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.

Strength Analysis on Brace Structure for Semi-Submersible in Consideration of Wave Slamming

Slamming on bracings of column stabilized units shall be considered as a possible limiting criterion under transit condition based on the requirements in DNV-OS-C103. However, the wave slamming loads under survival condition were ignored for the strength analysis of the brace structures in many semi-submersible projects. In this paper, a method of strength analysis of brace structure is proposed based on the reconstruction and extrapolation of numerical model. The full-scale mooring system, the wind, wave and current loads can be considered simultaneously. Firstly,the model tests of the semi-submersible platform in wind tunnel and wave tanker have been carried out. Secondly,the numerical models of the platform are reconstructed and extrapolated based on the results of model tests. Then, a nonlinear numerical analysis has been conducted to study the wave slamming load on brace in semi-submersible platform through the reconstructed and extrapolated numerical model. For the randomness of wave load, ten subcases under each condition have been carried out. The value of the 90% Gumble distribution values of the ten subcases are used. Finally, the strength on brace structure has been analyzed considering the wave slamming. The wave slamming loads have been compared between the survival condition and transit condition with the method. The results indicate that wave slamming under survival condition is more critical than that under transit condition.Meanwhile, the wave slamming is significant to the structural strength of the brace. It should be overall considered in the strength analysis of the brace structure.

Determination Method on Initial Pretension of Cables in Steel Mega Frame and Prestressed Composite Bracing Structure

Determining initial pretension values of pre-stressed cables is one of the key problems for a steel mega frame and pre-stressed composite bracing structure.Through the mechanical analysis of the composite bracing under vertical loading,the critical factors deciding the initial pretention value were found.According to these factors,a rule for the initial pretension value was put forward.The determination equations were acquired based on the principle of force equilibrium at nodes.The numerical results indicate that the internal force disequilibrium in composite bracings resulted from symmetrical load can be eliminated only in a symmetrical way,so that initial pretention values are decided only by vertical loads.The influencing coefficient leveling method,taking into account interactions between story and story,is accurate and feasible.

Seismic performance and resilience of composite damping self-centering braced frame structures

A magnetorheological self-centering brace(MR–SCB)has been proposed to improve the energy dissipation capability of the brace.In this paper,a 15-story MR–SCB braced frame is numerically analyzed to examine its seismic performance and resilience.The MR–SCB provides higher lateral stiffness than the buckling restrained brace and greater energy dissipation capability than the existing self-centering brace.The brace also exhibits a reliable recentering capacity.Under rare earthquakes,the maximum average residual deformation ratio of the structure is less than the 0.5%limit.Under mega earthquakes,the maximum average interstory drift ratio of the structure does not exceed the 2.0%elastoplastic limit,and its maximum average floor acceleration ratio is 1.57.The effects of mainshock and aftershock on the structural behavior are also investigated.The interstory drift and residual deformation of the structure increase with the increase of the intensity of the aftershock.Under aftershocks with the same intensity as the mainshocks,the maximum increment of the residual deformation ratio of the structure is 81.8%,and the average interstory drift ratios of the 12^(th),7^(th),and 3^(rd)stories of the structure are increased by 13.4%,9.2%and 7.5%,respectively.The strong aftershock may significantly cause increased damage to the structure,and increase its collapse risk and residual deformation.

Seismic behavior of concrete filled steel tubular arch structures

Shaking table tests of a 1:10 scale arch model performed to investigate the seismic behavior and resistance of concrete filled steel tubular (CFT) arch structures are described in this paper. The El-Centro record and Shanghai artificial wave were adopted as the input excitation. The entire test process can be divided into three stages depending on the lateral brace configurations, i.e., fully (five) braced, two braces removed, and all braces removed. A total of 46 tests, starting from the elastic state to failure condition, have been conducted. The natural vibration frequencies, responses of acceleration, displacement and strain were measured. From the test results, it is demonstrated that the CFT arch structures are capable of resisting severe ground motions and that CFT arches offer a credible alternative to reinforced concrete arches, especially in regions of high seismic intensity.

Design of controlled elastic and inelastic structures

One of the founders of structural control theory and its application in civil engineering, Professor Emeritus Tsu T. Soong, envisioned the development of the integral design of structures protected by active control devices. Most of his disciples and colleagues continuously attempted to develop procedures to achieve such integral control. In his recent papers published jointly with some of the authors of this paper, Professor Soong developed design procedures for the entire structure using a design - redesign procedure applied to elastic systems. Such a procedure was developed as an extension of other work by his disciples. This paper summarizes some recent techniques that use traditional active control algorithms to derive the most suitable （optimal, stable） control force, which could then be implemented with a combination of active, passive and semi-active devices through a simple match or more sophisticated optimal procedures. Alternative design can address the behavior of structures using Liapunov stability criteria. This paper shows a unified procedure which can be applied to both elastic and inelastic structures. Although the implementation does not always preserve the optimal criteria, it is shown that the solutions are effective and practical for design of supplemental damping, stiffness enhancement or softening, and strengthening or weakening.

A Slip-Force Device for Maintaining Constant Lateral Pressure on Retaining Structures in Expansive Soils

Expansive soils can pose tough issues to civil engineering applications. In a typical year, expansive soils can cause a greater financial loss than earthquakes, floods, hurricanes and tornadoes combined. Various means have been studied to tackle problems associated with expansive soils. The majority of the methods are based on treatment of the soils. While the methods may be effective in some cases, their limitations are also obvious: The treatment normally involves complex processes and may not be eco-friendly in the long run. In many cases, the effectiveness of the treatment is uncertain. A retaining system that maintains a constant lateral pressure is proposed, which consists of three components: the retaining sheet, the slip-force device and the bracing column. The retaining sheet bears the pressure exerted by expansive backfills and is not embedded into the soils. Placed between the retaining sheet and bracing column, the slip-force device permits displacement of the retaining sheet but keeps the force on the sheet and the bracing column constant. The governing equation of the motion of the piston in the slip-force device is derived and a numerical simulation of a practical case is conducted based on the derived governing equation. Numerical results show that as the expansive soil swell, the spring force will increase and the piston will move accordingly. When the pressure of the oil in chamber reaches the open threshold of the unidirectional relief valve, the valve will open and the spring force and the oil pressure in the chamber will keep constant. The results also show that some parameters, such as damping ratio, have very slight influences on the device behavior, say 2 × 10-6 or even 4.8 × 10-9. Theoretical and numerical studies prove the effectiveness of the proposed retaining system.

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。

柱脚不均匀沉降对单斜撑钢井架的影响与治理研究

长期的荷载作用可能导致矿井井架变形和不均匀沉降,甚至可能引起结构整体倾覆。针对童亭煤矿钢结构单斜撑井架的沉降和受力特点,采用ANSYS有限元软件构建了单斜撑井架结构模型,研究了斜撑基础不均匀沉降对井架结构内力的影响规律,并对井架内力受不均匀沉降影响机理进行分析。结果表明:①立架与斜撑间的沉降差值会引起立架C柱底和顶部横梁的应力呈线性增加,对斜撑影响较小;X方向沉降率达到2.04‰时,立架最大应力出现于C柱底,约为148 MPa,低于钢材设计强度的限值。②两斜撑基础间的不均匀沉降对单斜撑井架的不利影响更大,断绳工况下的Y方向沉降率为0.88‰时即发生应力超限破坏,略低于《矿山井架设计标准》中对单斜撑式钢井架斜撑基础间最大1‰的沉降差值限制。③不均匀沉降导致井架内力重分布,井架最大应力值和位移值均随沉降值增大而增大,其中立架C柱和斜撑上下天轮梁为最危险部位。针对井架沉降现状,提出了重点部位的加固和顶升方案,加固后井架内力和变形均大幅降低,静力性能提升30%。

钢支撑-钢筋混凝土掉层框架结构抗震性能试验研究

为改善坡地钢筋混凝土(RC)掉层框架结构抗侧刚度分布的不均匀性,设计了一栋在上接地层设置钢支撑的RC掉层框架结构,按1/4比例提取其顺坡向中榀框架下部5层子结构为试验对象,开展钢支撑-RC掉层框架拟静力试验,观测试件的破坏过程,并对比RC掉层框架试验所得试件的破坏形态,分析试件滞回性能、延性和刚度退化等抗震性能指标。结果表明:试件的最终破坏是以第4层柱底混凝土压溃,梁端混凝土剥落、底部钢筋断裂,顶层柱顶混凝土剥落为标志。与RC掉层框架试验结果相比,钢支撑-RC掉层框架试件上接地柱的破坏明显减轻,柱端破坏分布也更为均匀,避免了掉层框架结构“半层破坏模式”的出现,改善了结构的耗能和抗地震倒塌能力。但试件上接地层相邻上一层的变形和破坏程度较大,应对该楼层的柱端进行适当的抗震加强;设置钢支撑后,试件的滞回曲线较为饱满,并具有良好的延性(正、负向加载的位移延性系数分别可达5.13、5.69),正负向加载的刚度退化曲线也趋于对称。

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。

LY160钢屈曲约束支撑框架抗震性能研究

屈曲约束支撑(BRB)因其性能优越已在工程中广泛应用,目前工程中使用的BRB芯材多为Q235B钢,为研究软钢BRB框架的受力性能,设计了一榀LY160钢BRB框架进行低周反复试验。试验结果表明:LY160钢BRB框架滞回曲线饱满,耗能系数高达1.54,等效黏滞阻尼达到了0.255。为了进一步研究LY160钢BRB框架结构体系抗震性能,分别运用ABAQUS与PERFORM-3D对框架试验进行模拟,并将两个模拟结果与试验结果进行对比,分析了两个软件模拟计算的优缺点,验证了数值模拟的准确性。在此基础上,采用PERFORM-3D建立6层BRB框架结构(BRBS)模型并与无控框架结构(UCS)模型以及普通支撑框架结构(NBS)模型进行对比,BRBS的层间位移角、层剪力最高可分别降低34.47%、31.29%,远超NBS的19.39%和17.31%,且BRBS的塑性耗能几乎全为BRB提供,很好地保护了主体结构,具有较为稳定、良好的抗震性能。

防屈曲耗能支撑与框架节点的连接设计

防屈曲耗能支撑作为一种新型的消能减震元件,已被广泛、成功地应用于既有框架结构的抗震加固中。为使结构在地震作用下表现出良好的抗震效果,需保证防屈曲钢支撑与框架具备优良的协同工作性能,因此支撑与框架之间的连接性能尤为重要。防屈曲钢支撑与框架节点之间的连接方法有焊缝连接、螺栓连接以及销轴连接。通过对节点板-框架连接处和节点板-支撑连接处进行受力分析,破坏形态分析,完善了加支撑框架节点处的计算公式。

设置多级屈服耗能BRB的桥梁排架墩等能量设计方法

传统防屈曲支撑(BRB)被广泛用于桥梁排架墩的减震控制,但其屈服后刚度较低和变形能力较小,难以有效控制强震下的峰值位移和残余位移。为此,将传统单一材料组成的BRB核心变形段替换为两种具有不同屈服点的材料,使其整体力学特性呈分级屈服的多线性,形成多级屈服耗能的防屈曲支撑(MSBRB)。将MSBRB作为保险丝构件应用于排架墩以提升其抗震性能,采用等能量的设计方法,以设置MSBRB排架墩体系的能力曲线为设计目标,考虑体系在逐渐增强的地震动荷载作用下的塑性发展机制和能力曲线特征,在中国公路抗震设计规范基础上发展了三阶段的抗震设计流程。最后,结合一排架墩设计案例并通过非线性时程分析证明了所提出设计方法的可行性和准确性。结果表明:设计方法可以较好地预测不同地震水平下MSBRB排架墩体系的性能状态,设计值与模拟值最大误差不超过6%,能达到不同地震水平的设计目标;设置MSBRB能显著降低排架墩的墩顶位移,E2地震作用水平下可使排架墩保持弹性状态,在更强的地震水平下也可有效降低排架墩的损伤,说明MSBRB可更为高效地提升排架墩抗震性能,实现排架墩的损伤控制。

某新型半导体显示产业钢厂房备料区抗震性能分析

以某新型半导体显示产业钢结构厂房备料区为工程背景,建立了厂房钢框架-支撑结构的非线性有限元模型,分别对多遇地震和罕遇地震下的结构抗震性能进行了分析。结果表明,结构整体指标均满足设计规范要求,第3层和第6层的层间位移角较大;罕遇地震下构件损伤主要集中在支撑,而结构底层角柱和中部楼层的边跨梁有轻微损伤;钢支撑能够有效提高结构刚度,减小梁柱的损伤。

“两墙合一”深基坑工程设计与技术创新

北京CBD核心区某项目基坑深度36m,因受场地空间限制,采用“两墙合一”+内支撑支护体系,在实现基坑挡土、止水功能的同时完成了地下结构外墙施工。为提高工程质量和施工效率,针对地连墙与主体结构的连接、槽段接头处理方式、有限空间导墙结合近接建筑物预换撑等方面进行了技术创新,取得了较好的工程效果,可供类似工程参考。

核电汽轮发电机定子壳体振动故障分析与治理研究

对不同激振力作用下核电汽轮发电机定子壳体振动机理和特征开展研究,提出汽轮发电机定子壳体振动故障的分析和治理方法,并结合3台核电机组的工程实例进行分析验证。研究结果表明:定子壳体固有频率接近旋转频率或倍频电磁共振频率引起的结构共振是导致定子壳体振动超标的主要原因;转子激振力引起的定子壳体结构共振,可从减小激振力和调整定子壳体固有频率两方面进行治理,进行现场动平衡可有效降低转子激振力,调整定子壳体固有频率可通过定子底脚载荷分配调整实现;由于磁拉力大小调整范围有限,磁拉力引起的定子壳体结构共振应通过调整定子壳体固有频率进行治理。在发电机安装或检修时,应通过定子底脚载荷分配调整,使定子壳体固有频率避开旋转频率和倍频电磁共振频率,避免发电机定子壳体结构共振的发生。

超大跨度空间X撑结构屈曲强度特性研究

为了深入研究深水导管架平台超大跨度空间X撑结构的承载机理,合理地指导工程设计,本文在已有理论模型的基础上,研究了空间X撑结构(有面外支撑X撑结构)在典型的载荷模式、刚度特性、端点约束以及长度因子(交点位置)等参数下屈曲长度系数的变化规律,结合实际工程深水导管架结构,辅助有限元计算对超大跨度有面外支撑X撑结构进行了屈曲强度分析,最后得到了可为工程设计提供有效技术支撑的多个结论。

考虑连续山体影响的耐张型悬索支撑输电结构风振响应分析

针对适用于山区的新型输电结构——悬索支撑输电结构,为了评估连续山体数量对该结构性能的影响,该文进行了连续山体影响下边界层风洞试验;基于试验数据,分析了平均和脉动风速在不同数量连续山体影响下的演变趋势,并给出了平均风修正系数和脉动风修正系数的建议公式;提出了连续山体影响下悬索支撑输电结构的风致非线性动力分析方法;针对位于某耐张段的悬索支撑输电结构,评估了其风致动力响应受不同数量连续山体的影响。研究结果表明:当连续山体数量增加时,在山顶处,平均风修正系数先增大后平稳,在背风面山脚处,平均风修正系数先增大后减小,而最大脉动风修正系数呈现先减小后增大的趋势;就导线、支撑导线悬索的跨中位移和跨中张力而言,其均值和标准差随着连续山体数量增加呈现先减小再增加后逐渐平稳的趋势;不同数量连续山体对导线、支撑导线悬索跨中位移均值影响较为显著,对其标准差影响较小,而对于跨中张力则恰好相反。

高铁大跨双肢墩连续刚构桥减震系梁地震易损性分析

为了解地震作用下减震系梁对高铁大跨双肢墩连续刚构桥的减震效果,以某主跨180 m的山区高铁双肢墩连续刚构桥为背景,分别建立采用钢筋混凝土(RC)系梁、2种新型减震系梁(可屈服钢系梁与斜交筒式黏弹性阻尼器系梁)方案的全桥有限元模型,对比分析不同系梁方案下的结构损伤、桥面平顺性指标等。结果表明:2种新型减震系梁均不会在地震作用下出现负刚度,新型减震系梁方案较RC系梁方案能有效降低系梁和主墩的结构损伤概率,主墩最大压应变降低83.3%;但减震系梁对震后桥面平顺性指标无明显改善,需采用更具针对性的技术措施。