Lesson 1. Introduction to Structural Analysis.pdf
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Teoría de Estructuras y Construcciones Industriales. 2014-2015
CHAPTER 1. Introduction to Structural Analysis
Teoría de Estructuras y Construcciones Industriales. 2014-2015
Lesson 1. Introduction to Structural Analysis 1.1. Objectives of structural analysis. 1.2. Structural models. 1.3. Structural forms. 1.4. Simplified structural models. 1.5. Types of internal forces. 1.6. Types Types of external loading. 1.7. Types Types of supports and reactions. 1.8. Determinacy and freedom degrees. 1.9. Design hypothesis: first and second order theories.
Teoría de Estructuras y Construcciones Industriales. 2014-2015
1.1.. Obje 1.1 Obj ecti ctive ves s of str uctu r al anal an alys ysii s could S t r u c t u r e could
be a load-bearing element or a group of load-bearing elements with functional
requirements.
The
main objective of structural analysis is to determine how a structure responds to specified loads and actions. 3
Teoría de Estructuras y Construcciones Industriales. 2014-2015
1.1.. Obje 1.1 Obj ecti ctive ves s of str uctu ucturr al anal an alys ysii s
Th e str u ctur al des desi gn proc pr oce ess: Conceptual
and preliminary stages (types of structure, materials and loading),
Calculation
stage (internal forces and displacements),
Final
stage (design drawings with written specifications of materials and pertinent codes to be employed), Construction
stage. -4-
Teoría de Estructuras y Construcciones Industriales. 2014-2015
1.1.. Obje 1.1 Obj ecti ctive ves s of str uctu ucturr al anal an alys ysii s Structural model (elements, materials, supports)
Loading analysis
Calculation of displacements
Calculatin of internal forces
Calculation of stresses and strains
Checking limit states (design codes)
New structural design
NO
YES Final design
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Teoría de Estructuras y Construcciones Industriales. 2014-2015
1.2. Si 1.2. Si mpli f i ed str str uctu ucturr al mod mode el s (I de deali ali zation) Vari ar i ables ables to def def i ne: ne:
• Materials, • Structural forms, • Elements types, • Joints (connections) types, • Supports, • External loading, • Type Type of calculation (static, dynamic, dynamic, etc.) • Type Type of structural analysis
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Teoría de Estructuras y Construcciones Industriales. 2014-2015
1.3. 1. 3. Str u ctur al f or orms ms Clasi Clasi f i cation by str uctur al f unti on:
Houses, offices and industrial buildings.
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Teoría de Estructuras y Construcciones Industriales. 2014-2015
1.3. 1. 3. Str u ctur al f or orms ms
Industrial equipment (cranes, pressure vessels, silos)
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Teoría de Estructuras y Construcciones Industriales. 2014-2015
1.3. 1. 3. Str u ctur al f or orms ms
Gateways, bridges and slabs.
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Teoría de Estructuras y Construcciones Industriales. 2014-2015
1.4. 1. 4. Si mpl mplii f i ed str u ctur al model model s Clas Cl ass si f i cati cati on of str uctur uctu r es: Rigid and pin joint structures. Rigid : same angle before and after deformation. Rigid Rigid j oin t
Before deformation
After deformation
2D and 3D Rigid joint structures (Frames) - 10 -
Teoría de Estructuras y Construcciones Industriales. 2014-2015
1.4. 1. 4. Si mpl mplii f i ed str u ctur al model model s Pin Join Join t : free rotation (hinge)
2D Pin joint structures (Trusses)
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Teoría de Estructuras y Construcciones Industriales. 2014-2015
1.4. 1. 4. Si mpl mplii f i ed str u ctur al model model s E l emen men t type t ypes s:
1D elements (bar elements)
2D elements: - Membranes, - Plates, - Shells, - Shear walls.
3D elements.
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Teoría de Estructuras y Construcciones Industriales. 2014-2015
1.5.. Type 1.5 Types s of i n te terr n al f or orce ces s 1D el emen men ts: ts: bars bar s el emen men ts
Pin joint elements (Axial Force: Tension and Compression)
b)
2D and 3D Rigid elements (Axial and Shear Forces and Bending and Torsion Moments)
Cables (Axial Force: Tension)
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Teoría de Estructuras y Construcciones Industriales. 2014-2015
1.5.. Type 1.5 Types s of i n te terr n al f or orce ces s 2D el emen men ts: ts: M embr anes
Membranes examples - 14 -
Teoría de Estructuras y Construcciones Industriales. 2014-2015
1.5.. Type 1.5 Types s of i n te terr n al f or orce ces s 2D el ements ment s: Pl ates ates
Plates examples - 15 -
Teoría de Estructuras y Construcciones Industriales. 2014-2015
1.5.. Type 1.5 Types s of i n te terr n al f or orce ces s 2D el emen men ts: ts: Sh el l s
membrana Membrane
placa Plate
Shells examples - 16 -
Teoría de Estructuras y Construcciones Industriales. 2014-2015
1.5.. Type 1.5 Types s of i n te terr n al f or orce ces s 2D el emen men ts: ts: Sh ear wall wal l s
Shear wall example
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Teoría de Estructuras y Construcciones Industriales. 2014-2015
1.5.. Type 1.5 Types of i n te terr n al f or orce ces s 3D el emen men ts
Dam example
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Teoría de Estructuras y Construcciones Industriales. 2014-2015
1.6. 1. 6. Type Types s of ex te terr n al l oad oadii n g Clas Cl ass si f i cati cati on (ac ( acti ti ons): ons):
Surface and volume loads. Static and dynamic loads. Permanent and variable loads.
Clas Cl ass si f i cati cati on (ac ( acti ti ons): ons):
snow load
own weight load
Point and distributed loads. Thermal load. Enforced displacements. Fitting defects. wind load - 19 -
Teoría de Estructuras y Construcciones Industriales. 2014-2015
1.7. Type Types s of su ppor pports ts an and d r eacti action ons s Support upport clasi clasi f i cati cation: on:
Pin and roller (rocker) (r ocker) supports
Fixed or clamped (encastre) support
Guide
Spring supports: linear ad torsional springs.
Pin support
Roller support Spring support
Fixed support - 20 -
Teoría de Estructuras y Construcciones Industriales. 2014-2015
1.7. Type Types s of su ppor pports ts an and d r eacti action ons s
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Teoría de Estructuras y Construcciones Industriales. 2014-2015
1.7. Type Types s of su ppor pports ts an and d r eacti action ons s 3D element section (6 degrees of freedom) Restriction Restriction of 6 FD • Fixed: • Pin: Restriction Restriction of 3 FD
3 linear displacements (u, v, w ) 3 rotations (F (Fx, Fy, Fz) 6 Reactions (Unknowns) 3 Reactions (Unknowns)
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Teoría de Estructuras y Construcciones Industriales. 2014-2015
1.7. Type Types s of su ppor pports ts an and d r eacti action ons s 2D element section (3 degrees of freedom)
Pin support
2 linear displacements (u, v) 1 rotation (F ( F z)
Roller support
Fixed support
Guide
Schematic representation - 23 -
Teoría de Estructuras y Construcciones Industriales. 2014-2015
1.7. Type Types s of su ppor pports ts an and d r eacti action ons s pr i ng supports uppor ts: : • Spri partially limitation of linear and rotation partially displacements. The reactions depend on the rigid constant (k = s m).
RH RV
Linear spring support
Torsional spring support
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Teoría de Estructuras y Construcciones Industriales. 2014-2015
1.8. 1. 8. D ete terr mi minacy nacy gr grad ade e: D G ( = GH ) = r - 3
If DG < 0
Unstable structures (mechanisms) (No. unknowns < No. available equilibrium equations)
If DG = 0
Statically determinate structures (No. unknowns = No. available equilibrium equations)
If DG > 0
Statically indeterminate structures (No. unknowns > No. available equilibrium equations)
DG=1
DG=3 - 25 -
Teoría de Estructuras y Construcciones Industriales. 2014-2015
1.8. 1. 8.a) a) Stati Statica call l y inde in dete terr mi minate nate r i gid j oin t str str uctur es.
Rigid joint open structures: DG = DGext + DGint = r - 3 – a ao DGext = r – 3 3 – a ao DGint = 0
r = No. reactions ao = bo – 1 1 = hinge equations (open contours)
Rigid joint closed structures:
DG = DGext = 3
DG = DGext = 2
DG = DGext + DGint = r + 3 cc - 3 – (a (ao + ac) DGext = r – 3 3 - aa DGint = 3 cc – a ac r = No. reactions, cc = No. closed contours, ao = bo - 1= hinge equations (open ( open contours) ac = bc – 1 1 = hinge equations (closed contours)
DG = 3+3=6 DGext = 3
DG = 3+2=5 DGext = 3
Teoría de Estructuras y Construcciones Industriales. 2014-2015
1.8. 1. 8.b) b) Stati Statica call l y in de dete terr mi minate nate pin j oin t str str uctu ucturr es.
DG = DGext + DGint = r + b – 2n 2n DGext = r - 3 DGint = DG - DGext = b – 2n 2n + 3 b = No. bars, r = No. reactions, n = No. joints b = 17 r=3 n = 10
b = 17 r=3 n = 10
DG=0
50kN
50kN
b = 18 r=3 n = 10
d)
b=5 r=4 n=4
DG=0
D
3m B
A
C
Sm
DG=DGint=1
4m
4m
DG=DGext=1
Teoría de Estructuras y Construcciones Industriales. 2014-2015
1.8.c) Ki ne 1.8.c) nematicall maticall y in de dete terr mi minate nate str uctur es: D egre gree es of f r eedo dom m F D (= GL ) = N R + BR BR Structures without sidesway: If AE = ∞ (axial deformations, e = 0), kinematic unknowns (freedom degrees) are rotation of joints (NR) only, only, because bar rotation are cero (BR = 0).
jB A
jC
B
FD = NR = 2 (j (jB , jC)
C
D
CIR
q
q VB
jB y AB A
jC B UB
AE=∞ (axial (axial Structures with sidesway: If AE=∞ deformations, e deformations, e = 0), kinematic unknowns (freedom degrees) are both joint rotations (NR) and bar rotations (BR).
yBC
C
VC
FD = NR + BR = 3 (jB , jC , yAB)
UC
yBC = f (y (yAB)
yDC
D
(y AB) yDC = f ( - 28 -
Teoría de Estructuras y Construcciones Industriales. 2014-2015
1.9. D esi gn hypo h ypoth the esi s: F i r st and an d se second orde or derr th the eor orii es Requi Requirr ements ments of f i r st orde or derr the th eory: or y:
• Linear-elastic material behaviour. • Small strain and displacements Th ese condi condi ti ons per per mi t: • Equilibrium applied to undeformed structure geometry.
• Linear equation systems solution. • Superposition principle.
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Teoría de Estructuras y Construcciones Industriales. 2014-2015
1.9. D esi gn hypo h ypoth the esi s: F i r st and an d se second orde or derr th the eor orii es F i r st order order theory: theory:
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Teoría de Estructuras y Construcciones Industriales. 2014-2015
1.9. D esi gn hypo h ypoth the esi s: F i r st and an d se second orde or derr th the eor orii es Second or der der the th eory: or y:
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