31 Dec 93
Figure A-11. Stepped plate model
location of the centroids of the various portions of the
(3) Offset beams model. The elements for this
slab will need to be placed at the same elevation,
model are all placed at the centroid of the thin section
when in fact they are at different elevations.
of the base slab. At the location where the slab is
thicker, a grid of beams is added. The locations of
the elements and beams are shown in Figure A-12.
f. Shear, moments, and thrusts (CSMT). Since
The elevation of these beams should be located at the
output supplied by finite element programs is often in
centroid of the additional thickness being modeled,
the form of stresses and displacements, steps must be
and the section properties should also be computed
taken to convert the resulting stresses into moments,
based on the tributary area of the additional thickness.
axial thrusts, and shears which can used for design.
In order to use this model, the finite code being used
To assist in obtaining the necessary shears, moments,
must be capable of offsetting the location of the
and thrusts needed from a finite element analysis, the
beams through a member eccentricity command since
program CSMT was developed. The program is
the beams are located at the same nodes as the plates.
documented in Huff et al. (1988). The user inputs
stresses along a given line from the finite element
(4) Single centroid model. The base slab may
analysis into the CSMT program, and the program
be modeled using shell elements and assigning the
computes the thrust and moment from the axial stress
elements within the model with different thicknesses.
block as well as the resulting shear on the section
This will require some approximation since the
from the shear stress block. If the designer chooses,