Need a book? Engineering books recommendations...

# Re: A structural engineering journal

• To: seaint(--nospam--at)seaint.org
• Subject: Re: A structural engineering journal
• From: Roger Turk <73527.1356(--nospam--at)compuserve.com>
• Date: Mon, 20 Nov 2000 11:14:28 -0500

```Gil Brock wrote:

>>Roger,

In what way is the equivalent frame method "very conservative". A finite
element analysis results in the same total moments in a panel in each
direction as an equivalent frame analysis for a rectangular grid of
columns. This also shows that the total load needs to be carried in both
directions. The difference from a FE analysis is that it gives an elastic
distribution of those moments across the width of the panel and will also
show the distribution of moments for irregularly placed columns. The total
design moments in a panel, however, are the same from the 2 approaches for
the rectangular grid of columns.<<

The equivalent frame method is "very conservative" because it analyzes the
panels as one-way slabs in each direction, with each carrying the total
load.  Therefore, the shear forces in the panel at the column lines in
direction 1 have to equal the total load on the panel.  Similarly, the shear
forces in the panel at the column lines in direction 2 also have to equal the
total load on the panel.  Therefore, the total resisting shear on a panel is
equal to twice the load on the panel, a gross violation of statics.

There is nothing in the equivalent frame method that I have seen that
considers consistent deformation, one of the requirements of a two-way slab
or statically indeterminate system.

I cannot tell you why your FE program gives you the same results as the
equivalent frame method.  If the shear forces at all 4 panel edges total
twice the total load on the panel, I would suspect that the FE program was
written as an equivalent frame program and marketed as an FE program.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

```