Elsevier

Engineering Failure Analysis

Volume 36, January 2014, Pages 353-361
Engineering Failure Analysis

Analysis of a bridge collapsed by an accidental blast loads

https://doi.org/10.1016/j.engfailanal.2013.10.022Get rights and content

Abstract

Analysis of the structural failure of a bridge caused by an accidental fireworks explosion is presented in this paper. The equivalent mass of TNT due to the fireworks explosion and the structural response of the bridge due to the dynamic load imposed by the explosion are modeled by engineering algorithms and numerical simulations. Analysis confirmed that bridge failure occurred due to the blast load and there was no inherent design defect. The results of this investigation are relevant towards understanding future events wherein a dynamic load might be accidentally applied to fixed structures.

Highlights

  • The analysis of the structural failure of a bridge caused by a blast load is presented.

  • The structural response of the bridge due to the dynamic load is modeled.

  • The equivalent mass of TNT is modeled via engineering algorithms and numerical simulations.

  • The observed damage is consistent with the blast load imposed by the fireworks explosion.

  • There was no inherent design defect in the bridge.

Introduction

Military assaults, terrorist attacks and accidental explosions may cause serious damage to buildings and other infrastructures [1], [2], [3], [4]. Bridges are the most common infrastructures in a national highway system. As a result of terrorist threats and attacks, engineers and transportation office workers are becoming more active in physically protecting bridges from potential blast attacks [5], [6]. Damage effect analyses and assessments of bridges under blast loading are very important in the area of explosion accident analyses, blast-resistant design and anti-terrorist and military weapon design [7].

With the rapid development of computer hardware over the last decades, detailed numerical simulations of explosive events in personal computers have become possible and significantly increased the availability of such methods. New developments in integrated computer hydrocodes, such as the AUTODYN software [8] used in this paper, complete the tools necessary to conduct a numerical analysis successfully.

Although efforts have been exerted to model blast effects on civilian structures, mainly on building structures, relatively less attention has been directed toward bridge structures under blast loads. Two simulations of bridge structure responses to blast loads were conducted by Winget et al. [9] and Islam and Yazdani [5], who separately investigated the response of an AASHTO concrete girder bridge under blast impact using an uncoupled SDOF system and the commercial software STAAD.Pro, respectively. Both researchers considered various detonation positions to obtain a better perspective of bridge performance against blast loadings. Results indicate that the studied bridge type is highly vulnerable to failure under the impact of a conventional truck bomb. Winget et al. [9] concluded that bridge response under blast loads is highly dependent on bridge geometry, such as clearance of the bridge deck from the ground and the confinement effect resulting from the deep girder; these factors can significantly enhance the magnitude of the blast pressure acting on the structure.

Unintentional explosions are highly undesirable. In process industries, steps are frequently taken to minimize the causes and consequences of accidental explosions [10]. When an explosion occurs, attention shifts from prevention to attribution from the perspective of both cause and effect. A forensic engineer seeks to understand whether any resulting harm to persons or property can be attributed to negligence on the part of those responsible for the design, construction, maintenance or operation of the damaged structural system.

In this study, the aftermath of an accidental explosion on a bridge is reported. Observed structural damages are explained in detail. The determination of accident causes and bridge design defects is the main issue addressed when dealing with the accident. The equivalent TNT mass of the fireworks explosion and the structural response of the bridge attributed to the dynamic load imposed by the explosion are modelled by engineering algorithms and numerical simulations. The analysis confirms that bridge failure occurred because of the blast load without any inherent design defect. Thus, we can determine whether the power of the fireworks explosion can damage a well-designed bridge.

Section snippets

Incident

A truck loaded with fireworks exploded on a bridge in China in early 2013. This accident caused part of the bridge to collapse, and the local deck of the bridge was marred. Fig. 1 shows the ruptured configuration of the cross section of the bridge.

From the accident report, the explosion occurred on the third span of the bridge, as shown in Fig. 2. The length of one span of the bridge is 40 m, the width of the deck is 11 m, the least thickness of the deck is 17.7 cm and the largest thickness of the

Analysis of the equivalent mass of TNT in the accident by numerical simulation

Using numerical simulation [8], [11], three typical damage spots were reproduced. The least equivalent TNT mass to achieve the damage effects was affirmed.

The first damage spot was a car engine and its accessories weighing 380 kg and thrown 75 m away. The initial velocity of the car engine was calculated to be 35 m/s based on the height of the deck from the ground and the distance by which the engine was thrown away. By simplifying the engine and its accessory, a fluid–solid couple model with the

Analysis of the bridge quality and design defect

Based on the computation of the equivalent TNT mass in the explosion, the damage mode and good quality level of the bridge were investigated. A conclusion can then be made on whether the serious bridge damage was caused by a bridge design defect.

Conclusions

In this paper, the equivalent weight of TNT in an explosion accident was estimated based on damage characteristics and goods loaded on the accident truck. Based on the analysis of this work, the damage events of the damage spots were determined based on the final determinate equivalent mass of TNT using engineering algorithms and numerical simulation. The explosion dynamic load applied to the bridge and the damage state of the accident bridge were calculated.

The results show that this accident

Acknowledgement

This work is supported by the National Natural Science Foundation of China (No. 11302261). The financial supports are gratefully acknowledged.

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