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Check It And Look At the Different Steel Roof Truss Design

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Check It And Look At the Different Steel Roof Truss Design

On February 15, 2017, Posted by , In Roofing Blogs, With No Comments

A truss is essentially a triangulated system of straight interconnected structural elements. The most common use of trusses is in buildings, where support to roofs, the floors and internal loadings like services and suspended ceilings, are readily provided. The main reasons for using trusses are:

  • Long span
  • Lightweight
  • Reduced deflection (compared to plain members)
  • Opportunity to support substantial loads.

Definition of a Truss

A truss is basically a triangulated system of (usually) straight interconnected structural elements; it is sometimes also referred to as an open web girder. The individual components are connected at nodes; the connections are often assumed to be nominally pinned. The external forces applied to the system and the reactions at the supports are generally implemented at the nodes. When all the members and applied forces are in the exact same plane, the system is a plane or 2D truss.

History and Types of Steel Trusses

As a relatively new building material, steel has become especially useful when incorporated into engineered steel trusses and steel plate connected timber trusses. Attempts were made in the 17th and 18th centuries to use iron as reinforcing and structural members, especially in bridge design for railroads and other heavy load applications. Yet, it became tragically apparent that structural iron quality control and layout methods did not have the necessary reliability and cost factors required for widespread use. With the development of the Bessemer process in 1858 the cost of making steel began to drop, and with the Linz-Donawitz process, 100 years later steel started to seriously compete with wood as a structural framing element.

Electric arc furnaces enabled efficient steel recycling processes, further decreasing production costs. Finally, the cold rolled process for producing steel truss members now enables low-cost production of steel floor trusses, steel roof trusses, entire steel truss buildings, and the components used in the design of steel truss bridges. All have now become cost-effective, reliable, and safe alternatives to more traditional structural framing materials.

Use of Trusses in Buildings

Trusses are used in a broad array of buildings, primarily where there is a requirement for very long spans, such as in airport terminals, aircraft hangers, sports stadia roofs, auditoriums and other leisure buildings. Trusses are also used to carry heavy loads and are sometimes used as transfer structures. This article concentrates on typical single story industrial buildings, where trusses are widely used to serve two main functions:

  • To take the roof load
  • To provide horizontal stability.

See: How to Determine Steel Roof Damage

What is a Truss?

In Architecture and Structural Engineering, a truss is a structure comprising one or more triangular units constructed with straight slender members whose ends are joined at joints referred to as nodes.

External forces and reactions to those forces are considered to act only at the nodes and result in forces in the members which are either tensile or compressive forces.

Seconds (torsional forces) are explicitly excluded because, and only because, all the joints in a truss are treated as revolutes.

It’s important to note that the outside forces that appear here and their reactions are acting only in the node area, but the way the structure is built allows the dispersion of these forces, be it as comprehensive as they might be. Also, the joints in a truss are seen as revolute, which means that the torsional forces are excluded. But since there are different types of roof trusses, let’s find out which ones are the most popular and what distinct features they have.

King Post Truss

This particular truss is made out of wood most of the time, but it can also be constructed from a combination of steel and wood. It all comes down to the architect as well as the building construction. The King Post Truss spans up to 8m, which makes it perfect for multiple types of houses, particularly the smaller ones.

Pratt Truss

This is one of the most popular steel roof truss types and it is quite economical. This particular type of truss offers some interesting features mostly thanks to the fact that the vertical members supply tension, while the diagonal ones are bringing in compression. It’s crucial that you notice that these trusses can be used for bridges that range between 6-10m.

Queen Post Truss

The Queen Post Truss is designed to be a very dependable, simple and versatile form of roof truss that one can use at any given time. It provides a good span, around 10m, and it has a simple design that makes it perfect for a wide range of establishments.

Howe Truss

This type of truss is a combination of steel and wood, making it elegant, while also offering an extremely appealing layout. Virtually everything is made out of wood, however, the tension members or the perpendicular members are manufactured out of steel in order to offer extra support and reliability! One thing which makes the Howe Truss amazing is the fact that it’s a very wide span, as it can cover anything from 6-30m. This makes it versatile and very useful for an extensive range of project types.

Scissor Truss

Scissor trusses basically differ due to the truth that the braces cross one another, so as to support a comparatively high pitched roof. They then connect to the rafters on the opposite side. The main drawback with these kinds of trusses is that the shape will make insulation a bit more difficult.

Barrel Vaulted Truss

These trusses are different in the lower part, since they form a rounded, semi-circular structure, just like a barrel.

Raised Heel Truss

These are used when one wishes to have a good level of insulation in a building. They are ideal for energy efficiency. The roof pitch is relatively low.

Bowstring Truss

These trusses are utilized in buildings which feature an extremely large surface area. They develop an arched shape, consisting of several beams.

Flat Truss

Level trusses are used in cases where the roof has to be flat.

Hip Roof Truss

Such a roof trusses have 4 sides and develop sloping ends.

Dual Pitched Truss

These trusses come in a triangular form, but the apex is not exactly at the center. The two 2 chords come out of the apex and link to the beams beneath.

Hints for Installing Roof Truss Systems

A roof truss systems installation is a job that will almost certainly require more than a single workman. Not only does this kind of setup require heavy lifting to position the truss, but it also requires precision fitting and solid fastening. There are key factors involved that you must learn if you are to install a secure system.

Tip 1 Get Your Roof Closed Early

In the event that you may experience rain during your home building project, you need to protect the house on which you’re building the roof. Plan to complete the installation of your roof as quickly as possible. Get as much help as possible to get the roof closed. Otherwise, exposure to rain or other weather could damage material beneath your roof.

Tip 2 Vertical vs. Horizontal Pressure

To support a heavy roof without breaking or buckling, your trusses will provide more reliability if they can be positioned in more vertical positions, than if they are placed horizontally. Always place your trusses as close to perpendicular as you can.

Tip 3 Lifting and Positioning Your Truss

To avoid damaging your truss or alternative materials utilized to build your roof, particularly on homes that can be higher than a single story, use a crane to hoist the truss and hold it in place, while you position and fasten it.

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