![]() I suspect you have ridge BOARD, which is not substantial enough to resist any vertical loads/rafter reactions. However 30 ft is a VERY long ridge beam and based on even modest rafter spans would have to be pretty sizeable (definitely better than a single 2x). Because a ridge beam is substantial enough to carry the vertical reactions of the rafters (and the rafter reactions are vertical only - due to gravity as pointed out earlier) there is no kick out at the walls. The two are not the same or interchangeable and heavily influence reactions at the wall.Ī ridge BEAM will carry half the rafter vertical load. M1208 I think you need to clarify if you have ridge BOARD or BEAM. RE: Rafter horizontal reaction on the exteriro wall Jc67roch (Structural) 24 Nov 15 20:58 If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it. I like to debate structural engineering theory - a lot. We confuse a tendency towards lateral movement in a hypothetical unstable condition with a net lateral force in the stable condition. I think this is the crux of where we tend to go wrong with this stuff. In case two, forces are not in balance and it`s meaningless to discuss reactions. ![]() In case one, there is no net horizontal load delivered to the top of the wall. At a sloped wall to rafter connection, one of two things is true:ġ) the component of the vertical rafter reaction parallel to the rafter is able to be resisted and the system is stable OR Ģ) the component of the vertical rafter reaction parallel to the rafter is NOT able to be resisted and the system is unstable. ![]() I agree with this, as it is similar to BA`s point, but I don`t believe that it affects any of my statements. So technically no kick, but the wall can be unstable if the angle of friction is less than the slope. Having a flat bearing removes this shear load. Adding toenails or similar shear connection will prevent this if the slope is not huge. If the rafters have a sloped bearing at the top of the wall and no connection, they will tend to slide the wall inwards under gravity load. RE: Rafter horizontal reaction on the exteriro wall XR250 (Structural) 24 Nov 15 18:53 I forgot to throw in some load but you`ll get the idea. I believe the model shown below to be the appropriate way of visualizing the typical rafter condition. Only unrestrained lateral movement.ģ) Since there can be no lateral kick at the wall connection, there can also be no lateral kick at the ridge beam connection. The rafters must have flat bearing at the wall and at the ridge beam, assuming there is one, or there will be a lateral kick from the vertical load irrespective of any deflection induced kick.ġ) I believe the reactions delivered by the rafters to the supporting structure to be unrelated to whether or not the bearing surface is flat.Ģ) Since the supporting wall is pinned top and bottom, there can be no lateral kick at the wall.
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