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.     

Fragility assessment of high‐rise reinforced concrete buildings considering the effects of shear wall contributions

The effect of shear wall configurations on seismic responses of high‐rise RC buildings is investigated in this paper using fragility analysis method. Four lower high‐rise RC buildings that have the same plan dimensions and height but are different in configurations in lateral force resisting systems, were firstly designed following the standard code procedure. To consider uncertainties in earthquake motions, 16 real ground motion pairs were selected and scaled, then applied orthogonally to the four RC building models during the Incremental Dynamic Analysis (IDA). Fragility relationships were therefore derived based on the IDA results for the three limit states including slight damage, moderate damage and collapse to show the probabilistic comparison of seismic responses among the four buildings in both x and y‐directions. It was observed that generally adding shear walls will improve buildings' seismic performance at all limit states. However, shear wall configuration also plays a significant role in seismic behavior of the lower high‐rise regular RC buildings' and internal shear walls are generally more effective than external shear walls in improving building's seismic resistance. Copyright © 2016 John Wiley & Sons, Ltd.     

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.     

Behavior of coupled shear walls with buckling‐restrained steel plates in high‐rise buildings under lateral actions

Traditional coupling beams in coupled shear walls (CSWs) may be lack of required ductility or inconvenient to be fully repaired or replaceable after earthquake damage. To improve the CSW seismic performance, a type of new structural system, which is referred to as coupled shear walls with buckling‐restrained steel plates (CSW–BRSP), is proposed and thoroughly studied. In the system, a pair of individual concrete wall is coupled through buckling‐restrained steel plates instead of traditional concrete coupling beams. Based on the continuous medium method (CMM), stiffness and strength design formulas are developed for the seismic design of this system. Intensive investigations have been conducted to assess the undesirable axial forces in the buckling‐restrained steel plates induced by lateral loads. In order to facilitate the application of this system, a detailed design procedure is also explicitly stated. Finally, an example of typical high‐rise building is presented to illustrate the design procedure as well as demonstrate the excellent seismic performance of the proposed system by means of nonlinear time‐history analysis. Copyright © 2015 John Wiley & Sons, Ltd.     

Seismic performance and cost‐effectiveness of high‐rise buildings with increasing concrete strength

The relationship between the seismic performance and economics of high‐rise buildings when designed to different material strengths is investigated in this paper. To represent the modern high‐rise construction, five 60‐story reinforced concrete buildings with varying concrete strengths, ranging from 45 MPa to 110 MPa, are designed and detailed to fine accuracy keeping almost equal periods of vibration. Detailed fiber‐based simulation models are developed to assess the relative seismic performance of the reference structures using incremental dynamic analyses and fragility functions. It is concluded that a considerable saving in construction cost and gain in useable area are attained with increasing concrete strength. The safety margins of high‐strength concrete in tall structures may exceed those of normal‐strength concrete buildings, particularly at high ground motion intensity levels. The recommendations of this systematic study may help designers to arrive at cost‐effective designs for high‐rise buildings in earthquake‐prone regions without jeopardizing safety at different performance levels. Copyright © 2014 John Wiley & Sons, Ltd.     

Experimental tests for improving buildability of construction methods for high‐strength concrete columns in high‐rise buildings

High‐strength concrete columns have the advantage of increasing the amount of usable area in the building because the cross‐section of the columns takes up less space compared with columns using normal strength concrete. However, it is difficult to weld the steel reinforcement and steel members because of the narrow column width due to a decrease in the cross‐section of the column, thereby causing construction delay in many cases. In this paper, five construction methods with different details for high‐strength reinforced concrete columns are tested to improve the buildability of the columns. Five specimens with different construction details were tested and analyzed based on four aspects: (a) the relationship between load and displacements, (b) strain distributions, (c) axial stiffness, and (d) crack patterns. Specimens were constructed using concrete with a compressive strength of 55 MPa, and the design strength of all five specimens were set to about 10,740 kN. From results of the experiment, the specimen with a reduced number of vertical reinforcements from 24 of HD22 (SD400, Fy = 400 MPa) to 16 of UD22 (SD600, Fy = 600 MPa) was the most effective specimen to improve the buildability of the column without deteriorating the structural performance of the reference specimen.     

Prediction of nonlinear seismic demands of high‐rise rocking wall structures using a simplified modal pushover analysis procedure

This study presents a simplified analysis procedure for the convenient estimation of nonlinear seismic demands of high‐rise rocking wall structures. For this purpose, the displacement modification approach used in the nonlinear static procedure of ASCE/SEI 41‐13 is adopted. However, in the current study, this approach is extended to every significant vibration mode of the structure whereas the displacement modifying coefficients for different modes are calculated using the typical flag‐shaped hysteresis behavior of rocking walls. The parameters of this hysteresis behavior are selected to represent rocking walls with a practical range of energy dissipation capacity and postgap‐opening stiffness. The computed peak inelastic‐to‐elastic displacement ratios are presented as mean spectra, which can be used for the convenient estimation of pushover target displacement for every significant vibration mode. The accuracy of proposed procedure is examined using the seismic demands obtained from the nonlinear response history analysis of a 20‐story case study rocking wall structure. Furthermore, a modal decomposition technique is used to determine the individual modal seismic demands. The proposed procedure is found to predict both the combined and the individual modal demands with a reasonable accuracy and can serve as a convenient analysis option for the design and performance evaluation of high‐rise rocking wall systems.     

Structural design of high‐rise buildings using steel‐framed modules: A case study in Hong Kong

Steel‐framed modular buildings afford certain advantages, such as rapid and high‐quality construction. However, although steel‐framed modules have been adopted in several countries, most of them are limited to low‐to‐medium‐rise structures; modular high‐rise buildings are rare. This study proposes a feasible structural design solution for high‐rise buildings using a steel‐framed modular system. A 31‐story student hostel building in Hong Kong is redesigned as a steel‐framed modular building and used as a case study. The finite element models of the building are formulated, and the structural behaviors under wind and earthquake load scenarios are compared. Moreover, the structural design process used for the 31‐story building is applied to design a hypothetical 40‐story modular building to further examine the proposed design solution. The numerical analysis results indicate that the roof lateral displacements and interstory drift ratios of the redesigned modular building are within the allowable limits of design codes; moreover, the modular connections behave elastically under the most adverse loading scenarios. Accordingly, the proposed solution can be used to design steel‐framed modular buildings of up to 40 stories, while complying with relevant wind and seismic codes.     

Integrated multi‐type sensor placement and response reconstruction method for high‐rise buildings under unknown seismic loading

Structural health monitoring system has been implemented on high‐rise buildings to provide real‐time measurement of structural responses for evaluating their serviceability, safety, and sustainability. However, because of the complex structural configuration of a high‐rise building and the limited number of sensors installed in the building, the complete evaluation of structural performance of the building in terms of the information directly recorded by a structural health monitoring system is almost impossible. This is particularly true when seismic‐induced ground motion is unknown. This paper thus proposes an integrated method that enables the optimal placement of multi‐type sensors on a high‐rise building on one hand and the reconstruction of structural responses and excitations using the information from the optimally located sensors on the other hand. The structural responses measured from multi‐type sensors are fused to estimate the full state of the building in the modal coordinates using Kalman filters, from which the structural responses at unmeasured locations and the seismic‐induced ground motion can be reconstructed. The optimal multi‐type sensor placement is simultaneously achieved by minimizing the overall estimation errors of structural responses at the locations of interest to a desired target level. A numerical study using a simplified finite element model of a high‐rise building is performed to illustrate the effectiveness and accuracy of the proposed method. The numerical results show that by using 3 types of sensors (inclinometers, Global Positioning System, and accelerometers), the proposed method offers an effective way to design a multi‐type sensor system, and the multi‐type sensors at their optimal locations can produce sufficient information on the response and excitation reconstruction.     

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.     

Shaking table test and numerical analysis of a high‐rise building with steel reinforce concrete column and reinforce concrete core tube

This paper assesses the seismic performance of a high‐rise building with steel reinforce concrete column and reinforce concrete core tube in Shanghai, China. This building has 54 floors above the ground and 4 basements, and it has two strengthened layers, which are composed of outrigger truss and belt truss. In order to validate the reliability and the safety of this structure, besides the conventional analysis, shaking table test of scale model was conducted. In the test, the maximum responses of acceleration and deformation were measured and evaluated, as well as the dynamic characteristics, crack pattern, and failure mechanism of the building. Meanwhile, elastic‐plastic time‐history analysis for prototype structure was carried out by the finite element analysis program, and the experimental data were compared with the analytical results to gain a better understanding of the seismic performance of the building. The conclusions are summarized below:

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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.     

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.     

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.     

Numerical study of isolation in the backfill zone of foundation pit method to reduce railway generated vibration in high‐rise buildings

The conventional methods to reduce building vibration include isolation of vibration sources, isolation of buildings, and setting trenches in the propagation path. However, it is evidenced that these methods are not feasible for high‐rise buildings in crowded urban areas. This paper proposes a new method to reduce vibration for high‐rise buildings by using the existing construction backfill zone, the isolation in the backfill zone of foundation pit (IBF). Numerical analyses were first carried out to obtain a realistic excitation time history, and a finite element–infinite element model was developed and calibrated using test data from an actual building site. The contributions of the basement sidewalls and foundation slabs to floor vibration and the influence of infill material properties are investigated. Lastly, a composite isolation layer was suggested to provide both sufficient restraining effects to the building foundation and satisfactory vibration isolation. The analyses confirmed that the proposed IBF method reduces ground‐borne vibration in high‐rise buildings by up to 66% when railway is on the ground.     

Wind‐induced inter‐story drift analysis and equivalent static wind load for multiple targets of tall buildings

In super high‐rise buildings with varying story heights, the wind‐induced inter‐story drifts might violate the specified limit. However, these effects have seldom been concerned in wind‐induced response analysis. The theory and application of equivalent static wind load (ESWL) for wind‐induced inter‐story drifts of super high‐rise buildings were studied in this paper. A spectral decomposition method suitable for multi‐point excitation problems was firstly proposed. The formula of ESWL targeting for largest inter‐story drift was derived. For more reasonable structural design, the ESWL for multiple targets including displacement atop of building and inter‐story drifts at all story levels is put forward, in which the dominant modal inertial forces are adopted as the based load vectors. The presented methods were finally verified by its application for the wind‐induced response analysis for a tallest super tall building in Guangzhou. The researched results showed that the proposed spectral decomposition method not only has the same precision as the complete quadratic combination method but also possesses higher computation efficiency. The ESWL for multiple targets produces the same static responses for all the specified wind‐induced response, so it is much more rational for wind‐resistant structural design. Meanwhile, it is more reasonable to select the wind‐induced responses in the same direction simultaneously as the targeted values for obtaining the required ESWLs; however, the ESWL targeting for the wind‐induced responses in all degrees of freedom would generate more queer and unrealistic ESWLs distribution. Copyright © 2015 John Wiley & Sons, Ltd.