Prof. Sasankasekhar Mandal, Department of Civil Engineering, IIT (BHU) Varanasi, gave a talk on 20 February on the salient revisions in IS 875 (Part 3):2015 compared to the 1987 version, highlighting recent research advances in across-wind loading of tall structures.

The lecture focused on the key revisions introduced in IS 875 (Part 3):2015 and their implications for wind load estimation and structural design practice in India, presenting a structured comparison with the 1987 version of the code.

Dr. Mandal discussed the explicit inclusion of aerodynamic roughness heights for terrain categories, the revised treatment of turbulence intensity and mean wind speed profiles, and the renaming of the modification factor (k₂) as the terrain roughness and height factor. He explained the removal of earlier structural classifications, retention of relevant k₂ values, and the introduction of an important factor for cyclonic regions. The lecture further covered provisions related to directionality, area averaging, correlation of pressures, and updates to the gust factor method, including the background factor, energy ratio, and turbulence length scale. The inclusion of across-wind response evaluation for tall buildings and lattice towers, in line with international practices, was highlighted as a significant advancement. The session also addressed wind-induced interference effects between adjacent buildings, explaining shielding behaviour at different spacings and its relevance in preliminary design. Dr. Mandal briefly outlined the three major approaches in wind engineering: (i) statistical methods based on field data, (ii) boundary layer wind tunnel testing, and (iii) computational modelling, emphasizing their complementary roles in advanced analysis. The lecture concluded with an interactive discussion, strengthening participants’ understanding of the evolution and practical application of wind load provisions in IS 875 (Part 3): 2015.

YouTube Link: https://www.youtube.com/watch?v=TXJWfVcRaQ0

February 2026