Moments at Pinned Supports

[ivorm]

I'm really new to RISA and I'm fumbling my way around. I'm trying to model a somewhat strange balcony supported of the side of a building. The balcony has a angled rod hanger on one side and a continuous cranked (in the XZ plane) channel framing back into a channel ledger on the building on the other side. I'm wondering why when I frame my channels back into pinned supports (members 1 and 4) they have moments at the pinned support ends? I can fix it by releasing the Mz moments in member 4 but I don't know why this doesn't happen already with the pinned support. I've attached a model To help as my description is probably pretty terrible.

I'd attach some PDF's to but I don't know how to attach multiple files, or if I even can.

Thanks,
Ivor

 

[msquared48]

You have to go to the supports or reactions and release the moments there.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[ivorm]

I know I can go into member 4 end releases and release the moments on M1 but isn't that the default for a pinned joint? Also I thought that would cause an instability because I'd have a pinned boundary and an end release on the same joint. I think I uploaded the wrong model; this one shows the end moments more clearly. When I go into the joint information on N5 it shows rotation as free in all directions.

Sorry if these seems like simple stuff, most of my modelling has been 2D in the past which seems a little simpler.

 

[msquared48]

OK. There should be a tab that reads "Boundary Conditions". Go in there and release the moments. Leave the member end moments fixed. This should give you reactions with zero moments.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com