Analysis of Blast Resistance Structure

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 04 Issue: 08 | Aug -2017 www.irjet.net p-ISSN: 2395-0072
© 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 1807
ANALYSIS OF BLAST RESISTANCE STRUCTURE
Mr.Chandrashekhar1, Prof.N.S.Inamdar2,
1Student, Structural Engineering, B.L.D.E.A’s P.G.H.C.E.T Vijayapura
2Assist. Prof. Dept of Civil Engg. B.L.D.E.A’s P.G.H.C.E.T Vijayapura
--------------------------------------------------------------------------***--------------------------------------------------------------------------
Abstract: The effect of blast load on building is a serious
matter that should be taken into consideration in the
design. Even though designing the structure to be fully
blast resistant is not a realistic and economical option. We
can even improve the new and existing building to ease the
effect of a blast. In this study we have analysed the effects
caused by the blast loads and to find ways to reduce the
effects using Etab-2013 software. From these studies we
conclude that the variation could be analysed on
unsymmetrical structures.
Keywords: Blast Resistant structures, Stand-off
distance, Blast loading, Scaled distance.
1. INTRODUCTION
Since from few years, structures which are
subjected to blast loading have got importance hence
these are taken into consideration for design. Commonly
in conventional building blast load is not considered in
design because the magnitude of effect is high, it leads
towards uneconomical in both design and construction.
Due to blast, the buildings are liable to damage. Due to
recent past blast attacks in the country trigger the minds
of developers, architects and engineers to find the
solution to overcome the blast effects and to avoid the
disasters of the buildings.
Tall buildings majorly targeted structure. Tall
structures are designed primarily according to the needs
of purposeful requirement whether it is commercial,
residential or both. The technology developments, the
high performance materials discovery, new construction
techniques and the upward transportation made
possible the building of super tall structures. Some high-
rise buildings are built to enhance the prestige of a
nation, city or people. Tall buildings are also constructed
for many other reasons. In many big cities there is no
enough space due to the rapid growth of population and
increase in the number of people moving-to the cities.
The desire to preserve some land for agricultural
purpose, the high cost of land, the demand of business to
be as close as possible and some other factors have
contributed to drive buildings upward to create more
useable space in less land.
1.1 Problem statement
Most buildings are commonly designed for
conventional loads. Explosions costs catastrophic
damage and the trauma to society can be severe. There is
also an increase of threats to structures and terrorists
activities due to political and social instabilities in many
different parts of the world. An effective security system
may reduce to potential threat of an attack, but it will
never entirely eliminate its occurrence. Commercial
buildings are built quite differently compare to military
structures and are vulnerable to blast and ballistic
effects. On the other hand, one of the main challenges
associated with blast loading is that the information
related to blast phenomenon is scattered in many
different sources. What is more, certain information in
the field of blast effects remains classified and cannot be
accessed by all engineers.
Design consideration against explosion is very
important in high-rise facilities such as public and
commercial tall buildings. Therefore, it is important to
gather the available literature review on explosives, blast
phenomena, blast wave interaction and response of
structures to blast loads.
1.2 Objectives
This study is concerned with the behaviour of tall
structures when subjected to external explosion. The
objectives are as follows:
1. To understand the behaviour of blast of high rise
buildings by response spectrum analysis.
2. Modelling and analysis of high-rise building
models for external explosion.
3. Study and compare the behaviour of different
building models for analysed results.
1.3 Scope and Limitations of the study
The study focuses on the modelling of a
reinforced high rise building using ETABS program and
analysing its behaviour when subjected to blast loads.
The blast loads are calculated using the IS code IS: 4991-
1968. In this study the tall structure is assumed to be
isolated loaded by a blast explosion. Two different blast
magnitudes of 100kg and 300 kg, stability of the
structure is found out at a two different standoff distance
of 20m and 30m with R.C. Frame models.
2. METHODOLOGY
2.1 Introduction
Method Used: Response Spectra Analysis.
Response spectrum analysis is nothing but a
analysis or calculation of peak response at the time of
earthquake without using time history is known as
response spectrum analysis. Analysis can be done by

using the graph from IS-1893. It is plot of single degree
of freedom of response for various values period.
Figure 1.1: Design response Spectrum
2.2 Structural model
In this study, I have considered 12 story building.
The area of the building is 96 m2. The height of the each
story is 3m throughout the model or structure and mass
distribution is uniform over the height of the structure.
Plan of the building is shown below in figure 3.2 a.
Figure 3.2: Building Plan
2.3 Different Cases for Analysis
Case 1: Blast of 100kg explosive with standoff
distance of 30 m
TYPE 1 MODEL - Conventional frame structures.
TYPE 2 MODEL -Conventional frames with increased
column & beam sizes.
TYPE 3 MODEL -Conventional frames with addition of
shear walls at the corners.
steel bracing at the corners.
distance of 20 m
TYPE 2 MODEL -Conventional frames with increased
distance of 30 m
TYPE 2 MODEL - Conventional frame with increased
TYPE 3 MODEL - Conventional frames with addition of
distance of 20 m
TYPE 2 MODEL - Conventional frames with increased
Table 3.1: Cases Detailing of Different Models
STANDOFF
DISTANCE
(m)
BLAST
LOAD
(kg)
TYPE OF
MODEL
COLUMN
SIZES
(mm)
BEAM
SIZES
(mm)
Case 1 30 100
1 ,3 and 4 1200X1200 1200X800
2 1500X1500 1500X900
Case 2 20 100
1 ,3 and 4 1000X1000 200X650
2 1850X1850 1850X900
Case 3 30 300
1 ,3 and 4 1800X1800 1800X800
2 1950X1950 1950X900
Case 4 20 300
1 ,3 and 4 3000X3000 2000X800
2 3000X3000 2000X900
2ISMB600 is used for bracing system.
Shear wall thickness is 200mm
SEISMIC LOADING ZONE AS PER IS-1893
Figure 3.3: Type 1 Model

2.4 Input details
Table 3.2: Earthquake parameter
Detail Value
R 3
I 1
Z III
Sa/g 2
Where,
Z = Zone R = response reduction factor
Sa/g = Soil type II I = Importance factor
Table 3.3: Grade of Concrete
MODEL TYPEMATERIAL PROPERTIES ALL Model
Column / Wall M40
Beam M35
Slab M25
Thickness of the slab is 150mm.
Thickness of the wall is 200mm.
Unit weight of concrete is 25kN/m3.
2.5 Static load assignment
Dead Load, Live Load, Floor Finish, and Earth Quake
Load these are the loads considered in all 4 models.
i. Dead Load: This load is considered from IS-875 part
1-1987 (Table 1). Unit weight of RCC is 24.80kN/m3-
26.50 KN/m3. From the code book, 25kN/m3is
considered as unit weight of RCC. Dead load includes
the self-weight and floor finish of 1.5 KN/m2.
ii. Imposed Load: this load is obtained from code book
IS-875-1987 (PART 2) table 1. 4.0kN/m2 is assumed
as the UDL on the building.
On roof 1.5 KN/m2, and
On floors 4.0 KN/m2
iii. Earthquake Load: As per code IS 875-1987
part2 from Table1. The structure is assumed to be in
Zone-II. As per Table 2 of IS 1893 – 2002 zone factor is
considered. 5% damping is assumed, 1 as importance
factor considered from table 6 of IS 1893-2002.
Response reduction factor R is considered as 3 in this
case.
Soil type II, Importance factor is 1.
2.6 Load combinations: The combination of load is
taken from code IS 1893-2002 page 13.
DL earthquake in x direction= (DL+LL+FF+SPECX) 1.2
DL earthquake in y direction= (DL+LL+FF+SPECY) 1.2
Table 3.4: Blast load calculation
CASE1 CASE2 CASE3 CASE4
Blast Of (kg) 100 100 300 300
Standoff
Distance (m)
30 20 30 20
Scaled
Distance (m)
64.13 42.75 44.63 29.75
PU I I I I
Pso 0.35 0.71 0.67 1.41
Pro 0.81 1.81 1.68 4.26
qo 0.042 0.61 0.14 0.50
to 17.5 30.61 20.85 24.21
td 13.15 20.96 14.4 15.93
M 1.14 1.26 1.25 1.72
a 344 344 344 344
U 0.39 0.43 0.43 0.59
Bay Spacing
(m)
4 4 4 4
H 12 12 12 12
B 8 8 8 8
L 12 12 12 12

S 12 12 12 12
Story Ht (m) 3 3 3 3
tc 91.79 82.79 83.72 60.84
tc 30.59 27.59 27.90 20.28
tr 122.39 110.39 111.62 81.12
for roof and
sides Cd
-0.4 -0.4 -0.4 -0.4
Pso+Cd(qo) 0.33 0.47 0.61 1.21
Loads on front face joints (kg/m2)
L On Center
joint
972 2180.4 2016 5112
L On Side
Joints
486 1090.2 1008 2556
L On Edge
Joints
243 545.1 504 1278
Loads on Roof & side walls (kg/m2)
L On Center
joint
399.84 565.44 734.4 1457.32
L On Side
Joints
199.92 282.72 367.2 728.66
L On Edge
Joints
99.96 141.36 183.6 364.33
2.7 Analysis input
Table 3.5: Response spectra analysis input for all 4 types
of models.
TYPES OF MODELS ALL MODEL
R VALUE 3
Importance factor 1.0
structural and function damping 0.05
model combination CQC
directional combination SRSS
response spectra input (9.81)/(2)(3)
eccentricity ratio 0.05
3. RESULTS & DISCUSSION
Case-1: Blast of 100kg explosive with standoff distance
of 30m.
3.1 Frequency and Time Period
3.1.1 Time Period (sec)
Table 4.1: Time Period vs Modes
TP-T1.1 TP-T1.2 TP-T1.3 TP-T1.4
1 0.560531 0.471301 0.480266 0.471096
2 0.496807 0.416548 0.430791 0.42576
3 0.346143 0.281978 0.221467 0.264785
4 0.183875 0.15142 0.152155 0.160299
5 0.180294 0.148629 0.146586 0.155097
6 0.143775 0.11561 0.090726 0.112793
7 0.091443 0.074044 0.073187 0.076948
8 0.090099 0.073164 0.071147 0.076486
9 0.075406 0.060487 0.051194 0.058568
10 0.060171 0.047894 0.047364 0.053653
11 0.059412 0.047386 0.04645 0.051116
12 0.052497 0.041516 0.035098 0.041786
Figure 4.1: Time Period vs modes
As we can see in the above values the time
period gradually decreases as the modes increases.
When the time periods are compared with four different
models it is seen that the time period is more in model 1
while least in model 3. The graph is then plotted time
period with respect to modes.
3.1.2 Frequency (cyc/sec)
Table 4.2: Frequency vs Modes
FR-T1.1 FR-T1.2 FR-T1.3 FR-T1.4
1 1.784023 2.121786 2.082179 2.12271
2 2.012854 2.400684 2.321311 2.348741
3 2.888979 3.546376 4.515345 3.776649
4 5.438477 6.604147 6.572245 6.238342
5 5.546496 6.728162 6.821934 6.447578
6 6.955312 8.649771 11.0222 8.865798
7 10.93577 13.50548 13.66363 12.99579
8 11.0989 13.66792 14.05541 13.07429
9 13.26154 16.53248 19.53354 17.07417
10 16.6193 20.87944 21.11308 18.63829
11 16.83162 21.10328 21.52853 19.56335
12 19.04871 24.0871 28.49165 23.93146
0
0.1
0.2
0.3
0.4
0.5
0.6
1 2 3 4 5 6 7 8 9 10 11 12
TIMEPERIOEDsec
MODES
TP-T1.1
TP-T1.2
TP-T1.3
TP-T1.4

Figure 4.2: Frequency vs Modes
As we can see in the above values the Frequency
gradually increases as the modes increases. When the
frequencies are compared with four different models it is
seen that the frequency is more in model 3 while least in
model 1. The graph is then plotted frequency (cyc/sec)
with respect to modes.
3.2 Displacement (mm):
3.2.1 Earthquake In X-Direction
Table 4.3: Displacement vs Storey Level (X-Direction)
UX-T1.1 UX-T1.2 UX-T1.3 UX-T1.4
11th 4.4561 2.8648 2.9899 3.2512
10th 4.1665 2.6646 2.7567 2.9702
9th 3.8181 2.4271 2.4815 2.6473
8th 3.4184 2.1572 2.1768 2.2944
7th 2.9918 1.8729 1.8602 1.934
6th 2.5983 1.6156 1.5806 1.6278
5th 2.2558 1.4017 1.3745 1.4251
4th 1.8543 1.1529 1.1317 1.1885
3rd 1.4049 0.8718 0.8586 0.9156
2nd 0.925 0.5704 0.5698 0.618
1st 0.45 0.2746 0.2859 0.316
GF 0 0 0 0
Figure 4.3: Displacement vs Storey Level (X-Direction)
As we can see in the above values the
displacement gradually decreases as the storey level
decreases showing zero at ground floor. When the
displacement are compared with four different models it
is seen that the displacement is more in model 1 while
the displacements are less up to 7th storey level in model
3 when compared to model 2 and vice versa beyond this
level. This is because of the unsymmetrical structure.
Displacements are less in model 3 when compared to
model 4. The graph is then plotted displacement (mm)
with respect to storey level.
3.2.2 Earthquake in Y-Direction
Table 4.4: Displacement vs Storey Level (Y-Direction)
UY-T1.1 UY-T1.2 UY-T1.3 UY-T1.4
11th 86.4205 50.3247 73.7786 61.2324
10th 81.9795 47.4779 68.4305 57.4415
9th 76.7328 44.2026 62.4615 53.0501
8th 70.552 40.4251 55.8088 48.0136
7th 63.4841 36.1706 48.6013 42.4217
6th 53.6098 30.4451 40.5273 35.4206
5th 45.5944 25.6345 33.7605 29.8294
4th 37.1926 20.6899 26.984 24.2306
3rd 28.0498 15.4 20.0358 18.299
2nd 18.4052 9.9369 13.0926 12.1584
1st 8.8961 4.711 6.4887 6.1218
GF 0 0 0 0
Figure 4.4: Displacement vs Storey Level (Y-Direction)
As we can see in the above values the
displacement gradually decreases as the storey level
decreases showing zero at ground floor. When the
displacement are compared with four different models it
is seen that the displacement is more in model 1 while
the displacements are less in model 2 because the size of
columns and beams are heavy when compared to model
3 and 4. When the models with shear wall and bracings
(3 and 4 respectively) are compared it is seen that the
displacements are less in model 4. The graph is then
plotted displacement (mm) with respect to storey level.
0
5
10
15
20
25
30
1 2 3 4 5 6 7 8 9 10 11 12
FREQUENCYcyc/sec
MODES
FR-T1.1
FR-T1.2
FR-T1.3
FR-T1.4
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
11TH
10TH
9TH
8TH
7TH
6TH
5TH
4TH
3RD
2ND
1ST
GF
DISPLACEMENTmm
STOREY LEVEL
UX-T1.1
UX-T1.2
UX-T1.3
UX-T1.4
0
10
20
30
40
50
60
70
80
90
100
11TH
10TH
9TH
8TH
7TH
6TH
5TH
4TH
3RD
2ND
1ST
GF
DISPLACEMENTmm
STOREY LEVEL
UY-T1.1
UY-T1.2
UY-T1.3
UY-T1.4

3.3 Story Drift Ratio:
3.3.1 Earthquake in X-Direction
Figure 4.5 a: Drift Ratio vs Storey Level (X-Direction)
Figure 4.5 b: Drift Ratio vs Storey Level (Y-Direction)
As we can see in the above values the storey
drift ratio are compared with four different models, for
earthquake in both X and Y directions the storey drift
ratio is more in model 1 and less in model 2. When the 3
and 4th models are compared the storey drift are less in
model 4.
3.4 Story Shear (kN):
3.4.1 Earthquake In X-Direction
Table 4.5: Storey Shear vs Storey Level (X-Direction)
VX-T1.1 VX-T1.2 VX-T1.3 VX-T1.4
11th 280.92 324.33 264.96 289.67
10th 460.53 559.18 420.04 476.2
9th 615.93 761.59 550.97 635.52
8th 749.77 934.9 661.05 770.65
7th 863.86 1081.93 752.99 884.07
6th 512.64 765.1 371.24 531.31
5th 630.04 914.98 458.86 649.01
4th 728.28 1040.16 532.19 748.1
3rd 805.52 1137.95 589.85 826.48
2nd 859.63 1205.4 630.37 881.97
1st 887.72 1239.69 651.89 911.72
GF 891.07 1243.97 654.51 915.78
Figure 4.6: Storey Shear vs Storey Level (X-Direction)
shear which are compared with four different models,
for earthquake in X direction the storey shear is more in
model 2 and less in model 3. When the 3 and 4th models
are compared the storey shear are less in model 3 which
is due to the provision of shear walls.
Table 4.6: Storey Shear vs Storey Level (Y-Direction)
VY-T1.1 VY-T1.2 VY-T1.3 VY-T1.4
11th -896.7 -849.93 -902.64 -880.48
10th -3057.28 -2953.58 -3080.64 -3028.98
9th -5241.03 -5088.65 -5283.26 -5204.22
8th -7445 -7251.54 -7507.69 -7403.37
7th -9667.15 -9439.33 -9751.15 -9624.05
6th -12175.2 -11912.7 -12283.7 -12130.5
5th -15569.7 -15275.5 -15700.9 -15521.7
4th -18981.1 -18660.7 -19130.5 -18929.2
3rd -22410.8 -22070.4 -22574.6 -22355.2
2nd -25860.9 -25507.6 -26035 -25802.3
1st -29334.6 -28975.4 -29513.5 -29273.4
GF -31081.2 -30721.2 -31260.6 -31019.2
0
0.0005
0.001
0.0015
0.002
0.0025
0.003
0.0035
0.004
STOREYDRIFTRATIO
STOREY LEVEL
DriftX -T1.1
DriftY-T1.1
DriftX -T1.2
DriftY-T1.2
DriftX -T1.3
DriftY-T1.3
DriftX -T1.4
DriftY-T1.4
0
0.0005
0.001
0.0015
0.002
0.0025
0.003
0.0035
0.004
STOREYDRIFTRATIO
STOREY LEVEL
DriftX T1.1
DriftY T1.1
DriftX T1.2
DriftY T1.2
DriftX T1.3
DriftY T1.3
DriftX T1.4
DriftY T1.4
0
200
400
600
800
1000
1200
1400
11TH
10TH
9TH
8TH
7TH
6TH
5TH
4TH
3RD
2ND
1ST
GF
STOREYSHEARkN
STOREY LEVEL
VX-T1.1
VX-T1.2
VX-T1.3
VX-T1.4

Figure 4.7: Storey Shear vs Storey Level (Y-Direction)
shear which are compared with four different models,
for earthquake in Y direction the storey shear is more in
model 1 up to storey level 6 while it is more in model 3
beyond this storey level and overall it is less in model 2.
When the 3 and 4th models are compared the storey
shear are less in model 4 which is due to the provision of
bracings.
4. CONCLUSIONS
Time period:
 As the storey level increases the time period
increases
 When time period of all the types are compared
it is found that Type 3 model is having the least
value, which is having shear wall.
Frequency:
 As the storey level increases the frequency
decreases.
 When frequency of all the types is compared it is
found that Type 3 model is having the higher
value, which is having shear wall.
CASE 1: Displacement:
Earthquake analysis of a tall building for Blast
of 100kg explosive with standoff distance of 30 m has
given an idea how the different types of tall building like,
Type 1, Type 2, Type 3 and Type 4 behaves during the
Earth quake. It is seen that the Earthquake response in x
& y direction is reduced in the Building with increase
column - beam sizes.
Storey Drift:
The storey drift is less in Type 2 model
compared to other models.
Earth quake. It is seen that the Earth quake response in x
direction is reduced in the Building with increase column
- beam sizes. And in y direction, the Building with shear
walls located at corners has shown the reduction.
Storey Drift:
& y direction is reduced in the Building with increase
column - beam sizes.
Storey Drift:
& y direction is reduced in the Building with bracing
located at corners.
Storey Drift:
4.1 Overall Conclusion
 By increasing column and beam size in a
structure will improve the resistance but it is
not practical in most cases due to serviceability
problems because huge cross section of beam
and column needed to resist blast loads.
 Addition of shear wall and bracing helps to
resist the blast loads effectively.
 The addition of steel bracings gives good results
but shear wall more desirable results than steel
bracings and it is economical too compared to
other methods.
-35000
-30000
-25000
-20000
-15000
-10000
-5000
0
STOREYSHEARkN
STOREY LEVEL
VY-T1.1
VY-T1.2
VY-T1.3
VY-T1.4

4.2 Further work Recommendations
It is recommended that further research can be
undertaken in following areas
1. Compare the wind response of conventional tall
regular building with tall regular (having
different location of shear walls) building, by
doing Dynamic wind analysis to assess the exact
response.
2. Compare the Dynamic wind response of
conventional tall irregular building with tall
irregular (having different location of shear
walls) building, by using Static and Dynamic
wind analysis.
REFERENCES
1. Hrvoje Draganic, Vladmir sigmud (2012), “Blast
loading on Structures” IJERA-(ISSN) 1330-3651
UDC or UDK 624.01.04:662.15. 19, 3.
2. Payoshni Mali, Savita lokare, Chitra v. (2014).
“Effect of blast loading on reinforced concrete
structures” International journal of science and
research.
3. B.M. Luccion, R.D. Ambrosini and R.F. Danesi.
(2004), “Analysis of Building collapse under
blast loads” ELSEVIER Engineering structure 26,
63-71
4. Demin George and Vernitha M.S, (2016),
“Structural Analysis of Blast resistant
structures” (IJSRD) International journal for
scientific research and development/ volume 4,
issue 05, 2016/ ISSN: 2321 – 0613
5. I.N. Jayatilake, W.P.S. Diasal, M.T.R. Jayasinghe
(2010), “Response of Tall buildings with
symmetric setbacks under blast loadings” J.nath.
sci. foundation Sri-lanka, 38 (2): 115-123.
6. IS: 4991 – 1968, Criteria for blast resistant
design of structures for explosions above
ground.
7. IS: 1893 (Part – 1) – 2002, Criteria for
earthquake resistant design of structures (fifth
revision).
8. IS: 875 (Part – 1) – 1987, Dead Loads, Code of
practise for design loads other than earthquakes
for buildings and structures (second revision).
9. IS: 875 (Part – 2) – 1987, Imposed Loads, Code
of practise for design loads other than
earthquakes for buildings and structures
(second revision).
BIOGRAPHIES
Prof. N.S.Inamdar
Professor, Structural Engineering
Civil Engineering Department,
B.L.D.E.A’s Dr. P.G.H.C.E.T
Vijayapur.
Chandrashekhar
M.Tech Structural Engineering Student,
Civil Engineering Department,
B.L.D.E.A’s Dr. P.G.H.C.E.T
Vijayapur.

Analysis of Blast Resistance Structure

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