Concrete sway frames

[MHSpurs]

Concrete sway frames

Im new to staad and need some advice on modelling the above as lateral stability elements for a 4 story building.

I have 6 frames I can use for lateral stability at about 10 m centres.

Deflection limits are h/500

Should I use cracked or modified uncracked section properties?

Linear or non linear analysis?

2d frame or does it need to be FE?

Deadline looming and architect drops bombshell : new brief - minimal internal Walls!

Advice appreciated (on middling, not on dealing with architect)

Thanks

Mh

 

[JoshPlumSE]

Well, the code will let you do it a number of ways. My response will be limited to the method of analysis that I think is most common. An elastic analysis which considers the P-Delta effect.

Most of the time, the code will expect you to account for some degree of cracking (see ACI 318 section 10.11).

For drift (which may be a service level limit) you may be able to assume a different level of stiffness. Since I'm assuming a linear analysis, this essentially means maintaining two models... provided that STAAD cannot use one level of stiffness for the service load cases and a reduced level of stiffness for the ultimate load cases.

 

[structuresguy]

I'm basically with JoshPlum on this. I would modify the stiffness per ACI and run a linear analysis. Depending on the configuration in the building, I would try to run each frame as a 2D planar model. If you have nice uniform layout, with no weird torsional irregularities, this should work fine. Otherwise, I would run a 3D model, which would account for torsional results from the geometry of the building. Also, the code may require you to add torsional loading anyway, so 3D might be easier than trying to figure out the distribution of loads by hand. Make sure you turn on "torsion check" for the concrete design of the beams and columns. I think it is off by default. I would also consider P-delta, though for 4 stories it probably won't be too significant.