Assessment of the load-bearing capacity of building structures when changing the functional purpose of a building

Abstract

A change in the functional purpose of a building in service is accompanied by a redistribution and, as a rule, an increase of imposed loads on floors, which shifts the admissibility of repurposing into the domain of a verification analysis of load-bearing structures. The mismatch between the design function of a room and the intended one remains weakly formalised: the decision to change the purpose is often taken on the basis of a visual survey, without comparing the actual reserve of load-bearing capacity with the load increment. The aim of the work is to build a calculation scheme relating the normative increment of the imposed load, when moving between functional classes of rooms, to the utilisation ratio of the load-bearing capacity of a reinforced concrete floor. On an author’s calculation model of a monolithic slab, a verification analysis for the ultimate limit states was performed for five scenarios of a function change, from office use to archival storage. It was established that the transition from an office function at a normative load of 2.0 kPa to an archival one at 5.0 kPa raises the utilisation ratio of the slab from 0.79 to 1.07, taking the section beyond the load-bearing limit at unchanged reinforcement. The strength increment of a lightly reinforced section under an increase of the concrete class is small; the governing parameters are the working reinforcement area and the design span. Matching the utilisation ratio ranges with the technical-condition categories of the current survey standard gives grounds to refer the strengthening decision to the stage preceding the function change rather than to the moment when visible damage appears.