19-07-2014, 10:19 AM
Behaviour of Multistoried Building Frames under the effect of Wind Load
Multistoried Building Frames.doc (Size: 688.5 KB / Downloads: 39)
Abstract
Now a day’s many tall structures and high rise towers are being built all around the world .Wind plays an important role in design of tall structures because of its dynamic nature. Effect of wind is predominant on tall structures depending on location of the structure, height of the structure. In this paper gust effectiveness factor method is used for analysis of wind load on buildings for different terrain conditions. The analysis is carried out using STAAD PRO
INTRODUCTION
A great number of structures that are being constructed at present are wind sensitive because of their shape, sizes, flexibility, lightness & slenderness. The emergence of modern materials and construction techniques resulted in structures that are often, to a degree unknown in the past, remarkably low in damping, and light in weight. Generally such structures are more affected by the action of wind. The structural engineer should ensure that the structure should be safe and serviceable during its anticipated life even if it is subjected to wind loads.
Wind forms the predominant source of loads, in tall free standing structures .The effect of wind on tall structures can be divided into two components they are
WIND LOADS ON TALL BUILDINGS
The action of a natural wind, gusts and other aerodynamic forces will continuously affect a tall building. The structure will deflect about a mean position and will oscillate continuously. Swami studied that if the wind energy that is absorbed by the structure is larger than the energy dissipated by structural damping then the aptitude of oscillation will continue to increase and will finally lead to destruction. The structure becomes aerodynamically unstable. The structure forms used these days have greater flexibility with less mass and damping than those used in olden days. Knowledge on the maximum steady or time averaged wind loads can ascertain the overall stability of a structure IS 875-part –III & SP-64 deals with wind load. The effect of wind is high in case of buildings over 10 storeys. Wind loads must be considered for the design of buildings over 10 storeys.
NATURE OF WIND
The movement of air in the atmosphere is nothing but wind. . It is of great complexity because of the many flow situations arising from the interaction of wind with structures. The characteristics of wind govern the response of structures to wind. For convenience of assessing wind loads, it is divided in to two categories:
DETAILS OF PRESENT STUDY
The present study includes the study of nature and variation of gust pressures. For this study multistoried frame of 50m in length, 10m in width, and 60 m in height is considered. From this the variation of gust pressures with height will be clearly known. In the present study emphasis is on change of terrain category.
The typical size of column is 0.3m x 0.49 m. the size of beam is 0.3m x 0.4m.The height of each storey 4m and Bay length is 5m.
Wind data:
Wind zone: basic wind speed 50 m/s
Terrain category: I open terrain with few or no obstructions
MODELLING
STAAD PRO is user friendly interface which allows drawing the frames, applying loads of varying dimensions. This software helps in modeling the building frames, analyzing different parameters and changing the properties of all materials which are used for building structures. Fig.1, Fig.2,Fig.3, and Fig.4 shows the typical layout of columns, model frame, Live load and Wind load deformation respectively
RESULTS & DISCUSSION
VI. RESULTS & DISCUSSION
Generally, in case of medium height building dead & live loads are predominant. By increasing permissible stresses recommended by the IS code the wind
CONCLUSIONS
The gust factor method is much valid for computing design wind pressures on tall structures. Very tall structures are slender and flexible. The dynamic interaction between tall flexible structures and wind should be investigated. Hence, the gust factor method gives not only safer design pressures but also it is more rational compared to the static method. Thus, gust factor method gives more confidence to the designer because it takes into account all aspect