• Group A (Closed space).
• Group B (Connected space).
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Mitigation of Blast Propagation
in Undrground Spaces
Ehab Hanafi Mahmoud
Abstract— “Protection against Terrorism” is an emerging factor which influences the urban planning process offering a new dimension to town planning.In urban settings; such public buildings may be underground at the heart of major cities, offering closed or semi-closed collective spaces. In such spaces, enhancement of the blast waves can occur by reflection and the structures will receive multiple shocks.
This paper presents the findings from a programme of research, which explores the opportunities offered by an effective town planning approach. Specifically it looks at the protection, which derives from using spatial forms to mitigate the effect of blast waves in underground spaces, as as- sessed with the AUTODYN simulation package 3D V3.0.07.
Index Terms— Architecture, Autodyn, Blast, Protection, Computation, mitigation, propagation, Terrorism, Underground,
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n early civilizations, the main aims of establishing under- ground spaces were to provide protection against climate and to offer physical security.
Faced with the challenge of 21st century, the dominant threat to physical security is from terrorist attacks. In 1995, Japan suffered the world's first large-scale terrorist chemical gas attack in underground facilities, when a Japanese religious cult, Aum Shinrikyo or Aum Supreme Truth, attacked the To- kyo subway system, which is located underground, on March
20th. Five subway trains were simultaneously attacked, killing
12 people. About 5,500 people were sent to area hospitals for
treatment from symptoms of chemical poisoning from sarin
gas. Foreigners, including, one Swiss, one Irishman, two US
citizens and two Australians, were among those who sought treatment for chemical exposure [1-3]. In early civilizations, the aims of establishing underground spaces were to provide protection against climate and to offer physical security.
The Urban Planner has a contribution to make in the en- hancement of spatial survivability by optimising the town planning configuration (Space form, squares, landscape, street architecture… etc.) to provide a measure of protection without compromising appearance and utility.
Urban Planning is an integration process between the Ur- ban Planning positive phase “The Structures” and the Urban planning negative phase “The Spaces” (streets, squares, public space … etc.). Each of them has measurements to reduce the effects of the threat to certain protection level. If both are com- bined, the effect of the threat will be reduced to a minimum
Focusing on the urban planning negative phase, the spaces, especially underground spaces, this paper describes the con- cept of using specific underground space forms to mitigate the effects of the blast wave values on the structures.
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• Ehab Hanafi Mahmoud is Head of the Architecture Department, MTC, Cairo, Egypt.
PH: +2 0100 613 8182
Underground Space can be categorized on the basis of the ar- chitectural design for the plan and section of the space, [4] as shown in figure 1, which identifies two categories of simula- tions:
• Group A (Closed space).
• Group B (Connected space).
Fig. 1 Underground Space Classification
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Several scenarios were prepared to simulate a comprehensive range of spatial forms as shown in figure 2:
• Spaces with flat surfaces. [Triangular, cubic, penta- gon, hexagon … etc.]
• Spaces with curved surfaces. [Cylindrical, concave plan, convex plan … etc.]
Fig. 2 The Spatial forms of underground space.
The Reference scenario, with which each group of simulations will be compared, is an explosion in the centre of the cylindrical underground space as shown in figure 3.
This programme is based on measured impulse values from real events [Figure 4]. To aid comparison between simulations, all spaces were given the same dimensions, i.e. 10 m from centre of the space to any boundary, and 15 m in height
Fig. 4 Typical Reference scenario in Autodyn simulation with detonation after 7.923 ms
The impulse values are presented for the mid-point of the sides, which form the spaces since: These are always at the same range from the explosion; also, they represent the most critical locations from a structural point of view.
Figure 5 shows that the decrease in the impulse values, com- pared to the reference scenario, experienced by the walls of the enclosed space.
60
50
40
30
20
10
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Height above ground level (m)
Fig. 3 Reference Scenario
The AUTODYN simulation package 3D V3.0.07,[5], was used to evaluate the impulse values on the structural elements, which enclose the space. Values obtained using the AUTODYN simula- tion package were validated using the ConWep programme [6].
Triangular Square Pentagon Hexagon Octagon
Fig. 5 The decrease in impulse values (%),
compared with the reference scenario, Vs Height (m) of group A.
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• Triangular plan of the spatial form, three sides, the im- pulse values were reduced by up to 51 % when com- pared with the initial case [the cylindrical spatial form].
• Cubic spatial forms, four sides, offered a reduction in the impulse values of up to 30% when compared with the initial case.
• Pentagon plan of the spatial form, five sides, the impulse values were reduced by up to 23 % when compared with the initial case.
• Hexagon and octagon plan of the spatial form, six and eight sides, the impulse values were approximately the same, and offered a reduction of up to 14 % when com- pared with the initial case.
The connection openings between spaces offer evacuation routes for the blast waves. The reduction depends upon the number of openings and their dimensions. [For this paper, each underground spatial form has four openings with 4m width and 6m height]. Comparing fig. 6 with fig. 5 shows that spaces with connection openings show a greater reduction in impulse than the equivalent space without openings.
70
60
50
40
30
20
10
0
-10 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
-20
ues were reduced by up to 35 %, when compared with the initial case.
• The octagon plan of the spatial form, the impulse val- ues were reduced by up to 28 %, when compared with the initial case.
• The convex plan of the space caused an increase in the effect of the blast waves inside the space of up to 20
%, when compared with the initial case.
Cylindrical, hemi-spherical, frustum and inverted frustum spaces are examples of the spatial forms, which can be used in the architectural design of underground space as shown in figure 7. The initial case, with which all simulations are com- pared, is the hemi-spherical space. The impulse values are taken at the midpoints of the sides, which form the space and all spaces
Height above ground level (m)
Fig. 7 Underground spatial forms
60 | ||
Triangular Square Pentagon | 50 | |
Hexagon Octagon Convex space | 40 | |
Fig. 6 The decrease in impulse values (%), compared with the reference | 30 | |
scenario, Vs Height (m) at mid-point of sides of group B | 20 | |
10 | ||
• The triangular plan of the spatial form with connec- | 0 |
tion openings can offer reduction in the impulse val-
ues of up to 58% when compared with the initial case.
[The cylindrical spatial form without openings].
• The cubic spatial form offered a reduction in the im- pulse values of up to 55 %, when compared with the initial case.
• The pentagon plan of the spatial form, the impulse values were reduced by up to 50 %, when compared with the initial case.
• The hexagon plan of the spatial form, the impulse val-
-10 1 2 3 4 5 6 7 8 9 10
-20
-30
-40
Height above ground level (m)
Cylindrical space Frustum space Inverted Frustum space
Fig. 8 The decrease in impulse values (%), compared with hemi-
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spherical space Vs Height (m).
Figure 8 shows that the cylindrical spatial forms can offer reduction in the effects of the blast waves inside the space of up to 54%, when compared with a hemi-spherical spatial form, as an initial case.
The Frustum space can offer a reduction of up to 38%, when compared with the initial case, but increase of 30% at floors level. The Inverted frustum space can offer a reduction of up to 41%, when compared with the initial case.
1. Specific spatial forms can offer a significant reduction in the effects of blast waves inside underground space.
2. Cylindrical and inverted frustum geometries are better than a frustum and hemi-spherical geometries for reduc- ing the effects of the blast waves
3. The results declare that each spatial form can offer a cer- tain reduction in the effects of the blast waves.
4. The results declare that each spatial form can offer a cer- tain reduction in the effects of the blast waves.
5. Connection openings between underground spaces can offer a reduction of blast waves through venting.
6. The technique of using specific spatial forms to reduce the effects of blast waves can be used without affecting the functionality of the space.
7. The Autodyn simulation package was found to be a con- venient tool for measuring the effectiveness of using spa- tial forms in reducing the effects of the explosion.
[1] Scottish Development Department, the Welsh office report, ” Roads in
Urban Areas,”the Welsh office, 1993.
[2] I.Bently, A.Alcock, P.Murrain, S.McGlynn, and G. Smith, “Responsive Environments, architecture department and joint Centre for Urban De- sign,” Oxford polytechnic, 1996.
[3l H. Kady, ”The Architectural treatments for protecting structures,”
M.Sc. thesis, Military Technical Collage, Cairo, Egypt, 2003.
[4] E.H. Mahmoud,”Protection against Blast Waves,” 3rd International
Conference on SHOCK & IMPACT LOADS ON STRUCTURES, Singapore,
2003.
[5] “Autodyn program V3.1.17,” Century Dynamics Limited, 12 City Busi- ness Centre, Brighton Road, Horsham, USA, 2010.
[6] “ConWep Program,” U.S. Army Engineer Waterways Experiment Station,
3909 Halls Ferry Road, Vicksburg, MS 39180, 2010.
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