On the modal incremental dynamic analysis of reinforced concrete structures, using a trilinear idealization model

In order to estimate the seismic demands at the performance level, the inelastic behavior of concrete structures should be considered. Incremental dynamic analysis (IDA) based on a nonlinear response time history analysis (NL-RHA) is considered to be the most accurate method in seismic demand calculations. However, modal incremental dynamic analysis (MIDA), based on the equivalent single-degree-of-freedom (SDF) oscillator, is also often used in studying structural engineering performances. As the MIDA method has usually not been applied to reinforced concrete (RC) structures, in this study an attempt is made to investigate the performances of RC frames and to compare the results obtained through the MIDA against those obtained from exact IDA. Furthermore, an innovative suggestion on approximated pushover curves of the corresponding SDF model, by means of a trilinear idealization representation, is also offered. For this purpose, an eight-story concrete frame subjected to 30 different earthquake records is studied with the trilinear idealization model, and the damage measures, important for the seismic vulnerability of buildings, such as the maximum displacement and the interstory drift ratio, are considered. Comparison of the results has shown reasonable and/or acceptable precision and reveals good agreement of the MIDA method with the new idealization behavior model for concrete frames.     

Inelastic seismic response of steel bracing members

A survey of past experimental studies on the inelastic response of diagonal steel bracing members subjected to cyclic inelastic loading was carried out to collect data for the seismic design of concentrically braced steel frames for which a ductile response is required under earthquakes. The parameters that were examined are the buckling strength of the bracing members, the brace post-buckling compressive resistance at various ductility levels, the brace maximum tensile strength including strain hardening effects, and the lateral deformations of the braces upon buckling. Equations are proposed for each of these parameters. In addition, the maximum ductility that can be achieved by rectangular hollow bracing members is examined.     

Statistical evaluation of the damage potential of earthquake ground motions

This study focuses on the damage potential of earthquake ground motions based on the inelastic dynamic response of equivalent single degree of freedom structures. Their yield resistances are selected in accordance with seismic design codes. An index accounting for the accumulation of damage due to inelastic excursions is used to represent structural damage. A set of 94 ground motions are employed for this analysis, which are all scaled to the same peak ground acceleration of 0.4 g. Earthquake ground motions are classified with respect to both the ratio of peak velocity to peak acceleration (V/A ratio) and their effective excitation duration. The effect of these parameters on damage potential is investigated by using sensitivity analysis and probabilistic techniques. It is concluded that both V/A ratio and effective duration significantly influence the damage potential of earthquake ground motions, although they are not represented appropriately by the spectral definitions of earthquake excitations in seismic design codes.     

Evaluation of nonlinear static analysis methods and software tools for seismic analysis of highway bridges

The response of bridges when subjected to seismic excitation can be evaluated by a number of analysis methods. The traditional approach is to employ linear static or dynamic analyses coupled with appropriate modifiers to account for inelastic response while current design practice is moving towards an increased emphasis on nonlinear static analysis methods. In this study, a preliminary seismic response analysis of a two-span highway bridge was performed using linear dynamic analysis procedures to identify the potential for inelastic response. The bridge was subsequently analyzed in accordance with two nonlinear static analysis methods (capacity spectrum and inelastic demand spectrum methods) in an effort to evaluate the difference in global response predicted by the two methods and the effectiveness of various software programs for performing nonlinear static analysis. The results demonstrated that, for the two nonlinear static analysis methods used in this study, different predictions of nonlinear response occurred with neither method being regarded as producing correct results due to a number of simplifications inherent in the methods. Furthermore, the analysis revealed that some software programs are well suited to performing nonlinear static analysis, both from the point-of-view of performing comprehensive analyses and providing a graphical depiction of the evolution of damage (i.e. the behaviour of plastic hinges).     

强震作用下配置高强度钢筋的混凝土框架结构非线性动力反应

为研究配置高强度钢筋的混凝土框架的抗震性能,以抗震设防烈度8度区加速度0.3g为例,利用Perform-3D程序进行了5栋配置不同强度等级钢筋的混凝土框架结构在双向罕遇地震作用下的非线性动力反应分析。分析模型以一栋配置强度335 MPa级钢筋的框架结构为基础,分别以钢筋等强代换和规范要求为原则,设计了4栋分别配置强度500 MPa级和600 MPa级钢筋的框架结构。非线性动力反应分析结果表明：随着配筋强度等级的提高,框架的最大顶点位移、最大层间位移角虽有所增大,但仍小于规范的限值,梁端进入屈服较晚,梁端塑性铰的数量也有所减少,表明高强钢筋混凝土框架的整体抗震性能良好。分析结果还表明,以位移延性系数作为衡量构件延性的指标时,配置高强钢筋构件的位移延性系数限值应低于配置普通强度钢筋的构件;而当以极限位移角作为衡量构件的延性指标时,构件的极限位移角限值应随钢筋强度的提高而增大。     

Seismic performance of R/C plane frames irregular in elevation

The paper addresses multistorey reinforced concrete (R/C) frame buildings, irregular in elevation. Two ten-storey two-dimensional plane frames with two and four large setbacks in the upper floors respectively, as well as a third one, regular in elevation, have been designed to the provisions of the 2004 Eurocode 8 (EC8) for the high (DCH) and medium (DCM) ductility classes, and the same peak ground acceleration (PGA) and material characteristics. All frames have been subjected to both inelastic static pushover analysis and inelastic dynamic time-history analysis for selected input motions. The assessment of the seismic performance is based on both global and local criteria. It is concluded that the effect of the ductility class on the cost of buildings is negligible, while the seismic performance of all irregular frames appears to be equally satisfactory, not inferior to (and in some cases superior than) that of the regular ones, even for motions twice as strong as the design earthquake. As expected, DCM frames are found to be stronger and less ductile than the corresponding DCH ones. The overstrength of the irregular frames is found to be similar to that of the regular ones, while DCH frames are found to dispose higher overstrength than DCM ones. Pushover analysis seems to underestimate the response quantities in the upper floors of the irregular frames.     

钢支撑-混凝土框架动力非弹性扭转机理与抗扭设计研究

通过钢支撑-混凝土框架振动台试验研究了钢支撑失稳或其他构件损伤后引起的扭转突然增大问题,即非弹性扭转问题,结果表明钢支撑受压失稳或失效是导致此类结构出现非弹性扭转的重要原因。基于试验结果,分析了钢支撑失稳或失效导致结构非弹性扭转突增的机理;同时建立了设有偶然偏心的有限元模型算例并进行非线性分析,验证了在增加构件数量的条件下该类结构仍存在非弹性扭转突增问题,表明即使是对称结构,在普通钢支撑发生受压失稳及其反向受拉过程中,也会产生非弹性扭转及其突然增大现象。试验和案例分析均表明类似的现象,即在相同加载及偏心条件下纯混凝土框架非弹性扭转虽然存在,但其突然增大值比钢支撑框架结构要小;设置防屈曲支撑抗扭效果显著,优于设置钢支撑的混凝土框架和纯混凝土框架。建议工程设计中设置防屈曲支撑,可有效减控混凝土框架非弹性扭转危害;通过设置质量偏心,对钢支撑-混凝土框架结构进行强震下非弹性扭转响应分析,并在设计上对其最大值加以限制。     

Seismic design and assessment of structures with viscous dampers at limit state levels: Focus on probability of damage in devices

During large earthquakes, the seismic demand of viscous dampers may exceed their capacity. In this regard, current design codes must consider extreme conditions and preserve the damper at limit state levels. Here, by adjusting the damping coefficient, a procedure is introduced to mitigate device damages during severe earthquakes. To assess the procedure, 15 special moment resisting frames with a different number of stories (two, four, and eight) were designed by three methods: The recommended novel procedure, the seismic provisions of ASCE7, and the procedure proposed by Miyamoto et al. 1 for structures, installed with supplemental damping devices. A series of incremental dynamic analyses were then performed by modeling the limit state behavior of viscous dampers. Results indicated that the novel method reduces the damage probability of dampers as well as the maximum demands on the structure at different seismic hazard levels.     

确保钢框架梁铰机制的多目标抗震设计方法

前期研究表明:梁铰破坏机制下,抗弯钢框架节点处的柱梁抗弯强度比应高于1.0甚至2.0。同时也指出,为了防止结构出现薄弱层,对结构的全部节点仅使用单一的柱梁抗弯强度比限值是不切实际的。因此,需要对节点处的柱梁抗弯强度比进行优化设计。给出了确保抗弯钢框架结构中梁铰机制的多目标抗震设计方法,并将其应用于著名的抗弯钢框架结构的抗震设计中。除利用约束确保梁铰机制外,通过考虑两个不同的目标函数给出了结构的建筑费用和能量耗散能力的关系式。为了在替代方法中选出用于指导结构工程师工作的最佳设计方法,以耗散能量密度(耗能能力与结构重量之比)的形式给出一种简单的方法。     

Effects of soil‐structure interaction and lateral design load pattern on performance‐based plastic design of steel moment resisting frames

The effects soil‐structure interaction (SSI) and lateral design load‐pattern are investigated on the seismic response of steel moment‐resisting frames (SMRFs) designed with a performance‐based plastic design (PBPD) method through a comprehensive analytical study on a series of 4‐, 8‐, 12‐, 14‐, and 16‐story models. The cone model is adopted to simulate SSI effects. A set of 20 strong earthquake records are used to examine the effects of different design parameters including fundamental period, design load‐pattern, target ductility, and base flexibility. It is shown that the lateral design load pattern can considerably affect the inelastic strength demands of SSI systems. The best design load patterns are then identified for the selected frames. Although SSI effects are usually ignored in the design of conventional structures, the results indicate that SSI can considerably influence the seismic performance of SMRFs. By increasing the base flexibility, the ductility demand in lower story levels decreases and the maximum demand shifts to the higher stories. The strength reduction factor of SMRFs also reduces by increasing the SSI effects, which implies the fixed‐base assumption may lead to underestimated designs for SSI systems. To address this issue, new ductility‐dependent strength reduction factors are proposed for multistory SMRFs with flexible base conditions.     

Incremental dynamic analysis of steel frames equipped with NiTi shape memory alloy braces

This paper determines the seismic performance of four‐storey concentrically braced frames equipped with either steel buckling‐restrained braces or buckling‐restrained superelastic shape memory alloy (SMA) braces through incremental dynamic analysis. The incremental dynamic analysis technique is used to examine the behaviour of four‐storey braced frames with four different bracing configurations (including diagonal, split‐X, chevron‐V and inverted‐V) under 20 different ground motion records. The study reveals a satisfactory performance at the design intensity level for both types of braced frames. The results show that the SMA braces lead to a uniform distribution of inelastic response over the height of the buildings, as well as mitigating seismic response in terms of maximum inter‐storey drift and residual roof displacement. By comparing the responses of SMA and buckling‐restrained braced frames under higher intensities of earthquake loading, it is found that the SMA braces can be more beneficial especially under severe ground motion excitations. Copyright © 2014 John Wiley & Sons, Ltd.     

碳纤维布加固混凝土框架抗震性能静力弹塑性分析

在碳纤维布加固混凝土十字节点和框架试件低周反复加载试验的基础上,根据原型框架实际设防要求引入能力谱方法,对采用不同碳纤维布加固方法的框架结构进行了静力弹塑性分析,对设防罕遇地震作用下加固框架的抗震性能进行评估,并作为加固设计具体量化的参考指标。     

Response modification factor for steel moment-resisting frames by different pushover analysis methods

The earthquake loads imposed to the structures are generally much more than what they are designed for. This reduction of design loads by seismic codes is through the application of response modification factor (R-factor). During moderate to severe earthquakes, structures usually behave inelastically, and therefore inelastic analysis is required for design. Inelastic dynamic analysis is time consuming and interpretation of its results demands high level of expertise. Pushover analysis, recently commonly used, is however, a simple way of estimating inelastic response of structures. Despite its capabilities, conventional pushover analysis (CPA) does not account for higher mode effects and member stiffness changes. Adaptive pushover analysis (APA) method however, overcomes these drawbacks. This research deals with derivation and comparison of some seismic demand parameters such as ductility based reduction factor, R_μ, overstrength factor, Ω, and in particular, response modification factor, R, from capacity curves obtained from different methods of APA and CPA. Three steel moment-resisting frames of 3, 9 and 20 stories adopted from SAC steel project are analyzed. In pushover analyses for each frame, eight different constant as well as adaptive lateral load patterns are used. Among the main conclusions drawn is that the maximum relative difference for response modification factors was about 16% obtained by the methods of conventional and adaptive pushover analyses.     

Influence of the link overstrength factor on the seismic behaviour of eccentrically braced frames

The paper investigates the influence of the link overstrength factor on the seismic behaviour of eccentrically braced frames designed in accordance with capacity design principles. To this end, systems characterised by different level number and link length are designed according to the force-based approach, by either static or modal analysis. In order to correctly evaluate the ability of structures to develop global collapse mechanisms characterized by remarkable exploitation of the deformation capacity of links, incremental dynamic analyses are carried out with reference to either deterministic or random values of yield strength. While the first analyses are intended to lead to the conventional evaluation of the seismic response of EBFs, those referred to random values of yield strength are carried out to achieve a more correct verification of the capacity design principles and a deep comprehension of the sensitivity of the structural response to real strength distributions. On the basis of such results, the study also permits a critical analysis of the values of the behaviour factor generally proposed by building codes with reference to this structural typology.     

Seismic behaviour of beam-to-column partial-strength joints for steel-concrete composite frames

The paper presents a large experimental campaign carried out on ten steel-concrete composite beam-to-column sub-assemblages employing monotonic and cyclic loading test protocols. Structural members (beams, columns and slabs) were defined through the design of a full-scale 3D prototype frame subjected to PSD testing campaign; main design hypothesis was to dissipate seismic energy in the joints designed as partial-strength. Testing programme on beam-to-column sub-assemblages was executed in order to assess seismic performance varying structural details at beam-to-column connection level and material qualities. Different mechanical connecting systems between concrete slab and column, two end-plate configurations, weak and strong column web panel, two steel qualities and different concrete strengths.The analysis of sub-assemblages performance was realized in two steps: a first step in which the joints behaviour was assessed, characterizing response at local level (e.g. moment-rotation curves); a second step in which the response was assessed at global level (e.g. force-displacement curves). The structural behaviour (i.e. resistance, plastic deformation and stiffness) was evaluated at three stages-identified as initial, service and maximum load-in order to monitor the evolution of sub-assemblage response increasing solicitation level. Moreover, seismic behaviour of specimens-in terms of dissipated energy, ductility, over-strength and equivalent viscous damping-was also executed. Comparison between experimental results was made in order to identify those parameter suitable for improved and reliable seismic behaviour of steel-concrete composite partial-strength joints.     

钢筋混凝土框架结构基于时变的抗震性能研究

钢筋混凝土结构在使用过程中由于钢筋锈蚀抗震性能退化。为了研究钢筋混凝土框架结构在正常使用环境下随使用时间的增加其抗震性能的退化规律,采用通用有限元分析软件ABAQUS对锈蚀钢筋混凝土框架进行多尺度建模以提高计算精度并保证计算效率。基于锈蚀钢筋混凝土构件及单榀框架的试验数据,验证了多尺度建模方法的正确性。采用多尺度模型对4层钢筋混凝土框架结构进行了静力推覆分析及弹塑性时程分析,对比不同使用时间的钢筋混凝土框架结构的地震反应和损伤情况。结果表明：当使用时间为25a时,结构的抗震性能与新建结构接近;当使用时间超过50a时,随着使用时间的增加,结构的承载能力及刚度退化明显,在地震作用下的位移响应逐渐增大,地震损伤范围不断扩大;相比新建结构,当使用时间为50、75a和100a时,结构的抗侧承载力分别降低了6.2%、14.1%及18.1%,罕遇地震作用下的最大层间位移角分别增大了9.2%、19.8%及25.1%。     

8度区框－剪结构中框架在罕遇地震下的反应性态

框架剪力墙结构中的框架的受力性能不同于纯框架结构。为了考察框架剪力墙结构中的框架在强震下的抗震性态,首先严格按中国设计规范完成了1个8度0.3 g分区24层和1个8度0.2 g分区30层框架剪力墙结构的抗震设计。然后对结构进行了在相当于罕遇水准的多条地面运动输入下的非弹性动力反应分析,初步识别了结构的地震反应性态。分析结果表明,结构中的框架部分在强震下基本保持未屈服状态,而剪力墙连梁是结构主要的塑性耗能部件,部分墙肢底部也进入了屈服后的塑性变形状态。从框架部分所处的偏有利的受力状态和设计规范对其所采取的强化措施这2个方面分析了框架部分未进入屈服的原因。建议对我国8度区总高超过60m的框架剪力墙结构中的框架部分的现行抗震构造措施可有条件地适度放松。     

Seismic risk analysis for reinforced concrete structures with both random and parallelepiped convex variables

This article develops an improved seismic risk assessment formulation exhibiting both random and bounded uncertainties using a probability and parallelepiped convex set mixed model. Limit thresholds for different types of components are described via a probabilistic model. The distribution parameters of limit thresholds are originally treated by employing a multidimensional parallelepiped convex model, in which marginal intervals are utilised to represent scattering levels for the distribution parameters, while relevant angle are employed to express the correlation between uncertain distribution parameters. The structural responses, i.e., engineering demand parameters (EDPs), are considered as correlated random variables and are assumed to follow a multidimensional lognormal distribution. A performance limit state function, which allows considering the relationship between the EDPs and the corresponding limit thresholds, is employed to reflect the coexistence of both random and parallelepiped convex variables. The limit state function is mapped into the standard parameter space via a transformation technique. Then, the improved seismic risk formulation, characterised through a probability and parallelepiped convex mixed variables, can be derived with the combination of the seismic fragility function and the ground motion hazard curve. The main purpose is to illustrate that the performance limit states should be properly modeled as random and parallelepiped convex mixed variables rather than only random or deterministic quantities. A six-story reinforced concrete building designed according to Chinese codes are used to illustrate the proposed approach for constructing hazard curves. The interstory drift and the peak floor acceleration are the selected EDPs, calculated through incremental dynamic analysis. The results demonstrate that the calculated failure probabilities for different limit states in 50?years are found capable of meeting the requirements of Chinese seismic norms after the proposed seismic risk formulation is adopted.     

框架高剪压比中间层中节点抗震性能试验研究

完成了5个接近足尺的不同轴压比的高剪压比钢筋混凝土框架中间层中节点平面梁柱组合体的低周交变加载试验,弥补了国内外抗震节点试验在剪压比高参数区试验数据的不足。通过较全面测试和分析梁筋在节点中的粘结及滑移规律、节点水平箍筋各肢的受力规律以及组合体的滞回耗能及刚度变化规律,进一步揭示了这类节点的剪力传递机构特征、损伤发育特征及其综合抗震性能,为完善设计规范和在框架非弹性动力反应分析中建立更合理的分析模型和滞回模型提供了依据。     

配置HRB500钢筋的框架结构非弹性地震反应分析

为实现建筑行业的可持续发展,中国土木建筑工程界正在推广应用HRB500级高强钢筋,但是,以HRB500钢筋作为主要受力钢筋的混凝土结构的抗震性能研究还相对缺乏.该文按<混凝土结构设计规范>最新修订稿设计了3个配置不同强度钢筋的8度0.3 g区一级抗震等级的混凝土框架结构,并完成了该3个结构在多波输入下的非弹性地震响应分...