Keywords

1 Introduction

Blast loads are dynamic in nature and they cause catastrophic damage to the structures. An explosion releases a lot of energy in the form of light, heat, sound and shock waves. These waves can propagate through the structure in a very short duration and lead to the collapse of the structure. So, there is a significant need to design the structure as a blast-resistant structure. Structural irregularities also play a prominent role in designing blast-resistant structures. Therefore, it is important to understand these factors before designing. In this paper, we gathered the available literature on the blast loads on the structures and explained the special problems while defining the loads.

Terrorists attack by explosive loading along border territory by targeting both government buildings and also civilian houses. On the safety issue, the vulnerability of structures to blast loads must be protected. The explosives during a blast release huge kinetic energy and also produce heavy blast waves comprising of the pressure of about 3–5 kPa or even more [1].

1.1 Aims of the Study

The myth of blast is catastrophic causing loss of life and permanent structures. The residuals left after a blast pose threat to the environment for a long period. Increasing blast loads of the twenty-first century like the Beirut explosion and WTC blasts are the burning examples. India had to suffer from Improvised Explosive Device (IED) blasts in 337 numbers (2017), 268 (2015), 190 (2014), 283 (2013) and 365 (2012), respectively, as per NBDC data (National Bomb Data Centre, India). Therefore, it is high time that either we have to think of dissolution methods, or we shall have controlled blasting. For terrorist blast loads, structures must be blast-resistant (The Economic Times news, S. K. Gurung, Jul 12, 2018, 10:34 PM).

1.2 The Objective of the Present Paper

The following are the objectives of the present paper:

  • To review the studies done by the various researchers on blast load effects on different RC and Steel-framed structures.

  • To review various works done on blast effect on framed structures with different irregularities, viz., Geometric, Stiffness, Mass irregularities, etc.

  • To review the blast loads and blast-affected structures.

2 Literature Review

Terrorism is one of the major threats to humanity and its property. Gradually, the Naxal/terrorist groups are becoming unstructured and hostile to use blast loads to attack the public and their structural possessions like bridges, towers and structures.

The summary of timeline key inferences obtained from the various literature survey done from 1995 to 2018 is shown in Table 1.

Table 1 Chronological inferences derived from the literature survey
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2.1 Recent Studies on Blast Loads

Kumar et al. [41, 43] studied the performance of symmetric RC space framed buildings subjected to seismic and impact loads. They used time history analysis to study the response of the considered building. From their study, it has been observed that the maximum lateral displacement for a surface blast of 2500 kg TNT and seismic load were comparable at all storey levels. This maximum lateral displacement was obtained at 5 s in buildings subjected to the Northridge earthquake, while it was obtained at 0.5 s in the same building subjected to a surface blast of 2500 kg TNT. Applied Element Method-based software was used for their study.

Vangipuram et al. [44] observed that Blast loads do not act uniformly and may be symmetrical or skew. While designing for blast loads the reflected peak pressure and temperature varies at different points in a structure with diminution of the standoff distance.

Megha and Ramya [45] studied the impact of the blast load on buildings. A six-storey building is considered for the study. The building is modelled using ETABS 2016. The building is subjected to different charge weights of 200 g, 400 and 600 kg with a standoff distance of 20, 40 and 60 m. Blast parameters are determined as per the guidelines of IS:4991–1968. The time history analysis is carried out and the response of the structure is determined in terms of displacement versus time, velocity versus time and acceleration versus time. To make the building more resistible against blast load, shear walls and steel bracings were implemented. The results conclude that the storey displacement, storey drift and column forces are high when the blast is at a distance of 20 m from the building. The displacement and drift are more when the charge weight and distance are less.

Sunita and Bharati [46] have studied the effects of surface blasts on multi-storey buildings. Four seismically designed RC structures with 3, 6, 9 and 12 heights were considered. The parameters considered are standoff distance and charge weight. The non-linear time history analysis is used to obtain the response of the building. For analysis, SAP2000 software has been used. Charge weights of 500 kg TNT and 1000 kg TNT at a standoff distance of 5, 10, 15, 30, 40 and 60 m were considered for analysis. The results conclude that base shear produced by ground shock is greater than the base shear produced by air pressure for all the standoff distances in both high-rise and low-rise buildings. With the increase in charge weight, the effect of the ground shock increases more than air pressure.

2.2 Models Developed

Models are developed for finding the parameters of the shock waves generated by the blast loads based upon the scaled distance, and they are compartmentalized as Airburst (free air) and Surface burst models. The different burst models are the Brode mode (Brode [48]), Henrych and Major mode (Henrych et al. [49]), Held’s Model (Held [50]), Mill’s mode (Mills [51]), Sadovskiy mode (Sadovskiy et al. [52]), Bajie model (Bajie [53]) and Kinny & Graham model (Kinny et al. [54]) which is the development of the US Army TM5-855–1 model [55].

Similarly, the surface burst models developed by different researchers are Newmark & Hansen model (Newmark et al. [56]), Swisdak model (Swisdak [57]), Wu and Hao model (Wu and Hao [58]), Siddiqui and Ahmad model (Siddiqui et al. [59]), Iqbal and Ahmad model (Iqbal et al. [60]) and Badshah model (Badshah [61]).

2.3 Lapses and Research Gap

Investigating the past works, it is ascertained that a large number of works have been done on blast loads on regular and irregular structures, standoff distances and charge weight variations and behaviour on different types of buildings (SIMCON or SIFCON) than RCC structures. However, it is found that the impact on blast loads on the framed structure was meagre.

3 Preface to Blast Loads

3.1 Blast Materials

The blast materials (explosives) are a solid or liquid base that should have the properties as follows: The material is normal at ground state but undergoes a chemical change when stimulated, mainly Tri-nitro Toluene main base structure. This reaction may yield a very high temperature, huge amount of gases and produces explosion and undergoes exothermic reaction. The controlled explosions are intended during quarry blasting, demolition of structures, shaping foundation and tunnel excavation within a mountainous base.

The health issues (trauma/death) associated with improvised explosive device (IED) spasm are overpressure damage (heart, lungs, abdomen and other sensitive organs); fragmentation injuries from flying debris; thermal injuries, impact injuries, fall injuries and toxic exposure injuries (John Pichtel [62]).

3.2 Field Test Results

To have experimented on blast loads, it is difficult to conduct and generally military laboratories are preferred. Field tests are conducted by various researchers for different blast materials and the results are summarized in Table 2.

Table 2 Field tests for different specimens, explosives and standoff distance researches in the past
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Regarding Table 2, the notation followed is as follows:

RCC: Reinforced cement concrete;

RC + ACJ: Reinforced concrete with advanced composite jackets;

ALFC: Reinforced cement concrete with aluminium foam claddings;

FRC: Fibre-reinforced concrete;

SFRC: Steel fibre-reinforced concrete;

LCFRC: Long carbon fibre-reinforced concrete.

3.3 Discussion

Structures could not be completely safe and riskless. It is always against a distinct risk level. The distresses occurred to the building by an earthquake, blast loads and hurricane loads can be at a reduced level, and the distresses caused to the building shall be less. The mitigation strategies for the reduction of the threat level from blast loadings are strict surveillance through diligent intelligence, well vigilant security system, enhancing standoff distance between the approach to the target, constructing blast walls for attenuation of shocks, proper landscaping with the optimized alignment of the structure and constructing structural elements, to absorb the blast load impact.

4 Conclusions

After studying the above literature, the following conclusions have been drawn:

  1. 1.

    As the standoff distance increases, the blast pressure decreases and vice versa.

  2. 2.

    As the charge weight increases, the blast pressure increases.

  3. 3.

    The regular structure has higher resistance than the irregular structure.

  4. 4.

    The dynamic behaviour of SIMCON buildings is better than RCC buildings.

  5. 5.

    Dampers or stiffeners can be used to resist such heavy loads, and also joints should be designed to resist such heavy moments.

  6. 6.

    The dynamic behaviour of the SIFCON frame is better than that of the RCC frame.

From the literature review, it has been observed that no studies are made on the performance of Reinforced Concrete Framed structures subjected to blast loads by considering Soil-Structure Interaction.