Appunti del corso di dottorato:
INTRODUZIONE ALL'OTTIMIZZAZIONE STRUTTURALE
IIa parte
Lezione del 28 maggio 2014
Lecture of the Ph.D. Course on
STRUCTURAL OPTIMIZATION
2nd part
May, 28, 2014
TechTAC® CFD Report Summary: A Comparison of Two Types of Tubing Anchor Catchers
Corso di dottorato in Ottimizzazione Strutturale: applicazione mensola strallata - Bontempi
1. Franco Bontempi
Ordinario di Tecnca delle Costruzioni
Facolta’ di Ingegneria Civile e Industriale
Sapienza Universita’ di Roma
Introduzione alla
OTTIMIZZAZIONE STRUTTURALE:
APPLICAZIONE AD UNA
MENSOLA STRALLATA
7. 7
CONNECTION REGIONS
• Presence of high stress levels;
• Diffusive field of stress - so-called D-regions;
• Geometrical complexity, related to the position
and interference of different structural parts
converging there;
• Requirements of minimum space usage,
essentially due to architectural appearance;
• Necessity to guarantee a substantial good
structural behavior - strength, ductility, and
robustness;
• Demand from constructability point of view.
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11. 11
BASIS OF DESIGN (1)
• simplicity:
the structural configuration of the connection
must be made by very regular and flat parts,
by which
– the stress state has the most possible uniformity;
– there are no stress concentrations;
– the load transfer is obtained by the most straight
path;
– it is possible to develop a complete integration
between steel parts and concrete mass, with an
accurate structural anchorage.
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12. 12
BASIS OF DESIGN (2)
• dependability:
the structural configuration must be have
– suitable functional performance characteristics
(Serviceability Limit States, SLS),
– appropriate strength capacity
(Ultimate Limit States, ULS),
– capacity to support accidental situations, without
showing disproportionate consequences when
triggered by limited damage
(Structural Robustness).
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20. 20
FIRST ANALYSIS (A):
two dimensional geometry
column
a
Vsd
Vsd
a/2
Vsd*=Vsd/2
Vsd* =Vsd/2
column
a
Vsd
Vsd
column
a
Vsd
Vsd
a/2
Vsd*=Vsd/2
Vsd* =Vsd/2
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21. 21
• the steel parts, the longitudinal bars and the
stirrups are represented by bars working both
in tension and in compression, while concrete
parts are lumped into bars with no tension
behavior;
• one model a segment of concrete column
sufficient to extinguish the diffusive effects
connected with this D-region, i.e. until a B-
region is reached, governed by the so-called
Bernoulli stress regime;
FIRST ANALYSIS (B):
mechanical modeling by S&T
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22. 22
S & T Model Definition
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51. 51
CONCLUSIONS
• The evolution of the design of a bracket component,
supported by a cable-stayed system, is presented.
• This apparently simple element conceals a rather complex
structural geometry, developed to be suitable both for
strength requirements and constructability. The so devised
solution can assure:
– Manufacturing of precast elements without exterior parts;
– Minimal size of the bracket and completely hidden insertion in the
supported beams;
– Compliance with different standards.
• The evolution of the leading concepts and of the geometry
of this element is explained together with the numerical
analysis obtained both by synthetic models, like strut & tie,
and by full non linear finite element models.
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54. 54
INDEX PART 1
Basis of the Problem
Strut & Tie Modeling
Finite Element Analysis by
Substrucuring Technique and S&T
Improvement Strategies
Models and Programs Validation
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72. 72
DESIGN CRITERIA
• SIMPLICITY:
1. the load path from the loading appliction points to
the main internal region of the structural element
must be the simplest and the quitest; it means that
– the stress flow should be regular;
– stress concentrations should be avoided;
– the loading transfer should prefer direct
placement;
– integration between steel parts and concrete
must be accurate and anchorage truthful;
• DEPENDABILITY;
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73. 73
PERFORMANCE CRITERIA (i)
• Ultimate Limit State:
1. strength verified by partial safety factors
disequations; there are admitted yielded
parts of the bracket and damaged portions
of the concrete in the structural element;
– the strength capacity will be verified by non
linear analysis, starting from unloaded to
collapse loading;
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PERFORMANCE CRITERIA (ii)
• Serviceability Limit State:
1. the structural behavior should be elastic-
linear until an adequate loading level
(usually, the ultimate loading level / 1.5);
– in particular, steel parts must not be yielded
anywhere and the concrete must experience
a low stress level;
2. the displacements of the bracket for service
loading must be limited;
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75. 75
PERFORMANCE CRITERIA (iii)
• Structural Robustness:
1. the connection device failure should develop
after major failure of the structural elemnt at
which the connection device is inserted;
2. the connection device must be able to
support the failure of one of the external ties,
i.e. each tie and directly connected parts
must be able anyway to support the double
of the service limit loading;
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78. 78
-1000
-800
-600
-400
-200
0
200
400
600
800
1000
-2000 0 2000 4000 6000 8000 10000
N
M
SYM
ASYM
M [kNm]
compression
N [kN]
tension
stirrups
longitudinal
bars
As=5 ø 22
As’=5 ø 22
ø 8/2b 9 cm
COLUMN REINFORCEMENT DESIGN
Reinforcement
ACTION N [kN] M [kNm]
SYM 2100 0
ASYM 1050 462
50 cm
60 cm
79. 79
STRUCTURAL MODELING (i)
• A slice of half column is considered
(plane stress assumption)
column
a
Vsd
Vsd
a/2
Vsd*=Vsd/2
Vsd* =Vsd/2
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STRUCTURAL MODELING (model #1)
Strut & Tie modeling of the stayed bracket
STEP #1 STEP #2
STEP #3 STEP #4
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82. 82
STRUCTURAL MODELING (model #2)
Alternative S&T modeling of the stayed bracket
STEP #1
STEP #3 STEP #4
STEP #2
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83. 83
STRUCTURAL MODELING (model #3)
Alternative S&T modeling of the stayed bracket
STEP #1
STEP #3 STEP #4
STEP #2
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84. 84
STRUCTURAL MODELING
OF CONCRETE PART (I):
trusswork discretization
ab
lslAA
a
bsaAA
b
asbAA
ba
ba
ba
dd
yy
xx
2
2
2
2
2
8
3
2
3
8
3
2
3
8
3
2
,
,
,
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85. 85
4321
,,, uuuu
VIVIVIIIIII
NNNNNN ,,,,,
a
x
y
ux
b
y
y
vy
abx
v
y
u yx
b
l
aNNNN
N
VIVIII
x
a
l
bNNNN
N
VIVIVIII
y
l
NNN VIV
xy
xyyx NNN ,,
STRUCTURAL MODELING
OF CONCRETE PART (II):
stress representation
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111. 111
Legenda
Output Descrizione Valore di
Design
[N/mm^2]
SMAXBIEL tensione massima negli elementi rappresentanti i tiranti 580
SMAXTEL tensione massima negli elementi rappresentanti il telaio 290
SMINTEL tensione minima negli elementi rappresentanti il telaio -290
SMAXSTAF tensione massima negli elementi rappresentanti le armature lente
secondarie del pilastro
374
SMINSTAF tensione massima negativa negli elementi rappresentanti le armature lente
secondarie del pilastro
- 374
SMAXLONG tensione massima negli elementi rappresentanti le armature lente
principali del pilastro
374
SMINLONG tensione massima negativa negli elementi rappresentanti le armature lente
principali del pilastro
- 374
SMAXCA tensione massima negli elementi rappresentanti il calcestruzzo 1,5
SMINCA tensione massima negativa negli elementi rappresentanti il calcestruzzo -28
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ELASTIC- PLASTIC MATERIAL LAW
WITH VON MISES CRITERION
62519.4
]N/mm[10000
max
2
max
00138.0
]N/mm[290 2
y
y
][N/mm210000 2
0 E
*100/1 01 EE
x10^(-3)
E0
E1
y
y
max
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127. 127
>290
<-290
Vsd = 1050 kN – cap element stress:
e-plastic analysis (stress X)
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>290
<-290
Vsd = 1050 kN – cap element stress:
e-plastic analysis (stress Y)
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>290
<-290
Vsd = 1050 kN – cap element stress:
e-plastic analysis (Von Mises) (I)
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130. 130
>580
<-580
Vsd = 1050 kN – cap element stress:
e-plastic analysis (Von Mises) (II)
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131. 131
Vsd = 1050 kN – cap element strain:
e-plastic analysis (Von Mises strain)
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132. 132
Vsd = 1050 kN – reinforcement bar stress
• max tension = 132 MPa
• min compression = -54,9 MPa
stirrups longitudinal
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133. 133
Vsd = 1050 kN – ties and concrete stress
concrete
• max tension = 0 MPa
• min compression = -19,8 MPa
• tension = 582,7 MPa
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147. 147
COMMENTS
• The actual configuration of the Stayed Bracket
seems to be not able in sustaining adequately the
load of Vsd=1050 kN both in symmetric and
asymmetric load scenarios.
• In general, the frame stresses are greater than the
yielding values, also if they are less than the failure
values.
• The amplitude of the yielded zone suggest to adopt
strategies to improve the stayed bracket
performances:
Strategy 1: improve the frame thickNess
Strategy 2: improve the frame size
Strategy 3: downloading
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150. 150
Vsd = 1050 kN – cap element stress
e-plastic analysis (stress X)
>290
<-290
Strategy 1: improve the frame thickNess
Actual thickNess
th = 6 mm
Improved thickNess
th = 10 mm
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Vsd = 1050 kN – cap element stress
e-plastic analysis (stress Y)
Strategy 1: improve the frame thickNess
>290
<-290
Actual thickNess
th = 6 mm
Improved thickNess
th = 10 mm
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Vsd = 1050 kN – cap element stress
e-plastic analysis (Von Mises) (I)
>290
<-290
Actual thickNess
th = 6 mm
Strategy 1: improve the frame thickNess
Improved thickNess
th = 10 mm
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>580
<-580
Vsd = 1050 kN – cap element stress
e-plastic analysis (Von Mises) (II)
Actual thickNess
th = 6 mm
Strategy 1: improve the frame thickNess
Improved thickNess
th = 10 mm
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154. 154
Vsd = 1050 kN – cap element strain – e-
plastic analysis (Von Mises strain)
Strategy 1: improve the frame thickNess
Actual thickNess
th = 6 mm
Improved thickNess
th = 10 mm
155. 155
Vsd = 1050 kN – cap element strain
e-plastic analysis (Von Mises strain)
Improved thickNess
th = 10 mm
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156. 156
>580
<-580
Vsd = 1050 kN – cap element stress
e-plastic analysis (Von Mises)
th = 10mm
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157. 157
Vsd = 1050 kN – cap element stress
e-plastic analysis (Von Mises)
>290
<-290
th = 10mm
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158. 158
h0 h1
Strategy 2: improve the frame size
Actual Improved
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159. 159
Vsd = 1050 kN – cap element stress
e-plastic analysis (stress X)
>290
<-290
Strategy 2: improve the frame size
Actual size
h = 145 mm
Improved size
h = 200 mm
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160. 160
Vsd = 1050 kN – cap element stress
e-plastic analysis (stress Y)
>290
<-290
Strategy 2: improve the frame size
Actual size
h = 145 mm
Improved size
h = 200 mm
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161. 161
Vsd = 1050 kN – cap element stress
e-plastic analysis (Von Mises) (I)
>290
<-290
Strategy 2: improve the frame size
Actual size
h = 145 mm
Improved size
h = 200 mm
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162. 162
>580
<-580
Vsd = 1050 kN – cap element stress
e-plastic analysis (Von Mises) (II)
Strategy 2: improve the frame size
Actual size
h = 145 mm
Improved size
h = 200 mm
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>290
<-290
Vsd = 1050*1,33= 1396,5 kN SYM th = 12 mm
cap element stress / e-plastic analysis
>290
<-290
STRESS Y
STRESS X
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244. 244
>290
<-290
von MISES I
Vsd = 1050*1,33= 1396,5 kN SYM th = 12 mm
cap element stress / e-plastic analysis
>580
<-580
von MISES II
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246. 246
ANALISI E VERIFICHE STRUTTURALI
DELLE CONFIGURAZIONI
per Vsd = 1050 Kn
IN PRESENZA DI PLUVIALE / A 2 VIE
ISOTROPA
Dicembre 2007
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