Analysis and Design of Blast Resistant Structures

Analysis and Design of Blast Resistant Structures

Sharlin Sheeba

PG Student, Department of Civil Engineering The Oxford College of Engineering, Bangalore, Karnataka, India

B.K. Raghu Prasad,

Professor, Department of Civil Engineering, The Oxford college of Engineering, Bangalore, Karnataka, India

Abstract: To design structures to resist blast is becoming important these days. Although designing structures to blast is well understood to obtain the effect of attenuation through soil on buried structures using the certain existing software is to be explored, therefore a point worth highlighting in this paper is a novel technique of an imaginary boundary is created on which the overpressure from the explosive is determined based on distance and yield of the explosive. The pressure on the imaginary boundary is thus applied which furthers transferred to the building model through the soil which is modeled in SAFE SOFTWARE. The pressure which reaches the model would have been subjected to the soil properties like attenuation. The above novel technique is developed in order to obtain the effect of soil on buried structures.

Keyword: attenuation

1. INTRODUCTION

   Blast resistant materials or Blast resistance design might be a costly affair. Its knowledge is far beyond the reach of common people. But, the common people are not far from the reach of blast attacks.

   To help common people and our armed forces too to survive these kinds of blast. We have tried to find an affordable and accessible solution.

   Buildings get displaced enormously during blasts, due to which lives are lost.

   So considering this aspects of Blast, after doing lot of research and experiments

   We have developed a solution.

   We found out that instead of Blast resistant Structures or design, we can minimize the response and effects due to

   blast by the way we construct it.

   We have made an attempt to find out the responses of the structures situated above ground level and also structures situated below ground level using ETABS and SAFE software.

2. ABOUT : SAFE

   This paper describes blast response analysis results of a single storey (RCC and STEEL) using ETABS above ground level and is compared the analysis result with those from a SAFE below ground level.

   We have used SAFE mainly for soil modeling.

3. LITERATURE REVIEW

   Sourish Mukherjee et.al (2017)1

   The main aim of this paper is to study the review paper and its work on the effect of the blast loading on the structures that has previously done and is continuing till now. For designing the blast resistant structures would be uneconomic. It describes information about explosion.

   Gautam.C,pathak. R (2013)2

   They designed and developed a shock blast resistance structures capable of withstanding dynamic loading of 12psi and a static pressure of 1.5m earth cover due to blast.and evaluated it experimentally.

   Abhroop goswami, alaukk Singh satadru Das abhikary(2017)3 In this journal experiment had proved that ultra-high performance Fiber concrete is effective in resisting blast load.

   Sajal Verma, mainak choudhury purnachandra Saha (2015)4

   In this paper they made an attempt to review the different methods which are been applied to various type of structures like concrete, steel and masonry. In this paper they discussed FRP retrofit technique to protect the blast made of steel structures with dampers due to which no cracks are visible and there is no damage occurred in any of the walls and steel structures as the internal energy is dissipated by the dampers.

4. OBJECTIVE:

   The main aim of this work is to find out the responses of the structure situated below and above the Ground level. Thus analyzing which structure is more blast resistant.

5. METHODOLOGY

   Two similar models of plan dimensions 5m*4m*3m are considered. The thickness of wall and slab are 200mm and 150 mm respectively. The plan of structure situated above ground level is as shown in figure 1. To this structure an over pressure is applied to the side of the model and also a soil pressure is applied to the model and is analyzed. The plan of a structure situated below ground level is as shown in figure 2. To this structure an over pressure is applied considering an imaginary line away from the model and a soil pressure is applied around it and is analyzed. Thus analyzing which structure is more blast resistant. The calculations are based on IS: 4991-1968 which is the criteria for blast resistant design of structures for explosions above ground. Basically the manual calculation is done using code IS: 4991-1968 keeping the same blast load and varying the standoff distance the overpressure is calculated and then the manually calculated overpressure is applied to the models. The analysis is carried out using ETABS (2016) and SAFE

6. MODELING AND ANALYSIS

   A single storey building of plan dimension 5*4*3m the size of beam 200*300 and size of column 300*300 for concrete structures are used for modeling. For steel structures ISWB is used for column and ISLB is used for beams. In the above structures the models are made using ETABS and below structures are made using SAFE softwares.

   MANUAL CALCULATION

   200kg yield used from 20m standoff distance. x= actual distance/w1/3

   x=20/(0.2)1/3 x=34.199m

   From IS 4991-1968

   Pso=1.12006kg/cm2 Pro=3.17kg/cm2 qo=0.388kg/cm2 Scaled time to and td

   to =25.65*(0.2)1/3=15.002 td =16.9614*(0.2)1/3=9.919 M=1.396

   a =344m/s u=480.224=0.48m/millisecond Pressure on building

   H=3m L=4m B=5m

   S=H or B/2 whichever is less

   tc= 3S/u=3*2.5/0.4802=15.6184millisecond tt =L/u=4/0.4802=8.329millisecond tr=4s/u=4*2.5/0.4802millisecond

   tr> td no pressure on back face and is zero For roof and sides cd=-0.4

   Pso+cdqo= 1.120+ (0.4)*0.388=0.964kg/cm2 Conversion from kg/cm2 t kN/m2

   Pso+cdqo =94.56kN/m2 3.17kg/cm2=3.17*9.81 N/cm2

   = (31.09N)/ (10-4m2)

   =310.9kN/m2

   Pressure diagram

   310.9~311

   Average Front Face Loading KN/ m

   Time 9.9

   The analysis was carried out for the model as described as follows.

   Model 1: Reinforced structure situated above ground level Model 2: Reinforced structure situated below ground level Model 3: Steel structure situated above ground level Model 4: Steel structure situated below ground level

   Average Front Face Loading KN/ m2

   95

   Time

   9.9

   Different Models:

   MODEL1.1- Blast load of 200kg yield at 20m standoff distance

   MODEL1.2- Blast load of 200kg yield at 40m standoff distance

   MODEL1.3- Blast load of 300kg yield at 20m standoff distance

   MODEL 1.4- Blast load of 300kg yield at 40m standoff distance

   Pso= Peak side-on overpressure Pro =Peak reflected overpressure

   M= Mach number for incident shock front

   400

   300

   200

   100

   0

   blast load

   distance displacement

   Plan of the structure above ground level

   Response values for concrete above ground level

   Blas t load (Kg)	stan doff dist ance (m)	Ove rpr ess ure (kN /m2 )	displac ement (mm)	Mome nt (kN- m)	Max stres s	Shear force (kN)
   200	20	311	0.0629	0.0635	– –
   					0.08	0.026
   						2
   200	40	72	0.01421	–	0.02	0.004
   				0.0094	55	4
   300	20	419	0.0827	–	–	–
   				0.0547	0.15	0.025
   						4
   300	40	91.8	0.01813	0.012	–	–
   		8	5		0.02	0.005
   					2	6

   	Blast load	distance	displaceme nt
   Model 1	200	20	0.0629
   Model 2	200	40	0.01421
   Model 3	300	20	0.0827
   Model 4	300	40	0.018135

   3-D view of a structure above ground level

7. ANALYSIS AND RESULTS:

   The overpressure is applied to the models and is analyzed. The analysis results are tabulated below

   Response values for steel above ground level Response values for structures below ground level

   Blas t load (Kg)	stan doff dist ance (m)	Over pres sure (kN/ m2)	displ ace men t (mm )	M ax str ess	Mom ent (kN- m)	Shea r forc e (kN)
   200	20	311	0.00	–	0.091	–
   			75	0.2	4	0.05
   				4		16
   200	40	72	0.00	–	–	–
   			174	0.0	0.021	0.01
   				28	2	19
   300	20	419	0.01	–	0.123	–
   			01	0.4	1	0.06
   				8		95
   300	40	91.8	0.00	–	–	–
   		8	222	0.0	0.027	0.01
   				68		52

   Plan of a structure above ground level

   350

   300

   250

   200

   150

   100

   50

   0

   blast load

   distance

   displacemen t

   Here we considered imaginary line away from structure; soil pressure is applied around it and An overpressure is applied to the side of a structure

   	Blast load	distanc e	displacement
   Model 1	200	20	0.0075
   Model 2	200	40	0.00174
   Model 3	300	20	0.0101
   Model 4	300	40	0.00222

   3-D view of a structure below ground level

   400

   300

   200

   100

   0

   blast load

   distance displacement

   350

   300

   250

   200

   150

   100

   50

   0

   blast load

   distance displacement

   Blast load( Kg)	stand off distan ce(m)	Ove rpre ssur e (kN/ m	Nodal displa ceme nt (mm)	M ax st re ss	mo men t	Shea r force
   200	20	311	0.009	10	740.	199.
   			3	7.	36	80
   				54
   200	40	72	0.004	11	23.5	–
   			5	.9	649	82.8
   				05		17
   300	20	419	0.008	72	57.1	–
   			8	.1	206	566.
   				68		02
   300	40	91.8	0.008	15	30.1	–
   		8	7	.3	223	108.
   				12		24

   Blast load(K g)	stand off dista nce( m)	Ove rpre ssur e (kN/ m2)	Noda l displ acem ent (mm)	Ma x stre ss	mo me nt	Shear force
   200	20	311	0.010	62.	113	–
   			85	25	.81	333.65
   200	40	72	0.014	14.	26.	–
   			732	43	94	77.316
   300	20	419	0.011	86.	153	–
   			02	16	.34	456.56
   300	40	91.8	0.014	18.	34.	-95.31
   		8	736	016	24
   				7

   	Blast load	distance	displacemen t
   Model 1	200	20	0.01085
   Model 2	200	40	0.014732
   Model 3	300	20	0.01102
   Model 4	300	40	0.014736

   Response value of concrete below ground level Response value of steel below ground level

   	Blast load	distance	displacement
   Model 1	200	20	0.0093
   Model 2	200	40	0.0045
   Model 3	300	20	0.0088
   Model 4	300	40	0.0087

8. CONCLUSIONS

   1. Although, effect of blast loads on structures above ground is well understood, the effect of buried structures is not so well understood because to model and soil which attenuates the blast effect is very complex.

   2. Very important structures like government offices, historical structures and malls should be analyzed and designed to withstand blast load.

   3. With the advent of the modern software such as SAFE which can model soil effectively it has been possible to set the effect of attenuation through soil.

   4. But even modeling using SAFE is not very straightforward, a new technique of creating an imaginary boundary on which the overpressure are obtained .then the effect of attenuation of the blast effect from the imaginary boundary onwards towards the building is obtained.

   5. In the present work, using SAFE the soil has been modeled and the effect of a attenuation has been obtained.

   6. It is found that the effect of the blast loads on buried structures is significantly less compared to that on above structures.

9. ACKNOWLEDGMENT

   I would like to thank Professor B.K. RAGHUPRASAD and also our principal R V PRAVEENA GOWDA who gave me a chance for doing this innovative technique on ANALYSIS AND DESIGN OF BLAST RESISTANT STRUCTURES

   .At last I would like to thank my loved parents and friends.

10. REFERENCES

1. Sourish Mukherjee et.al review paper on blast loading and blast resistant structures,(IJCIET) Volume8, issue8, August 2017.

2. Gautam. C andpathak. R defence science journal volume 47, no.2. (2013).

3. abhroop goswami, alaukk Singh satadru Das adhikary,blast resistant of ultra high performance of concrete structures, IJETAE, volume 7,(2017).

4. sajal Verma, mainak choudhury, purnachandra Saha, blast resistant design of structures, IJRET, volume 4, special issue 13, Dec 2015