钢筋混凝土房屋自振周期的经验公式

一、前言 众所周知,地震力计算常采用弹性地震反应谱的底部剪力法和振型分解反应谱法。所涉及到的标准反应谱是以α与T曲线的形式表述的。因此,需先给出建筑物的自振周     

建筑自振周期经验公式一些问题的探讨

用统计分析方法归纳出的自振周期值的经验公式,具有形式简单、使用方便的优点。本文就基本周期经验公式的参数、脉动实测修正系数、误差等问题进行一些控讨。同时,通过统计分析给出第二振型、第三振型周期与基本周期比值的经验公式。采用这一结果,可推出求高振型周期经验公式。     

填充墙框架结构自振周期折减系数研究

目前规范针对混凝土空心砌块、加气混凝土砌块等一些新型砌体填充墙材料周期折减系数的取值问题尚未明确规定,但是自振周期折减系数对地震作用下RC框架结构的动力响应有着重要的影响。针对新型砌体填充墙RC框架结构的自振周期折减系数,运用Sap2000有限元软件进行分析研究并探讨了由于框架填充墙材料的不同、楼层层数的不同导致自振周期和周期折减系数的取值不同问题,给自振周期折减系数的取值提出了合理建议,为今后在结构设计中针对RC框架结构周期折减系数的取值大小问题提供有力的参考依据。     

高层钢筋混凝土框架结构自振周期估算的研究

对高层钢筋混凝土框架结构基本自振周期的估算方法进行了探讨,建立了计算更简便、平均误差更小的估算公式。     

关于单层钢筋混凝土厂房自振周期经验公式的若干问题

一、前言 众所周知,振动作为机械运动的特例就在于它具有在平衡位置附近做往复运动的特征,因此自振周期就成为表示这种运动特征的重要参数之一。我国的抗震设计规范规定,单层工业厂房的抗震计算可主要采用基     

柔性连接多高层钢框架结构的基本自振周期近似计算方法

提出了在底部剪力法计算柔性连接多、高层钢框架结构的基本自振周期时 ,应考虑节点柔性对它的影响 ,该方法也可同时考虑梁柱效应的影响。通过分析和算例表明 ,考虑节点柔性对钢框架基本自振周期的影响是必要的 ,这样不会使设计过于保守 ,与多、高层钢框架结构实际的受力和变形特点相一致 ,供钢框架设计时参考。     

填充墙对框架结构自振周期的影响分析

建立29个带填充墙的10层框架结构有限元模型,研究填充墙的材料、空间布置、各层墙数量等因素对结构自振周期的影响。分析表明:填充墙材料对自振周期影响较小,而薄弱层填充墙的数量及其在楼层中的位置是影响周期的两个主要原因。根据分析,提出考虑填充墙影响的框架结构自振周期修正模型。     

钢结构单管通信塔自振基本周期的研究

单管塔是目前通信铁塔中应用越来越广泛的一种形式,但在设计单管塔时,由于现行规范提供的自振基本周期经验公式计算结果与实际计算结果有较大的差异,导致风荷载计算值的不同,因此本文以壳体振动理论为基础,通过有限元计算拟合出估算单管通信塔结构自振基本周期的实用公式,以供实际工程设计参考。     

高层建筑结构基本自振周期合理范围研究

高层建筑基本自振周期T₁反映了高层建筑质量和刚度分布特性,在结构方案设计阶段,控制基本自振周期在合理范围不仅能自动满足结构的主要设计指标,还能导向更合理的结构设计。通过分析国内837栋高度50 m以上高层建筑统计数据,得出不同设防烈度、不同高度分组高层建筑的基本自振周期的合理范围和分布规律,并基于简化模型推导了基本自振周期与结构高度关系的实用公式。统计数据分析以及实用公式均表明,T₁与结构高度的平方根■成正比,且■随高度增加而增大,随设防烈度提高而减小。高度250 m以上高层建筑基本自振周期合理范围上限值在■左右,其中8度设防区为■、7度设防区为■、6度设防区为■;如果达到或超过■,则结构刚度过柔。     

框架结构最优刚度与临界自振周期计算方法

本文根据在一定条件下推导得到的规则框架结构自振周期、振型、地震作用、楼层剪力及水平位移等的解析表达式［１］，利用振型分解反应谱法，建立了框架结构基本周期与水平位移限值的关系，通过电算给出了２～２０层不同层高框架结构的临界自振周期与最优刚度，以供设计人员参考。     

Drift control in moment resisting steel frame structures

This paper presents the development of a design methodology for the control of interstory drift caused by equivalent static earthquake loads in tall moment resisting steel frame structures. The methodology captures the flexural and shear drift modes through approximate behavior-based equations and attempts to minimize the total weight of the structural system with due consideration given to both strength and stiffness requirements. The methodology presented is part of an effort to develop a computer-based design support system for the conceptual design of steel frame structures. This design support system, ‘Building Engineering and Reasoning Tool’ (BERT), together with the application of the drift control methodology, are discussed in a companion paper.     

Fundamental period of irregular moment‐resisting steel frame structures

The determination of the fundamental period of vibration of a structure is essential to earthquake design. Current code equations such as American Society of Civil Engineers Standard (ASCE) 7‐10 provide formulas for the approximate period of moment‐resisting frames (MRFs), which are dependent only on the height of the structure or number of stories. Such a formulation is overly conservative and unable to account for structures with geometric irregularities. This study investigated the fundamental periods of MRFs with varying geometric irregularities. The fundamental periods based on vibration theory for each example were compared with empirical equations, including current code equations as well as equations proposed in recent literature. New equations are proposed for the fundamental periods of MRFs, which take into account vertical and horizontal irregularities. Through statistical comparison, it was found that a three‐variable power model that is able to account for irregularities resulted in a better fit to the Rayleigh data than equations that were dependent on height only. The proposed equations were validated through a comparison of available measured period data for MRFs. They will allow design engineers to quickly estimate the fundamental period of MRF structures by taking into account irregularities. Copyright © 2013 John Wiley & Sons, Ltd.     

钢框架结构基于位移的抗震设计方法

与传统基于力的抗震设计方法相比,基于位移的抗震设计方法更易于实现基于性能的抗震设计.在若干文献的基础上,提出了一种钢框架结构基于位移的抗震设计方法.该方法建立在钢框架结构屈服位移可由几何尺寸确定的基础上,然后根据结构的性能水平确定其目标位移(即极限位移),计算相应的延性系数,采用相应的折减弹性谱,据此计算出结构的设计基底剪力,然后对钢框架结构进行刚度设计和承载力设计.算例分析表明,钢框架结构基于位移的抗震设计方法安全可靠,便于操作,而且还能够实现钢框架结构在不同性能水平下的抗震设计.     

Seismic behavior of post-tensioned column base for steel self-centering moment resisting frame

This paper presents experimental and analytical investigation of cyclic response of a post-tensioned column (PT) base connection. The PT column base connection is designed to eliminate structural damage at column bases in self-centering moment resisting frames (SC-MRFs) under seismic loading; the softening behavior at the connection is provided by gap opening and elongation of PT bars rather than yielding in the column. Additional shear resistance is provided by bolted keeper plates; additional energy dissipation is provided by buckling restrained steel (BRS) plates. To investigate the cyclic behavior of the PT column base connection, a series of PT column base connection subassemblies were subjected to axial load and cyclic lateral displacements. Test parameters included initial post-tension force, initial axial force in column (constant or varying), column size and loading history. Limit states investigated for the PT column base connections included PT bar yielding and fracture of BRS plates. The test results demonstrated that properly designed PT column base connections were able to undergo lateral displacement up to 4% interstory drift while the columns and grade beams remained elastic. Also, the BRS plates showed good energy dissipation capacity by yielding in tension and compression without fracture. Structural damage at column bases was limited to the replaceable fuse BRS plates. In addition, analytical models were developed to predict the moment–rotation relationship of the PT column base connection and showed good correlation with the experimental data.     

Seismic performance of moment resisting steel frame subjected to earthquake excitations

This study presents static and dynamic assessments on the steel structures. Pushover analysis (POA) and incremental dynamic analysis (IDA) were run on moment resisting steel frames. The IDA study involves successive scaling and application of each accelerogram followed by assessment of the maximum response. Steel frames are subjected to nonlinear inelastic time history analysis for 14 different scaled ground motions, 7 near field and 7 far field. The results obtained from POA on the 3, 6 and 9 storey steel frames show consistent results for both uniform and triangular lateral loading. Uniform loading shows that the steel frames exhibits higher base shear than the triangular loading. The IDA results show that the far field ground motions has caused all steel frame design within the research to collapse while near field ground motion only caused some steel frames to collapse. The POA can be used to estimate the performance-based-seismic-design (PBSD) limit states of the steel frames with consistency while the IDA seems to be quite inconsistent. It is concluded that the POA can be consistently used to estimate the limit states of steel frames while limit state estimations from IDA requires carefully selected ground motions with considerations of important parameters.     

Fundamental period of masonry infilled moment‐resisting steel frame buildings

It is known to be a necessary practice to study the effect of infill walls on fundamental period and revise the equations included in the current building codes. In this research, the fundamental period of vibration, by modeling an infill wall as a compression strut in three‐dimensional numerical models of moment‐resisting steel frames, was studied. Areas studied in the present research were structures of symmetric infill wall arrangements wherein the effects of various infill percentage, various moduli of elasticity of masonry wall materials, and different numbers of spans were investigated. The mean fundamental period obtained by the formula provided in FEMA450 was 1.3 times greater than the value resulted from the numerical modeling of infilled moment‐resisting steel frames. Moreover, the corresponding coefficient of determination, R², of the curve fitted to numerically obtained periods was found to be 0.65 when the fundamental period of the infilled frames was only estimated based on the height of buildings, indicating a great deal of variation within the results. A new formula was proposed to estimate the fundamental period based on the structure height, infill wall percentage, and modulus of elasticity, at an acceptable level of accuracy so that the R² coefficient was determined to be 0.99 for the results of the proposed formula.     

A moment resisting connection for earthquake resistant structures

This paper proposes a new moment resisting detail for use in earthquake resistant structures. The wedge detail tested in this project is a new design that builds upon the idea of inducing a plastic hinge away from the column face to dissipate the energy that would otherwise yield the connection. The plastic capacity of the beam is locally reduced by decreasing the depth of the web and reforming the flange to the new beam profile. This makes the section more plastic, so reducing the buckling problem suffered by other reduced section joints.Laboratory testing shows that the joint is capable of plastic rotations greater than 0.05 rad without any significant loss of energy dissipation capability, which is far in excess of the requirements for a joint given by the latest standards based on post-Northridge data.     

Fundamental period of irregular concentrically braced steel frame structures

This paper presents the results of investigation on the fundamental periods of concentrically braced frame (CBF) structures with varying geometric irregularities. A total of 12 CBFs are designed and analyzed. On the basis of the results obtained from vibration theory, equations for the approximate fundamental periods are put forth for CBFs, which take into account vertical and horizontal irregularities. Through statistical comparison, it was found that a three‐variable power model that is able to account for irregularities resulted in a better fit to the Rayleigh data than equations that were dependent on height only. The proposed equations were validated through a comparison of available measured period data for CBFs. These proposed equations will allow design engineers to quickly and to accurately estimate the fundamental period of CBF structures by taking into account irregularities. Copyright © 2013 John Wiley & Sons, Ltd.     

Reliability-based assessment of deteriorating steel moment resisting frames

One of the objectives in performance-based earthquake engineering is to quantify the seismic reliability of a structure due to future random earthquakes at a designated site. For that purpose, two performance evaluation processes that do incorporate the effect of aleatory and epistemic uncertainties are illustrated and used in order to calculate the reliability of different height Special Moment Resisting frames through two probabilistic-based measures. These two measures are the confidence levels for satisfying the desired performance levels at given hazard levels and mean annual frequency of exceeding a specified structural capacity.Analytical models are employed including panel zone and a comprehensive model for structural components that not only include strength and stiffness degradation in back bone curve, but also incorporate gradual deterioration of strength and stiffness under cyclic loading. Incremental dynamic analysis is then utilized to assess the structural dynamic behavior of the frames and to generate required data for performance based evaluations. This research is intended to contribute to the progress in improvement of the performance knowledge on seismic design and evaluation of special steel moment resisting frame structures.     

锈蚀RC框架结构连续倒塌抗力机制研究

为研究钢筋锈蚀对钢筋混凝土(RC)框架结构连续倒塌抗力机制的影响,对3个1/2缩尺RC梁-柱子结构开展了拟静力Pushdown试验,其中1个未锈蚀RC梁-柱子结构作为对照,另2个RC梁-柱子结构在节点区采用电化学加速锈蚀方法模拟钢筋锈蚀。试验结果表明：钢筋锈蚀会影响RC梁-柱子结构的裂缝开展顺序及钢筋断裂位置,同时钢筋锈蚀会削弱压拱机制及悬链线机制对RC结构抗连续倒塌能力的提升作用。在边节点锈蚀率为28.6%和中节点锈蚀率为5.2%的情况下,RC梁-柱子结构的第一峰值荷载和极限荷载分别降低了31.2%和57.4%。基于试验结果,通过对比分析验证不同压拱机制理论计算模型及悬链线机制理论计算模型评估锈蚀RC梁-柱子结构连续倒塌抗力机制的有效性。通过对比分析发现：Lu等提出的模型用于评估锈蚀RC梁-柱子结构压拱机制下的第一峰值荷载的准确性高且离散性低;Yu等所提模型对锈蚀RC梁-柱子结构悬链线机制下极限荷载的评估结果较为准确,但偏于保守。