. Individual connection specimens have been fabricated and tested to verify their performance under cyclic static loads in a test frame designed to simulate conditions in a moment resisting frame. The connection configuration was found to fare better from the standpoint of both strength and stiffness in comparison with previous attempts at developing GFRP beam-to-column connections.     

Room Temperature Shear Band Development in Highly Twinned Wrought Magnesium AZ31B Sheet

Failure mechanisms were studied in wrought AZ31B magnesium alloy after forming under different strain paths. Optical micrographs were used to observe the shear band formation and regions of high twin density in samples strained under uniaxial, biaxial, and plane strain conditions. Interrupted testing at 4?pct effective strain increments, until failure, was used to observe the evolution of the microstructure. The results showed that shear bands, with a high percentage of twinned grains, appeared early in the samples strained under biaxial or plane strain tension. These bands are similar to those seen in uniaxial tension specimens just prior to failure where the uniaxial tensile ductility was much greater than that observed for plane strain or biaxial tension conditions. A forming limit diagram for AZ31B, which was developed from the strain data, showed that plane strain and biaxial tension had very similar limit strains; this contrasts with materials like steel or aluminum alloys, which typically have greater ductility in biaxial tension compared to plane strain tension.     

Further Tests of Beam-to-Column Connections for Pultruded Frames: Flange-Cleated

Four full-sized physical tests have been conducted to determine the behavior of semirigid beam-to-column connections for frames of pultruded profiles. The tests were on 203 mm (8 in.) sized joints with connection details specifically chosen to provide moment resistant connections, thereby making it an option to include their semirigid action in frame design. Full details on the preparation of specimens and the physical test results are presented. Experimental moment-rotation curves have been obtained under short-term loading and modes of failure established. The suitability of the four connections to provide acceptable semirigid properties is assessed and future work recommended.     

Performance of Steel Frame Building which Experienced Intense Ground Motion

A two-story, steel moment frame building that was severely damaged during the Northridge earthquake (1994) is studied in detail. Immediately following the earthquake, the building was judged unsafe for occupancy due to a residual displacement of 7.6 cm (3 in.) in the first story. Opening of the exterior facade revealed severe cracking in the moment connections. All connections contained cracks that started in the weld at the bottom flange of the beam and propagated across the column flange and into the column panel zone. Four welded, beam-to-column, moment connections were taken from the building for additional cyclic testing under controlled conditions in the laboratory to evaluate their residual strength and deformation capacity. Results indicate that the badly damaged specimens still have significant residual strength and deformation capacity. All damaged specimens were tested to 3% rotation.     

Forming response of retained austenite in a C‐Si‐Mn high strength TRIP sheet steel

TRIP sheet steels typically consist of ferrite, bainite, retained austenite, and martensite. The retained austenite is of particular importance because its deformation‐induced transformation to martensite contributes to excellent combinations of strength and ductility. While information is available regarding austenite response in uniaxial tension, less information is available for TRIP steels with respect to the forming response of retained austenite in complex strain states. Therefore, the purpose of this work was to study the austenite transformation behaviour in different strain paths by determining the amount of retained austenite before and after forming. Forming experiments were performed on a high strength 0.19C‐1.63Si‐1.59Mn TRIP sheet steel 1.2 mm in thickness in two different strain conditions, uniaxial tension (ε₁ = ‐2ε₂) and balanced biaxial stretching (ε₁ = ε₂). Specimens were formed to strains ranging from zero to approximately 0.2 effective (von Mises) strain. Specimens were tested both longitudinally and transverse to the rolling direction in uniaxial tension, and subtle mechanical property differences were found. The volume fraction of austenite, determined with X‐ray diffraction subsequent to forming, was found to decrease with increasing strain for both forming modes. Some modification in the crystallographic texture of the ferrite was observed with increasing strain, in specimens tested in the balanced biaxial stretch condition. This trend was not evident in the uniaxial tensile test results. Slight differences were found in the transformation behaviour of the austenite when formed in different strain conditions. More austenite transformed in specimens tested parallel to the rolling direction than transverse to the rolling direction in uniaxial tension. The amount of austenite transformed during biaxial stretching was determined to be greater than the amount transformed in uniaxial tension for specimens tested transverse to the rolling direction at an equivalent von Mises strain. The amount of austenite that transformed in biaxial tension, however, was comparable to the amount of austenite that transformed in specimens tested longitudinal to the rolling direction in uniaxial tension.     

Biaxial Low Cycle Fatigue Behavior and Martensite Formation of a Metastable Austenitic Cast TRIP Steel Under Proportional Loading

In this paper the biaxial low cycle fatigue behavior under proportional loading of a recently developed metastable austenitic stainless cast steel is presented. Total strain controlled tests were carried out on a 250 kN biaxial servohydraulic tension‐compression testing machine equipped with a biaxial orthogonal extensometer to measure the principal strains in the gauge area of the used cruciform specimens. The principal stresses were determined based on the compliance after the load reversals. The low cycle fatigue behavior under biaxial synchronous loading is compared to the uniaxial behavior. Therefore, biaxial single step tests and a biaxial multiple step load increase test were carried out. The dependence of the stress state on the cyclic deformation curves, cyclic stress‐strain curves and the formation of martensite are described. Finally, the fatigue life relationship according to Basquin and Manson‐Coffin was determined and compared to the Smith, Watson and Topper damage parameter, which provides a satisfactory fatigue life prediction.     

Repair of New Long-Span Bridges Damaged by the 1995 Kobe Earthquake

The 1995 Hyogo-ken Nanbu (Kobe), Japan earthquake provided the world’s first experience with earthquake damage to new long-span bridges designed to 1990s seismic standards. This paper reviews damage and describes techniques used to repair three major steel bridges along the Wangan route (Bayshore route) in Kobe—the 885 m Higashi-Kobe Bridge, the 217 m Rokko Island Bridge, and the 252 m Nishinomiya Port Bridge. These bridges, in service for less than three years, were essential components in the highway transportation system in the Kobe region. Extremely large ground motions, and failure of bearings, connections, and seismic restrainers were principal contributors to the damage sustained by these bridges. Repairs utilized heavy-lift floating cranes (up to 4,100 ton capacity) and various jacks to stabilize the structures and to realign spans. In one case, reconstruction of a collapsed span was required, with lifting weight a prime concern. Significant constraints on the repair included confined working space and requirements for maintaining maritime navigational clearances. The closure times for the repair of the bridges ranged from three to nine months.     

Assessment of Seismic Performance of Two Pile-Deck Wharf Connections

This paper examines the seismic response of two full-scale pile-to-deck connections of marginal wharves built in the 1980s at the Port of Los Angeles. The first test represented a precast pretensioned concrete pile-deck connection at Berth 145. This berth required extending the deck for a new crane rail and a new line of piles. The proposed wharf upgrade considered leaving the existing piles if their lateral displacement capacity exceeded the expected seismic demands. A representative connection was tested to assess the rotation capacity under reversed cyclic loading. The second test represented a typical steel pile-deck connection used in Berth 226. In this structure, the piles support a crane rail. A reversed cyclic loading test was also conducted to assess the connection deformation capacity. Both connections were able to carry the imposed axial load throughout, even when the flexural strength had degraded. The precast pile-deck connection maintained the flexural strength up to a rotation of 0.04?rad, and the steel pile-deck connection maintained its flexural strength up to a rotation of 0.015?rad.