Building Design and Construction Handbook - Merritt - Ventech!

7.28 SECTION SEVEN
FIGURE 7.14 Steel rigid frames: (a) single bent; (b) continuous frame with
underfloor tie; (c) connection of tie to a column; (d) with two-hinged.
placed perpendicular to the span on the column center line. Many designers prefer
to obtain a hinge effect by concentrating the column load on a narrow bar, as shown
in Fig. 7.14c; this refinement is worthwhile in larger spans.
Regardless of how the frame is hinged, there is a problem in resisting the horizontal
shear that the rigid frame imparts to the foundation. For small spans and
light thrusts, it may be feasible to depend on the foundation to resist lateral displacement.
However, more positive performance and also reduction in costs are
usually obtained by connecting opposite columns of a frame with tie rods, as illustrated
in Fig. 7.14b, thus eliminating these horizontal forces from the foundation.
For ties on small spans, it may be possible to utilize the reinforcing bars in the
floor slab or floor beams, by simply connecting them to the column bases. On
larger spans, it is advisable to use tie rods and turnbuckles, the latter affording the
opportunity to prestress the ties and thus compensate for elastic elongation of the
rods when stressed. Prestressing the rod during erection to 50% of its value has
been recommended for some major installations; but the foundations should be
checked for resisting some portion of the thrust.
Single-story, welded rigid frames often are chosen where exposed steelwork is
desired for such structures as churches, gymnasiums, auditoriums, bowling alleys,