Frame behaviour in regions of columns

To be continued >

Bending moment diagrams of joists of structure modelled with members

project <B_336>


The model using both members and more accurate two-dimensional finite elements, takes into account the slab frame behaviour in regions close to columns, in contrast to the inexpensive approach of simply supported slab throughout its length.

In case of members, the two main side joists (of slab) forming a common frame with the columns, have greater torsional rigidity than the intermediate nearly simply supported main joists and bear heavier loads, thereby to develop strong negative bending moments at their supports and relatively low positive bending moments at their spans. The interim main joists develop strong positive bending moments at their spans, while being supported on the end joists through the secondary joists stressed by significant positive bending moments at their spans.



Bending moment diagrams of slab strips modelled with triangular finite elements

project <B_331>, pi-FES


In the more accurate model using two-dimensional finite elements, the main side strips behave intensively as frames. Τhe results are similar to those of using members with the following differences: (a) In the main side strips (corresponding to the main side joists) the frame behaviour is more intensive, since the moments at the supports are greater and moments at the spans are smaller, (b) In the interim main strips (corresponding to the interim main joists) the span moments are smaller, (c) The span moments of the secondary strips (corresponding to secondary joists) end up to be greater. This is due to the fact that the internal torsional stiffness of the slab elements (torsion) is stronger than the respective of members.