Damage‐controlled performance‐based design optimization of steel moment frames

In the present paper, performance‐based design of steel moment‐resisting frames (SMRFs) is implemented to minimize total cost of the structures. The total cost is summation of the initial construction cost and the seismic damage cost in operational lifetime of the structures subjected to seismic loading. In order to evaluate the seismic damage cost, Park–Ang damage index (DI), as one of the most realistic measures of structural seismic damage, is utilized. To calculate the DI, nonlinear time‐history response of the structure needs to be evaluated during the optimization process. As the computational burden of the process is very high, neural network techniques are utilized to predict the required nonlinear time‐history structural responses. As the design constraints, besides the drift checks at immediate occupancy and collapse prevention performance levels, the global DI is also checked at collapse prevention level to control the amount of seismic damage. In order to achieve the optimization task, a sequential enhanced colliding bodies optimization II is proposed. Numerical studies are conducted to demonstrate the efficiency of the proposed methodology involving 2 illustrative examples of a 6‐story SMRF and a 12‐story SMRF.     

Advanced energy‐based analyses of trusses employing hybrid metaheuristics

Total potential optimization using metaheuristic algorithm (TPO/MA) is an alternative method in structural analyses, and it is a black‐box application for nonlinear analyses. In the study, an advanced TPO/MA using hybridization of several metaheuristic algorithms is investigated to solve large‐scale structural analyses problems. The new generation algorithms considered in the study are flower pollination algorithm (FPA), teaching learning‐based optimization, and Jaya algorithm (JA). Also, the proposed methods are compared with methodologies using classic and previously used algorithms such as differential evaluation, particle swarm optimization, and harmony search. Numerical investigations were carried out for structures with four to 150 degrees of freedoms (design variables). It has been seen that in several runs, JA gets trapped into local solutions. For that reason, four different hybrid algorithms using fundamentals of JA and phases of other algorithms, namely, JA using Lévy flights, JA using Lévy flights and linear distribution, JA with consequent student phase, and JA with probabilistic student phase (JA1SP), are developed. It is observed that among the variants tried, JA1SP is seen to be more effective on approaching to the global optimum without getting trapped in a local solution.     

The effect of design drift limit on the seismic performance of RC dual high‐rise buildings

Current building codes aim to ensure the acceptable performance of structures implicitly. Because these provisions are empirically developed for low‐ to medium‐rise buildings, their applicability to high‐rise building warrants further investigation. In this paper, the effect of design drift limit on the seismic performance of reinforced concrete dual high‐rise buildings is considered. Nine buildings are designed for 3 drift limits: the code limit (i.e., 2%), one that is lower than the code limit (i.e., 1.5%), and one that is higher than the code limit (i.e., 3%). For each drift limit, buildings of 3 heights (20, 25, and 30 stories) are designed. Finite element models are constructed in OpenSees, and incremental dynamic analysis is performed. The results are used to develop probabilistic seismic demand models, where model parameters are determined using maximum likelihood estimation to incorporate equality and censored data. Reliability analysis using probabilistic demand models is conducted to derive seismic fragility and demand hazard curves. In addition, the collapse performance of the drift limits is evaluated using the Federal Emergency Management Agency (FEMA) P695 procedure. The study results show that the design drift limit affects the building's seismic performance, and the effect depends on the performance level considered. Moreover, from a structural integrity perspective, a larger design drift limit does not induce a significantly higher risk and might yield a more cost‐effective design.     

基于构件重要性指标的RC框架结构抗震优化设计研究

通过引入基于结构广义刚度的构件重要性指标,提出了考虑构件重要程度差异的RC框架结构抗震优化设计方法。根据“构件重要性越大,承载力储备也越大”的结构系统设计策略,以构件的重要性程度由小到大逐渐发生损伤破坏的破坏模式为目标,根据现有一般构件的安全储备取值,建议了基于构件重要性指标的安全储备表达式。以广义结构刚度损失率作为结构失效判定依据,通过一RC框架结构抗震设计算例,分别对采用基于构件重要性指标方法和现行规范方法设计的结果进行对比,结果表明,建议方法的设计结果,其配筋分布更加合理,抗震性能得到显著改善,且总用钢量略有降低。     

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.     

Direct displacement‐based design of steel‐braced reinforced concrete frames

This study investigates a direct displacement‐based design procedure for dual system structures composed of reinforced concrete frames and steel bracings. In this procedure, in order to establish the design displacement profile before any analysis, strength proportions between bracings and frames are assigned. By using the displacement profile and damping characteristics of the structural components, the structure can be represented as an equivalent single‐degree‐of‐freedom system. The effective period and secant stiffness of the structure are then calculated, and finally, after the base shear was computed, the design process can be implemented. Structures with 4, 8 and 12 stories have been designed using this methodology, and in order to validate it, seven accelerograms have been used for nonlinear time‐history analysis of the above structures. The results demonstrate the efficiency of this procedure. Copyright © 2012 John Wiley & Sons, Ltd.     

Performance‐based seismic design of an irregular tall building in Istanbul

Structural design of a 50‐story tall reinforced concrete residential building, which was planned to be constructed in Istanbul and given up afterwards by the investor, has been completed in accordance with the draft version of Seismic Design Code for Tall Buildings in Istanbul that adopts performance‐based seismic design as the basic approach as Tall Buildings Initiative Guidelines do. Seismic design of the building has formed the main part of the structural design process due to high seismicity of the proposed location and extremely irregular floor plan not conforming to usual tall building structures. The building consists of two individual buildings linked through sky floors at the top 12 stories whose design was one of the most challenging works. The building has been designed for design basis earthquake by elastic response spectrum analysis, and its seismic performance has been checked for maximum considered earthquake by nonlinear time‐history analyses carried out using PERFORM‐3D. Copyright © 2015 John Wiley & Sons, Ltd.     

Estimation of optimum design of structural systems via machine learning

Three different structural engineering designs were investigated to determine optimum design variables, and then to estimate design parameters and the main objective function of designs directly, speedily, and effectively. Two different optimization operations were carried out: One used the harmony search (HS) algorithm, combining different ranges of both HS parameters and iteration with population numbers. The other used an estimation application that was done via artificial neural networks (ANN) to find out the estimated values of parameters. To explore the estimation success of ANN models, different test cases were proposed for the three structural designs. Outcomes of the study suggest that ANN estimation for structures is an effective, successful, and speedy tool to forecast and determine the real optimum results for any design model.     

Performance‐based plastic design and collapse assessment of diagrid structure fused with shear link

A diagrid structure fused with shear link (DSSL) is an innovative earthquake resilient structural system. The DSSL combines the steel diagrid structural system with shear links to dissipate the earthquake energy with the goal to minimize structural repair and downtime after strong earthquake shaking. The SLs are placed between diamond‐shaped grid units and decoupled from the gravity system. To facilitate the design of the proposed DSSL system, the performance‐based plastic design (PBPD) procedure is extended to design a prototype building utilizing DSSL. Detailed finite element model is developed to simulate the non‐linear dynamic response of the structure under a range of earthquake shaking intensities. The results of non‐linear dynamic analyses show that the DSSL has excellent seismic performance and can be efficiently designed using PBPD. Lastly, detailed collapse risk assessment of the prototype building is performed using the FEMA‐P695 methodology. The result shows that the PBPD‐designed DSSL has adequate margin against collapse. Hence, it can be used as an effective seismic force resisting system.     

Optimum placement of supplementary viscous dampers for seismic rehabilitation of steel frames considering soil–structure interaction

In this paper, the significance of soil–structure interaction (SSI) in optimal placement of viscous dampers in steel frames is studied. Optimal placement of dampers is determined with the purpose of achieving performance objectives at three hazard levels using genetic algorithm optimization. Endurance time method is used for seismic nonlinear response analysis of the fixed‐base and SSI included frames. The soil beneath the structures is considered as a homogeneous elastic half‐space, and the soil–structure systems are modeled by the substructure method. Results indicate that at low excitation intensities, consideration of SSI results in maximum drift ratio reduction at all stories of the frames. At higher intensity levels, more drift is observed in the upper stories of the soil–structure systems in comparison with the fixed‐base frames. Higher damping in the upper stories is required to optimally rehabilitate soil–structure systems as compared with the corresponding fixed‐base ones. In most of the frames, SSI leads to the reduction of total required damping. However, the optimal damper placement based on the analysis of fixed‐base frames can be unconservative due to changes in damping distribution patterns.     

Performance‐based evaluation and strengthening of tall buildings in the Los Angeles region by using Bayesian structural reliability

This paper presents the motivation and the mathematics required for the introduction of Bayesian structural reliability theory into the process of evaluating and strengthening any tall building located in the Los Angeles region. Copyright © 2013 John Wiley & Sons, Ltd.     

Seismic performance of Y‐type eccentrically braced frames combined with high‐strength steel based on performance‐based seismic design

In the Y‐type eccentrically braced frame structures, the links as fuses are generally located outside the beams; the links can be easily repairable or replaceable after earthquake without obvious damage in the slab and beam. The non‐dissipative member (beams, braces, and columns) in the Y‐type eccentrically braced frames are overestimated designed to ensure adequate plastic deformation of links with dissipating sufficient energy. However, the traditionally code design not only wastes steel but also limits the application of eccentrically braced frames. In this paper, Y‐type eccentrically braced steel frames with high‐strength steel is proposed; links and braces are fabricated with Q345 steel (the nominal yield stress is 345 MPa); the beams and columns are fabricated with high‐strength steel. The usage of high‐strength steel effectively decreases the cross sections of structural members as well as reduces the construction cost. The performance‐based seismic design of eccentrically braced frames was proposed to achieve the ideal failure mode and the same objective. Based on this method, four groups Y‐type eccentrically braced frames of 5‐story, 10‐story, 15‐story, and 20‐story models with ideal failure modes were designed, and each group includes Y‐type eccentrically braced frames with ordinary steel and Y‐type eccentrically braced frames with high‐strength steel. Nonlinear pushover and nonlinear dynamic analyses were performed on all prototypes, and the near‐fault and far‐fault ground motions are considered. The bearing capacity, lateral stiffness, story drift, link rotations, and failure modes were compared. The results indicated that Y‐type eccentrically braced frames with high‐strength steel have a similar bearing capacity to ordinary steel; however, the lateral stiffness of Y‐type eccentrically braced frames with high‐strength steel is smaller. Similar failure modes and story drift distribution of the prototype structures designed using the performance‐based seismic design method are performed under rare earthquake conditions.     

Optimum seismic design of steel framed‐tube and tube‐in‐tube tall buildings

The relatively large number of structural elements and the variety of design code requirements complicate the design process of tall buildings. This process is exacerbated when the target is to obtain the seismic code‐compliant optimal design with minimum weight. The present paper aims at providing a practical methodology for the optimal design of steel tall building structures considering the constraints imposed by typical building codes. The applicability of the proposed approach is demonstrated through the determination of the optimal seismic design for 20‐, 40‐, and 60‐story buildings with a framed tube as well as a tube‐in‐tube system. Such a design gives rise to a basis for the fair comparison of the behavior of the framed tube with that of the tube‐in‐tube system under applied loads. The optimal weight of the buildings with the tube‐in‐tube system turns out to be slightly less than that of the buildings with the conventional framed‐tube system.     

A_y-D_y格式地震需求谱及其在结构性能抗震设计中的应用

在结构基于位移抗震设计的改进能力谱法基础上建议了屈服谱加速度和屈服位移(Ay-Dy)格式的地震需求谱,其特点是:过原点的射线与不同位移延性系数的需求谱曲线相交,各个交点对应的周期都相同,从而为在结构基于位移抗震设计方法中实现“小震不坏、中震可修和大震不倒”的多级性能目标提供了方便。借助于Pushover分析具体给出了一钢筋混凝土框架结构在不同风险水平地震作用下抗震性能评价实例。     

基于整体承载极限状态的钢结构可靠度设计方法及其在门式钢刚架设计中的应用

本文提出了基于整体承载极限状态的钢结构可靠度设计思路。这种思路建立在钢结构整体非线性分析和验算的基础上,并确保结构整体而非构件的可靠度水平,使结构整体的实际可靠度水平尽可能地接近于设计的目标值。本文针对门式钢刚架结构建立了一套实现这种设计的方法,包括结构整体非线性分析、结构体系可靠度计算以及实用的设计表达式。通过三个门式钢刚架结构设计实例比较了传统的构件设计方法,不考虑体系可靠度的整体承载极限状态设计方法和本文考虑体系可靠度的整体承载极限状态设计方法的设计结果,说明本文所提出设计思想的先进性。     

ISCS method for the performance‐based seismic design of vertically irregular reinforced concrete frame structures

The procedure to obtain the inelastic demand curves for the multi‐degree‐of‐freedom system, composed of inter‐story shear versus inter‐story displacement curve is introduced. The demand curves are established by using mode spectrum method, and the dynamical characteristic of structure under different earthquake hazard levels is taken into account. The relation of structure performance object and displacement ductility is adopted to deduce the relation of structure performance object and inter‐story demand curve. Therefore, the inter‐story demand curves take into account the inelastic behavior of structure under earthquake action adequately. Then, considering the seismic responding characteristic and the capacity curve of the frame structure, a new method named Inter‐Story Capacity Spectrum (ISCS) is put forward for the performance‐based seismic design of vertically irregular frame structures. Examples are presented to demonstrate the applicability and the utility of the proposed method. It is concluded that the new method can control the inter‐story drift, the order and position of hinges of vertically irregular structures under different earthquake hazard levels. Comparing with time‐history analysis method, it leans to safe and is superior to direct displacement‐based design method. Copyright © 2011 John Wiley & Sons, Ltd.     

钢筋混凝土桥墩基于位移的抗震设计方法

通过改进能力谱法,给出了一个可以实现“小震不坏、中震可修和大震不倒”多级性能目标的钢筋混凝土桥墩直接基于位移的抗震设计方法。首先以钢筋和混凝土的应变幅值建立了钢筋混凝土桥墩不同破损极限状态的量化准则,并基于曲率延性系数和位移延性系数关系转化为墩顶位移的表述形式。再以屈服位移和位移延性系数作为设计参考变量,采用屈服谱加速度和屈服位移(Ay-Dy)格式的地震需求谱求解系统在不同风险水平地震作用下的反应。最后以能力设计原理保证桥墩截面的抗剪强度需求。通过一个具体设计算例说明了建议方法的可行性。     

Reduction of inelastic seismic demands in a mid‐rise rocking wall structure designed using the displacement‐based design procedure

Precast post‐tensioned rocking wall structural system has been developed in the recent past as a damage‐avoidance structural system for seismic regions. For a widespread use of this structural system, suitable design procedures are required to ensure a reliable and well‐predicted performance under different levels of seismic hazard. In the current study, a mid‐rise 20‐story rocking wall structure is selected and designed using the displacement‐based design procedure. Furthermore, two different capacity design procedures are used to predict the increased force demands due to higher mode effects. The time history results against moderate and severe level of seismic hazards show the effectiveness of displacement‐based design procedure in predicting and controlling the displacement and drift demands, while the simplified procedure and the modified modal superposition procedure for the capacity design are found to be unconservative and conservative, respectively. To further investigate the seismic demands, modal decomposition of inelastic seismic responses is carried out, and the contribution of different modes in the total responses is calculated. Based on this improved understanding, a mitigation technique of dual gap opening is employed. A detailed discussion about the location and design strength of the extra gap‐opening is carried out by considering different performance parameters. Copyright © 2016 John Wiley & Sons, Ltd.     

基于可靠度的结构抗震优化设计

介绍了结构抗震设计的目的与目标,并对基于概率可靠度的结构抗震设计方法进行了阐述,根据“投资—效益”准则,提出了基于功能的结构体系目标可靠度优化决策的三种模型,从而为结构抗震优化设计的进一步研究奠定了理论基础。