Super-tall Buildings Research Articles

Autonomous and resilient infrastructure with cognitive and self-deployable load-bearing structural components

Abstract This paper explores concepts and pilot studies for realizing autonomous and disaster-resistant infrastructures through integrating cognitive and self-deployable load-bearing structural components. These components act as secondary, and independent structural systems, that allow civil construction to autonomously reconfigure their internal structure to adapt to severe loading conditions in real-time. As a result, an autonomous infrastructure can achieve higher levels of structural resilience under extreme events (i.e. fire, earthquake etc.). This improved performance mitigates premature failure (collapse), thus providing occupants with sufficient time to evacuate, and allowing first responders to tackle the adverse effects of disasters. The practicality of the proposed concepts is illustrated through a comprehensive case study that covers fundamental aspects of structural performance and human evacuation in a super-tall 80-storey high-rise building undergoing an extreme event.

Evaluation of Wind Effects on Super-Tall Buildings using CFD Simulation and 3D Visualization

Evaluation of Wind Effects on Super-Tall Buildings using CFD Simulation and 3D Visualization

Analysis of outrigger‐braced reinforced concrete supertall buildings: Core‐supported and tube‐in‐tube lateral systems

SummaryThis study is primarily focused on the approximate analysis of reinforced concrete outriggers which are commonly used in the design and construction of supertall buildings subject to distributed horizontal loads. Existing global analysis formulae that provide preliminary results for lateral deflections and moments are reviewed for two lateral load resisting systems, namely, core‐supported‐with‐outrigger (CSOR) system and less frequent tube‐in‐tube‐with‐outrigger (TTOR) system. These formulae are only applicable for CSOR and neglect the reverse rotation of the outrigger actually suffered due to the propping action from the outer columns and give rather high predictions of the deflections compared with advanced numerical finite element (FE) models. An improved model is proposed which overcomes this issue and provides more consistent results to FE predictions. The same can also be extended to TTOR. Several case studies are investigated to verify the accuracy of the proposed methodologies. The global analysis is followed by the local analysis of reinforced concrete outrigger beams using strut‐and‐tie modelling and non‐linear FE analysis to obtain optimized reinforcement layouts (reduction of quantities of reinforcement). The results highlight the different challenges in detailing such structural members which are heavily loaded (high congestion of reinforcement), and the behaviour at failure can be brittle.

Tianjin CTF Finance Centre: wind, form and structure

The Tianjin CTF Finance Centre is a 530m super-tall building nearing completion in the People's Republic of China. For a building of this height, wind forces and associated wind-induced motion in the upper levels can become dominant factors in the structural design of its foundations and lateral-stability system. This article describes how an initial aerodynamic shape-optimisation workshop allowed the design team to develop a finely tuned architectural form capable of minimising the detrimental effects of vortex shedding. This process, approx. 10 hours of wind tunnel time, was able to deliver key design information (e.g. peak dynamic overturning moments and wind-induced peak accelerations) in real time for a total of 17 aerodynamic variations of the tower form: a result which, previously, would only have been possible through an extensive and time-consuming campaign of wind tunnel tests. The way in which the wind loading was then refined, making use of simultaneous pressure integration and aeroelastic techniques, will also be described. Details about other wind engineering studies, aimed at investigating the pedestrian-level wind microclimate, the facade wind pressure, as well as the stack effect, will also be briefly presented.

A Gibbs sampling algorithm for structural modal identification under seismic excitation

SummaryIdentification of structural modal parameters under seismic excitation using operational modal analysis (OMA) is a challenging task because it violates the basic assumptions of OMA: linear time‐invariant model, stationary white noise input, and adequately long data. The consequence is significant uncertainties associated with the identified modal parameters. This study aims at developing an algorithm to quantify these uncertainties from a Bayesian perspective. Representing the structure and the seismic excitation by a state‐space model, a probabilistic OMA scheme is formulated. The analytical solution for the posterior statistics is not achievable, and a Gibbs sampling algorithm is developed to provide an efficient and robust numerical solution appropriate for practical applications. The performance of the proposed method is validated by identifying a shear‐type building using simulated response data under 4 recorded earthquake motions, and a supertall building—the One Rincon Hill in San Francisco—using field‐recorded data under seismic and ambient excitations. The computed posterior distributions of modal parameters represent the knowledge extracted from the measured data; they can be reliably used for model validation and health monitoring.

Advances in Structural Systems for Tall Buildings: Emerging Developments for Contemporary Urban Giants

New developments of tall buildings of ever-growing heights have been continuously taking place worldwide. Consequently, many innovations in structural systems have emerged. This paper presents a retrospective survey of the main structural systems for tall buildings with emphasis on the advancements of recent, emerging, and potentially emerging systems. A structural systems chart that was previously developed by the authors has been updated in this paper to recognize, categorize and add the more recent structural systems. Recent trends of tubular structural systems in modified forms including the braced megatubes and diagrids are presented. Core-outrigger structural systems are discussed with emphasis on their adaptability. The potential of employing superframes for stand-alone and conjoined megatall buildings is predicted. As a means to solve today’s various project-specific complex design requirements, different mixed structural systems for supertall and megatall buildings are presented. This paper also discusses the widespread application of composite structural systems and recent trends of concrete cores for contemporary tall buildings. Finally, the future of tall buildings is predicted as the race for height continues.

Identification of wind loads on super-tall buildings by Kalman filter

An inverse method based on the discrete time Kalman filter is developed to simultaneously estimate the unknown wind-induced responses and wind loads of high-rise buildings using limited response measurements. The accuracy and effectiveness of the presented estimation method are assessed based on both wind tunnel test results and field measurements of wind effects on a super-tall building. The wind-induced responses obtained by wind tunnel test are used to identify the wind loads on the super-tall building and evaluate the effects of crucial factors, such as covariance matrix of noise, initial estimation error, noise in measurements, modelling errors of structural dynamic properties and number of vibration modes, on the identification results. In addition, the wind loads are also estimated based on the field measured displacements during Typhoon Neoguri. Comparisons between the identified wind loads from the field measured displacements and the wind tunnel test results are made to verify the applicability of the inverse technique. The results of this study illustrate that the proposed inverse method is an efficient tool for predicting the wind loads on super-tall buildings from limited measurements of structural responses.

Monitoring Structural Performance of a Supertall Building during 14 Tropical Cyclones

Field measurements of wind effects on a 420-meter-high supertall building in Hong Kong were analyzed during the passages of 14 tropical cyclone (TC) events, from 2008 to 2016, with a total recording time duration of 360 h. In this paper, statistical results of wind characteristics of these TCs are presented and discussed; modal parameters of the building such as natural frequencies and damping ratios are estimated using the random decrement technique, which is a deterministic time domain method, as well as the Bayesian spectral density approach, which is a recently proposed probabilistic frequency domain method; and the serviceability of the skyscraper during these violent TC events are evaluated against three comfort criteria. This study uses a substantial amount of field data to yield accurate estimations of the modal parameters of the building to further the understanding of wind effects on supertall buildings in TC-prone regions to provide useful information for their wind-resistant designs.

Supertall in Seoul

The first supertall building in South Korea, the 555 m Lotte World Tower, in Seoul, features a gently curving, tapered shape and a mast, dubbed the “lantern,” that consists of two separate diagrid structures that extend 50 m above the top occupied floor. Although the tapering shape presented significant challenges during design and construction of the 123-story structure, it effectively minimizes the wind loads on the tower.

An improved defining parameter for long-period ground motions with application of a super-tall building

This paper focuses on defining long-period ground motions and analyzing the effect of them on building structures. Increasing attention has been paid to the effect of long-period ground motions on building structures. However, long-period ground motions are not quantitatively defined due to the lack of numerous ground motion investigations. In this paper, based on the statistical analysis of 39,744 ground motions, an improved frequency-domain defining parameter, namely βl, is firstly proposed to identify long-period ground motions without the necessity of seismological information. Then, based on the definition, long-period ground motions are selected for the time history analysis of a super-tall building structure. The structural responses are obtained under three scenarios: the original ground motion record, the ground motions scaled to minor earthquakes and major earthquakes. To assess the validity of the proposed parameter βl in identifying long-period ground motions, correlation between the structural response and the defining parameter is obtained.

An experimental study on the wind pressure distribution of tapered super high‐rise buildings

SummaryStudies on the effect of different shape strategies on wind‐induced responses of super tall buildings have been extensive. However, little systematic research on the influence of aerodynamic shapes on wind pressure distributions of super high‐rise building having a height more than 500 m is reported in the literature. In this paper, a series of wind tunnel tests are conducted on models simulating tapered buildings taller than 500 m with an aspect ratio of 9:1 by applying synchronous pressure measurement technology to investigate the influence of different shape strategies on the wind force coefficients of the cross section (Cs) and on the peak negative pressure distributions on surfaces. The shape strategies considered include tapering of the cross section of a building along its height, chamfered modification, and opening ventilation slots. It is found that the wind force coefficient Cs increase with an increase of the tapering ratio. It is shown that chamfered modification can effectively reduce most of the wind force coefficients Cs to less than 0.9. As for peak wind pressures, a zone having a higher negative pressure is found to locate at the bottom of the side faces of the model. With an increase of the tapering ratio, the peak negative pressure of side faces of the model slightly decreases. Chamfered modification can significantly increase the peak negative pressure at the chamfered location. Furthermore, it is demonstrated that opening ventilation slots had less effect on Cs, but the peak negative pressure can significantly increase at the area of opening ventilation slots and adjacent areas.

GNSS-Based Verticality Monitoring of Super-Tall Buildings

In the construction of super-tall buildings, it is rather important to control the verticality. In general, a laser plummet is used to transmit coordinates of reference points from the ground layer-by-layer, which can effectively control the verticality of super-tall buildings. However, the errors in transmission will accumulate with increasing height and motion of the buildings in construction. This paper presents a global navigation satellite system (GNSS)-based method to check the results of laser plumbing. The method consists of four steps: (1) Computing the coordinate time series of monitoring points by adjusting the GNSS monitoring network observations at each epoch; (2) Analyzing the horizontal motion of super-tall buildings and its effect on vertical reference transmission; (3) Calculating the deflections of the vertical at the monitoring point using an Earth gravity field model and a geoid model. With deflections of the vertical, the static GNSS-measured coordinates are aligned to the same datum as used by the laser plummet; and (4) Finally, validating/checking the result of laser plumbing by comparing it with static GNSS results corrected by deflections of the vertical. A case study of a 438-m high building is tested in Guangzhou, China. The result demonstrates that the gross errors of baseline vectors can be eliminated effectively by GNSS network adjustment of the first step. The two-dimensional displacements can be measured at millimeter-level accuracy; the difference between the coordinates of the static GNSS measurement and laser plumbing is less than ±2.0 cm after correction with the deflections of the vertical, which meets the design requirement of ±3.0 cm according to the Technical Specification for Concrete Structures of Tall Buildings in China.

Decision framework for optimal installation of outriggers in tall buildings

Abstract Installation sequence of outrigger system, an important structural component of high-rise buildings, is often determined simply based on engineers' experience, posing a threat to the structural safety and stability. This paper proposes a comprehensive decision framework for developing the optimal installation plan for the outrigger system, in which construction simulation and safety analysis of the overall structural system are well integrated. The proposed framework is applied to a super-tall building with a height of 600 m. First, the finite element method (FEM) model of the skyscraper used for construction simulation is validated by field measurements during Typhoon ‘Nida’. Based on the validated FEM model, the lower limits (earliest) for installing the outrigger system are obtained through the outrigger trusses' safety analysis for the service stage of the building, while the upper limits (latest) are determined through the analysis of structural stiffness and global stability for the construction stage. Thereupon, a rational plan is established for installing the outrigger system into the skyscraper, and the viability and efficiency of the proposed decision framework are examined by analyzing the construction simulation models. The outcomes of this study are expected to be of use and interest for structural engineers and researchers involved in construction management of installing outriggers into high-rise buildings, and therefore provide valuable implications for other similar projects.

Influence of soil‐structure interaction on performance of a super tall building using a new eddy‐current tuned mass damper

SummaryTuned mass dampers (TMDs) can be used as vibration control devices to improve the vibration performance of high‐rise buildings. The Shanghai Tower (SHT) is a 632‐m high landmark building in China, featuring a new eddy‐current TMD. Special protective mechanisms have been adopted to prevent excessively large amplitude of the TMD under extreme wind or earthquake loading scenarios. This paper presents a methodology for simulating behavior of the new eddy‐current TMD that features displacement‐dependent damping behavior. The TMD model was built into the SHT finite element model to perform frequency analysis and detailed response analyses under wind and earthquake loads. Furthermore, soil‐structure interaction (SSI) effects on wind and seismic load responses of the SHT model were investigated, as SSI has a significant impact on the vibration performance of high‐rise buildings. It was found that SSI has more significant effects on acceleration response for wind loads with a short return period than for wind loads with a long return period. Some of the acceleration responses with SSI effects exceed design limits of human comfort for wind loads with shorter return periods. As to the seismic analyses, it was found that SSI slightly reduces the displacement amplitude, the damping force, and the impact force of the TMD.

Monitoring of wind effects on 600 m high Ping-An Finance Center during Typhoon Haima

This paper presents analyzed results of field measurements of wind-induced pressures on building claddings and structural responses of 600 m high Ping-An Finance Center (PAFC) in Shenzhen, China during the passage of Typhoon Haima. The characteristics of cladding pressures during the typhoon were investigated with highlights on energy distribution, non-Gaussian probability and coherence features. Then, the natural frequencies, damping ratios and mode shapes of the skyscraper were presented. Based on the field measurements, the amplitude-dependent characteristics of the modal parameters were discussed and the range of selection of damping ratio for the wind-resistant design of super-tall buildings was recommended. Finally, the serviceability of the skyscraper under typhoon condition was assessed. This paper aims to further understand the wind effects on super-tall buildings and provide useful information for the design of skyscrapers in tropic cyclone prone regions.

Outrigger system analysis and design under time‐dependent actions for super‐tall steel buildings

SummaryThe outrigger system has been widely adopted as an efficient structural lateral‐load resisting system for super‐tall buildings in recent years. Although the outrigger system has many structural advantages, it has a significant defect due to differential shortening, which cannot be neglected. Due to the shrinkage and creep of concrete, as well as the differential settlement of foundation, the shortening of the structural member is an important time‐dependent issue, which leads to additional forces in the outriggers after the lock‐in of the outriggers. As a result, it will increase the size of the structural member cross section in the design. In a real project, engineers can delay the lock‐in time of the outrigger system to release the additional forces caused by the differential shortening during the construction phase. The time‐dependent actions, such as the column shortening and the differential settlement of the foundation, were estimated. A mega frame steel structure was employed to illustrate the analysis and design of the outrigger under the time‐dependent actions. Furthermore, a simple optimal method, considering the structural stability and overall stiffness, was proposed to optimize the construction sequence of the outrigger system.

Field measurements of wind pressures on a 600 m high skyscraper during a landfall typhoon and comparison with wind tunnel test

As high-rise structures are constantly emerging worldwide, wind effects on wind-sensitive structures are correspondingly getting increasing concerns, especially in tropic cyclone prone areas. This paper presents the analyzed results from field measurements of wind effects on a 600 m high skyscraper located in Shenzhen during a landfall typhoon. Field monitoring of wind-induced pressures on the skyscraper was conducted by a structural health monitoring system. The major objective of this study is to further understand typhoon-generated wind pressures on super-tall buildings. In addition, wind tunnel test of simultaneous pressure measurements on the building model was performed. Full-scale and wind tunnel measurements of wind-induced pressures on windward, leeward and side faces of the super-tall building were analyzed and compared. A whole range of characteristic properties, including pressure coefficient, probability distribution, peak factor, power spectral density, and correlation of cladding pressures were presented and discussed. The findings of this study are expected to be of interest and practical use to professional and researchers involved in the wind-resistant designs of super-tall buildings in tropic cyclone prone regions.

Experimental study of aerodynamic damping of a twisted supertall building

The aerodynamic damping ratios and aeroelastic instability of a 180° helical supertall building with good aerodynamic behavior in both the along-wind and across-wind responses were investigated using an aeroelastic model test (rocking vibration model test). The aerodynamic damping ratios for the 180° helical and square models were evaluated using the random decrement technique. Furthermore, the effect of the triggering level and number of time segments on the evaluation of the aerodynamic damping ratio was also investigated. It was found that both the mean and fluctuating displacement responses of the 180° helical model in the along- and across-wind directions showed better aerodynamic behaviors than those of the square model. Aeroelastic instability of the 180° helical model was not observed at any of the reduced velocities considered in the study. In the along-wind direction, the aerodynamic damping ratios of the 180° helical model exhibit similar trends to those of the square model. However, in the across-wind direction, the aerodynamic damping ratios of the 180° helical model show significantly different trends than those of the square model. Furthermore, there was no effect of the variation in the wind direction on the aerodynamic damping ratio of the 180° helical model. We found that in the evaluation of the aerodynamic damping ratio, it is possible to adopt the triggering level at the value of the standard deviation or √2 times of the standard deviation of the displacement responses if the random decrement signature has a high number of triggering points.

EXPERIMENTAL STUDY ON THE SEISMIC PERFORMANCE OF DAMPED OUTRIGGERS

The outriggers are the key components of super tall buildings. Increasing the energy dissipation capacities of outriggers has significant value on improving the structural seismic performance. Based on the pseudo-static test of a conventional outrigger, the seismic performance of outriggers with different dampers was investigated through experiments in this study. The results indicated that the auxiliary devices should be installed to ensure the pure shear deformation state of the dampers. Installing either mild steel dampers or friction dampers at the end of the outrigger could improve its energy dissipation capacity and prevent its components from being damaged. As the stiffness and strength of a friction damper can be decoupled, the design process of such damper in the outriggers was much operable, making it more adoptable and promotable in engineering practice. Moreover, the feasibility of using mild steel dampers in the outriggers was also analyzed in this study. It was found that due to the coupling of stiffness and strength of mild steel dampers, the design requirements for the stiffness and strength of outriggers were hard to meet simultaneously. Therefore, further in-depth studies on the application of outrigger with mild steel dampers are needed.

Numerical studies on fire hazards of elevator evacuation in supertall buildings

Long evacuation time is a key fire safety concern for crowded supertall buildings. Elevator evacuation appears to be the only choice but fire safety provisions are not specially designed for the use of elevators. A fire safe elevator system was proposed earlier for supertall buildings by providing elevator accessible on each floor level and passing through the refuge place. The fire hazard associated with this design has been studied numerically through an example building in this paper. Smoke spread to the elevator system was considered in the study. The effect of ventilation of the shaft, stack effect and wind effect on smoke movement were studied by empirical equations in fire engineering and justified by computational fluid dynamics. Different designs of smoke extraction with pressurization system were evaluated by analysing the smoke dispersion and pressure distributions. The effect of fire at different heights on smoke spread was also investigated. Results show that the smoke extraction system can only delay smoke spread to the elevator shaft near the fire source for a short time. The “four-floor approach” pressurization system can confine the smoke in the area of fire floor for a sufficiently long time period for safe evacuation.