• International Journal of High-Rise Buildings
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• v.4 no.1
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• pp.57-64
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• 2015

Recently, new keywords such as "Resilience" and "Repairability" have been discussed from the perspective of the sustainability of damaged structures after a severe disaster. To evaluate the repairability and recovery of structures, it is necessary to establish an analytical method that can simulate the behavior of repaired structures. Furthermore, it is desirable to establish an evaluation method for the structural performance of repaired structures. This study investigates the repairability and recovery of steel members that are damaged by local buckling or cracks. This paper suggests a simple analytical model for repaired steel members, in order to simulate the inelastic behavior and evaluate the recoverability of the structural performance. There is good agreement between the analytical results and the test results. The proposed analytical method and model can effectively evaluate the recoverability.

• International Journal of High-Rise Buildings
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• v.8 no.3
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• pp.211-220
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• 2019

Three cases of supertall connected structures are presented and each of them represents a quite style. The first case is a strong-connected structure. The coupling function of towers and connector contributes a lot to the structural stiffness and stability. Its special construction scheme had great impact on the construction quality and the structural safety, and must be accurately considered. For the second case which is a weak-connected structure, the influences of different connecting modes to the structural dynamic characteristic were explained. Then the combined bearings were proposed to achieve the design presume. In the third case which represents the multi-supported structures, the structural distinctive mechanical properties were discussed. For the structural state during construction process is quite different from that in final service condition, two construction procedures were simulated to get an optimal one. Although there are great challenges to designers, the advantages of the supertall connected buildings are obvious. Further work is needed in this area to adapt to the development of future cities.

• International Journal of High-Rise Buildings
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• v.10 no.4
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• pp.323-334
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• 2021

Concrete structures may rarely collapse in fire incidents but fire induced damage to structural members is inevitable as a result of material degradation and thermal expansion. This requires certain repairing measures to be applied to restore the performance of post-fire members. A brief review on investigation of post-fire damage of concrete material and concrete structural members is presented in this paper, followed by a review of post-fire repair research regarding various types of repairing techniques (FRP, steel plate, and concrete section enlargement) and different type of structural members including columns, beams, and slabs. Particularly, the fire scenarios adopted in these studies leading to damage are categorized as three levels according to the duration of gas-phase temperature above 600℃ (t₆₀₀). The repair effectiveness in terms of recovered performance of concrete structural members compared to the initial undamaged performance has been summarized and compared regarding the repairing techniques and fire intensity levels. The complied results have shown that recovering the ultimate strength is achievable but the stiffness recovery is difficult. Moreover, the current fire loading scenarios adopted in the post-fire repair research are mostly idealized as constant heating rates or standard fire curves, which may have produced unrealistic fire damage patterns and the associated repairing techniques may be not practical. For future studies, the realistic fire impact and the system-level structural damage investigation are necessary.

• International Journal of High-Rise Buildings
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• v.8 no.2
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• pp.107-116
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• 2019

The use of computational fluid dynamics (CFD) is becoming an increasingly popular means to model wind flows in and around buildings. The first published application of CFD to both indoor and outdoor building airflows was in the 1970's. Since then, CFD usage has expanded to include different aspects of building design. Wind tunnel testing (WTT) on buildings for wind loads goes back as far as 1908. Gustave Eiffel built a pair of wind tunnels in 1908 and 1912. Using these he published wind loads on an aircraft hangar in 1919 as cited in Hoerner (1965 - page 74). The second of these wind tunnels is still in use today for tests including building design ($Damljanovi{\acute{c}}$, 2012). The Empire State Building was tested in 1933 in smooth flow - see Baskaran (1993). The World Trade Center Twin Towers in New York City were wind tunnel tested in the mid-sixties for both wind loads, at Colorado State University (CSU) and the [US] National Physical Laboratory (NPL), as well as pedestrian level winds (PLW) at the University of Western Ontario (UWO) - Baskaran (1993). Since then, the understanding of the planetary boundary layer, recognition of the structures of turbulent wakes, instrumentation, methodologies and analysis have been continuously refined. There is a drive to replace WTT with computational methods, with the rationale that CFD is quicker, less expensive and gives more information and control to the architects. However, there is little information available to building owners and architects on the limitations of CFD for flows around buildings and communities. Hence building owners, developers, engineers and architects are not aware of the risks they incur by using CFD for different studies, traditionally conducted using wind tunnels. This paper will explain what needs to happen for CFD to replace wind tunnels. Ultimately, we anticipate the reader will come to the same conclusion that we have drawn: both WTT and CFD will continue to play important roles in building and infrastructure design. The most pressing challenge for the design and engineering community is to understand the strengths and limitations of each tool so that they can leverage and exploit the benefits that each offers while adhering to our moral and professional obligation to hold paramount the safety, health, and welfare of the public.

• Wind and Structures
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• v.21 no.2
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• pp.119-158
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• 2015

The characteristics of the coherence functions of X axial, Y axial, and RZ axial (i.e., body axis) wind forces on the Shanghai World Trade Centre - a 492 m super-tall building with section varying along height are studied via a synchronous multi-pressure measurement of the rigid model in wind tunnel simulating of the turbulent, and the corresponding mathematical expressions are proposed there from. The investigations show that the mathematical expressions of coherence functions in across-wind and torsional-wind directions can be constructed by superimposition of a modified exponential decay function and a peak function caused by turbulent flow and vortex shedding respectively, while that in along-wind direction need only be constructed by the former, similar to that of wind speed. Moreover, an inductive analysis method is proposed to summarize the fitted parameters of the wind force coherence functions of every two measurement levels of altitudes. The comparisons of the first three order generalized force spectra show that the proposed mathematical expressions accord with the experimental results well. Later, the influences of coherence functions on wind-induced dynamic responses are analyzed in detail based on the proposed mathematical expressions and the frequency-domain method of random vibration theory.

• Wind and Structures
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• v.18 no.4
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• pp.347-373
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• 2014

Since its development in the early 1980's the force balance technique has become a standard method in the efficient determination of structural loads and responses. Its usefulness lies in the simplicity of the physical model, the relatively short records required from the wind tunnel testing and its versatility in the use of the data for different sets of dynamic properties. Its major advantage has been the ability to provide results in a timely manner, assisting the structural engineer to fine-tune their building at an early stage of the structural development. The analysis of the wind tunnel data has evolved from the simple un-coupled system to sophisticated methods that include the correction for non-linear mode shapes, the handling of complex geometry and the handling of simultaneous measurements on multiple force balances for a building group. This paper will review some of the components in the force balance data analysis both in historical perspective and in its current advancement. The basic formulation of the force balance methodology in both frequency and time domains will be presented. This includes all coupling effects and allows the determination of the resultant quantities such as resultant accelerations, as well as various load effects that generally were not considered in earlier force balance analyses. Using a building model test carried out in the wind tunnel as an example case study, the effects of various simplifications and omissions are discussed.

• Wind and Structures
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• v.32 no.2
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• pp.143-159
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• 2021

The 246.8-m-tall Beijing Olympic Tower (BOT) is a new landmark in Beijing City, China. Its unique architectural style with five sub-towers and a large tower crown gives rise to complex dynamic characteristics. Thus, it is wind-sensitive, and a double-stage pendulum tuned mass damper (DPTMD) has been installed for vibration mitigation. In this study, a finite-element analysis of the wind-induced responses of the tower based on full-scale measurement results was performed. First, the structure of the BOT and the full-scale measurement are introduced. According to the measured dynamic characteristics of the BOT, such as the natural frequencies, modal shapes, and damping ratios, an accurate finite-element model (FEM) was established and updated. On the basis of wind measurements, as well as wind-tunnel test results, the wind load on the model was calculated. Then, the wind-induced responses of the BOT with the DPTMD were obtained and compared with the measured responses to assess the numerical wind-induced response analysis method. Finally, the wind-induced serviceability of the BOT was evaluated according to the field measurement results for the wind-induced response and was found to be satisfactory for human comfort.

• KIEAE Journal
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• v.7 no.4
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• pp.147-152
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• 2007

Numerous non-destructive tests(NDT) to assess the safety of real structures have been developed. System identification(SI) techniques using dynamic responses and behaviors of structural systems become an outstanding issue of researchers. However the conventional SI techniques are identified to be non-practical to the complex and tall buildings, due to limitation of the availability of an accurate data that is magnitude or location of external loads. In most SI approaches, the information on input loading and output responses must be known. In many cases, measuring the input information may take most of the resources, and it is very difficult to accurately measure the input information during actual vibrations of practical importance, e.g., earthquakes, winds, micro seismic tremors, and mechanical vibration. However, the desirability and application potential of SI to real structures could be highly improved if an algorithm is available that can estimate structural parameters based on the response data alone without the input information. Thus a technique to estimate structural properties of building without input measurement data and using limited response is essential in structural health monitoring. In this study, shaking table tests on three-story plane frame steel structures were performed. Out-put only model analysis on the measured data was performed, and the dynamic properties were inverse analyzed using least square method in time domain. In results damage detection was performed in each member level, which was performed at story level in conventional SI techniques of frequency domain.

• Wind and Structures
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• v.31 no.2
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• pp.103-142
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• 2020

One of the next frontiers in structural wind engineering is the design of tall buildings using performance-based approaches. Currently, tall buildings are being designed using provisions in the building codes and standards to meet an acceptable level of public safety and serviceability. However, recent studies in wind and earthquake engineering have highlighted the conceptual and practical limitations of the code-oriented design methods. Performance-based wind design (PBWD) is the logical extension of the current wind design approaches to overcome these limitations. Towards the development of PBWD, in this paper, we systematically review the advances made in this field, highlight the research gaps, and provide a basis for future research. Initially, the anatomy of the Wind Loading Chain is presented, in which emphasis was given to the early works of Alan G. Davenport. Next, the current state of practice to design tall buildings for wind load is presented, and its limitations are highlighted. Following this, we critically review the state of development of PBWD. Our review on PBWD covers the existing design frameworks and studies conducted on the nonlinear response of structures under wind loads. Thereafter, to provide a basis for future research, the nonlinear response of simple yielding systems under long-duration turbulent wind loads is studied in two phases. The first phase investigates the issue of damage accumulation in conventional structural systems characterized by elastic-plastic, bilinear, pinching, degrading, and deteriorating hysteretic models. The second phase introduces methods to develop new performance objectives for PBWD based on joint peak and residual deformation demands. In this context, the utility of multi-variate demand modeling using copulas and kernel density estimation techniques is presented. This paper also presents joined fragility curves based on the results of incremental dynamic analysis. Subsequently, the efficiency of tuned mass dampers and self-centering systems in controlling the accumulation of damage in wind-excited structural systems are investigated. The role and the need for explicit modeling of uncertainties in PBWD are also discussed with a case study example. Lastly, two unified PBWD frameworks are proposed by adapting and revisiting the Wind Loading Chain. This paper concludes with a summary and a proposal for future research.

• International Journal of High-Rise Buildings
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• v.9 no.2
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• pp.175-185
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• 2020

Currently, few studies have been conducted to comprehend the seismic reliability of post-tensioned (PT) CLT shear wall structures, due to the complexity of this kind of structural system as well as due to lack of a reliable structural model. In this paper, a set of 4-, 8-, 12-, and 16-storey benchmark PT CLT shear wall structures (PT-CLTstrs) were designed using the direct displacement-based design method, and their calibrated structural models were developed. The seismic reliability of each PT-CLTstr was assessed based on the fragility analysis and based on the response surface method (RSM), respectively. The fragility-based reliability index and the RSM-based reliability index were then compared, for each PT-CLTstr and for each seismic hazard level. Results show that the RSM-based reliabilities are slightly less than the fragility-based reliabilities. Overall, both the RSM and the fragility-based reliability method can be used as efficient approaches for assessing the seismic reliabilities of the PT-CLTstrs. For these studied mid- and high-rise benchmark PT-CLTstrs, following their fragility-based reliabilities, the 8-storey PT-CLTstr is subjected to the least seismic vulnerability; while, following their RSM-based reliabilities, the 4-storey PT-CLTstr is subjected to the least seismic vulnerability