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.

Ductility demands on buckling-restrained braced frames under earthquake loading

Accurate estimates of ductility demands on buckling-restrained braced frames(BRBFs)are crucial to performance-based design of BRBFs.An analytical study on the seismic behavior of BRBFs has been conducted at the ATLSS Center,Lehigh University to prepare for an upcoming experimental program.The analysis program DRAIN-2DX was used to model a one-bay,four-story prototype BRBF including material and geometric nonlinearities.The buckling- restrained brace(BRB)model incorporates both isotropic and kinematic hardening.Nonlinear static pushover and time- history analyses were performed on the prototype BRBF.Performance objectives for the BRBs were defined and used to evaluate the time-history analysis results.Particular emphasis was placed on global ductility demands and ductility demands on the BRBs.These demands were compared with anticipated ductility capacities.The analysis results,along with results from similar previous studies,are used to evaluate the BRBF design provisions that have been recommended for codification in the United States.The results show that BRB maximum ductility demands can be as high as 20 to 25.These demands significantly exceed those anticipated by the BRBF recommended provisions.Results from the static pushover and time- history analyses are used to demonstrate why the ductility demands exceed those anticipated by the recommended provisions. The BRB qualification testing protocol contained in the BRBF recommended provisions is shown to be inadequate because it requires only a maximum ductility demand of at most 7.5.Modifications to the testing protocol are recommended.

Application of buckling-restrained braces in the seismic control of suspension bridges

Buckling-restrained braces(BRBs)are widely used to improve the seismic performance of buildings.This paper aims to introduce BRBs to suspension bridges and assess the seismic performance of bridges with BRBs.Taking the Dadu River Bridge as a case study,an FEA model of the bridge is established,and different seismic measures(BRBs between the deck and the tower,BRBs at the middle of the span to replace the inclined suspenders to connect the deck and the main cables,fluid viscous dampers(FVDs)between the deck and the tower,the combination of BRBs to replace the inclined suspenders as well as FVDs between the deck and the tower)are applied to the suspension bridge.The influence of the parameters of BRBs on the seismic response of the suspension bridge is studied,and the performance of the bridge with BRBs is compared with that of the bridge with FVDs.The results indicate that the use of BRBs in place of the inclined suspenders is beneficial to reduce the displacement of the deck and limit the shear force and bending moment of the tower.The seismic performance of the suspension bridge with BRBs and FVDs is better than that of the bridge with BRBs or FVDs.Therefore,the application of BRBs is a feasible method to improve the seismic performance of the suspension bridge.

Assessment of buckling-restrained braced frame reliability using an experimental limit-state model and stochastic dynamic analysis

Buckling-restrained braces （BRBs） have recently become popular in the United States for use as primary members of seismic lateral-force-resisting systems. A BRB is a steel brace that does not buckle in compression but instead yields in both tension and compression. Although design guidelines for BRB applications have been developed, systematic procedures for assessing performance and quantifying reliability are still needed. This paper presents an analytical framework for assessing buckling-restrained braced frame （BRBF） reliability when subjected to seismic loads. This framework efficiently quantifies the risk of BRB failure due to low-cycle fatigue fracture of the BRB core. The procedure includes a series of components that： （1） quantify BRB demand in terms of BRB core deformation histories generated through stochastic dynamic analyses; （2） quantify the limit-state of a BRB in terms of its remaining cumulative plastic ductility capacity based on an experimental database; and （3） evaluate the probability of BRB failure, given the quantified demand and capacity, through structural reliability analyses. Parametric studies were conducted to investigate the effects of the seismic load, and characteristics of the BRB and BRBF on the probability of brace failure. In addition, fragility curves （i.e., conditional probabilities of brace failure given ground shaking intensity parameters） were created by the proposed framework. While the framework presented in this paper is applied to the assessment of BRBFs, the modular nature of the framework components allows for application to other structural components and systems.

Stability Performance of Buckling-Restrained Brace with Brace Joints

The stability and ductility of four buckling-restrained braces (BRBs) with brace joints were studied. The load-carrying element of BRB was fabricated with steel (Chinese Q235), and a layer of colloidal silica sheet (0.5 mm in thickness) or four layers of plastic film (0.2 mm in thickness) were used as unbonding materials to provide space to prevent the buckling of inner core in higher modes and facilitate its lateral expansion in case of compression. Based on the equation of BRBs with brace joints of different restrained stiffnesses, the buckling load is calculated considering the initial geometric imperfections and residual stress, and the theoretical values agree well with the experiment results. It is concluded that the buckling load and ductility of BRBs are influenced greatly by the restrained stiffness of brace joints. If the restrained stiffness is deficient, the unstrained segment of BRBs with less stiffness will buckle firstly. As a result, the ultimate load of BRBs decreases, and the maximum compression load is reduced to about 65% of the maximum tension load; the stiffness also degenerates, and there is a long decreasing stage on the back-bone curve in compression phase; the ductility decreases, i.e., the ultimate tension ductility and ultimate compression ductility are approximately 15 and 1.3 respectively, and the cumulative plastic ductility is only approximately 200. If the restrained stiffness of joint is large enough, the stability will be improved as follows: the yielding strength and ultimate strength of BRBs are nearly the same, and there is an obvious strain intensification in both tension and compression phases; the ductility of brace also increases obviously, i.e., the ultimate tension ductility and ultimate compression ductility are both approximately 14, and the cumulative plastic ductility reaches 782.

Development and subassemblage cyclic testing of hybrid buckling-restrained steel braces

Buckling-restrained braced frames(BRBFs) are vulnerable to relatively higher post-earthquake residual drifts under high intensity ground shakings. This is primarily due to the low axial elastic and post-elastic stiffness of bucklingrestrained braces(BRBs) satisfying the design force demand requirements. In the present study, a hybrid buckling restrained bracing system consisting of a short yielding core length BRB component and a conventional buckling-type brace component connected in series has been developed with an aim to increase the axial stiffness of braces. This study is focused on the experimental investigation of six hybrid bucking restrained braces(HBRBs) to investigate their overall behavior, loadresisting capacity, strength-adjustment factors and energy dissipation potential. The main parameters varied are the crosssectional area, the yielding length of core elements as well as the detailing of buckling-restraining system of short yielding core length BRBs. Test results showed that the HBRBs with yielding core length in the range of 30% of work-point to workpoint lengths withstood an axial strain of 6% without any instability and can deliver stable and balanced hysteretic response and excellent energy dissipation under reversed cyclic loading conditions.

Experimental study of the pinned double rectangular tube assembled buckling-restrained brace

In this study, seven pinned double-rectangular tube assembled buckling-restrained brace （DRT-ABRB） specimens were experimentally charaeterised by means of an axial cyclic test. The core member of the specimens was a single flat-plate. Two rectangular tubes were assembled using high strength bolts to form an external restraining member. Each rectangular tube was composed of an external steel channel and a cover plate. A gap or thin rubber filler was set between the core and the external restraining member to form an unbonded layer. The influence of several design parameters on the failure mode and energy dissipation capacity of the ABRB was investigated, including the height of the core wing plate, thickness of the external cover plate, and height of the external channel flange. This experimental study demonstrated that a local pressure-bearing failure at the end of the external member arises when the external cover plate is too thin or if the end construction detail is unreasonable. When the end rotations of the DRT-ABRB were restricted, the hysteretic performance was shown to be superior to that of a pure pinned DRT-ABRB. Finally, all the tested DRT-ABRBs exhibited excellent energy dissipation performance which amply satisfied existing regulation requirements.

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.

Effect of Variable Concrete Strength on the Behavior of Buckling Restrained Braced Frames under Blast Load

BRBF(buckling restrained braced frame)is a relatively new lateral force resisting system for building structures.BRBFs are used mostly to resist seismic force due to their high ductility after yielding and the ability to absorb higher strain energy.ASCE(American Society of Civil Engineers)first permits the use of BRBFs as a single seismic force-resisting system by quantifying the seismic parameters such as response modification coefficient(R),over-strength factor(Ωo)and deflection amplification factor(Cd)for a structure built with BRBF,in their 2010 code(ASCE 7-10).But it has not been investigated how a structure built with BRBF,which is primarily designed to resist seismic force,and behaves under sudden occurrence of a blast load.This research investigates the performance of a BRBF subjected to blast loading.In other words,this paper focuses on the effect of blast loading on BRBF.The architype for this investigation is a chevron type braced frame.The frame is subjected to a short duration blast load that lasts only 21.7 mili-second(ms).Blast loading effects on the braced frame are assessed by identifying the weakest plane of failure,deformation characteristics and out of plane bending.The research investigates how the properties of the surrounding concrete,especially compressive strength,affect the overall strength of the BRBF on resisting blast loading.It is observed that the compressive strength of the surrounding concrete plays a significant role in reducing the deformation characteristics,both in-plane and out-of-plane.

滑移螺杆连接的BRB-RC框架节点抗震性能试验研究

为减小大震下防屈曲支撑(BRB)钢筋混凝土(RC)框架节点开合效应对子结构抗震性能的不利影响,提出一种滑移螺杆连接方法,通过对预埋螺杆和锚板表面进行无黏结处理,减小节点板对RC子结构梁柱变形的切向约束,从而将BRB轴力以抗拉不抗剪的方式有效传递至RC子结构。对2个滑移节点板连接和1个传统节点板连接的BRB-RC梁柱组合件进行拟静力试验,以验证滑移螺杆连接的有效性。试验结果表明,与传统焊接节点连接相比,滑移螺杆连接性能更加稳定,简化了子结构梁柱的受力状态。当层间位移角为2%时,子结构梁剪力和累积耗能降低幅度分别可达37.6%和29%,有效减轻了子结构损伤。

地震与风作用下钢框架-自复位支撑筒结构损伤分析

为揭示地震‐风同时作用和先后作用下自复位支撑结构的损伤分布规律,对一50层钢框架‐自复位支撑筒在不同强度地震动与50年重现期风荷载下的梁/柱构件和结构整体损伤进行分析。结果表明,地震单独作用和地震‐风同时作用下,支撑筒梁均比外框架梁先受损,支撑筒柱较外框架柱损伤发展更快;地震‐风同时作用增大了柱的损伤程度,使31层柱的最大损伤值增大了78.6%;随着地震动强度的增大,风荷载作用对结构整体损伤的加重程度逐渐增大。在不同强度的地震动与50年重现期风荷载先后作用下,风荷载增大了震损结构的最大残余变形角均值;当峰值地面加速度为10 m/s2时,风荷载使震损结构的最大残余变形角均值由0.325%增至0.330%,但风荷载对震损结构损伤最大构件的损伤状态影响不大。

Seismic performance of a reinforced concrete building retrofitted with self-centering shape memory alloy braces

Self-centering earthquake-resistant structures have received increased attention due to their ability to reduce post-earthquake residual deformations and,thus,repair time and cost.This stimulated the development of recentering shape memory alloy(SMA)dampers that use superelastic nitinol wires to dissipate energy and self-center the structure.However,there are still a few case studies applications on full-scale RC buildings in the literature.Moreover,general guidelines or even simplified approaches for the practical design of SMA damped braces are still lacking.This paper focuses on evaluating the effect of using self-centering shape memory alloy dampers for buckling-restrained braces applied for the seismic retrofit of a complex RC building structure.A design method originally proposed for elastoplastic dampers was implemented to size the SMA dampers to be placed on selected spans and stories of a building.The effectiveness of the design procedure was demonstrated by nonlinear time-history analyses under different sets of earthquake strong ground motions.The analysis results show that the recentering shape memory alloy bracing system is effective in limiting the maximum transient inter-story drifts and reducing the residual inter-story drifts after strong seismic events,due to its excellent recentering behavior together with its not negligible energy dissipation capacity.

冷弯型钢剪切耗能框架-K形支撑结构抗震性能研究

为提升冷弯型钢结构抗震性能,推动多层冷弯型钢结构的发展,该文提出了冷弯型钢剪切耗能框架-K形支撑结构体系。共设计2个足尺单层单跨框架试件进行拟静力试验研究,通过变化耗能板宽厚比,得到试件的抗震性能指标并进行评估。同时,为了考察蒙皮效应的影响,在ABAQUS中对上述2个试件双面覆12 mm厚石膏板并对其滞回性能进行研究。此外,还建立多层冷弯型钢剪切耗能框架-K形支撑结构体系模型并对其进行弹塑性动力时程分析。试验及有限元分析结果表明:该结构滞回曲线饱满,在层间位移角达到2%以前,损伤主要集中在耗能板上,并依靠耗能板的滞回塑性变形耗能。双面覆石膏板之后,结构的极限承载力及抗侧刚度有所提高,但是不会影响结构的破坏模式。与冷弯型钢-钢板剪力墙结构相比,该文提出的新型结构在地震作用下各层层间位移角均明显减小,在8度罕遇地震作用下,结构横、纵向层间位移角减小幅度分别为43.29%和46.25%。

节段预制波形钢腹板组合箱梁桥节段 存放及吊装方案的优化设计

为了优化节段预制波形钢腹板组合箱梁桥节段划分、存放及吊装方案,以南京长江五桥引桥——立新路跨线桥为研究背景,采用数值模拟方法对波形钢腹板组合箱梁桥节段进行合理划分长度,分析标准节段梁存放及吊装期的应力变化及变形特征,并提出合理的控制措施.结果表明:节段长度为240~400 cm时,对梁体抗弯承载力影响较小,波形钢腹板组合箱梁桥节段长度的合理划分取决于吊装及运输条件;节段梁存放层数不宜超过2层,如采用双层存放,需在波形钢腹板节段梁混凝土顶板与底板之间设置临时刚性支撑;节段梁吊装宜采用四吊点方案,即在靠近腹板处设置4个吊点,且起吊时在顶板与底板之间设置临时刚性支撑,以避免顶板变形过大,增加现场拼装控制的难度.

轻质墙板对钢管组合异形柱框架结构自振特性影响分析

为合理考虑轻质墙板刚度对钢框架整体结构自振特性的影响,提出了一种对角弹簧斜撑简化模型。推导了对角弹簧刚度与墙板刚度贡献的换算关系;采用有限元精细分析方法,对比了墙板刚度简化模型和实体模型的分析结果,验证了简化模型的可靠性。利用对角弹簧斜撑简化方法考虑内嵌墙板刚度的影响,对内嵌轻质墙板的方钢管混凝土组合异形柱(SCFST柱)框架算例进行了结构自振特性分析,研究了墙板填充率、墙板布置对整体结构自振特性的影响。结果表明:考虑轻质墙板的刚度贡献,周期折减系数取值为0.85~1.00,设计中可按墙板填充率在该区间线性插值得到合理的周期折减系数。结构平动振型的周期折减主要与平动方向上的墙板填充率有关;扭转振型的周期折减不仅与墙板填充率有关,也受墙板布置的影响。

Clinical evaluation of endoscopic biliary stenting in treatment of malignant obstructive jaundice

BACKGROUND Malignant obstructive jaundice(MOJ)is characterized by the presence of malignant tumors infiltrating or compressing the bile duct,causing poor bile drainage,generalized yellowing,pain,itching,and malaise.MOJ is burdensome for both the society and the families of affected patients and should be taken seriously.AIM To evaluate the clinical effect of stent placement during endoscopic retrograde cholangiopancreatography for relieving MOJ and the efficacy of percutaneous transhepatic biliary drainage in terms of liver function improvement,complication rates,and long-term patient outcomes.METHODS The clinical data of 59 patients with MOJ who were admitted to our hospital between March 2018 and August 2019 were retrospectively analyzed.According to the treatment method,the patients were divided into an observation group(29 patients)and a control group(30 patients).General data,liver function indices,complications,adverse effects,and 3-year survival rates after different surgical treatments were recorded for the two groups.RESULTS There were no significant differences in baseline information(sex,age,tumor type,or tumor diameter)between the two groups(P>0.05).Alanine aminotransferase,aspartate aminotransferase,and total bilirubin levels were significantly better in both groups after surgery than before surgery(P<0.05).The overall incidence of biliary bleeding,gastrointestinal bleeding,pancreatitis,and cholangitis was 6.9%in the observation group and 30%in the control group(P<0.05).No significant differences in the rates of blood transfusion,intensive care unit admission,or death within 3 years were observed between the two groups at the 1-month follow-up(P>0.05).The 3-year survival rates were 46.06%and 39.71%in the observation and control groups,respectively.CONCLUSION Endoscopic biliary stenting effectively relieves MOJ and significantly improves liver function,with minimal complications.This technique is a promising palliative approach for patients ineligible for radical surgery.However,further research is needed to optimize current treatment strategies and to explore their potential in treating nonmalignant cases of obstructive jaundice.

高压开关柜手车安全移位装置设计与试验

目前在变电所中,高压开关柜手车转修过程都是采用人工进行作业,但高压开关柜手车重心偏高、偏前,存在倾倒的危险,极易造成设备损坏甚至威胁人身安全,而且人工作业成本高,安全系数低。因此,设计了一款移位装置,使得开关柜手车能通过设置的固定斜面轨道依附在移位装置上,凭借移位装置得到稳定的牵引力、强大的支撑力,平稳移出落地,完成整个移位作业。该装置降低了运维人员劳动强度,保障了人身安全和提高了工作效率。

关节镜下改良双束修复前交叉韧带Sherman Ⅰ型损伤

背景:前交叉韧带重建术后产生的腘绳肌肌力减弱、髌前区疼痛、重建后较高的骨关节炎发生率及本体感觉丧失等问题导致术后功能恢复不佳;前交叉韧带关节镜下修补结合动态或静态增强修补,保留了原有韧带结构,并取得了良好的近期疗效。目的:观察关节镜下改良双束修复前交叉韧带Sherman Ⅰ型损伤的功能疗效及影像学表现。方法:选择2020年1月至2022年9月在佛山市中医院运动医学科就诊的前交叉韧带损伤患者60例,根据治疗方案分为2组,每组30例,修复组采用双束修补结合内支架固定,重建组采用自体腘绳肌单束解剖重建。术后所有病例随访12个月,分别于术后3,6,12个月评估两组患者国际膝关节评分委员会评分、Lysholm评分及KT-1000患侧-健侧差值。结果与结论:①术后3个月,两组患者的国际膝关节评分委员会评分、Lysholm评分及KT-1000患侧-健侧差值比较差异均有显著性意义(P<0.05),术后功能修复组优于重建组;②术后6,12个月,两组患者的国际膝关节评分委员会评分、Lysholm评分及KT-1000患侧-健侧差值比较差异无显著性意义(P>0.05);③结果表明,前交叉韧带修复保留了原有韧带结构,避免了因重建钻取较大的骨髓道及自体肌腱取出,可减少对原有正常结构的损伤,并发症少,术后早期疗效优于前交叉韧带保残重建,但术后6个月之后两组疗效无明显差异。

Damping characteristics of friction damped braced frame and its effectiveness in the mega-sub controlled structure system

Based on energy dissipation and structural control principle, a new structural configuration, called the megasub controlled structure （MSCS） with friction damped braces （FDBs）, is first presented. Meanwhile, to calculate the damping coefficient in the slipping state a new analytical method is proposed. The damping characteristics of one-storey friction damped braced frame （FDBF） are investigated, and the influence of the structural parameters on the energy dissipation and the practical engineering design are discussed. The nonlinear dynamic equations and the analytical model of the MSCS with FDBs are established. Three building structures with different structural configurations, which were designed with reference to the conventional mega-sub structures such as used in Tokyo City Hall, are comparatively investigated. The results illustrate that the structure presented in the paper has excellent dynamic properties and satisfactory control effectiveness.

超高层建筑中高支模关键施工技术的应用研究

本文针对超高层建筑中高支模关键施工技术的应用进行深入研究,在阐述超高层建筑中高支模施工技术特性的基础上,以某超高层建筑为实例,通过分析其工程概况与施工难点,详细阐述高支模施工技术在构造设置、剪刀撑设置、混凝土浇筑及支撑体系拆除等关键环节的应用。结果显示,施工过程安全有序,支撑体系稳定性强,混凝土浇筑质量良好,拆除工作顺利且未损伤结构,工程进度提前,表明合理运用该技术可保障超高层建筑高支模施工的质量、安全与进度,为类似工程提供重要技术参考。