The aim of this paper is a comparative analysis of the experimental test results of twenty T-section beams reinforced with glass fiber reinforced polymer (GFRP) bars without stirrups with predicted values of the shear capacity according to the following design guidelines: draft Eurocode 2, Japanese JSCE, American ACI 440, Italian CNR- DT-203/2006, British BS according to fib Bulletin 40, Canadian CSA-S806-12 and ISIS-M03-07. Standard procedures for FRP reinforced beams based on traditional steel reinforced concrete guidelines. The longitudinal FRP reinforcement has been taken into account by its stiffness reduction related to the steel reinforcement. A basis of this modification is the assumption that the FRP-to-concrete bond behaviour is the same as it is for steel reinforcement. To assess the compatibility of predicted values (Vcal) with the experimental shear forces (Vtest) the safety coefficient η = Vtest / Vcal was used. The results corresponding to values η < 1 indicates overestimation of the shear capacity, but η > 1 means that shear load capacity is underestimated. The most conservative results of the calculated shear capacity are obtained from the ACI 440 standard. In contrast to them the best compatibility of the calculated shear values to the experimental ones indicated British BS standard, fib Bulletin 40 and Canadian CSA-S806-12 standard.

The paper presents results of experimental tests carried out on concrete beams reinforced with glass fibre polymer reinforced (GFRP) bars, which have become recently one of the main substitutes for traditional steel reinforcement. GFRP bars were used in this research as the longitudinal and transverse reinforcement. An objective of the study was to investigate the influence of the shear reinforcement ratio on the shear capacity of GFRP reinforced concrete beams in comparison with the corresponding beam without shear reinforcement. Single-span, simply-supported T-section beams reinforced in flexure with 5 GFRP bars of 25 mm diameter were reinforced in shear with closed GFRP stirrups of 8 mm diameter applied in three variable spacings: 250 mm, 200 mm and 120 mm. The analysis of test results, failure modes and shear capacity is discussed in the paper in respect to investigated parameters.

The paper presents selected issues related to the load carrying capacity of joints between concretes cast at different times. The most important factors affecting the shear resistance, such as: surface roughness (profile), shear reinforcement ratio, concrete strength as well as the aggregate composition are discussed, including results of previous experimental studies conducted on push-off specimens and composite reinforced concrete beams. The differences in behaviour and shear resistance of contacts between ordinary concretes, lightweight aggregate concretes and recycled aggregate concretes are presented. Principles of interface design in the light of codes of practise: AASHTO-LRFD, ACI 318-19, EN 1992-1-1 and prEN 1992-1-1 were described. The theoretical predictions were compared with 184 results of experimental tests on push-off specimens. It has been found that most of the procedures allow for a safe estimation of the load carrying capacity of interfaces – with and without shear reinforcement. However, the obtained results were mostly conservative (depending on the considered design procedure, ratio of the experimental to theoretical load carrying capacity lies in range 1.51÷2.68). This may indicate that the description of shear transfer mechanism between concretes cast at different times is still imperfect and need to be improved.