JET BLAST DEFLECTOR FENCE - IJMTER · PDF filemade to focus on design criteria, ... Jet blast deflector fence can be solved by construc ting a jet blast deflector of height 4.914m,

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JET BLAST DEFLECTOR FENCE

Bhagyashree S.Zope1 Dr. R.S.Talikoti

2 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 jet-

blast 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

International Journal of Modern Trends in Engineering and Research (IJMTER) 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 Value Unit Name of parameter Value Unit

Basic wind speed,

Vb 134 m/s

Length to width ratio (l/w) 49.70

Wind pressure co-

efficient VZ

=Vbk1k2k3

130.93

m/s

Height to width ratio

(h/w)

5

Design wind pressure Pz =

0.6Vz2

10.23 KN/m

2

Thickness of the base slab 500 mm

Number of stories 15 nos. Effective Depth 444 mm

Length of the Jet

Blast Fence 74.55 m

Grade of concrete, fck 30 N/mm

²

Width of the Jet

Blast Fence 1.50 m

Grade of steel

reinforcement, fy

500 N/mm

²

Height of the Jet

Blast Fence (h) 4.914 m



2.2 Details of Models

Fig.2 Typical plan view of base slab Fig.3 Three-dimensional base slab of Blast fence

Fig.4 3D computer model of blast fence Fig.5 3D view uniform live load

Fig.6 3D view uniform load (Wind) 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 3.1.2 Resultant Vmax due to live load

Fig.8 Resultant Vmax due to dead 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



3.2.1 Resultant Mmax due to dead load 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. Time Period Mode No. Time Period

1 0.0459 7 0.0013

2 0.0037 8 0.0013

3 0.0024 9 0.0012

4 0.0021 10 0.0012

5 0.0019 11 0.0011

6 0.0015 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 Elevation Location X-Dir Max Y-Dir Max X-Dir Min Y-Dir Min

mm mm mm mm mm STORY15 4914 Top 2.8 0.03806 -0.1 0.0006127 STORY14 4500 Top 2 0.002641 -0.1 0.00002567 STORY13 4093 Top 1.6 0.1 -0.1 0.0003105 STORY12 3695 Top 1.1 0.1 -0.1 0



STORY11 3307 Top 0.8 0.02554 -0.04588 0 STORY10 2932 Top 0.8 0.01303 -0.00577 0.0000520

STORY9 2571 Top 0.8 0.02207 0.005702 0

STORY8 2225 Top 0.5 0.02047 -0.00992 0

STORY7 1897 Top 0.2 0.01956 - 0.0073 0 STORY6 1586 Top 0.5 0.01831 0.02484 0 STORY5 1295 Top 0.9 0.01587 0.04963 0.001322 STORY4 1025 Top 0.8 0.01468 0.04884 0.0008222 STORY3 778 Top 0.4 0.01337 0.02538 0.0002952

STORY2 553 Top 0.03737 0.004228 0.001829 0.0000136 STORY1 500 Top 0 0 0 0

BASE 0 Top 0 0 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

Elevation

Location

X-Dir

Max

Y-Dir

Max

X-Dir

Min

Y-Dir

Min mm

STORY15

4914

Top

0

0 - 0.117389

0.000613

STORY14 4500 Top 0 0 - 0.103599 0.000026

STORY13 4093 Top 0 0 - 0.079236 0.00031

STORY11 STORY11

3307 3307

Top Top

0 0

0 0

- 0.045877 0

STORY10 2932 Top 0 0 - 0.00577 0.000052

STORY9 2571 Top 0 0

0 0.005702 0

STORY8 2225 Top 0

0 0 - 0.009921 0

0 STORY7 1897 Top 0 0

0 - 0.005735 0

STORY6 1586 Top 0 0 0.024843 0

STORY5 1295 Top 0

0

0

0 0.049625 0.001322

STORY4 1025 Top 0 0 0.04884 0.000822

STORY3 778 Top 0

0

0

0 0.025382 0.000295

STORY2 553 Top 0 0 0.001829 0.000014

STORY1 500 Top 0

0

0

0

0

0

0

0



BASE 0 Top 0 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



Bottom 0 0 -124370.2 0

STORY4 1025 Top 0 0 -124370.2 0

Bottom 0 0 -132269.3 0

STORY3 778 Top 0 0 -132269.3 0

Bottom 0 0 -139464.8 0

STORY2 553 Top 0 0 -139464.8 0

Bottom 0 0 -137769.8 0

STORY1 500 Top 0 0 0 0

Bottom 0 0 0 0

BASE 0 Top 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


mm N/mm N/mm N/mm N/mm

STORY15 4914 Top 0 0 0 -640836.37

STORY14 4500 Top 0 0 779968.36 -17363085

STORY13 4093 Top 0 0 1532589.8 -42201778

STORY12 3695 Top 0 0 2281380.2 -73581408

STORY11 3307 Top 0 0 3027527.1 -110896920



STORY10 2932 Top 0 0 4051350.4 -153476053

STORY9 2571 Top 0 0 4895040.3 -199315985

STORY8 2225 Top 0 0 5728985.3 -247504793

STORY7 1897 Top 0 0 6549992.8 -296614502

STORY6 1586 Top 0 0 7345284.6 -345511884

STORY5 1295 Top 0 0 8128780.3 -392833005

STORY4 1025 Top 0 0 8898873.7 -437155423

STORY3 778 Top 0 0 9653328 -477042014

STORY2 553 Top 0 0 10226491 -511562048

STORY1 500 Top 0 0 0 0

BASE 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


mm N-mm N-mm N-mm N-mm

STORY15 4914 Top 298156 0 0 -640836.4

STORY14 4500 Top 6906075 -2E+06 779968 -17363085

STORY13 4093 Top 1.5E+07 -3E+06 1532590 -42201778

STORY12 3695 Top 2.5E+07 -5E+06 2281380 -73581408

STORY11 3307 Top 3.5E+07 -6E+06 3027527 -1.11E+08

STORY10 2932 Top 4.7E+07 -8E+06 4051350 -1.53E+08

STORY9 2571 Top 6.1E+07 -9E+06 4895040 -1.99E+08

STORY8 2225 Top 7.5E+07 -1E+07 5728985 -2.48E+08

STORY7 1897 Top 9E+07 -1E+07 6549993 -2.97E+08

STORY6 1586 Top 1.1E+08 -1E+07 7345285 -3.46E+08

STORY5 1295 Top 1.2E+08 -1E+07 8128780 -3.93E+08

STORY4 1025 Top 1.4E+08 -1E+07 8898874 -4.37E+08



STORY3 778 Top 1.6E+08 -1E+07 9653328 -4.77E+08

STORY2 553 Top 1.8E+08 -2E+07 1E+07 -5.12E+08

STORY1 500 Top 0 0 0 0

BASE 0 Top 0 0 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.



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

Documents

JET BLAST DEFLECTOR FENCE - IJMTER · PDF filemade to focus on design criteria, ... Jet blast deflector fence can be solved by construc ting a jet blast deflector of height 4.914m,