For full utilization, all ties in tied columns must be fully developed (for full tie yield strength) at each corner enclosing a vertical bar or, for circular ties, around the full periphery.
Splices. The ACI 318 Building Code provides arbitrary minimum sizes and maximum spacings for column ties (Art. 9.83). No increases in size nor decrease in the spacings is required for Grade 40 materials. Hence, the minimum design requirements for splices of ties may logically be based on Grade 40 reinforcing steel.
The ordinary closed, square or rectangular, tie is usually spliced by overlapping standard tie hooks around a longitudinal bar. Standard tie patterns require staggering of hook positions at alternate tie spacings, by rotating the ties 90 or 180. (Manual of Standard Practice, Concrete Reinforcing Steel Institute). Two-piece ties are formed by lap splicing or anchoring the ends of U-shaped open ties. Lapped bars should be securely wired together to prevent displacement during concreting.
Tie Arrangements. Commonly used tie patterns are shown in Figs. 9.52 to 9.54.
In Fig. 9.53, note the reduction in required ties per set and the improvement in bending resistance about both axes achieved with the alternate bundled-bar arrangements.
Bundles may not contain more than four bars, and bar size may not exceed No. 11.
Tie sizes and maximum spacings per set of ties are listed in Table 9.25.
Drawings. Design drawings should show all requirements for splicing longitudinal bars, that is, type of splice, lap length if lapped, location in elevation, and layout in cross section. On detail drawings (placing drawings), dowel erection details should be shown if special large longitudinal bars, bundled bars, staggered splices, or specially grouped bars are to be used.
