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Assessment of the load carrying capacity of existing bridges has become a frequent task for structural engineers. Here, the shear capacity is often one of the main concerns since the amount of shear reinforcement often does not comply with the amount that is required according to design codes nowadays, e.g. for post-tensioned concrete slab bridges, the amount of shear reinforcement is often very low or non-existing. Since the shear capacity of beams has been found to be proportional to the width, the shear capacity of one-way spanning slabs can be simulated by rectangular beams. However, in the literature, the majority of the available experimental campaigns on the shear capacity of post-tensioned concrete beams is performed on beams with I- or T-sections. The shear-failure mechanism is, however, not the same for rectangular beams as for beams with I- or T-sections.This paper studies the shear capacity and the shear failure mechanism of post-tensioned concrete beams (slab strips) without shear reinforcement. The experimental programme comprises 10 post-tensioned beams and varies two important design parameters; the shear span and the level of prestressing. All beams had a cross-sectional height of 700mm and, outside of the anchorage zone, a width of 250mm.The shear failure mechanism and the development of the critical shear crack are studied by use of Digital Image Correlation. The test results are compared to existing design codes with varying accuracy.

Curtailing of reinforcement in concrete beams and slabs is often carried out in practice for different reasons; in continuous beams, top reinforcement is often curtailed in accordance with the extent of the hogging moments and generally, in concrete structures it is often necessary to add extra reinforcement for practical reasons, which is normally considered to be safe.It is generally accepted that the shear capacity of concrete members without stirrups is influenced by factors such as the crack width. On the other hand, it has been up for discussion how curtailed reinforcement may influence the crack width and the failure mechanism. In the fib Model Code for Concrete Structures 2010 the shear capacity decreases in a zone near the curtailed end of reinforcement bars. In some practical design situations, this means that adding extra reinforcement with curtailed ends would decrease the shear capacity. This influence is not even mentioned in Eurocode 2. This paper presents a large experimental programme dedicated to study the influence of curtailed reinforcement on the shear capacity. The programme includes 30 simple three-point bending tests of beams governed by shear failure. The main parameters varied in the tests are the relative amount and the length of the curtailed reinforcement. The tested shear capacities show that the shear capacity was not affected. During tests, Digital Image Correlation was used to measure the crack propagation. From these measurements, it appeared that the curtailed reinforcement had no influence on the crack widths nor on the observed failure mechanisms. Finally, the tested shear capacities are compared to shear capacities calculated by the Eurocode 2 and the fib Model Code 2010. While Eurocode 2 is quite accurate, the fib Model Code 2010 underestimate the shear capacity.

Formålet med nærværende Bulletin er at vise en forholdsvis simpel beregningsmetode til bestemmelse af wiresløjfesamlingers forskydningsbæreevne.Dokumentet er hovedsageligt baseret på Henrik Brøner Jørgensens ph.d. afhandling. Ph.d.‐projektet var delvis finansieret af Betonelement‐Foreningen og blev gennemført under vejledning af Linh Cao Hoang og Lars German Hagsten. De udviklede beregningsmodeller er sammenholdt med forsøg udført ved danskeuniversiteter de sidste 15 år.Der er til dette dokument udarbejdet et baggrundsdokument, hvor den teoretiske baggrund samt sammenligninger med forsøg er vist. Derudover er der udarbejdet et baggrundsdokument, som redegør for de foreslåede partialkoefficienter. Nærværende Bulletin skal derfor ses som en praktisk guide til beregningaf forskydningsbæreevnen af samlinger udført med wirebokse.I forbindelse med udarbejdelse af dokumentet har der været tilknyttet en følgegruppe, engageret af Betonelement‐Foreningen. Følgegruppen bestod af følgende personer; Thomas Markvardsen (CRH Concrete), Tim Gudmand‐Høyer (Rambøll) og Bernt Suikkanen (COWI A/S).