fsuenginerd
Structural
- Jul 29, 2008
- 4
Hello all,
I'm trying to model a precast shear wall with four large openings. A few screen shots are posted in the attached link. This is a 24' wide wall; the exterior column portions are 2' wide and the center column portion is 4' wide. There are three beam sections of varying depths above and below the blockouts.
My first inclination was to model it as a concrete frame with 3 column elements and 3 beam elements with a rigid offset equal to half the column width at each end. From sheet 2 of the attached pdf the rendering seems to show the beam sections beginning where they're supposed to, but sheet 3 shows the deformed shape and there's a conflict between the end of the beam and the column. The dead load reactions seemed a little high to me, so I double checked the weights by hand and ETABS is double counting the concrete where the beam overlaps the column. Calculating the correct reactions is an easy fix, but something tells me that having more concrete in the model than in the form would pose other problems.
Is there a way to define the offset portion of the beam as having zero mass, or would I have to define a massless rigid member instead?
Is there a way to force the column and beam to rotate together for the full width of each beam section? It behaves as I would expect at the node, but it doesn't seem to think the beam would brace against rotation elsewhere.
Am I barking up the wrong tree? Lateral loads are applied at each elevated level and the center column receives an inverted tee beam with an eccentric bearing condition, so a frame analysis made sense, but I'm starting to think that modeling it as a wall is a better approach.
I'd appreciate any help you can give me. I'm new to ETABS, so I'm still learning how to get realistic results.
Thanks,
Nick
I'm trying to model a precast shear wall with four large openings. A few screen shots are posted in the attached link. This is a 24' wide wall; the exterior column portions are 2' wide and the center column portion is 4' wide. There are three beam sections of varying depths above and below the blockouts.
My first inclination was to model it as a concrete frame with 3 column elements and 3 beam elements with a rigid offset equal to half the column width at each end. From sheet 2 of the attached pdf the rendering seems to show the beam sections beginning where they're supposed to, but sheet 3 shows the deformed shape and there's a conflict between the end of the beam and the column. The dead load reactions seemed a little high to me, so I double checked the weights by hand and ETABS is double counting the concrete where the beam overlaps the column. Calculating the correct reactions is an easy fix, but something tells me that having more concrete in the model than in the form would pose other problems.
Is there a way to define the offset portion of the beam as having zero mass, or would I have to define a massless rigid member instead?
Is there a way to force the column and beam to rotate together for the full width of each beam section? It behaves as I would expect at the node, but it doesn't seem to think the beam would brace against rotation elsewhere.
Am I barking up the wrong tree? Lateral loads are applied at each elevated level and the center column receives an inverted tee beam with an eccentric bearing condition, so a frame analysis made sense, but I'm starting to think that modeling it as a wall is a better approach.
I'd appreciate any help you can give me. I'm new to ETABS, so I'm still learning how to get realistic results.
Thanks,
Nick