J1D
Structural
- Feb 22, 2004
- 259
Re: thread507-143980
The thread is closed. Here is some follow-up informatioin
Following the description of damo74, I set up a SAP model using shell elements and material close to timber. Model I has an all-the-way opening parallel to front/rear walls, at the middle 1/3 of the floor. Two columns along each opening edge are added from ground up to floor and to roof. Model II is the same as Model I except that the opening is filled with sloped shell elements. Wind loads are applied in two directions separately (WLX=the wind on front and rear walls; WLY=wind on the gable walls). The following findings basically agree with what you pointed out.
1. Under WLX, no big difference between the two models (in terms of structural deformation and support reactions), the two floor panels still act as shear diaphragms and carry the wind to the end walls. The local stress in the gable walls near the opening is much higher than that without opening.
2. Under WLY, although the opening breaks down the floor shear diaphragm, the stepped floors together with the gable walls (acting as chords in compression and tension) can still effectively transfer shear load to front and rear walls, as described by DaveAtkins and kxa. The compression and tension in the chords (front and rear gable walls between step points) are substantial. But again, the structural deformation and support reactions are about the same as that without opening.
3. Extremely, move the opening to one side, say, near the front wall (Model III), the structure is still very stable under WLY. The wind load on the gable wall in the middle portion mainly goes to the remaining floor and transfer to the rear wall. There is no need to transfer shear across the opening, the system keeps good equilibrium. This panel-chord mechanism differs from the beam with a web cutting analogous. Model III exhibits a very slight twist near the floor.
4. The local high stress on the gable wall at the floor opening points can be released if the “chords” are pinned to rest of the walls.
Hope the info helps
The thread is closed. Here is some follow-up informatioin
Following the description of damo74, I set up a SAP model using shell elements and material close to timber. Model I has an all-the-way opening parallel to front/rear walls, at the middle 1/3 of the floor. Two columns along each opening edge are added from ground up to floor and to roof. Model II is the same as Model I except that the opening is filled with sloped shell elements. Wind loads are applied in two directions separately (WLX=the wind on front and rear walls; WLY=wind on the gable walls). The following findings basically agree with what you pointed out.
1. Under WLX, no big difference between the two models (in terms of structural deformation and support reactions), the two floor panels still act as shear diaphragms and carry the wind to the end walls. The local stress in the gable walls near the opening is much higher than that without opening.
2. Under WLY, although the opening breaks down the floor shear diaphragm, the stepped floors together with the gable walls (acting as chords in compression and tension) can still effectively transfer shear load to front and rear walls, as described by DaveAtkins and kxa. The compression and tension in the chords (front and rear gable walls between step points) are substantial. But again, the structural deformation and support reactions are about the same as that without opening.
3. Extremely, move the opening to one side, say, near the front wall (Model III), the structure is still very stable under WLY. The wind load on the gable wall in the middle portion mainly goes to the remaining floor and transfer to the rear wall. There is no need to transfer shear across the opening, the system keeps good equilibrium. This panel-chord mechanism differs from the beam with a web cutting analogous. Model III exhibits a very slight twist near the floor.
4. The local high stress on the gable wall at the floor opening points can be released if the “chords” are pinned to rest of the walls.
Hope the info helps
