for sloped rafters bearing on the top plate of a wall on either side of a ridge beam, on a gabled roof...dont the rafters offer vertical support for the ridge. thus the ridge span is the rafter spacing. or is this for roofs with enough pitch that the rafters have a significant vertical component versus horizontal. of course, a light gage shallow CEE or ZEE section may not carry much, but steel beams would.
by the way, the roof Im talking about is of steel welded members. A Free Body Diagram is unneccessary as this is a simple question.
What happens if you remove the ridge board altogether? No ridge board. A FBD stays the same. Do you know the difference in a ridge board versus a ridge beam? There are a lot of 100 year old houses with no ridge board but have conventional rafter and ceiling joist roof framing.
Also, at some shallow pitches (such as 3:12), rafters do not act very "raftery". They act more like horizontal members.
The answer to the original question is - yes BUT.... It does not look like the capacity to resist the thrust is necessarily provided based on the relative size of the members indicated.
In a sense, knowing the magnitude of the forces (aka drawing a FBD) would help one to see whether or not the members will be sufficient and therefore they will or will not "support the ridge".
So... perhaps the answer should be:
Yes the rafters will support the ridge, PROVIDED that the system can resist the thrust.
OR
No, unless the thrust can be resisted by the system.
You write that the thrust can be resisted but if you understand that, then someone might reasonably wonder why you are asking the question.
Even when the rafters are well suited to support the ridge, a ridge member of some sort will be helpful to "compensate" for slight offsetting between the rafters. Other features might do that too but a ridge "board" is a convenient way to hold everything together.
