International Journal of Computer Applications (0975 – 8887)
International Conference on Advances in Emerging Technology (ICAET 2016)
Analysis of Concrete Wall under Blast Loading
Ashish Kumar Tiwari
Aditya Kumar Tiwary
Anil Dhiman
PhD Scholar
Thapar University
Patiala, Punjab
Assistant Professor
Civil Engineering Department
Chandigarh University
Associate Professor
Civil Engineering Department
JUIT, Solan
ABSTRACT
The terrorist attacks and threats are the growing problem all
over the world that not only affect the life of human being but
also affect the structure integrity and its resistance. Explosive
devices, human bomb and the other bomb equipments are the
major weapon choices for these attacks, significantly threatens
civilians and military personnel. As we know that ceasefire
and bombing activities are increasing day by day also the
terrorist attacks on major buildings can cause catastrophic
failure on the building’s external and internal structural
frames, collapsing of walls and shutting down of critical lifesafety system. Because of all these threat from such extreme
condition, effort has been made from the last few decades to
find suitable method of structural analysis and design to resist
blast load. Detail understanding is required about the blast
phenomena and the propagation of waves towards the
structure and also response of structure against such shock
waves. This paper presents a comprehensive study of concrete
wall against this dynamic loading. Concrete wall subjected to
blast loading is modeled in Finite Element package Ansys and
then analyzed in Autodyn with and without steel plate to study
the impact of blast loading.
Keywords
Blast Load, Explosion Phenomena, Material Behaviour,
ANSYS Autodyn®
1. INTRODUCTION
The terrorist attacks and threats are the growing problem all
over the world that not only affect the life of human being but
also affect the structure integrity and its resistance. Explosive
devices, human bomb and the other bomb equipments are the
major weapon choices for these attacks, significantly threatens
civilians and military personnel. A comprehensive overview
of the effect of explosion on structures and explanation of
explosion and the mechanism of blast waves in free air is
given by T.Ngo [1]. Zeynep Koccaz, Fatih Sutcu and Necdet
Torunbalci [2] shed light on blast resistant building design
theories, the enhancement of building security against the
effects of explosives in both architectural and structural
design process and the design techniques that should be
carried out. A.M. Remennikov [3] showed some of the
currently available analytical and numerical techniques that
can be employed to effectively predict loads on structures
when a terrorist weapon is detonated in urban environment.
Harvoje Draganic, Vladimir Sigmund [4] describes the
process of determining the blast load on structures and
provides a numerical example of a fictive structure exposed to
this load. The blast load was analytically determined as a
pressure-time history and a numerical model of the structure
was created in SAP2000. Manmohan Das Goel, Vasant
A.Matsagar, Anil K. Gupta and Steffen Marburg [5] providing
various blast computation equations, charts, and references in
a concise form at a single place and to serve as a base for
researchers and designers to understand, compare, and then
compute the blast wave parameters. The Recommendations
are presented to choose the best suitable technique from the
available methods to compute the pressure-time function for
obtaining structural response. A. Khadid et al. [6] studied the
fully fixed stiffened plates under the effect of blast loads to
determine the dynamic response of plates. The effect of an
external explosion on the outer reinforced concret shell of a
typical nuclear containment structure was studied by A.K.
Pandey. [7]. The effect of spherical and hemi-spherical TNT
(trinitrotoluene) in blast waves was first introduced by J.M.
Dewey [8] and also determined the density throughout the
flow by application of Lagrangian conservation of mass
equation which used for calculating the pressure by assuming
the adiabatic flow for each air element between the shock
fronts.
Analysis of structure under blast loading requires a careful
understanding about the blast phenomena and its impact on
structural elements and response of materials against such a
high strain rate loading. Analysis consists of several steps: (a)
estimation of risk; (b) determination of computational load;
(c) structural behaviour analysis; (d) selection of structural
system; (e) evaluation of structural behaviour.
2. EXPLOSION PHENOMENA
An Explosion is defined a sudden and rapid release of energy
on large scale. On the basis of nature explosion can be
categorised as physical, nuclear and chemical explosion.
Modelling and Analysis of explosive detonations requires a
good understanding of chemistry because the chemical
composition of an explosive source governs its physical
properties like detonation velocity. Explosive detonations are
products of complex physical and chemical processes within
and in the immediate vicinity of the explosive and are
accompanied by a near-instantaneous release of a huge
amount of energy in the form of heat, light and sound. The
chemical reactions involved in a detonation are thus
oxidation and exothermic reactions because the reactants are
oxidized to give a mixture of hot gaseous products. There are
two major types of oxidation reactions involved in a
detonation a) In the first type, there are two reactants, a fuel
and an oxidizer, that react to form the products of the
explosion; b) The second type of reaction, involves a single
reactant where the fuel and the oxidizer are contained in the
same molecule, which decomposes during the reaction and is
transformed into oxidized products. It is more common in
explosives.
The majority of the explosives consist of single molecules
made up of Carbon (C), Hydrogen (H), Nitrogen (N) and
Oxygen (O). These are called CHNO explosives and can be
represented by the general formula Cc Hh Nn Oo, where n, c,
h, o are the number of nitrogen, carbon, hydrogen and
oxygen atoms, respectively, contained in a molecule of the
explosive. During the decomposition reaction, the reactant
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International Journal of Computer Applications (0975 – 8887)
International Conference on Advances in Emerging Technology (ICAET 2016)
molecule breaks down into its individual component atoms as
follows:
Cc Hh Nn Oo
→
cC + h H + nN + oO
These individual atoms then recombine to form the final
products of the reaction. The order of reaction is
2N → N2
2H + O → H2O
C + O → CO
CO + O → CO2
If oxygen remains after the formation of CO 2, then the
explosive is called over-oxidized. Any oxygen left after the
formation of CO2 forms O2. However most explosives, with
the exception of nitro-glycerine and ammonium nitrate, do
not have sufficient oxygen to convert all of the carbon to CO 2
and these are called under-oxidized explosives. For such
explosives, the products of the reaction extract oxygen from
the surrounding air as they expand freely. While doing so,
these products mix with oxygen and may burn to form CO2.
These secondary reactions are part of a process known as
afterburning.
The relative amount of oxygen in an explosive is therefore an
important factor in determining the nature and reactivity of
the detonation products; it is quantitatively expressed as
oxygen balance. The heat generated by an oxygen-deficient
explosive (such as trinitrotoluene (TNT)) is less than that
generated by an explosive that oxidizes completely.
accordingly. It should be pointed out that surface structure
cannot be protected from a direct hit by a nuclear bomb; it
can however, be designed to resist the blast pressures when it
is located at some distance from the point of burst.
The rapid and sudden release of energy forms a pressure
wave in the surrounding medium, known as a shock wave as
shown in (see Figure 1a). When an explosive source burst,
the expansion of the hot gases produces a pressure wave in
the surrounding air. This wave moves away from the centre
of explosion and the inner part moves through the region that
was compressed and is now heated by the leading part of the
wave. The pressure waves moves with the velocity of sound,
the temperature is very high about 3000-4000 degree Celsius
and the pressure is nearly about 300 kilo bar of the air
causing increase in velocity. The inner part of the wave starts
to propagate faster and gradually overtakes the leading
waves. After a small interval of time the pressure wave front
becomes abrupt, thus forming a shock front (see Figure 1b).
The peak overpressure is the maximum overpressure occurs
at the shock front. Behind the shock front, the overpressure
falls very rapidly to about half of the peak overpressure and
remains almost uniform in the central region of the
explosion. As the expansion continuous, the overpressure in
the shock wave front decreases steadily; the pressure behind
the front does not remain constant, but fall off in a regular
manner. After a short time, at a certain distance from the
centre of explosion, the pressures behind the shock wave
front becomes lesser than that of the surrounding atmosphere
and so called negative-phase or suction (see Figure 2).
3. PREDICTION OF BLAST LOADING
The study and analysis of the blast loading on the structure
started in 1960’s. There are three methods available for
predicting blast load i.e. a) Empirical method; b) Semiempirical Method; c) Numerical Method.
The first method i.e. empirical methods are correlated with
experimental data. The accuracy of all empirical equations
diminishes as the explosive event becomes increasing near
field. Semi-empirical methods are based on simplified model
of physical phenomena. Extensive data and case studies is
important parameters on which semi-empirical method
depends. Numerical methods are based on mathematical
equations that describe the basic laws of physics governing a
blast problem. These principles include conservation of
energy, mass and momentum. Now these models are
commonly called as computational fluid dynamics (CFD)
models.
The key elements are the loads generated from explosive
sources, how they interact with structures and how structures
respond to them. Sources of explosion include gas, high
explosives, nuclear and dust materials. The basic features of
the blast wave and explosion phenomena are presented along
with a discussion of TNT (trinitrotoluene) equivalency and
laws of blast scaling.. The type of burst mainly classified as
a) Air Burst; b) Surface Burst; c) High Altitude Burst; d)
Underground Burst; e) Under water Burst. Here study is
limited to surface and air burst. This information is then used
to determine the dynamic loads on surface structures that are
subjected to such blast pressures and to design them
Fig. 1a: Shock wave-front
Fig. 1b: Abrupt shock wave-front
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International Journal of Computer Applications (0975 – 8887)
International Conference on Advances in Emerging Technology (ICAET 2016)
Fig 2: The variation of overpressure with distance at a given time from center of explosion
4. BEHAVIOUR OF MATERIAL AT
HIGH STRAIN RATE
Loads due to blast or explosion typically produce very high
2
4
strain rates in the range of 10 -10 s-1. This high strain rate
loading would changes the dynamic mechanical properties of
target structures and, accordingly, the expected damage
mechanisms for various structural parts and elements. For
RCC structures subjected to blast effects the strength of steel
reinforcing bars and concrete can increase significantly due to
strain rate effects. It can be seen that ordinary static strain rate
-5
is located in the range: 10 to 10-6 s-1, while blast pressures
normally yield loads associated with strain rates in the
2
4 -1
range:10 to 10 s (see Figure 3). The mechanical properties
of concrete under high strain rate loading conditions can be
quite different from that under static loading. But the dynamic
stiffness does not vary from the static stiffness; the stresses
which are sustained for a short period of time under dynamic
loading conditions may gain values that are exceptionally
higher than the static compressive strength. Strength
magnification factors as high as 6 in tension and 4 in
compression for strain rates in the range: 103-10-3/sec have
been
reported
(Grote
et
al.,
2001).
Fig 3: Strain rate associated with different types of loading
5. BLAST SIMULATION USING ANSYS
AUTODYN
ANSYS Autodyn® is a versatile explicit analysis software
tool for modelling the nonlinear dynamics of gases, solid,
fluid and their interactions. The product has been developed to
provide advanced capacities within a robust, easy-to-use tool.
Less effort is required for simulation projects, less time and
lower labour costs than with the other explicit softwares. It
saves time and effort in problem setup and analysis by options
to define contact, by interfaces coupling and by minimizing
requirements of inputs using safe logical defaults.
M30 concrete wall with different shapes with and without
steel plates is analysed in ANSYS-Autodyn to study the
behaviour of concrete in such a high strain loading. The
properties of concrete used are tabulated in Table 1.
Table 1. Properties of concrete
Properties
Value
Unit
Density
2400
Kg/m
Young Modulus
30000
Mpa
Poisson’s ratio
0.18
3
5.1 Single concrete wall (with or without
steel plate cladding)
The concrete wall is modelled in Explicit Dynamics module
of ANSYS with the plan dimensions as 5m × 3m in V and W
directions, respectively with thickness of 0.2 (see Figure
4a).The same concrete wall with steel plate having thickness
0.005 m (see Figure 4b). The analysis is done by using a
charge weight of 100 kg TNT at a height of 1m above ground
surface with a stand-off distance of 3m.
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International Journal of Computer Applications (0975 – 8887)
International Conference on Advances in Emerging Technology (ICAET 2016)
Fig 4a: Geometry of single concrete wall without steel plate cladding
Fig 4b: Geometry of single concrete wall with steel plate cladding
The concrete wall is firstly analysed for a pressure of 50 Mpa
in FE Modeller and then transferred to Autodyn for blast
scenario. Gauge point is defined at the centre of wall.
Analysis output is showed in terms of pressure contours (see
Figure 5a and 5b) and pressure time history (see Figure 6a and
6b).
without 5 mm thick plate (see Figure 7). Concrete wall is
modelled as a solid part and gauge points is defined at the
centre of these 2 solid parts. Detonation point is define at a
coordinate of -3000, 1000, -3000 in X,Y and Z directions i.e.
at an angel of 45 degree and at a height of 1m from joint.
Pressure contour and time history plot at defined gauge point.
5.2 Case 2: L shape concrete wall with or
without steel plate cladding
Analysis output is showed in terms of pressure contours of Lshape wall (see Figure 8) and Pressure-Time history (see
Figure 9).
L-shape concrete wall is modelled in geometry module of
Ansys Explicit Dynamic. Concrete wall is modelled with and
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International Journal of Computer Applications (0975 – 8887)
International Conference on Advances in Emerging Technology (ICAET 2016)
Fig 5a: Pressure contour of wall without steel cladding
Fig 5b: Pressure contour of wall with steel plate cladding
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International Journal of Computer Applications (0975 – 8887)
International Conference on Advances in Emerging Technology (ICAET 2016)
Fig 6a: Pressure time history of wall without steel plate cladding
Fig 6b: Pressure time history of wall with steel plate cladding
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International Journal of Computer Applications (0975 – 8887)
International Conference on Advances in Emerging Technology (ICAET 2016)
Fig 7: Geometry of L-shape concrete wall without and with steel plate cladding
Fig 8a: Pressure contour of wall without steel plate cladding
Fig 8b: Pressure contour of wall with steel plate cladding
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International Journal of Computer Applications (0975 – 8887)
International Conference on Advances in Emerging Technology (ICAET 2016)
Fig 9a: Pressure-Time history without steel plate cladding
Fig 9b: Pressure-Time history with steel plate cladding
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International Journal of Computer Applications (0975 – 8887)
International Conference on Advances in Emerging Technology (ICAET 2016)
5.3 Case 3: U-shape wall without and with
steel plate cladding
Another shape of concrete wall is used to study the behaviour
of blast pressure on wall without steel plate and with steel
plate. The geometry of C-shape (in plan) concrete wall along
with dimensions is shown (see Figure 10). The detonation
point is same as used in case 2 and gauge point are defined at
the centre of middle wall. End conditions are fixed and steel
plate is bonded with concrete at the outer side which is
exposed to explosion source. The pressure contour and
pressure time history plots for this case is showed below (see
Figure 11 and Figure 12).
Fig 10: Geometry of wall without and with steel plate cladding
Fig 11a: Pressure contour of wall without steel plate cladding
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International Journal of Computer Applications (0975 – 8887)
International Conference on Advances in Emerging Technology (ICAET 2016)
Fig 11b: Pressure contour of wall with steel plate cladding
Fig 12a: Pressure-Time history plot without steel plate cladding
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International Journal of Computer Applications (0975 – 8887)
International Conference on Advances in Emerging Technology (ICAET 2016)
Fig 12b: Pressure-Time history plot with steel plate cladding
6. CONCLUSION
It is observed from literature survey that for the estimation of
blast load or pressure the empirical approach (Kinney and
Graham’s) proves to be ideal as blast phenomenon is complex
in nature. Complexity arises due to unpredictability of charge
weight and standoff distance, the behavior of material under
different loading conditions and post blast triggering events.
Ansys Autodyn is an efficient and user friendly tool for
simulating explosives and impact loading linking it with
workbench environment. The blast simulation was carried out
using JWL as equation of state for explosive materials. The
concrete walls of different shapes with or without steel plates
cladding are analyzed in Autodyn to obtain pressure contours
and pressure time history plots to study the behavior and
effect of using steel. Autodyn Simulation gave good estimate
of pressure time history of observed positive and negative
phase. Pressure contour and time history plots signify that
using a steel plate reduces the effect of blast pressure on the
concrete wall thus reducing the damage due to pressure
created by the 100 kg TNT with standoff distance and height
of 3 m and 1 m. Similar observation goes for other plan
shapes. The pressure time history plots shows that in case of
L- shape wall without steel plate blast pressure fluctuates
throughout the cycle but in case wall with steel plate pressure
is initially negative but after completion of certain cycle the
value changes to positive itself. This is due to the bonded steel
plate. Also it is found that pressure is reduced by large amount
due to steel plate. In case of U-shape concrete wall, pressure
time history plots clearly shows the impact and pressure on
concrete wall is reduced by large amount by using a 5mm
thick plate. It has been observed that in case of steel plate with
concrete wall initially pressure is negative but after some
cycles and time the pressure becomes positive but less then
pressure on concrete wall without steel plate.
7. REFERENCES
[1] T. Ngo, P. Mendis, A. Gupta & J. Ramsay 2007, “Blast
Loading and Blast Effects on Structures – An Overview”,
EJSE Special Issue: Loading on Structures.
[2] Zeynep Koccaz, Fatih Sutcu and Necdet Torunbalci
2008, “Architectural and Structural Design for Blast
Resistant Building.”, the 14th World Conference on
Earthquake Engineering
[3] Alexander M. Remennikov 2003, “A review of methods
for predicting bomb blast effects on buildings”, Journal
of battlefield technology, vol 6, no 3. pp 155-161.
[4] Harvoje Draganic, Vladimir Sigmund, “Blast Loading on
Structures”, UDC/UDK 624.01.04:662.15, ISSN 13303651
[5] Manmohan Das Goel, Vasant A.Matsagar, Anil K. Gupta
and Steffen Marburg 2012 “An Abridged Review of
Blast Wave Parameters”, Defense Science Journal, Vol.
62, No. 5, pp. 300-306.
[6] A. Khadid et al. 2007, “Blast loaded stiffened plates”
Journal of Engineering and Applied Sciences,Vol. 2(2)
pp. 456-461.
[7] A.K. Pandey et al. 2006 “Non-linear response of
reinforced concrete containment structure under blast
loading” Nuclear Engineering and design 236. Pp 9931002.
[8] J.M. Dewey, 1971 “The Properties of Blast Waves
Obtained from an analysis of the particle trajectories”,
Proc. R. Soc. Lond. A.314, pp. 275-299.
[9] Kirk A. Marchand, Farid Alfawakhiri 2005 “Blast and
Progressive Collapse” fact for Steel Buildings, USA.
[10] M.V.Dharaneepathy et al. 1995 “Critical distance for
blast resistance design”, computer and structure Vol. 54,
No.4.pp.587-595.
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International Journal of Computer Applications (0975 – 8887)
International Conference on Advances in Emerging Technology (ICAET 2016)
[11] P.Desayi and S. Krishnan. 1964, “Equation for the stressstrain curve of concrete”. Journal of the American
Concrete Institute, 61, pp 345-350.
load”. Civil Engineering Department,
Virginia.
Blacksburg,
[13] ANSYS Theory manual, version 5.6, (2000).
[12] Ronald L.Shope. 2006 “Response of wide flange steel
columns subjected to constant axial load and lateral blast
IJCATM : www.ijcaonline.org
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