Comprehensive Study Of Wind Effects On L- And T-Shaped Low-Rise Buildings With Hip Roofs

Low-rise buildings constructed for industrial and residential purposes form the majority of structures around the world.Regarding the wind effects on low buildings,extensive research has been carried out,in which most of the theoretical study and design practice were focused on rectangular low buildings with gable roofs.In recent years,the requirements of structural shapes and functions are improved continually.Consequently,the L-and T-shaped low-rise buildings with hip roofs are widely built.However,the related wind effect study of such buildings is limited.Moreover,no clear design provisions of wind loads are available in the current international and Chinese wind load codes for the building configurations.These limitations seriously threaten their wind-resisting security.Therefore,this thesis comprehensively examines the wind effects on L-and T-shaped low-rise buildings with hip roofs based on wind tunnel tests and computational simulations.Four main innovations are presented as follows.1.Based on the wind tunnel test technique,the wind pressure data on components and cladding of rectangular,L-and T-shaped gable-and hip-roofed low building with different length-to-width ratios are measured.The impacts of roof shapes,building plans,length-to-width ratios and wind directions on the mean,peak and most critical roof and wall pressure distributions are particularly investigated.Results show that the wind-resisting aerodynamic characteristics of the rectangular hip roofs are better than those with gable roofs,since the local most critical wind pressure magnitudes on hip roofs are smaller than those on the gable roof by more than 30%;However,for the L-and T-shaped buildings with hip roofs,the peak roof wind pressure around building re-entrant corners is nearly 75%larger than that on rectangular hip roofs.Moreover,unsymmetrical wind pressure distributions are found for the L-and T-shaped buildings;Considering the local pressure distribution features of extremely large magnitudes and asymmetry,refined zones are proposed for the L-and T-shaped hip roofs.In each zone,the area-averaged pressure variations as a function of tributary areas are presented,which provides a scientific basis for the international and Chinese code revisions about wind loads on components and cladding of the L-and T-shaped hip roofs.2.To explain the particular wind load distribution characteristics of L-and T-shaped hip-roofed buildings in terms of wind flow features,the numerical simulation of wind flow patterns and velocity distributions around representative building models under typical wind direction cases with different roof shapes and building plans are performed by using the three-dimensional steady RANS method.Moreover,the sensitivity analysis of computational domain sizes,grid numbers and turbulence models is carried out,which can be used as the basis of modeling for such building configurations and corresponding parameter setups.It is seen that the wind separation magnitudes and velocity gradients around the windward edges of the rectangular hip roof are considerably reduced,compared with those of the gable roof.This is mainly due to the sloped hip-end surfaces.Accordingly,the resulting wind pressure on hip roofs are decreased related to that on the gable roof;Regarding the non-rectangular hip-roofed cases,particular and strong vortex appears around the building re-entrant corners,which may directly lead to the local increased and unsymmetrical wind pressure distributions around these regions of the hip-roofed buildings with non-rectangular building plans.3.In terms of the distinctive wind pressure distributions and structural arrangements of the L-and T-shaped low buildings with hip roofs,refined three-dimensional finite element models are created,which relatively reasonably consider wind load sharing paths and structural spatial effects.The peak wind-induced force and moment distributions varying with wind directions and most critical wind responses along main frames of L-and T-shaped low buildings with hip roofs are obtained.The common effects of the roof shapes,building plans,horizontal aspect ratios,boundary conditions and stiffness ratios of columns and rafters on the wind-induced structural loads are studied.Results indicate that compared with the gable-roofed case,the shear force and bending moment coefficients for hip-roofed buildings decrease significantly;Whereas,the most critical structural loads around frame knees near the re-entrant corners of L-and T-shaped buildings show almost 25%increase related to the rectangular hip-roofed cases;Moreover,the peak wind structural loads on end and intermediate frames of hip-roofed buildings are intensified by 20%,with the constraint release of boundary conditions and the increase of column sizes.4.To examine the applicability of the current wind load codes and standards for the L-and T-shaped low buildings with hip roofs,the peak wind pressures on building surfaces and structural wind forces on critical locations of main frames are compared with those determined by the Chinese and American wind load provisions.Results reveal that the current Chinese wind load criterions of components,cladding and main frames are mainly concentrated on the rectangular low buildings.The peak wind pressure coefficients on components and cladding are small.Moreover,for the main frames,only the mean wind response is considered,but it may neglect the quasi-static background components of wind responses.All these reasons may cause serious underestimations of the wind effects on the L-and T-shaped low buildings with hip roofs;Considering the American wind load standard,approximate 20%-40%underestimation occurs for the negative pressure on edge zones of walls and positive pressure on both wall zones.However,the design wind pressure on roof components and cladding is generally conservative.For the shear forces and bending moments of main frames,an approximate 30%underestimation in average appears comparing those determined according to the ASCE-specified values and experimental data.