Fuzzy‐sliding mode control of nonlinear smart base‐isolated building under earthquake excitation

In this paper, the effectiveness of the fuzzy sliding mode control strategy on three‐dimensional benchmark building with smart base isolation under seismic excitation has been examined. One of the appropriate control theories for such this nonlinear system is the sliding mode control theory; discontinuous sliding mode theory has weakness such as chattering phenomena. In this paper, we used a combination of fuzzy logic and sliding mode theory for the deletion of this defect. The proposed control theory has been scrutinized by applying on lately developed nonlinear three‐dimensional base‐isolated benchmark building. This building because of the three‐dimensional nature, coalescing of lateral and torsional responses, continuity of responses of the superstructure, and base is modeled with three degrees of freedom on every floor. In this building eight actuators assigned only at the base level and in the two directions (x, y). In other words, 16 actuators are located underneath the structure. Furthermore, the base isolation system has been modeled by considering lateral coupled equations for a better examination of the performance of the system. The results indicate that reduction of control performance is remarkable. Also, utilizing proposed control theory can decrease the responses of building in two main directions and, particularly, in the rotational degree of freedom.     

Seismic response control of base‐isolated buildings using multiple tuned mass dampers

Seismic response of a base‐isolated building equipped with single tuned mass damper (STMD), multiple tuned mass dampers (MTMDs), and distributed multiple tuned mass dampers (d‐MTMDs) under real earthquake ground motions is investigated. Numerical study is carried out using analytical models of five‐, 10‐, and 15‐storey base‐isolated buildings equipped with the STMD, MTMDs, and d‐MTMDs. The buildings are modeled as shear‐type structure with a lateral degree of freedom at each floor level, and the buildings are isolated using the laminated rubber bearing, lead‐core rubber bearing, friction pendulum system, and resilient‐friction base isolator. The coupled differential equation of motion for the buildings are derived and solved in the incremental form using Newmark's step‐by‐step method of integration. From the numerical study conducted, it is concluded that installing a tuned mass damper at each floor level of a base‐isolated building reduces the structural response in terms of top floor acceleration and bearing displacement. It is found that installing the MTMDs and d‐MTMDs are significantly beneficial in reducing top floor acceleration as compared with the STMD. Further, almost comparable reduction in the bearing displacement could be obtained by installing the STMD, MTMDs at top, and d‐MTMDs in the base‐isolated buildings. The d‐MTMDs are more beneficial as compared with the STMD and MTMDs as otherwise huge controller mass can now be divided and distributed on different floor levels.     

On the efficiency of semi‐active smart structures: self‐regulating MR dampers control system for tall buildings

Many severe dynamical loadings such as earthquakes and strong winds may subject to structural systems during their lifetime and lead to changes in structural characteristics. Hence, employing an adaptive control strategy that can deal with these alterations compound with design of the structural elements would undoubtedly be the most effective alternative design for the old‐fashioned design methods, which are relatively inefficient in response to these unforeseen conditions. In the current study, benefits of employing the modern control systems for design of tall buildings in comparison with the uncontrolled traditionally designed structures are thoroughly investigated. To contract the vibrational responses due to seismic excitations, the innovative direct‐modulating semi‐active controller is designed for magneto‐rheological dampers, which are installed in an 11‐storey sample building converting it to a smart structure. Copyright © 2013 John Wiley & Sons, Ltd.     

Energy dissipation of tall core‐wall structures with multi‐plastic hinges subjected to forward directivity near‐fault and far‐fault earthquakes

In this study, different energy components in the tall reinforced concrete core‐wall buildings with numerous plastic hinges over the height are investigated using nonlinear time history analysis. The effect of near‐fault and far‐fault earthquakes is compared. The idea of one‐plastic, two‐plastic, three‐plastic and whole‐plastic hinge approaches along the core wall is examined. The input energy, inelastic, damping, kinetic and elastic strain energy during the earthquakes are studied. The results show that a large energy quantity transfers to the structure at the arrival time of the near‐fault motion pulse. Inelastic energy distribution over the height shows a considerable amount of inelastic energy dissipation occurring at the base and above the mid‐height of the walls. Copyright © 2016 John Wiley & Sons, Ltd.     

Adaptive control of base-isolated structures against near-field earthquakes using variable friction dampers

This paper investigates the effectiveness of two adaptive control strategies for modulating the control force of variable friction dampers (VFDs) that are employed as semi-active devices in combination with laminated rubber bearings for the seismic protection of buildings. The first controller developed in this study is an adaptive fuzzy neural controller (AFNC). It consists of a direct fuzzy controller with self-tuning scaling factors based on neural networks. A simple neural network is implemented to adjust the input and output scaling factors such that the fuzzy controller effectively determines the command voltage of the damper according to current level of ground motion. A multi-objective genetic algorithm is used to learn the shape of the activation functions of the network. The second controller is based on the simple adaptive control (SAC) method, which is a type of direct adaptive control approach. The objective of the SAC method is to make the plant, the controlled system, track the behavior of the structure with the optimum performance. Here, SAC methodology is employed to obtain the required control force which results in the optimum performance of the structure. For comparison purposes, an optimal linear quadratic Gaussian (LQG) controller is also developed and considered in the simulations together with maximum passive operation of the friction damper. The results reveal that the developed adaptive controllers can successfully improve the seismic response of base-isolated buildings against various types of earthquake.     

Energy‐based predictive algorithm for semi‐active tuned mass dampers

There are various control strategies proposed and implemented for the protection of structures against different types of dynamic excitations. Currently, semi‐active control devices are very popular due to their adaptability and low power requirement. In this paper, a novel energy‐based predictive (EBP) algorithm is proposed, and its effectiveness is studied when applied to semi‐active tuned mass damper (SATMD). The mechanical energy of the primary structure is taken as the key parameter to be used by the algorithm to predict a suitable value of the manipulated variable, the damping of the tuned mass damper (TMD). The choice of the damping is made such that the damping used at a time interval leads to the least possible mechanical energy of the primary structure. The efficacy of the proposed control algorithm is studied by employing the EBP algorithm on single‐story and multistory structures equipped with the SATMD. The performance of the proposed algorithm when applied to the SATMD is also compared with that with the passive TMD for similar parameters. The results of the study show that the implementation of the EBP algorithm leads to significantly reduced dynamic response as compared with the passive TMD. Furthermore, numerical studies are conducted to gain insight into the effect of various parameters such as the mass ratio, the TMD damping ratio, and the flexibility of the structure.     

Simplified procedures for seismic design verification and evaluation of lead rubber bearing base‐isolated buildings based on free‐vibration response

Base isolation has seen widespread application to buildings and infrastructures over the past four decades. However, there is a lack of methods for assessing the performance of a base‐isolated structure at the end of construction and during its service life. To this end, simplified methods are developed for verifying isolation design and evaluating seismic demands of rubber‐bearing‐supported base‐isolated buildings based on their free‐vibration response, which could be obtained using field (on‐site) testing. The base isolation layer consists of lead rubber bearings (LRBs) and linear natural rubber (LNR) bearings. For design verification purposes, analytical solutions are provided to benchmark the free‐vibration response of base‐isolated buildings, considering the general case of a multilinear hysteretic isolation response representing multiple LRBs with distinct mechanical specifications. In seismic demand evaluation, seismic capacity of an isolation system is estimated using free‐vibration response of various amplitudes that cover a range of expected seismic intensity of interest. Seismic demands are obtained when capacity coincides with an earthquake response spectrum at a compatible damping level. Procedures are developed for the potential use of snap‐back tests and verified using experimental and numerical data.     

智能隔震结构能量响应初步分析及控制效率评判

本文采用能量响应的观点揭示被动和智能隔震体系的减震机理,评判采用三种不同控制算法时智能隔震结构的控制效果。采用解析手段,导出了被动和智能隔震体系的累积能量平衡方程和结构瞬时能量传递的定性关系,揭示智能隔震在抑制结构能量响应方面的优势。在对能量传递取得定性认识的基础上,选用几个主要的能量响应指标,对被动隔震与智能隔震的能量响应进行分析,并对比采用三种不同控制算法的智能隔震结构能量响应规律。文末选用本文作者承担设计过的一个实际隔震工程作为算例,分别比较了输入两种不同地震波和两种不同地震强度水准时各种算法的控制效果。结果表明,本文作者建立的序列最优控制算法能更有效地抑制能量响应,再次显示了该算法综合性能优于现有两种结构最优控制算法。     

A new pushover procedure for two‐way asymmetric‐plan tall buildings under bidirectional earthquakes

Conventional pushover analyses despite of extensive applications are unable to estimate the general responses of asymmetric‐plan tall buildings because of ignoring the effects of higher modes and torsion. A consecutive modal pushover procedure is one of the recent nonlinear static pushover procedures that used to analyse the seismic response of one‐way asymmetric‐plan tall buildings under one‐directional seismic ground motions. In this paper, a modified consecutive modal pushover procedure (MCMP) has been proposed to estimate the seismic demands of two‐way asymmetric‐plan tall buildings under two horizontal components of earthquakes simultaneously. The accuracy of the MCMP procedure is evaluated using different buildings and comparing with the results of FEMA (Federal Emergency Management Agency) procedures, the practical modal pushover procedure and nonlinear time history analyses as an exact solution. The results show the proposed MCMP procedure is able to estimate the displacements and storey drifts accurately and introduces a great improvement in predicting the plastic hinge rotations. Copyright © 2013 John Wiley & Sons, Ltd.     

Seismic performance of steel mega braced frames equipped with shape‐memory alloy braces under near‐fault earthquakes

This paper has two main objectives. The first objective is to compare the dynamic behavior of mega shape‐memory alloy (SMA) braced frames subjected to far‐fault and near‐fault ground motions. Therefore, four mega SMA braced frames with various stories located in the vicinity of an active fault were considered. Fourteen near‐fault records with two well‐known characteristics of these records, i.e. forward directivity and fling step, were selected to test near‐fault earthquake characteristics. Furthermore, other seven far‐field records were selected for comparison. Through the nonlinear dynamic analyses, the results showed that for high‐rise frames, the near‐fault earthquakes resulted in more demands than the far‐field, but for low‐rise frames, far‐fault records imposed more demands. It was also found that mega configuration and SMA stiffening at large strains played key roles in seismic vibration control of frames. The second objective of this paper is to study the superior performance of SMA braces over the buckling restrained braces by exploiting the super‐elastic characteristic of the SMA. Identical buildings equipped with buckling restrained braces were also studied for comparison purposes. The results revealed the excellent performance of SMA braces under near‐fault records by reducing both interstory drift and residual displacement of the top floor. Copyright © 2015 John Wiley & Sons, Ltd.     

An improved multidimensional modal pushover analysis procedure for seismic evaluation of latticed arch‐type structures under lateral and vertical earthquakes

Pushover methods for seismic assessment of buildings under multidimensional earthquakes have been studied and retrofitted. However, these current methods are not suitable when applied to widely adopted arch‐type structures characterized by strong geometrical nonlinearity and coupling effects. An improved multidimensional modal pushover procedure with two‐stage analyses is proposed for seismic evaluation of latticed arches. Taking overall multidimensional response into consideration, modal stiffness of the equivalent single‐degree‐of‐freedom system is derived, and its capacity curve is determined during the first‐stage analysis. To provide a deformation profile with algebraic signs of response retained, the second‐stage analysis is conducted using the pushover load pattern derived from modal displacement superposition. The objective of the improved procedure is to overcome the drawback of the conventional modal pushover method, which describes the capacity curve resorting to base shear and roof displacement, and that of quadratic combination rules which eliminate the sign reversals of response. To validate its serviceability, nodal displacements and element stresses, as well as the yielding members, of two typical latticed arches are calculated. Through comparative analysis, the results by the improved procedure exhibit good agreement with those by response history analysis. Additionally, this procedure demonstrates great superiority over the conventional method for its satisfying accuracy.     

Dual‐steel frame consisting of moment‐resisting frame and shape memory alloy braces subjected to near‐field earthquakes

In this paper, concentric braced frames are combined with moment‐resisting frame (MRF) as a dual system subjected to near‐field (NF) pulse‐like and far‐field ground motions. The braced frame in this system configuration consists of steel buckling‐restrained braces (BRB model), braces with shape memory alloy (SMA model), or combination of BRB and SMA braces (COMBINED model). Some prototype structures of the proposed systems are designed according to the code recommendations. Then, the nonlinear models of the considered structures are developed in SeismoStruct software, and nonlinear time history analysis (NLTHA) is implemented. NLTHA is performed subjected to earthquake record sets at maximum considered earthquake (MCE) and design base earthquake (DBE) levels, and responses of the systems are investigated and compared with each other. Among the examined models, the SMA and COMBINED models exceed the CP level subjected to NF‐MCE record set. Therefore, more investigation is needed for using short‐segment SMA braces in the dual‐steel frames in NF area.     

Using orthogonal pairs of rollers on concave beds (OPRCB) as a base isolation system—part II: application to multi‐story and tall buildings

Application of orthogonal pairs of rollers on concave beds (OPRCB) isolating system to short‐ and mid‐rise buildings is presented in this paper. At first, the analytical formulation of the set of equations, governing the motion of Multi Degree of Freedom (MDOF) systems, isolated by OPRCB isolators, has been developed. Then, some multi‐story regular buildings of shear type have been considered, once on fixed bases and once installed on the OPRCB isolators. Next, some horizontal and vertical accelerograms of both far‐ and near‐fault earthquakes with low‐ to high‐frequency content, particularly those with remarkable peak ground displacement values, have been selected and normalized to three peak ground acceleration levels of 0.15 g, 0.35 g and 0.7 g, and their stronger horizontal component simultaneous with their vertical component have been used for response analysis of the considered buildings. Story drifts and absolute acceleration response histories of isolated buildings have been calculated by using a program, developed in MATLAB environment by using the fourth‐order Runge–Kutta method, considering the geometrically nonlinear behavior of isolators. Maximum relative displacement and story drifts as well as absolute acceleration responses of considered isolated buildings for various earthquakes have been compared with those of corresponding fixed‐base buildings to show the high efficiency of using OPRCB isolators in multi‐story and tall regular buildings. Copyright © 2010 John Wiley & Sons, Ltd.     

A displacement‐based adaptive pushover method considering modal sign reversal for RC frame structures

Nonlinear static procedures are favored tools for practical applications in the structural engineering profession. However, some limitations are associated with them, including their deficiencies to properly reflect higher modal effects and inertial seismic forces fluctuations in their responses. Some different adaptive pushover methods intended to improve these limitations have been proposed in the literature, but each one has come out with a special deficiency. In this study, based on the concepts of the displacement‐based adaptive pushover, a new dual‐run procedure method called Improved DAP (IDAP) has been developed, aiming to improve higher modal and sign reversal consideration of pushover methods. The seismic scope of this study has been focused on near‐fault regions. Four concrete SMRF with different heights have been employed for the evaluations. The results of the proposed method in terms of capacity curves, interstory and shear profiles are compared with those of the IDA method. Results indicate that the ability of the new method in reproducing seismic story forces and capacity curves, as well as interstory drifts, has been improved in comparison with its primitive counterpart. Copyright © 2015 John Wiley & Sons, Ltd.     

Seismic response of mega buckling‐restrained braces subjected to fling‐step and forward‐directivity near‐fault ground motions

Special characteristics of earthquakes in the near‐fault regions caused failures for many modern‐engineered structures. Fling‐step and forward‐directivity are the main consequences of these earthquakes. High‐amplitude pulses at the beginning of the seismograph have been obviously presented in forward‐directivity sites. These pulses have high amount of seismic energy released in a very short time and caused higher demands for engineering structures. Fling‐step is generally characterized by a unidirectional large‐amplitude velocity pulse and a monotonic step in the displacement time history. These monotonic steps cause residual ground displacements that are associated with rupture mechanism. In this paper, the seismic performance of steel buckling‐restrained braced frames with mega configuration under near‐source excitation was investigated. Fourteen near‐fault records with forward‐directivity and fling‐step characteristics and seven far‐faults have been selected. Nonlinear time‐history analyses of 4‐story, 8‐story, 12‐story and 15‐story frames have been performed using OpenSees software. After comparing the results, it is shown that, for all frames subjected to the selected records, the maximum demand occurred in lower floors, and higher modes were not triggered. Near‐fault records imposed higher demands on the structures. The results for near‐fault records with fling‐step were very dispersed, and in some cases, these records were more damaging than others. Copyright © 2014 John Wiley & Sons, Ltd.     

A novel machine learning‐based algorithm to detect damage in high‐rise building structures

A novel model is presented for global health monitoring of large structures such as high‐rise building structures through adroit integration of 2 signal processing techniques, synchrosqueezed wavelet transform and fast Fourier transform, an unsupervised machine learning technique, the restricted Boltzmann machine, and a recently developed supervised classification algorithm called neural dynamics classification (NDC) algorithm. The model extracts hidden features in the frequency domain of the denoised measured response signals recorded by sensors on different elevations or floors of a structure. The extracted features are used as an input of the NDC to detect and classify the global health of the structure into categories such as healthy, light damage, moderate damage, severe damage, and near collapse. The proposed model is validated using the data obtained from a 3D 1:20 scaled 38‐story reinforced concrete building structure. The results are compared with 3 other supervised classification algorithms: k‐nearest neighbor (KNN), probabilistic neural networks (PNN), and enhanced PNN (EPNN). NDC, EPNN, PNN, and KNN yield maximum average accuracies of 96%, 94%, 92%, and 82%, respectively.     

A variable gain state‐feedback technique for an AMD control system with stroke limit and its application to a high‐rise building

As the auxiliary mass of an active mass damper/driver (AMD) control system in a high‐rise building has excessive strokes and its relative velocities are in the same direction with the strokes, the auxiliary mass probably collides with its anti‐collision device. As a result, the structural responses increase and even the structural safety is endangered. In this paper, a variable gain state‐feedback control system is proposed to limit the strokes and relative velocities of the auxiliary mass, so as to ensure the safety of the system. Firstly, the limited state of the auxiliary mass is defined, and a regional pole assignment algorithm that utilizes only a damping factor is realized as a control gain. Then the relationship between the control gain corresponding to the stroke and its threshold limit value is deduced. A suitable threshold limit value is chosen to reduce the strokes and the relative velocities. Finally, the performance characteristics of the control systems with or without stroke limit are analyzed. The results demonstrate that the controller limits the strokes effectively on the premise of guaranteeing the control effects and the AMD parameters. To verify its effectiveness, the proposed methodology is also applied to an experiment of a four‐storey frame.     

基于渐进地震失效模式的高层结构抗罕遇地震设计方法研究

针对高层结构罕遇地震作用下局部集中损伤破坏易导致整体倒塌的问题,及超静定次数消耗集中且不充分的结构地震失效本质,确定了高层结构耗能构件分批次充分消耗超静定次数的多阶段塑性发展路径,提出了高层结构塑性发展充分、失效方向可控、失效路径延长的渐进地震失效模式。同时,考虑结构多阶段塑性发展过程中地震作用的往复特性、高阶振型影响和非线性内力重分布特点,建立基于多阶段振型组合的标准地震作用,给出了多阶段塑性发展的抗震性能量化需求,建立了基于渐进地震失效模式的高层结构抗罕遇地震设计方法。该方法将高层结构渐进地震失效全过程的复杂设计简化为有限塑性阶段的分段抗罕遇地震设计,解决了高层结构难于抗罕遇地震量化设计的难题。为验证该设计方法的有效性,对一幢10层高层结构进行了抗罕遇地震设计,通过非线性时程分析方法验证了按所提方法设计的结构能够实现结构渐进地震失效模式以及结构抗震性能目标,并对比分析了按所提方法设计的结构与按现行规范方法设计的结构的抗震性能,得到按所提方法设计的结构在地震动峰值加速度为0.22g作用下耗能提高了57%,在非线性静力推覆作用下非线性抗力（基底剪力）最大值提高了15.59%。     

Study on seismic design method of high-rise structures resistant to rare earthquakes on basis of progressive seismic failure mode

针对高层结构罕遇地震作用下局部集中损伤破坏易导致整体倒塌的问题，及超静定次数消耗集中且不充分的结构地震失效本质，确定了高层结构耗能构件分批次充分消耗超静定次数的多阶段塑性发展路径，提出了高层结构塑性发展充分、失效方向可控、失效路径延长的渐进地震失效模式。同时，考虑结构多阶段塑性发展过程中地震作用的往复特性、高阶振型影响和非线性内力重分布特点，建立基于多阶段振型组合的标准地震作用，给出了多阶段塑性发展的抗震性能量化需求，建立了基于渐进地震失效模式的高层结构抗罕遇地震设计方法。该方法将高层结构渐进地震失效全过程的复杂设计简化为有限塑性阶段的分段抗罕遇地震设计，解决了高层结构难于抗罕遇地震量化设计的难题。为验证该设计方法的有效性，对一幢10层高层结构进行了抗罕遇地震设计，通过非线性时程分析方法验证了按所提方法设计的结构能够实现结构渐进地震失效模式以及结构抗震性能目标，并对比分析了按所提方法设计的结构与按现行规范方法设计的结构的抗震性能，得到按所提方法设计的结构在地震动峰值加速度为0.22g作用下耗能提高了57%，在非线性静力推覆作用下非线性抗力（基底剪力）最大值提高了15.59%。     

Plastic hinge length of reinforced concrete columns subjected to both far‐fault and near‐fault ground motions having forward directivity

In a strong earthquake, a standard reinforced concrete (RC) column may develop plastic deformations in regions often termed as plastic hinge regions. A plastic hinge is basically an energy dampening device that dampens energy through the plastic rotation of a rigid column connection, which triggers redistribution of bending moments. The formation of a plastic hinge in an RC column in regions that experience inelastic actions depends on the characteristics of the earthquakes as well as the column details. Recordings from recent earthquakes have provided evidence that ground motions in the near field of a rupturing fault can contain a large energy or ‘directivity’ pulse. A directivity pulse occurs when the propagation of the fault proceeds at nearly the same rate as the shear wave velocity. This pulse is seen in the forward direction of the rupture and can cause considerable damage during an earthquake, especially to structures with natural periods that are close to those of the pulse. In the present paper, 1316 inelastic time‐history analyses have been performed to predict the nonlinear behaviour of RC columns under both far‐fault and near‐fault ground motions. The effects of axial load, height over depth ratio and amount of longitudinal reinforcement, as well as different characteristics of earthquakes, were evaluated analytically by finite element methods and the results were compared with corresponding experimental data. Based on the results, simple expressions were proposed that can be used to estimate plastic hinge length of RC columns subjected to both far‐fault and near‐fault earthquakes that contain a forward‐directivity effect. Copyright © 2011 John Wiley & Sons, Ltd.