Truss derives from the Old French word trousse, from around 1200, which means "collection of things bound together". The term truss has often been used to describe any assembly of members such as a cruck frame. The development of railroads in the 1820s has a particular significance for structural engineers. Railroads created an urgent need for bridges able to carry heavy moving loads and for new building

1. BUILDING
STRUCTURE
S-5
PLANAR
TRUSSES
Done by
Indrajit koner
b.Arch
Sem-4

2. HISTORY OF TRUSSES
 Truss derives from the Old French word trousse, from
around 1200, which means "collection of things
bound together". The term truss has often been used
to describe any assembly of members such as a
cruck frame.
 The development of railroads in the 1820s has a
particular significance for structural engineers.
 Railroads created an urgent need for bridges able to
carry heavy moving loads and for new building forms
for terminals and maintenance facilities.
 The rush to satisfy those needs accelerated the
application of the scientific principles of mechanics
in the structural design process and fostered
advances in the production and fabrication of iron
parts.

3. HISTORY OF TRUSSES
 In particular, by the middle of the nineteenth
century engineers understood and applied
principles of mechanics to the design of an
important structural form: the truss.
 Of course trusses were widely used as
structures before the nineteenth century.
 Trusses were constructed primarily of wood,
with ropes sometimes serving as tension bars.
Hogging structures in early Egyptian boats and
indeed much of the strength of a sailing ship
depended on truss action of the posts (or
masts), the ropes and the hull

4. HISTORY OF TRUSSES
 Wooden roof-frames, wooden formwork for
masonry arches and wooden bridges were often
essentially trusses.
 Notable existing examples of sixteenth and
seventeenth century wooden roof frames are
those of the Uffizi gallery by Vasari, and those
 designed by Sir Christopher Wren for the
Sheldonian Theatre .
 Framed wooden bridges were widely used in
Switzerland and in Germany in the sixteenth and
seventeenth centuries.

5. PLANAR TRUSSES
 A truss is a structure of straight, long
, slender members joined at end
points.
 In planar truss all of its members lie
in the same plane .Roofs and bridges
consists of parallel planar truss.
 Members can be joined together by a
number of ways such as welding,
riveting, bolting etc .There are certain
assumptions which are made to
analyze a truss

6. TENSION AND COMPRESSION
 The force which tends to elongate i.e. increase in the length of the
member of truss is known as tension or tensile force.
 The force which tends to compress the member i.e. tries to reduce the
length of a member in truss is known as compression or compressive
force.

7. TRANSMISSION OF LOADS ON ROOFS
 The truss ABCD shows a typical roof supporting truss
 Roof load is transmitted to the truss at joints by means of a series of
purlins ,such as DD’.

8. TYPES OF TRUSSES

9. METHOD OF ANALYZING OF PLANAR
TRUSSES
 Method of Joints
 Method of Sections
 Graphical Method

10. METHOD OF ANALYZING OF PLANAR
TRUSSES- METHORD OF JOINTS
 We start by assuming that all members are in tension reaction. A tension member
experiences pull forces at both ends of the bar and usually denoted by positive (+ve) sign.
When a member is experiencing a push force at both ends, then the bar is said to be in
compression mode and designated as negative (-ve) sign.
 In the joints method, a virtual cut is made around a joint and the cut portion is isolated as a
Free Body Diagram (FBD). Using the equilibrium equations of ∑ Fx = 0 and ∑ Fy = 0, the
unknown member forces can be solved. It is assumed that all members are joined together in
the form of an ideal pin, and that all forces are in tension (+ve reactions).
 An imaginary section may be completely passed around a joint in a truss. The joint has
become a free body in equilibrium under the forces applied to it. The equations ∑ H = 0 and ∑
V = 0 may be applied to the joint to determine the unknown forces in members meeting there.
It is evident that no more than two unknowns can be determined at a joint with these two
equations.

11. METHOD OF ANALYZING OF PLANAR
TRUSSES- METHORD OF JOINTS

12. METHOD OF ANALYZING OF PLANAR
TRUSSES-METHORD OF SECTIONS
 The section method is an effective method when the forces in all members of a truss are to be
determined. If only a few member forces of a truss are needed, the quickest way to find these
forces is by the method of sections. In this method, an imaginary cutting line called a section
is drawn through a stable and determinate truss. Thus, a section subdivides the truss into two
separate parts. Since the entire truss is in equilibrium, any part of it must also be in
equilibrium. Either of the two parts of the truss can be considered and the three equations of
equilibrium ∑ Fx = 0, ∑ Fy = 0, and ∑ M = 0 can be applied to solve for member forces.

13. METHOD OF ANALYZING OF PLANAR
TRUSSES-METHORDS OF SECTION
 The 3 forces cannot be concurrent, or else it cannot be solved.A virtual cut is introduced
through the only required members which is along member BC, EC, and ED. Firstly, the
support reactions of Ra and Rd should be determined. Again a good judgment is required to
solve this problem where the easiest part would be to consider either the left hand side or the
right hand side. Taking moment at joint E (virtual point) clockwise for the whole RHS part
would be much easier compared to joint C (the LHS part). Then, either joint D or C can be
considered as the point of moment, or else using the joint method to find the member forces
for FCB, FCE, and FDE. Note: Each value of the member’s condition should be indicate
clearly as whether it is in tension (+ve) or in compression (-ve) state.

14. METHOD OF ANALYZING OF PLANAR
TRUSSES-GRAPHICAL ANALYSIS
 The method of joints could be used as the basis for a graphical analysis of trusses. The graphical
analysis was developed by force polygons drawn to scale for each joint, and then the forces in each
member were measured from one of these force polygons.The number of lines which have to be
drawn can be greatly reduced, however, if the various force polygons are superimposed. The
resulting diagram of truss is known as the Maxwell’s Diagram.
 In order to draw the Maxwell diagram directly, here are the simple guidelines:
1. Solve the reactions at the supports by solving the equations of equilibrium for the entire truss,
2. Move clockwise around the outside of the truss; draw the force polygon to scale for the entire truss,
3. Take each joint in turn (one-by-one), then draw a force polygon by treating successive joints acted
upon by only two unknown forces,
4. Measure the magnitude of the force in each member from the diagram,
5. Lastly, note that work proceeded from one end of the truss to another, as this is use for checking of
balance and connection to the other end.

15. METHOD OF ANALYZING OF PLANAR
TRUSSES-GRAPHICAL ANALYSIS
 A simple triangle truss with degree of angle, θ is 60° on every angle (a equilateral) and same
member’s length, L on 2 types of support. Yet again, evaluating the support reaction plays an
important role in solving any structural problems. For this case, the value of Hb is zero as it is
not influenced by any horizontal forces.The procedure for solving this problem could be quite
tricky and requires imagination. It starts by labeling the spaces between the forces and
members with an example shown above; reaction Ra and applied force, P labeled as space 1
and continue moving clockwise around the truss. For each member, take example between
space 1 and 5 would be the member AC and so forth. Note: Choose a suitable scale for
drawing the Maxwell diagram.

16. METHOD OF ANALYZING OF PLANAR
TRUSSES-GRAPHICAL ANALYSIS

17. CONCLUSION
 In conclusion, the truss internal reactions as well as its member forces could be
determined by either of these 3 methods. Nonetheless, the methods of joints becomes
the most preferred method when it comes to more complex structures

18. LONG SPAN TRUSSES:
 A truss is essentially a triangulated system of straight interconnected structural elements.
The most common use of trusses is in buildings, where supports to the roof, the floor and
internal loading such as services and suspended ceilings, are readily provided the main
reasons for using trusses are:
 LONG SPAN
 LIGHTWEIGHT
 REDUCED DEFLECTION
 OPPORRUNITY TO SUPPORT CONSIDERABLE LOADS
TYPES OF LONG SPAN TRUSSES:
1. PRATT TRUSS
2. WARREN TRUSS
3. NORTH LIGHT TRUSS
4. SAW TOOTH TRUSS
5. FINK TRUSS

19. PRATT TRUSS:
 BASIC DIMENSIONS :The length of the bridge is 40 m, and the width of the roadway is 7 m. The
main distance between the truss members is 5 m.
 ANALYSIS TYPES :The model includes two different analyses of the bridge: The goal of the first
analysis is to evaluate the stress and deflection fields of the bridge when exposed to a pure
gravity load and also when a load corresponding to one or two trucks crosses the bridge. Finally,
an Eigen frequency analysis shows the Eigen frequencies and Eigen modes of the bridge.
 LOADS AND CONSTRAINTS: To prevent rigid body motion of the bridge, it is important to
constrain it properly. All translational degrees of freedom are constrained at the left-most
horizontal edge. Constraints at the right-most horizontal edge prevent it from moving in the
vertical and transversal directions but allow the bridge to expand or contract in the axial direction.
This difference would however only be important if thermal expansion was studied.

22. MATERIAL PROPERTIES:
 The material in the frame structure is structural steel. The roadway material is concrete; the effect
of reinforcement is ignored. The frame members have different cross sections:
 The main beams along the bridge have square box profiles with height 200 mm and thickness 16
mm. This also includes the outermost diagonal members.
 The diagonal and vertical members have a rectangular box section 200x100 mm, with 12.5 mm
thickness. The large dimension is in the transverse direction of the bridge.
 The transverse horizontal members supporting the roadway (floor beams) are standard HEA100
profiles.
 The transverse horizontal members at the top of the truss (struts) are made from solid rectangular
sections with dimension 100x25 mm. The large dimension is in the horizontal direction.

23. WARREN TRUSS
 The Warren truss consists of longitudinal members joined only by angled cross-members,
forming alternately inverted Equilateral triangle shaped spaces along its length.
 This gives a pure truss: each individual strut, beam, or tie is only subject to tension or
compression forces, there are no bending or torsion forces on them.
 Loads on the diagonals alternate between compression and tension (approaching the centre),
with no vertical elements, while elements near the centre must support both tension and
compression in response to live loads.
 This configuration combines strength with economy of materials and can therefore be
relatively light. The girders being of equal length, it is ideal for use in prefabricated modular
bridges.
 It is an improvement over the Neville truss which

24.  The span of the truss varies from 20m to 100m.
 The Warren Truss is a very common design for both real and model bridges.
 How are the forces spread out?
 When the load is focused on the middle of the bridge, pretty much all the forces are
larger.
 The top and bottom chord are under large forces, even though the total load is the
same

25. EXAMPLES:
BADGERY CREEK AIRPORT, New
South WALES
Long span curved truss
ROBIN HOOD Airport,
Doncaster