EFFECT OF INTERFERENCE BETWEEN TALL BUILDINGS

Abstract

Ultimately increasing population and shortage of space available for new constructions vividly evident the increasing demand of tall structures. Whenever a tall building comes in picture, a designer must be concern about the lateral loads i.e. wind load and earthquake load. With increase in height of tall structures, wind loads become critical therefore, a need of accurate calculation of wind loads is emerge for safer and economical design. Generally structures have the regular common cross-sectional shape like square, rectangular etc. but architect may think of any shape, any irregular cross-section to fulfilling the aesthetic and architectural purpose. For buildings with regular cross-sections like square and rectangular, force and pressure coefficients are available in relevant design codes and one can use them to design for wind loads. But for these simple regular shapes also, the available data can be used only for isolated configuration and there is very less information available for design in interference configurations. However, for irregular shape cross-sections, no information is available in design codes for isolated as well as for interference condition. Cross-sectional shape plays an important role in case of wind loads. Also the information available in design codes of various countries are of very limited extent in case of interference. A lot of studies on interference effects have been carried since the collapse of three out of eight natural drift cooling towers at Ferry Bridge, England. Various wind tunnel experiments and Computational Fluid Dynamics packages are used all over the world to completely understand the phenomenon of interference. An attempt has, therefore, been made in the present study to understand the phenomena of interference with the help of wind tunnel experiments along with varying cross-sectional shape buildings. Five different cross-sectional shape tall structures are considered. Experimental study is carried out under two major heads: Force measurements in isolated and interference configurations, Pressure measurements in isolated and interference configurations. Rigid models of plywood and Perspex sheet models are fabricated at a scale ratio of 1:200 and are tested under isolated and interference configurations for force and pressure measurements respectively in an open circuit boundary layer wind tunnel. Vortex generators, barrier wall and small wooden and concrete blocks are used to generate the required wind flow corresponding to terrain category 2. Results of force study for isolated configurations are presented in X-Y plots showing variation of force parameters with wind incidence angles. For interference configurations, X-Y plots showing variation of interference factor for along-wind force and twisting moment for various interference configurations are plotted. Comparison of drag force coefficients for different models is also done. [iv] Results of pressure study is presented in the form of contour plots and cross-sectional variation diagrams of mean wind pressure coefficients for both isolated and interference cases. Pressure study is done on three models only. A comparative study is also done between pressure study and force study results to validate the experiments. Experimentally obtained external pressure coefficients for square shape model is also compared with data available in standard code. Conclusions drawn from the complete study are listed out at the end for isolated and interference configurations. Results presented in this dissertation can be used by structural designers to design the high-rise buildings of same or similar cross-sectional shapes studied in this report.