Comparative evaluation of finite element direct design and equivalent frame methods for reinforced concrete flat slabs with and without drop panels under Eurocode 2

Reinforced concrete flat slabs concentrate bending and shear at the slab-column region, and the analytical method chosen governs how those actions are estimated. This study compares three methods for the same nine-panel flat slab with and without drop panels under a single Eurocode 2 ultimate load basis: the Direct Design Method (DDM), the Equivalent Frame Method (EFM), and a three-dimensional linear-elastic finite element model (FEM) built in SAFE 2016. A 3 × 3 grid of 6.5 m bays with a 250 mm slab, 400 mm square columns and 2.5 m square, 100 mm drop panels was analysed under the fundamental combination 1.35Gk + 1.5Qk (17.96 kN/m 2 ). Bending moments, one-way shears, punching stresses, deflections and reinforcement areas were extracted on a consistent per-metre-width strip basis so that the three methods report comparable quantities. Adding drop panels reduced sagging moments by 7.9% (EFM), 9.2% (DDM) and 18.6% (FEM) and hogging moments by 7.9%, 8.1% and 25.4%, respectively, showing that the two-dimensional idealisations recover only a fraction of the connection stiffening that the continuum model attributes to the drop. The finite element model concentrated moment and shear into the column strip more strongly than the coefficient-based methods, so the simplified methods returned lower design actions at the slab-column region and should be regarded as non-conservative there. The three methods are treated as alternative predictions rather than as deviations from an assumed-correct benchmark, because the finite element model is linear-elastic, uncracked and not experimentally validated. On the uncracked section the finite element deflections were unrealistically small (6–7 mm); once Eurocode 2 cracked-section stiffness is applied they rise to 18–24 mm, in line with the simplified methods, confirming that uncracked linear-elastic analysis must not be used for service deflection. The study concludes that DDM and EFM are suitable for preliminary sizing, while final verification of the slab-column region, and of any slab with drops, should use a cracked or nonlinear finite element analysis.