The use of reliability based structural optimisation is a rational
approach that can accounts for the inherents uncertainities
associated with the design varaibles. Despite the availability
of this powerful tool its application on real life structures
remains a crtitical issue amongst practicing engineers,
principally due to high numerical cost involved in finding
solutions using this method. Studies have shown, the few
available literatures are mostly on steel structures, and very
few covers concrete structures, specifically RC slab. In order
to bridge this cavity, this paper present a non-conventional
slab depth optimisation for the design of continuous RC slab
types. The study seeks to know the effect of reducing the
current minimum design depth applicable for two-way slab
confirming to standard fire resistance requirement, REI240 on
flexural capacity requirement along both axes with the use of
first order reliability method. The study was limited to four
different rectangualr slab ends condition. The study safety
analysis results in comparison with weighted least square and
objective cost functions evaluation shows good prospect in
terms of cost saving and yet avoiding flexural failure through
the application of the aforementioned rational method
