This construction article sheds light on how to measure lowest Bar Spacing for Bundle Bars in Cast-in Place Concrete according to AASHTO provisions.

Lowest Bar Spacing

In accordance with AASHTO LRFD, section 5.10, the lowest bar spacing for bundled bars is computed on the basis of the derived diameter rather than making calculation out of seperate diameters.

Sample Calculation

As for instance, while applying 2 nos. 32 mm dia bars, the corresponding diameter identical to 2×32 is 45mm. There, 45 should be employed to use the following clauses from AASHTO.

Toward 2×32 dia bars, clear spacing is ~68mm for Cast-in Place concrete and 60mm for precast concrete.

Relate following Clauses from AASHTO LRFD 5th Edition 2010

5.10.3.1.1—Cast-in-Place Concrete

For cast-in-place concrete, the clear distance among parallel bars in a layer must not be under:

• 5 times the nominal diameter of the bars,
• 5 times the maximum size of the coarse aggregate, or 1.5 in.

5.10.3.1.2—Precast Concrete

For precast concrete that is developed under plant control conditions, the clear distance among parallel bars in a layer must not be under:

• The nominal diameter of the bars,
• 33 times the maximum size of the coarse aggregate, or 1.0 in.

5.10.3.1.5—Bundled Bars

The number of parallel reinforcing bars accumulated in contact to function as a unit that should not surpass four in any one bundle, excluding that available in flexural members, the number of bars greater than No. 11 should not go beyond two in any one bundle.

Bundled bars are surrounded between stirrups or ties. Separate bars in a bundle, cut off inside the span of a member, shall be discontinued at various points with minimum 40-bar diameter stagger. Where restrictions on spacing are dependent on bar size, a unit of assembled bars is considered as a single bar of a diameter came from the corresponding total area.

Article Source: www.civildigital.com