SCI P427: Structural Use of Steelwork in Buildings to BS 5950 — Appraisal of Existing Structures

About this book

SCI P427: Structural Use of Steelwork in Buildings to BS 5950 — Appraisal of Existing Structures, published by the Steel Construction Institute (SCI), provides technical guidance for structural engineers undertaking the assessment and appraisal of existing steel-framed buildings — whether for continued use, change of use, refurbishment, or extension purposes. This publication complements the SCI's main design guidance documents by addressing the specific challenges and opportunities of working with existing structural steelwork rather than designing new structures from first principles. The appraisal process described in SCI P427 begins with information gathering: locating original design drawings, mill test certificates, and any previous inspection or load test records; establishing the original design standard (BS 449, CP 113, BS 5950 successive parts); and identifying the steel grade from test certificates or, where unavailable, through chemical analysis or hardness testing.

The document provides guidance on interpreting historical steel specification systems, including the pre-metric rolled section designations still encountered in pre-1970s structures, and on the assessment of riveted versus bolted versus welded connections in different eras of construction. Condition assessment methods are reviewed for the principal deterioration modes affecting structural steelwork: general corrosion (assessed through thickness measurements using ultrasonic gauging), pitting corrosion at water traps and crevice locations, fire damage (assessed through hardness testing and chemical analysis for heat exposure exceeding approximately 600°C), impact damage, and fatigue cracking in dynamically loaded structures. Structural analysis for assessment purposes uses the load combination and partial factor framework of BS 5950 but allows for the use of measured material properties in place of minimum specified values where testing evidence is available.

For structures where the original design standard predates BS 5950, equivalent capacity calculations are required. The document addresses the common scenario where loading has changed from original design intent — particularly the addition of imposed loads for change of use from industrial to retail or residential purposes. The guide also addresses the reuse of structural steelwork following deconstruction: the assessment requirements for second-hand steelwork, the documentation standards for material traceability, and the capacity recalculation requirements when members are reassigned to new structural roles.