With the innovative composite material carbon-reinforced concrete, thin-walled, high-performance components can be realized. A combination of carbon fiber reinforced polymer (CFRP) bars and non-metallic textile grids is advantageous as it exploits the full potential of the high-performance materials to reduce dead loads, increases durability, and extends lifespan. For new components with such mixed reinforcement, applicable design concepts and engineering rules are necessary to accurately determine the structural and deformation behavior. To validate models and detailing rules previously developed, three large carbon reinforced concrete I-beams were designed and tested to failure with a realistic line load. CFRP bars served as principal bending reinforcement, whereas shear and flange reinforcement consisted of textile grids. Results showed that existing models for bending using variation of strain distribution as well as non-linear finite-element analysis predicted the flexural behavior of structural components with mixed reinforcement in ultimate limit state (ULS) appropriately. Yet, calculation of shear capacity requires further studies to determine textile reinforcement contribution and estimate reduction for concrete strength in reinforced compression struts. For serviceability limit state (SLS), three methods for determination of deflection delivered good results. In future, a rethinking is required with regard to the ductility and robustness of CFRP-reinforced concrete components. In this respect, pronounced cracking as well as the large ultimate strain and deflection compensate for the lacking yield capacity of the reinforcement.

The determination of the ultimate shear capacity and the identification of the corresponding load-carrying mechanisms of concrete members without shear reinforcement has been an ongoing research topic for over 100 years. Based on a full mechanical model, the Shear Crack Propagation Theory (SCPT) enables to analyze and understand the ever-changing interplay of crack propagation, evolution of stresses at the crack tip and in uncracked concrete parts, as well as the activation of shear transfer actions within the growing shear crack during the entire loading process. In this paper, selected experimental investigations for further validation of the SCPT are presented. These beam shear test results are then compared to the theoretical results emerging from the SCPT algorithm. Finally, the evolution of different shear transfer actions (e.g., aggregate interlock and dowel action) during the entire loading process is evaluated and discussed.

Due to their high cost efficiency and flexibility, semi-precast concrete slabs with lattice girders are widely used in constructions all over the world. Prefabricated concrete slabs, combined with in situ concrete topping, exhibit a quasi-monolithic structural behavior in which lattice girders serve as vertical shear reinforcement and ensure the transfer of longitudinal shear within the interface, acting in combination with concrete-to-concrete bonding mechanisms. To be applicable in industrial and bridge construction, semi-precast slabs need to have sufficient resistance against fatigue failure. To improve and expand the limits of application, theoretical and experimental investigations are conducted at the Institute of Structural Concrete (IMB), RWTH Aachen University. To investigate the fatigue behavior of lattice girders, small size tests with lattice girder diagonals were carried out. These test results have been used to derive an S–N curve (S: stress, N: number of load cycles) for lattice girders for a more refined fatigue design. Subsequently, the fatigue behavior of semi-precast slabs with lattice girders was investigated by fatigue tests on single-span slab segments. The fatigue design regulations of lattice girders according to technical approvals can generally be confirmed by this test program; however, they tend to be conservative. The use of the derived S–N curve leads to significantly improved agreement of fatigue behavior observed in tests and design expressions.

Flexural shear behavior, which mainly concerns reinforced concrete (RC) slabs without shear reinforcement, is usually investigated by means of simply supported, beam‐shaped specimens. Only few tests are available where the cross‐section properties correspond to a slab ( b ≫ h ) or the support conditions lead to moment and shear force distributions of multi‐span slab systems. The moment distribution in the vicinity of inner supports can decrease shear slenderness and, hence, increase shear strength. An increase in member width is also often associated with a beneficial effect on load bearing behavior. Firstly, the course of the shear crack changes along the width which, both, increases the crack face area, and potentially allows for an increased interlocking effect of the two crack faces. Secondly, a (wide) slab's ability to redistribute inner stresses in lateral direction can compensate inner irregularities. However, the likelihood of irregularities to occur after all, increases with increasing concrete volume, so larger member widths. A comparison of existing investigations shows that the findings are partly inconclusive. Also, no studies addressing the influence of the member width exist with tests in the vicinity of intermediate supports despite being the typical shear‐critical section in actual members. To address related open questions, an experimental campaign comprising 20 shear tests on slab segments without shear reinforcement was conducted. Essentially, member width ( b = 0.3 or 2.4 m) and support conditions were varied within the test program. Main goal of the experimental campaign was finding answers to the question whether one‐way flexural shear strength is influenced by the member's width. This has been addressed by generating results from pairs of tests which differed only in their width while having otherwise equal properties ( b / h ≈ 1.0 and b / h ≈ 8.5). Eight such pairs were tested featuring different shear span lengths, rotational restrains at the support and longitudinal reinforcement ratios. In contrast to other experimental campaigns, shear tests near inner supports were incorporated in the experimental program. On average, the gain in shear capacity of the wide members compared to the reference linear member was proportional to the increase in width. It can thus be concluded that linear (beam‐shaped) specimens are suitable for representing one‐way shear capacity of RC slabs. Enhanced shear response of actual slabs can rather be ascribed to beneficial effects from loading and support conditions which enable to partially activate two‐way stress distribution or compressive membrane action. Additionally, rare occurrence of damages in RC slabs is not only to be attributed to an underestimation of capacity but probably also to an overestimation of design load.