Lattice girder installation

Well, you install one, of course! Our next step, therefore, was to work on the lattice girder installation. A lattice girder would be lighter and cheaper than an I-beam and just as strong.

Our K-Span roof installers voiced their concerns regarding the structural stability of the design. They were surprised to discover the roof arcs were dipping on installation. We had limitations in regard to the height of the building as per the regulations as set out by Swartland Municipality. Therefore, for this installation, it is true that the machine and roof arcs were pushed to their limits. A few adjustments to the roof corrected the level, but our structural engineer asked us to install a beam as a backup.

A more obvious choice as a roof beam is a steel I-beam. The I-beam that we would have had to install would have weighed over four tonnes. Kevin had a better plan and set about designing a lattice girder. John Moll our structural engineer double checked and adjusted the required dimensions for the lattice girder. Whatever we install needs to be able to take the weight of the entire roof, should every bolt fail and we have a freak snow storm. The lattice girder is exceptionally strong because of the forces of tension and compression.

One evening, Kevin tried to explain it to me while we were washing the dinner dishes. The first step was to order all the material and have the tubes laser cut for ease of welding. Once all the pieces arrived, Kevin had to decide where to make the girder. He needed somewhere flat to lay out the pieces. It also needed to be an area big enough to take the full size of the girder.

He had the option of building it in one of the shipping containers. Building it in a shipping container would have resulted in one big disadvantage. It would have been difficult to move it to the correct place for installation. Finally, Kevin decided that the best option would be to build it half way up the scaffolding with each end resting on the containers that make the East and West sides of our house. He used the scaffold jacks to level the scaffolding.

This ensured that the girder poles were in the right place before he began welding so that the girder would be straight. It has an intentional, but very slight, bow in it which will straighten as it takes the weight of the settling roof.

He began by welding the girder upside down. When he had completed all the welding that he could reach, he then flipped it around, using a block and tackle, in order to reach the other points. It was also then in the correct orientation for installation. The installation of the rather impressive lattice girder filled me with much anxiety.

I had to keep reminding myself that it was light and the weight is only that of about five adults as opposed to five hatchbacks. How in the world was Kevin going to get this rather large and bulky girder the full six metres up in the air? Just before the real work began, the guys had a work break with tea and chocolate. They needed the energy for a 25 hour day! They discussed the plan until everyone knew exactly what they were doing. In the end, all it took was the scaffolding , a block and tackle, a bit of leverage and lots of watchful eyes.

The guys attached the block and tackle to the middle of the bottom pole of the girder, so that the girder could swing up and down like a see-saw. Everyone was sure to watch carefully to make sure it did not hook on anything. At the same time, as the girder rose, the team clipped in extra scaffolding poles under it as a safety measure.

This way, if the block and tackle gave way, the girder would only have a short distance to fall. Lattice Girders used in combination with shotcrete support DSI Underground has been a leader in the development and manufacturing of underground support systems for over 80 years and has been producing lattice girders in the USA since the s.

Lattice girders serve some of the same basic functions in tunneling as steel arch supports. They are part of the temporary lining which initially supports the excavation and, in some cases, are part of the finished lining.

Used with the New Austrian Tunneling Method NATM of shotcrete application, lattice girder systems offer a very economical alternative to other support methods for a wide variety of ground conditions.

Applications The use of lattice girders should be considered for projects where shotcrete will be used for temporary or permanent support.

These include mining through soft ground, mixed face and rock, or tunnels in which widths or heights may vary. Lattice girders are applied equally well to circular and horseshoe shaped excavations, whether driven full face or heading and bench.