Roof Slab Safety Index (Rssi): A Framework for Evaluating Structural Adequacy of RC Roof Slabs with Rooftop Antennas

Abstract

The growing deployment of satellite antenna systems atop low-rise reinforced concrete (RC) buildings introduces concentrated loads that the original slab design did not account for. This study introduces and validates the Roof Slab Safety Index (RSSI) a practical performance-based metric to assess RC roof slab structural adequacy under combined antenna and building loads. A G+1 RC residential building integrated with an S/Ka-band satellite antenna pedestal was modelled and analyzed using STAAD.Pro 2024 in compliance with IS 456:2000, IS 875 (Parts 1–3), and IS 1893 (Part 1):2016. The RSSI is defined as the minimum ratio of slab capacity to imposed demand across two failure modes: flexure, and shear. For the modelled 300 mm thick roof slab (M25 concrete, Fe500 steel, 10 mm bars at 100 mm c/c both ways), the governing flexural safety index was 2.21 and the shear safety index was 1.33, yielding an overall RSSI of 1.33. All serviceability checks, including span-to-depth ratio (l/d = 15.79 vs. permissible 32), were satisfied. An RSSI ≥ 1.33 confirms that the slab is structurally safe without requiring redesign, despite carrying the combined weight of the RC pedestal and the 145kN antenna assembly. The RSSI framework offers practitioners a concise diagnostic index for screening existing roof slabs prior to antenna installation, directly supporting safe and economical communication infrastructure integration in urban environments.