Joint 2D DOA and Doppler frequency estimation for L-shaped array using compressive sensing

A joint two-dimensional(2D)direction-of-arrival(DOA)and radial Doppler frequency estimation method for the L-shaped array is proposed in this paper based on the compressive sensing(CS)framework.Revised from the conventional CS-based methods where the joint spatial-temporal parameters are characterized in one large scale matrix,three smaller scale matrices with independent azimuth,elevation and Doppler frequency are introduced adopting a separable observation model.Afterwards,the estimation is achieved by L1-norm minimization and the Bayesian CS algorithm.In addition,under the L-shaped array topology,the azimuth and elevation are separated yet coupled to the same radial Doppler frequency.Hence,the pair matching problem is solved with the aid of the radial Doppler frequency.Finally,numerical simulations corroborate the feasibility and validity of the proposed algorithm.

Experimental Study on Seismic Behavior of Exterior Joints of Special-shaped Columns with Different Lengths of Limbs

Four exterior joints with special-shaped columns which have different lengths of limbs are tested under low cyclic loading. Speeial-shaped columns adopted are L- and T-shaped in section. It can be concluded that crack pattern, failure mode and shear strength of joints are affected by the length of limb, and that shear strength and ductility increase with the length of limb; the joints with the flexural failure of the beam have better seismic behavior than those with the shear failure of the joint core.

Pushover analysis of reinforced concrete frames considering shear failure at beam-column joints

Since most current seismic capacity evaluations of reinforced concrete （RC） frame structures are implemented by either static pushover analysis （PA） or dynamic time history analysis, with diverse settings of the plastic hinges （PHs） on such main structural components as columns, beams and walls, the complex behavior of shear failure at beam-column joints （BCJs） during major earthquakes is commonly neglected. This study proposes new nonlinear PA procedures that consider shear failure at BCJs and seek to assess the actual damage to RC structures. Based on the specifications of FEMA-356, a simplified joint model composed of two nonlinear cross struts placed diagonally over the location of the plastic hinge is established, allowing a sophisticated PA to be performed. To verify the validity of this method, the analytical results for the capacity curves and the failure mechanism derived from three different full-size RC frames are compared with the experimental measurements. By considering shear failure at BCJs, the proposed nonlinear analytical procedures can be used to estimate the structural behavior of RC frames, including seismic capacity and the progressive failure sequence of joints, in a precise and effective manner.

Effects of interface slip and semi-rigid joint on elastic seismic response of steel-concrete composite frames

The stiffness matrix of semi-rigidly connected composite beams considering interface slip was established and the calculation method for elastic seismic response of composite frame was derived.The corresponding calculation programs were developed.Introducing the dimensionless quantities that were related to the connector shearing stiffness and the joint rotation stiffness,the influences of interface slip and semi-rigid joint on composite frame were transferred to quantitative parameter analysis,taking account of cross sectional properties,materials and linear stiffness of composite beam synthetically.Based on the calculation programs,free vibration frequencies and seismic responses of semi-rigid joint steel-concrete composite frame considering interface slip were calculated.The influences of interface slip and semi rigid joint on dynamic characteristics and seismic response were analyzed and the seismic design advices were presented.The results show that the interface slip decreases the free vibration frequencies and increase the seismic responses of composite frame.The semi-rigid joint reduces the free vibration frequencies and increases seismic responses of composite frame compared with rigid joint.With the increase of joint rotational stiffness,the elastic seismic responses of composite frame increase firstly and then decrease.The effects are related to the ratio of joint rotation stiffness to linear stiffness of composite beam.

Fatigue Reliability Assessment of Correlated Welded Web-frame Joints

The objective of this work is to analyze the fatigue reliability of complex welded structures composed of multiple web-frame joints, accounting for correlation effects. A three-dimensional finite element model using the 20-node solid elements is generated. A linear elastic finite element analysis was performed, hotspot stresses in a web-frame joint were analyzed and fatigue damage was quantified employing the S-N approach. The statistical descriptors of the fatigue life of a non-correlated web-frame joint containing several critical hotspots were estimated. The fatigue reliability of a web-frame joint wasmodeled as a series system of correlated components using the Ditlevsen bounds. The fatigue reliability of the entire welded structure with multiple web-frame joints, modeled as a parallel system of non-correlated web-frame joints was also calculated.

Experimental Research and Finite Element Analysis on Setting Stiffening Rib of Corner Joints in Gabled Frames

In order to clear constructional design of corner joint, it is necessary to further investi-gate mechanical property of corner joint in gabled frames. Through static test and finite element software analysis of comparing the panel zone with and without inclined stiffener. Some conclusions are given in the article. The load displacement curves show that the capacity of oblique nodes installed within stiffening rib components is enhanced i.e. 40% more than those without stiffening rib nodes. The results reveal that in the gabled frames, the corner node with the inclined stiffening rib can improve the bearing capacity of the specimens. When the extraterritorial flange is tension, the erection of the inclined stiffening rib can prevent structural failure and improve effectually the ductility of the structure.

Experimental Study on Seismic Behavior ofSeismic-damaged Lateral Joints in CompositeFrame Consisting of CFSST Columns and SteelBeams Strengthened with Enclosed ReinforcedConcrete

A new composite strengthening method of seismic-damaged lateral joints in composite frame consisting of Concrete-Filled SquareSteel Tubes （CFSST） columns and steel beams strengthened with enclosed Reinforced Concrete （RC） at the ends of columns andwelding steel plates at the ends of beams was presented. Based on the current design specifications, one half scaled models of 4lateral joints in composite frame consisting of CFSST columns and steel beams were designed and manufactured. One model wasoriginal control specimen, one was strengthened by enclosed RC, and the others were strengthened after pre-damage. The destructiontests under lateral cyclic load on the models were carried. The effectiveness of seismic-damaged joints strengthened with enclosedRC and the reinforcement effect on different levels of seismic damage were studied. The test results show that seismic- damagedjoints in composite frame consisting of CFSST columns and steel beams strengthened with enclosed RC meets the strongcolumn-weak beam joints requirement of seismic design, and the failure modes are of all joints are the bending failure of steel beam.The reinforcement with enclosed RC has a significant on increasing the ultimate capacity and the seismic behaviors of joints. Thestudy indicated the rehabilitated joints recover the level of their original seismic performances before seismic damage in a certainextent damage level. Based on the test data, namely the ultimate capacity, limit displacement, ductility, the energy consumptioncoefficient, limit displacementthe strengthening method of seismic-damaged joints by strengthened with enclosed RC is an effectivemethod for seismic strengthening.

基于转动摩擦铰阻尼器的干式装配梁-柱节点抗震性能试验

基于转动摩擦铰阻尼器(RFHD),提出了转动摩擦耗能干式装配梁-柱节点(DRFDBJ)。为了验证DRFDBJ结构对于实现预期力学性能的可行性和合理性,以施加在摩擦片表面的螺栓预紧力(P_(c))为变量,开展了2个工况下的DRFDBJ试件低周往复拟静力试验研究。结果表明:DRFDBJ结构的力学性能主要由RFHD提供并控制,试验中节点呈现了稳定的承载力和理想的变形、耗能能力,并实现了预期的损伤集中;2个不同P_(c)水准下节点承载力的试验值与理论值误差不超过5%,通过调整P_(c)可实现节点承载力的调控,为DRFDBJ结构承载力的可调控提供了支撑。

新型分层装配式节点钢框架地震易损性分析

为提高装配式钢框架的装配效率,结合节点抗震性能要求,提出一种新型全螺栓分层装配式节点。对新型和传统两类节点进行抗震性能试验研究,并把节点参数引入整体框架模型中,采用SAP2000建立两类框架模型并进行增量动力分析。考虑基于层间位移角的单参数损伤模型和基于变形与累积耗能的双参数损伤模型,定义结构性能水准限值并划分破坏等级,对结构进行地震易损性分析。结果表明:在单、双参数损伤指标下,新型节点框架的易损性曲线都包络于传统节点钢框架的易损性曲线内,且新型节点框架的抗倒塌储备系数更大,说明采用新型节点能降低结构在各破坏状态下的失效概率,提高框架的抗倒塌能力;在LS1、LS2极限状态下结构基于单参数损伤指标的峰值加速度中位值比基于双参数损伤指标下的峰值加速度中位值小,在LS3、LS4极限状态下则相反,说明累积耗能对结构抗震性能评估影响明显,结合双参数损伤指标能更好地预测结构的损伤程度;新型节点框架在单、双参数损伤模型下的倒塌储备系数均高于传统框架,说明新型框架的抗倒塌储备能力更高,有利于结构抗震。

四川大学博物馆结构设计重难点分析研究

四川大学博物馆采用钢框架结构体系,并设置屈曲约束支撑改善结构的抗震性能。介绍了四川大学博物馆的结构设计参数及抗震性能目标。针对结构设计中的重难点,开展了屈曲约束支撑的工作机理分析、框架柱计算长度与穿层柱分析、东侧大悬挑空间的相关分析。利用反应谱分析及时程分析探究了屈曲约束支撑工作机理,分析结果表明,屈曲约束支撑能够有效改善钢结构产生塑性铰的状况,起到保护主体钢框架的作用。针对东侧大悬挑空间的功能要求,设计采用了屋顶桁架结合钢拉杆吊挂东侧大楼梯的结构形式,通过结构防连续倒塌分析、楼板应力分析、楼盖舒适度分析、关键节点有限元分析等确保该部位结构设计安全合理。对整体结构受力机理和薄弱部位进行了研究,提出了重点部位的设计原则和加强措施。

基于新型耗能板提升钢框架节点抗震和抗连续倒塌能力

针对全焊节点在地震和连续倒塌条件下有限的抗倒塌能力,该文基于新型耗能板对其进行改进提升。首先通过试验、数值模拟和理论分析相结合的方法揭示了新型耗能板在单调荷载和循环荷载作用下的力学性能;进而通过新型耗能板与节点在地震作用和连续倒塌条件下的协同作用,给出了新型耗能板节点的设计方法。结果表明:新型耗能板在单调和循环荷载作用下的力学性能不同,在单调荷载作用下表现为受拉破坏,在循环荷载作用下表现为剪切破坏;通过算例分析表明,新型耗能板节点的抗震与抗连续倒塌设计方法是合理的;新型耗能板全焊节点在地震和连续倒塌条件下主要经历双塑性区域形成阶段和硬化阶段,其中新型耗能板全焊节点的抗震和抗连续倒塌性能的差异主要体现在硬化阶段;新型耗能板的增加可同时有效提高全焊节点在地震和连续倒塌条件下的承载力、变形和耗能能力。

铰接方钢管组合异形柱框架抗震性能研究

为解决村镇住宅体系存在的装配式程度及标准化程度较低、现场焊接工作繁多、室内建筑面积浪费等问题,提出了一种铰接方钢管组合异形柱框架体系。该体系中异形柱采用3根空钢管通过钢板与加劲肋组合而成的L形柱,梁柱节点为腹板螺栓连接的铰接节点。通过拟静力试验对该体系的抗震性能进行研究。研究结果表明:相比于铰接钢管混凝土组合异形柱,铰接空钢管组合异形柱框架体系先于梁端出现转角,最后破坏模式为柱脚破坏,具有更优良的抗震耗能和更缓慢的强度与刚度退化,并通过对比刚接节点和铰接节点的骨架曲线,发现节点刚接程度对结构整体的抗侧刚度影响较大。

榫卯灌浆钢管框架节点抗震性能试验研究

为探索建筑钢结构低能耗循环利用技术,研究方钢管柱-矩钢管梁采用榫卯连接、砂浆灌浆阻滑的钢框架节点的抗震性能。对榫卯灌浆节点及传统全焊接节点进行了低周往复荷载试验,对比分析其破坏形态、荷载-位移滞回曲线、延性系数以及极限承载力,并建立有限元分析模型,与试验结果进行对比。研究表明:榫卯灌浆节点在弹性阶段的承载力与全焊接节点相当,但榫卯灌浆节点的极限承载力高于全焊接节点,塑性发展平台更长;榫卯灌浆节点的破坏方式为砂浆磨损挤碎,钢构件损伤小;摩擦耗能效果好,滞回曲线饱满,且震后砂浆易修复。

非对称加强与狗骨式削弱型钢框架节点抗震性能数值模拟

为有效防止梁柱节点处发生脆性破坏并提高节点抗震性能,提出一种非对称加强与狗骨式削弱型钢框架节点。以边柱节点为例,利用ABAQUS有限元软件对非对称加强与狗骨式削弱型节点、非对称加强型节点、狗骨式削弱型节点和普通型节点共4个节点模型进行抗震性能对比分析,研究了节点的破坏形态、滞回曲线、骨架曲线、延性、耗能能力和刚度退化等方面的区别。研究表明:非对称加强与狗骨式削弱型节点能够有效实现塑性铰外移,防止节点发生脆性破坏,同时不仅能够提高节点的耗能能力和延性,还可以保持较好的承载能力。

高效装配T型框架节点优化及足尺抗震试验研究

为解决装配式混凝土框架节点在预制梁拼装时节点区钢筋易发生碰撞的问题,提出一种将柱箍筋肢距和纵筋间距放大处理的措施,对箍筋肢距正常和放大的装配式足尺框架T型节点进行低周往复加载试验,分析2个节点的破坏模式、滞回性能、强度退化、刚度退化、延性和耗能能力等。采用ABAQUS有限元软件对节点试件建模,分析轴压比对节点抗震性能的影响。结果表明:装配式混凝土框架T型节点试件的破坏模式均为梁端弯曲破坏,核心区混凝土基本完好;与箍筋肢距正常试件相比,箍筋肢距放大试件在低轴压比下的承载力更高、强度和刚度退化延缓、变形性能和耗能能力均有所增强,而在高轴压比下承载力与延性较差。在低轴压比下,满足“强柱弱梁”装配式混凝土框架T型节点可对预制混凝土柱纵筋间距和箍筋肢距进行放大处理来实现节点的顺利拼装。

折叠装配式框架结构静力试验研究

为获得折叠装配式框架结构的静力性能,设计了两个折展框架榀足尺试件,通过开展结构静力加载试验对单榀折展框架在不同荷载工况下的变形特征、承载性能与破坏形态进行了研究。试验结果表明:对于正常使用状态,进行静力加载时,有支撑的单榀框架结构整体变形处于弹性范围,水平作用下受推和受拉位移变化趋势基本一致,且增设支撑对折展框架的刚度影响较大;水平极限荷载作用下,有支撑的单榀框架结构在支撑连接处首先出现不可逆的塑性变形,单榀框架在边柱下端与下部拉条连接处发生局部破坏;上、下层梁柱节点弯矩-转角曲线变化趋势一致,但上层节点初始刚度明显弱于下层节点初始刚度,同层梁柱节点初始刚度基本相同;单榀框架的各关键点处等效应力在往复加载过程中推拉对称,结构总体处于安全状态。

可恢复功能装配式钢框架梁柱节点力学性能研究

装配式钢结构具有施工快、工期短、污染小的优点。基于此,提出一种由方钢管柱、H型钢梁、保险丝、高强螺栓和现浇楼板组成的可恢复功能装配式钢框架梁柱节点,并变换保险丝处梁间缝隙宽度、保险丝长细比和保险丝屈服强度三个参数,共建立了13个有限元模型进行分析。研究结果表明:保险丝能够实现损伤控制,保护主体结构免受损伤;保险丝处梁间缝隙宽度大于5mm时,可以保证梁段不发生碰撞,损伤集中在保险丝处,工程应用中建议采用10mm的缝隙宽度;保险丝长细比为43时,能够保证可恢复功能装配式钢框架梁柱节点具有足够的承载能力;当主体结构选用Q345B钢材时,保险丝宜采用Q235B钢材,以实现保险丝的损伤控制。

模块化钢框架模块间内套筒连接节点抗震性能试验研究

设计了3个足尺模块化钢框架模块间内套筒连接节点试件,针对节点试件的抗震性能开展了拟静力低周往复加载试验,研究了节点试件的滞回曲线、骨架曲线、延性、耗能、刚度退化、层间位移角和转动刚度等抗震性能指标,并对影响节点试件的抗震性能参数进行分析。研究结果表明:节点试件的滞回环呈梭形,且形状较为饱满,其具有较强的耗能能力;3个节点试件均出现明显的刚度退化现象且下降坡度平缓;3个节点试件的层间位移角分别为0.085 rad、0.082 rad和0.096 rad,节点试件均具有良好的转动能力和延性性能且满足节点抗震设计要求。试件破坏特征表明,在模块柱内梁的上、下翼缘对应位置设置内隔板对节点的抗震性能有显著改善作用。

分体式全灌浆套筒连接在装配式框架结构梁柱节点中的应用

装配式框架结构是国际上公认的最适合装配的结构形式之一,但由于传统的梁柱节点内梁筋连接方法存在诸多难点,一定程度上限制了装配式框架结构在国内的发展。介绍了一种适用于小空间梁柱节点内钢筋对接连接的新型分体式全灌浆套筒,并在装配式框架结构项目中进行了应用实践,总结了分体式全灌浆套筒连接应用过程中节点深化设计、构件生产及安装施工的要点等。项目实施结果表明,分体式全灌浆套筒连接可有效缩短所需的安装操作空间,可以实现构件标准化设计、方便构件生产、加快现场安装速度。

框架柱托换节点抗震性能研究

为了研究框架柱托换节点的抗震性能,设计了5个包裹式托换节点,进行往复加载试验,分析结合面高度和界面钢筋对托换节点破坏形态和抗震性能的影响。建立了托换节点的非线性数值计算模型,验证了数值计算模型的正确性。试验和分析结果表明:结合面高度对托换节点的抗震性能影响显著,结合面高度为200 mm时,界面钢筋影响托换节点的破坏模式,托换节点的初始刚度随着界面钢筋数量的增加而增大;结合面高度为300 mm时,界面钢筋对托换节点的抗震性能影响较小。