Structural Models Seen As Teaching Aids

 By RONALD SHAEFFER, Instructor
 College of Architecture & Fine Arts
 University of Florida


 During the winter trimester, 1964,
a new type of teaching device was
introduced in the Department of
Architecture at the University of
Florida. Structural models of balsa
wood were constructed and tested by
the third-year students enrolled in
AE 352, the second in a sequence of
five courses concerned with the anal-
ysis and design of architectural struc-
tures. The initial idea for this project
came from an article by Boyd C.
Ringo in the February, 1964, issue
of CIVIL ENGINEERING maga-
zine. In this article Professor Ringo
describes a model balsa-wood project
undertaken by students in the Civil
Engineering Department at the Uni-
versity of Cincinnati.
 The project as assigned to the
architecture students involved the de-
sign and construction of an efficient
transversely loaded structure. The


two equal concentrated loads at the
third point. This loading results in
and area of pure moment or zero
shear between the loads. The depth,
width and rise or depression were all
limited to a maximum of four inches.
The only materials permitted were
balsa wood and glue, the brand of
which was specified.


 The problem was assigned as a
practical supplement to the relatively
rigorous treatment of elementary
theory involved in the course. Balsa
wood, a material that is definitely
not isotropic and really not very
homogeneous, seldom behaves in a
manner precisely consistent with basic
theory. Since these models were to


Fig. 2 A barrel vault solution. Note load receivers.


 Fig. 1 A combination truss and plate solution.

major design goal of the project was
the achievement of the highest pos-
sible ratio of superimposed load to
dead weight at collapse. The class of
nineteen students was organized into
two- and three-man teams for this
one-week assignment, and certain spe-
cifications controlling the design of
the models were adopted to insure
a reasonable basis for competition
among the teams. The structure was
to be designed to span 33 inches be-
tween simple supports and to carry
APRIL, 1965


 be loaded to their ultimate capacity,
 the plastic nature of the material was
 of prime importance. Unfortunately,
 it is in this strain region that the be-
 haviour of balsa wood becomes most
 erratic. For this reason an empirical
 approach to this problem was adopted
 by most of the teams. All of the
 teams built and tested several pre-
 liminary models to locate and remedy
 (Continued on Page 8)
Fig. 3 An underslung truss design which weighed
 only 0.215 Ibs. but supplied a load of 157.6 lbs.