Experimental data on RC members subjected to pure torsion is compiled from published studies so far. Interestingly, the past studies have concentrated largely on members with small to moderate concrete covers, with handful data on members with thick concrete cover. Widely accepted torsion models including the diagonal compression field theory (CFT), softened truss model (STM) and softened membrane model for torsion (SMMT) are verified on the domains of experimental data missing-in specimens with thick concrete cover. With increasing demand for durability design of RC structures use of thick concrete cover, say up to 75 mm, is being introduced in practice. Recent experimental investigation by the authors demonstrated that spalling of concrete cover, particularly in cases of thick covers, significantly impacts the torsional behavior of RC members. The present study uses these set of experiments to look at the response prediction capability of the existing advanced models and assess the reliability of existing concrete cover spalling theories. For cases with thick cover, the existing models either did not adequately capture the ultimate capacity or erroneously predicted the torsional behavior of the members due to the different mechanics between RC beams with thin and thick covers. Similarly, the spalling theories failed to fully explain the physically observed spalling behavior. Guided by the recent experimental observations and the apparent gaps, the study provides a rational theory for the spalling of concrete cover. The initiation and gradual evolution of concrete cover spalling is traced by observing the acting spalling moment and spalling resistance formulated in the proposed spalling model. The proposed spalling model inherently assumes members susceptibility to spalling of cover concrete and is governed by, the thickness of the concrete cover, tensile strength of concrete, presence of rebar cage and their location, and size of the member. The theory is unified and can explain the spalling of cover due to torsion as well as shear. Its capability is examined by integrating the approach into existing truss model. When compared with state-of-the-art models, the proposed method provides consistent prediction with a relatively smaller scatter, for cases with thick concrete cover as well.

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Typically precast girders are designed and utilized as simple supported members. Alternatively, the precast girders can be made continuous at the intermediate support using cast-in-place concrete topping. Once the girders are made continuous, time-dependent restraint moments will occur. The magnitude of the restraint moment is mainly affected by the creep and shrinkage behaviour of the concrete and the age of the girders at continuity. The developing restraint moment may affect the stress conditions near the support region and, in extreme cases, result in the loss of the integrity of the structural member. Currently, full-scale experimental campaign is underway on the shear behaviour precast continuous girders at Delft University of Technology. Inverted T girders are individually cast and later made continuous after a certain period. To investigate the influence of restrained action and quantify the prestress losses, fiber optic sensors (FOS) are embedded in the girders. By utilizing the FOS, the evolution of the concrete strain is monitored. This paper presents the measurement of the time-dependent strains. Furthermore, the concrete strains are analysed to evaluate the prestress loss and time-dependent restraint moment effect.@en

There are a large number of precast girder bridges in the Netherlands that are made continuous utilizing cast in situ layers and cross beams. When controlled by the Eurocode minimum shear reinforcement requirement, the majority of these bridges that were constructed before the 1970s have insufficient amount of transverse reinforcement, which could make them shear critical. Furthermore, when the continuity is created at intermediate support, the prestressing strands in the precast beams are usually located in the compression zone. This may limit the positive effect of the prestress to the shear capacity of members without transverse reinforcement. The aforementioned concern is not considered by the standard shear design approach of Eurocode. Because of its empirical nature, the shear capacity of these bridges cannot be rationally assessed by the code. Currently, an experimental campaign on full-scale 15m long specimens is underway at Delft University of Technology to investigate the existing challenges. In this paper, the effect of the above-mentioned concerns is illustrated using the predictions of Eurocode and the Dutch Guidelines for the Assessment of Existing Bridges (RBK). Moreover, the difficulties and insights gained from the design and execution of the experiments are discussed.@en