Truss structure features, advantages and disadvantages
Truss structure is a common type of metal structure in construction and is called a structure in which the forces applied to the structure are transmitted to the ground by triangular steel beams with articulated connection to the supports.
Finally, beams, supports, and other truss components form a lattice structure that typically consists of 5 or more triangular units. These units have straight and smooth components, the ends of which are connected to each other in joints (Node).
In this metal structure, external forces and reactions to these forces are applied only in the area of the joints and lead to the creation of forces in the tensile or compressive components. In general, the components are put together so that the overall composition acts as a single shape in practice.
Classification of truss structures
Two-dimensional truss: In this truss structure, all the members can be placed on one page. This means that geometrically, there is no next difference in the way the truss members are positioned and oriented. The ability to withstand stresses and plate loads is one of the advantages of this type of truss.
Three-dimensional truss structure
The placement of structural members along all three axes is a characteristic feature of this type of truss. The ability to withstand loads and three-dimensional stresses is one of the advantages of this type of truss, which of course increases the construction cost and dimensions of the structure.
Multiple trusses
These truss structures are designed to reduce weaknesses and increase the strengths of the previous two trusses. The strength of bearing plate loads and proper flexural and buckling strength in various directions, while maintaining proportionate dimensions are among the strengths of this group of trusses.
Pratt Truss is also more suitable for building bridges and arch-like structures in which the maximum pressure is applied in the vertical direction.
Warren truss is another type of truss that is very common in building bridges. One of the major advantages of this truss structure is the ability of the structure to distribute the loads that are applied to its various members. Therefore, when the load is applied to the structure from all directions, using this type of truss will be a good idea option.
Pratt Truss
Pratt Trusses have been used as an effective truss method for over two centuries. Diagonal members are in tension, while vertical members are compressed. As a result, the diagonal members (in tension) are simplified and a more efficient design is achieved. The benefits of this are that it reduces the cost of the structure by using more efficient members, it reduces the weight of the structure, and it is easier to build. Trusses of this type are best suited to spans with a predominantly vertical force.
Warren Truss
The Warren Truss structure is another very popular truss structure system. Its construction is made up of equilateral triangles. In general, Warren Trusses have the advantage of spreading the load evenly across multiple members; however, this is usually for situations in which the structure is being stressed (a distributed load). One of its main advantages is also its main disadvantage – the truss will undergo concentrated force when a point load is applied. As a result of these concentrated loads, the structure is less effective at evenly distributing the load across its members. Warren trusses are therefore more suitable for distributed loads, but not for loads that are concentrated in one place.
K truss
This type of truss structure is a more complex version of the Pratt truss, except that the vertical members of this type of truss are shorter than the Pratt type, which results in better resistance of the structure to flexural stresses.
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Different types of metal structures
Advantages of Truss structure
Quick installation of truss structure is one of its most important advantages because this structure is prefabricated in the factory and installed in the workshop. Another advantage of truss structure is the possibility of increasing the span length of the structures because the force distribution in it is triangular and reduces the concentration of forces. Triangular spaces between truss members themselves create access paths for the installation of electrical and mechanical installations.
Disadvantages of Truss structure
One of the most important disadvantages of Truss structure is that it requires a lot of space because the interconnected triangular components must be large to withstand and distribute heavy loads.
In addition, their high maintenance costs are also important disadvantages. Of course, these are not the only disadvantages of this structural system, but since truss bridges are very large, their weight will be inevitable.
Structure of steel frame system in truss metal structure
As mentioned, a truss structure is a set of straight rods that are articulated together to form triangular grids. The truss members are connected to each other by welding, riveting or screwing. Truss structures are widely used to build roofs, especially roofs with large openings and stairs.
Trusses have high strength and are light in weight. The connection of the members of a truss is sometimes done directly and sometimes by a sheet called the connecting sheet.
Therefore, in practice, not only are there articulated joints at the ends of the members, but their connection to each other and to the connecting plate is also considerably entangled. Paying attention to special points makes the assumption of joint connection and net axial force in truss members more real
One of the most important considerations in this case is that the truss design tries to pass the axis of the bars through a common point. The application of external forces to the nodes is another condition of this assumption.
The amount of steel used for the truss is less than the H-beam, and it weighs less and is more durable. It is also widely used in high-rise buildings, structures with large openings and stairs.
Advantages of steel frame structures
As mentioned, the use of steel structures is very widespread and the reason is the superiority and high consumption of these structures. Among the advantages of this structure, the following can be mentioned.
Suitable mechanical properties such as high strength and high resistance to tension and pressure
Ability to control the quality of steel in the factory during production, compared to concrete and building materials
Possibility of structural development
Possibility of prefabricated parts
High installation speed
Occupy less space
Can be used at high altitudes
Ability to connect several pieces to each other by welding or bolts
Disadvantages of steel frame structures
As mentioned in the section on framed steel structures, steel is sensitive to air humidity and high temperatures, and this leads to corrosion of the steel frame; Therefore, to prevent this, methods such as painting with anti-corrosion paints, fire-retardant coatings, fire-retardant paints and other protective methods should be used.
Disadvantages of these structures include the possibility of poor connections with poor welding quality and low fire resistance.