Final conclusion

The regulations refer to bar elements, in both analysis and (mainly) reinforcement design. No matter how 'accurate' static and dynamic analysis methods may be, or models of two-dimensional or three-dimensional finite elements may be used, the results (moments-shear forces) should refer always to the appropriate bars, allowing the design of slabs subjected to bending. A slab strip can also be considered as an appropriate bar. In the centroidal axis of this strip, moments and shear forces are being determined by integrating the appropriate stresses along the respective finite elements. The assumption of a structure with beams of adequate depth, providing significant stiffness to the structural frames, results in a pure space frame model consisting of bars which is reliable for both analysis and design.

In conclusion, the assumption of the bar elements for modelling structural frames and the approach of independent functionality of slabs are both acceptable and, under certain circumstances, form an adequately reliable solution. In finite element analysis, the common assumptions adopted for slab supports are: zero torsional stiffness, hinged supports on beams and columns, and monolithic supports on shear walls. Regardless of the calculation method, the minimum structural provisions of the regulations regarding the minimum (secondary, negative) reinforcement of slabs should be followed diligently.