Tall Building Model Research Articles

Effects of Attached Afterbody Shapes on Wind Forces on Rectangular Tall Buildings

ABSTRACTThe knowledge of aerodynamic forces has important implications for the wind‐resistant design of tall buildings. At present, the aerodynamic characteristics of conventional rectangular‐shaped tall buildings have been extensively studied, while those of irregular‐shaped tall buildings have received relatively less attention. Therefore, in the current study, several tall building models are designed to investigate the aerodynamic characteristics of a rectangular tall building with and without attaching different shapes of afterbody. The influences of the afterbody shapes (i.e., semicircle, rectangle, and triangle attached to a rectangular tall building called the basic model in this paper), atmospheric boundary layer (ABL) flows, and models' aspect ratios on the aerodynamic forces are analyzed and discussed in detail based on wind tunnel test of pressure measurements on the models. It is shown that the attached afterbodies can significantly increase the local fluctuating lift coefficients and base fluctuating moment coefficients comparing to those of the basic model. Moreover, a larger aspect ratio causes the increase of local fluctuating lift coefficients and base fluctuating moment coefficients of the basic model attached with rectangular afterbody in suburban terrain. On the other hand, the above increases are strongly attenuated or even suppressed by the ABL flow over urban terrain. The results of this study are expected to provide useful information for the wind‐resistant design of irregular‐shaped tall buildings.

Effects of turbulence integral scale on the fluctuating pressures on side face of the standard tall building model

Effects of turbulence integral scale on the fluctuating pressures on side face of the standard tall building model

Formulation of justifiable wind loading distributions up tall buildings derived from HFFB measurements

For the general case of non-linear and combined sway and twist mode shapes, analysis of HFFB measurements gives rise to serious challenges and various techniques have been developed using significant assumptions. This is because it is not possible to directly obtain the distribution of varying fluctuating wind loads throughout the height of tall buildings. This paper proposes a straightforward HFFB-based wind load/twist distribution approach in the time domain to predict the wind-induced dynamic response of tall buildings. Using this framework, it is possible to overcome the deficiencies of mode shape correction factor approach, and the complexity and impracticality of alternative approaches for tall buildings. Two 1:300 scale rigid models of benchmark tall buildings, IAWE Buildings A and B, have been selected to perform a detailed wind tunnel investigation as subjects to evaluate this proposed HFFB approach study. Building A has complex 3D mode shapes combining sway and twist, whereas the simpler Building B has uncoupled linear mode shapes in sway and twist. The high frequency pressure integration (HFPI) wind tunnel technique was utilised to measure surface pressure information in separate tests to obtain the reference wind loading for validation of the HFFB predictions. Furthermore, a commonly used HFFB mode shape correction factor approach was used to estimate the dynamic wind responses which were compared to those from the proposed approach. From the comparison between the aerodynamic and dynamic wind results from proposed HFFB approach and reference HFPI results, it is found that the proposed HFFB approach can predict the vertical distributions of the wind forces and torque (wind loads) with acceptable accuracy for carrying out the conceptual stage of tall building design.

Aerodynamic loads of tapered tall buildings: Insights from wind tunnel test and CFD

Tapered modifications have been widely utilized for tall buildings to reduce their wind effects in practical engineering. However, the flow mechanisms caused by tapering and relevant empirical models for wind loads estimations of tapered tall buildings are still unknown. In this study, both wind tunnel test and CFD were used to study the aerodynamic performance of tapered tall buildings. Taken the CAARC standard tall building model as the benchmark model, another four modified models with taper ratio of 0.05, 0.10, 0.15 and 0.20 were designed and tested by pressure measurements and large eddy simulation (LES). The variations of wind pressure coefficients, local wind force coefficients, base moment coefficients, wind load power spectrum and vertical coherence function of five models with different taper ratios were discussed and compared. Also, the streamline of mean and fluctuating velocity around tapered tall building models are provided for better understanding of the flow mechanisms. The results showed that aerodynamic performance of the tapered tall buildings has been improved effectively, especial for across-wind effects. This study aims to provide reference for aerodynamic optimization design of tapered tall buildings.

Numerical simulation of wind-structure-soil interaction effects on the CAARC tall building model using hybrid CUDA-OpenMP parallelization

In the present work, the dynamic effects of the wind action over the Commonwealth Advisory Aeronautical Council (CAARC) tall building model are numerically evaluated considering the influence of soil-foundation interaction. A numerical model is developed considering a partitioned coupling scheme for fluid-structure-soil interaction, in which the fluid, structure and soil subsystems are solved sequentially using independent algorithms. The Finite Element Method (FEM) is adopted for spatial discretization, where linear hexahedral elements with underintegration techniques are used. The fundamental flow equations are kinematically described using an arbitrary lagrangian-eulerian (ALE) formulation and numerically solved using the explicit two-step Taylor-Galerkin scheme, while Large Scale Simulation (LES) is employed for the treatment of turbulent flows. Structure and soil are considered as deformable elastoplastic media, using a corotational approach to deal with physical and geometric nonlinearities. Dynamic equilibrium equation is solved using the generalized-α method and infinite elements are utilized in the soil domain to avoid elastic wave reflections. Load transfer between soil and structure is performed using a three-dimensional contact algorithm based on the penalty method that allows separation and sliding along soil-structure interfaces. A hybrid parallelization strategy based on CUDA-OpenMP techniques is proposed to accelerate the processing time associated with the present simulations. Numerical results obtained here are compared with numerical and experimental results reported by other authors, where one can observe that soil-structure interaction may significantly influence the building response due to wind loading and effects of aeroelastic instability may be considerably reduced in the presence of soil support.

Evaluation of Wind Effects on High-Rise Buildings Using Ansys CFX

Tall building is the growing pattern of cities, these buildings are highly vulnerable to wind loads. Wind load effects on the high-rise building can be found using wind tunnel testing and CFD tools. Wind tunnel facilities are limited all around the world, so CFD tools can be incorporated. In this study, ANSYS CFX is used to investigate the effects of wind on different shapes of high-rise buildings. The results of numerical simulation are compared with the international standards of various countries. Streamline patterns and pressure contours on different faces are discussed in this paper. It is found that building shape and size are having a direct effect on the pressure distribution on various surfaces of the building model. Windward face pressure will always be positive in nature. In this study, the comparison is presented for the variation in the cross-sectional shape of the building model. For this purpose Model C and Model I are having considerable variations and Model X is considered for validation purposes only. It is well established that the results are within the allowable limit. This paper aims to discuss these windgenerated effects in the tall building model.

Effect of Aerodynamic Modification on ‘V’ plan Shaped Tall Building Under Wind Excitation

Advanced high-rise buildings with peculiar cross-sectional plan is the major challenging concern to all structural engineers as well as researchers due to variation in dynamic wind response. Irregular shaped tall buildings are vulnerable to wind force due to height and nonuniformity of the structure. In the present study, the principal objective is to investigate the significant role of the aerodynamic modification of the building model to reduce the aerodynamic effect of wind force on ‘V’ plan shaped high-rise building and to modify aerodynamic design criteria accordingly. Various cases have been made by considering different local modification like corner chamfered and corner rounded of ‘V’ plan shaped building model. The angle between the limbs is 90° which remain unchanged. The percentage is gradually increased from 5% to 20% of the total plan area with 5% regular increment for both chamfered and rounded corner. Wind incident angle is increased from 0° to 90° with 30° regular interval for each case. Computational Fluid Dynamics (CFD) is the basis of method to perform the numerical simulation of ‘V’ plan shaped building with local modifications such as corner chamfered, corner rounded which is similar wind environment as in urban terrain. Grid convergence study is performed to improve the accuracy of result by adopting very finer meshing of Computational Domain. Pressure coefficient of each face, force coefficient, velocity variation, pressure variation on each face is obtained by numerical analysis. Further, a comparison has been made with basic ‘V’ plan shaped tall building model without any modification to study the effectiveness of aerodynamic modification on wind-induced response of ‘V’ plan shaped building exposed to different wind incidence angle and observations have been made on the suitability of aerodynamic modification based on the numerical result.

A novel mechanism - smart morphing façade system - to mitigate wind-induced vibration of tall buildings

Wind-induced vibration plays a significant role in the design of tall buildings, primarily due to serviceability requirements for occupant comfort and structural safety. As a result, several approaches have been developed to address this concern. This paper describes a novel control mechanism, a smart-morphing-façade (Smorphacade) system, using the concept of an aerodynamically modified building façade to mitigate wind-induced vibration of tall buildings. Compared to a fixed-façade system, since a Smorphacade can be dynamically modified in real time based on rapidly-changing wind speed and wind direction during a windstorm, it can be further developed into an active control system. The Smorphacade is comprised of a set of circular ducts embedded in a flat plate and arranged in a matrix formation that is fixed on the original façade but with a gap between the two facades. Each circular-shaped duct is comprised of two parts, a fixed base with alternate open and closed surfaces shaped like a fan-blade and a rotating part similar in shape like the fixed one but placed inside the fixed one and capable of rotation by a protruding fin. By rotating the fin, the porosity of the duct and the fin inclination angle can be simultaneously changed, enabling flow control through the duct. The performance of a Smorphacade system in different configurations was studied using the CAARC standard tall-building model under atmospheric boundary layer wind; its effectiveness in reducing building response was examined by comparing the results of a building with a Smorphacade system to those from one without it. It was found that the effectiveness of the Smorphacade system in reducing the average combined vibration among all three directions (2 transverse and 1 torsional) varied between 16.7 and 18.6%, with a maximum reduction of 32% and 59.7% in across-wind direction and torsional direction, respectively, depending on factors such as Smorphacade configuration, wind speed, and angle of attack.

A comparative study on structural design alternatives for twisted tall buildings with outriggers

Tall buildings are seen as iconic landmarks because of their bold effect on the city silhouette. To control this bold effect in an aesthetically desired manner, designers search for intriguing forms such as twisted buildings. There are two main approaches for designing the structural system of a twisted tall building. In the first approach, the twisted form of the building is obtained only by the rotation of the floors, and the structural system is maintained in a conventional, perpendicular way. Alternatively, the structural system and the floors of the building twist together. This study designates these as non-adaptive and adaptive, respectively. With different heights and angles of twist, non-adaptive and adaptive tall building models are created and analysed under the combined effect of wind and gravity loads. The dynamic properties, drift, moment, and torsion demands are compared to scrutinize and assess the potentials and limitations of these alternative approaches.

Blockage Effects in Wind Tunnel Tests for Tall Buildings with Surrounding Buildings

To study the blockage effects in wind tunnel tests for tall buildings with surrounding buildings and establish a reasonable calculation method for the blockage ratio, this paper carried out fifty-one test conditions of pressure model wind tunnel tests with three scale ratios. The tests considered the relative location, relative height, and model number of the surrounding buildings to those of the target building by the rigid pressure models. Based on the wind tunnel tests, the blockage effects on the pressure coefficients and drag coefficients were studied in detail. The results showed that the blockage effects were different when the relative positions of the surrounding models to the target model were different, even if the blockage ratio was the same. The blockage effects caused by the surrounding models with unit blockage ratio were usually more significant than those caused by the target pressure-measuring model itself. The existing correction methods for the blockage effects are mainly derived from the wind tunnel tests of an isolated building model. Using existing calculations to evaluate the blockage effect of wind tunnel tests for tall buildings with surrounding buildings may result in obvious deviations. Finally, the concept of the equivalent blockage ratio was proposed, which can be used to calculate the blockage ratio of wind tunnel tests of tall buildings with surrounding buildings. The proposed calculation method of this equivalent blockage ratio can provide a reference for the determination of scale ratios for wind tunnel test models of tall buildings.

Effect of aspect ratio subjected to wind hazard in tall buildings situated along the coastal line of India

SummaryThe escalating growth of the tall buildings as well as the increasing number of extreme wind events in the Indian coastal region have certainly arisen the question of the safety and stability of these buildings situated in the metropolitan cities along the coastline. In such a scenario where there have been a constant focus on more researches for a unified wind code, however a comprehensive comparative study is required not only to assess and analyze the dynamic peak factors of the tall building models due to wind load, but also to enlighten the differences in the obtained results as well as their patterns respectively. The aspect ratio of buildings essentially governs the stability as well as contributes to a great extent on the dynamic responses in terms of base shear, base moment and torsional effects at the base. However, a framework based on the Indian wind database could ease the complexity of such parametric survivability studies of such structures. Distinguished variations in the dynamic responses for a series of models of tall buildings with varying aspect ratios along the height are analyzed as well as discussed in the present study, and the pattern of the deviation of the results with a parallel framework is also addressed to propose a mechanism for assessing the behaviors of tall buildings under specific wind speed predominant in the Indian coastal region that would help to ensure the safety and stability of structures subjected to wind hazards in Indian context in future.

A computational approach for modelling composite slabs in fire within OpenSees framework

Modelling tall buildings responding to fires, especially multi-floor fires, requires the consideration of composite slabs as the composite action can significantly affect the structure fire response. Modelling composite slabs in fire is tedious and complex due to the existence of ribs and complicated thermal action. In view of the complexity of the existing modelling approaches, this paper aims to propose a computational approach for modelling composite slabs in fire in the open-source program of ‘OpenSees for fire’. The proposed approach adopts a unified reference plane in the shell element discretization along with built-in approximation of the ribbed section and temperature loading. The modelling approach is incorporated into a new version of layered shell thermal section with a vision of enabling efficient modelling of tall buildings in fire. Benchmark tests are performed using T-shaped plain concrete beams to verify the approach. A collection of tests on composite slabs or composite floor systems are then modelled to extensively validate the approach with respect to the ambient loading and fire tests. Validation results demonstrate good performance of the modelling approach even without extra calibration. The work implemented in OpenSees will be made open source and can significantly simplify the modelling efforts of including multiple floors of composite slabs in a tall building model when investigating its fire performance.

Cyber-physical aerodynamic shape optimization of a tall building in a wind tunnel using an active fin system

This study explores the use of a cyber-physical systems (CPS) framework for the design and optimization of the aerodynamics of a tall building through aeroelastic boundary layer wind tunnel (BLWT) testing. The framework is a fully-automated combination of traditional experimental wind tunnel testing with numerical optimization strategies to evaluate a wide range of candidate designs both accurately and quickly. In this study, candidate designs are achieved through the physical adjustment of the aerodynamic shape of a multi-degree-of-freedom (MDOF) aeroelastic tall building model. BLWT testing is carried out at the University of Florida Natural Hazard Engineering Research Infrastructure (NHERI) Experimental Facility (EF). The specimen is equipped with an actuation system consisting of a series of individually-controllable slotted fins comprising an active fin system (AFS), which enable precise modifications of the aerodynamic shape of the envelope. The wind-induced building response of the specimen is directly captured using a series of accelerometers and laser displacement sensors. A stochastic optimization algorithm is then employed in the aerodynamic CPS framework to evaluate the fitness of each candidate design based on specified performance criterion related to either occupant comfort or building drift. Optimization results indicate that the CPS framework can reliably achieve the optimal solution which minimizes the response (i.e., horizontal accelerations and lateral displacements) of the aeroelastic specimen.

Prediction of wind pressures on tall buildings using wavelet neural network

For wind-resistant design of tall buildings, it is routine to obtain complete surface wind pressure distribution based on experimental data recorded at limited locations. The main goal of this study is to examine the usability of a hybrid artificial neural network method, i.e., Wavelet Neural Network (WNN), for simulating and interpolating wind pressures on tall buildings. Wind pressure measurement tests were carried out on two scaled tall building models. The performance of three different prediction models, namely back-propagation neural network (BPNN), genetic algorithm-back-propagation neural network (GA-BP), and WNN were examined for comparison purposes. The results are overall promising, in which all the three models were capable to reasonably replicating wind pressure characteristics (i.e., time series, power spectra and wind pressure coefficient distribution) using experimental data at selected locations. In particular, WNN was shown to produce the most satisfactory prediction results. This evidences that WNN can be considered as a useful and reliable tool to predict surface wind pressure on tall buildings. The outcomes of this study are expected to provide important implications to practically aid the wind-resistant design of tall buildings.

Reduction of wind loads on rectangular tall buildings with different taper ratios

To explore the influence of different taper ratios on wind loads reduction on rectangular tall buildings, the CAARC standard tall building model is selected as the benchmark model and four other rigid models with different taper ratios ranging from 5% to 20% are tested for pressure measurement in a boundary layer wind tunnel. Based on the test results, the distribution of wind pressure coefficients, local wind force coefficients, base moment coefficients and their power spectral densities from the five models are compared and discussed. Moreover, correlation factors for base moment coefficients and their power spectral densities concerning the effects of different taper ratios are provided. It has been proved that the aerodynamic performance of the rectangular tall building has been improved by the increasing of taper ratio. This study aims to provide useful information for the wind-resistant design of rectangular tall buildings.

Nonlinear Inelastic-Degrading Structural Modeling Approach to Assess the Seismic Soil–Structure Interaction Response of Tall Buildings

Oversimplifying structural modeling in the analysis of the seismic performance of tall buildings introduces variability and biases in the computed seismic response. Engineering demand parameters (EDPs) from coupled soil–structure interaction (SSI) systems can only be realistically determined when nonlinear constitutive soil and structural behaviors are adopted in the numerical formulation. Large-magnitude earthquakes mobilize soil and structural demands that are beyond the elastic response of both materials. This paper aims at evaluating the influence of the structural modeling assumptions in the computed soil response due to seismic excitations using a direct fully coupled nonlinear SSI approach. Numerical analyses are conducted on elastic and nonlinear inelastic-degrading tall building models supported on a mat foundation-to-soil continuum domain using a multiple-yield surface plane-strain constitutive model. The models were subjected to multiple ground motion scenarios representative of broadband frequency content. Large discrepancies occur between linear and nonlinear inelastic tall buildings in terms of interstory drifts, peak horizontal accelerations, structural displacements, hysteretic energy, foundation rotation, and soil settlements. The results show how using nonlinear inelastic-degrading structural models of tall buildings largely affect the computed seismic response of the entire SSI system relative to linear elastic structural modeling approaches. More realistic responses are obtained using nonlinear degrading building models including SSI effects, because energy distribution and tradeoff among both the supporting soils and structure vary significantly as the seismic demands induce stresses and strains in the building beyond the onset of structural yielding.

Influence of Small Vehicle on Transiting Test Method for Measuring Building Wind Pressure Coefficients

The transiting test method is a new approach for structural wind resistance research. However, traffic on the test road inevitably influences test results. In this study, the symmetrical CAARC standard tall building model was used to investigate the influence of a small vehicle near the test vehicle. A small vehicle was set up as an interference vehicle to drive around the test vehicle under different cases during the test. Results indicate that the mean wind pressure coefficient during the overtaking period is higher than that during the no overtaking period. The enlarged relative velocity and the small test vehicle velocity increase the overtaking interference and the data calculation time required to eliminate the overtaking influence. The overtaking influence only occurs if the test vehicle is overtaken by the small vehicle in the adjacent lane. The influence of the overtaking behavior of a small vehicle can be eliminated after the data calculation time exceeds 26 s. Moreover, the wake of small interference vehicle no longer influences the transiting test results after the spacing reaches 24 m.

Progressive collapse and robustness of modular high-rise buildings

Contrary to conventional buildings, the structural robustness of modular high-rise buildings has not been studied due to the lack of the numerical and experimental studies and design guides. To gain a better understanding of their structural robustness against progressive collapse, this paper investigates the robustness of modular high-rise buildings using the alternative load path method with nonlinear time-history analysis. A numerical model of a typical modular tall building subjected to a corner module removal scenario was developed to explore its typical response, resistance mechanism and progressive collapse. A comprehensive parametric study was then performed to examine the effects of a wide range of parameters (e.g. column cross-section, inter-module connection and bracing system) and configurations on the progressive collapse and structural robustness of modular buildings. The result showed that bracing systems can enhance the structural robustness effectively by sharing redistributed loads and restraining structural members. The removal of corner members is more critical because there are limited adjacent members for sharing the redistributed loads. Inter-module connections should provide adequate strength to develop more alternative load paths when extreme events occur. Finally, design recommendations for improving the robustness of modular buildings were also proposed based on the findings from the parametric study.

HFBB model test for tall buildings: A comparative benchmark with a full-aeroelastic model

A novel approach to full-aeroelastic model design is presented, considering continuous structures and coupled modes. Its validity is proven by building a full-aeroelastic CAARC standard tall building model featuring 12-degrees-of-freedom at 1:360 scale. A complete description of its design, manufacturing, tuning, and dynamic identification is reported. The model is tested in a novel wind-tunnel experimental campaign performed at the CRIACIV facility (Prato, Italy). A comparative study of aerodynamic and full-aeroelastic response in terms of base moment and accelerations shows that the aerodynamic model tends to overpredict the response along the broader side of the model. The contribution of second modes is found to be relevant for induced acceleration at the rooftop.

Reducing Processing Time of Nonlinear Analysis of Symmetric-Plan Buildings

Nonlinear response history analysis has been a powerful tool in performance-based earthquake engineering for validating the proposed design of new structures or evaluating existing ones. When it is applied to structural systems with a large number of degrees of freedom, such as three-dimensional (3D) models of tall buildings, bridges, or dams, the analyses can be time-consuming. The prolonged computing times become more prominent in parametric studies or in incremental dynamic analyses. In order to reduce the computation time, this study proposes a practical method—a reducing time steps (RTS) procedure—whereby leading and trailing weak signals in the input acceleration record are trimmed, and the remaining record is downsampled. The test results based on several different 3D computer models of reinforced-concrete idealized structures demonstrate that the RTS method is practical, and it provides estimates of engineering demand parameters such as peak values of story drift, floor acceleration, and floor velocity within 10% of the results obtained by using the original records. The RTS procedure was further validated on three symmetric-plan steel buildings with 5, 9, and 15 stories. For all analyzed cases, the average reduction in computational time was around 50%.