Wind Loads On Slab-type High-rise Buildings

With the acceleration of urbanization and the scarcity of land resources,high-rise buildings have witnessed rapid development over the past several decades.For better natural ventilation and lighting effects,high-rise buildings are often designed with slab-type shapes,i.e.,with narrow-shaped rectangular sections.This kind of buildings often have a large range of plan aspect ratios,varying from 2 up to 8 or 9.Although slab-type high-rise buildings are fairly common today,there are limited studies on wind loads for high-rise buildings with large plan aspect ratios,neither are there clear stipulations on wind load design for such kind of buildings in current load codes or standards.In light of this,the main objective of this research is to explore the wind load distributions and patterns for slab-type high-rise buildings and develop a better understanding of the interior mechanisms inducing the aerodynamic forces,in order to provide more comprehensive theoretical and experimental proofs for wind load analyses,related code revisions and engineering applications of buildings with the similar geometry.To achieve this objective,scale-model wind tunnel pressure tests were carried out for rectangular high-rise buildings with plan aspect ratios ranging from 1 to 9,and the following issues regarding on wind loads on slab-type high-rise buildings with a large range of plan ratios have been systematically investigated:(1)Effects of plan dimensions on wind loads for Main Wind Force-Resisting System(MWFRS)of rigid rectangular high-rise buildings.Mean,fluctuating,and peak wall pressure coefficient distributions and area-averages were investigated,together with comparisons with GB 50009-2012 and ASCE 7-16 provisions for the MWFRS.The results show that the plan ratio has significant effects on pressure coefficients on the leeward and side walls for plan ratios less than about 4;the largest mean base shear coefficient occurs for plan ratio of about 0.67,with large values in the range of 0.5 to 1,but decreasing for larger or smaller plan ratios;for plan ratios below 0.67,generally the MWFRS load coefficients decrease as the plan ratio decreases;while for plan ratios above 4,the effects of plan ratios on the MWFRS load coefficients are limited.GB 50009 and ASCE 7 tend to underestimate the mean load coefficients on the leeward wall and on the side wall for plan ratio between 0.33 and 1.5.ASCE 7 also underestimates the peak load coefficients up to 40%due to both underestimations of the mean pressure coefficients and the gust effect factor.(2)Effects of plan dimensions on wind pressures for Components and Claddings(C&C)of rectangular high-rise buildings.Based on the pressure measurements,subsequent extreme value analyses for wind tunnel fluctuating pressure time series were conducted.Peak pressure coefficient distributions for buildings with different plan ratios under the orthogonal wind direction were investigated,comparisons with GB 50009-2012 were made,and distributions of peak pressure coefficient envelopes under all wind directions and the patterns varying with plan dimensions were also discussed.Results show that the plan ratio has significant effects on peak pressure coefficients on the leeward and side walls.In general,negative peak pressures are worse for buildings with plan ratios between 0.5 and 1.5.The GB 50009 pressure coefficients for C&C on the leeward and side walls tend to be unsafe under many circumstances.Furthermore,peak pressure coefficient envelopes under all wind directions tend to show simpler distribution patterns on the walls and simpler variation patterns with plan dimensions.A new method for determination of wind pressures on C&C of rectangular buildings is proposed based on distributions of peak pressure coefficient envelopes,which is more convenient and can better reflect actual pressure distribution conditions.(3)Aerodynamic admittance functions(AAF)of wind loads on rectangular high-rise buildings.Based on the wind tunnel pressure tests,patterns of the AAFs for area-averaged fluctuating wind pressures on each wall and for base drag under the orthogonal wind direction were investigated,together with comparisons with Vickery's model and Solari's model,which are based on the quasi-steady assumption.Closed-form expression for the AAF for base drag of buildings with different plan ratios was obtained through fitting analysis.Results show that when the plan ratio is higher than 0.5,the decay rate of the AAF for windward fluctuating pressures and for base drag becomes slower,and Vickery's model and Solari's model are significantly lower than the measured values;on the leeward and side walls,due to the effects of body-generated turbulence such as flow separation,reattachment and vortex shedding,peaks of different sizes appear at the high frequencies of the AAFs for fluctuating pressures,and the varying pattern and magnitudes of Vickery's model will no longer match.The fitted formula in power function form that proposed in this paper can well predict the AAF for base drag of rectangular buildings with different plan ratios.(4)Value estimation model for gust effect factor of rigid buildings based on the experimental approach.The derivation of the gust effect factor in ASCE 7-16 was carefully reviewed,and the qualitative and qualitative relations between the gust effect factor and the aerodynamic admittance function(AAF)were examined.A new model for gust effect factor value estimation based on the experimental approach was proposed,together with detailed comparisons with the ASCE 7 model.The results show that the AAF has direct influence on the value of the gust effect factor,the shape of the AAF and the value of the gust factor around unity depend on whether the non-contemporaneous gust actions effects or the body-generated turbulence effects are playing a leading role.The ASCE 7-16 gust effect factor for rigid buildings usually shows underestimations mainly due to the underestimation of the theoretical AAF,the underestimation of the Gaussian peak factor and the use of the 3-sec moving average filter in the calculations.The gust effect factor can be more rationally predicted using the value estimation model proposed in this paper.(5)Effects of turbulence characteristics on wind loads on rectangular high-rise buildings.Based on the wind tunnel pressure tests under 4 different terrains,effects of turbulence intensity and integral length scale on mean,fluctuating and peak pressures,together with cross-wind aerodynamic force spectra and separated and reattaching flow characteristics for rectangular buildings with different plan ratios were examined.Results show that as turbulence intensity increases,earlier reattachment occurs,with the reattachment point under suburban terrain appearing about 30%earlier than open terrain case.Under the separated flow,magnitudes of mean and peak wind pressures decrease,and the most unfavorable fluctuating and peak pressures occur closer to the leading edge.As integral length scale decreases,mean and peak pressures on the windward,leeward and side wall decrease,but the scale has limited effects on flow patterns and pressure distributions under the separated and reattaching flow.Comparing to larger plan ratios,turbulence characteristics show more significant effects for buildings with plan ratios between 1 and 2.