Presented To

Sabreena Nasrin

B.Sc. Engg. (Civil), BUET

Lecturer at Ahsanullah University of Science & Technology

&

Munshi Galib Muktadir

B.Sc. Engg. (Civil), BUET

Lecturer at Ahsanullah University of Science & Technology

Md. Neshar Ahmed

Student ID: 10.01.03.151

4th Year, 2nd semester

Department of Civil Engineering

Ahsanullah University of Science & Technology

Welcome to my Presentation on Truss & Frames

Presented By

CE-

416

A truss is a structure composed of slender members joined together at their end points. Planar trusses lie in a single plane. Typically a truss is a joint framed structure which is designed to sustain inclined, vertical or horizontal loads occurring at or between its points of supports and has the following characteristics:

Truss

Typical figure of Truss & Frames

Straight Members

Members connected at their intersections by means of frictionless pins or hinges

Members so arranged that the truss is loaded only at the joints

Components of Truss

Pitched Truss- Characterized by its triangular shape. It is most often used for roof construction.

Parallel Chord Truss- Its named from its parallel top and bottom chords. It is often used for roof construction.

Basic Types of Truss

Various Types of Truss

Flat Truss

King Post Truss

Queen Post Truss

Lenticular Truss Lattice Truss

Bowstring Truss

Calculations for AnalysisThe analysis of trusses is usually based on the following simplifying assumptions:

The centroidal axis of each member coincides with the line connecting the centers of the adjacent members and the members only carry axial force.

All members are connected only at their ends by frictionless hinges in plane trusses.

All loads and support reactions are applied only at the joints.

Method of Joints

Method of Joints: The axial forces in the members of a statically determinate truss are determined by considering the equilibrium of its joints.

Tensile(T) axial member force is indicated on the joint by an arrow pulling away from the joint.

Compressive(C) axial member force is indicated by an arrow pushing toward the joint.

Truss Design Considerations

Effect of tension vs. compression on member sizes

Potential for stress reversal

Potential buckling failure modes and approaches to preventing

Overall lateral stability (lateral- torsional buckling)

Member redundancy: Determinate vs. Indeterminate Trusses

Truss Determinacy Formula

n = 2j – 3 →for determinacy

n = Number of truss bars�

j = Number of joints�

n > 2j -3 →indeterminate

n < 2j -3 →unstable

Eifel Tower

Some renowned Trussed Structures

Frames Multi forced members are generally known as

Frames.

Frames are commonly used to support various external loads.

Figure of Frames

Advantageous features of Framed structure

1. Speedy construction due to simplicity in geometry –consist of only columns and beams (or partially by the floor slab) as the main structural elements

2. Very rigid and stable –able to resist tremendous vertical (dead load) and lateral loads (wind)

3. Reduced dead load –absent of thick shear wall etc.

4. Roofed over at an earlier stage –every floor slab being finished becomes an cover to protect the lower floors from sun and rain

5. Offer large unobstructed floor areas –without obstacle between columns

6. Flexible utilization of space

Advantages features of Framed structure (continued)

7. Adaptable to almost any shape

8. Easily altered within limits of frame –regular or non-regular grid system is very adaptable in spatial arrangement

9. Offsite preparation possible –especially for prefabricated construction using pre-cast concrete or structural steel elements

10. May be designed to accommodate movement

11. Acceptable distribution of natural light –window openings can be provided easily on eternal walls

12. Easy to design structurally including computer design –again, due to simple geometry

Principle factors affecting choice of frame

Structural Design consideration

Foundation consideration

Standardization of members or design

Span and floor loads

Fire resistance requirement

Maintenance consideration

Integration of architectural & structural elements

Features of In-situ concrete frame construction

Construction aspects

1. In-situ concrete is inconsistent in quality in performance -mixing, delivery, placing and compacting of concrete require very tight quality control

2. Overlapping formwork, steel fixing and concreting process make site operations more difficult –these works are to be done almost at the same time at the same location

3. Formwork erection is often timely, expensive, environmental unfriendly and labour intensive

4. Increase a lot of wet-work –difficult to maintain site in a clean and tidy environment

Draw the FBD of the frame or machine and its members as necessary.

Then identify any two-forced members

For a joint with more than two members or an external force, it is advisable to draw a FBD of the pin.

Analysis for Frame

Some Examples Framed Structures

DIFFERENCE BETWEEN TRUSSES AND FRAMES

Trusses Frames

Members are subjected to tension/compression

only

At least one member is subjected to bending,

shear or torsion

Composed of rods Composed of bars

Usually more simple to calculate, more weight

effective

Usually more simple to manufacture, and to place in tight layout

DIFFERENCE BETWEEN TRUSSES AND FRAMES

Connection by riveting,

moment-resistant

DIFFERENCE BETWEEN TRUSSES AND FRAMES

Connection by welding,moment-resistant

Cost Effective Can be installed quickly even without heavy

equipment to lift it into place Unique properties of a triangular object allow

trusses to span across longer distances A triangular truss maintains its shape,

preventing shift and sag. Thus giving stability to the structure.

The shape of a triangle allows all of the weight applied to the sides to be redistributed down and away from the centre.

Advantages of Truss & Frames