Projected Loads and Snow Loads - Intro to Structural Analysis

This video defines projects loads and presents an example problem using the most common type of projected load, snow loading on a roof truss.

In this example, we will:
1) Compute the reactions forces for combined dead plus snow loading
2) Convert projected loads to distributed loads in the axial and shear directions
3) Compute the axial, shear, and moment diagrams.

For a projected load S, with an angle A between the loading plane and the element to which the load is applied, there are a few shortcut equations:
~ Distributed Shear Load = S*cos(A)*cos(A)
~ Distributed Axial Load = S*cos(A)*sin(A)
Try these out, and you'll see they match exactly the results shown in the video! In this example, cos(A) = 12/13 and sin(A) = 5/13.

[WG-fttz]

Professor, thanks for the video. Was hoping you could address a question if time allows. Per ASCE, for roof exposure factor Ce, having a hard time understanding why a fully exposed roof has a reduced factor VS a sheltered roof. Wouldn't a fully exposed roof see the more snow load when compared to the sheltered roof?

[andrewbolduc]

The reality is that snow does not fall straight down and with a symmetric roof will build up more on one side than on the other. Also with asphalt shingles, as I know all too well in New England, heavy, wet snow does not slide off the roof by itself

[vancewilkins]

Thanks for a well explained video. In spite of that, I do have a couple of questions. I have learned that a truss that is statically indeterminate can't be solved. Is that just for internal forces(you obviously did solve it). secondly could you make a video on how to use these figures to design a wooden truss? How many members and what size they need to be.

[fatimamancuso]

dumb question, but around minute 7:48 dividing the forces into their components, f/13 and 12/13, can this be explained more? That was the issue I was having was projecting the loads and snow loads onto a beam. Thank you very much for the video.

[TheItinerantCraftsman]

@StructuresProfH
How would I calculate the dead and dynamic load capacity on a ridge beam for the purpose of hanging substantial weight from it?

[sublimina]

Very well explained thank you, I have a question tho, if we had the wind load as well which would be perpendicular to the roof how could we calculate it as well?

[Snowbird]

So the Ax and Cx reactions would dictate the required thrust force to be resisted. Would you do an example where a collar tie is installed and no ceiling tie as in many wood framed homes?

[WG-fttz]

Thanks for the video. Is it correct to state that the only reason the reactions have an X component is due to the hinge at the peak of the roof?

[johnfitzpatrick]

G, day from Sydney Australia.
Once you have calculated the forces applied in compression and tension, what is the easiest way to select materials that can resist that load per foot: manufacturers specifications or actually testing?
🌏🇭🇲