Vulnerability assessment of a high‐rise building subjected to mainshock–aftershock sequences

Strong aftershocks have the potential to further aggravate the damage state of structures, and much less attention has been given to the seismic vulnerability of high‐rise buildings than that of low‐ to medium‐rise buildings. This study assesses the seismic vulnerability of a 32‐storey frame–core tube building by performing the incremental dynamic analysis on the material‐based three‐dimensional numerical model. A storey damage model based on the material damage is developed using the weighted average method. Eighteen recorded mainshock–aftershock sequences, whose mainshock records match the target spectrum, are selected. The results indicate that the developed stroey damage model can effectively reflect the additional damage induced by aftershocks. Strong aftershocks have high potential to change the location of weak storeys. Notably, shifts of weak storeys are observed in more than 30% of aftershocks with relative spectral acceleration of 0.8. As the mainshock‐induced damage state becomes more severe, the mainshock‐damaged building becomes increasingly fragile to the aftershock excitation and more sensitive to aftershock intensities. The probability of exceeding severe damage state increases from 35.3% to 62.1% due to the effects of strong aftershocks. The results in this study can provide supports to the seismic resilience assessment of this high‐rise building.     

Vertical deformation analysis of a high‐rise building with high‐position connections

In this paper, a high‐rise frame‐core tube structure with strengthened stories and high‐position connections, a new landmark building in Wuhan, whose height is 238.6 m, is selected as an example. Construction simulation analysis is carried out by the finite element analysis software ETABS to study the vertical deformation and deformation difference of vertical members under the gravity load, taking the influence of construction processes and shrinkage and creep of concrete into consideration. The results show that there is a significant difference between the vertical deformation of the twin‐tower model with connections and that of the single‐tower model. Some engineering countermeasures are put forward to reduce the vertical deformation difference of the twin‐tower connected structure.     

Effects of grid curtains on the wind loads of a high‐rise building

The effects of grid curtains on the local and overall wind loads of a high‐rise building are investigated in detail according to a series of wind pressure and wind force tests on rigid model in a wind tunnel. The effects of grid curtains on the mean and fluctuating wind pressures on windward and sideward walls when the wind direction is parallel to the geometrical axes are investigated, along with the effects of the most unfavorable wind pressures for all wind directions. Furthermore, the effects of grid curtains on the mean and fluctuating aerodynamic forces on the entire building are also analyzed for various wind directions, along with the effects of grid curtains on the aerodynamic force spectra when the wind direction is parallel to the geometric axes. The test results indicate that grid curtains affect the mean and fluctuating windward pressure slightly but greatly influence the large sideward negative pressures. Grid curtains increase the mean and fluctuating windward aerodynamic forces and reduce the fluctuating aerodynamic torsions. According to the aerodynamic force spectra, grid curtains can mainly affect the wind forces in the low‐frequency range. Copyright © 2015 John Wiley & Sons, Ltd.     

Wind‐induced torsion vibration of the super high‐rise building of Shenzhen Energy Center

The synchronous multipoint scanning system technique in wind tunnel tests and random vibration theory method were used to analyze the wind‐induced torsion vibration of some irregularly shaped super high‐rise buildings in downtowns. The torsion vibration modes and the spectra of torsion wind load were studied, and the proportions of mean wind torsion, inertia torsion and the mass eccentricity torsion caused by horizontal inertia forces are discussed. The following conclusions can be drawn. First, the third and fourth modes have torsion vibration shapes, and their frequencies are in the high‐energy area of the spectra of the torsion wind load; the third and fourth modes are included in the resonant component of the spectra of the top torsion angle of the building, and the third mode is dominant. Second, the torsion stiffness is weak in the high stories of the building, so the inertia torsion is dominant, whereas the torsion stiffness is strong in the low stories; the mean wind torsion is dominant. The proportion of the mass eccentricity torsion moment caused by horizontal inertia forces is small. Finally, the wind‐induced torsion moment at a 90° wind angle is the largest, whereas the torsion eccentricity is 46% of the radius of gyration and is much greater than the mass eccentricity; thus, the wind‐induced torsion should be considered. The wind‐induced torsion vibration of the building is sensitive to wind directions. Copyright © 2011 John Wiley & Sons, Ltd.     

Seismic performance of high‐rise building with a rock‐slip isolation system with cables

To avoid the overturning hazard of high‐rise buildings with traditional isolation technology, a rock‐slip structure with cables (RSSC) was proposed to improve their seismic performance. The mechanical model was established, and the motion behaviour equation of the RSSC was derived. Shake‐table tests of the RSSC were performed, and the results were compared with the corresponding finite‐element model simulations. The influences of key structural parameters and earthquake motion characteristics were analysed. The study results showed that the RSSC could effectively reduce the internal seismic force response and interlayer deformation under a severe earthquake, as well as decrease the overturning probability. The seismic reduction effect was influenced by the prestressed force, the aspect ratio of the structure, and the friction coefficient between the superstructure and foundation as well as seismic site type. The motion equation derived in this paper can be used to theoretically predict the motion behaviour of RSSC.     

A simplified model for analysis of high‐rise buildings equipped with hysteresis damped outriggers

A simplified model is developed to estimate the seismic response of high‐rise buildings equipped with hysteresis damped outriggers. In the simplified model, the core tube is considered as a cantilever beam, and the effects of outriggers on the core tube are considered as concentrated moments. Modal decomposition method is adopted to obtain the seismic response of the simplified model. To investigate the accuracy and effectiveness of the simplified model, a high‐rise building with a height of 160 m was adopted as the example structure, and its response subjected to a ground motion was analyzed using the simplified model. A corresponding finite element model was built and analyzed by a finite element program called SAP2000 (Computers and Structures, Inc. Berkeley, California, United States). The analysis results obtained from the two models were compared. To consider the randomness of the ground motion, comparisons between the two models were further conducted using another 22 ground motions. It is found that the analysis results obtained from the simplified model agree well with those obtained from the finite element model, and the computation time used for the simplified model is almost negligible compared to that used for the finite element model. Such observations demonstrate that the simplified model is accurate and effective. Copyright © 2013 John Wiley & Sons, Ltd.     

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.     

Numerical study of the static and dynamic characteristics of reinforced concrete cassette structures for high‐rise buildings

High‐rise buildings are extensively built in China, and the structure of these buildings is composed of different types of conventional system of which framed structures are more commonly employed. A new cassette structure with advantageous performance properties is proposed. Static and dynamic numerical simulations were applied to investigate the characteristics of this new structure. First, the components and other details are presented. A comparative analysis was conducted between the cassette structure and traditional structures using eight finite models with fiber elements in three different heights. A static pushover analysis and an incremental dynamic analysis were conducted based on 18 near‐ground motion records recommended by the Federal Emergency Management Agency. The seismic characteristics, deformation curve, interstory drift, roof displacement, and fragility curve are investigated. Based on the analysis of the models with three different heights and the variety of seismic records, the economic advantage and application of cassette structures for building industrialization are also discussed.     

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.     

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.     

Aerodynamic interference effects of a proposed taller high‐rise building on wind pressures on existing tall buildings

When a large super high‐rise building taller than the surrounding tall buildings is built in a dense urban area, the aerodynamic interference effects of the surrounding buildings on the proposed building attract much attention, while the interference effects of the taller high‐rise building on the nearby existing buildings are often ignored. Based on a series of wind tunnel tests, the interference effects of a proposed taller high‐rise building, an adjacent equal‐height partner building, and relatively short background buildings on the target building's local wind pressures are analysed in this paper. Two‐dimensional numerical simulation are carried out to further understand the interference mechanism in some cases. The test results show that the influence of a nearby proposed taller high‐rise building may lead to wind‐induced damage on the interfered shorter buildings' envelopes. The envelope structures of other surrounding buildings facing the side of the proposed building need to be given more attention.     

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.     

Peak factor estimation of non‐Gaussian wind pressure on high‐rise buildings

A vast quantity of measurements of wind‐induced non‐Gaussian effects on buildings call for the burgeoning development of more advanced extrema estimation approaches for non‐Gaussian processes. In this study, a well‐directed method for estimating the peak factor and modeling the extrema distribution for non‐Gaussian processes is proposed. This method is characterized by using two fitted probability distributions of the parent non‐Gaussian process to separately fulfill the estimations of the extrema on long‐tail and short‐tail sides. In this method, the Johnson transformation is adopted to be the probabilistic model for fitting the parent distribution of the non‐Gaussian process due to its superior fitting goodness and universality. For each dataset, two Johnson transformations will be established by two parameter estimation methods to individually estimate the extrema on two sides. Then a Gumbel assumption is applied for conveniently determining the non‐Gaussian peak factor. This method is validated through long‐duration wind pressure records measured on the model surfaces of a high‐rise building in wind tunnel test. The results show that the proposed method is more accurate and robust than many existing ones in estimating peak factors for non‐Gaussian wind pressures.     

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.     

Seismic performance analysis of viscous damping outrigger in super high‐rise buildings

This paper introduces a seismic energy dissipation technology—viscous damping outrigger (VDO)—which is composed of outrigger truss and viscous damper. The viscous damper is set up vertically at the end of outrigger truss, which is an innovative and high‐efficiency arrangement. VDO can fully utilize the characteristic of structural lateral deformation of super high‐rise buildings to increase the efficiency of viscous dampers for enhancing structural security, improving seismic performance, and reducing construction expenditure. In this paper, working principle and seismic energy dissipating mechanism of VDO are explained firstly. Then, the influence of viscous damper parameters on energy dissipation efficiency is studied. Next, the optimal position of VDO in a super high‐rise building is analyzed in detail. Lastly, the application of VDO in structural seismic design of a super high‐rise building in China will be clearly verified based on their feasibility, economy, and safety.     

A multi‐time‐delay compensation controller using a Takagi–Sugeno fuzzy neural network method for high‐rise buildings with an active mass damper/driver system

An active mass damper/driver (AMD) control system with a single mass has such problems as the excessive weight of the auxiliary mass and the insufficient capacity of its driving equipment. It is necessary to work through multiple subsystems to achieve effective control of high‐rise buildings. However, the time‐delay effect in each subsystem impedes its application in engineering practices. In the paper, an augmented system based on a zero‐order hold is proposed for discrete‐time systems with multiple time delays, and then the system is designed according to the compensation strategy using a classical linear quadratic regulator algorithm. After that, the sample data obtained from the zero‐order hold compensation controller is trained through a Takagi–Sugeno fuzzy neural network method. Finally, a new simplified compensation controller is designed to further shorten the time consuming calculation on the premise of guaranteeing its control effects and parameters. To verify its effectiveness, an AMD system in a high‐rise building is regarded as an example, and the proposed methodology is also applied to an experiment of a four‐story frame. Both results demonstrate that the method can enhance the performance of an AMD system with multiple time delays.     

Experimental investigation on structural performance of mega column to spandrel beam connections used in high‐rise building

In this paper, a new type of concrete mega column to steel spandrel beam connection was developed for the application to a high‐rise building under construction in Korea. To transfer shear force from the spandrel beams to columns, shear connectors were used, which are steel subassemblies composed of embed plates, connection plates, dowel bars and bearing plates. Experimental studies were performed using two test specimens with a 1/5 scale; in one test specimen, dowel bars welded on embed plates in a column were used, while in the other test specimen, both dowel bars and bearing plates were used. According to the test results, the design methods of the current design codes used in this study effectively addressed the failure mechanisms of the mega column‐spandrel beam connections, and the test specimens developed greater strengths than those evaluated by the current design codes. It was also found that the use of bearing plates at the connections significantly reduces the number of dowel bars used for shear transfer purposes. Copyright © 2013 John Wiley & Sons, Ltd.     

Experimental study of across‐wind aerodynamic damping of super high‐rise buildings with aerodynamically modified square cross‐sections

Across‐wind aerodynamic damping ratios are determined from the wind‐induced acceleration responses of 10 aeroelastic models of square super high‐rise buildings in an urban flow condition (exposure category C in the Chinese code) using the random decrement technique. Moreover, the influences of amplitude‐dependent structural damping ratio on the estimation of aerodynamic damping ratio are discussed. The validity of estimated damping is examined through a comparison with previous research achievements. On the basis of the estimated results, the characteristics of the across‐wind aerodynamic damping ratios of modified square high‐rise buildings are studied. The effects of aerodynamically modified cross‐sections, such as chamfered, slotted and tapered cross‐section, on the across‐wind aerodynamic damping ratio are investigated. The results indicate that modifications of cross‐sections are not always effective in suppressing the aeroelastic effects of super high‐rise buildings. Low corner‐cut ratios (chamfer ratios from 5% to 20% and slot ratios from 5% to 10%) and low taper ratio (1%) significantly decrease the magnitudes of absolute aerodynamic damping ratios. However, large modifications of cross‐sections (slot ratio of 20% and taper ratios from 3% to 5%) increase wind‐induced responses by changing the aerodynamic damping ratios. According to the database, empirical aerodynamic damping function parameters are fitted for high‐rise buildings with aerodynamically modified square cross‐sections. Copyright © 2013 John Wiley & Sons, Ltd.     

Effects of tuned mass damper on correlation of wind‐induced responses and combination coefficients of equivalent static wind loads of high‐rise buildings

Tuned mass dampers (TMDs) are employed to control the wind‐induced responses of tall buildings. In the meantime, TMD may have an impact on the correlation of wind‐induced responses and combination coefficients of equivalent static wind loads (ESWLs). First, the mass matrix and stiffness matrix were extracted in this paper in accordance with the structural analysis model of two high‐rise buildings, and on that basis, the wind‐induced vibration responses analysis model with and without TMD was established. Second, the synchronous multipoint wind tunnel test to measure the pressure was performed for two high‐rise buildings, and the time history of wind‐induced vibration responses with and without TMD was studied. Finally, the impact of TMD on the correlation of wind‐induced responses and combination coefficients of ESWLs was discussed. The results of two examples suggest that after the installation of TMD, the increase of ρ_xy was 2.1% to 35.0% and ρ_yz was 2.8% to 45.6% at all wind directions for Building 1, and the increase of ρ_xy was 3.9% to 17.1% and ρ_yz was 6.8% to 38.3% for Building 2. The combination coefficients of ESWLs of two buildings were 3% to 6% larger than that of the original structure. The conclusion of this paper can be referenced by the wind resistant design of high‐rise buildings with TMD.