Experimental and numerical study of buckling-restrained braces configured with out-of-plane eccentricity under cyclic loading

This study focuses on variations in the hysteretic behavior of buckling-restrained braces(BRBs)configured with or without out-of-plane eccentricity under cyclic loading.Quasi-static experiments and numerical simulations were carried out on concentrically and eccentrically loaded BRB specimens to investigate the mechanical properties,energy dissipation performance,stress distribution,and high-order deformation pattern.The experimental and numerical results showed that compared to the concentrically loaded BRBs,the stiffness,yield force,cumulated plastic ductility(CPD)coefficient,equivalent viscous damping coefficient and energy dissipation decreased,and the yield displacement and compression strength adjustment factor increased for the eccentrically loaded BRBs.With the existence of the out-of-plane eccentricity,the initial yield position changes from the yield segment to the junction between the yield segment and transition segment under a tensile load,while the initial high-order buckling pattern changes from a first-order C-shape to a secondorder S-shape under a compressive load.

Deterministic and probabilistic analysis of great-depth braced excavations:A 32 m excavation case study in Paris

The Fort d’Issy-Vanves-Clamart(FIVC)braced excavation in France is analyzed to provide insights into the geotechnical serviceability assessment of excavations at great depth within deterministic and probabilistic frameworks.The FIVC excavation is excavated at 32 m below the ground surface in Parisian sedimentary basin and a plane-strain finite element analysis is implemented to examine the wall deflections and ground surface settlements.A stochastic finite element method based on the polynomial chaos Kriging metamodel(MSFEM)is then proposed for the probabilistic analyses.Comparisons with field measurements and former studies are carried out.Several academic cases are then conducted to investigate the great-depth excavation stability regarding the maximum horizontal wall deflection and maximum ground surface settlement.The results indicate that the proposed MSFEM is effective for probabilistic analyses and can provide useful insights for the excavation design and construction.A sensitivity analysis for seven considered random parameters is then implemented.The soil friction angle at the excavation bottom layer is the most significant one for design.The soil-wall interaction effects on the excavation stability are also given.

The wave and vibratory power transmission in a finite L-shaped Mindlin plate with two simply supported opposite edges

In this paper,wave and vibratory power transmission in a finite L-shaped Mindlin plate with two simply supported opposite edges are investigated using the wave approach.The dynamic responses,active and reactive power flow in the finite plate are calculated by the Mindlin plate theory （MPT） and classic plate theory （CPT）.To satisfy the boundary conditions and continuous conditions at the coupled junction of the finite L-shaped plate,the near-field and far-field waves are entirely contained in the wave approach.The in-plane longitudinal and shear waves are also considered.The results indicate that the vibratory power flow based on the MPT is different from that based on the CPT not only at high frequencies but also at low and medium frequencies.The influence of the plate thickness on the vibrational power flow is investigated.From the results it is seen that the shear and rotary inertia correction of the MPT can influence the active and reactive power at the junction of the L-shaped plate not only at high frequencies but also at low and medium frequencies.Furthermore,the effects of structural damping on the active and reactive power flow at the junction are also analyzed.

Axial Compression Behavior and Analytical Method of L-Shaped Column Composed of Concrete-Filled Square Steel Tubes

Based on the characteristics of an L-shaped column composed of concrete-filled square steel tubes, the axial compression experiment and nonlinear finite element analysis were carried out to study the mechanical property of the L-shaped column. The load-displacement curve for the L-shaped column, the deflection and load-strain curves for the mono columns were obtained by the axial compression experiment. The results show that the L-shaped column exhibits a flexural-torsional buckling failure mode. The numerical simulation by the finite element analysis shows that the bearing capacity and failure mode are in accordance with those of the axial compression experiment and the feasi- bility of the finite element analysis is proved. For the calculation of the bearing capacity of the L-shaped column com- posed of concrete-filled square steel tubes, an analytical method is proposed based on the theory of the elastic stability and spatial truss model. The results of the analytical method are in good agreement with those of the axial compression experiment and the finite element analysis.

Research on vibration characteristics of L-shaped plate using a mobility power flow approach

L-shaped plates have become an important focuses in structural vibration research. To determine their vibration characteristics, this paper applied a mobility power flow method. Firstly, the L-shaped plate was divided into two substructures to simplify analysis. The coupled bending moment was then deduced by applying a continuous vibration property on the common edge. Next, the response on any point of the plate and the input and transmitted power flow formulas were calculated. Numerical simulations showed the distribution of the coupled bending moment and the response of the whole structure. The validity of this method was verified by the SEA approach.

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.

Laboratory test on the combined cooling effect of L-shaped thermosyphons and thermal insulation on high-grade roadway construction in permafrost regions

With the completion of the Qinghai-Tibetan Railway,economic development of related areas has been greatly accelerated.This,in return,calls for building or upgrading more roadways,especially high-grade roadways.In cold regions,the thawing of permafrost can induce settlement damage of and even failure to railway (or roadway) embankments.Thermosyphons (self-powered refrigera-tion devices that are used to help keep the permafrost cool) have proved effective in mitigating thaw settlement by maintaining the thermal stability of the embankments.However,for high-grade roadway embankments of great width,stabilizing or cooling ef-fects of traditional geotechnological measures may be limited.To enhance the cooling effect of thermosyphons,an L-shaped thermosyphon was designed.A laboratory test was carried out to study the combined cooling effect of the L-shaped thermosyphon and thermal insulation applying to roadbed construction.The angle between the evaporator and condenser sections of the L-shaped thermosyphon is 134 degrees,and the L-shaped thermosyphon was inserted into the soil at an angle of 5 degrees with the road surface.The tested results show that the L-shaped thermosyphon is effective in removing heat from a roadway in winter.When the ambient air temperature is lower than the soil temperature,the thermosyphon is active and extracts the heat in the soil around it.When the ambient air temperature is higher than the soil temperature,the thermosyphon is inactive,and no heat is in-jected into the soil through the L-shaped thermosyphon.Compared to embankments with straight thermosyphons,the inner parts of the embankments with L-shaped thermosyphons were significantly cooled.It is hoped that the present study would be useful to the application of L-shaped thermosyphons in the construction of high-grade roadways in cold regions.

Test on mechanical behavior of SRC L-shaped columns under combined torsion and bending moment

Investigations of the seismic behavior of steel reinforced concrete L-shaped columns under constant axial compression and cycled bending-shear-torsion load were performed.Six specimens,which considered two parameters,i.e.,the moment ratio of torsion to bending(γ)and the aspect ratio(column length-to-depth ratio,φ),were prepared for the experiment.In this study,the failure process,torsion-displacement hysteresis curves,and flexure-displacement hysteresis curves were obtained.The failure characteristics,mechanical behavior of specimens such as the failure patterns,hysteresis curves,rigidity degradation,ductility and energy dissipation,are analyzed.The experimental research indicated that the major failures of the specimens were bending failure,bending-shear failure and bending-torsion failure as the moment ratio of torsion to bending(γ)increased.The torsion-displacement hysteresis curves were pinched in the middle,formed a slip platform,and the phenomenon of“load drop”occurred after the peak load.The bending-displacement hysteresis curves were plump,which showed that bending capacity of the specimen was better than its torsion capacity.Additionally,the energy dissipation of the specimen was dominated by torsion in the early stage and ultimately governed by the bending moment in the later phase.Test results also indicated that the displacement ductility coefficient and interstory rotation angle of the failure point were less than 3.0 and 1/50,respectively,which means the test specimen performance does not meet the requirement of the Chinese Code for Seismic Design of Buildings(GB 50011-2014)in this respect.

Bandwidth Numerical Analysis of Triangular Patch Antenna Fed by L-Shaped Probe

A single layer triangular patch antenna fed by an L-shaped probe was investigated numerically by using FDTD (Finite Difference Time Domain) method. It achieves >40% impedance bandwidth (VSWR<2) and stable radiation pattern across the passband. The triangular patch antenna with two orientations of L-shaped probe has almost the same characteristics, such as impedance bandwidth and radiation pattern. The bandwidth vs feeding position was also investigated, the broadband characteristic can be observed when the feeding position is only in a small segment along the centerline.

The Effects of Cross Sectional Dimensions on the Behavior of L-Shaped RC Structural Members

The behavior of L-Shaped RC （reinforced concrete） shear walls was investigated in the Erciyes University Earthquake Investigation Laboratory under the influence of constant axial load together with reversed cyclic lateral load. The objective of this study was to evaluate the effects of cross sectional dimensions on the behavior of L-shaped structural members and to assess their earthquake performance. In order to investigate L-shaped RC structural members, the special experiment setup and four type of 1/2 scaled specimens which have different aspect ratio were constructed. The specimens were loaded in line with the major principal axes direction laterally. Axial load ratio was 0.1 and cross section height to thickness ratios were＇ 3：1, 5：1, 8：1, 10：1. Cross section thickness was 120 mm which corresponds to （360：120）, （600：120）, （960：120）, （1,200：120） wall legs cross sectional dimensions in mm. The specimens height was 1,500 mm, together with upper and lower slabs overall height was 2,000 mm. Concrete compression strength was 30 N/mm2, steel yield stress 420 N/mm2 and vertical reinforcement ratio was 1% for all specimens. According to the test results, the specimen of which the aspect ratio is 3 （360：120） has shown column behavior, the specimen of which the aspect ratio is 5 （600：120） has shown slender wall behavior and last two specimens of which the aspect ratios are 8 （960：120） and 10 （1,200：120） have shown squat wall behavior. When considering the cracking patterns and hysteretic behavior, since the aspect ratio 8, the specimens show flexure-shear interaction behavior and prone to brittle failure.

Multicut L-Shaped Algorithm for Stochastic Convex Programming with Fuzzy Probability Distribution

Two-stage problem of stochastic convex programming with fuzzy probability distribution is studied in this paper. Multicut L-shaped algorithm is proposed to solve the problem based on the fuzzy cutting and the minimax rule. Theorem of the convergence for the algorithm is proved. Finally, a numerical example about two-stage convex recourse problem shows the essential character and the efficiency.

Internal brace与带线锚钉通过改良Broström术治疗慢性踝关节不稳的疗效对比

目的比较internal brace(IB)与带线锚钉通过改良Broström术治疗慢性踝关节不稳的临床疗效。方法回顾性分析2019年5月至2022年2月在桂林市人民医院本院关节骨科行手术治疗的42例慢性踝关节外侧不稳患者资料,根据距腓前韧带修补所用材料的不同将患者分为IB组(19例)和带线锚钉组(23例)。比较两组患者一般资料、手术时间、并发症发生率、术后完全负重行走时间、术后恢复跑步的时间、美国足踝外科协会(American Orthopedic Foot and Ankle Society,AOFAS)踝-后足功能评分、视觉模拟评分法(visual analog scale,VAS)评分。结果所有患者术后均获得随访,随访时间12~18个月,平均(13.8±5.3)个月。两组患者基线资料差异无统计学意义(P>0.05);两组各有1例术口拆线后再出现渗液,换药后愈合;两组各有2例术口区域感觉障碍,除IB组有1例术后半年仍未完全恢复外,其余3例术后2~3个月恢复;IB组患者术后6周随访时AOFAS评分优于带线锚钉组,差异有统计学意义(t=2.239,P=0.025),但术后6周时VAS评分比较差异无统计学意义(t=0.308,P=0.760);末次随访时AOFAS评分和VAS评分比较,两组之间差异无统计学意义(t=0.045,P=0.965;t=0.203,P=0.840);IB组术后完全负重行走时间、术后恢复跑步的时间显著早于带线锚钉组,差异有统计学意义(t=26.566,P<0.01;t=4.838,P<0.01)。结论IB与带线锚钉通过改良Broström术开放治疗慢性踝关节不稳的临床疗效满意,且使用IB在早期康复和重返运动方面优于带线锚钉。

一类brace中的thin边

证明若一个brace含有一个四圈C_(4),且该四圈中包含两个相邻的三度点,则该brace至少有一条thin边在该C_(4)中.

Internal-Brace联合改良的Brostrom术治疗慢性踝关节外侧不稳的疗效

目的评价Internal-Brace联合改良的Brostrom术治疗慢性踝关节外侧不稳的疗效。方法回顾性分析陆军第八十一集团军医院骨科2019-01至2021-12收治的29例慢性踝关节外侧不稳患者,全部行Internal-Brace联合改良的Brostrom术,采用美国足踝外科协会(AOFAS)踝-后足评分系统,前抽屉试验,Karlsson-Peterson评分系统进行手术效果评价,采用视觉模拟评分法(VAS)评价手术前、后踝部疼痛。结果所有患者均获得随访,其中28例末次随访时均能完成3 km跑等训练任务,基本恢复伤前训练水平,1例术后3 d出现切口感染,感染率3.4%;28例AOFAS评分由手术前(34.7±7.4)分提高到末次随访时的(86.6±3.3)分,差异有统计学意义(P<0.01),所有患者术后前抽屉试验阴性,Karlsson-Peterson评分由术前(62.4±9.5)分提高到末次随访时的(92.6±4.5)分,差异有统计学意义(P<0.01),VAS评分由术前(7.1±0.7)分降低到末次随访时的(2.3±0.8)分,差异有统计学意义(P<0.01)。结论Internal-Brace联合改良的Brostrom术治疗慢性踝关节外侧不稳效果显著,能明显改善患者踝关节功能。

耐张型悬索支撑输电结构风振非线性有限元分析

耐张型悬索支撑输电结构是一类适用于山地地形的新型输电结构,其主要受风荷载控制。为此,该研究发展了该输电结构风振非线性有限元分析模型并开展了结构风振响应分析。考虑结构的几何非线性,通过单元应变能与位移的关系推导了支撑悬索和输电线的三维杆单元切线刚度矩阵;给出了支撑悬索和输电线的单元质量矩阵、阻尼矩阵以及由风荷载等效而得的单元节点荷载向量;基于非线性有限元理论,建立了耐张型悬索支撑输电结构风振非线性动力方程,并采用了结合Newton-Raphson迭代法的Newmark-β法求解非线性动力方程;通过所建立的动力学分析模型对两跨耐张型悬索支撑输电结构进行了风致非线性振动分析。算例分析结果表明:①提出的模型具有较好的计算精度和较高的计算效率;②悬索支撑导线部分的低阶固有频率比悬索支撑地线部分的低阶固有频率更低;③该输电结构的输电线位移响应受风荷载影响较大;④输电线侧向位移和支撑悬索张力受风速和风向角影响均较显著。

新型GFRP-钢屈曲约束支撑设计与受力性能分析

为发展轻质、耐腐蚀的屈曲约束支撑,以玻璃纤维(GFRP)拉挤型材和缠绕工艺构造支撑约束构件,H型钢为内芯,提出一种新型GFRP-钢屈曲约束支撑.通过理论分析与数值模拟,探究了支撑内芯的屈曲模态发展规律;结合GFRP的各向异性和层合板结构特性,建立了GFRP约束构件的设计参数计算公式;分析了支撑间厚比、翼缘和腹板宽厚比及纤维角度对GFRP约束构件与内芯相互作用特征的影响规律,并给出了合理取值;通过算例分析,验证了该设计方法的可靠性.结果表明:H型钢内芯依次发生翼缘局部屈曲、绕弱轴整体屈曲、腹板局部屈曲和绕强轴整体屈曲,且整体屈曲模态较低,而局部屈曲模态较高;间厚比和宽厚比均会影响内芯的屈曲模态发展,进而改变约束构件的受力状态,间厚比宜为0.125 0~0.50,宽厚比宜小于6.29;GFRP约束构件主应力方向接近45°,为充分发挥纤维纵向承载能力,纤维宜按45°相互垂直交叉布置.

钢框架-偏心支撑结构消能梁暗置侧向支撑设计

在钢框架-偏心支撑结构中,针对钢结构住宅等建筑中不能接受常规消能梁侧向支撑的情况,设计了一种在消能梁段端部的楼板内设置型钢连接件及暗梁组成的暗置侧向支撑。有限元模拟分析表明,在规范规定的消能梁段下翼缘侧向水平荷载的作用下,该消能梁暗置侧向支撑能显著减小消能梁的扭转变形和侧向弯曲变形;在考虑消能梁上局部楼板失效的情况下,暗置侧向支撑也能提供消能梁合适的扭转约束刚度。通过某工程的原位静荷载试验,验证了该暗置支撑对消能梁发挥的预期侧向支撑作用。

附加消能子结构在抗震加固工程中的应用

介绍了消能子结构的研究现状,文中以某小学教学楼抗震加固工程为例,阐述了采用附加消能子结构配合屈曲约束支撑进行抗震加固的设计过程,采用阵型分解反应谱法和时程分析法分析并对比了加固前后结构的抗震性能变化,基于现有研究成果,进行了消能子结构的加固设计和罕遇地震作用下的承载力复核。结果表明:采用附加消能子结构对结构进行抗震加固,在提高建筑抗震性能的同时,可以不影响建筑内部功能。加固后,结构整体刚度增加,自振周期变短,层间剪力增大,整体变形变小,结构的整体受力状态和变形模式得到改善,房屋整体抗震性能提升。罕遇地震作用下,结构整体塑性程度较低,损伤屈服机制更加合理,可以实现“大震不倒”的设防目标。消能子结构为连接消能器和主体结构的关键构件,应重点进行设计,采用柱的N-M曲线进行承载力复核比较便捷。文中设计思路可为类似工程提供借鉴和参考。

集中荷载作用下弹性支撑矩形钢管混凝土翼缘工字形梁稳定性能研究

为研究弹性支撑刚度对矩形钢管混凝土翼缘工字形梁稳定性能的影响,开展了集中荷载作用下3根带有不同弹性支撑刚度的矩形钢管混凝土翼缘工字形梁的稳定性能试验,研究试验梁的位移及应变的变化规律,获得梁的失稳形式和稳定承载力。试验结果表明,整个加载破坏过程分为三个阶段,即弹性阶段、弹塑性阶段和破坏阶段,3根试验梁均发生整体弯扭屈曲失稳。随着弹性支撑刚度增加,梁稳定承载力增大,验证了设置弹性支撑可有效地提高该梁的稳定承载力。在试验基础上,利用ANSYS有限元软件对该梁进行非线性屈曲分析,将获得的稳定承载力与试验结果进行对比,误差均小于5%,从而验证有限元分析方法的正确性。最后,研究了混凝土强度、上翼缘含钢率和腹板高厚比等参数对该类梁稳定性能的影响规律。研究表明,增大上翼缘钢管含钢率和减小腹板高厚比均可明显提高该类梁的稳定承载力,而增强混凝土强度对梁的稳定承载力提高较小。

单边螺栓连接中心支撑钢框架抗震性能分析

目的为研究支撑-半刚接钢框架结构体系的抗震性能,方法设计了一榀由嵌套式单边螺栓与T型钢构成的半刚性梁柱节点的中心支撑钢框架,并进行了拟静力试验与有限元数值模拟,通过观测整个试验现象,分析了其滞回、承载力、刚度退化、耗能等抗震指标。结果结果表明:试件破坏过程明显经历了弹性段、塑性段、破坏段三个阶段,试件破坏模式主要为支撑受压失稳破坏,塑性变形主要累积在支撑体系上,整体呈现延性破坏特征;支撑断裂后,梁柱及T型钢节点无明显塑性变形,钢框架仍具有较高的安全储备,符合“强节点、弱构件”设计原则,表明了结构具有两道抗震防线;结论支撑与半刚接钢框架协同工作使得试件具有较高的抗侧刚度抵抗水平变形,且承载力较高、滞回性能稳定、耗能能力优良;单边螺栓在试验过程中的受力性能较普通高强螺栓并无较大差别,未出现严重的预紧力松弛现象,并能高效的保持螺栓预紧力。通过有限元数值模拟分析可知,减小支撑长细比,虽能有效提高结构的抗震性能,但长细比较小会导致支撑刚度增大,加速其余构件的损坏。故应以考虑结构的延性为前提,降低支撑的长细比,才能有效提高结构的抗震性能。