The intensity and number of terrorist activities have

The intensity and number of terrorist activities have
increased the concerns toward the infrastructure systems’ safety. Transportation infrastructures have
been seemed attractive targets owing to their accessibility and potential impacts
on human lives and economical activities. Different
researchers have studied on explosive load effects on bridges. The
effects of blast loads on RC structures have been investigated by Krauthammer
and Otani (1997) and the important of a detailed
modeling of rebars for the simulation of blast load effects on concrete
structures have been observed. The erosion criteria for
frictional materials subjected to explosive load have been presented by
Luccioni and Araoz (2011). A scaled model of a
multi-column pier bent with concrete-filled steel tube (CFST) columns subjected
to explosive loads have been tested by Fujikura and Bruneau (2011). Results of
the test indicated that the seismically designed and steel jacketed RC columns did not show ductile performance under explosive loading and
instead of flexural yielding at their base, they failed in shear. The response of RC bridge columns under explosive loads have
been investigated by Williamson et al. (2011a, b) and three separate blast
design categories using the scaled standoff distance have been
recommended as the primary variable to evaluate the severity of threat. A
simplified procedure for predicting explosive loads acting against bridge
columns have been proposed by Williams and Williamson (2011) by focusing on the
slender structural components in which the effects of
cross-sectional geometry, clearing effects, and engulfment of blast pressures
intensely influence the loading history. A prediction method for the response
of steel bridge girders and beams under fragment and blast loads have
been presented by Baylot et al. (2003) through
developing a load measure, a single number that could be easily evaluated
for any combination of blast and fragment loads. The
beam failure can be predicted If the load measure is exceeded for a given
combination of fragment and blast loads. The prediction of explosive
loads under a bridge overpass with high-, medium- and low- resolution FE models
have been compared by Ray et al. (2003), and the influences of factors, such as
clearing distance and charge shape on the prediction of blast load have been
discussed. The effects of the blast load on orthotropic deck trusses which is
commonly utilized in suspension and cable-stayed bridges, have been
investigated by Son and Astaneh-Asl (2009) by means of FE simulation. This
investigation indicated that decks with mild steel, behaved better while subjecting
to explosive load than those with high-strength steel; also, suspension
bridges, in which the main cables are anchored to the anchor blocks in the
ground, behave extremely well under explosive loads on the deck; Furthermore,
self-anchored suspension bridges, in which the main cables are anchored to the
bridge deck instead of anchor blocks, had poor behavior and underwent
progressive collapse and global P-D instability. Large-scale experimental blast
tests and analytical studies on steel bridge towers subjected to blast loads
has been carried out by Ray (2006). The blast loads effect on the
superstructures of highway bridges, in a preliminary study for a two-span
bridge model subjected to underdeck blasts, have been addressed by Marchand et
al. (2004). Their study indicated that the breaching failure of the concrete
governs in cases of large truck bombs with limited standoff or counterforce
charges. An extensive investigation on blast load effects on a three-span RC
highway bridge has been performed by Yi (2009) and all dominant failure modes
during blast loads has been identified. The influence of explosive load on
reinforced concrete slab-on-girder girder bridges have been investigated by Pan
et al. (2012). The damage mechanisms and dynamic performance of the whole
bridge have been established and the critical blast event for a typical
slab-on-girder bridge have been identified. According to the analysis of a
single degree of freedom (SDOF) system, several analysis results and design
recommendations have been presented by Williamson and Winget (2005) and Winget
et al. (2005) for bridges under explosive load. According to the best practices
achieved from an international literature review, the incorporation of site
layout principles and physical security into the design process have been
discussed by these authors and the structural retrofit and design solutions to
counter potential influences of explosive loads on bridges have been
recommended. It was indicated by Anwarul Islam and Yazdani (2008) that the
typical AASHTO girder bridges were unable to resist probable explosive loads. Numerical
simulations of dynamic responses of a large cable-stayed bridge under explosive
loadings from a 1,000-Kg TNT-equivalent explosion at 1.0 m above the deck and
0.5 m from the bridge pier and tower have been carried out by Tang and Hao
(2016) to investigate the damage mechanism and the it’s severity to the deck,
piers and tower of the bridge.