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.     

An improved consecutive modal pushover procedure for estimating seismic demands of multi‐storey framed buildings

An improved consecutive modal pushover (ICMP) procedure is proposed to enhance the accuracy of conventional CMP procedure for estimating seismic demands of tall buildings. It accounts for inelastic structural properties and interaction between vibration modes. The displacement increment at the roof of buildings used in each stage of pushover analyses is modified based on the displacement contribution of each mode. The performance of the proposed ICMP procedure is verified against three high‐rise frames subjected to various ground motions. The results obtained from the ICMP procedure are compared with those from the nonlinear time history analysis, conventional pushover analysis, and CMP analysis. The comparison shows the advantages of the ICMP over the other pushover procedures. It is concluded that the ICMP procedure is more accurate than the CMP procedure.     

Optimal reduction of inelastic seismic demands in high‐rise reinforced concrete core wall buildings using energy‐dissipating devices

Recently, the issue of large inelastic seismic force demands at severe ground shakings such as maximum considered earthquake level has been highlighted in the conventionally designed high‐rise reinforced concrete core wall buildings. Uncoupled modal response history analysis was used in this study to identify the modes responsible for the large inelastic seismic force demands. The identification of dominant modes and mean elastic design spectra of seven representative ground motions for different damping ratios has led to the identification of three control measures: plastic hinges (PHs), buckling‐restrained braces (BRBs) and fluid viscous dampers (FVDs). The identified control measures were designed to suppress the dominant modes responsible for the large inelastic seismic force demands. A case‐study building was examined in detail. Comparison of the modal as well as the total responses of the case‐study building with and without the control measures shows that all the control measures were effective and able to reduce the inelastic seismic demands. A reduction of 33%, 22% and 27% in the inelastic shear demand at the base and a reduction of 60%, 22% and 26% in the inelastic moment demand at mid‐height were achieved using the PHs, BRBs and FVDs, respectively. Furthermore, a reduction of about 30–40% in the inelastic seismic deformation demands was achieved for the case of the BRBs and FVDs. The study enables us to gain insight to the complex inelastic behavior of high‐rise wall buildings with and without the control measures. Copyright © 2011 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.     

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.     

Alternative approach to compute shear amplification in high‐rise reinforced concrete core wall buildings using uncoupled modal response history analysis procedure

The seismic response of the high‐rise reinforced concrete (RC) wall structures is really complicated as several vibration modes other than the fundamental mode normally contribute significantly to the response—commonly recognized as ‘higher mode effects’. Response spectrum analysis (RSA) procedure, which can account for higher mode effects, is usually employed to compute the seismic design demand for the high‐rise structures. Recent studies show that the inelastic seismic force demands obtained from the rigorous nonlinear response history analysis procedure are much larger than the seismic force design demands obtained from the code‐based RSA procedure for the high‐rise RC wall structures. Though, the nonlinear response history analysis procedure is widely accepted for its ability to provide the most accurate estimate of nonlinear seismic responses, the obtained responses are generally so complex that it is quite difficult for engineers to grasp the overall picture of the responses and gain some insight into them and use them to understand the cause of high seismic demands. Another important issue related to the nonlinear seismic response prediction of the high‐rise RC wall structures is the realistic and accurate numerical modeling of RC walls. In this study, a simplified but reasonably accurate procedure called the uncoupled modal response history analysis procedure is used to interpret the complex nonlinear behavior of high‐rise RC wall structures. Moreover, a finite element model based on modified compression field theory is employed for accurate numerical modeling of RC walls by incorporating the axial‐flexure‐shear interaction. This study, by making use of a better computer modeling approach and an in‐depth analysis by modal decomposition, aims to resolve some of the unanswered questions regarding realistic prediction of nonlinear seismic demands of high‐rise structures.     

A consecutive modal pushover procedure for nonlinear static analysis of one-way unsymmetric-plan tall building structures

Seismic responses of unsymmetric-plan tall buildings are substantially influenced by the effects of higher modes and torsion. Considering these effects, in this article, the consecutive modal pushover (CMP) procedure is extended to estimate the seismic demands of one-way unsymmetric-plan tall buildings. The procedure uses multi-stage and classical single-stage pushover analyses and benefits from the elastic modal properties of the structure. Both lateral forces and torsional moments obtained from modal analysis are used in the multi-stage pushover analysis. The seismic demands are obtained by enveloping the peak inelastic responses resulting from the multi-stage and single-stage pushover analyses. To verify and appraise the procedure, it is applied to the 10, 15, and 20-storey one-way unsymmetric-plan buildings including systems with different degrees of coupling between the lateral displacements and torsional rotations, i.e. torsionally-stiff (TS), torsionally-similarly-stiff (TSS) and torsionally-flexible (TF) systems. The modal pushover analysis (MPA) procedure is implemented for the purpose of comparison as well. The results from the approximate pushover procedures are compared with the results obtained by the nonlinear response history analysis (NL-RHA). It is demonstrated that the CMP procedure is able to take into account the higher mode influences as well as amplification or de-amplification of seismic displacements at the flexible and stiff edges of unsymmetric-plan tall buildings. The extended procedure can predict to a reasonable accuracy the peak inelastic responses, such as displacements and storey drifts. The CMP procedure represents an important improvement in estimating the plastic rotations of hinges at both flexible and stiff sides of unsymmetric-plan tall buildings in comparison with the MPA procedure.     

A modified response spectrum analysis procedure to determine nonlinear seismic demands of high‐rise buildings with shear walls

The standard response spectrum analysis (RSA) procedure prescribed in various design codes is commonly used by practicing engineers to determine the seismic demands for structural design purpose. In this procedure, the elastic force demands of all significant vibration modes are first combined and then reduced by a response modification factor (R) to get the inelastic design demands. Recent studies, however, have shown that the response of higher vibration modes may experience much lower level of nonlinearity, and therefore, it may not be appropriate to reduce their demand contributions by the same factor. In this study, a modified RSA procedure based on equivalent linearization concept is presented. The underlying assumptions are that the nonlinear seismic demands can be approximately obtained by summing up the individual modal responses and that the responses of each vibration mode can be approximately represented by those of an equivalent linear SDF system. Using 3 high‐rise buildings with reinforced concrete shear walls (20‐, 33‐, and 44‐story high), the accuracy of this procedure is examined. The inelastic demands computed by the nonlinear response history analysis procedure are used as benchmark. The modified RSA procedure is found to provide reasonably accurate demand estimations for all case study buildings.     

Assessment of modal pushover analysis and conventional nonlinear static procedure with load distributions of federal emergency management agency for high‐rise buildings

The nonlinear static pushover analysis technique is mostly used in the performance‐based design of structures. However, the pushover analysis with load distributions of Federal Emergency Management Agency (FEMA) loses its accuracy in estimating the seismic responses of long‐period structures where higher mode effects are important. Recently, modal pushover analysis (MPA) has been proposed to consider these effects. Hence, FEMA load patterns and MPA are evaluated in the current study and compared with inelastic response history analysis. These approximate procedures are applied to medium‐rise (10 and 15 stories) and high‐rise (20 and 30 stories) buildings; advantages and limitations of them are elaborated. It is shown that MPA procedure presents significant advantage over FEMA load distributions in predicting story drifts. MPA is able to compute hinge plastic rotations better than FEMA load distributions at upper floor levels of high‐rise buildings due to considering higher mode effects by this procedure, but both are unsuccessful in predicting hinge plastic rotations with acceptable accuracy. Copyright © 2008 John Wiley & Sons, Ltd.     

Approximate method of estimating seismic performance of high‐rise buildings with oil‐dampers

When subjected to long‐period ground motions, many existing high‐rise buildings constructed on plains with soft, deep sediment layers experience severe lateral deflection, caused by the resonance between the long‐period natural frequency of the building and the long‐period ground motions, even if they are far from the epicenter. This was the case for a number of buildings in Tokyo, Nagoya, and Osaka affected by the ground motions produced by the 2011 off the Pacific coast of Tohoku earthquake in Japan. Oil‐dampers are commonly used to improve the seismic performance of existing high‐rise buildings subjected to long‐period ground motion. This paper proposes a simple but accurate analytical method of predicting the seismic performance of high‐rise buildings retrofitted with oil‐dampers installed inside and/or outside of the frames. The method extends the authors' previous one‐dimensional theory to a more general method that is applicable to buildings with internal and external oil‐dampers installed in an arbitrary story. The accuracy of the proposed method is demonstrated through numerical calculations using a model of a high‐rise building with and without internal and external oil‐dampers. The proposed method is effective in the preliminary stages of improving the seismic performance of high‐rise buildings.     

剪力墙平面布置对异形柱框剪结构地震响应的影响分析

通过调整某异形柱框架-剪力墙结构的剪力墙布置方案,进行改进后模型的模态分析和弹性时程分析,研究剪力墙和异形柱不同平面布置对地震响应的影响。分析发现,改进后模型的抗震性能显著提高,底部剪力变化不大,最大楼层位移和结构自振周期得到明显改善,最大楼层位移值减小14.4%,自振周期减小4.34%。     

New method for modal identification of super high‐rise building structures using discretized synchrosqueezed wavelet and Hilbert transforms

Measured signals obtained by sensors during dynamic events such as earthquake, wind, and wave contain nonlinear, nonstationary, and noisy properties. In this paper, a new approach is presented for modal parameter identification of structures particularly suitable for very large real‐life structures such as super high‐rise building structures based on the integration of discretized synchrosqueezed wavelet transform, the Hilbert transform, and the linear least‐square fit. Its effectiveness is demonstrated first by application to a two‐dimensional frames from the literature, and then to the 123‐story Lotte World Tower (LWT) under construction in Seoul, Korea. The LWT measurements are very low‐amplitude ambient vibrations. Extracting the natural frequencies and damping ratios from such low‐amplitude signals are known to be very challenging. Further, the new methodology was compared with the empirical mode decomposition. It is demonstrated that the new method is capable of extracting both natural frequencies and damping rations from low‐amplitude signals effectively and with a higher accuracy compared with the empirical mode decomposition approach. The results of this research indicate a super high‐rise building like LWT has a damping ratio in the range 0.7–3.4%. The new method is quite promising for practical implementations of health monitoring of large real‐life structures.     

Design and compilation of specifications for a modular‐prefabricated high‐rise steel frame structure with diagonal braces. Part I: Integral structural design

Prefabricated steel structures have certain obvious advantages, that is, rapid construction, industrial production, and environmental protection. Although prefabricated structures have been applied in a number of countries in the world, in most cases, these structures are suitable only for low‐rise buildings, and their applications in high‐rise buildings are nota\bly rare. This paper proposes a new type of prefabricated steel structure called the modular‐prefabricated high‐rise steel frame structure with diagonal braces. Based on the T30 building, which is a hotel building with 30 storeys above the ground, the mechanical properties, failure mode, failure mechanism, and elastic–plastic development laws of the structure were studied via elastic and elastic–plastic design and analyses under various load cases and combinations. The analysis of the internal force and displacement response with frequent earthquakes was performed using the response spectrum and elastic time‐history methods, and an analysis under rare earthquakes is performed via static elastic–plastic pushover analysis. This paper summarizes the elastic and elastic–plastic structural design methods and process. This study provides important references for the design of this kind of modular‐prefabricated high‐rise steel structure, and the design method has been compiled into a design specification named Technical Specifications for Prefabricated Steel Frame Structure with Diagonal Bracing Joints.     

A temporal hybrid dynamic integration algorithm strategy for inelastic time history analysis of high‐rise reinforced concrete structures under strong earthquakes

A complete earthquake time history analysis (THA) requires a stable, accurate, and efficient dynamic integration algorithm. It is not rare to encounter numerical divergence when some implicit algorithms are used to deal with severe materially or geometrically nonlinearities. For explicit algorithms, computational efficiency is always a major concern. A temporal hybrid dynamic algorithm (THDA) strategy, which is specialized in the inelastic THAs of high‐rise reinforced concrete (RC) structures experiencing severe plasticity development, is developed herein. A preliminary evaluation is carried out on three low‐rise structural models, that is, two frame structures and one wall‐frame structure, for each group of collected implicit algorithms and explicit algorithms. From the evaluation, four alternatives are generated for the subsequent detailed assessment. A general framework for the THDA is proposed and implemented on a finite element analytical platform. The four alternatives are assessed based on their performance on a high‐rise frame core‐tube RC structure. The assessment indicates that the proposed THDA strategy can give rise to a more compatible dynamic integration algorithm for the complete THAs of high‐rise building structures when they are experiencing severe damage. The concerns about the computational stability, accuracy, and efficiency of the dynamic algorithms can be well balanced by the THDA.     

Estimating the peak structural response of high‐rise structures using spectral value‐based intensity measures

With increasing trend towards performance‐based design in earthquake engineering, running nonlinear time history analysis is becoming the routing process to quantify the relationship between ground motions intensity measure (IM) and the structural responses. Because a high‐rise structure contains many higher modes, a newly proposed spectral value‐based IM is presented in this paper to quantify the structural response of high‐rise structures. The newly proposed IM uses the modal participation masses to combine higher modes. An actual high‐rise structure is taken as an example to demonstrate the efficiency of using the newly proposed IM to quantify the peak structural response of high‐rise structures. Five alternative IMs were compared in this study: (a) PGA ‐ peak ground acceleration; (b) S₁ ‐ spectra acceleration with only 1 mode; (c) S^* ‐ modified S₁ with the consideration of period elongation after structure yielded; (d) S₁₂‐ spectra acceleration with 2 modes; and (e) S₁₂₃ ‐ spectra acceleration with 3 modes. Linear regression is fitted between the peak structural response and the IM considered. The IM with the highest correlation coefficient to the engineering demand parameter is considered the most efficient IM. The results show that S₁ has better correlation to the structural response compared with PGA. S₁₂₃ has better correlation than S^* and S₁₂. It is found that the IM with higher modes can provide better correlation than IM with lower number of structural information. For engineering applications, IM with up to 3 modes (S₁₂₃) is sufficient to produce an accurate prediction to quantify the structural response of high‐rise structures.     

Minimum‐weight design of high‐rise structures subjected to flexural vibration at a desired natural frequency

In this paper, a parametric approach for design of high‐rise structures subjected to flexural vibration is proposed. The optimization problem is formed based on a preselected value for the fundamental natural frequency, and it is formulated for minimum structural weight. In a two‐step approach, first, an alternative formulation aimed at maximizing structural stiffness that in turn maximizes structure's fundamental frequency is introduced. Then, optimized results are used in obtaining a closed‐form solution of the actual problem. Because the resulting equations are rather complicated, approximate forms are developed in order to simplify the design process. In all relations, contributions from shear forces to lateral displacement are assumed to be negligible; hence, bending resistance is the only design variable, and its optimal value is computable using simple relations. Two numerical examples are presented in order to illustrate the efficiency of this method in practice.     

Response surface‐based finite‐element model updating of a historic masonry minaret for operational modal analysis

This study aimed to use the response surface (RS) method for finite element (FE) model updating, using operational modal analysis (OMA). The RS method was utilized to achieve better agreement between the numerical and field‐measured structure response. The OMA technique for the field study was utilized to obtain modal parameters of the selected historic masonry minaret. The natural frequencies and mode shapes were experimentally determined by the enhanced frequency domain decomposition (EFDD) method. The optimum results between the experimental and numerical analyses were found by using the optimization method. The central composite design was used to construct the design of experiments, and the genetic aggregation approach was performed to generate the RS models. After obtaining the RS models, an attempt was made to converge the natural frequency values corresponding to the five‐mode shapes with the frequency values identified by the experimental analysis. ANSYS software was used to perform 3D finite element (FE) modeling of the historic masonry minaret and to numerically identify the natural frequencies and mode shapes of the minaret. The results of the experimental, initial, and updated FE model were compared with each other. Significant differences can be seen when comparing the experimental and analytical results with the initial conditions.     

Wind effect of a twin‐tower super high‐rise building with weak connection

An analysis and estimation method of multibalance synchronous test is established to study the wind effect of a complex super high‐rise building with weak connection. First, the frequency domain method is applied to deduce the calculation process of the wind effect of the multitower structure on the basis of the high frequency force balance (HFFB) technique. Then, the synchronous force test of HFFB is conducted on a twin‐tower super high‐rise building connected by a bridge. The wind‐induced response and loads and the interference effect between the two towers are analyzed based on the wind tunnel test data. The displacement correlation between the towers and the relative displacement of the multitower structure are investigated. Results show that the maximum and minimum relative displacements in the along‐bridge direction are 0.26 m in the along‐wind direction and ?0.26 m in the crosswind direction, respectively. The channeling effect formed by the surrounding buildings is the main cause of the maximum cross‐bridge displacement. The influence of the correlation between the two towers can be ignored for the along‐bridge relative displacement. The results of the HFFB and high‐frequency pressure integral test agree with each other, thereby indicating the reliability and effectiveness of the proposed method.     

Seismic retrofit of a high‐rise steel moment‐resisting frame using fluid viscous dampers

The Tall Building Initiative project of Pacific Earthquake Engineering Research Center has been expanded to investigate the seismic performance and possible retrofit of existing tall buildings. A candidate 35‐story steel building with representative details from the early 1970s was analyzed following several guidelines, which revealed a wide range of potential inadequacies. Thus, a two‐level retrofit approach was examined that focused on achieving the collapse prevention limit state under the major basic safety earthquake (BSE‐2E) hazard level prescribed by ASCE 41. This paper focused on a Level‐2 retrofit that used fluid viscous dampers to augment Level‐1 retrofits. For this approach, feasible damper locations and overall effective damping ratios were first evaluated through a series of preliminary studies, and then a two‐phase design method was used to refine the distribution and mechanical properties of the dampers. Thorough assessments of the refined design were carried out following several design guidelines, including ASCE 41, FEMA 351, and FEMA P‐58. The results indicated that the proposed retrofit method of using fluid viscous dampers could achieve the retrofit goal and provide a cost‐effective means of improving the structural behavior and reducing economic losses in a major seismic event.     

Experimental study on the seismic behavior of a shear wall with concrete‐filled steel tubular frames and a corrugated steel plate

Shear walls and core tubes in shear walls constitute the core anti‐earthquake vertical systems of high‐rise buildings. This paper proposes a new type of composite shear wall with concrete‐filled steel tubular frames and corrugated steel plates. The seismic behavior of the new shear wall is studied using a cyclic loading test and damage analysis. The failure mode, load‐carrying capacity, ductility, stiffness degradation, hysteresis behavior, and energy dissipating capacity exhibited in the test are studied. The test results show that when the proposed wall is broken, the tension side of concrete‐filled steel tubes is torn. The concrete at the bottom of the wall is detached and peels off along the through cracks. The energy dissipation capacity of concrete walls is more fully utilized. The proposed wall exhibits excellent deformability, energy dissipation capacity, and the stiffness degradation was slower than that of other walls. The use of corrugated steel plate significantly improved the seismic performance while simultaneously increasing the ductility and reducing the damage. In addition, this paper modified the energy dissipation factor in the Park & Ang model based on the situation of the specimen and experiment. It can be used to evaluate the damage degree of this new type of shear wall.