A3. Adjacent Laps

Code Compliance & Reference
This detail complies with HKRC2004 Clause 8.7.2 and Figure 8.4 regarding adjacent laps.

Comments
To be frank, after reading this clause several times, and even after looking up the similar clause in Eurocode 2, I still don't fully understand this clause.
Questions & Confusions:

1. Is there a difference between ‘staggered’ lap and ‘adjacent’ lap? Or are they actually the same thing? If adjacent laps need to have a 0.3L distance between the laps, won't it make the lap a ‘staggered’ lap?
2. Then, the clause mentions that if the three conditions (including the “0.3L distance between laps” requirement) are fulfilled, then “the requirement on staggered laps can be waived”. I'm very confused: if there can be no staggered laps, why will there be a requirement on “distance between lap”?? So, either staggered’ laps and ‘adjacent’ laps are two different things (which I can’t figure out yet), or the clause imply that by fulfilling the other two requirement (i.e. the space between lapping bars and space between adjacent bars) the requirement of staggered lap can be waived. I have doubts for either explanation.
3. Why is the minimum clear spacing between adjacent bars only 20mm?? Shouldn’t it be “hagg+ 5mm or bar size”?? This requirement on minimum clear spacing seems meaningless as there is a more stringent requirement on bar spacing in Clause 8.2.
4. The distance between lapping bars can be increased beyond 4d (or 50mm); it can be done by increasing the lap length “by a length equal to the clear space exceeding 4d or 50mm”. Is there a maximum distance that such increase is allowed? What if someone increase the spacing of lapping bars to 1m??
5. Sumarizing the above three: (i) minimum clear spacing of adjacent bars of 20mm is not critical; (ii) spacing between lapping bars of 50mm can be increased by lap length; and (iii) with no staggered laps, there is no horizontal distance of adjacent laps. That means staggered laps can always be waived by increasing lap lengths. Is it truly the intention of this clause?? I think it is intended to reduce the congestion of lap zones; but now I can avoid this just by making the lapping zone longer.
6. The final confusion: is this lapping arrangement required for ALL laps, or is it required only if I want to avoid staggered laps? My first impression is the latter, but the code didn’t explicitly say so (neither did EC2). BD seems to interpret it as “all laps should comply”. But if that’s the case, I wonder why should it bother to mention that “staggered laps can be waived IF…”.
   

Regardless of all these confusion, this detail has to be included in the typical details because of BD’s requirement during previous approvals. SE wants them in the approval plans, and so be it. This detail is almost identical to Figure 8.4 in the CoP except for some additional description for clarity.

Just one additional comment:

• As mentioned above, the distance between lapping bars can be increased beyond 4d (or 50mm) by increasing the lap length “by a length equal to the clear space exceeding 4d or 50mm”. I personally do not like this “leniency” especially when there is no restriction on the maximum increase; and hence I didn’t add this to my typical details.

Blog note: Somehow I still think there must be some rationale behind this detail. I hope someone can give some insight on what this detail is meant for??