WIND EFFECTS OF TALL BUILDING HAVING DIFFERENT CORNER CONFIGURATION USING CFD

Abstract

Population is increasing at an exponential rate and availability of the land in the regular shape is limited. Hence structural designer needs the developed the irregular plan shape tall buildings also because of the huge population, now a days structural designers are shifting to develop the tall buildings. Tall building which are coming up all around the world is serving the purpose of residential and commercial. Tall building is best suitable for residential, institutional, industrial and assembly purposes. These buildings are constructed in regular and irregular shape this is mainly due to the constraint in the availability of regular shape land. Because of irregular land the building at present time is constructed in irregular cross-sectional shape, tall building need investigation of wind effects on such irregular shape buildings. Available information regarding wind pressure coefficients on different type of building is not updated in the codal provision and international standards are silent about the various type of irregular cross-sectional shape. As the height increase the wind load increases and wind load becomes the governing criteria for the design of tall buildings hence the investigation of wind effects is necessary for such tall buildings.

As the flow pattern around the tall building is generally varies as per the plan cross sectional shape and thus creating the change in pressure distribution. Also, a quantum of change in the wind angle changes the distribution of pressure on a high-rise building. Investigation of wind effects is required for high rise buildings, as shape changes and since there is very few numbers of studies are available for equal area building having the regular and irregular shape. Wind tunnel tests and computational fluid dynamic (CFD) are the only possible solution as on today to evaluate the wind loads on a high-rise building. Aim of the present study is to investigate the wind effects on tall building models with varying cross-sectional shape in CFD simulation to measure wind generated effects. In the present study, high-rise buildings with eight types of building models are considered and the available information about corner modification of equal dimensions is very limited. In this entire study the comparison of equal area building having “rectangular” and “Y” shape is performed and the modification of same corners such as corner cut, chamfer and fillet of equal dimensions is applied in plan cross sectional shape. Wind effect are investigated using ANSYS CFX, 2020 and results are presented in various forms like pressure is represented in the form of contours while the pressure distribution along the v

peripheral distance of building and pressure on the vertical center line of each face is represented using graphs. Many more results are depicted in various graphical forms and critical values are tabulated.

In this numerical study, the models of high-rise buildings with different corner configuration are made at a scale of 1:200. These models are numerically investigated for wind effects in the domain having the dimension as, from top of the building model to top of the domain is at 5H, while both sides are kept at 5H, inlet is placed at 5H from the building model and the outlet is provided as 15H, where H is the height of the building model. The numerical simulation is done using k-ε turbulence model. The pressure data is exported by ANSYS CFX post processing, the data of pressure is exported by the creating the set of lines which act as pressure tapping and are configured with the experimental procedure adopted in the wind tunnel testing. The models are investigated in a numerical simulation having a total length of domain as 20 H such domain dimensions are kept so that the wind flow recirculation can be prevented. The prototype buildings are considered to be situated in a sub urban terrain with well scattered objects having height between 1.5 m to 10 m, defined as Terrain Category 2 in IS: 875 (Part-3) 2015. Turbulence is defined as medium turbulence and wind speed is modelled according to power law which is applied at the inlet of the domain.

Wind pressure distribution on the surface of all eight model is measured using ANSYS CFX post processing for varying wind incidence angle starting from 00 to 1800 at an interval of 150. The various corner configuration such as corner cut, chamfer and fillet are having the same dimensions in both (regular and irregular buildings) type of high-rise building model. Wind pressure on each surface is represented in the form of contours with label so that the designer can use such pressure contours while designing the corresponding type of building.

Values of mean wind pressure coefficients (Cp) are evaluated from the measured values of wind pressures at each surface of the tall building. Results of the study are presented in the form of contours and cross-sectional variation of Cp for each building model. The results are also presented in the graphical form for peripheral distribution of pressure around the model at top one third which is at 500 mm height from the base of the model and second is presented at mid height of the model which is at 375 mm from the base of the model while the pressure along the peripheral distance at bottom one third which is at 250 mm from the vi

ground is presented. The result of pressure along the vertical center lines at each face is also presented in the graphical form while the result of wind force and moment coefficient is presented for eight building models for varying wind incidence angle starting from 00 to 1800 at the interval of 150.

The results presented in the present study can be used in future for the revision of codal recommendations about wind loads on high- rise buildings with different corner configuration. These can also be used by the architects and structural designers while designing such building of equal cross-sectional area.