Blast resistant design for roof systems

The design of structures to resist explosive loads has become more of a concern to the engineering community. Different structural members, such as walls, have been thoroughly evaluated under blast loads. This research focuses on the design techniques for the loading on roof structures and the resistance of open web steel joists, a common roof component. Blast loads are dynamic, impulsive and non-simultaneous over the length of a roof. To design against explosions, a procedure has been developed to devise a uniform dynamic load on a roof that matches the response from blast loads. The objective of this research is to test this procedure and compare its results to the deflections from blast loads. This research uses finite element analysis to evaluate the responses from numerically calculated blast loads and compares them to the equivalent loading response. The numerical pressures are calculated using the Conventional Weapons Effects Program (CONWEP) (Hyde, 1992) and the Single-degree-of-freedom Blast Effects Design Spreadsheet (SBEDS) from the Army Corps of Engineers Protection Design Center. Also, the response of experimentally measured roof blast pressures is compared to the equivalent loading response. While the responses from finite element modeling matched the experimental responses, the equivalent loading procedure did not adequately predict the initial peak deflection or the maximum deflection.;The response of several structural members used in roof construction, such as hot-rolled steel beams and reinforced concrete slabs, are well documented and understood. Open web steel joists (OWSJ) are other types of common roof components. Their responses under loading are not clearly defined, and current methods extrapolate techniques used in the design and analysis of hot-rolled steel beams and reinforced concrete. The resistance function currently used for these members are linear elastic and perfectly plastic after the elastic deflection limit. It is believed that the failure mechanisms of OWSJ significantly are not accurately being taken into account. Three tests consisting of different steel joist pairs are performed. The resistance function is computed from these results and compared to current methodologies. The current resistance methods calculate larger maximum loads than the experimental values and the assumption of a perfect plastic post-peak response ignores the buckling failure of web members. It is recommended that additional research is to be done on the prediction of blast pressures on roofs and on the development of an equivalent uniform dynamic load. It is also recommended that an analytical resistance function for OWSJ be clearly defined, which includes all failure limit states.