Download - Anaisis estructural
-
8/12/2019 Anaisis estructural
1/14
1
1. STRUCTURAL ANALYSIS -
FUNDAMENTALS
-
8/12/2019 Anaisis estructural
2/14
2
1.1 INTRODUCTION
1.1 INTRODUCTION
What is a structure? - General Types: Based on deformation and type of
primary loadcarried [Axial (tensile, compressive), flexure, shear and
torsion]; combinationsof various types - How to determine? Strip it down toits basic skeleton
What does a structure do? - Carriesthe load - Loads actingon the structure:
Dead & Live (people, equipment, wind, wave, seismic)- Superposition
Principle- Keeps the structurein static and dynamic equilibrium-
Transfersthe load to contiguous structural components - Transfers the load
safely - Transfers the loads to the foundation
-
8/12/2019 Anaisis estructural
3/14
-
8/12/2019 Anaisis estructural
4/14
4
Figure 1.2bThe spidersweb is
a good example
of a tension
structure. The
weight of the spider
and its prey is
supported by tensile
strength of the web
-
8/12/2019 Anaisis estructural
5/14
5
Figures 4 and 5
All materials and structures deflect,
to greatly varying extents, when
they are loaded. The science of elasticity is about the interactions between forces and
deflections. The material of the bough is stretched near its upper surface and compressed
or contracted near its lower surface by the weight of the monkey
Fig.4
Fig.5
-
8/12/2019 Anaisis estructural
6/14
6
Figure 1.1
A building structure safely transmits loads down to Earth
-
8/12/2019 Anaisis estructural
7/14
7
1.1 INTRODUCTION (Contd)
Collapse or failure under applied extreme loads - Loads due to extremeenvironmental loads (acting, earthquake, wind) - Modes of failure: Plastic deformation(ductile, yielding), Brittle fracture, Buckling (elastic or inelastic), Fatigue, Vibration
(resonance), foundation settlement and failure.
Unserviceability:Excessive deformation, acoustic deformation
Unexpected load scenario or unwise design: Lack of or faulty sprinkler (firedamage), Inadequate sealing and paint protection (leakage and corrosion), Improper
anchorage of roof, reinforcement, etc. (Roof blown off or beam collapsing), Lack of sufficient
indeterminacy (collapse)
-
8/12/2019 Anaisis estructural
8/14
8
1.2. DETERMINACY AND INDETERMINACY
What do we understand by determinate and indeterminate structures?Determinate:Forces and Moments are determined by statical equations of
equilibrium
Humbleys problem:Stool with three or four legs on irregular floor
Indeterminate structures:Less equations are available than the number of
unknown forces that constrain the body in space. Extra conditions of deformation
compatibility have to be introduced to solve the problem. These conditions will give
the extra number of equations required to solve the problem, which will indicate the
degree of indeterminacy
Determinacy and indeterminacy- Stable and unstable structures
Unstable:When more equations are available than the number of forces that
constrain the body in space, then the structure is unstable
.0,0 MF
-
8/12/2019 Anaisis estructural
9/14
9
1.3 ASSESSING THE DEGREE OF INDETERMINACY
Easy to deal with by specifying simple types of structures - Truss structures:
2-D, 3-D, - Framed structures:2-D, 3-D Two-dimensional truss structures:m + r 2j, where m = number of
members, j = number of joints and r = number of external constrains.
-
8/12/2019 Anaisis estructural
10/14
10
1.3 ASSESSING THE DEGREE OF INDETERMINACY (Contd)
Three dimensional truss structure:m + r 3j, where m = number of members,
j = number of joints, and r = number of external constraints
-
8/12/2019 Anaisis estructural
11/14
11
1.3 ASSESSING THE DEGREE OF INDETERMINACY(Contd)
Two-dimensional framed structure:3m + r 3j +ec
-
8/12/2019 Anaisis estructural
12/14
12
1.3 ASSESSING THE DEGREE OF INDETERMINACY(Contd)
Three-dimensional framed structure:6m + r 6j +ec
-
8/12/2019 Anaisis estructural
13/14
13
ASSESSING THE
DEGREE OF
INDETERMINACY
(Contd)
-
8/12/2019 Anaisis estructural
14/14
14
ASSESSING THE
THE DEGREE OF
INDETERMINACY
(Contd)