Robustezza Strutturale
191
ROBUSTEZZA STRUTTURALE Franco Bontempi Professore Ordinario di Tecnica delle Costruzioni Facolta’ di Ingegneria Civile e Industriale Sapienza Universita’ di Roma franco.bontempi@uniroma 1.it
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Transcript of Robustezza Strutturale
ROBUSTEZZA STRUTTURALE
Franco BontempiProfessore Ordinario di Tecnica delle Costruzioni
Facolta’ di Ingegneria Civile e IndustrialeSapienza Universita’ di Roma
Requisiti
2
Requisiti strutturali
Condizioni• di esercizio: Rigidezza•
Condizioni• ultime: Resistenza•
Stabilita• ’
Duttilita• ’
Durabilita• ’
Condizioni• estreme:Robustezza•
Resilienza•
Configurazione• nominaledella struttura
Configurazione• danneggiatadella struttura
3
Robustezza / Durabilita’
4
RESILIENCE
5
Definizioni
6
Levels of Structural Crisis
Usu
al
UL
S &
SL
S
Ve
rifi
ca
tio
n F
orm
at
Structural Robustness
Assessment
1st level:
Material
Point
2nd level:
Element
Section
3rd level:
Structural
Element
4th level:
Structural
System 7
8
Structural Robustness (1)
ATTRIBUTES
RELIABILITY
AVAILABILITY
SAFETY
MAINTAINABILITY
INTEGRITY
SECURITY
FAILURE
ERROR
FAULT
permanent interruption of a system ability
to perform a required function
under specified operating conditions
the system is in an incorrect state:
it may or may not cause failure
it is a defect and represents a
potential cause of error, active or dormant
THREATS
NEGATIVE CAUSEST
RU
CT
UR
AL
QU
AL
ITY
more robust
less robust
Capacity of a construction to show • regular decrease of its structural quality due to negative causes.
It implies: •
some smoothness of the decreasea) of structural performance due to negative events (intensive feature); some limited spatial spreadb) of the rupture (extensive feature).
9
Structural Robustness (2)
1010
Compartimentazione
11
12
13
Es.
14
es.
15
16
17
18
19
1846
RUNAWAY (1)
effect
time 20
EFFECT
RU
NA
WAY
(2)
21
222222
Connessione
Es.
23
24
25
26
27
Bad vs Good CollapseSTRUCTURE
& LOADSCollapse
Mechanism
NO SWAY
“IMPLOSION”OF THE
STRUCTURE
“EXPLOSION”OF THE
STRUCTURE
is a process in which
objects are destroyed by
collapsing on themselves
is a process
NOT CONFINED
SWAY
28
29
30
31
WTC 7
Simulated exterior buckling of WTC 7 during the collapse.
32
Es.
33
34
Es.
35
36
37
Bad vs Good CollapseSTRUCTURE
& LOADSCollapse
Mechanism
NO SWAY
“IMPLOSION”OF THE
STRUCTURE
“EXPLOSION”OF THE
STRUCTURE
is a process in which
objects are destroyed by
collapsing on themselves
is a process
NOT CONFINED
SWAY
38
• Capacity of a construction to show regular decrease of its structural quality due to negative causes.
• It implies: a) some smoothness of the decrease of
structural performance due to negative events (intensive feature);
b) some limited spatial spread of the rupture (extensive feature).
39
Structural Robustness (2)
40
Structural Robustness (1)
ATTRIBUTES
RELIABILITY
AVAILABILITY
SAFETY
MAINTAINABILITY
INTEGRITY
SECURITY
FAILURE
ERROR
FAULT
permanent interruption of a system ability
to perform a required function
under specified operating conditions
the system is in an incorrect state:
it may or may not cause failure
it is a defect and represents a
potential cause of error, active or dormant
THREATS
NEGATIVE CAUSEST
RU
CT
UR
AL
QU
AL
ITY
more robust
less robust
Analisi
41
Levels of Structural Crisis
Usu
al
UL
S &
SL
S
Veri
fica
tio
n F
orm
at
Structural Robustness
Assessment
1st level:
Material
Point
2nd level:
Element
Section
3rd level:
Structural
Element
4th level:
Structural
System42
Risposta strutturale e formati di verifica
43
44
Materiale
45
Sezione
46
Momento–curvatura sezione
47
Elemento
SMEARED:Plasticita’
diffusa
LUMPED:Plasticita’
Concentrata
1
48
Momento–curvatura sezione: idealizzazione
2
1 2+ = CERNIERA PLASTICA
49
1/ψ
Interazione M-N
50
Interazione M-N
51
52
53
54
55
56
57
58
59
Carico imposto
60
Carico / Spostamento imposto (1)
61
Carico / Spostamento imposto (2)
62
Carico / Spostamento imposto (3)
63
Push-over (1)
64
Push-down (1)
65
66
Es.
67
68
Applicazione
69
https://en.wikipedia.org/wiki/B-25_Empire_State_Building_crash
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-sta
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tml
https://en.wikipedia.org/wiki/2002_Pirelli_Tower_airplane_crash
93
Esempio: edificio alto
D0
Es.
D1 D2
Scenari (1-2)
96
D3 D4
Scenari (3-4)
97
Modalità di collasso (1-2)
D1 D2 9898
Modalità di collasso (3-4)
D3 D4 9999
0
4
Lo scenario D4
è quello più cattivo:
l’elemento strutturale
critico individuato è la
colonna più esterna!
100
Sintesi dei risultati: elemento critico
100
Modellazione edificio alto
Scenario 1
(1 asta
eliminata)
Scenario 2
(3 aste
eliminate)
Scenario 3
(5 aste
eliminate)
Scenario 4
(7 aste
eliminate)
Scenari di danneggiamento
Collasso secondo scenario 1
Collasso secondo scenario 2
Collasso secondo scenario 3
Collasso secondo scenario 4
Moltiplicatore Ultimo e sua variazione
4,053,57
3,192,64 2,40
0,480,86
1,41 1,65
0,00
0,50
1,00
1,50
2,00
2,50
3,00
3,50
4,00
4,50
D0 D1 D2 D3 D4
Scenario di danneggiamento
uDelta F
F
Sintesi dei risultati
Δ u
u
Progetto
109
Design Strategy #1: CONTINUITY
110
Design Strategy #2: SEGMENTATION
PROGETTAZIONE STRUTTURALE ANTINCENDIO
Es.
Stiffener, bulkhead & deck layout
118
Hull sections with and without the outer hull
119
USS San Francisco after collision with an underwater mountain
120
Es.
Es.
http://pressurevesseltech.asmedigitalcollection.asme.org/article.aspx?articleid=16970
68#
Definizioni: compartimentazione
• CAPACITÀ DI COMPARTIMENTAZIONE IN CASO D’INCENDIO: attitudine di un elemento costruttivo a conservare, sotto l’azione del fuoco, oltre alla propria stabilità, un sufficiente isolamento termico ed una sufficiente tenuta ai fumi e ai gas caldi della combustione, nonché tutte le altre prestazioni se richieste.
• COMPARTIMENTO ANTINCENDIO: parte della costruzione organizzata per rispondere alle esigenze della sicurezza in caso di incendio e delimitata da elementi costruttivi idonei a garantire, sotto l’azione del fuoco e per un dato intervallo di tempo, la capacità di compartimentazione.
Esempi
128
Es.
For six days in January 1998, freezing rain coated Ontario, Quebec and New Brunswick with 7-11 cm (3-4 in) of ice. Trees and hydro wires fell and utility poles and transmission towers came down causing massive power outages, some for as long as a month. It was the most expensive natural disaster in Canada. According to Environment Canada, the ice storm of 1998 directly affected more people than any other previous weather event in Canadian history.
Es.
htt
ps:
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wat
erb
log.
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01
6/0
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ate
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19
14
/
Es.
http://urbanplanet.info/architecture/paris-air-terminal-collapse-report-france/
Es.
Es.
Bonus track
163
Es.
http://www.confederationbridge.com/about/confederation-bridge/design.html
https://www.tuhh.de/sdb/starossek/Veroeffentlichungen/Dateien/Progressive%20collapse%20of%20bridges%20(Uwe%20
Starossek).pdf
Es.
1) Minimum number of removed hangers and most sensitive location for the triggering of the progressive collapse: the bridge results to be more sensible to the damage at mid-span, where the removal of just 5 hanger for the symmetrical rupture and 7 hangers for the asymmetrical rupture is needed in order to trigger the collapse propagation.Shifting the initial damage location aside (about at 1/3 of the span) the asymmetrical rupture of 9 hangers is required for the collapse propagation, while moving the initial damage near the tower even the asymmetrical removal of 12 hangers has no global effects on the structure and very 7 hangers must be symmetrically removed on both sides in order to trigger the propagation of the ruptures on the adjoining hangers.
2) Preferential direction for the collapse propagation: to the higher damage sensibility of the bridge central zone counterpoises a lower acceleration of the collapse progression triggered by central ruptures, with respect to that one triggered by lateral ruptures.This effect is due to the particular configuration of the structural system that requires a growing hanger length from the centre to the sides of the bridge: when a chain rupture trigger, the ultimate elongation required to the hangers adjoining the failed ones increases as the collapse propagates (because the unsupported deck length also increases).If the initial damage occurs at mid-span, it involves the shortest hangers and the collapse propagation is partially slowed down from the growing element ductility of sideward hangers. On the contrary, a more intense initial damage is required sideways to trigger chain ruptures, but then the hanger breakdowns speeds up when moving toward the centre, where the hanger length decreases.
3) Qualitative measure that could possibly lead the collapse to an halt: in the case of a central rupture a closer increment in the section of the hangers (that remain instead the same for about 5/6 of the span length) could possibly provide for a collapse standstill. In
the case of a chain rupture triggered in a lateral zone the preferential direction showed by the progressive collapse would probably make less effective such a measure.
3) Qualitative measure that could possibly lead the collapse to an halt: in the case of a central rupture a closer increment in the section of the hangers (that remain instead the same for about 5/6 of the span length) could possibly provide for a collapse standstill. In the case of a chain rupture triggered in a lateral zone the preferential direction showed by the progressive collapse would probably make less effective such a measure.
4) Sensibility to modality of damage (asymmetrical or symmetrical failure): another consideration about the possible collapse standstill concerns the higher susceptibility of the bridge to an unsymmetrical hanger failure than to a symmetrical one: in the last case the symmetrical hinge formations determines a symmetrical moment increment on the
deck box-girders, thus possibly allowing for an early deck segment detachment that would arrest the collapse
4) Sensibility to modality of damage (asymmetrical or symmetrical failure): another consideration about the possible collapse standstill concerns the higher susceptibility of the bridge to an unsymmetrical hanger failure than to a symmetrical one: in the last case the symmetrical hinge formations determines a symmetrical moment increment on the deck box-girders, thus possibly allowing for an early deck segment detachment that would arrest the collapse
