Structural Analysis
One of the simple structure is a simply
supported beam, Pined at one end and roller support at the other end. At pined
end bending moment is zero and at roller support no horizontal force is
allowed. Other types of beams are fixed at both ends or continuous at supports,
these are complicated to analyse. At fixed ends there are 3 unknowns, one
moment and 2 reactions. For a 2 span beam one reaction is unknown. They are
indeterminate structures; it cannot be analyzed by three equations of statics
alone.
For longer spans trusses are used. In a
beam load is resisted by shear and moment, truss members transmit the load by
axial force. Truss may be considered as a simply supported beam, where top
chord members are in compression and bottom chord members are in tension, under
vertical loading. Under similar conditions in a beam in simple bending top
fibers are in compression and bottom fibers are in tension. Arch is another
type of structure it is having high axial thrust but low bending moment.
Another type of structure, used in
industrial and residential buildings are frames which are 3dimensioal, for ease
of analysis it is taken as 2D. Frames are characterized by moment resisting
members at some or all the joints. And the structure is highly indeterminate.
Analysis and Design
The design of a structure has 2 parts, the
1st part is to find forces acting and the 2nd is to size
the members to resist these forces. The 1st part is called analysis
and the 2nd part is designing. The purpose of any analysis is to
know-how the structure is reacted to a given loading system. And evaluating the
stresses and deformations.
Loads and Forces
Loads are classified as dead load and live
loads. Live loads are converted equivalent dead loads, which will be a
confusion in computer analysis. Dead loads are weight of fixed components of
the structure, such as beams columns and floor slab and other immovable loads.
Live loads are loads that are moving like people or machine installations.
Another type of live load or forces are moving vehicles usually on bridges.
Wind Loads
For tall buildings wind load is considered
in the design. In coastal areas the low height structures also analyzed for
wind loads. If the height of the building is less than 1.5 times the least
width, then wind loads need not be considered.
Earthquake Forces
The random shaking of the ground causes acceleration
to the structures and the mass resists the motion Newton 2nd law is
applicable here.
Soil and Hydrostatic Forces
Foundation walls, retaining walls and
tunnels are subjected to soil pressures, it can be estimated with established
theories. Hydrostatic force is P = wh, where w is the unit weight of water and
h is the height of water column.
Erection Loads
Storage of materials is one kind of
erection load .Loads due to erection equipments also is considered
Other Forces
Vibrations, temperature effects, shrinkage,
settlement of foundations are may be large forces and taken in to account
Social Plugin