DEFINITION OF FRAME
A-Frame is a basic structure designed to bear a load in a
light weight economical manner.
A frame is a structural system that supports other
components of a physical construction.
Multi forced members are generally known as Frames.
Frames are commonly used to support various external
ANALYSIS OF FRAME
A free body diagram of the complete
frame is used to determine the
external forces acting on the frame.
Internal forces are determined by
dismembering the frame and
creating free-body diagrams for each
WHAT IS TRUSS ?
A truss is a structure comprising one or more triangular units constructed
with straight members whose ends are connected at joints or nodes.
If all the bars lie in a plane, the structure is a planar truss.
The main parts of a planar truss.
In other words, Trusses are designed to form a stable
Following characteristics of Truss
* The members of the truss should be in a plane.
* Members are connected at their intersections by means of
frictionless pins or hinge.
* Loads and reactions are applied only at joint.
* The centroid of the members must coincide with centroid of
The members which from the outline or perimeter of a truss are
generally called the chord members.
There are two chord members -
01. Top Chord: Top members
02. Bottom Chord: Bottom members
Web Members – The interior members connecting the joints of the
chords are called the web members.
There are two members-
01. Diagonal members
02. Vertical members
Why are trusses strong?
Trusses derive their strength from the triangle.
The simplest of plane polygons, a triangle is unique in
that it is defined by the length of its sides. That is, one
and only one triangle can be drawn if the length of all
three sides is given.
Why are triangles used in trusses?
Rectangles and squares are not very strong because the
middle of each side would tend to bend or buckle easily.
And these are not used in truss.
A truss is a structure made up of triangles. Because
triangles are strong because when you define the length of
the three sides the relationship between the nodes is fixed.
Similarly when you identify any two angles an a side or two
sides and a common angle all other properties are fixed. In
any other shape there are more degrees of rigidity required
to create a fixed structure.
Triangles have sides that reinforce each
other. They divide up the load.
Application of trusses-
Roof of factory shade.
Sport Stadium Truss
Determine the Support
Apply Fx = 0 and Fy = 0 to
every node and determine
Dismember the truss and create
a free-body diagram for each
member and pin.
METHOD OF TRUSS ANALYSIS
SECTI ON METHOD
Determine the Support Reaction.
To determine the force in member
BD, pass a section through the
truss as shown and create a free
body diagram for the left side.
With only three members cut by
the section, the equations for static
equilibrium may be applied to
determine the unknown member
forces, including FBD.
METHOD OF TRUSS ANALYSIS
Comparison of Trusses and Frames
Members are subjected to
At least one member is subjected
to bending, shear or torsion
Forces are applied at the joints
Forces may act anywhere on the
Member does not bend. Members may bend/may not
Composed of rods. Composed of bars.
Used for large loads. Used for small and medium
Advantages of Truss & Frame
Can be installed quickly even without heavy equipment to lift it into
Unique properties of a triangular object allow trusses to span
across longer distances
Common Types of Trusses-
King post & Queen post Truss.
Also known as Crescent Truss
Is a truss consisting of curved
top chord meeting bottom
chord at each end.
Has diagonal load-bearing
Often confused with tied arch
It is used for simple short-span
Fewest number off truss
members.- two diagonal
members, kingpost braces, that
meet at the apex of the
truss, one horizontal beam and
the king post which connect the
apex to the horizontal beam
King post & Queen Post Truss-
It has two vertical post.
Very strong and stable.
It s more stable and can support
a wider span than a kingpost.
King post & Queen Post Truss-
It uses equilateral triangles to
spread out the loads on the
bridges. The equilateral
triangles minimize the forces to
only compression and tension.
This bridges are often used
with verticals to reduce the
It became very popular and was
considered one of the best
designs for railroad bridges back
in the day.
Wooden beams for the diagonal
members, which were in
compression. It used iron (and
later steel) for the vertical
members, which were in tension.
Very common type but has many
(Baltimore, Pennsylvania, and the
The basic identifying features are
the diagonal web members which
form a V-shape. (Howe truss bridge
has a A-shape).
Commonly used for supporting
The Pratt truss’s verticals
functioned as compression members
and diagonals functioned as tension
The Pratt truss required more iron
than a Howe truss,
The length of members
undergoing compression is
reduced. This reduction in length
enables components of bridges to
endure the compressional force.
The design is complicated and it
is considered to be one of the
hardest bridges to build.
Roof trusses, which are
structural components of houses
buildings, support the weight of
roof timbers and coverings.
Usually, they are constructed
from pieces of timber or steel
which are nailed, bolted, or
pegged together to form a
mutually supporting and strong
base for a roof.
Design of industrial roof truss:
Steps of work
1. Selection of truss type.
2. Estimation of loads.
3. Analysis & design of purlin.
4. Analysis & design of sag rod.
5. Dead load(DL) and Wind load(WL) analysis
of truss member.
6. Combination of DL and WL to determine
the design bar forces.
7.Design of member according to the bar forces.
8.Design of bracing system.
9.Design of connection.
We will design a Industrial roof truss
Design of Purlin
Then calculating of purlin number and Purlin spacing.
Then load analysis-
01. Dead load analysis.
02.live load analysis.
Then we find out member force by grasp software.
01. Top chord bracing.
02. Bottom chord bracing.
03. Vertical bracing.
Types of Truss Connection-
01. Pinned Connection.