This paper investigated the blast performance of a three-storey composite steel building subjected to external explosion by a package bomb. Analysis was based on load combinations and damage criteria in accordance with three general design approaches relevant for civil design applications in predicting blast loads and structural system responses. The main objective is to provide a rapid blast evaluation and simplify the model when blast wave first impacts the structure. For first dynamic stage, direct simulation method was chosen for modelling blast loads on members exposed to explosion using the Friedlander blast load equation, and an empirical A.T.-BLAST method estimated its parameters to deduce the simplified blast-wave overpressure profile. For second static stage, the original Alternate Load Path method was used to check the probable stability of columns' damage due to heat after blast on adjacent elements using the standard temperature-time curve due to local fire. Results showed that structural elements were deformed away from their elastic limit and yield points, resulting in plastic behavior with considerable post-yielding deformations so ductility ratio, plastic hinge rotation, internal forces limits, Demand-Capacity-Ratio (DCR shear/moment) and material damage model are the judged adequacy in blast design and structural members' evaluation considering blast load as the initial cause of failure. After explosion, re-loading process resulted in structure' stability (non-collapse) due to ductility and introduced vierendeel effect to be reused again. Some guidelines have un-provided data on damage evaluation limit criteria while others overestimate the realistic damage conditions.