Trusses are the key engineering feature in the emerging civil engineering contest. Indeed, long span structures with light weight is the main reason for the increase in the demand of trusses in the construction industry. Since from the usage of steel as a construction material, due to its higher strength with lower mass, trusses took a major role in the civil structures together with the advancement of steel industry. Over the past years and even for now considering aesthetic feature these trusses are made with the timber planks as well. Roof trusses, bridges, electricity and telecom towers and even the structural frames are making use of these trusses as their integral structural forms.
Definition of Truss
Trusses are simply defined as triangulation of members to make the stabilized structure. Triangulation is the stable configuration mathematically. Generally, a truss has the members called as top chord, bottom chord, vertical chord and diagonal chord. The main functions of the trusses are
- Carrying the loads from the over structures
- Providing adequate lateral stability to the entire structure
There are some basic assumptions in the designing process. It should be clarified that the construction of the trusses should conform with the design assumptions to avoid the unwanted failures due to the dispersion of the forces and loads. Following are the assumptions in truss design.
- Truss members will carry only the axial forces
- The nodes i.e the connections of the members are designed as pinned joints so that moments won’t be transferred to the members of the truss
- All the external loads and the reactions are act only on the nodes
- Generally, the truss should be in a plane.
Typically the members of the trusses are made as I sections, angles, T sections, Tube sections, Square sections and channel sections. I sections are more preferable as a optimized section in terms of the structural forces.
Types of trusses
- Simple truss – indicates a single triangular truss. These trusses are most often used as the roof trusses.
- Planar truss – as the name implies it is a two dimensional truss. If all the members and the nodes are in a planar surface, then this truss is a planar truss.
- Space frame truss – Contrast to planar truss, the members and the nodes are located in the three dimensional space. Electrical and telecom towers are the one of the simplest example that we are seeing in the day to day life.
Forms of Trusses
1. Pratt truss
Pratt truss form for the loads in gravity direction
Pratt truss form for the uplift loads(loads opposite to gravity)
2. Warren truss
3. North light truss
4. Vierendeel truss
King post truss, Bowstring truss, Queen post truss, Flat truss, Lenticular truss are some other forms of trusses in the use of the industry.