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Q. Jiang

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Reliability assessment of corroded reinforced concrete structures

The effect of using random fields and nonlinear finite element analysis

Master thesis - Q. Jiang, M.A.N. Hendriks, M.A. Hicks, J.G. Rots, Árpád Rózsás, A.T. Slobbe, Y. Yang

One of the most severe deteriorations in reinforced concrete structures is associated with reinforcement corrosion, where the corrosion distribution shows considerable spatial variability. In the existing investigations of spatial variability of corrosion on the reliability of reinforced concrete structures, symbolic expressions are used for the structural performance. However, structural behaviors like stress redistribution and plasticity spread are not captured. In this research, a computational framework is designed to couple the probabilistic analysis with the nonlinear finite element analysis. Random fields is used with the computational framework to represent the spatial variability of corrosion.A 60 m girder of a reinforced concrete bridge is taken as the case study to explore the effect of spatial variability of corrosion on reliability of static indeterminate reinforced concrete structures. The reliability analysis is target on ultimate capacity of the beam to carry the traffic load. The girder is modeled as a 3 span continuous beam. The modelling of corrosion damages on reinforcement (area of cross section and physical properties) is based on assumption of pure pitting corrosion. In the axial direction of the beam, spatial variability is modeled with random field. In order to study the effect of different level of spatial variability, the correlation length of the random field is set from infinite large to 125 mm. Between adjacent bars, extreme cases of fully spatial correlated and totally spatial independent are studied.The case study shows:i) when corrosion develops, pitting corrosion can severely reduce resistance of the structure and localized damage may lead to a brittle structural response.ii) spatial variability of pitting corrosion in the axial direction of the beam leads to higher failure probability of the structure.iii) spatial variability of pitting corrosion between adjacent bars leads to lower failure probability of the structure.iv) the effect of spatial variability of corrosion on reliability of static indeterminate reinforced concrete structure is a collective effect of probabilistic and physical characteristic.In order to facilitate the reliability assessment of corroded reinforced concrete structures, additional efforts are also contributed to: quantification of uncertainty for the bond model of corroded reinforcement; comparison of various reliability methods with the probabilistic nonlinear finite element analysis framework.The thesis fills the knowledge gap of probabilistic nonlinear finite element analysis of reinforced concrete structures with spatial varied corrosion and quantifies the effects of spatial variability of corrosion on the reliability of a static indeterminate reinforced concrete structure. The analysis framework designed in this thesis is also applicable for other reliability assessment of corroded reinforced concrete structures.

Numerical Simulation of Mixed Mode Crack of Concrete

A Case Study Based on Experiment of Double Notched Specimen

Student report - Q. Jiang, M.A.N. Hendriks, Y. Yang

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Cleavage fracture during multiaxial loading: identifying stress parameters in ferritic steels

Master thesis - T.W. van Zelst, C.L. Walters, Q. Jiang, V. Popovich

Brittle fracture in ferritic steels is a field in which a lot of research has been performed over the years. Most of this research has been done on uniaxially loaded specimens, such as single edge notched bend specimens. From these experiments, the maximum principal stress criterion is used in the Weibull distribution method as proposed by Beremin, and is observed to accurately predict the fracture toughness distribution. However, when multiaxial specimens are considered, the maximum principal stress criterion no longer accurately predicts the fracture toughness distribution. In this thesis, other failure criteria than the standard maximum principal stress are considered as a solution to this problem. Using the data provided in the 2006 paper "An Experimental Investigation of the Effect of Biaxial Loading on the Master Curve Transition Temperature in RPV Steels" by R. Link, A Joyce and C. Roe, the properties of Shoreham pressure vessel steel are obtained. Furthermore, the fracture toughness from the tested cruciform specimens allows for the reconstruction of the stress state around the crack tip during fracture. This is done by creating various cruciform specimens in the Abaqus finite element analysis program, which are loaded in accordance with the paper. The resulting stress state is used in the calibration of the Weibull parameters in the Weibull distribution. It was found that uniaxially loaded specimens show good agreement with the predicted failure probabilities. Additionally, it was confirmed that the biaxially loaded specimens do not show good agreement when the maximum principal stress is the failure criterion. When the failure criterion is altered so that only microcracks that do not experience large triaxiality contribute to fracture, good agreement is obtained for both the uniaxially and biaxially loaded specimens. Hence, it is found that triaxiality is very important for cleavage fracture, with high levels of triaxiality preventing microcracks from propagating. This leads to a proposed failure criterion where the maximum principal stress criterion is applied, and only elements that do not experience high levels of triaxiality contribute. It is suggested to further test these conclusions under a variety of loading conditions, for which an alternate specimen is proposed.