jet blast deflector fence

JET BLAST DEFLECTOR FENCE
1
2
Bhagyashree S.Zope Dr. R.S.Talikoti
1
Department of civil engineering, L.G.N.S.C.O.E.Nasik,
2
Department of civil engineering, L.G.N.S.C.O.E.Nasik,
Abstract— A jet blast produces tremendous amount of thermal energy and noise. In order to prevent
mishaps or equipment failure of machines nearby blast fences are used. A blast fence is often called
as a “blast deflector” by the layman. A blast fence or a jet blast deflector (JBD) is a safety device
which redirects the high energy from a jet engine to prevent accidents/damages. The structure is
strong enough to deflect the high velocity debris carried by the turbulent air and heat. It is designed
to provide a simple and aesthetically pleasing appearance. Blast deflector provides positive
protection for ground vehicle, pedestrians and other airport facilities that may be subjected to jetblast hazards from nearby runways .The structure includes two structural members, a curved rib
channel member securely and hingedly attached to an airport apron and a vertical King Post of angle
iron which is rigidly secured at its lower end and hingedly attached at its upper end to the channel.
At airports blast fences are complementarily used with sound-deadening walls with which a
jet/aircraft can be tested silently and safely. Without blast fence, the high intensity jet blast can be
dangerous to people or other machines near the aircraft. In the present paper an attempt has been
made to focus on design criteria, selection of structural members for analysis of jet blast deflector
fence using E-TAB software.
Keywords— E-TAB, Jet blast deflector (JBD), Structural members, curved rib channel member,
vertical king post member.
I.
INTRODUCTION
Jet aircraft the areas in and around airports have been subjected to hazardous rear ward jet blasts
which are composed of hot gases that have been accelerated to high velocities. The hazard of the jet
blast gave rise to the blast deflector fence which normally redirects the horizontal jet blast to a
vertical direction in order to protect persons and property on the ground. The apparatus for use at
airports, ‘on aircraft carriers, and at other places where-airplanes are warmed up, tested, serviced,
etc., and relates more particularly to means for deflecting the high temperature, high velocity jets of
air and gases issuing from the nozzles‘ of the turbo-jet and turbo-propeller engines of aircraft. In
warming up and testing such engines the jet blasts are extremely hazardous and a person in vertently
entering such a blast, even at a point several feet behind the airplane, is liable to be killed or at least
seriously injured. Accordingly, it has been necessary to take unusual precautions when servicing,
testing, and warming up such engines, and to arrange the airplane in a location where there is a large,
open unusable space behind the airplane. The blast fences or blast walls often used at air fields and
designed to partially deflect and break up the relatively low velocity and low temperature air blasts
created by propellers are wholly inadequate to deflect the hot, high velocity jets of jet engines.
During the past thirty (30) years blast deflector fences have developed into expensive complex
structures requiring many supporting members shaped into complex rib frames to which a corrugated
steel deflecting surface is bolted. Heights of 6 feet to 8 feet were sufficient to deflect the blasts of
commercial and military aircraft of 25 to 30 years ago. However, with passing time, aircraft have
been developed with more powerful engines with thrust centre lines of up to 32 feet or more above
grade level. The average and most used height of deflector now at modern airports is 14 feet, rather
than the 7 foot to 8 foot heights of 25 to 30 years ago. The 14 foot height requires numerous braces
to form a rib truss, in addition to horizontal stringers across the back of the rib frames, and diagonal
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Volume 02, Issue 07, [July– 2015]
ISSN (Online):2349–9745 ; ISSN (Print):2393-8161
braces to prevent side to side movement or swaying, and to reduce vibration of the rib frames caused
by the pulsating blasts, not always normal to the longitudinal axis of the deflector.
Fig 1. Typical example of jet blast deflector fence
II.
METHODOLOGY
In the present paper E TABS software is used for analysis of jet blast deflector fence. Response
spectrum method is observed for maximum shear force and bending moment due to dead load and
live load, and mode shape are taken of seismic zone factor 0.24, Response reduction factor 5.
2.1 Model Description
Jet blast deflector fence can be solved by constructing a jet blast deflector of height 4.914m, width
1.5 m & spacing between two column 2 m for all aircrafts. Minimum distance required: 35 feet
(10.67m) to the tail of aircraft and 60 feet (18.29m) to the aircraft engine. The structure can be
designed by using ETAB software. Linear analysis will be carried out for the models and the results
will be compared. The other data used for the analysis is shown in table 1.
Table 1. Data used for analysis
Name of parameter
Basic wind speed,
Vb
Wind pressure coefficient VZ
=Vbk1 k2k3
Design wind
pressure Pz =
0.6Vz2
Number of stories
Length of the Jet
Blast Fence
Width of the Jet
Blast Fence
Height of the Jet
Blast Fence (h)
Value
Unit
134
m/s
130.9
3
10.23
m/s
KN/m
Name of parameter
Value Unit
Length to width ratio (l/w) 49.70
Height to width ratio
(h/w)
5
Thickness of the base slab
500
mm
Effective Depth
444
mm
Grade of concrete, fck
30
2
15
nos.
74.55
m
1.50
m
4.914
m
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Grade of steel
reinforcement, fy
N/mm
²
500 N/mm
²
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ISSN (Online):2349–9745 ; ISSN (Print):2393-8161
2.2 Details of Models
Fig.2 Typical plan view of base slab
Fig.4 3D computer model of blast fence
Fig.6 3D view uniform load (Wind)
Fig.3 Three-dimensional base slab of Blast fence
Fig.5 3D view uniform live load
Fig.7 Steel Design sections used for mode
III.
RESULTS AND DISCUSSION
The analysis of all the frame models that includes Maximum Story Displacement, Story Shears,
Story Stiffness, has been done by using ETABS and the results are shown below.
3.1 Zone of forces acting on base slab with maximum shear force due to dead load and live load
3.1.1 Resultant Vmax due to dead load
Fig.8 Resultant Vmax due to dead load
3.1.2 Resultant Vmax due to live load
Fig.9 Resultant Vmax due to live load
3.2 Zone of forces acting on base slab with maximum bending moment due to DL and LL
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International Journal of Modern Trends in Engineering and Research (IJMTER)
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3.2.1 Resultant Mmax due to dead load
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3.2.2 Resultant Mmax due to live load
Fig.10 Resultant Mmax due to dead load
Fig.11 Resultant Mmax due to live load
Table 2. Time Period Response of Base Slab
Mode No.
1
2
3
4
5
6
Time Period
0.0459
0.0037
0.0024
0.0021
0.0019
0.0015
Mode No. Time Period
7
0.0013
8
0.0013
9
0.0012
10
0.0012
11
0.0011
12
0.0010
Fig.12 3D view of mode 1
Fig.13 3D view of mode 7
Fig.14 3D view of mode 12
3.3 Results for Properties of Blast Fence Structue along all Storeys from ETAB Software:
3.3.1 Maximum Story Displacement
This is story response output for a specified range of stories and a selected load case or load
combination (DL +LL+WL)
Table 3. Max. Displacement in X and Y Direction
Story
STORY15
STORY14
STORY13
STORY12
Elevation Location X-Dir Max Y-Dir Max X-Dir Min Y-Dir Min
mm
4914
4500
4093
3695
Top
Top
Top
Top
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mm
2.8
2
1.6
1.1
mm
0.03806
0.002641
0.1
0.1
mm
-0.1
-0.1
-0.1
-0.1
mm
0.0006127
0.00002567
0.0003105
0
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Volume 02, Issue 07, [July– 2015]
STORY11
STORY10
STORY9
STORY8
STORY7
STORY6
STORY5
STORY4
STORY3
STORY2
STORY1
BASE
3307
2932
2571
2225
1897
1586
1295
1025
778
553
500
0
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
ISSN (Online):2349–9745 ; ISSN (Print):2393-8161
0.8
0.8
0.8
0.5
0.2
0.5
0.9
0.8
0.4
0.03737
0
0
0.02554
0.01303
0.02207
0.02047
0.01956
0.01831
0.01587
0.01468
0.01337
0.004228
0
0
-0.04588
-0.00577
0.005702
-0.00992
- 0.0073
0.02484
0.04963
0.04884
0.02538
0.001829
0
0
0
0.0000520
0
0
0
0
0.001322
0.0008222
0.0002952
0.0000136
0
0
Fig.15 Max. Displacement in X and Y Direction
From above graph, it shows the displacement occure along Y- Direction. In graph displacement (mm)
Vs storey height. The red line shows displacement along Y-axis and blue line shows displacement
along X-axis.
3.3.2 Maximum Story drift
Table 4. Max. Storey Drift in X and Y Direction
Story
STORY15
STORY14
STORY13
STORY11
STORY11
STORY10
STORY9
STORY8
STORY7
STORY6
STORY5
STORY4
STORY3
STORY2
STORY1
Elevation
Location
mm
4914
4500
4093
3307
3307
2932
2571
2225
1897
1586
1295
1025
778
553
500
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
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X-Dir Y-Dir
Max Max
0
0
0
0
00
0
0
0
0
0
0
0
0
0
0
0
0
0
0
00
0
0
0
0
0
0
0
0
0
0
X-Dir
Min
Y-Dir
Min
- 0.117389
- 0.103599
- 0.079236
- 0.045877
- 0.00577
0.005702
- 0.009921
- 0.005735
0.024843
0.049625
0.04884
0.025382
0.001829
0
0
0.000613
0.000026
0.00031
0
0.000052
0
0
0
0
0.001322
0.000822
0.000295
0.000014
0
0
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Volume 02, Issue 07, [July– 2015]
BASE
0
Top
0
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0
0
0
Fig.16 Max. Storey Drift in X and Y Direction
From above graph, it shows that drift occure along Y- direction is zero in graph drift Vs storey height.
The red line shows drift along Y-axis and blue line shows drift along X-axis.
3.3.3 Maximum Story shear
Table 5. Max. Storey shear in X and Y Direction
Story
Elevation Location X-Dir Y-Dir X-Dir Min Y-Dir Min
mm
N
N
N
N
STORY15
4914
Top
0
0
0
0
Bottom
0
0
-13239.72
0
STORY14
4500
Top
0
0
-13239.72
0
Bottom
0
0
-26255.58
0
STORY13
4093
Top
0
0
-26255.58
0
Bottom
0
0
-38983.62
0
STORY12
3695
Top
0
0
-38983.62
0
Bottom
0
0
-51391.86
0
STORY11
3307
Top
0
0
-51391.86
0
Bottom
0
0
-63384.36
0
STORY10
2932
Top
0
0
-63384.36
0
Bottom
0
0
-74929.14
0
STORY9
2571
Top
0
0
-74929.14
0
Bottom
0
0
-85994.22
0
STORY8
2225
Top
0
0
-85994.22
0
Bottom
0
0
-96483.66
0
STORY7
1897
Top
0
0
-96483.66
0
Bottom
0
0
-106429.4
0
STORY6
1586
Top
0
0
-106429.4
0
Bottom
0
0
-115735.6
0
STORY5
1295
Top
0
0
-115735.6
0
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Volume 02, Issue 07, [July– 2015]
STORY4
1025
STORY3
778
STORY2
553
STORY1
500
BASE
0
ISSN (Online):2349–9745 ; ISSN (Print):2393-8161
Bottom
Top
Bottom
Top
Bottom
Top
Bottom
Top
Bottom
Top
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
-124370.2
-124370.2
-132269.3
-132269.3
-139464.8
-139464.8
-137769.8
0
0
0
0
0
0
0
0
0
0
0
0
0
Bottom
0
0
0
0
Fig.17 Max. Storey shear in X and Y Direction
In above graph Force (KN) Vs storey breadth ,shear force acting at top and bottom of the joints.
Along Y-axis the result is constant straight line as force is acting along breadth of base slab.
3.3.4 Maximum Story stiffness
Table 6. Max. Storey stiffness in X and Y Direction
Story
STORY15
STORY14
STORY13
STORY12
STORY11
Elevation
mm
4914
4500
4093
3695
Location X-Dir Y-Dir X-Dir Min
N/mm N/mm
N/mm
Top
0
0
0
Top
0
0 779968.36
Top
0
0 1532589.8
Top
0
0 2281380.2
3307 Top
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0
0
Y-Dir Min
N/mm
-640836.37
-17363085
-42201778
-73581408
3027527.1 -110896920
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STORY10
STORY9
STORY8
STORY7
STORY6
STORY5
STORY4
STORY3
STORY2
STORY1
2932
2571
2225
1897
1586
1295
1025
778
553
500
BASE
ISSN (Online):2349–9745 ; ISSN (Print):2393-8161
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
4051350.4
4895040.3
5728985.3
6549992.8
7345284.6
8128780.3
8898873.7
9653328
10226491
0
-153476053
-199315985
-247504793
-296614502
-345511884
-392833005
-437155423
-477042014
-511562048
0
0 Top
0
0
0
0
Fig.18 Max. Storey stiffness in X and Y Direction
Graph shows that there is no stiffness occurred in maximum X and Y direction.
3.3.5 Maximum Story overturning moments
Table 7. Max. Storey overturning moment in X and Y Direction
Story
STORY15
STORY14
STORY13
STORY12
STORY11
STORY10
STORY9
STORY8
STORY7
STORY6
STORY5
STORY4
Elevation
mm
4914
4500
4093
3695
3307
2932
2571
2225
1897
1586
1295
1025
Location
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
Top
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X-Dir
N-mm
298156
6906075
1.5E+07
2.5E+07
3.5E+07
4.7E+07
6.1E+07
7.5E+07
9E+07
1.1E+08
1.2E+08
1.4E+08
Y-Dir X-Dir Min Y-Dir Min
N-mm
N-mm
N-mm
0
0 -640836.4
-2E+06
779968 -17363085
-3E+06
1532590 -42201778
-5E+06
2281380 -73581408
-6E+06
3027527 -1.11E+08
-8E+06
4051350 -1.53E+08
-9E+06
4895040 -1.99E+08
-1E+07
5728985 -2.48E+08
-1E+07
6549993 -2.97E+08
-1E+07
7345285 -3.46E+08
-1E+07
8128780 -3.93E+08
-1E+07
8898874 -4.37E+08
446
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STORY3
STORY2
STORY1
BASE
778
553
500
0
Top
Top
Top
Top
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1.6E+08 -1E+07
1.8E+08 -2E+07
0
0
0
0
9653328
1E+07
0
0
-4.77E+08
-5.12E+08
0
0
Fig.19 Max. Storey overturning moment in X and Y Direction
In above graph moment (Nmm) Vs storey breadth, overturning moment acting at top and bottom of
the joints. Along Y-axis the result is constant straight line as moment is acting along breadth of
base slab.
IV.
CONCLUSION
From the analysis of jet blast deflector fence structure with varying parameters following
conclusions can be drawn.
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1. We can conclude that the jet we used having speed of 300 miles/hr and the blast fence we have
designed is capable for wind speed because of explosion fuel through air-jet of 10.23 KN/m2 and
less than 10.23 KN/m2.
2. For the analysis purpose basic parameters taken are maximum shear force, bending moment and
mode shapes. Their performances are interpreted on the basis of this parameters.
3. The above time period response vs. mode number table shows that for different time period
and number of modes, deflection takes place. Mode 12 is extreme load condition act on base slab
and maximum deflection takes place at this point.
4. The blast we have designed can easily divert the explosive wind on upward side without any
harm to aerodrome or any other structures of airport and living things.
5. The above time period response vs. mode number table shows that for different time period
and number of modes, deflection takes place. Mode 12 is extreme load condition act on base slab
and maximum deflection takes place at this point.
REFERENCES
[1] Shosuke watanabe late of Tokyo, Japan Naoko Watanabe “Jet Engine Blast Fence”, Nippon Steel
Corporation, „ Tokyo, Japan, Mar. 19, 1974.
[2] B. Stanley Lynn, Pajaro Dunes,” Split Exhaust Jet Blast Deflector Fence” H- 11, Watsonville,
Calif. 95076, Jul. 4, 1995.
[3] Earl A. Phillips, La Grange Park, And Richard P. Molt, “Retractable Blast Deflector Fence”, Olympia Fields,
111., Assignors To Stanray
Corporation, A Corporation Of Delaware, Nov. 28, 1961.
[4] Bernard` Stanley Lynn, “Blast Fence.”, 19451 Black Road, Los Gatos, Calif, Mar. 14, 1951.
[5] Fischer, Eugene C. And Dale A. Sowell, John Wehrle, Peter O. Cervenka. ”Cooled Jet Blast Deflectors For
Aircraft Carrier Flight Decks”. U.S. Patent 6,575,113, Issued June 10, 2003.
[6] Morrison, Rowena. ASRS Directline, Issue Number 6, August 1993. "Ground Jet Blast Hazard." Retrieved on
November 13, 2009.
[7] Harold J. Hayden,, “Jet Engine Exhaust Deflector”, Seattle, Airplane Company, Mar. 11, 1958.
[8] Bernard Stanley-Lynn,” Blast Fence”,19451 Black Road, Los Gatos, Calif, Mar. 24,‟ I954.
[9] Brown, Edward L.”Blast Fence For Jet Engines”. U.S. Patent 2,726,830, Issued December 13, 1955.
[10] Federation of American Scientists. "CV-9 Essex Class: Overview." USS Oriskany (CV-34) began a major refit in
October 1947 and was returned to service in August 1951 with a number of modernizations including jet blast
deflectors.
[11] B. Stanley Lynn, Pajaro Dunes, “Jet Blast Defletor Fence”, H-11, Watsonvrlle, Calif. 95076-0000, Jul.
7, 1992
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