Full Paper Proc. of Int. Conf. on Advances in Civil Engineering 2012
Behaviour of R.C.C. Tall Buildings Having Different Shapes Subjected to Wind Load Prof. Sarita Singla1, Taranjeet Kaur2, Megha Kalra3 and Sanket Sharma4 1
PEC University of Technology/Civil Engineering Department, Chandigarh, India Email:ssaritasingla@yahoo.com 2 Baddi University/Civil Engineering Department, Baddi(HP), India Email: taran_madaan@yahoo.co.in 3 PEC University of Technology/Civil Engineering Department, Chandigarh, India Email: Duskmk@gmail.com 4 PEC University of Technology/Civil Engineering Department, Chandigarh, India Email: sanket414@gmail.com Abstract—Buildings are defined as structures utilized by the people as shelter for living, working or storage. As now a days there is shortage of land for building, the vertical construction is given due importance. A designer is interested in storey wise horizontal forces for analysis and design of structural frames. Hence, emphasis is given to compute the storey wise lateral forces due to wind on building. In the present study, a 35 storeyed building of different shapes- Square, Hexagonal and Octagonal, having equal plan area and equal stiffness of the columns has been analysed. Based upon the study, it is concluded that shape of the structure plays an important role in resisting wind loads. Octagonal shaped building performed the best followed by hexagonal shaped and square shaped building. Index Terms—wind load, tall building, gust factor, square, hexagonal, octagonal
I. INTRODUCTION Tall buildings are critically affected by wind loads. Wind exerts forces and moments on the structure and its cladding and also it distributes the air in and around the building mainly termed as wind pressure. Sometimes because of unpredictable nature of wind it takes so devastating form that it can upset the internal ventilation system when it passes into the building. For these reasons the study of air flow is becoming integral with the planning of a building and its environment. Tall buildings are flexible and are susceptible to vibrate at high wind speeds in all the three directions (x, y, and z) and even the building codes do not incorporate the expected maximum wind speed for the life of the building and does not consider the high local suctions which cause the first damage. Due to all these facts the wind load estimation for tall buildings are very much important.
features. The average wind speed over a time period of the order of ten minutes or more tends to increase with height, while the gustiness tends to decrease with height. (Fig. 1)
Fig. 1. Generation of eddies
B. Effects of wind load A mean wind force acts on a building. This mean wind force is derived from the mean wind speed and the fluctuating wind force produced by the fluctuating flow field. The effect of the fluctuating wind force on the building or part thereof depends not only on the characteristics of the fluctuating wind force but also on the size and vibration characteristics of the building or part thereof. Therefore, in order to estimate the design wind load, it is necessary to evaluate the characteristics of fluctuating wind forces and the dynamic characteristics of the building. The factors generally considered in determining the fluctuating wind force are: 1) Wind turbulence (temporal and spatial fluctuation of wind 2) Vortex generation in wake of building 3) Interaction between building vibration and surrounding air flow For most buildings, the effect of fluctuating wind force generated by wind turbulence is predominant. In this case, horizontal wind load on structural frames in the along-wind direction is important. However, for relatively flexible buildings with a large aspect ratio, horizontal wind loads on structural frames in the across-wind and torsional directions should not be ignored.
A. Importance of Wind Loads on the Tall Buildings Wind is a phenomenon of great complexity because of many flow situations arising from the interaction of wind with structures. Wind is composed of multitude of eddies of varying sizes and rotational characteristics carried along in a general stream of air moving relative to the earth’s surface. C. Hourly Mean Wind Speed (VZ) These eddies give wind its gusty or turbulent character. The The basic wind speed (Vz) for any site shall be obtained gustiness of strong winds in the lower levels of the from Fig 1(IS: 875(Part 3)-1987) and shall be modified to include atmosphere largely arises from interaction with surface 156 © 2012 ACEE DOI: 02.AETACE.2012.3.17