engleski

Behaviour of medium and short length bridges subjected to blast load

Bridges are an important part of every country transportation infrastructure. Their damage or destruction can cause interruption of traffic communication between individual places which can be disastrous for the economy and population. In situations of imminent threat of terrorist attacks key bridges of large span are usually monitored and guarded ; however, many bridges located at major traffic routes can’t be monitored. In this work we will discuss the passive ways to reduce the risk of severe damage or collapse of bridges under explosive load. In order to use, explosives must be inert and stable, which means that the explosion is triggered and not spontaneous reaction. The detonation is explosive reaction that produces a high intensity shock wave followed with a high pressure and temperature gradient. As the wave spreads from the source to the ambient air its strength decreases, speed reduces and duration lengthens. Because of the increased danger, in the past few years, engineers are starting to consider the explosion as a load on structures. Volume of the experimental data is relatively small, and most of its use is restricted to military use only, the experiments are expensive and very dangerous, so most of the research is conducted by numerical modeling. Numerical modeling is performed by so called hydrocode software that have been developed for modeling the behavior of continuous media i.e. for modeling of fluid flow at different speeds and are suitable for the treatment of structural behavior taking into account the mechanical properties of the material. One of these programs is Autodyn, part of the software package Ansys, in which bridges will be modeled. Modeling in hydrocode software is based on three pillars: Newton’s laws of motion, equations of state and constitutive material models, which are used to determine the forces acting on the structure at each time step. The aim is to develop a model of the bridge that will be sufficiently accurate and reliable, and will serve as a reference for modeling other types of bridges exposed to blast loads. It is also aimed to demonstrate the possibility of simulating the blast wave interaction with the bridge and the variety of responses of the bridges due to their different geometry. The basic idea is to reduce the risk of explosion damage by use of passive measures (by increasing the standoff distance, varying the geometry). Two types of overpasses will be modeled: overpass with vertical abutment as an end support and an overpass with skew embankment. These models are to check the effect of the inclination of end supports on the pressures exerted on the bridge superstructure. It is assumed that the skew embankment contributes to increasing the load on the superstructure because it causes blast waves mutual reflection and amplification. Apart from this, different types of bridge cross sections will be examined in order to establish a state of vulnerability of bridges on Croatian roads.

Overpass; Terrorist attacks; Blast load; Numerical models

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