metoda anmetoda analizei globale dupa ec3alizei globale dupa ec3_ig.ppt

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METOD A ANALIZEI GLOBALE  A STRUCTURILOR DUP A EN V 1993-1-1    C  .    T    E    L    E    M    A    N  .    I    N    G    I    N    E    R    I    E    G    E    O    T    E    H    N    I    C    A      M    A    S    T    E    R  .    C    U    R    S    1 1

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Page 1: METODA ANMETODA ANALIZEI GLOBALE DUPA EC3ALIZEI GLOBALE DUPA EC3_IG.ppt

7/27/2019 METODA ANMETODA ANALIZEI GLOBALE DUPA EC3ALIZEI GLOBALE DUPA EC3_IG.ppt

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METODA ANALIZEI GLOBALE A STRUCTURILOR DUPA ENV 1993-1-1

   C .

   T   E   L   E   M   A   N .

   I   N   G   I   N   E   R   I   E

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   E   O   T   E   H   N   I   C   A  -   M   A   S   T   E   R .

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 ANALIZA STRUCTURALA A

CONSTRUCTIILOR CU SCHELET DIN OTEL

Comportarea structurilor metalice este consecinţă  directă a caracteristicilor şi  proprietăţilor fizico

mecanice ale oţelului: Sectiunile elementelor sunt uniforme datorita omogenitatii otelului asadar este usor de anticipat 

rezistenta elementului in sine,

Masa raportata la sectiune a elementelor de otel este considerabil redusa fata de cea a elementelor

din beton armat cu aceeasi destinatie in structura,

Elementele din otel prezinta o zveltete crescuta raportata la elementele din beton armat datorita

sectiunilor reduse ce rezulta din calculul de dimensionare,

Rezistenta pe sectiune a elementelor de otel este mult mai mare decat a elentelor de beton armat 

supuse la aceleasi solicitari, Innadirile respectiv imbinarile dinte elementele din otel prezinta tolerante foarte reduse.

Structurile din otel sunt usoare, zvelte si in consecinta relativ sensibile la toate formele de

instabilitate

In acelasi timp datorita caracteristicilor de material otelul are o comportare duala: elastic pana la

limita de proportionalitate a deformatiilor (0.2%) dar si ductil (plastic) cu rezerve importante de

rezistenta pe sectiune (cel putin 20% la otelul structural). Datorita acestor rezerve sectiunile de otel

pot dezvolta deformatii importante care sunt luate in consideratie in calculul in domeniul plastic.

Formarea articulatiilor plastice este usor de anticipat si dirijat in intreaga structura tocmai datorita

omogenitatii sectiunilor din otel.

Structurile din otel pot fi proiectate atat in elastic cat si in plastic datorita rezervelor de

rezistenta peste limita de curgere f y pana la limita de rupere f u (f u/f y1,2)

   C .   T  e   l  e  m  a  n .

   S   t  e   l   S   t  r  u  c   t  u  r  e  s   I   I   I .

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• Evaluarea comportarii structurale (forte interne, momente si deformatii) sub actiuni

statice si apoi dinamice este utila in identificarea optiunilor de optimizare cat si de

asigurare a sigurantei in exploatare pe toata durata de viata a constructiei.

• Sub termenul generic de “analiza globala” aceasta evaluare se dezvolta pe baza mai

multor metode specifice care se bazeaza pe diferiti factori de influenta: abilitatea de

deformatie a structurii, caracteristicile geometrice precum si proprietatile

materialului, toate acestea aducand o contributie individuala la asigurarea

capacitatii de rezistenta a structurii la solicitari exterioare prin deformari lanivelul

tuturor elementelor componente ale acestei structuri.

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   S   t  e   l   S   t  r  u  c   t  u  r  e  s   I   I   I .

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 ANALIZA STRUCTURALA A

CONSTRUCTIILOR CU SCHELET DIN OTEL

TIPUL DE ANALIZA

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Structurile curente din otel sunt modelate pe baza sistemului de cadre orientate

bidirectional si alcatuite din elemente lineare care preiau solicitarile exterioaredezvoltand tensiuni interne si deformatii.

Deformatiile sunt la inceput infinitezimale dar la cresterea fortelor interne si

momentelor aceste deformatii cresc ajungand la limita impusa de rezistenta,

stabilitate sau de alte criterii anexa.

Amplitudinea acestor deformatii este cea care sta la baza clasificarii structurilor incadre in categorii cu caracteristici importante:

Cadre cu noduri deplasabile sau ne-deplasabile (fixe),

Cadre cu noduri rigide, semi-rigide sau articulate (flexibile);

Cadre contravantuite sau ne-contravantuite.

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   S   t  e   l   S   t  r  u  c   t  u  r  e  s   I   I   I .

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 ANALIZA STRUCTURALA A

CONSTRUCTIILOR CU SCHELET DIN OTEL

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 ANALIZA IN DOMENIUL ELASTIC 

• Analiza in domeniul elastic este cea mai utilizata in vdrul proiectarii structurilor din oteldtorita faptului ca ea se poate aplica oricarui tip de structura datorita faptului ca in cadrulacesteia nu se impun restrictii sau alte conditii pentru asigurarea comportrii dutile a

imbinarilor.• Structurile analizate in elastic sunt structuri ce conserva energia datorita incapacitatii

disiparii acesteia (structuri nedisipative).

• Verificarile au ca scop mentinerea tensiunilor combinate rezultate din eforturisectionale si momente de incovoiere sub nivelul capacitatii de plasticizare pesectiune.

• Baza conceptului:

Analiza la nivelul unui element structural:

Efecte de ordin II globale (P- ), si locael (P-  ) 

Deformatii in urma

imperfectiunilor locale la nivel

de element

Deformatii globale hHhM;xHxM

VhHLM

h

xVVxHxM  

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   S   t  e   l   S   t  r  u  c   t  u  r  e  s   I   I   I

 .

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Imperfectiunil

e locale sunt

neglijate

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CRITERII DE CLASIFICARE STRUCTURALA

PE BAZA SENSIBILITATII LA EFECTELE DE ORDIN II

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EFECTELE DE ORDIN II

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EFECTUL DEPLASARILOR

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METODE DE SIMULARE A EFECTELOR DE ORDIN II

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EFECTELE CURBURII INITIALE e0DATORITA INCOVOIERII DIN FLAMBAJ

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Daca NNcr /4 structura este considerata cu noduri fixe iar efectul curburii initiale

asupra comportarii globale se neglijeaza ;

Rezulta ca:

Daca se tine cont de curbura

valoarea critica se modifica:

Curbura initiala depinde de mai multi factori:

- fveltete,

- axa flambaj,

- forma sectiunii,

- clasa sectiunii,

- curba de flambaj,

- metoda de analiza globala.

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 ANALIZA DE ORDIN II PRIN METODA PAS CU PAS (ITERATIVA)

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Unghiurile i se stabilesc la fiecare pas iterativ al analizei

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EVALUAREA SARCINII CRITICE SI FACTORUL DE AMPLIFICAREcr 

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Actiunile laterale se voramplifica cu acest coeficient 

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DETERMINAREA RAPORTULUI V/VcrSAUcr

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CONSIDERAREA EFECTUL UI IMPERFECTIUNILOR

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INCLINAREA GENERALA A STRUCTURII

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VALORILE CURBURII INITIALE ECHIVALENTE e0,d

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SECTIUNEA TRANSVERSALA  METODA DE ANALIZA GLOBALA 

VERIFICARI DE

REZISTENTA

TIPURILE DE SECTIUNI SI AXELE  ELASTICA SAU RIGID-PLASTICA 

SAU ELASTICA CU ARTICULATIIPLASTICE PERFECTE 

ELASTO-PLASTICA (MEODA

ZONELOR DE PLASTICIZARE) 

ELASTICA  Oricare 

LINEAR PLASTICA Oricare 

NE-LINEAR

PLASTICA 

Sectiuni in I- Axa y-y 

Sectiuni in I- Axa z-z 

Sectiuni tubulare rectangulare 

Sectiuni tubulare circulare 

Curba de flambaj    eff   k 

M1 =1,05 M1 = 1,1 M1 =1,15 M1 = 1,2

a  0,21  l/600  0,12  0,23  0,33  0,42 

 b  0,34  l/380  0,08  0,15  0,22  0,28 

c  0,49  l/270  0,06  0,11  0,16  0,20 

d  0,76  l/180  0,04  0,08  0,11  0,14 

Elemente neuniforme: Wel/A sau pl/A se utilizeaza la centrul lungimii de flambaj  

AW k  el  y /2,0   

AW k   pl  y /2,0   

AW k   pl  y /2,033,1    AW k   pl  y /2,0   

 /0,2 eff   y ek   /eff   y ek 

AW k   pl  y /2,033,1    AW k   pl  y /2,0   

 /5,1 eff   y ek   /eff   y ek 

0,121     k k k  y

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IMPERFECTIUNILOR SISTEMELOR CU ZABRELE

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 ANALIZA ELASTICA GLOBALA

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CRITERII DE ANALIZA PLASTICA

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EVALUAREA EFECTELOR DE ORDIN II

   C

 .   T   E   L   E   M   A   N .

   I   N   G   I   N   E   R   I   E

   G

   E   O   T   E   H   N   I   C   A  -   M   A   S   T   E   R

 .

   C   U   R   S   1

21

ELASTICA

RIGID-

PLASTICA

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CLASIFICAREA STRUCTURILOR PE BAZA IMBINARILOR STRUCTURALE

   C

 .   T   E   L   E   M   A   N .

   I   N   G   I   N   E   R   I   E

   G

   E   O   T   E   H   N   I   C   A  -   M   A   S   T   E   R

 .

   C   U   R   S   1

22

CRITERIILE DE CLASIFICARE A IMBINARILOR STRUCTURALE

DUPA

REZISTENTA

DUPA

RIGIDITATE

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   C

 .   T   E   L   E   M   A   N .

   I   N   G   I   N   E   R   I   E

   G

   E   O   T   E   H   N   I   C   A  -   M   A   S   T   E   R

 .

   C   U   R   S   1

23

MODELAREA INFLUENTEI IMBINARILOR

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RIGIDITATEA LA ROTIRE Sj.

LIMITE IN CLASIFICAREA IMBINARILOR STRUCTURALE

   C

 .   T   E   L   E   M   A   N .

   I   N   G   I   N   E   R   I   E

   G

   E   O   T   E   H   N   I   C   A  -   M   A   S   T   E   R

 .

   C   U   R   S   1

24

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CURBELE STANDARD DE MOMENT-ROTIRE

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 .   T   E   L   E   M   A   N .

   I   N   G   I   N   E   R   I   E

   G

   E   O   T   E   H   N   I   C   A  -   M   A   S   T   E   R

 .

   C   U   R   S

   1

25

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   C

 .   T   E   L   E   M   A   N .

   I   N   G   I   N   E   R   I   E

   G

   E   O   T   E   H   N   I   C   A  -   M   A   S   T   E   R

 .

   C   U   R   S

   1

26

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Imperfections of the steel elements and structures 

The structural analysis of the steel frames takes into account the effects of imperfections,

local or global.

Local imperfections of the individual compressed member are: residual stresses;

geometrical imperfections.

The lack of verticality, of straightness, of flatness, of fit and other eccentricities present in

joints of the unloaded structure are considered local imperfections. Some the

imperfections are taken care of by EN 1090 and limited at specific allowed tolerances.

In the process of analysis and design the local imperfections are considered by using

equivalent geometric imperfections unless their effects are already included in the resistance

formulae used for the design of the individual members.

The equivalent imperfections that should be taken into account are:

• a) global imperfections for frames and bracing systems (P- effect )

• b) local imperfections for individual members ( P-  effect).

   C .   T  e

   l  e  m  a  n .

   S   t  e   l   S   t  r  u  c   t  u  r  e  s   I   I

   I .

   L  e  c   t  u  r  e

   2

   2   7

Elastic instability of a framed structure: a) sway frame ; b) non sway frame

a b

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Imperfections considered in the global analysis of frames 

In the analysis of the frame the elastic buckling mode of a structure is considered for every

plane of buckling so both in and out of plane buckling including torsional buckling with

symmetric and asymmetric buckling shapes should be taken into account in the most un-

favourable direction and form.

Imperfections of the sway frames

The effect of the imperfections is inserted in the frame analysis by means of an equivalent 

imperfection:

- initial sway imperfection,

- individual bow imperfections of members.

The imperfections may be determined from:

a) global initial sway imperfections:

mh0       0 – basic value of the imperfection,  0=1/200;

 h – reduction factor depending on the height of the columns:

132

h

2

h

h

 

 h – height of the structure (m) ;

 m – reduction factor for the number of columns in a row:

 

  

 m

115.0m

 

m – the number of columns in a row including only those columns

which carry a vertical load N Ed not less than 50% of the average

value of the column in the vertical plane considered.

For structures with a dominant sway buckling mode, the effects of global and local imperfections

are considered as a deviation from verticality to which a bow is added. The initial sway

imperfections should apply in all relevant horizontal directions, but will be considered in one

direction at a time.

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   S   t  e   l   S   t  r  u  c   t  u  r  e  s   I   I

   I .

   L  e  c   t  u  r  e

   2

   2   8

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Equivalent sway imperfections

Imperfections considered in the global analysis of frames 

For building frames sway imperfections

may be disregarded when:

EdEd V15.0H

For the determination of horizontal

forces applied to floor diaphragms

the configuration of imperfections

should be applied, where    is a

sway imperfection obtained fromassuming one storey with height h. 

Global imperfections are

represented by lateral equivalent 

forces acting at each floor level,

much easy to be considered in the

analysis than to incline the

structure.

The equivalent forces are

determined from the

multiplication of the

gravitational loads at every level

with the initial imperfection

angle . The equilibrium on theheight of the structure imposes a

reaction at the base of every

column.

Sway imperfections applied to the horizontal forces

acting on floor diaphragms

   C .   T  e

   l  e  m  a  n .

   S   t  e   l   S   t  r  u  c   t  u  r  e  s   I   I

   I .

   L  e  c   t  u  r  e

   2

   2   9

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b) relative initial local bow imperfections e0 /L of the members in flexural buckling with

a length L. The values e0 / L may be chosen in the National Annex.

Imperfections considered in the global analysis of 

frames 

Buckling curveElastic analysis Plastic analysis

a0  1/350 1/300

a 1/300 1/250

b 1/250 1/200

c 1/200 1/150

d 1/150 1/100

Le0

Design values of initial local bow imperfection e0/L

Le0

Local bow imperfections may be neglected during the global analysis for determining

end forces and moments for members checking;

For frames sensitive to II order effects local bow imperfections of members additionally

to global sway imperfections should be introduced in the structural analysis of theframe for each compressed member if the following conditions are met:

at least one moment resistant joint at one member end;

the reduces slenderness is increased:

Ed

y

 N

f A5.0

 

N Ed  – the design value of the compression force; - in-plan reduced slenderness for the member considered as hinged at its ends.  

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   I .

   L  e  c   t  u  r  e

   2

   3   0

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Local bow imperfections are taken into account in the members verifications

considering the buckling curves.

The effects of initial sway imperfection and local bow imperfections may be replacedby systems of equivalent horizontal forces, introduced for each column.

Imperfections considered in the global analysis of 

frames 

Replacement of initial imperfections by equivalent horizontal forces:

a)- sway imperfections; b)- initial bow imperfections

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   S   t  e   l   S   t  r  u  c   t  u  r  e  s   I   I

   I .

   L  e  c   t  u  r  e

   2

   3   1

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Imperfections considered in the analysis of bracing systems 

The structural bracing systems of framed structures are required to provide lateral

stability within the length of beams or of the members in compression (columns). The

effects of imperfections are included by means of an equivalent geometric imperfection

of the members to be restrained, in the form of an initial bow imperfection:

500

Le m0    L – the span of the bracing system;

 

  

 m

115.0m

  m – the number of members to be stabilized.

The effects of the initial bow imperfections of the members to be stabilized by the

bracing system may be replaced by the equivalent stabilizing force:

2

q0

EddL

e8 Nq

 δ q - in plane deflection of the bracing system due to the load q to

which any external loads calculated from first order analysis is

added; if second order theory is used then δ q may be considered 0.

e0

– imperfection;

qd  – equivalent force per unit length.

Equivalent stabilizing force for the bracing system

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   S   t  e   l   S   t  r  u  c   t  u  r  e  s   I   I   I .

   L  e  c   t  u  r  e

   2

   3   2

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Imperfections considered in the analysis of bracing systems 

Where the bracing system is required to stabilize the compression flange of a beam of 

constant height, the force N Ed may be obtained from:

h

M N

Ed

Ed

M Ed  – the maximum moment in the beam;

h - the overall depth of the beam.

When a beam is in compression under N Ed , this force should include a part of the

compression force resulted from the imperfections of the bracing system. At points where

beams or compression members are spliced, it should also be verified that the bracingsystem is able to resist a local force equal to:

% NS EdmEd  

Force which is applied to it by each beam or compression member which is spliced at that 

point, and to transmit this force to the adjacent points at which that beam or compression

member is restrained.

For checking to the local force, any external loads acting on bracing systems should also beincluded, but the forces arising from the imperfection may be omitted.    C

 .   T  e

   l  e  m  a  n .

   S   t  e   l   S   t  r  u  c   t  u  r  e  s   I   I   I .

   L  e  c   t  u  r  e

   2

   3   3

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Imperfections considered in the analysis of bracing systems 

Forces at splices in compression elements

The vertical bracing system may have continuity connections which are spliced. Global

imperfection is transferred in the most un-favourable way to the splices and must be

consequently taken into account when designing the connection.The rotation  is determined identically as the previous value of the global imperfections:

100 N N2

;2001

;

EdmEd

0

0m

 

 

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   S   t  e   l   S   t  r  u  c   t  u  r  e  s   I   I   I .

   L  e  c   t  u  r  e

   2

   3   4

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The effects of local bow imperfections of members are considered within the

relationships used for the determination of the buckling resistance for members.

A second order analysis may be developed considering the imperfection of one element as

a bow with the deflection in the middle.

In order to simplify the computation process, this imperfection (a variation in a parabola

shape along the element) may be introduced in the equation as a uniform distributed

loading and the reactions at both ends of the element:

Imperfections of individual

members

2

d0

eqL

e

8 Nq L

e

4 NR d0

Individual imperfections of the structural elements

For the verification of the lateral torsional buckling of a member in bending, the equivalent 

initial bow imperfection of the weak axis of the profile, the eccentricity e0,d  is considered by

adopting the value k∙e0 d

, where for k the value recommended is 0.5.

   C .   T  e

   l  e  m  a  n .

   S   t  e   l   S   t  r  u  c   t  u  r  e  s   I   I   I .

   L  e  c   t  u  r  e

   2

   3   5