Conference Agenda

Corrosion of steel in concrete is responsible for 70-90% of the premature deterioration of reinforced concrete structures and can even cause structural failure, as infamously documented by the recent collapse of aerated concrete panels in the UK. Under field conditions, corrosion of reinforced concrete is a slow process that takes years or decades. Therefore, high corrosion rates are artificially applied in laboratory conditions to shorten the duration of experiments. It has been known for decades that this underestimates the damage caused by corrosion under natural conditions, but the reasons for this have been unclear. Based on recent experimental results, we propose a hypothesis that explains this phenomenon by the variability of the chemical composition of rust, in particular the variable ratio of iron oxides and iron hydroxy-oxides, with the applied corrosion rate. The simulation results obtained were found to be able to reproduce the hitherto puzzling trends in the experimental data for different corrosion rates. The proposed model can be used to estimate the error caused by the acceleration of corrosion tests and to extrapolate the results to the natural corrosion regime.

The present work attempts to address the issue of constitutive response and consistency of plastic strain-induced anisotropy of Lee-Fenves Concrete Damaged Plasticity (CDP) constitutive model. The CDP model, which comes to be available within the ABAQUS commercial FEM platform, shall be able to reproduce typical features of the failure process of quasi-brittle materials subjected to multiaxial cyclic loadings, according to FEM modelizations and simulations at the structural scale that may arise in different challenging engineering contexts. This is achieved by combining an effective stress-based nonassociative hardening/softening plasticity model, with an isotropic damage model based on plastic strains and stiffness loss/recovery capabilities during microcrack opening/closing, at a smeared continuum scale. Herein, several numerical analyses are performed, starting at a constitutive-driver level, to experiment the outcomes of the constitutive description and to quantify the amount of material anisotropy induced by plastic deformation, for representative non-proportional loading histories, which may involve the rotation of principal strains/stresses (Willam’s test). Extrapolating implications and outcomes at the structural scale may then consistently follow, in the realm of significant practical applications within different structural engineering contexts.

Reinforcement corrosion due to chloride ingress or carbonation is an important deterioration mechanism, which may compromise the service life of reinforced concrete structures. This paper presents an efficient macro-scale model, aiming to capture the most important aspects of the deterioration of reinforced concrete structures due to reinforcement corrosion. A chemo-mechanical model covers the initiation and propagation of chlorides using a 1D time-dependent model. This model is combined with the nonlinear modeling of cracking, bond failure, and reinforcement yielding. These models are implemented in the ATENA software and have been previously proven to provide a reliable prediction of structural performance deterioration. An example of an application from the consultancy practice is presented in the paper.

The need for improved punching shear performance is constantly under review, particularly for slabs between stories or in indoor parking garages of collective buildings. As a part of this effort, the detailed finite element model for this slab was discussed. For the benchmark and parametric analysis of the failure tests conducted by fib, the overall punching shear load-vertical displacement relationship, local reinforcement strain, and concrete cracking pattern were investigated through a nonlinear finite element model. A square slab with a length of 2,550 mm and a thickness of 180 mm is modeled with a three-dimensional solid element incorporated with conventional rebars and hooked-end steel fiber inclusions. The two-step mechanical homogenization was conducted in order to extract the effective properties of this fiber reinforced concrete composites. Damaged plasticity was applied for the concrete nonlinearity. The punching shear load was applied to the central part of the slab in the vertical upward direction, until the radial cracks occured to failure in the simulation. In order to develop a possible ductility guarantee for the punching shear condition with relatively high uncertainty, the shear resistance performance of a steel fiber reinforced concrete slab was discussed in accordance to arbitrary fiber directions and different fiber aspect ratios.