A5. Crank Laps

Code Compliance & Reference
No requirements in HKRC2004. I saw the detail of cranked bars in many consultant’s drawings, but only two of them specifically indicated where to use the cranked bars.

Comments
Purpose of this detail is to specify where to use crank laps. To my understanding, cranked bars are used to avoid congestion of lapping bars. Just a couple of comments:

1. One of the consultant use 50mm as the criteria on bars spacing to determine when to use cranked laps. I like this idea, so I keep it as 50mm. However, as the HKRC2004 states that the minimum clear spacing between bars is 25mm, I was tempted to change criteria to 25mm. However, I decide against it – spacing of 25mm is really small.
2. A consultant specifies the use of crank laps in beams & columns, and non-crank laps in slabs & walls. However, I didn't specify it this way because there can be beams & columns with wider bar spacings, and slabs & walls with smaller bar spacings.

Blog note: Any idea on how troublesome it is to make a crank bar? How slow and how costly? If it is indeed very troublesome I can consider revising the 50mm minimum bar spacing criteria to something like “minimum hagg+ 5mm or bar size” to make contractor’s life easier (and without much compromise on construction quality).