钢筋混凝土框架结构抗震超强系数分析

基于我国建筑抗震规范要求设计的14栋代表不同抗震特征要求的多高层规则钢筋混凝土框架,通过静力弹塑性分析详细地评估了框架结构的体系超强能力。分析中采用与抗震规范等效静力地震作用效应分布模式相同的单调递增侧向荷载,以二维平面框架为分析对象。分析结果表明地震分区对超强系数的影响较大;有填充墙框架比无填充墙框架的超强能力明显要大;内框架的超强能力比外框架的超强能力大;超强系数随框架楼层数的增加而减小。     

Seismic fragility of lightly reinforced concrete frames with masonry infills

Seismic fragility of lightly reinforced concrete frames with masonry infills is assessed through numerical simulations considering uncertainty in ground motion and building materials. To achieve this aim, a numerical model of the components is developed, a rational approach to proportion and locate individual struts in the equivalent three‐strut model is proposed, and an explicit nonlinear column shear response model accounting for the infill–column interaction and soft‐story mechanism is employed. The proposed numerical model is used to (1) generate probabilistic seismic demand models accounting for a wide range of ground motion intensities with different frequency content and (2) determine limit state models obtained from nonlinear pushover analysis and incremental dynamic analysis. Using the demand and limit state model, fragility curves for the masonry‐infilled frames are developed to investigate the impact of various infill properties on the frame vulnerability. It is observed that the beneficial effect of the masonry infill diminishes at more severe limit states because of the interaction with the boundary frame. In some cases, this effect almost vanishes or switches to an adverse effect beyond a threshold of ground motion intensities. Copyright © 2015 John Wiley & Sons, Ltd.     

Seismic energy demands on reinforced concrete moment-resisting frames

This paper examines the seismic energy demands on reinforced concrete ductile moment-resisting frames. Three frames having 4, 10 and 18 storeys, representing low, medium and tall frames, were designed to the current Canadian seismic provisions and structural design requirements. Three groups of earthquake records having different frequency contents were selected as input ground motions. The input, hysteretic and damping energies were evaluated for these three frames and correlation was established with other response parameters. The use of equivalent single-degree-of-freedom systems to estimate the energy demands on these frames was examined in order to simplify the computational effort. It is shown that the energy demand concept together with the equivalent single-degree-of-freedom system is a viable design approach for low-rise frames. Additional research to allow for the higher modal effect is required before the same concept can be extended to medium and tall frames.     

Seismic tests on reinforced concrete and steel frames retrofitted with dissipative braces

Seismic tests have been conducted on two 3‐storey structures protected with pressurized fluid‐viscous spring damper devices. One of the structures was a reinforced concrete frame with clay elements in the slabs, while the other one was a steel frame with steel/concrete composite slabs. The spring dampers were installed through K bracing in between the floors. The tests were performed by means of the pseudodynamic method, which allowed the use of large and full‐size specimens, and by implementing a specific compensation strategy for the strain‐rate effect at the devices. The test results allowed the verification of the adequacy of the attachment system as well as the comparison of the behaviour of the unprotected buildings with several protected configurations, showing the benefits of the application of the devices and the characteristics of their performance. The response of the protected structures was always safer than that of the unprotected ones mainly due to a significant increase of equivalent damping. The increase in the damping ratio depends on the level of deformation. Copyright © 2004 John Wiley & Sons, Ltd.     

基于耐震时程法的钢筋混凝土框架弹塑性地震响应及损伤发展

耐震时程法（ETA）仅需少量的非线性时程分析,便可以掌握结构倒塌破坏的全过程。但是,此方法目前较少应用于结构倒塌失效分析。本文探讨了耐震时程曲线的特性及拟合思路,以钢筋混凝土框架为研究对象,应用ETA方法分析了钢筋混凝土框架的地震响应及损伤发展。研究结果:（1）混凝土框架结构的地震响应分析结果表明:采用ETA方法分析时结构顶点位移和层间位移角与采用IDA方法分析时接近,而最大基底剪力会略大;但是,两种方法的结果相关系数均接近于1。（2）强震下的结构倒塌分析结果表明:ETA方法能较为准确的预测结构的塑性铰分布、塑性铰出现概率及塑性铰发展顺序。当采用多条耐震时程加速度曲线作为输入时,评估结果准确性更高。由于ETA方法仅需进行少量几条耐震时程分析且计算高效,因此ETA方法可以成为预测结构失效模式的高效方法。     

Seismic performance evaluation of a self-centering precast reinforced concrete frame structure

The seismic performance of a five-story, four-bay, self-centering precast reinforced concrete frame(SC-RCF), which was redesigned using the direct displacement-based design method, was analytically investigated. The analytical model of the overall structure was developed in Open Sees. The multi-spring contact element was adopted to simulate gap open-close behavior at connection interfaces. The limit states of external mild steel dampers and unbonded post-tensioning strands were considered. Static pushover analyses were performed up to the roof drift of 10%. The nonlinear dynamic responses under four groups of ground motions(with different fault distances and site conditions) at six hazard levels(from the service to the very rare earthquake(VRE)) were compared. Incremental dynamic analyses were implemented to quantify the structural collapse risk. The results showed that the structural responses of SC-RCF were satisfactory under all levels of earthquakes. The collapse safety of the structure under earthquakes up to VRE1 was adequate, while the structure would collapse to a large extent under VRE2 and VRE3.     

Inelastic spectra for infilled reinforced concrete frames

In two companion papers a simplified non‐linear analysis procedure for infilled reinforced concrete frames is introduced. In this paper a simple relation between strength reduction factor, ductility and period (R–µ–T relation) is presented. It is intended to be used for the determination of inelastic displacement ratios and of inelastic spectra in conjunction with idealized elastic spectra. The R–µ–T relation was developed from results of an extensive parametric study employing a SDOF mathematical model composed of structural elements representing the frame and infill. The structural parameters, used in the proposed R–µ–T relation, in addition to the parameters used in a usual (e.g. elasto‐plastic) system, are ductility at the beginning of strength degradation, and the reduction of strength after the failure of the infills. Formulae depend also on the corner periods of the elastic spectrum. The proposed equations were validated by comparing results in terms of the reduction factors, inelastic displacement ratios, and inelastic spectra in the acceleration–displacement format, with those obtained by non‐linear dynamic analyses for three sets of recorded and semi‐artificial ground motions. A new approach was used for generating semi‐artificial ground motions compatible with the target spectrum. This approach preserves the basic characteristics of individual ground motions, whereas the mean spectrum of the whole ground motion set fits the target spectrum excellently. In the parametric study, the R–µ–T relation was determined by assuming a constant reduction factor, while the corresponding ductility was calculated for different ground motions. The mean values proved to be noticeably different from the mean values determined based on a constant ductility approach, while the median values determined by the different procedures were between the two means. The approach employed in the study yields a R–µ–T relation which is conservative both for design and performance assessment (compared with a relation based on median values). Copyright © 2004 John Wiley & Sons, Ltd.     

Seismic retrofit of reinforced concrete frames using buckling‐restrained braces with bearing block load transfer mechanism

A new method of retrofitting reinforced concrete (RC) frames with buckling‐restrained braces (BRBs) to improve frame strength, stiffness and energy dissipation is proposed. Instead of typical post‐installed anchors, load is transferred between the BRB and RC frame through compression bearing between an installed steel frame connected to the BRB, and high‐strength mortar blocks constructed at the four corners of the RC frame. This avoids complex on‐site anchor installation, and does not limit the allowable brace force by the anchor strength. Cyclic displacements of increasing amplitudes were imposed on two RC frame specimens retrofitted with different BRB strength capacities. In one of the frames, the bearing blocks were reinforced with wire mesh to mitigate cracking. A third RC frame was also tested as a benchmark to evaluate the retrofit strength and stiffness enhancements. Test results indicate that the proposed method efficiently transferred loads between the BRBs and RC frames, increasing the frame lateral strength while achieving good ductility and energy‐dissipating capacity. When the bearing block was reinforced with wire mesh, the maximum frame lateral strength and stiffness were more than 2.2 and 3.5 times the RC frame without the BRB respectively. The BRB imposes additional shear demands through the bearing blocks to both ends of the RC beam and column member discontinuity regions (D‐regions). The softened strut‐and‐tie model satisfactorily estimated the shear capacities of the D‐regions. A simplified calculation and a detailed PISA3D analysis were shown to effectively predict member demands to within 13.8% difference of the measured test results. Copyright © 2016 John Wiley & Sons, Ltd.     

空间钢筋混凝土框架结构的非弹性地震反应

对两个缩比为十五分之一的三层、双跨、两开间的钢筋混凝土框架模型进行了振动台试验,一个模型模拟质量中心与刚度中心不一致的偏心结构,另一个模型模拟承受双向地面运动的结构。研究了结构的空间非弹性地震反应。计算结果表明,理论分析与实测结果有较好的吻合性。     

Earthquake behavior of steel cushion-implemented reinforced concrete frames

The earthquake performance of vulnerable structures can be increased by the implementation of supplementary energy-dissipative metallic elements. The main aim of this paper is to describe the earthquake behavior of steel cushion-implemented reinforced concrete frames (SCI-RCFR) in terms of displacement demands and energy components. Several quasi-static experiments were performed on steel cushions (SC) installed in reinforced concrete (RC) frames. The test results served as the basis of the analytical models of SCs and a bare reinforced concrete frame (B-RCFR). These models were integrated in order to obtain the resulting analytical model of the SCI-RCFR. Nonlinear-time history analyses (NTHA) were performed on the SCI-RCFR under the effects of the selected earthquake data set. According to the NTHA, SC application is an effective technique for increasing the seismic performance of RC structures. The main portion of the earthquake input energy was dissipated through SCs. SCs succeeded in decreasing the plastic energy demand on structural elements by almost 50% at distinct drift levels.     

RC框架结构地震塑性损伤分析

基于经典塑性模型与连续损伤模型,根据广义应力空间塑性力学确定了塑性变形的演化法则,文中发展了一种地震塑性损伤分析方法。用来进行混凝土框架结构的抗震分析,将塑性损伤的本构关系运用于两端具有塑性铰的梁模型,模拟框架结构的梁柱。同时该方法的损伤指数可以确定结构各单元和整体的地震时性能,确定结构极限荷载,算例表明该方法具有可靠的精度。     

Tests on cyclic behavior of reinforced concrete frames with brick infill

This paper reports the results of cyclic loading tests performed on four specimens consisting of reinforced concrete frames with brick infill walls. The brick infill is pre‐laid, followed by the cast in‐place RC columns and beams. Test parameters include the height‐to‐length ratio of the brick infill wall and the mortar compressive strength. Test results reveal that the in‐plane lateral strength of brick infill wall is related to the fracture path. The fracture path for brick infill walls with large height‐to‐length ratios includes bed joints, cross joints, and vertical splitting of bricks. As a result, the lateral strength of this type of brick infill wall is larger. In comparison, the fracture path for brick infill walls with small height‐to‐length ratios only passes through joints, which is the reason why they have lower lateral strength. Mortar with higher strength improves the lateral strength of brick infill wall. In addition to presenting experimental observations in detail, this paper compares the test results with those obtained from existing methods for assessment of seismic resistance. Comments and recommendations are offered with respect to the capabilities of the assessment methods in predicting stiffness, strength, and ultimate deformation capacity of brick infill walls. Copyright © 2015 John Wiley & Sons, Ltd.     

Seismic fragilities of single-column highway bridges with rocking column-footing

Rocking isolation has been increasingly studied as a promising design concept to limit the earthquake damage of civil structures. Despite the difficulties and uncertainties of predicting the rocking response under individual earthquake excitations (due to negative rotational stiffness and complex impact energy loss), in a statistical sense, the seismic performance of rocking structures has been shown to be generally consistent with the experimental outcomes. To this end, this study assesses, in a probabilistic manner, the effectiveness of using rocking isolation as a retrofit strategy for single-column concrete box-girder highway bridges in California. Under earthquake excitation, the rocking bridge could experience multi-class responses (eg, full contacted or uplifting foundation) and multi-mode damage (eg, overturning, uplift impact, and column nonlinearity). A multi-step machine learning framework is developed to estimate the damage probability associated with each damage scenario. The framework consists of the dimensionally consistent generalized linear model for regression of seismic demand, the logistic regression for classification of distinct response classes, and the stepwise regression for feature selection of significant ground motion and structural parameters. Fragility curves are derived to predict the response class probabilities of rocking uplift and overturning, and the conditional damage probabilities such as column vibrational damage and rocking uplift impact damage. The fragility estimates of rocking bridges are compared with those for as-built bridges, indicating that rocking isolation is capable of reducing column damage potential. Additionally, there exists an optimal slenderness angle range that enables the studied bridges to experience much lower overturning tendencies and significantly reduced column damage probabilities at the same time.     

Retrofit of reinforced concrete frames with buckling‐restrained braces

Damage to buildings observed in recent earthquakes suggests that many old reinforced concrete structures may be vulnerable to the effects of severe earthquakes. One suitable seismic retrofit solution is the installation of steel braces to increase the strength and ductility of a building. Steel bracings have some compelling advantages such as their comparatively low weight, their suitability for prefabrication, and the possibility of openings for utilities, access, and light. The braces are typically connected to steel frames that are fixed to the concrete structure using post‐installed concrete anchors along the perimeter. However, these framed steel braces are not without some disadvantages such as heavier steel usage and greater difficulties during the installation. Therefore, braces without steel frames appear to be an attractive alternative. In this study, braces were connected to gussets furnished with anchor brackets, which were fixed by means of a few post‐installed concrete anchors. The clear structural system and the increased utilization of the anchors allowed the anchorage to be designed precisely and economically. The use of buckling‐restrained braces (BRBs) provides additional benefits in comparison with conventional braces. BRBs improve the energy dissipation efficiency and allow the limitation of the brace force to be taken up by the highly stressed anchorage. Cyclic loading tests were conducted to investigate the seismic performance of BRBs connected with post‐installed anchors used to retrofit reinforced concrete frames. The tests showed that the proposed design method is feasible and increases strength as well as ductility to an adequate seismic performance level. Copyright © 2014 John Wiley & Sons, Ltd.     

Seismic performance of laminated timber frames with fiber‐reinforced joints

A series of dynamic experiments was performed on two‐story glue‐laminated timber frames. The tests included sinusoidal sweeps in one direction, arbitrary signals simulating earthquake loads in two directions, and harmonic free vibration at the fundamental frequency. Two experimental frames were manufactured and tested: (1) a control with horizontal laminations and no reinforcement at joint areas, and (2) a new frame design with densified material in the joint area that was further reinforced by glass‐fiber composite material. Preliminary tests of scaled and full‐size beam‐to‐column connections were performed to obtain connection characteristics needed for subsequent analytical modeling. Copyright © 2004 John Wiley & Sons, Ltd.     

钢筋混凝土框架延性破坏准则研究

结构试验研究和理论分析均表明框架变形能力强弱对抗震性能具有显著影响,已有框架破坏准则无法全面反映不同延性结构变形能力差异.文中提出了一种框架结构最大变形能力的定义和计算方法;通过研究柱轴压比、配箍率、结构变形能力、试验加载制度与整体性能退化之间的相互关系,提出了钢筋混凝土框架的延性破坏准则.通过对25榀平面框架试验的计...     

钢筋混凝土分体柱的抗震机理

为揭示钢筋混凝土分体柱的抗震机理,在以前模型试验基础上,考虑隔板与单元柱之间的非线性接触及钢筋与混凝土之间的黏结滑移,数值模拟了钢筋混凝土分体柱的抗震性能。结果表明:分体柱可实现变短柱为“长”柱的设想;分体柱具有理想的变形能力和延性,延性系数达到4.0;分体柱的刚度随变形增加呈指数衰减,后期刚度退化较为缓和;分体柱具有较高的耗能能力,其耗能系数达1.44;隔板与单元柱的切向接触应力较小,可忽略隔板对单元柱的变形协调作用。进一步验证了钢筋混凝土分体柱具有理想的抗震性能,完善和发展了钢筋混凝土分体柱的设计理论和应用技术。     

Stochastic analysis of reinforced concrete frames under seismic excitation

The theoretical background and capabilities of a program for stochastic analysis of plane frames of reinforced concrete, under seismic excitation with emphasis on the analysis of stiffness degradation due to severe plastic deformations, are presented. As a constitutive moment-curvature relation an extended version of the model of Roufaiel-Meyer, taking into account the transition from uncracked to cracked sections, has been applied. Further, a different mechanism for the strength deterioration is utilized.Different positive and negative yield moments for unsymmetrical cross-sections may be specified, as well as moments and axial forces due to gravity loads or due to residual stresses from plastic deformations during previous earthquake excitations. The effect of axial forces on the moment-curvature relationship is taken approximately into account through a modified initial yield moment. The P − σ effect of the axial force is considered by the introduction of a global geometrical stiffness matrix. The finite length of plastic length of plastic end zones is taken into account, controlling the plasticity at the end sections and at three internal cross-sections of the member. Incremental bending stiffness between these control sections is determined by linear interpolation. The stochastic earthquake excitation may be specified either as a standardized acceleration time-series, applied at the earth-surface and scaled with stochastically varying maximum acceleration and duration, or as an intensity modulated Gaussian white noise process filtered through a Kanai-Tajimi filter. Based on Monte-Carlo simulation the program calculates the mean values and the standard deviations of storey displacements and bending moments in critical sections, as well as the mean values, standard deviations and correlation coefficients of various maximum softening damage indicators, defined from time-averaged first and second eigen-periods.In order to reduce the calculation time during extensive simulations, a system reduction scheme has been implemented, based on a truncated expansion of external nodal point degrees-of-freedom in the linear eigenmodes of the initial undamaged structure. Further, only beam-elements, with non-linear behaviour are treated as nonlinear elements. These elements are identified adaptively during the simulation process. In order to demonstrate the ability of the program to predict the actual seismic response of reinforced concrete structures, computed results have been successfully compared to the experimentally recorded results of a 10-storey 4-bay reinforced concrete model.     

Quantitative approach for damage detection of reinforced concrete frames

The objective of this paper is to provide an analytical basis for the quantitative evaluation of damage to a reinforced concrete structure based on the vibration data obtained by using the damage detection technique. A partial reinforced concrete system of a weak beam/strong column moment frame is chosen as an example. A pushover analysis is carried out in order to numerically examine both the story shear-relative displacement characteristics and the associated damage level. In the analysis, a two dimensional nonlinear finite element analysis is employed considering several constitutive models. As a result, the degradation of the stiffness at the damaged story is characterized in association with the story relative displacement. It is also pointed out that the rotation angle of the column-base is highly correlated with the story relative displacement. Based on the analytical findings, quantitative approaches for a structural health monitoring system are suggested considering both the current sensor technologies and those available in the future. Supported by: Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research (Base Research (c) (1), Research No. 14550555)     

钢筋混凝土渡槽结构地震反应数值分析

首先介绍了钢筋混凝土渡槽结构在地震荷载作用下的分析理论,根据这些理论建立了渡槽结构的动力有限元分析模型,分别采用干模态法、附加质量法和ALE法考虑渡槽结构液固耦合作用,通过具体的工程算例,对钢筋混凝土渡槽结构进行了不同工况下的数值模拟研究,包括混凝土非线性材料分析、渡槽结构静水与动水响应分析、渡槽结构自振特性分析和槽墩的能力曲线分析。研究表明,考虑固液耦合作用的渡槽实体有限元模型能较好地模拟渡槽结构地震反应,并得到相应的渡槽结构地震反应规律。