Structural Response of the Building under Dynamic Along-wind Loading

Abstract

Wind load is one of the basic loads acting on various structures. Flexible and Slender structures like Tall Buildings, Chimneys, Transmission Towers, Suspension Bridges, Offshore structure, etc are mostly govern by wind load. Thus, estimation of wind load is a most important design input for flexible and slender structures. Wind load is complex in nature and hence difficult to characterize. Wind load can be characterized by Power Spectrum Density (PSD) function derived from any of the, Von-Karman method, Wind Tunnel Test and Computational Fluid Dynamics (CFD). Prof Solari [3] has developed Equivalent Wind Spectrum Technique (EWST), to estimate wind load in structure, wherein fluctuating wind velocity is given by PSD function. Main subjective of the present study are, (i) To implement EWST that captures dynamic nature of wind unlike code based Static and Gust Factor Method (GFM) for the Indian scenario. (ii) To develop wind response spectrum based on site specific inputs and parametric study in terms of PSD functions available in the literature, is also carried out. A G+40 storey and G+80 storey high rise Reinforced Concrete (RC) Buildings are considered. Wind load estimation is carried out for both buildings using code IS : 875 (Part - III) - 2015, through both Static and GFM, for three terrain categories and six wind speed in each category. EWST is studied in detail and is developed for Indian scenario wherein wind velocity fluctuation are simulated using PSD function considering various parameters. Each building, under consideration, is modeled as lumped mass model and response quantities - Displacement, Lateral load, Base Shear, Overturning Moment are extracted by MATLAB based programming. Response quantities, using three different modal combination rules - The Square Root of Sum of Square Method (SRSS), The Sum Method (SUM), The Cut-off Frequency Method (COF) obtained by EWST and IS : 875 (Part - III) based Static and GFM are computed. It has been found that Lateral Load, Base Shear and Overturning Moment estimated by EWST are significantly lower as compared to codal based methods. Parametric study carried out for G+40 storey RC building in terms of PSD function reveals that there is no major difference in response quantities for considered four PSD functions. Wind Response spectrum are also generated for G+40 and G+80 storey RC building for three terrain categories, six wind speed for each category, for wind in both the direction, both in Time domain and Frequency domain. It has been observed that response quantities through wind response spectrum shows a good agreement with EWST.