Important Deflections: RC Slabs

[Anonymous]

I am asking some critical questions ahead of a study of our slab models for an RC structure. 

Design to Eurocode.

Consider CIRIA C734: Design for Movement in Buildings

Section 3.1 Deflection of beams and slabs.

The most important deflection is often not the total deflection but the additional deflection that occurs
after installation of cladding, partitions and other finishes, which will depend on the construction
sequence and timing. The critical stage is usually the installation of cladding, in which case the relevant
deflection is the sum of:

• the remaining long-term deflection from the self-weight
• the total long-term deflection from the cladding (ie including the initial elastic deflection)
• the total long-term deflection from a proportion of the imposed load
• the short-term deflection from the remainder of the imposed load.

In Eurocodes, the third deflection is given by the quasi-permanent load combination, the fourth by the
difference between the characteristic combination and the quasi-permanent combination.

In short, this text says what many probably already understand: For cladding, the deflection of interest is the long-term quasi-permanent, less the initial elastic deflection that occurs within the early construction stage.

I have a complicated flat slab on a complex grid of columns and walls, and facade on the edges and in the mid-span of some slabs, so I am very hesitant to just take a round estimate of a number.

Ideally, I would like to subtract the initial elastic deflection map (from a self-weight-only case) from the long-term deflection map, but I suspect that's impossible. But this philosophy absolutely must be a common way of doing things -- or are we always taking the full long-term deflection when we do designs, extremely uneconomically?

How can I achieve this?