Quantitative investigation on collapse margin of steel high-rise buildings subjected to extremely severe earthquakes

Reponses of structures subjected to severe earthquakes sometimes significantly surpass what was considered in the design.It is important to investigate the failure mechanism and collapse margin of structures beyond design,especially for high-rise buildings.In this study,steel high-rise buildings using either square concrete-filled-tube（CFT） columns or steel tube columns are designed.A detailed three-dimensional（3 D） structural model is developed to analyze the seismic behavior of a steel high-rise towards a complete collapse.The effectiveness is verified by both component tests and a full-scale shaking table test.The collapse margin,which is defined as the ratio of PGA between the collapse level to the design major earthquake level（Level 2）,is quantified by a series of numerical simulations using incremental dynamic analyses（IDA）.The baseline building using CFT columns collapsed with a weak first story mechanism and presented a collapse margin ranging from 10 to 20.The significant variation in the collapse margin was caused by the different characteristics of the input ground motions.The building using equivalent steel columns collapsed earlier due to the significant shortening of the locally buckled columns,exhibiting only 57% of the collapse margin of the baseline building.The influence of reducing the height of the first story was quite significant.The shortened first story not only enlarged the collapse margin by 20%,but also changed the collapse mode.

Dynamic response characteristics of super high-rise buildings subjected to long-period ground motions

Spectrum characteristics of different types of seismic waves and dynamic response characteristics of super high-rise building structures under long-period ground motions were comparatively analyzed. First, the ground response wave (named LS-R wave) of a soft soil site with deep deposit, taking long-period bedrock seismic record as input, was calculated by wave propagation method. After that, a TOMAKOMAI station long-period seismic record from the Tokachi-Oki earthquake and conventional El-Centro wave were also chosen. Spectrum characteristics of these waves were analyzed and compared. Then, a series of shaking table tests were performed on a 1:50 scale super high-rise structural model under these seismic waves. Furthermore, numerical simulation of the prototype structure under these excitations was conducted, and structure damages under different intensive ground motions were discussed. The results show that: 1) Spectrum characteristics of ground response wave are significantly influenced by soft soil site with deep deposit, and the predominant period has an increasing trend. 2) The maximum acceleration amplification factor of the structure under the TOM wave is two times that under the El-Centro wave; while the maximum displacement response of the structure under the TOM wave is 4.4 times that under the El-Centro wave. Long-period ground motions show greater influences on displacement responses than acceleration responses for super high-rise building structures. 3) Most inelastic damage occurs at the upper 1/3 part of the super high-rise building when subjected to long-period ground motions.

Effects of high modes on the wind-induced response of super high-rise buildings

For super high-rise buildings, the vibration period of the basic mode is several seconds, and it is very close to the period of the fluctuating wind. The damping of super high-rise buildings is low, so super high-rise buildings are very sensitive to fluctuating wind. The wind load is one of the key loads in the design of super high-rise buildings. It is known that only the basic mode is needed in the wind-response analysis of tall buildings. However, for super high-rise buildings, especially for the acceleration response, because of the frequency amplification of the high modes, the high modes and the mode coupling may need to be considered. Three typical super high-rise projects with the SMPSS in wind tunnel tests and the random vibration theory method were used to analyze the effect of high modes on the wind-induced response. The conclusions can be drawn as follows. First, for the displacement response, the basic mode is dominant, and the high modes can be neglected. Second, for the acceleration response, the high modes and the mode coupling should be considered. Lastly, the strain energy of modes can only give the vibration energy distribution of the high-rise building, and it cannot describe the local wind-induced vibration of high-rise buildings, especially for the top acceleration response.

A review on research of fire dynamics in high-rise buildings

Since serious fire occurred frequently in recent years, fire safety of high-rise building has attracted extensive attention. A National Basic Research Program （973 program） of China has been set up by Ministry of Science and Technology （MOST） of China in 2012 to meet the research requirements of fire safety in high-rise buildings. This paper reviews the current state of art of research on fire dynamics of high-rise buildings, including the up-to-date progress of this project. The following three subjects on fire dynamics of high-rise buildings are addressed in this review： the ejected flame and fire plume behavior over facade out of the compartment window, the flame spread behavior over facade thermal insulation materiMs, and the buoyancy-driven smoke transportation characteristics along long vertical channels in high-rise buildings. Prospective future works are discussed and summarized.

Numerical Simulation of Wind Field Characteristics around Two Adjacent High-Rise Buildings

This paper based on Reynolds-averaged Navier-Stokes equations standard ?model [1];the surface pressure on the wind field around two adjacent high-rise buildings was numerically simulated with software Fluent. The results show that with the influence of adjacent high-rise building, numerical simulation is a good way to study the wind field around high-rise building and the distribution of wind pressure on building’ surface. The pressures on the windward surface are positive with the maximum at 2/3 H height and have lower values on the top and bottom. The pressures on the leeward surface and two sides were negative. Due to the serious flow separation at the corner of building’s windward, the wind field has a high turbulent kinetic energy.

Field measurements for calibration of simplified models of the stiffening effect of infill masonry walls in high-rise RC framed and shear-wall buildings

As a type of nonstructural component, infill walls play a significant role in the seismic behavior of high-rise buildings. However, the stiffness of the infill wall is generally either ignored or considered by simplified empirical criteria that lead to a period shortening. The difference can be greatly decreased by using a structural identification methodology. In this study, an ambient vibration test was performed on four on-site reinforced concrete high-rise buildings, and the design results were compared with the PKPM models using corresponding finite element(FE) models. A diagonal strut model was used to simulate the behavior of the infill wall, and the identified modal parameters measured from the on-site test were employed to calibrate the parameters of the diagonal strut in the FE models. The SAP2000 models with calibrated elastic modulus were used to evaluate the seismic response in the elastic state. Based on the load-displacement relationship of the infill wall, nonlinear dynamic analysis models were built in PERFORM-3 D and calibrated using the measured modal periods. The analysis results revealed that the structural performance under small/large earthquake records were both strengthened by infill walls, and the contribution of infill walls should be considered for better accuracy in the design process.

Development of the Separate Air-Supply Type of Pressurization Smoke Control System for the Stairwells of High-Rise Buildings in Korea

The pressurization smoke control system has been commonly used as a smoke control system at the emergency stairs of high-rise buildings. However, a higher possibility of overpressure between the lobby and the accommodation or pressure drop in the lobby could lead to failure in achievement of the purpose of pressurization system, particularly when supplying the leakage and supplementary air flow through one air-supply path at a time. To improve this particular issue, the devise configurations, as well as the different ways to supply the leakage and supplementary air flow through the different flow passages have been proposed. The performance of the trial product was evaluated on the test bed, ultimately providing a safe evacuation environment if high-rise buildings fired.

Method for Evaluating the Influence of Obstruction of Sea Breeze by Clusters of High-Rise Buildings on the Urban Heat Island Effect

This study aims to propose a method for quantitatively evaluating the influence which the obstruction of sea breezes by clusters of high-rise buildings has on the urban heat island effect using a weather simulation model and Geographic Information Systems (GIS). Specifically, a method of evaluating the influence of the obstruction of sea breeze by high-rise buildings on the urban heat island effect was proposed. In the method, two scenarios that imagine urban forms which differ with regard to whether or not they contain high-rise buildings are created and weather simulation is conducted, and the results of the simulations are comparatively analyzed focusing on temperature and wind speed. Evaluation was conducted in two stages, and Shiodome of Minato City in the Tokyo Metropolis was selected as the region for evaluation. In two stages of evaluation, a rise in temperature of approximately 0.3 K and a reduction in wind speed of approximately 1 m/s were observed in a region approximately five to ten kilometers square downwind of high-rise buildings in the period 6 PM to 9 PM, and a higher temperature caused by the obstruction of sea breeze by high-rise buildings was identified. The fact that such a higher temperature was confirmed in the time period from 6 PM onwards, in which the temperature decreases, reveals that obstruction of sea breeze by high-rise buildings dulls the decrease in temperature which occurs from evening onwards, and influences nighttime urban heat island formation.

Survey-Based Analysis of Water Consumption Law in High-Rise Public Buildings and Water-Saving Performance of Pressure-Reducing Measures

Facing the contradiction of water scarcity and water wastage in most cities of China, this study aims at probing into the factors influencing water-use efficiency and assessing water-saving potential by adopting pressure control measures based on field survey conducted in 23 high-rise buildings in Suqian, China and laboratory tests. Results showed that per capita water consumption (PCWC) exceeding water consumption norms is common in these buildings. The hourly water consumption variation law is quite different among different types of buildings. These differences should be considered in designing building water supply systems to lower water and energy consumption. On the basis of correlation analysis, the order of factors influencing the PCWC follows average tap water pressure, percapita building area, and building age, suggesting pressure management in high-rise buildings is a key water-saving measure. Field tests of outflow characteristics under different water pressures indicated that over-pressure outflow (OPO) is a common cause of water wastage in buildings, however, no branch pipe pressure control measures were found in all the surveyed buildings. Laboratory tests showed that branch pipe pressure-reducing measures can lower water consumption and improve the comfortability of use as well. Therefore, in addition to applying high efficiency water-saving devices, we strongly recommend that branch pipe pressure-reducing measures should be strictly implemented in designing new building water supply systems and reconstruction of existing old building water supply systems, thereby, promoting water, energy saving and development of green building.

Model Reduction Methods for High-Rise Buildings with Active Mass Damper Control Systems

To improve the performance of an active mass damper control system,the controller should be designed based on a reduced-order model. An improved method based on balanced truncation method was proposed to reduce the dimension of high-rise buildings,and was compared with other widely used reduction methods by using a framework with ten floors. This optimized method has improvement of reduction process and choice of the order. Based on the reduced-order model obtained by the improved method and pole-assignment algorithm,a controller was designed. Finally,a comparative analysis of structural responses,transfer functions,and poles was conducted on an actual high-rise building. The results show the effectiveness of the improved method.

Investigation on Fire Protection System of Highrise Buildings in the Context of Bir Uttam Aminul Haque Avenue in Dhaka, Bangladesh

Rapid high-rise building construction of different occupancies is becoming popular in Dhaka due to its economic gain and functional flexibility. Fire prevention poses a significant difficulty to this type of construction due to its complexity and economic worth as well. Therefore, construction of high-rise building without following the proper fire safety measures, is a common practice at present in the city and it poses a greater threat to urban life considering its associated loss. Even though, most of the owners or authorities do not respect the construction code and the majority of them lack sufficient awareness and basic fire control knowledge and practice. More often, they are unable to comprehend the magnitude and severity of severe fire hazards, and recognize the causes and implementing effective mitigation measures are rare. As a result, the number of fire hazard in high-rise construction is increasing day by day. Hence, investigating the present condition of high-rise buildings (already built) in terms of Fire Protection System is imperative to prevent the upcoming fire hazard. An urban chunk of 33 plots along with Bir Uttam Aminul Haque Avenue, located in Banani, has been chosen for the study area considering its vulnerability to fire hazard. Among these buildings, STAR Tower and HBR Tower, these two high-rise buildings are assessed thoroughly using FRI (Fire Risk Index) Method. The method is semi-quantitative in nature with seventeen parameters associated with fire protection. This assessment represents a scenario in what extent fire codes are being followed in the selected area. It concludes that most of the buildings lack in providing protection against fire hazards for not following the code strictly. This research provides some recommendations which can be followed to improve the fire safety measures in this existing context. It is expected that this research could be a unique addition to firefighting knowledge by contributing to mitigating the consequences of fire related hazards in any densely populated city like Dhaka.

Optimization of Grouping Evacuation Strategy in High-rise Building Fires Based on Graph Theory and Computational Experiments

It is difficult to rescue people from outside, and emergency evacuation is still a main measure to decrease casualties in high-rise building fires. To improve evacuation efficiency, a valid and easily manipulated grouping evacuation strategy is proposed. Occupants escape in groups according to the shortest evacuation route is determined by graph theory. In order to evaluate and find the optimal grouping, computational experiments are performed to design and simulate the evacuation processes. A case study shown the application in detail and quantitative research conclusions is obtained. The thoughts and approaches of this study can be used to guide actual high-rise building evacuation processes in future.

Safety analysis of optimal outriggers location in high-rise building structures

This paper presents the restraining moments of outriggers acting on the core wall and the equation of the horizontal top deflection based on a simplified outrigger model. The deformation compatibility conditions between outriggers and core wall as well as the finite rigidities of outriggers are also considered. One case study was carried out to analyze the horizontal top deflection and the mutation of the restraining moments caused by the variation of outrigger location. The results showed that the method adopted in the paper is simple and reasonable. Some conclusions are valuable to the safety design of high-rise building structures.

Wind tunnel test and numerical simulation of wind pressure on a high-rise building

We carried out a wind tunnel test to measure cladding loads for a high-rise building of 295 m in height,which would be located in the business center of Chongqing Municipality,P.R.China.The rigid model was used to determine fluctuating local pressures on the exterior surfaces of the building.The wind tunnel test results show the critical zone of wind pressures on building surfaces in both standalone and interference conditions.The computational fluid dynamics(CFD)was conducted by using the FLUENT Code to compare with the wind tunnel test results,and the steady three-dimensional turbulent flow with Realizable k-ε as a turbulence model was used.The CFD results are agree with the wind tunnel test results in regards to distributions of wind pressures over a high-rise building's surfaces.

Multi-hazard performance assessment of a transfer-plate high-rise building

Many urban areas are located in regions of moderate seismicity and are subjected to strong wind. Buildings in these regions are often designed without seismic provisions. As a result, in the event of an earthquake, the potential for damage and loss of lives may not be known. In this paper, the performance of a typical high-rise building with a thick transfer plate （TP）, which is one type of building structure commonly found in Hong Kong, is assessed against both earthquake and wind hazards. Seismic- and wind-resistant performance objectives are first reviewed based on relevant codes and design guidelines for high-rise buildings. After a brief introduction of wind-resistant design of the building, various methodologies, including equivalent static load analysis （ESLA）, response spectrum analysis （RSA）, pushover analysis （POA）, linear and nonlinear time-history analysis （LTHA and NTHA）, are employed to assess the seismic performance of the building when subjected to frequent earthquakes, design based earthquakes and maximum credible earthquakes. The effects of design wind and seismic action with a common 50-year return period are also compared. The results indicate that most performance objectives can be satisfied by the building, but there are some objectives, such as inter-story drift ratio, that cannot be achieved when subjected to the frequent earthquakes. It is concluded that in addition to wind, seismic action may need to be explicitly considered in the design of buildings in regions of moderate seismicity.

High-rise building fire pre-warning model based on the support vector regression

Aiming at reducing the deficiency of the traditional fire pre-warning algorithms and the intelligent fire pre-warning algorithms such as artificial neural network,and then to improve the accuracy of fire prewarning for high-rise buildings,a composite fire pre-warning controller is designed according to the characteristic（ nonlinear,less historical data,many influence factors）,also a high-rise building fire pre-warning model is set up based on the support vector regression（ SV R）. Then the wood fire standard history data is applied to make empirical analysis. The research results can provide a reliable decision support framework for high-rise building fire pre-warning.

Influence of Horizontal Flow on Atrium in High-Rise Residential Building

In this study a 10-storied residential building model was employed to clarify the ventilation characteristics of the atrium and the rooms,which were effected by the different forms of lateral openings.The experiment was conducted under the combined effect of wind force and thermal buoyancy,and the similarity requirements were satisfied.The results have shown that the different forms of lateral openings cause the different ventilation effect of the building,and also have some certain regularity.The conclusions provide a theoretical foundation for how to use the ventilation of atrium better in high-rise residential building.

Simulation on spread of fire smoke in the elevator shaft for a high-rise building

Spread of fire smoke in the elevator shaft of a high-rise building is influ- enced by many driving facts. We simulate smoke spreading in the elevator shaft, stair room, and pre-chamber with and without different supplied pressurized air. The simulation shows that smoke moves very fast in the elevator shaft. When a 12 floor high-rise building is in fire, smoke can fill up the elevator shaft in less than 1.5 min after a fire started, temperature in the elevator shaft can be higher than 187℃ in 5 rain, and the concentration of CO can also reach a high level. The elevator shaft has a very low visibility in less than about 100 s.