Comparative Study of Response of Structures Subjected To Blast and Earthquake Loading

Aditya C. Bhatt.et al. Int. Journal of Engineering Research and Applications www.ijera.com
ISSN: 2248-9622, Vol. 6, Issue 5, (Part - 2) May 2016, pp.62-66
www.ijera.com 62 | P a g e
Comparative Study of Response of Structures Subjected To Blast
and Earthquake Loading
Aditya C. Bhatt1
, Snehal V. Mevada2
, Sumant B. Patel3
1
P.G. Student, 2
Assistant Professor, 3
Associate Professor,
Structural Engineering Department,
Birla Vishvakarma Mahavidyalaya [Engineering College], Vallabh Vidyanagar, Gujarat, India.
ABSTRACT
The increase in the number of terrorist attacks especially in the last few years has shown that the effect of blast
load on building is a serious challenge that should be taken in to consideration for designing of structures. This
type of loading damages the structures, externally as well as internally. Hence the blast load should be
considered with same importance as earthquake load. The present study includes the comparative performance
of G+3 storey building subjected to blast and earthquake loading using ETABS. For four storey building using
different input parameters like charge explosive, stand-off distance and layout of building the blast pressure are
conducted and linear time history analysis is carried out. Comparative study for blast and earthquake loading is
carried out for different parameters like maximum storey displacement, storey drift and quantity of materials.
Safe charge explosive and safe stand-off distance are obtained for the RCC structure with the sections of
structural elements same as per the requirement for earthquake resistance. Displacement is higher for the blast
loading as compared to earthquake loading and very high for the storey at which blast load is applied. Quantity
of concrete is 40 percentages higher for blast resistant building than the earthquake resistant building.
Keywords: blast, earthquake, explosion, charge weight, safe stand-off distance
I. INTRODUCTION
Protecting civilian buildings from the threat of
terrorist activities is one of the most essential
challenges for structural engineers. Events of the
past decades have greatly increased the
attentiveness of structural designers about the threat
of terrorist attacks using explosive devices.
Extensive research into structural analysis
considering blast effects and techniques to protect
buildings has been initiated in many countries to
build up methods for protecting critical
infrastructure and the built environment. There are
a number of means available to prevent a booming
terrorist attack on a building [3]
. Structures analysed
for blast loads are subjected to entirely different
types of load than that considered in conventional
design. Here structures are subjected to quickly
moving shock wave which may exert pressures
many times greater than those experienced under
the greatest of hurricanes. However, in blast
phenomenon, the peak intensity lasts for a very
small duration only [1]
. The blast can generally
categorize as external and internal blast. External
blast can further recognized as surface burst or air
burst.
An explosion which is located at a distance from
and above the structure is known as air burst
explosion, while surface blast will occur when
detonation is situated close to or on the ground. An
internal or confined explosion will produce shock
loads or, gas pressure loads from the confinement
of the products of the explosion. This pressure has
a long duration in comparison to that of the shock
pressure, due to external explosion. Due to highly
uncertainty in predicting blast loads, it is difficult
to construct blast proof building. But various
structural and non-structural precautions can be
taken to minimize structural damage and physical
injuries [5]
.
Shallan et al. [3]
showed that the effect of blast load
decrease with increasing the standoff distance from
the building and with variation of the aspect ratios
of the buildings there is no variation in the
displacement of the column in the face of the blast
load but with increasing the aspect ratio the effect
of blast load decrease in other element in the
building. Kashif and Varma (2015) [1]
analysed a
five storey RCC symmetric building for blast load
for 100 kg and 500 kg of Tri-Nitro-Toluene placed
at 30 m distance from point of explosion. It was
concluded that building was not behaving as a
RESEARCH ARTICLE OPEN ACCESS

cantilever structure under blast load, which is
different from the earthquake and wind. Results of
the performance level of building, maximum
displacement , plastic hinges locations were
defined and compared for both 100 kg and 500 kg
TNT explosives.
Based on the literature review carried out, it is
observed that some researchers have investigated
the effect of blast load on structures. However there
is a need for detail parametric investigation in this
area. Following are the main objective of the
present study. i ) To obtain the response of multi
storied structures under blast and earthquake
loading. ii) To obtain the safe standoff distance for
multi storied building which is safe in earthquake.
1.1 Blast Load And Earthquake Load
Similarities and differences between seismic and
blast loading are noticeable. Both of these loads are
dynamic loads and they produce dynamic structural
response. The structural behavior in response to
these loads is inelastic as well. The focus of
structural design against these loads is on life safety
as opposed to preventing structural damage.
Differences between blast and seismic loading are
presented in Figure 1. [7]
II. NUMERICAL STUDY
In the numerical study carried out herein, the G + 3
storied RCC building is considered.. Figure 2
shows the plan and 3D view of the building
considered. Table 1 represents the physical
properties and input parameters of the considered
building. The analysis and design is carried out in
ETABS software.
For G+3 storied RCC building, both blast and
earthquake loading are applied. Comparative study
has been carried out for the same for different
criteria like storey displacement, storey drift and
quantity of concrete. For the earthquake resistant
building, calculation of both safe charge-explosive
and safe stand-off distance have been carried out
2.1 Methodology
First of all consider the buildings subjected to a
blast equivalent in yield to some tonne of TNT at a
certain standoff distance. For the dynamic analysis
of structures, the blast effects are most
conveniently represented by a loading-time history
which is applied to the structural members as
transient loading. The magnitude and the pressure-
time history of the blast load is calculated as per IS
4991-1968. Then pressure calculated is applied as
UDL on column. Linear time history analysis is
carried out and the response of structure is obtained
subjected to blast loading.
2.2 Blast Load Calculation as per the IS
4991:1968.
For the study carried out herein explosive of 0.1
tonne TNT equivalent is considered. Building is
situated 21 m from the ground zero. Analysis of the
same building is carried out for Blast load
combinations. Table 2 shows the blast parameters
for 0.1 Tonne TNT and 21 m stand-off distance.
Table 3 reprents the load combination considered
in the present study.
2.2.1 Characteristics of the blast load
Scaled distance = 21/ (0.1) (1/3)
= 45.243 m
Assuming pa = 1 kg/cm² ( From IS 4991:1968,
Table: 1)
Sr.
No.
Parameter Value
1 Height of the story 3.5 m
2 Span of each bay 5 m
3 Plan dimension of
building
15 m x 15
m
4 Number of storey G+3
5 Grade of concrete M25
6 Height of plinth 1.5 m
7 Zone V
8 Importance factor 1
9 Soil type Medium
Figure 1: BLAST AND SEISMIC WAVES
Table 1: PROPERTIES OF BUILDING

q0 = 0.142 kg/cm2
t0 =31.25 * (0.1) 0.33
= 14.505 milliseconds
td =21.6 * (0.1) 0.33
= 10.026 milliseconds
M = 1.25
a = 344 m/s
U = 0.43 m/milliseconds
2.2.2 Blast Pressure on the building
S is lesser of H or B/2 = 7 m
tc = 3S/U = 10.026 milliseconds
tt = l/U = 34.884 milliseconds
tr = 4S/U = 65.116 milliseconds
As tr>td there is no pressure on back face
For roof & sides (from IS 4991:1968 Table 2)
For front face Cd = 1
For roof and side face Cd = -0.4
ps0 + Cdq0 = 59.15 kN/m²
EARTHQUAKE BLAST
1.5*DL+1.5*LL 1.5*DL+1.5*LL
1.2*DL+1.2*LL±1.2*EQX±1
.2*EQY
1.2*DL+1.2*LL+
1*BL
1.5*DL+±1.5*EQX±1.5*EQ
Y
1.5*DL+1*BL
0.9*DL+±1.5*EQX±1.5*EQ
Y
0.9*DL+1*BL
Figure 3 shows the isometric view of the building
in which blast load is applied as udl to the column.
Figure 4 shows the pressure-time diagram for the
front and side faces for the considered blast
loading. For the earthquake loading linear static
analysis is considered.
2.3 Comparative Study of G+3 Storied Building
For Blast And Earthquake Loading
2.3.1 Displacement Comparison
Figure 5 shows the storey displacement for blast
and earthquake loading. Total four cases are
discussed here. „BLAST-EQ SECTION‟ means,
the blast load is applied in the building which is
designed for Earthquake resistance. „BLAST-
REVISED SECTION‟ means the section provided
are revised based on the representation of blast
resistance, In this case, 0.1 Tonne TNT is
considered. The third case of „EQ-section‟, the
Table 3 : LOAD COMBINATIONS FOR EARTHQUAKE AND
BLAST LOAD
Figure 3: BLAST LOAD APLLIED AS UDL AT FRONT FACE
Table 2 : BLAST PARAMETERS FOR 0.1 TONNE TNT AND
21 M STAND-OFF DISTANCE

sections are designed only for earthquake loading.
In the last case of „EQ SECTION SAFE IN
BLAT‟, the maximum charge weight is obtained to
make the earthquake resistant building safe during
blast. The charge weight for each case in
mentioned in the bracket From the figure 5, it is
observed that the storey displacement for blast
loading is higher than the same for earthquake and
at level 1st
and 2nd
storey displacements are higher
in comparison to other storey level. But in case of
Earthquake load the displacement is proportionally
increasing.
2.3.2 Storey Drift Comparison
As far as the structural as well as non structural
safety of building in terms of functional aspect is
concerned the storey drift is a critical parameter.
Figure 6 shows the storey drift for blast and
earthquake loading. From the figure 6 it is observed
that for the earthquake load, the storey drift comes
out to be within permissible limit specified by
code. Whereas, in the case of blast load the storey
drift exceeds than the permissible limit specially on
the storeys where blast is applied.
2.4 Quantity of Material
Table 4 shows the size of the optimum sections
which are designed for blast resistant and
earthquake resistant building. From the table 4 it is
observed that the blast resisting building is having
mostly same size of beams but size of columns is
much more up to the plinth and at the level where
blast load applied. Table 5 represent the difference
of quantity of concrete between blast resistant and
earthquake resistant. From the table 5 it is observed
that the quantity of concrete for the blast resistant
building is 40 percentage higher than the
earthquake resistant building as higher section are
required for blast case.
2.4 Safe Charge explosive and Safe Stand-Off
Distance Calculations
Safe charge explosive and safe stand-off distance
for earthquake resistant RCC building is obtained
by trial and error method. The safe charge
explosive and safe stand-off distance are obtained
as 0.03 tonne TNT and 31.5 meter respectively.

III. CONCLUSIONS
Behaviour of structures subjected to blast load as
compared to earthquake load is significantly
different as the blast pressure is of very high
intensity which is applied in milliseconds in form
of impact load. Based on the numerical study
carried out herein the following major conclusions
are drawn.
 In blast, the storey displacement is higher than
the same for earthquake and at 1st
and 2nd
storey, displacements are higher in comparison
to other storey level. But in case of earthquake
load, the displacement is proportionally
increasing.
 As far as the structural as well as non structural
safety of building in terms of functional aspect
is concerned, the storey drift is a critical
parameter. For earthquake load, the storey drift
comes out to be within permissible limit
specified by code. Whereas in the case of blast
load, the storey drift exceeds than the
permissible limit specially on the storeys
where blast is applied.
 Quantity of concrete for blast resistant building
is around 40 % higher than the earthquake
resistant building.
 Safe charge explosive of 0.03 Tonne TNT is
obtained for the RCC structure with the
sections of structural elements same as per the
requirement for earthquake resistance.
 For the earthquake resistant RCC building, the
safe stand-off distance is 31.5 m for the charge
weight of 0.1 Tonne TNT.
REFFERENCES
[1] Kashif, Q., and Verma, M. B.,(2014),
“Effect of Blast on G+4 RCC Frame
Structure”, International Journal of
Emerging Technology and Advanced
Engineering, 4(11),pp-145-149.
[2] Marjanishvili, S., and Agnew E.,(2006),
“Comparison of various procedures for
progressive collapse analysis”, Journal of
performance of constructed facilities,
20(4),pp-365-374.
[3] Rose, T.A., Smith, P.D. and Mays, G.C.
The effectiveness of walls designed for the
protection of structures against airblast
from high explosives. Proceedings of the
Institution of Civil EngineersStructures
and Buildings. 1995; 110(1):78-85
[4] Shallan, O., Eraky, A., Sakr, T. and Emad,
S.,(2014), “Response of Building
Structures to Blast Effects”, International
Journal of Engineering Innovative
Technology, 4(2), pp-167-175.
[5] Singla, S., Singla, P., and Singla,
A.,(2015), “Computation of blast loading
for a multi storeyed framed building”,
International Journal of Research in
Engineering and Technology,4(2),pp-759-
766.
[6] Zhao, C.F., Chen, J.Y., Wang, y., Lu,
S.J.,(2012),” Damage mechanism and
response of reinforced concrete
containment structure under internal blast
loading”, Journal Theoretical and Applied
Fracture Mechanics,61,pp-12-20
[7] IS Code IS: 4991-1968 ―Criteria for blast
resistant design of structures for explosion
above ground‖, Bureau of Indian
Standards (1968)
[8] Web: www.wbdg.com , Hinman
E,(2011),”Blast safety of the building
envelope”, whole building design guide.

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