Evaluation of load-carrying capacity of damaged reinforced concrete structures

Paper in proceeding, 2008

The growing need for reliable methods to evaluate the load-carrying capacity and remaining service life of deteriorated concrete structures has exposed the request for improved understanding of damage effects upon structural integrity. The presented research deals with the two most common causes of deterioration due to environmental impacts which are corrosion of reinforcement and freezing. Corrosion process leads to reduction of the reinforcement area and volume expansion of the steel which generates splitting stresses in the concrete and spall the concrete cover and affect the bond-slip between reinforcement and concrete. Through frost process, the volume expansion of frozen water initiates tensile stresses and micro/macro cracks into the concrete body leading to change of concrete behaviour in tension and compression as well as bond properties. In earlier work by K. Zandi Hanjari et al. a methodology to analyse the mechanical behaviour and remaining load-carrying capacity of corroded reinforced concrete structures has been developed and implemented in the finite element program DIANA. A method to quantify the frost damage has been explained in K. Zandi Hanjari et al (2007), where the effect of internal frost damage was proposed to be modelled as change of material properties; such as compressive/tensile strength, Young’s modulus and bond properties. In the study presented here, change of material and bond properties for different damage situation is described quantitatively which provides a guideline for assessment of damaged structures, due to freezing and corrosion, from field measurement to analysing the mechanical behaviour of the deteriorated structure and evaluating the remaining load-carrying capacity of the structure. The effect of corrosion as a change in geometry and properties, i.e. reduction of steel area, removal of spalled concrete and modification of bond-slip properties is evaluated based on previous research where a detailed finite element model has been developed and used to determine the bond-slip response for corroded reinforcement, Lundgren (2004). The effect of freezing on material properties of concrete and bond properties for different level of frost damage is established through extensive experimental program which includes six different test types: fundamental transverse frequency test, compressive strength, modulus of elasticity, splitting tensile strength, wedge splitting test and pull-out test