Properties of Beam-to-Column Joint in Steel-Concrete Composite Frame Unpropped or Partly Propped During Slab Execution

Abstract

The issues of load-bearing capacity and stiffness of end-plate beam-to-column composite joints under monotonic or cyclic bending moment loading have been discussed in numerous publications. Publicly available descriptions of various computational models and reports from experimental research concern joints with structure not changing in their entire load range. However, it is difficult to find the results of experimental tests or theoretical analyses of the load-bearing capacity and rotational capacity of a beam-to-column joint in composite frame with a reinforced concrete slab or steel-concrete composite slab executed on not propped steel member. Meanwhile, there are structural solutions in which floor slabs are executed using permanent formwork and temporary formwork girders arranged between the girders of a steel frame before concreting, without vertical slab props or with a limited number of them. In such a structure with a variable static scheme, the results of the internal forces analysis in the ultimate limit state may be different from the results for a structure made with full support. These differences are related among other to different characteristics of seemingly the same joints. The aim of the work was therefore an attempt to assess the impact of technology of the structure execution on the load capacity and rotational capacity of the beam-column connection in the steel-concrete composite frame in the ultimate limit state. The examples of steel-concrete composite joints of frame made with full temporary support as well as without vertical slab props were analysed. A modified two-stage non-linear component method was used in the calculations. Load capacities of the basic components as well as their initial stiffness were adopted according to Eurocode 3 and Eurocode 4, while their ultimate deformation values in ULS were adopted according to the author’s own analysis or other available results. The rotational capacity of composite joints made at several levels of the steel joint’s effort during slab concreting was considered. It was assumed that during execution the steel beams are always protected against torsional buckling. Conclusions regarding the estimation of the load capacity and rigidity of the joint as well as its rotational capacity depending on the assembly method are presented.