Original Research Article Effects of upstream terrain characteristics on aerodynamic coefficients of structures Chitra Ganapathi S * , Harikrishna P, Selvi Rajan S CSIR-SERC, Chennai 600113, India 1. Introduction The rapid growth of urban population has lead to increase of vertical construction of high rise buildings. High rise buildings are predominantly affected due to lateral forces of the wind than other loads. The magnitude of intensity of these wind loads acting on the structure is significantly affected by terrain conditions than other parameters. The actual exposure condition of structures subjected to wind load is usually different from uniform condition drafted in most wind standards since most such structures erected in cities are embedded in boundary layer flow. In the present study, the effect of terrain on structures against wind load has been considered. While considerable research has been reported for wind induced load effects regarding the effect of side ratio, angle of wind incidence and the slenderness effect of tall rectangular building models. Only limited researches are reported for boundary layer flow conditions. Amin and Ahuja [1] carried out wind tunnel studies on 1:300 scaled-down models of rectangular buildings having same plan area and height but different side ratios ranging from 0.25 to 4 under open terrain for the mean velocity of 15 m/s. Effectiveness of the side ratios of models in changing the surface pressure distribution was assessed at wind incidence angle of 08 to 908 at an interval of 158. Quan et al. [2] studied the influence of side a r c h i v e s o f c i v i l a n d m e c h a n i c a l e n g i n e e r i n g 1 7 ( 2 0 1 7 ) 7 7 6 – 7 8 5 a r t i c l e i n f o Article history: Received 28 January 2016 Accepted 20 February 2017 Available online Keywords: Wind tunnel Upstream exposure Aerodynamic characteristics Rectangular building model a b s t r a c t Most research investigations and standards have not emphasized the effects of upstream terrain characteristics on aerodynamic coefficients of structures. Hence in this investigation, pressure measurements study on a 1:2:3 rectangular building model has been simulated through wind tunnel test under uniform, open and suburban terrain condition for 08 and 908 angles of wind incidence. From the variation of pressure and force coefficient values of present study, it is seen that the mean pressure and force coefficient values of all levels of uniform flow condition are on higher side by about 15–40% than the open and suburban terrain values for 08 angles of wind incidence as expected. However the mean pressure and force coefficient values of uniform flow condition are also showed that the values of all levels for 908 angle of wind incidence are on lower side with 20–40% difference than the boundary layer flow values when compared to the values of 08 angle of wind incidence. In addition, the mean pressure and force coefficients of present study has been compared with the Indian and international guidelines to highlight the limitations of codal standards. © 2017 Politechnika Wroclawska. Published by Elsevier Sp. z o.o. All rights reserved. * Corresponding author: Scientist, Wind Engineering Laboratory, CSIR-SERC, Chennai, India. E-mail addresses: chitra.ganapathi@gmail.com, chitrag@serc.res.in (C.G. S), hari@serc.res.in (H. P), sselvi@serc.res.in (S.R. S). Available online at www.sciencedirect.com ScienceDirect journal homepage: http://www.elsevier.com/locate/acme http://dx.doi.org/10.1016/j.acme.2017.02.005 1644-9665/© 2017 Politechnika Wroclawska. Published by Elsevier Sp. z o.o. All rights reserved.