OPTIMIZATION OF THE TALL BUILDINGS STRUCTURAL SYSTEM AGAINST PROGRESSIVE COLLAPSE. Vertical bracing systems and outriggers play a decisive role on the progressive collapse susceptibility. In relation to a steel tall building. Evaluation of structural performances of steel tall building is performed thought full non-linear analyses on finite element models. Performances of initial and optimized configuration are compared.

1. Institute for Sustainability and
OPTIMIZATION OFInstitute for Sustainability and
Innovation in Structural Engineering
Filippo Gentili Franco Bontempi
OPTIMIZATION OF
THE TALL BUILDINGS STRUCTURAL SYSTEM
AGAINST PROGRESSIVE COLLAPSEfilippo.gentili@uc.pt franco.bontempi@uniroma1.it
INTRODUCTION
AGAINST PROGRESSIVE COLLAPSE
Vertical bracing systems and outriggers play a
Fire Scenario 1
filippo.gentili@uc.pt franco.bontempi@uniroma1.it
Vertical bracing systems and outriggers play a
decisive role on the progressive collapse
susceptibility.
Scala A Ascensore
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54 55 56 57 58 59 60
Fire Scenario 1
Scala A Ascensore
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54 55 56 57 58 59 60
Scala A Ascensore
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54 55 56 57 58 59 60
In relation to a steel tall building (Figure 1).
Evaluation of structural performances of steel tall
building is performed thought full non-linear
analyses on finite element models
Ascensore Scala A
Scala B
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HEA240
HEM280
HEA240IPE270
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HEA 240 IPE 270
IPE270
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HEM 260 HEM 260 HEM 260
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160
m
Frame B
Ascensore Scala A
Scala B
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270
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HEA 240 IPE 270 IPE 300
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IPE
270
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IPE270
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IPE300
IPE270
HEA240
HEM280
HEA240IPE270
IPE300
IPE270
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HEA 240 IPE 270
IPE270
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IPE270
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IPE300
IPE270
IPE270
IPE 270 HEA 260 IPE 270 HEA 240 IPE 270
HEM 260 HEM 260 HEM 260
IPE 270IPE 270
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35 m
Ascensore Scala A
Scala B
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270
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HEA 240 IPE 270 IPE 300
HEM 260 IPE 270
IPE
270
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IPE270
IPE270
IPE300
IPE270
HEA240
HEM280
HEA240IPE270
IPE300
IPE270
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HEA 240 IPE 270
IPE270
IPE300
IPE270
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HEM 260 HEM 260 HEM 260
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analyses on finite element models
Performances of initial (Figure 2) and optimized
(Figure 3) configuration are compared.
Figure 1 – Case Study:
Three-dimensional view and Fire Scenarios
Figure 2 – Initial Configuration:
In blue vertical bracing systems
Figure 3 – Optimized Configuration:
in red the added vertical bracing systems
in light blue the outrigger at 29th floor
Fire Scenario 2Frame A
35 m
OPTIMIZATION PROCEDURE
in light blue the outrigger at 29 floor
Heated FireSteel FireSeveral configurations (Figure 4) have been A1 A2 A3 A4 A5Heated
Columns
Fire
Resistance
No. Cases Avg Min Max
1 8 180 180 180
2 7 180 180 180
Conf.
Steel
Mass
[ton]
Fire
Resistance
[min]
A1 799 75
A2 857 75
Several configurations (Figure 4) have been
assessed. The displacement on the top floor (1
meter) has been considered as indicator of the
global colapse.
A1 A2 A3 A4 A5
2 7 180 180 180
3 6 143.6 80 180
4 5 88.4 78 103
5 4 67.5 66 69
A2 857 75
A3 877 180
A4 877 180
A5 877 180
The collapse can be avoided with outriggers
(Table 1). The position has been varied in order
to minimize lateral displacement. Table 1 – Mass and Fire Table 2 – Fire Resistance ofto minimize lateral displacement.
Spatial extension of fire has been increased in
the best configurations (Table 2).
Figure 4 – Sectional Configurations considered for Frame ATable 1 – Mass and Fire
Resistance of Frame A
Table 2 – Fire Resistance of
Frame A5 increasing fire extension
FIRE STRUCTURAL PERFORMANCES ANALSYS
the best configurations (Table 2).
Three–dimensional spatial models have been
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I
Time
[min]
Collapsed Floor
Area [m2]
Collapsed Floor
Area Percentage [%]
Original Optimized Original Optimized
Three–dimensional spatial models have been
used.
An explicit dynamic solver allowed to trace
Scala A Ascensore
Ascensore Scala A
Scala B
IPE 270
IPE 270 HEA 240
HEA 240 IPE 270 IPE 300 IPE 300 IPE 270 HEA 240 IPE 270
IPE270
IPE300
IPE270
IPE270
IPE270
IPE300
IPE270
IPE270
IPE 270 HEA 260 IPE 270 HEA 240 IPE 270
IPE270
IPE270
23 24 25 26 27 28 29 30
31 32 33 34 35 36 37 38
39 40 41 42 43 44 45 46 47
Scala A Ascensore
Ascensore Scala A
Scala B
IPE 270
IPE 270 HEA 240
HEA 240 IPE 270 IPE 300 IPE 300 IPE 270 HEA 240 IPE 270
IPE270
IPE300
IPE270
IPE270
IPE270
IPE300
IPE270
IPE270
IPE 270 HEA 260 IPE 270 HEA 240 IPE 270
IPE270
IPE270
23 24 25 26 27 28 29 30
31 32 33 34 35 36 37 38
39 40 41 42 43 44 45 46 47
Scala A Ascensore
Ascensore Scala A
Scala B
IPE 270
IPE 270 HEA 240
HEA 240 IPE 270 IPE 300 IPE 300 IPE 270 HEA 240 IPE 270
IPE270
IPE300
IPE270
IPE270
IPE270
IPE300
IPE270
IPE270
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IPE270
IPE270
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I
N
I
T
I
A
[min]
Original Optimized Original Optimized
60 130.26 0.00 11.21 0.00
75 208.71 76.71 17.97 6.60
90 325.21 76.71 28.01 6.60
An explicit dynamic solver allowed to trace
down the propagation of failures.
Reduction in displacements of Initial and
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270
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IPE 270 HEA 240 IPE 270 IPE 300
HEM 260 IPE 270
IPE
270
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IPE270
IPE270
IPE300
IPE270
HEA240
HEM280
HEA240IPE270
IPE300
IPE270
IPE270
HEA 240 IPE 270
HEM 260 HEM 260 HEM 260
IPE 270IPE 270
1 2 3 4 5 6 7
8 9 10 11 12 13
14 15 16 17 18 19 20 21 22
IPE 270
IPE 270
IPE
270
IPE 270
IPE 270 HEA 240 IPE 270 IPE 300
HEM 260 IPE 270
IPE
270
IPE 300 IPE 270
IPE270
IPE270
IPE300
IPE270
HEA240
HEM280
HEA240IPE270
IPE300
IPE270
IPE270
HEA 240 IPE 270
HEM 260 HEM 260 HEM 260
IPE 270IPE 270
1 2 3 4 5 6 7
8 9 10 11 12 13
14 15 16 17 18 19 20 21 22
IPE 270
IPE 270
IPE
270
IPE 270
IPE 270 HEA 240 IPE 270 IPE 300
HEM 260 IPE 270
IPE
270
IPE 300 IPE 270
IPE270
IPE270
IPE300
IPE270
HEA240
HEM280
HEA240IPE270
IPE300
IPE270
IPE270
HEA 240 IPE 270
HEM 260 HEM 260 HEM 260
IPE 270IPE 270
1 2 3 4 5 6 7
8 9 10 11 12 13
14 15 16 17 18 19 20 21 22
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A
L
O
P120 350.21 230.31 30.16 19.83
150 No Con. 397.22 No Con. 34.21
Reduction in displacements of Initial and
Optimized (Figure 5 top and bottom
respectively) Configuration is considerable.
Table 3 – Comparison of collapsed floor area between
Original and Optimized Configuration for Fire Scenario 1
Scala A Ascensore
Ascensore Scala A
Scala B
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HEA 240 IPE 270 IPE 300 IPE 300 IPE 270 HEA 240 IPE 270
IPE270
IPE300
IPE270
IPE270
IPE270
IPE300
IPE270
IPE270
IPE 270 HEA 260 IPE 270 HEA 240 IPE 270
IPE270
IPE270
23 24 25 26 27 28 29 30
31 32 33 34 35 36 37 38
39 40 41 42 43 44 45 46 47
Scala A Ascensore
Ascensore Scala A
Scala B
IPE 270 HEA 240
IPE270
IPE300
IPE270
IPE270
IPE270
IPE300
IPE270
IPE270
IPE 270 HEA 260 IPE 270 HEA 240 IPE 270
IPE270
IPE270
23 24 25 26 27 28 29 30
31 32 33 34 35 36 37 38
39 40 41 42 43 44 45 46 47
Scala A Ascensore
Ascensore Scala A
Scala B
IPE 270 HEA 240
IPE270
IPE300
IPE270
IPE270
IPE270
IPE300
IPE270
IPE270
IPE 270 HEA 260 IPE 270 HEA 240 IPE 270
IPE270
IPE270
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P
T
M
I
Z
Also the portion of building, involved in the
collapse, changes substantially (Table 3).
Figure 5 – Displacement of the top floor over 1m of Initial (Figure 5 top) and Optimized
(Figure 5 bottom) Configuration for Fire Scenario 1
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270
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HEM 260 IPE 270
IPE
270
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IPE270
IPE270
IPE300
IPE270
HEA240
HEM280
HEA240IPE270
IPE300
IPE270
IPE270
HEA 240 IPE 270
HEM 260 HEM 260 HEM 260
IPE 270IPE 270
1 2 3 4 5 6 7
8 9 10 11 12 13
14 15 16 17 18 19 20 21 22
IPE 270
IPE 270
IPE
270
IPE 270
IPE 270 HEA 240 IPE 270 IPE 300
HEM 260 IPE 270
IPE
270
IPE 300 IPE 270
IPE270
IPE270
IPE300
IPE270
HEA240
HEM280
HEA240IPE270
IPE300
IPE270
IPE270
HEA 240 IPE 270
HEM 260 HEM 260 HEM 260
IPE 270IPE 270
1 2 3 4 5 6 7
8 9 10 11 12 13
14 15 16 17 18 19 20 21 22
IPE 270
IPE 270
IPE
270
IPE 270
IPE 270 HEA 240 IPE 270 IPE 300
HEM 260 IPE 270
IPE
270
IPE 300 IPE 270
IPE270
IPE270
IPE300
IPE270
HEA240
HEM280
HEA240IPE270
IPE300
IPE270
IPE270
HEA 240 IPE 270
HEM 260 HEM 260 HEM 260
IPE 270IPE 270
1 2 3 4 5 6 7
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14 15 16 17 18 19 20 21 22
Z
E
D
Non-linear push-over analyses are
conducted. A triangular lateral load has
(Figure 5 bottom) Configuration for Fire Scenario 1
(Eq. 1)
ROBUSTNESS AND EFFICIENCY INDICES
(Eq. 3)conducted. A triangular lateral load has
been applied at ambient temperature
and after 30, 60 and 90 min fire
exposure.
(Eq. 1)
(Eq. 2)
(Eq. 3)
(Eq. 4)
1.11
1.40
1.19
1.5
2
1.00
0.72 0.710.75
1A robustness index at ambient (Eq. 1)
and elevated (Eq. 2) temperature,
function of stiffness K, strength R and
1.06 1.11 1.19
0.5
1IE [-]0.50
0.12
0.27
0.25
0.5
IR [-]
function of stiffness K, strength R and
ductility μ is proposed (Figure 6).
A quantitative evaluation (Figure 7) of
the performance improvement due to 0
No Fire 30 min 60 min 90 min
Fire Scenario 1
0.12
0.00
0
No Fire 30 min 60 min 90 min
Initial Optimized
the performance improvement due to
structural measures is achieved through
the definition of an efficiency index (Eq.
3 and Eq. 4). Figure 7 – Evolution of Efficiency IndexFigure 6 – Evolution of Robustness Index3 and Eq. 4). Figure 7 – Evolution of Efficiency Index
Str
StroNGER S.r.l.
Figure 6 – Evolution of Robustness Index
Str
o N
GER
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