Behavior of lap splices in reinforced concrete beams after bar yielding

Abstract

Structural ductility in the case of plastic hinges forming close to a lap splice has been an open issue with the revision process of the next version of Eurocode EC2 concerning reinforced‐concrete structures. This research has provided experimental evidence by the large experimental campaign for the background for revision of the Eurocode EC2. Within this context, 38 specimens were tested in four‐point bending, with the longitudinal bars either lap‐spliced (partly or fully), or un‐spliced (for reference). The tests were carried out involving the variation of the bar diameter (12, 16, 20, and 25 mm), and the lap length (20–60 times the bar diameter). The main result is the sizeable enhancement of the structural ductility brought in by the extension of the lap length in excess of the length required by the yielding of the longitudinal bars. Based on these findings, a preliminary model is developed to describe the bond‐stress profiles in lap splices, after the yielding of the bars.

Anchorages and laps according to the next‐generation Eurocode 2—Overview and comparison to current provisions

“…While staggering of the lapped bars influences the deformation capacity and the post-peak load behavior, an influence on the maximum structural capacity could not be observed. 8 The design value of the lap length l sd is given in prEC2 as a function of the anchorage length l bd as formulated in Equation (9). As a result of the enquiry and the discussions at the European level, the parameter k ls , which is comparable to the lap factor α 6 in EC2, has been defined as a nationally determined parameter (NDP), with a proposed value of k ls = 1.2.…”

“…However, in these cases, it is important to ensure the deformation capacity and to enhance the post-peak load behavior of the lap. 8,9 This can be achieved either by the arrangement of confinement reinforcement, transverse reinforcement, or by staggering the lapped bars. At least five stirrups or transverse bars should be arranged within the lap length.…”

“…However, since large plastic deformations may reduce the structural capacity of laps, an increased design steel stress has to be applied to ensure ductile behavior of the structural members and to avoid sudden failure of the lap. 4,9…”

“…For this reason, prEC2 also allows the arrangement of laps in highly loaded areas where plastic deformations may occur. However, in these cases, it is important to ensure the deformation capacity and to enhance the post‐peak load behavior of the lap 8,9 . This can be achieved either by the arrangement of confinement reinforcement, transverse reinforcement, or by staggering the lapped bars.…”

“…To obtain an announcement of failure, the reinforcement should be designed in such a way that its yielding—accompanied by large deformations—occurs prior to structural failure. However, since large plastic deformations may reduce the structural capacity of laps, an increased design steel stress has to be applied to ensure ductile behavior of the structural members and to avoid sudden failure of the lap 4,9 …”