Wind- and Seismic-Zone-Calibrated Selection of Roof-to-Beam Base Connections for Long-Span Trussless Roofing Systems: A Mechanics-Based Framework for Indian Design Practice

Abstract

Introduction: Trussless (self-supported) roofing systems built from curved, cold-formed Galvalume steel sheets have become a default long-span roofing solution for Indian warehouses, logistics parks, and industrial sheds, yet Indian design practice still lacks codified guidance for the roof-to-support base connection through which the entire wind-uplift and seismic reaction of the arched roof is transferred to the substructure. Validated finite-element and response-surface studies have compared candidate base-connection types, but their loading envelopes are expressed in generic pressure and acceleration units that are not referenced to the wind and seismic zone maps used in Indian design, IS 875 (Part 3):2015 and IS 1893 (Part 1):2016. Practicing engineers are consequently left without a direct, code-referenced basis for selecting a base-connection type for a given Indian site.
Methods: Four field-constructible roof-to-beam base connections — traditional mechanical anchor, cap plate, support bracket, and continuous steel frame — were evaluated under identical wind-uplift and seismic loading using coupled shell-contact finite element analysis (ANSYS Mechanical; SHELL181 shell elements; Coulomb-friction surface contact; multipoint-constraint bolt formulations) together with a two-factor response surface methodology (RSM) design (Design-Expert v13). The analysed loading envelope (wind pressure 1.0–2.0 kN/m²; seismic acceleration 0.10–0.25g) was explicitly mapped, using the IS 875 (Part 3):2015 design wind pressure equation and the IS 1893 (Part 1):2016 zone-factor table, onto the basic wind speed range (33–55 m/s) and seismic zones (II–V) that govern Indian construction.
Results: Peak von Mises stress at the base connection fell by 60.1% and mid-span deflection by 20.0% moving from the traditional anchor to the continuous frame, while per-bolt load demand was halved. ANOVA confirmed wind pressure as the sole statistically significant driver of vertical response (p < 0.0001), with no measurable seismic contribution across the tested envelope (p = 1.0000). Mapping the tested wind-pressure range against IS 875 (Part 3):2015 shows that it corresponds to basic wind speeds of approximately 43–61 m/s for eave heights of 10 m or more — spanning India's high-wind-speed and cyclone-exposed zones — while the tested seismic range (0.10–0.25g) covers IS 1893 (Part 1):2016 Zones II through just above Zone IV, leaving Zone V (Z = 0.36) outside the validated envelope.
Discussion: For Indian sites with basic wind speeds at or above approximately 44–47 m/s — much of the eastern and western coastline and the cyclone belt — the traditional bolted anchor develops base stresses and per-bolt demands large enough to make the cap plate, bracket, or continuous frame the mechanically justified choice; the continuous frame is recommended without qualification wherever wind speed, redundancy, or maintenance access is design-critical. The seismic-insignificance finding holds for Zones II–IV but should not be extrapolated to Zone V without further validation.
Conclusion: This zone-calibrated framework provides Indian design engineers with connection-selection guidance for trussless roofing systems that is, for the first time, directly referenced to IS 875 and IS 1893 provisions rather than to generic laboratory load ranges.