Equivalent SDOF Load Transformation Factors for One-Way Members Subjected to Air Blast Loading

The equivalent single-degree-of-freedom (SDOF) load transformation factor expressions of the simply supported, fixed end and simply-fixed one-way members subjected to air blast loading are derived by finite series-expansion method or finite point-fitting method. Moreover, figures are used to show the relative relationship between the load transformation factors KL and the ratio of stand-off distance to structural span (γ). The typical calculation conditions show that the load transformation factors are sensitive to the piecewise function of peak overpressure when γ is less than 0.5. The load transformation factor will be a smooth curve for peak overpressure adopting a single smooth continuous function. For the blast-resistant structural design, if the error of 3% in the elastic stage and 5% in the plastic stage can be allowed, γ = 1.0 is the demarcation point between near field blast and far field blast. In addition, if the error of 0.5% can be allowed, γ ≥ 2.0 can be treated as the far field blast. The calculation results of far field blast show that the values of KL of simply supported, simply-fixed, and fixed-end members are 0.64, 0.58, and 0.54, respectively, which means that the load transformation factor is insensitive to the selection of shape function in vibration mode function or static deflection curve function. The calculation accuracy of KL expression for simply supported beam structure in this paper has been verified through near field blast experiments. This paper provides a clear numerical definition for the distinction between near field and far field explosions. It provides qualification criteria for analyzing explosion categories in blast-resistant structural design and a reference for the selection of theoretical calculation formulas.

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