How to measure minimum bar spacing for Bundle Bars in Cast-in Place Concrete as per AASHTO provisions
Minimum Bar Spacing: As per AASHTO LRFD, section 5.10, the minimum bar spacing for bundled bars should be measured on the basis of the acquired diameter rather than computing from individual diameters.
As for instance, if there are 2 nos. 32 mm dia bars, the similar diameter in accordance with 2?32 is 45mm. Therefore, 45 should be employed to utilize the following clauses from AASHTO.
For 2?32 dia bars, clear spacing should be provided as ~68mm for Cast-in Place concrete and 60mm for precast concrete.
Refer following Clauses from AASHTO LRFD 5th Edition 2010
For cast-in-place concrete, the clear distance among parallel bars in a layer should not be under :
5 times the minimal diameter of the bars,
5 times the maximum size of the coarse aggregate, or 1.5 in.
For precast concrete fabricated under plant control conditions, the clear distance among parallel bars in a layer should not be under :
The minimal diameter of the bars,
33 times the maximum size of the coarse aggregate, or 1.0 in.
The number of parallel reinforcing bars bundled in contact to function as a unit should not go beyond four in any one bundle, apart from flexural members, the number of bars greater than No. 11 should not go beyond two in any one bundle.
Bundled bars should be attached within stirrups or ties. Individual bars in a bundle, cut off inside the extent of a member, should be abandoned at several points with minimum a 40-bar diameter stagger. Where spacing limitations are dependent on bar size, a unit of bundled bars should be considered as a single bar of a diameter taken from the corresponding total area.