Bottom and top of column member forces do not match

RE: Bottom and top of column member forces do not match

Seth Guthrie — Tue, 01 Mar 2016 17:18:51 GMT

Yes, I think that would be fine.

RE: Bottom and top of column member forces do not match

Lee Oldfield — Tue, 01 Mar 2016 17:13:22 GMT

Okay, thanks for clearing this up for me, Seth.

Based on this, I'd say that it's safe to take the axial and shear loads from the frame reaction tables and use those for futher calculations, correct?

RE: Bottom and top of column member forces do not match

Seth Guthrie — Tue, 01 Mar 2016 17:07:27 GMT

I ran your file with the latest version, 15.01. At level Interior FDN there is a 5" thick solid concrete slab that is continuous and thus able to redistribute vertical column loads somewhat. It also has self-weight turned on (in addition to the column self-weight which you mentioned), let's consider the lateral column at D-1. At the bottom story the axial loads are:

Dead - 109k;

Above that story there is a column with 84k axial load and two braces with 16.6 and 5.3 kips axial load. I did not check the angle of the braces, but if they are around 45 deg then the sum of those is about 96 kips. The extra comes from the slab weight and any potential force transfer through slab shear.

Looking at one of the wind loads, say W1 we have -18.6 kips in he column below and above the slab we have -12.45 kips in the column plus -8.7 kips in one brace. That works out to -18.6 kips so the redistribution through the slab is very small.

Was there another column you were concerned about? Everything seems to be fine to me.

RE: Bottom and top of column member forces do not match

Lee Oldfield — Tue, 01 Mar 2016 16:38:56 GMT

The model has been uploaded.

RE: Bottom and top of column member forces do not match

Lee Oldfield — Tue, 01 Mar 2016 16:33:21 GMT

No, all loads do not match (dead, live, snow, wind, seismic). I'm taking loads at the column bases. There is no other framing at this point - I've defined the ground level at the column base/top of pier, however, I've detached all nodes at this level to avoid all load being transferred into the diaphragm. I will upload the model shortly via the Secure File Upload.

RE: Bottom and top of column member forces do not match

Seth Guthrie — Tue, 01 Mar 2016 16:27:05 GMT

Are we talking about dead loads only (i.e. no live load reduction)? If so, then the loads must have found another load path via a continuous beam or 2-way slab with stiffness to redistribute the loads. (Assuming there are no walls involved). You should be able to confirm through member forces output.
You may want to upload your model using the Secure File Upload process link below left if that's not the answer.