WIND LOADS ON SLOPING ROOFS WITH SKY LIGHT

Abstract

Whereas flat roofs are generally used for residential buildings, sloping roofs are employed for both residential as well as industrial buildings due to its advantages namely easy drainage of rain, water and snow, and availability of large column free area. Sloping roofs, specially in case of industrial buildings, require entry of natural light through its roof surface. Northlight or saw-tooth and sloping roofs with sky light are solutions to this need. Evaluation of design wind loads on buildings, requires information on design wind speed and pressure or force coefficients besides other parameters. Whereas information regarding wind pressure coefficients on shed, gable and hip types of sloping roofs are available in various codes of practice, the information is sky light. In the present dissertation and roofs with a study of wind loads on scanty for north light roofs sloping roofs with sky light has been made. The work carried out comprises of testing of building models in boundary layei--\wind. tunnel. Six number rigid models of sloping roof have been prepared and tested to study the effect of various geometric and flow parameters such as slope of roof, height to breadth ratio, wind velocity and wind incidence angle on the mean wind pressures at various points on all the surfaces of the building. The results are presented in the form of non-dimensional pressure coefficients both in the form of tables and pressure contours. The pressure coefficients are also compared with the available codal values. (iv) A computer programme has been developed for further analysis of experimental results. The results so obtained have been presented as face average and centre line average pressure coefficients for all the cases. Weighted area at each and every pressure point is calculated for each case by Theissen Polygon Method. A relationship is developed between pressure coefficients and length to breadth ratio for. suction on leeward face of the building. Comparison between face average pressure coefficients and centre line average pressure coefficients has been presented in tabular form. As a results of the present study, it is observed that the 3fe wind incidence angle has the maximum suction in sloping parts of the building while maximum pressure is observed at 900 wind incidence angle. It is also seen that at 30° wind incidence angle some faces of the building have almost zero pressure coefficients meaning thereby no pressre or suction. The effect of wind velocity on wind pressure coefficients is found to be negligible. The effects of height to breadth ratio and roof slopes on pressure coefficients are found to be appreciable. It is found that high suction developes at edge and corner regions for roof having lb° - Or slope and the same decreased for GJ slope. it is also seen that there is increase in suction and pressure on most of the •-.4faces with the increase in height to breadth ratio.