Fastener requirements of "Sistering" members

[Cmitty]

Hi all,

I have been looking into existing timber sub-floor systems that have undersized timber floor joists under load-bearing walls. It seems like the most economical and simple construction option is sistering timber joists to increase the section modulus, bending strength, and stiffness in the built-up member.

I cannot seem to find anything in the timber design standard (New Zealand) regarding this type of "sistering" option in terms of calculating the fastener requirements to ensure the built-up member acts as one beam, where the sister joist cannot span the full length and is not supported by the bearer. This is for a loading scenario that includes a uniform distributed load (UDL) and a central point load.

Does anyone have any good tips, assuming the same grade and size of timber is used for the sister joist and the existing joist is sufficient in shear strength requirements?

Is this as simple as:
1. calculating the total load (F) on the built up member (UDL x Length + Point Load)
2. Calculate the design shear capacity (Qn) of the nails
3. F/Qn = total nails required
4. Distributing the total nails required evenly and alternating sides along the length of the member

Thanks in advance!