钢管混凝土框架-核心筒混合结构连续倒塌非线性动力分析

为研究钢管混凝土框架-核心筒混合结构在局部构件失效后的连续倒塌机制,基于ABAQUS纤维梁单元和分层壳单元,采用课题组开发的材料本构子程序iFiberLUT,进行了一栋33层钢管混凝土框架-核心筒混合结构在1、17、33层柱和核心筒墙体失效工况下的连续倒塌非线性动力分析,研究了典型柱和剪力墙失效后剩余结构的抗连续倒塌机制。结果表明:33层构件失效时上部节点位移反应最大,17层次之,1层最小,相比核心筒墙体失效,柱失效时上部节点竖向位移更大,震荡更明显;各工况作用对核心筒影响均较小,且核心筒的存在增强了楼板的薄膜效应,提高了结构抗倒塌能力,失效位置距核心筒越近提高越显著;典型构件失效后结构的传力路径遵循"就近原则"向周围构件传递,楼板和核心筒有力的提高了结构的冗余传递路径和整体性。     

建筑结构中抗震分析模型的优化研究

大多数建筑结构由梁、柱、支撑、剪力墙、地基和楼板等主要结构组成。一般而言,楼板对建筑结构的抗震性能可以忽略不计,所以进行建筑结构分析的模型是无楼板的。因此,楼板被刚性隔板代替,以提高分析效率。本文提出的建筑结构抗震分析解析模型考虑了楼板抗弯刚度,该模型采用超级单元、刚性隔板和子结构技术来减少自由度。通过实例分析,验证了该模型在多层建筑结构抗震分析中的有效性和准确性。且此模型能够显著减少计算量,提高分析效率,振动周期和响应时间等分析结果的精度与精化模型的结果非常接近,说明该模型的提出是合理的。     

Seismic response of simple structures using spring-assisted sliding slabs with coulomb damping

Coulomb damping can be utilized effectively to reduce the dynamic response of structures subjected to seismic ground motions. To activate this damping, some parts of a vibrating structure are allowed to slide at rough interfaces. The dynamic response of structures provided with sliding interfaces at the base, between a floor slab and frame and in the cross bracings of a frame has been examined recently. In this paper, a simple slab sliding system provided with a spring to introduce a recovery mechanism and to reduce the sliding displacement requirement for low frequency structures has been examined. The equations of motion for this system are developed. An approach is presented to solve these coupled equations for earthquake induced ground motions. Structures with varying frequency and friction characterisics are considered and the numerical results are presented in response spectrum form. It is observed that, in low frequency structures, provision of a rather weak spring can reduce the sliding displacement requirements without significantly increasing the forces in the supporting frame and the acceleration input to supported secondary systems.     

楼板及其配筋在RC框架结构实现抗震延性机制中的作用分析

总结采用梁有效翼缘来考虑楼板及配筋对"强柱弱梁"机制形成的影响的实验和数值仿真研究.基于SAP2000采用三种侧向加载模式对RC框架结构不带楼板、不带楼板考虑梁刚度放大、带楼板的三个模型进行pushover分析,对力与位移的关系曲线、塑性铰的出铰顺序以及顶点位移与层间位移等方面进行探讨.结果表明:三个模型的"强柱弱梁"...     

微动测试技术在古建筑拱桥结构检测中的应用

在古桥梁建筑结构保护中,无损高精度检测一直是一个重要的研究课题。为识别古桥梁拱桥的结构损伤问题,以上海青浦迎祥桥为研究对象,采用全站仪对桥梁结构的变形进行观测及分析,评价桥梁的变形及受力状态;采用微动测试技术,获取结构的损伤动力特性参数,包括固有频率及振动模态。通过分析现有桥梁的模态分布,观测振动模态的突变位置确定结构损伤位置,比较结构的变形特性,对结构的损伤程度进行评价。     

正弦行波激励下单层偏心框架结构扭转响应的解析解

文中针对单层偏心框架结构,利用正弦行波激励研究了质量偏心率和激励频率对偏心框架结构行波扭转响应的影响规律.建立了行波激励下单层偏心框架结构的振动方程,采用相对运动法求解给出了正弦行波激励下单层偏心框架结构楼板的质心平动位移和转角位移以及楼板扭矩和柱剪力的解析解.计算了一个钢筋混凝凝土单层偏心框架结构的峰值楼板扭矩和峰值...     

Generation of floor response spectra including oscillator-structure interaction

A method is presented for generating floor response spectra for aseismic design of equipment attached to primary structures. The method accurately accounts for tuning, interaction and non-classical damping, which are inherent characteristics of composite oscillator-structure systems. Modal synthesis and perturbation techniques are used to derive the modal properties of the composite system in terms of the known properties of the structure and the oscillator. Floor spectra are generated directly in terms of these derived properties and the input ground response spectrum using modal combination rules that account for modal correlations and non-classical damping. The computed spectra, in general, are considerably lower than conventional floor response spectra due to the effect of interaction. They provide more realistic and economical criteria for design of equipment. The method is accurate to the order of perturbation and is computationally efficient, as it avoids time-history analysis and does not require numerical eigenvalue evaluation of the composite oscillator-structure system. The results of a parametric study demonstrate the accuracy of the method and illustrate several key features of floor response spectra.     

Dynamics of elastic–plastic shear frames with secondary structures: shake table and numerical studies

Results from experimental and numerical studies of earthquake‐excited small‐scale primary–secondary structures are presented. The primary structure considered is a plane three‐storey shear frame with a fundamental frequency of 5.5 Hz. The columns of the first floor are built with soft aluminium and they are stressed beyond its linear range of behaviour. After each test the elastic–plastic columns are replaced by a new set of undeformed virgin aluminium bars. The elastic–plastic shear frame is tested with and without an attached secondary structure. The secondary structure is modelled as an elastic SDOF oscillator, and its natural frequency is tuned to the fundamental frequency of the shear frame. Alternatively, the oscillator is mounted on the horizontal beam of the second and third floor. The base excitation of the structural model is characterized by a broad band random process with constant spectral density in a frequency range between 3 and 30 Hz. In the numerical study, the digital recorded acceleration of the base excites the mechanical model of the investigated structures. Numerical outcomes assuming fictitious unlimited elastic material behaviour of the shear frame are set in contrast to results from experiments and computational simulations where the measured non‐linear force displacement relation of the elastic–plastic floor is approximated by a piecewise linear curve. The effect of elastic–plastic materials on the dynamic interaction between primary and secondary structure is shown and the difference to unlimited elastic material behaviour is worked out in detail. Copyright © 2001 John Wiley & Sons, Ltd.     

近年来华北南部地区地震活动增强的力学背景分析

依据青藏高原东北缘与秦岭大地构造格局相关联的地质构造背景,青藏高原物质东流和“稳定”块体的阻挡是华北南部地区构造活动的主要动力来源之一的基本认识,分析了青藏高原东北缘4次8级地震前华北南部地区地震活动的基本特征。8级地震震中区附近地震活动异常变化不明显,但华北南部地区地震异常活跃,其异常活跃过程与青藏高原东北缘强震的孕育与发生存在明显的相关性．具有一定的异地震情指示意义。     

强震下钢筋混凝土框架和砖混结构的动力响应分析——以云南漾濞6.4级地震为例

以2021年5月21日云南漾濞6.4级地震所获取的漾濞台强震动记录作为输入,对不同高度(低层、多层和高层)钢筋混凝土框架结构以及一低层砖混结构进行动力时程分析,探讨不同高度钢筋混凝土框架结构动力响应特点,对比砖混结构与低层框架结构地震响应的不同,并对结构进行性能评定.主要分析结果表明,所有结构的楼层加速度响应中,竖向加速度放大效应显著,尤其是低层框架;框架结构Y方向楼层傅里叶幅值谱峰值主要在1~2.5 Hz频率范围;多层框架的层间位移角响应更大;所有框架结构以及设防的砖混结构层间位移角均未超过中等破坏限值;与低层框架结构相比,基本周期更短的砖混结构水平向楼层加速度放大效应更为显著;设防的砖混结构具有良好的抗震性能.分析结果可为灾区震害评估和震后修复提供指导,同时为建筑结构抗震设计提供一定参考.     

Optimum damping in linear isolation systems

Optimum isolation damping for minimum acceleration response of base-isolated structures subjected to stationary random excitation is investigated. Three linear models are considered to account for the energy dissipation mechanism of the isolation system: a Kelvin element, a linear hysteretic element and a standard solid linear element, commonly used viscoelastic models for isolation systems comprising natural rubber bearings and viscous dampers. The criterion selected for optimality is the minimization of the mean-square floor acceleration response. The effects of the frequency content of the excitation and superstructure properties on the optimum damping and on the mean-square acceleration response are addressed. The study basically shows that the attainable reduction in the floor acceleration largely depends on the energy dissipation mechanism assumed for the isolation system as well as on the frequency content of the ground acceleration process. Special care should be taken in accurately modelling the mechanical behaviour of the energy dissipation devices.     

A study of seismic response characteristics of structures with friction damping

The effectiveness of introducing Coulomb damping in structures to reduce seismic response is evaluated. Response characteristics of simple one-degree-of-freedom structures with sliding interfaces between the top slab and supporting frame and between the base and foundation are studied and compared. It is shown that, analytically, the top slab sliding system is a special case of the base sliding system. The slab sliding system is seen to offer certain advantages over the base sliding system inasmuch as it provides a more effective reduction in the lateral forces in the supporting frame as well as a better isolation of supported secondary systems, as depicted by a significantly reduced level of floor spectrum response. The analytical ease of predicting the response of the slab sliding system is also demonstrated. The required unobstructed sliding displacements seem to be reasonable except, may be, for flexible systems. The similarities and differences between the hysteretic and slab sliding systems are also highlighted by comparison of their response results.     

Evaluation of diaphragm conditions in AAC floor structures with RC beams

Diaphragm action in floor structures is an important aspect that affects both local behaviors of individual members and consequently, the global response of a structure. The diaphragm action of a built structure, therefore needs to be compatible with the assumed diaphragm condition in the design phase to prevent unpredicted overloading of load bearing members in a seismic action. Autoclaved aerated concrete (AAC) is a cost-effective, lightweight and energy efficient material, and its usage as a construction material has rapidly increased in recent decades. However, there is a limited experience regarding the in-plane behavior of the floor structures made of AAC panels in terms of diaphragm action. In this paper, the in-plane response of AAC floors is experimentally investigated and the floor performance of a typical building is analytically investigated according to ASCE 7-16 (ASCE/SEI in Minimum design loads for buildings and other structures, The American Society of Civil Engineers, Reston, 2016). Full-scale experiments carried out through loading AAC floors in lateral directions to the panels, either parallel or perpendicular, provided important information about the damage progress and overall performance of such floors. A number of finite element modeling techniques that are generally used for modeling of AAC floors were examined and then validated through comparisons with test results. Finally, the diaphragm condition of a three-story building made of AAC walls and floor panels was assessed. The results indicated that the AAC floors in the examined building can be idealized as rigid diaphragms according to ASCE 7-16.     

Tuned mass dampers for structures with closely spaced natural frequencies

Analytical results are developed for vibration control of structures with one or more Tuned Mass Dampers (TMDs). The input is a harmonic load with a range of possible frequencies. The control objective is to reduce the maximum amplitude of the structural response. Perturbation theory is used with three sets of small parameters: the ratio of TMD and structural modal masses, the damping of the system, and the differences between the structural and loading frequencies. It is shown analytically that for structures with widely spaced natural frequencies, the response can be approximated accurately by the response of the well-known single-mode structure/TMD system. For structures with p closely spaced natural frequencies, more general analytical results are developed to describe the coupling between the motions of the p modes of the structure and the multiple TMDs. The results show that at least p TMDs with properly placed attachments to the structure are necessary to control the response. If fewer TMDs are used, the maximum frequency response has a lower bound which is independent of the properties of the TMDs. The TMD placement is shown to be always important, regardless of the spacing of the structure's natural frequencies. The results are illustrated for both lumped-mass and continuous structures.     

Dynamic response analysis of a multiple-beam structure subjected to a moving load

In this study, the dynamic response of an elastically connected multi-beam structure subjected to a moving load with elastic boundary conditions is investigated. The boundary conditions and properties of each beam vary, and the difficulty of solving the motion equation is reduced by using a Fourier series plus three special transformations. By examining a high-speed railway (HSR) with mixed boundary conditions, the rationality for the newly proposed method is verified, the difference in simulated multiple-beam models with different beam numbers is explored, and the influence of material parameters and load speed on the dynamic response of multiple-beam structures is examined. Results suggest that the number of beams in the model should be as close to the actual beam number as possible. Models with an appropriate beam number can be used to describe in detail the dynamic response of the structure. Neglecting the track-structure can overestimate the resonant speed of a high-speed railway, simply-supported beam bridge. The effective interval of foundation stiffness (EIFS) can provide a reference for future engineering designs.

     

近海大气环境下钢框架自振频率评估研究

由于沿海地区的钢结构建筑常暴露在露天,不可避免地受到大气环境的腐蚀。本文在材料力学和结构分析的基础上,研究沿海地区钢框架结构自振频率的变化,进而对结构在近海大气环境下存在的潜在损伤进行评估。基于工字形与箱形截面,提出结构自振频率与结构构件厚度变化的关系式,并分别考虑构件内外表面腐蚀的影响。以一榀钢框架结构为例,分析其在腐蚀5、10、20年后结构前10阶自振频率的变化。分析结果表明,随着腐蚀程度的增加,结构自振频率降低的越大。研究成果可为锈蚀钢框架损伤评估提供一定的参考依据。     

水平地震作用下建筑顶层重力荷载能力研究

地震灾害的发生给人们的生命财产安全带来了极大的威胁,为了保障在地震发生时建筑的安全,需要时刻对试件的荷载、初始刚度、延性系数、建筑模型的竖向位移等信息进行检测,一旦重力荷载高于峰值荷载,建筑安全将不能得到保障。为分析水平地震作用下建筑的顶层重力荷载能力,首先建立用于实验的一榀三层三跨式的房屋建筑模型,检测这种模型处于重力荷载作用情况下的侧向刚度,用来了解在建筑顶层结构在处于水平地震作用情况下重力荷载对其检测刚度的影响程度。然后从模型中选取5个试件,对这些试件的材料属性、实验结果、荷载位移进行分析,再通过实验模型的重力荷载位移曲线确定建筑的峰值荷载为700 kN,即当建筑顶层的峰值荷载超过700 kN时,建筑的安全性将难以保证。     

An investigation on the ground motion parameters and seismic response of underground structures

Peak ground acceleration (PGA), frequency content and time duration are three fundamental parameters of seismic loading. This study focuses on the seismic load frequency and its effect on the underground structures. Eight accelerograms regarding different occurred earthquakes that are scaled to an identical PGA and variation of ground motion parameters with ratio of peak ground velocity (PGV) to PGA, as a parameter related to the load frequency, are considered. Then, concrete lining response of a circular tunnel under various seismic conditions is evaluated analytically. In the next, seismic response of underground structure is assessed numerically using two different time histories. Finally, effects of incident load frequency and frequency ratio on the dynamic damping of geotechnical materials are discussed. Result of analyses show that specific energy of seismic loading with identical PGA is related to the seismic load frequency. Furthermore, incident load frequency and natural frequency of a system have influence on the wave attenuation and dynamic damping of the system.     

Relaxation base seismic isolator

This paper deals with the use, for seismic applications, of a Maxwell element in parallel with a low damping isolator. The study of the properties of the frequency response function shows that this isolator is capable to reduce the base displacement of isolated structures with no considerable amplification of the non‐isolated modes. This is, also, confirmed by the floor response spectra under earthquake excitations. Hence, the previously mentioned isolator does not present the drawbacks met when base displacement is reduced by increasing damping. Moreover, it seems that its performance is comparable with that of more elaborated and expensive techniques combining passive and semi‐active devices. Copyright © 2016 John Wiley & Sons, Ltd.     

Modal parameter identification and damping ratio estimation from the full-scale measurements of a typical Tibetan wooden structure

Tibetan heritage buildings have a high historical and cultural value. They have endured adverse environmental loadings over hundreds of years without significant damage. However, there are few reports on their structural characteristics under normal environmental loadings and their behavior under dynamic loadings. In this research, a typical Tibetan wooden wall-frame building is selected to study its dynamic characteristics. Field measurements of the structure were conducted under environmental excitation to collect acceleration responses. The stochastic subspace identification (SSI) method was adopted to calculate the structural modal parameters and obtain the out-of-plane vibration characteristics of the slab and frames. The results indicated that the wall-frame structure had a lower out-of-plane stiffness and greater in-plane stiffness due to the presence of stone walls. Due to poor identified damping ratio estimates from the SSI method, a method based on the variance upper bound was proposed to complement the existing variance lower bound method for estimating the modal damping ratio to address the significant damping variability obtained from different points and measurements. The feasibility of the proposed method was illustrated with the measured data from the floor slab of the structure. The variance lower and upper bound methods both provided consistent results compared to those from the traditional SSI method.