APPENDIX
B
625
General Procedure
for Using Structural
Analysis Software
Popular structural analysis software programs currently available, such as
STAAD, RISA, SAP, etc. are all based on the stiffness method of matrix
analysis, described in Chapters 13 through 15.* Although each program has
a slightly different interface, they all require the operator to input data
related to the structure.
A general procedure for using any of these programs is outlined below.
Preliminary Steps. Before using any program it is first necessary
to numerically identify the members and joints, called nodes, of the
structure and establish both global and local coordinate systems in order
to specify the structure’s geometry and loading. To do this, you may want
to make a sketch of the structure and specify each member with a
number enclosed within a square, and use a number enclosed within a
circle to identify the nodes. In some programs, the “near” and “far” ends
of the member must be identified. This is done using an arrow written
along the member, with the head of the arrow directed toward the far
end. Member, node, and “direction” identification for a plane truss,
beam, and plane frame are shown in Figs. B–1, B–2, and B–3. In Fig. B–1,
node ➁ is at the “near end” of member
4
and node ➂ is at its “far end.”
These assignments can all be done arbitrarily. Notice, however, that the
nodes on the truss are always at the joints, since this is where the loads
are applied and the displacements and member forces are to be
determined. For beams and frames, the nodes are at the supports, at a
corner or joint, at an internal pin, or at a point where the linear or
rotational displacement is to be determined, Fig. B–2 and B–3.
Since loads and displacements are vector quantities, it is necessary to
establish a coordinate system in order to specify their correct sense of
direction. Here we must use two types of coordinate systems.
Global Coordinates. A single global or structure coordinate
system, using right-handed x, y, z axes, is used to specify the location of
each node relative to the origin, and to identify the sense of each of the
external load and displacement components at the nodes. It is convenient
to locate the origin at a node so that all the other nodes have positive
coordinates. See each figure.
*A more complete coverage of this method including the effects of torsion in three-
dimensional frames, is given in books related to matrix analysis.
3
4
2
1
1
3
5
2
4
y
x
200 N
2 m
2 m
4 m
3
2
4
x¿
y¿
Fig. B–1