(a)blast loading (b)fragment loading (c)combined loading Fig.5 failure modes of the concrete beam Fig.5 (a) when blast loading effect on the bridge separately, the largest deformation occurs in mid-span, steels restrict the beam became more damaged. Some beam border became damaged. Fig.5 (b) when fragment loading effect on the bridge separately, some pits and holes occur on the beam surface, the longitudinal steels become curved and stressed the main pressure. Fragments pieces splash nearby during the penetrating process. Fig.5 (b) when combined loading effect on the bridge, the beam damaged seriously. The longitudinal steels yield under the fragments effect and then expand the deformation because of the blast impact wave. The biggest displacement occurs in mid-span, many pits and holes occur on the beam surface, and seriously damage the beam border. 4.3 Dynamic response of the bottom midpoint Fig.6 acceleration of the bottom midpoint Fig.7 displacement of the bottom midpoint Figure 6 and 7 indicate that the acceleration response under synergetic effect is larger than the response under fragment or blast wave effect separately, further more larger than the sum of the separate responses. And the displacement response under the synergetic effect is larger than the separate responses.
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