A4. Minimum Transverse Reinforcement for Lapped Splices

Code Compliance & Reference
This detail complies with HKRC2004 Clause 8.7.4 and Figure 8.6 regarding the minimum transverse reinforcement for lapped bars.

Comments

1. I understand from BD that this detail is applicable to all structural elements, including slabs, beams, columns, walls, staircases and transfer plates (only applicable for laps with bar size equal to or more than 20mm).
2. Stirrups in beams, binders in columns and horizontal reinforcement in walls can be regarded as “transverse reinforcement”.
3. There will likely be conflicts between the specified stirrups in beams details (or the like) and the minimum transverse reinforcement UNLESS the designer specifies the location of the laps and put in the increased transverse reinforcement accordingly. However, it may be beneficial to both the contractor and the engineer NOT to specify the locations of the laps (such that the engineer can save time in preparing the drawings, and the contractor can place the lap location to suit site constraints). Hence, the designer should remind the contractor about this detail and the contractor should check and place the minimum transverse reinforcement wherever they place a lap.
4. Slabs, staircase& transfer plates may have a slight problem because the code specifies that the transverse reinforcement have to be placed “between the bar and the surface of concrete”. This could mean an additional layer of bars! Luckily, most slabs and staircases have bar size less than 20mm. As for transfer plates, I think the contractor can/should avoid that additional layer of bar by ensuring that the 'percentage of lapped bars in any one section is less than 25%'
5. The size/spacing of transverse reinforcement is based on the following principle: (i) calculate the required reinforcement according to code and distribute them within the lap length (ii) Always use T10 unless the spacing is less than 100mm; (iii) maximum spacing is 150mm as required in code (hence in some case the provided steel is much more than required); (iv) Round down to nearest 10.

Blog note: (i) I hope to present the calculations both for the lap length and the minimum transverse reinforcement LATER. (ii) I wonder any consultants (who specified this detail in their drawing) notice whether the contractors really add theses minimum transverse reinforcement… (iii) Any comments on the readability of the table?