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D. BS8110 Slab Design Principles

The BS8110 Slab Design Brief is for any slab modeled with F.E. regardless of boundary restrained conditions.

Slabs are designed for flexure in two orthogonal directions for both hogging and sagging moments. It dose not include design for shear or punching shear checks.

Analysis results for plate elements that form a ‘Slab’ are used to generate design moments with respect to the axis of the slab. These moments are then used to generate required reinforcement contours. An option if available in the slab design brief to use moment theory developed by Wood an Armer ("The Theory of the Strip Method for Design of Slabs" Proceedings, Institution of Civil Engineers, London; Vol. 41, October 1968, pp. 285-313).

The level of accuracy of results depends on the meshing density used to model the slabs. It is recommended that you examine the accuracy of the model at the analysis stage and ensure satisfactory results are obtained prior to the design stage.

Design for Flexure

Longitudinal and transverse reinforcement are calculated for both sagging and hogging moments on the basis of the slab thickness and parameters defined in the Design Brief.  Compression reinforcement is provided where required.

The design of a slab is based on an envelope of design forces and thus at each element center, the program determines the required area of steel for both the maximum hogging moment and maximum sagging moment in the two orthogonal directions (i.e., Slab/Region local axis).

Reinforcement calculation is based on the BS8110 recommendations for the design of rectangular beams assuming a unit meter width together with the elements thickness.  

Slab end restrained conditions are not catered for at the design stage, however to ensure accuracy of design results, they must be incorporated in the analytical model of the structure.

Note: The program does not perform shear checks per BS 8110.