The intensity and number of terrorist activities haveincreased the concerns toward the infrastructure systems’ safety. Transportation infrastructures havebeen seemed attractive targets owing to their accessibility and potential impactson human lives and economical activities. Differentresearchers have studied on explosive load effects on bridges. Theeffects of blast loads on RC structures have been investigated by Krauthammerand Otani (1997) and the important of a detailedmodeling of rebars for the simulation of blast load effects on concretestructures have been observed. The erosion criteria forfrictional materials subjected to explosive load have been presented byLuccioni and Araoz (2011). A scaled model of amulti-column pier bent with concrete-filled steel tube (CFST) columns subjectedto explosive loads have been tested by Fujikura and Bruneau (2011). Results ofthe test indicated that the seismically designed and steel jacketed RC columns did not show ductile performance under explosive loading andinstead of flexural yielding at their base, they failed in shear.
The response of RC bridge columns under explosive loads havebeen investigated by Williamson et al. (2011a, b) and three separate blastdesign categories using the scaled standoff distance have beenrecommended as the primary variable to evaluate the severity of threat. Asimplified procedure for predicting explosive loads acting against bridgecolumns have been proposed by Williams and Williamson (2011) by focusing on theslender structural components in which the effects ofcross-sectional geometry, clearing effects, and engulfment of blast pressuresintensely influence the loading history. A prediction method for the responseof steel bridge girders and beams under fragment and blast loads havebeen presented by Baylot et al. (2003) throughdeveloping a load measure, a single number that could be easily evaluatedfor any combination of blast and fragment loads.
Thebeam failure can be predicted If the load measure is exceeded for a givencombination of fragment and blast loads. The prediction of explosiveloads under a bridge overpass with high-, medium- and low- resolution FE modelshave been compared by Ray et al. (2003), and the influences of factors, such asclearing distance and charge shape on the prediction of blast load have beendiscussed. The effects of the blast load on orthotropic deck trusses which iscommonly utilized in suspension and cable-stayed bridges, have beeninvestigated by Son and Astaneh-Asl (2009) by means of FE simulation. Thisinvestigation indicated that decks with mild steel, behaved better while subjectingto explosive load than those with high-strength steel; also, suspensionbridges, in which the main cables are anchored to the anchor blocks in theground, behave extremely well under explosive loads on the deck; Furthermore,self-anchored suspension bridges, in which the main cables are anchored to thebridge deck instead of anchor blocks, had poor behavior and underwentprogressive collapse and global P-D instability. Large-scale experimental blasttests and analytical studies on steel bridge towers subjected to blast loadshas been carried out by Ray (2006).
The blast loads effect on thesuperstructures of highway bridges, in a preliminary study for a two-spanbridge model subjected to underdeck blasts, have been addressed by Marchand etal. (2004). Their study indicated that the breaching failure of the concretegoverns in cases of large truck bombs with limited standoff or counterforcecharges. An extensive investigation on blast load effects on a three-span RChighway bridge has been performed by Yi (2009) and all dominant failure modesduring blast loads has been identified. The influence of explosive load onreinforced concrete slab-on-girder girder bridges have been investigated by Panet al. (2012). The damage mechanisms and dynamic performance of the wholebridge have been established and the critical blast event for a typicalslab-on-girder bridge have been identified.
According to the analysis of asingle degree of freedom (SDOF) system, several analysis results and designrecommendations have been presented by Williamson and Winget (2005) and Wingetet al. (2005) for bridges under explosive load. According to the best practicesachieved from an international literature review, the incorporation of sitelayout principles and physical security into the design process have beendiscussed by these authors and the structural retrofit and design solutions tocounter potential influences of explosive loads on bridges have beenrecommended. It was indicated by Anwarul Islam and Yazdani (2008) that thetypical AASHTO girder bridges were unable to resist probable explosive loads.
Numericalsimulations of dynamic responses of a large cable-stayed bridge under explosiveloadings from a 1,000-Kg TNT-equivalent explosion at 1.0 m above the deck and0.5 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.