I'm am new to RISA 3D. I was trying to model an equipment platform for roof equipment to verify the design of the steel beams. I have a row of W8x10's 7 total spaced at 2' o.c. (covered with grating where the equipment will sit) on the north end a W8x10 closes off the 7 other W8x10's while on the south a W8x10 runs approximately 30' where it can catch a column of the rooftop. In the north east corner a W10x12 is connected beneath the W8x10 structure that creates the platform at an angle and connects beneath the 30' W8x10 span. The W10x12 is bolted to the W8x10s at 3 locations (NE corner, last member of the platform and where the 30' W8x10 span ends and is bolted on top of the W10x12).

My issues are I am not sure how to correctly model the W10x12 that runs beneath the W8x10 structure and is bolted at 3 locations. Attached the model I constructed on RISA. I am trying to learn this program and any help and suggestions would be appreciated.

If I understand the situation correctly, you model the lower beam as continuus, with the transverse beams as continuous over the top.

You could either have a short dummy vertical members between the upper and lower beams, or frame all the beams at the same level.

Mike McCann
MMC Engineering
http://mmcengineering.tripod.com

Antnyt -

Open up the RISA-3D help file or the general reference manual. There will be a main topic called "Modeling Tips" with a subtopic called "Modeling One Member Over Another". I believe that this is essentially what you are trying to model. The discussion in the help file / general reference manual says essentially the same thing that Mike said above.... model a small "link" beam to connect the W10 and W8's wherever they are bolted together.

Thank you. Both posts were helpful. I having a feeling I will use this a lot.