truss design Archives

Truss Tuesday: Will it Bend?

by Seth Duncan | Apr 30, 2024 | Educational, Truss Tuesday

This week’s truss:

Question: Which member of this hip girder has the highest stress? There are jacks every 2 feet across most of the bottom chord.

Building Code: FBC2020

Loads (psf unless otherwise noted):
TC Live Load 20
TC Dead Load 10
BC Live Load 0
BC Dead Load 10

Wind: 160 mph

The answer will be posted on Thursday!

This is not a production truss! This is simply an example for Truss Tuesday conversation.

Updated Thursday, May 2nd 2024

Answer: The highest stress occurs at the vault in member B3. The lumber grade would have to be upgraded to Dense Select Structural to handle the bending.

Request a Drawing

Truss Tuesday: Floored

by Seth Duncan | Apr 23, 2024 | Educational, Truss Tuesday

This week’s truss:

Question:

While the TPI Technical Advisory Committee recommends that the minimum grade of visually stress-related lumber used for truss chords should be No. 2 grade, could you hypothetically use No. 3 for either one and still perform under capacity?

Top and Bottom Chords are Southern Pine No. 2
Webs are Southern Pine No. 3

Building Code: IBC 2021

Loads (psf unless otherwise noted):

TC Live Load 40
TC Dead Load 10
BC Live Load 0
BC Dead Load 5

The answer will be posted on Thursday!

This is not a production truss! This is simply an example for Truss Tuesday conversation. Join the conversation on LinkedIn.

Updated: April 25th, 2024

Answer: T1 can be replaced with No. 3, but replacing B1 with No. 3 would cause the truss to go over capacity.

Request a Drawing

Understanding Horizontal Distance to Windward Edge

by Seth Duncan | Apr 16, 2024 | Educational

Why it matters

The horizontal distance to the windward edge provides context to the loading calculations about where the truss design is located within the building and is used to set the internal and external pressure coefficients. Generally, the closer the component is to an edge of the building that receives wind, the greater the pressures from the wind will be. A truss that is a distance of 0 from the windward edge is going to receive the most pressure from the wind on that side. Setting the distance too low for a truss that is far away from a windward edge could result in wind loading that is much greater than necessary for that truss.

The horizontal distance to windward edge is the shortest perpendicular distance from a truss to an edge that receives wind (note that the wind direction is considered perpendicular to the edge). Here, truss design 5 appears twice, so its horizontal distance to windward edge is the minimum of the two–equal in this case, 5’ 10-1/12”.

For the girder, truss design 1, the horizontal distance to windward edge also happens to be 5’ 10-½”, which is the shortest perpendicular distance to a windward edge from its location.

For Truss Design 7, of which 3 are pictured, the shortest distance to the windward edge from any of the trusses, 7’ 10-½”, should be used for all of the trusses. The worst case gets used for all of the designs.

The king jack, truss design 2, may be the most confusing case. The short answer is that its horizontal distance to windward edge is 0 because it intersects a windward edge. If you try to measure to the closest windward edge in a direction perpendicular to the truss, you’ll find that 0 is in fact the shortest distance.

If you found this helpful, check us out on LinkedIn to join the conversation.

Request a Drawing

Truss Tuesday: Tower of Terror

by Seth Duncan | Apr 9, 2024 | Truss Tuesday

This week’s truss: Tower of Terror

Question:

This truss has one chord member that needs to be upgraded to Number 1, but all the rest will work at Number 2. Which one do you think it is?

Chords are 2×4 Southern Pine #2
Webs are 2×4 Southern Pine #3
End Vertical is 2×8 Southern Pine #3

Building Code: FBC 2020

Loads (psf unless otherwise noted):

TC Live Load 20
TC Dead Load 10
BC Live Load 0
BC Dead Load 10

Wind: 130 mph

The answer will be posted on Thursday!

This is not a production truss! This is simply an example for Truss Tuesday conversation. Join the conversation on LinkedIn.

Updated: Thursday, April 11th

Answer: It’s B2! That span is long enough to cause significant bending in the bottom chord. The tower is well-supported by the thick end vertical and permanent bracing.

Request a Drawing

Truss Tuesday: 2 x 4 or not 2 x 4…that is the question

by Seth Duncan | Apr 2, 2024 | Truss Tuesday

This week’s truss:

Question:

This truss is over capacity. What are some ways to fix it?

Top Chords are Southern Pine No 2
Bottom Chords are Southern Pine No 1
Webs are Southern Pine No 3Building

Code: IBC 2021

Loads (psf unless otherwise noted):
TC Live Load 20
TC Dead Load 10
BC Live Load 0
BC Dead Load 10

Application: ResidentialWind: 130

The answer will be posted on Thursday!

This is not a production truss! This is simply an example for Truss Tuesday conversation. Join the conversation on LinkedIn.

Updated Thursday, April 04, 2024

The “simplest” way to get this truss under capacity is to upgrade T3 to a 2×6! How did you do it?

Request a Drawing