Carpentry 2: Residential Truss System Part B
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When is the best time to inspect for missing or damaged trusses?
While they are being unloaded on site so it can be shown you were not at fault.
You should find a package of documents included with truss delivery. What type of information should be included in this package?
- Truss design drawings
- Truss placment and layout drawings
- Detail drawing for laminated girders
- Applying "T" braces and other installation details
- Hanger installation
- WWTA handling, erecting, & bracing recommendations
When trusses are delivered to the site, they are usually banded together. Is it good practice to use the banding for lifting the pile of trusses off of the truck?
Why must care be taken when lifting a truss that is laying flat on the ground?
Very weak laterally and bending can easily cause damage at connector plates.
What is the maximum amount of lateral deflection that can be applied to a truss before it is likely to start causing enough stress at the connector plates to begin weakening the joints?
Greater than 6 inches (150mm) over 6m (20ft).
What is the best position in which to keep a truss while it is being lifted and moved?
When should you consider getting a crane or picker in to hoist your trusses into plate rather than lifting the trusses by hand?
When the size and situation make it difficult to place without undue stress.
For what size of truss is a single pickup point suitable hoisting?
Trusses 20 ft and under
When lifting a truss over 30 ft in length it is recommended that 2 lifting lines be used. What is the maximum recommended angle between the 2 lines and why is this recommendation made?
60 degrees to minimize truss buckling.
What type of equipment is recommended when lifting trusses ranging in length from 30-60ft?
Spreader bar and short cable slings
A strongback should be used when lifting large trusses over 60 ft in length. Where should the strongback be positioned in relation to the truss?
2/3 to 3/4 of truss length. For flat should be tied to top chord. For pitched at or above mid-height and tied at 3m intervals.
What are the 2 main advantages in using a crane for lifting multiple trusses onto a roof?
What are the 4 types of braces that should be installed when performing multiple truss lifts with a crane?
- 1. Lateral bottom chord
- 2. Lateral top
- 3. Diagonal top
- 4. Diagonal centre
Why should care be taken to limit the amount of extension of braces and lifting beams beyond the ends of the trusses on a multiple truss lift?
So that the lift doesn't interfere with already installed trusses
Where can you find information regarding appropriate pickup points on a truss when performing a crane lift with multiple trusses?
Why is it critical to ensure that the first truss is solidly anchored and properly braced before setting the subsequent trusses?
Because all others are anchored to it.
What is the function of top chord bracing?
- Transfers loads
- Keeps the trusses plumb
- Maintains proper spacing between trusses until sheathing or purlins are installed
When placing lateral top chord braces, how should they be positioned in relation to the vertical braces?
Directly in line to allow forces to be transferred directly to the ground or floor rather than through the final chord and then down.
What is the maximum distance recommended between runs of bottom chord bracing?
Where is diagonal bracing required on the bottom chord?
At either end of a bulding and repeated at a maximum of 6m (20') between diagonal braces
What are the 3 main functions of permanent bracing in a trussed roof system?
- To decrease the unsupported length of compressive membrane
- To increase the stability of the truss system
- To assist the truss system with load transfer
What are the 3 main types of permanent bracing?
- Top chord
- Bottom chord
- Bracing of the web member plane
How is lateral movement prevented if purlins are installed as opposed to continuous sheathing?
Diagonal bracing should be installed on the underside of the top chords
Where will permanent web bracing be specified?
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