A Review: Effect of Roof Geometry on Wind Response in Tall Structures Using ETABS and IS 875 (PART 3): 2025 Draft

Abstract

High-rise construction in urban India has surged due to land scarcity, making wind loads the primary design consideration for buildings over 20 storeys where lateral forces exceed gravity and seismic effects. Roof shape plays a decisive role in aerodynamic behavior, as flat roofs create excessive uplift and vortex shedding while sloped or stepped designs promote smoother airflow and reduced pressures. This review consolidates research on wind response of tall RCC structures with varied roof configurations—flat, gable, pyramidal, and terraced—modeled in ETABS using the updated IS 875 (Part 3): 2025 draft provisions. The new code offers enhanced pressure coefficients tailored to roof inclinations, terrain categories, and height-velocity exposure, surpassing limitations of 1987/2015 versions. Literature from 2016-2025 demonstrates sloped roofs (15°-30°) lower windward pressures by 12-18% and stepped profiles cut leeward suction, though Indian zone-specific validations remain sparse. ETABS studies confirm pyramidal roofs excel in Zone III-IV, yielding 10-15% less drift and base shear. Present work synthesizes findings to highlight research gaps in hybrid roof optimization and recommends code-compliant design strategies integrating architectural form with structural wind performance for safer tall buildings

Introduction

Rapid urbanization in India has led to widespread high-rise construction, particularly in metro cities and Tier-2 urban centers, shifting design concerns from gravity-dominated low-rise behavior to wind-induced lateral forces that govern base shear, overturning moments, inter-storey drifts, and occupant comfort. Wind pressures vary across building faces—stagnation on windward walls, suction on leeward sides, and vortex-induced roof uplift—making roof geometry a key modifiable factor to improve aerodynamic performance. Flat roofs tend to amplify flow separation and peak pressures, while sloped, pyramidal, or stepped roofs promote smoother airflow, reduce vortex shedding, and lower wind loads.

IS 875 (Part 3) Draft 2025 introduces updated provisions compared to earlier codes (1987/2015), including:

• Refined wind speed zones (Vb)

• Terrain and exposure coefficients (k1–k4)

• Geometry-specific external pressure coefficients (Cpe) accounting for roof slope, edge distances, and wind directionality
  These provisions enable more accurate wind load estimation, reducing overdesign while maintaining safety.

ETABS Modeling and Findings:
High-rise RCC buildings (G+20 to G+30) were modeled with various roof configurations—flat, sloped (15°–30°), pyramidal, gable, and stepped—under IS 875:2025 wind loads. Key observations from literature and parametric studies include:

• Sloped roofs reduce lateral displacements by 12–18% and improve drift ratios.

• Pyramidal roofs minimize torsional effects and overturning moments (11–15% reductions).

• Stepped or pyramidal terraces reduce corner suctions by ~16%.

• Curved, pitched, and hybrid roofs mitigate vortex shedding and roof uplift by 15–20%.

• Roof geometry optimization improves occupant comfort, structural economy, and serviceability compliance.

Methodology:

• Wind loads applied via IS 875:2025 Cp values for terrain and wind zones (III–IV)

• Both static equivalent and response spectrum analyses performed

• Performance metrics include base shear, top displacement, storey drift, overturning moments, and roof uplift pressures

Expected Results:

• Sloped/pyramidal roofs significantly reduce base shear, top displacement, storey drift, corner suction, and roof uplift compared to flat roofs.

• Proper geometry optimization (15°–30° slopes, pyramidal, stepped profiles) can lower roof uplift by 15–20% while maintaining serviceability.

• Flat roofs may overestimate wind pressures, missing aerodynamic benefits of optimized geometries.

Discussion:
Roof geometry has a substantial impact on wind response in tall RCC buildings. IS 875:2025 draft provisions combined with ETABS enable realistic modeling of aerodynamic effects, allowing safer, more economical, and code-compliant high-rise designs. Geometry optimization is particularly critical when serviceability or economy drives design decisions, especially in high wind regions (Zones III–IV).

Conclusion

The review of roof geometry studies and proposed ETABS methodology shows that roof configuration significantly alters wind response of tall RCC buildings under IS 875:2025 provisions. Modified roofs (sloped 15°-30°, pyramidal, stepped) expected to reduce base shear 10-18%, displacements 12-20%, and uplift 15-20% compared with flat roof assumptions, indicating conventional profiles may not optimize economy for wind-dominated high-rises. Pyramidal roofs excel in minimizing drift and overturning moments particularly for Zone III-IV regions above G+20 where wind governs design. Sloped configurations provide consistent 12-16% load reduction across parameters while maintaining serviceability limits. For roof design, IS 875:2025 slope-specific Cp values enable realistic pressure distributions absent in older codes, supporting better edge detailing and vortex control through geometry alone. The integrated ETABS workflow provides practical framework incorporating aerodynamic optimization in routine high-rise design under Indian standards. Geometry optimization proves more effective than member sizing for wind performance. Overall, flat-roof assumptions adequate only for preliminary sizing, whereas explicit roof geometry modeling recommended when serviceability, economy, or Zone III-IV exposures critical. Adopting IS 875:2025 provisions bridge simplified assumptions and realistic wind behavior for safer tall RCC construction.

References

[1] Sharma and D. Patel, \"Influence of Roof Configurations on Wind Load Response in Tall Buildings Using IS 875:2025 Draft,\" International Journal of Structural Engineering and Analysis, vol. 11, no. 1, pp. 45-52, 2024 [2] M. Tripathi and R. Singh, \"Comparative Study of Wind Effects on Flat and Sloped Roof High-Rise Buildings Using ETABS,\" Journal of Wind and Structural Engineering, vol. 9, no. 3, pp. 122-130, 2023 [3] L. Gupta and P. Mehra, \"Wind Load Analysis on RC Buildings with Different Roof Shapes According to IS 875 (Draft 2025),\" International Journal of Research in Civil Engineering, vol. 10, no. 2, pp. 90-98, 2023 [4] S. K. Jaiswal and N. Thakur, \"Impact of Geometrical Roof Variations on Tall Structures Under Wind Loads,\" International Research Journal of Engineering and Technology (IRJET), vol. 9, no. 12, pp. 2011-2018, 2022 [5] V. Kulkarni and H. Deshmukh, \"A Study on Aerodynamic Behavior of High-Rise Buildings with Modified Roof Profiles,\" International Journal of Civil Engineering and Technology, vol. 13, no. 5, pp. 754-761, 2022 [6] A. Tiwari and R. Pandey, \"ETABS Based Modelling and Wind Analysis of Buildings with Stepped, Flat and Sloped Roofs,\" International Journal of Modern Engineering Research, vol. 8, no. 3, pp. 310-317, 2021 [7] S. Mishra and P. Yadav, \"Effect of Roof Geometry on Wind Load Distribution on Tall Buildings,\" Journal of Building Performance and Design, vol. 7, no. 1, pp. 40-48, 2021 [8] P. R. Sawant and N. G. Waghmare, \"Design Optimization of Tall Buildings Under Wind Loads Using Different Roof Profiles,\" International Journal of Advanced Structural Engineering, vol. 6, no. 4, pp. 355-363, 2020 [9] R. Rameshwar, A. Gupta, and K. Jain, \"Comparative Study on Wind Response of Buildings with Irregular Roof Profiles Using IS 875 Provisions,\" Journal of Civil Engineering and Technology, vol. 14, no. 2, pp. 233-240, 2019 [10] S. Agarwal, P. Desai, and R. Sharma, \"Influence of Roof Inclination on Wind Load Reduction in Medium and Tall Buildings,\" International Journal of Wind and Engineering Research, vol. 6, no. 1, pp. 89-96, 2018

Copyright

Copyright © 2025 Pratik Patle, Rahul Hinge. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.