Tubular Steel roof trusses are used for large span constructions such as factories, industry worksheds, shopping malls, huge exhibition centres, multiplexes etc. They are generally used for spans as large as 25-30m.
There is a similar kind of a truss called “Tubular Steel Monitor Roof Truss“. There are projections on the roofs called “Monitors” to admit daylight into the space.
- It is in two halves with bolted joints at P and Q, the remaining joints being 5mm fillet welds made in the workshop.
- The main tie member rises 130mm from L to N to counteract any appearance of sag that would be evident if it were horizontal.
- A bend a N reduces the midspan height to 2m so that the half truss is a manageable size for transportation.
- The eaves detail L is given at G, where the rafters and the main tie tubes are fillet welded to an end plate.
- The site connection to the column is with 16mm diameter bolts using an angle cleat, a further angle bracket at the top is used for the purlin attachment . Small plates are welded to the purlin for this purpose, this purlin also acts as a sheeting rail for the side cladding.
- The roof covering in this thickness of asbestos sheeting which should have bitumen bonded glass wool insulation between the sheets.
- The ridge joint at E show plates which are welded to the rafters, these are bolted to the four site bolts.
- The plates are used to connect vertical end tubes of the two halves of the truss.
- The corresponding joint at Q of the tie member is given at J and K, the two bottom holes in the circular plate are used to fix a longitudinal tie at right angles to the trusses, the two holes above these can also be used to fix braces against the gable walls of the building in the end bays.
Advantages of Tubular Steel Roof Trusses
- Structures designed for material handling equipments (e.g., a bridge and a tower crane) where weight savings may be very substantial economic consideration.
- 30% to 40% less surface area than that of an equivalent rolled steel shape. Therefore, the cost of maintenance, cost of painting or protective coatings reduce considerably.
- The moisture and dirt do not collect on the smooth external surface of the tubes. Therefore, the possibility of corrosion also reduces.
- The ends of tubes are sealed. As a result of this, the interior surface is not subjected to corrosion. The interior surface do not need any protective treatment.
- They have more torsional resistance than other section of the equal weight.
- They have a higher frequency vibrations under dynamic loading than the other sections including the solid round one.