# Concrete industrial ground floor slab (TR34) - UDL loading

For a floor slab with a UDL loading TR34 states (on page 59, the paragraph below eqn 9.18) that you should not use eqn 9.8. Thus value Mn governs both positive and negative bending moment values. Why does the proforma give the load capacity of the slab (for a UDL) as the lesser of eqn 9.18 and 9.19 when - according to the worked example on TR34 page 94 - the load capacity relates to eqn 9.19 only?

## Solution

TR34 clause 9.9.5 includes two equations for calculating w, namely 9.18 and 9.19, but the paragraph immediately under equation 9.19 states that:

"*As with line loads, this is based on an elastic distribution of bending moment, therefore Mp as well as Mn should be taken as the cracking moment, i.e. the value from Equation 9.6. The residual moment (e.g. from Equation 9.8 for fibre-reinforced concrete) should not be used. Thus Equation 9.19 will govern*."

Our interpretation is that this statement would lead to 9.18 never being used and is out of context of the rest of the section. We have taken the engineering decision to not implement this in the calculation as it would lead to a less conservative design. Where there is ambiguity we will always tend to take the conservative route.