Overlap
An overlap joint is used in reinforced concrete construction in order to connect two reinforcing bars in a force-locking manner by means of a planned overlap of the ends and thus to enable the reinforcement bar to be extended to transmit tensile or compressive forces. The reinforcing bars are connected to the surrounding concrete , which in the overlapping area transfers the forces of the ending reinforcing bar to the beginning.
A model for the load-bearing behavior of overlapping joints is a three - dimensional framework , which, based on the respective reinforcing steel ribs, consists of tension rings and pressure cones. In addition, there is a more direct power transmission between the reinforcing steel, which can be represented as a strut framework. The forces between the bars, starting from the respective reinforcing steel ribs, are transmitted directly via tension and compression struts.
Overlapping joints represent a constructive weak point and should therefore be arranged in areas with less stress (e.g. moment zero points) and carefully dimensioned and designed. The required length of a lap joint is regulated in Europe in Eurocode 2 (Part 1-1), whereby national annexes must be observed. The lap length depends inter alia on the compressive strength of concrete , the concrete steel grade (in Germany: B 500) from, the rod diameter of the concrete steel voltage, the position of the jointed reinforcing bars in the component and the percentage of no longitudinal offset overlapping rods on the cross-section of a reinforcement layer. For bar diameters of 16 mm or more and for normal concrete of strength class C20 / 25, it can be 47 to 135 times the bar diameter, depending on the position in the component, the joint portion of a reinforcement layer and the national annex. The minimum length required is 15 rod diameters or 20 cm.
As an alternative to lap joints , welded joints , socket joints or, in the case of pure pressure loading, contact joints are possible for power transmission .