低周反复荷载下钢筋钢纤维混凝土连梁的斜截面承载力

通过低周反复荷载下5个钢筋钢纤维混凝土连梁和1个普通钢筋混凝土连梁的抗剪性能试验,研究了钢纤维对钢筋混凝土连梁裂缝和破坏形态的影响,探讨了钢筋钢纤维混凝土连梁的斜截面承载力随钢纤维掺量的变化规律,结合普通钢筋混凝土连梁斜截面承载力的计算方法,提出了钢筋钢纤维混凝土连梁斜截面承载力的计算公式,比较结果表明,计算值和试验值吻合较好。     

Consolidation of inelastic clays under rectangular cyclic loading

This paper presents a semi-analytical solution for one dimensional consolidation problem of inelastic clays under cyclic loading considering the effect of the change of the consolidation coefficient of the soil layer. Due to change of the consolidation coefficient, and time-dependant loading, Terzaghi's theory would not be applicable in cyclic conditions. In this research, a method based on the time variable exchange along with the superimposing rule is employed to overcome these shortcomings. Changes in the consolidation coefficient are applied in the solution by modifying the loading and unloading durations introducing a Virtual Time. Based on the superimposing rule a set of continuous static loads in specified times are used instead of the cyclic load in the transformed time space. Each full cycle of loading is replaced by a pair of static loads with different signs. Based on the Terzaghi's theory the pore-water pressure distribution and the degree of consolidation are calculated for each static load and the results are superimposed. A set of laboratory consolidation tests under cyclic load and numerical analysis are performed in order to verify the presented method. The numerical solution and laboratory tests results showed the accuracy of the presented method.     

Effect of types of reinforcement on plastic hinge rotation parameters of RC beams under pushover and cyclic loading

Experimental evaluation of reinforced concrete beam specimens with different characteristics of reinforcement subjected to pushover and cyclic loading is presented.Plastic hinge rotation parameters are determined based on the idealization of pushover and hysteresis curves of reinforced concrete beam specimens constructed in two percentage of reinforcement(0.471%and 0.71%) with different ductile characteristics.The experimental test results provide a clear demarcation of the effect of types of loading and the types of reinforcement on the nonlinear performance characteristics of beam specimens.These results are helpful to update the nonlinear modeling parameters of beam components for the specific type of reinforcement used in the construction of a structure.The updated non-linear modeling parameters of beam components in lumped plasticity model are compared with the values of ASCE/SEI 41-06(2007) used for the performance based design of structures.     

钢框架异型节点核心区的受剪机理及承载力计算

为了研究钢框架异型节点的抗震性能以及节点两侧梁的截面高度比和轴压比对核心区抗剪承载力的影响,对6个强构件弱节点型式的异型节点进行了低周反复加载试验,获得了异型节点的破坏模式、滞回性能和承载能力。理论分析和试验结果表明,异型节点在加载过程中上核心区先发生屈服,紧接着下核心区屈服,最终破坏模式有4种;异型节点下核心区对上核心区有约束作用,使得上核心区屈服以后,其所受的剪力仍可以增大,直到下核心区屈服;常规节点核心区的抗剪承载力计算公式对异型节点核心区已不适用。根据试验结果,推导了异型节点核心区的抗剪承载力计算公式。     

往复荷载作用下矩形钢管混凝土压弯构件承载力计算

本文基于往复荷载作用下矩形钢管混凝土压弯构件的实验结果,比较了国内外比较典型的设计规范(程),包括英国BS5400(1979)、美国ACI318—99(1999)和AISC-LRFD(1999)、日本AIJ(1997)、欧洲EC4(1994)、中国GJB4142-2000(2001)和福建省地方标准(送审稿),及本文数值方法在计算往复荷载作用下矩形钢管混凝土压弯构件承载力的差异。结果表明,在进行往复荷载作用下矩形钢管混凝土压弯构件承载力计算时,各种计算方法获得的承载力都偏于安全,其中,数值计算结果与实验结果最接近,GJB4142—2000(2001)的计算结果与实验结果吻合程度稍差,ACI318—99(1999),EC4(1994)和福建省地方标准(送审稿)的计算结果比实验结果约低20％,而BS5400(1979)、AISC—LRFD(1999)和AIJ(1997)的计算结果比实验结果总体上低30％以上。本文结果可供进行矩形钢管混凝土结构设计时参考。     

考虑结构构件退化特性评估大震下RC框架抗整体性倒塌能力

基于大震和特大震下倒塌率目标的抗震分析与设计是结构抗震领域的主要发展方向,而大震及特大震作用下结构抗整体性倒塌能力的准确评估是其中的关键科学问题.首先对国内外结构抗整体性倒塌能力的研究工作进行了总结,重点介绍了多种微观和宏观本构模型特性及大震作用下考虑结构构件退化特性对抗整体性倒塌能力的影响.在此基础上,详细阐述了通过增量动力分析获得结构抗倒塌能力易损性曲线及确定结构抗倒塌能力极限状态的方法.最后以一个RC单层单跨平面框架结构分析模型为例,利用OpenSees分析软件,研究了钢筋后期强度退化对结构抗整体性倒塌能力评估结果的影响,结果表明不考虑钢筋后期强度退化会明显高估结构的抗倒塌能力.     

多层钢框架连续倒塌动力效应分析

为研究多层钢框架连续倒塌由于初始破坏引起的动力效应,本文采用集中塑性铰杆模型,以需求能力比(DCR)为参数,利用瞬时加载法对一榀多层平面钢框架和一个多层空间钢框架进行了弹塑性动力反应分析。分析结果表明:随着DCR的增大,各柱列沿竖向动力放大效应基本不变;当DCR≤0.5时,随着DCR的增大,各柱列动力放大效应基本不变,且一般情况下含失效构件的柱列动力放大效应最显著;当DCR>0.5时,含失效构件的柱列动力放大效应随着DCR的增大而增大,其余柱列动力放大效应随着DCR的增大而减小或基本不变。     

设置粘滞阻尼器的钢框架防连续性倒塌分析

为了研究设置有粘滞阻尼器的减震钢框架结构的防连续倒塌性能,对设置阻尼器的减震钢框架和未设置阻尼器的原钢框架分别进行了地震弹塑性时程分析,比较了两种情况下的层间位移角.分析结果表明,地震作用下,与原结构相比减震结构的层间位移角最大降低了64.3％.接着采用瞬时加载法对底层各柱失效时的减震钢框架和不设置阻尼器的原钢框架分别进行了动力倒塌分析,比较了减震结构和原结构防连续倒塌的能力,分析结果表明,底层柱失效时,减震结构各柱端点处位移均比原结构降低,最大处降低了63.5％.因此减震结构的阻尼器对结构防连续倒塌能起到较大的作用.     

Evaluating the inelastic displacement ratios of moment-resisting steel frames designed according to the Egyptian code

Seismic codes estimate the maximum displacements of building structures under the design-basis earthquakes by amplifying the elastic displacements under the reduced seismic design forces with a deflection amplification factor(DAF). The value of DAF is often estimated as ρ× R, where R is the force reduction factor and ρ is the inelastic displacement ratio that accounts for the inelastic action of the structure according to the definition presented by FEMA P695. The purpose of this study is to estimate the ρ-ratio of moment resisting steel frames(MRSFs) designed according to the Egyptian code. This is achieved by conducting a series of elastic and inelastic time-history analyses by two sets of earthquakes on four MRSFs designed according to the Egyptian code and having 2, 4, 8 and 12 stories. The earthquakes are scaled to produce maximum story drift ratios(MSDRs) of 1.0%, 1.5%, 2.0% and 2.5%. The mean values of the ρ-ratio are calculated based on the displacement responses of the investigated frames. The results obtained in this study indicate that the consideration of ρ for both the roof drift ratios(RDRs) and the MSDRs equal to 1.0 is a reasonable estimation for MRSFs designed according to the Egyptian code.     

Efficiency of employing fiber-based finite-length plastic hinges in simulating the cyclic and seismic behavior of steel hollow columns compared with other common modelling approaches

The accuracy and efficiency of the modelling techniques utilized to model the nonlinear behavior of structural components is a significant issue in earthquake engineering. In this study, the sufficiency of three different modelling techniques that can be employed to simulate the structural behavior of columns is investigated. A fiber-based finite length plastic hinge (FB-FLPH) model is calibrated in this study. In order to calibrate the FB-FLPH model, a novel database of the cyclic behavior of hollow steel columns under simultaneous axial and lateral loading cycles with varying amplitudes is used. By employing the FB-FLPH model calibrated in this study, the interaction of the axial force and the bending moment in columns is directly taken into account, and the deterioration in the cyclic behavior of these members is implicitly considered. The superiority of the calibrated FB-FLPH modelling approach is examined compared with the cases in which conventional fiber-based distributed plasticity and concentrated plasticity models are utilized. The efficiency of the enumerated modelling techniques is probed when they are implemented to model the columns of a typical special moment frame in order to prove the advantage of the FB-FLPH modelling approach.

     

Development of steel dampers for bridges to allow large displacement through a vertical free mechanism

Isolation bearings and dampers are often installed between piers and superstructures to reduce the seismic responses of bridges under large earthquakes. This paper presents a novel steel damper for bridges. The damper employs steel plates as energy dissipation components, and adopts a vertical free mechanism to achieve a large deformation capacity. Quasi-static tests using displacement-controlled cyclic loading and numerical analyses using a finite element program called ABAQUS are conducted to investigate the behavior of the damper, and a design methodology is proposed based on the tests and numerical analyses. Major conclusions obtained from this study are as follows:(1) the new dampers have stable hysteresis behavior under large displacements;(2) finite element analyses are able to simulate the behavior of the damper with satisfactory accuracy; and(3) simplified design methodology of the damper is effective.     

Finite element investigation of steel built-up shear links subjected to inelastic deformations

Non-linear finite element models accounting for large displacements have been used to investigate the behavior of steel built-up shear links that had previously been tested using large-scale experiments. The links were designed using steel grades with yield points ranging from high to low strengths. The objectives of the numerical analyses were to further investigate the non-linear behavior and to correlate the numerical results with experimental observations. Elasto-plastic as well as cyclic stress-strain material properties were incorporated to study the influence of material behavior on the overall shear link response. Non-linear monotonic analyses of the shear links incorporating the cyclic stress-strain steel properties resulted in similar trends in the response as the backbone curves recorded from the physical experiments. The numerical models of built-up shear links utilizing structural grade steels closely correlated to the experimentally recorded shear strength.Models utilizing low yield point steels overestimated the shear strength, which was caused by the characteristics of cyclic behavior of those steels. The detailed numerical models also allowed for investigation of the plastic strain demands on the different components of the link. It was shown that finite element models combined with appropriate stress-strain relationship may be used with confidence to check the design of shear links of different steel grades and sectional geometries.     

Earthquake-induced collapse mechanism of two types of dangerous rock masses

As the economy of China develops, an increasing number of key traffic projects have been undertaken in the west of China, where there are high, steep rock slopes. The collapse of dangerous rock masses, especially following a strong earthquake, is one of common geological disasters known in rock slope engineering. Therefore, it is important to study the collapse mechanism of dangerous rock masses induced by an earthquake and the analysis approach of its stability. This study provides a simple and convenient method to determine the collapse mechanisms of two types of dangerous rock masses (i.e. cantilever and upright) associated with the definition and calculation of the safety factor, which is based on the flexure theory of a constant-section beam by combining with the maximum tensile-stress criterion to depict the process of crack propagation caused by seismic waves. The calculation results show that there are critical crack depths in each form of the dangerous rock masses. Once the accumulated depth of the crack growth during an earthquake exceeds the critical depth, the collapse will occur. It is also demonstrated that the crack extension amount of each step is not a constant value, and is closely associated with the current accumulated crack depth. The greater the cumulative crack depth, the more easily the crack propagates. Finally, the validity and applicability of the proposed method are verified through two actual engineering examples.     

巨型梁设置对巨型钢框架结构地震反应的影响

本文以2个巨型钢框架结构作为算例,通过改变巨型梁数量和位置,假设了不同的结构计算方案,输入代表不同场地条件的5条典型地震动和4个场地类别的设计反应谱,应用有限元分析方法,对不同计算方案的算例进行三维弹性地震反应分析。通过对不同计算方案结果的比较分析,研究了巨型梁的数量和位置对巨型钢框架结构地震反应的影响,为进一步深入研究巨型钢结构的抗震性能及抗震设计方法提供基础。     

型钢混凝土柱受剪承载力的统一计算公式

随着高强、超高强混凝土应用于型钢混凝土结构,型钢混凝土柱受剪承载力的计算缺乏统一的计算公式。为了能够反映型钢混凝土柱的实际受力,提出了以混凝土抗拉强度为基础、考虑型钢与混凝土共同工作的受剪承载力公式。公式形式简单并且能够与《混凝土结构设计规范》(GB50010-2002)衔接,适用于工程实践。通过77根型钢高强、普强混凝土柱的对比分析,计算结果与试验结果吻合。公式可应用于混凝土强度在C30~C80之间的型钢混凝土柱,可以将型钢普强混凝土柱和型钢高强混凝土柱的受剪承载力计算统一,因此可称之为型钢混凝土柱受剪承载力的统一计算公式。     

Investigation of story ductility demands of inelastic concrete frames subjected to repeated earthquakes

The present study focuses on the influence of repeated earthquakes on the maximum story ductility demands of three-dimensional inelastic concrete frames. A comprehensive assessment is conducted using generic frames with 3-, 6-, 12-, and 18-story structures. Each is assumed to have behaviour factors of 1.5, 2, 4, and 6 referring to Eurocode 8. Stiffness and strength degrading hysteresis rule to represent reinforced concrete structure is considered in the plastic hinge of members. Twenty ground motions are selected, and single, double, and triple events of synthetic repeated earthquakes are considered. Some interesting findings are provided showing that repeated earthquakes significantly increase the story ductility demand of inelastic concrete frames. On average, relative increment of maximum story ductility demand is experienced 1.4 and 1.3 times when double and triple events of repeated earthquakes are induced, respectively. Empirical relationships are also provided to predict these increments where their efficiency is presented examining characteristic 3- and 8-story reinforced concrete buildings.     

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 buckling-restrained 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, load-resisting capacity, strength-adjustment factors and energy dissipation potential. The main parameters varied are the cross-sectional 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 work-point 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.

     

桥梁高墩位移延性能力的探讨

本文运用增量动力分析方法来计算高墩的屈服位移、极限位移和位移延性，给出了应用IDA方法计算屈服位移、极限位移的主要过程，探讨了高阶振型对高墩位移延性能力的影响。通过算例分析表明：现行计算桥墩位移延性系数的方法，如直接应用到高墩，将会导致较大误差；高阶振型对高墩的屈服位移、极限位移和位移延性系数都有较大的影响。