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Section 3
3-7
combinations of forces and moments, whereas a primary load case
is revised during the pdelta analysis based on the deflections. Also,
the proper factored loads (such as 1.4 for DL etc.) should be
provided by the user. STAAD does not factor the loads
automatically.
3.6 Beam Design
Beams are designed for flexure, shear and torsion. For all these
forces, all active beam loadings are prescanned to locate the
possible critical sections. The total number of sections considered
is 12 (twelve) unless this number is redefined with an NSECTION
parameter. All of these equally spaced sections are scanned to
determine moment and shear envelopes.
3.6.1 Design for Flexure
Reinforcement for positive and negative moments are calculated on
the basis of the section properties provided by the user. If the
section dimensions are inadequate to carry the applied load, that is
if the required reinforcement is greater than the maximum
allowable for the cross section, the program reports that beam fails
in maximum reinforcement. Effective depth is chosen as Total
depth - (Clear cover + diameter of stirrup + half the dia. of main
reinforcement), and a trial value is obtained by adopting proper bar
sizes for the stirrups and main reinforcements. The relevant
clauses in Sections 10.2 to 10.6 of ACI 318 are utilized to obtain
the actual amount of steel required as well as the maximum
allowable and minimum required steel. These values are reported
as ROW, ROWMX and ROWMN in the output and can be printed
using the parameter TRACK 1.0 (see Table 3.1). In addition, the
maximum, minimum and actual bar spacing are also printed.
It is important to note that beams are designed for flexural moment
MZ only. The moment MY is not considered in the flexural design.