Overlap

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Concrete and reinforcing steel in combination
Spatial framework model of an overlap joint
Strut truss model of an overlap joint

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 .