Failure and design limit criteria for blast loaded structures

The majority of buildings located at petrochemical plants, exclusive of control rooms, are of conventional construction and do not explicitly provide for resistance to blast loads. Typical construction types include steel frame with metal cladding, concrete masonry unit, and brick clad with concrete or steel frame. These buildings are designed for conventional loads without regard for high overpressures and fragments resulting from an accidental explosion. Current regulatory trends are causing many companies to evaluate design standards for new and existing support structures especially in the wake of recent accidental explosions. Response criteria is an important part of these design standards especially when they are used to analyze existing structures for blast protection. Structural evaluations at several sites have revealed that few existing structures meet current design criteria primarily due to weak member connections. Previous work has shown that many conventional structures can develop a surprising degree of resistance to blast loading if proper detailing is used in design, thus allowing members to develop their full capacity. This paper discusses response criteria currently used for new structures and examines the problem of determining acceptance criteria for existing structures. Data from explosion accidents and test programs is reviewed to determine the degree of conservatism in current criteria. Finally, alternatives for establishing blast capacity of existing structures are discussed.