Conference Agenda

Concrete is one of the most abundantly used materials in the building industry and corrosion of the reinforcement steel is one of the main reasons of degradation in concrete structures. Corrosion of the rebars not only reduces the steel cross-section, it is also accompanied by a volume increase due to the formation of rust products, resulting in rising internal expansion stresses on the concrete. Eventually, cracks may form when the tensile stress reaches the tensile strength of concrete, and further propagation of these cracks towards adjacent rebars or to the surface may lead, respectively, to delamination and spalling of the concrete cover. In this work, spalling behaviour due to a uniform radial pressure, relevant for carbonation-induced corrosion, is analysed using a 2D Finite Element model. This numerical model is used to assess the adequacy of existing analytical models in literature predicting the peak pressure during spalling. The allowable peak pressure can be seen as a resistance against spalling, which may be related to the corrosion level and hence is relevant in relation to the reliability-based assessment of degrading structures.

As a kind of ductile fiber-reinforced cementitious composite, Engineered Cementitious Composite (ECC) has great crack width control ability and improved durability. However, there are only limited studies on the durability of steel reinforced ECC (R/ECC) members. This makes the service life quantification of R/ECC members lack of research data. The present study investigates the interaction behaviour between steel rebar and ECC after corrosion exposure. Results from four R/ECC and four reinforced concrete (RC) ties with the dimension of 75×75×600 mm and corrosion levels up to about 5% were reported herein. Corrosion-induced cracks were recorded during accelerated corrosion tests. After corrosion, the corroded ties were tested under uniaxial tension together with the uncorroded ties. Steel strain distributions of specimens during tension were
monitored by distributed optical fiber sensors (DOFS) to examine the stress transfer mechanism between rebar and matrix. The impacts of steel corrosion on the tension-stiffening behaviour of R/ECC specimens were compared with those of RC ones. It was found that the corrosion-induced cracking degree in ECC was much smaller than that in concrete. Moreover, corrosion improved tension-stiffening effect in all R/ECC ties and decreased in all RC ties from the load-average strain curves. The number of transverse major cracks in corroded R/ECC ties was kept similar as in the uncorroded tie, but the microcracks number decreased. In the group of RC ties, the transverse major cracks were only seen in the uncorroded specimen whereas several secondary cracks emerging from longitudinal cracks appeared in corroded specimens. Further, DOFS data displayed that steel reinforcement in ECC generally exhibited more uniform deformation than that in concrete. The strain distributions in corroded R/ECC ties were not changed apparently, and the steel strains in the
corroded R/ECC ties are slightly larger than those in the uncorroded R/ECC tie at similar average corrosion level. This implies that bond strength can be well maintained in uncorroded R/ECC. The distance of strain peaks in corroded RC ties increased compared to that in the uncorroded RC tie, which reflected a decrease of bond strength in corroded RC ties for the investigated corrosion levels. The results from this study reveal that R/ECC members are less impaired by steel corrosion compared to concrete.

This work addresses the uncertainties inherent in civil engineering, arising from various sources such as the spatiotemporal variations in material properties, the complexity of concrete behavior, variations in applied loads and the impreciseness of theoretical models. This research aims to explore the advantages of accounting for some uncertain parameters in the numerical damage-based modeling of cracking in reinforced concrete structures, specifically investigating their impact on the accuracy and reliability of simulated outputs. By accounting for these uncertainties, the study aims to improve the predictive capability of numerical models, resulting in simulated responses that align more closely with observed on-site behavior. To achieve this aim, a case study involving a Representative Structural Volume (RSV) of a part of a 1450MWe nuclear power plant containment building is considered. It is based on the PACE-1450 experimental campaign [1], which aims to thoroughly characterize cracking and air flow through these cracks for various tensile loads and temperatures. Experimental results show strong asymmetric cracking even though the applied tensile loads are mostly unidirectional using hydraulic jacks. To accurately represent the experimental distribution of the cracking pattern, several input parameters including material properties and boundary conditions during testing are considered as uncertain. The spatial variability of concrete properties is described using discretized random fields associated with the tensile strength [2]. In addition, uncertainties are considered in the angle of application of tensile loads applied via hydraulic jacks, which are suspected to deviate slightly from the surface normal rather than being perfectly perpendicular. These deviations may significantly influence the observed cracking behavior. First, a sensitivity analysis is performed to identify the most influential input parameters on the computed cracking patterns. Second, based on the obtained results, an attempt is made to determine the set of input parameters that replicate the observed cracking patterns. The obtained results highlight the critical need for comprehensive uncertainties quantification to objectively assess the results of complex experimental campaigns. They also indicate that accounting for random uncertainty alone is insufficient to replicate the experimental results. Indeed, considering the epistemic uncertainty is needed, particularly regarding the boundary and loading for a comprehensive consideration of uncertainties and better understanding of the observed behavior.

In the paper, the probabilistic assessment of cracking resistance of concrete flexural members is presented. The aim of the performed analysis was to verify an alternative formula for cracking resistance calculation and to compare the proposed method with two standard methods. The experimental investigation performed at Lublin University of technology was used to verify the design models. The accuracy and reliability of the calculation methods was assessed by analyzing the model uncertainty θ. When model uncertainty θ > 1.0 the prediction model yields a lower value of cracking resistance and is thus conservative, while a value of θ < 1.0 implies that the prediction model yields higher cracking resistance than is actually available in the structure and is thus un-conservative. A high model uncertainty θ = 1.53 was found when the cracking resistance was calculated by standard method assuming a linear distribution of normal stresses over the cross section and taking the maximum tensile stress as the concrete axial tensile strength. When applying the flexural tensile concrete strength defined in Eurocode 2 instead of axial tensile strength in a cracking resistance formula, the model uncertainty decreased to θ = 1.15 but the model was still conservative. The best prediction of cracking resistance was obtained for the proposed method in which the influence of a size effect and fracture properties of concrete on cracking moment were included. In this case the model uncertainty was close to 1.0 (θ = 0.94) with a relatively small scatter.

Modern codes allow advanced nonlinear formats to calculate the bearing-buckling capacity of slender reinforced concrete column elements. In a previous part of this paper series, investigations of a priori collaborative Round-Robin tests of numerical simulations showed that the load capacity of slender single columns obtained by Nonlinear Finite Element Methods (NLFEM) is significantly overestimated when compared to experimental values. On the other side, the simplified formats adopted by design codes (e.g. nominal curvature-based method) provide too conservative results concerning the experimental derived bearing buckling capacity. The investigations are divided into two parts. Part I considers the experiments' findings and the nonlinear modelling. Part II aims twofold: (i) provide a quantitative comparison of the Eurocode column design rules with the international design regulations from the USA, China, Japan, and Canada concerning the safety and design format and (ii) identify possible strengths and weaknesses in the different approaches.