Inamullah Khan

Structural performance of a 26-year-old corroded reinforced concrete beam

This article presents experimental results and the modelling of a highly corroded beam subjected to a chloride environment to assess the performance of long-term-corrosion-damaged beams. A reinforced concrete beam corroded by 26 years of exposure to a chloride environment was tested until failure, as was a control beam of the same age. Cracking maps and corrosion maps were drawn for the corroded beam. Force displacement curves for both beams and stress strain curves for the steel bars were also plotted. From the results it appears that corrosion has a significant impact on the load carrying capacity, stiffness and deflection of beams. The modelling approach using Macro Finite Element (MFE) shows good agreement with experimental results in terms of load capacity, stiffness of the beam and ultimate deflection. Cet article présente les résultats expérimentaux et la modélisation du comportement mécanique d’une poutre sévèrement corrodée par 26 années de conservation en atmosphère saline. Après avoir été testée en flexion jusqu’à la rupture, la poutre a été désossée afin de déterminer la carte de corrosion des armatures et de faire des tests de traction sur les armatures corrodées. Les résultats montrent que la corrosion des armatures a une influence importante sur la capacité portante, la raideur en service et la ductilité (flèche à rupture) L’approche de modélisation par macro-élement montre une bonne corrélation en terme de charge ultime, raideur et déplacement maximal.

Study of the impact of localised cracks on the corrosion mechanism

Corrosion is one of the major problems that the reinforced concrete industry is facing nowadays. Much research has been carried out to investigate the influence of cracks on rebar corrosion. In this project ring shaped mortar samples with an 8mm steel bar inside were cracked with different crack widths and then subjected to continuous wetting and drying cycles in salt solution having 35 g/L of NaCl, to accelerate the corrosion process in laboratory conditions. The samples were broken after 1.5 years and 2.5 years to observe the corrosion pattern. Results show that cracks whatever their width allow the corrosion onset at the bottom of cracks and along the steel–concrete interface damaged zone caused by the creation of cracks. This process leads to corrosion cracks formation time dependant of the crack opening, which modify the environmental conditions at the level of steel leading to the generalisation of corrosion all along the re-bars. Cet article étudie les relations entre la fissuration pré-existante d’origine mécanique sur la corrosion des armatures du béton armé. Le programme expérimental utilise un cœur expansif permettant de générer des fissures d’ouvertures contrôlées dans des échantillons armés qui sont ensuite soumis à des cycles d’immersion-séchage en solution saline. Les échantillons ont été dépouillés après 1an et demi et 2 an et demi pour étudier l’évolution de la corrosion au cours du temps. Les résultats montrent que quelque soit l’ouverture des fissures, la corrosion démarre en fond de fissure et se propage le long de l’interface acier-béton endommagée en fond de fissure par la création de la fissure. Ce processus dont la durée est influencée par l’ouverture des fissures, conduit alors à la création de fissures de corrosion qui modifient l’environnement local au contact de l’armature et conduit alors à une généralisation de la corrosion.

Mechanical Behavior of Long-Term Corroded Reinforced Concrete Beam

This paper presents both experimental results and modelling of a highly corroded beam subjected to chloride environment to assess the performance of long-term corrosion damaged beams. A 26 year old corroded reinforced concrete beam exposed to chloride environment was tested along with a control beam of same age till failure. Cracking maps and corrosion maps were drawn for corroded beam. Also force displacement curves for both beams and stress strain curves for steel bars were drawn. From the results it appeared that corrosion has a significant impact on load carrying capacity and deflection of beams. The modelling approach using Macro Finite Element (MFE) shows a good agreement with experimental results in terms of load capacity, stiffness of the beam and ultimate deflection.

Modeling Steel Concrete Bond Strength Reduction Due to Corrosion

Reinforcement corrosion in reinforced concrete (RC) structures induces concrete cracking and leads to a reduction in both steel cross section and steel-concrete bond strength. In this paper, a new model is proposed based on a scalar damage parameter Dc that depends on the loss of cross-sectional area of steel due to corrosion. The model predictions are plotted against experimental data from the literature based on both accelerated and natural corrosion processes and compared to other existing empirical models. The proposed new model significantly improves the prediction of the bond strength of corroding steel bars and is valid for all diameters ranging between 10 and 20 mm (0.39 and 0.79 in.). Moreover, two additional parameters have been implemented in the model, allowing for the consideration of natural (localized) corrosion and the presence of stirrups. A stirrups confinement coefficient st and a pit penetration depth coefficient a have been successfully calibrated using experimental results from the literature.

Development length in reinforced concrete structures exposed to steel corrosion: a correction factor for AS3600 provisions

Abstract In reinforced concrete structures, reinforcement corrosion induces concrete cracking and leads to a reduction in both the steel cross-section and the steel-concrete bond strength and ultimately affects the development length. In this paper, a new correction factor is proposed to calculate the development length of reinforced concrete structures prone to corrosion. A scalar bond damage parameter is introduced to relate bond strength reduction to corrosion. The new model agrees well with all experimental results found in the literature. The bond damage parameter is further used as a correction factor modifying the AS3600 provisions for the development length of reinforcement in reinforced concrete structures located in a saline environment. The relationship between steel-concrete bond damage and corrosion induced concrete cracking is also discussed.

Prediction of early-age creep and cracking age of concrete: a proposed modification for AS3600 provisions

Abstract Early-age thermal and shrinkage-induced cracking is a major problem in concrete structures. The risk of early-age thermal cracking is increased if the degree of restraint to early-age contraction is increased. At this early age, tensile creep plays a key role in relaxing shrinkage-induced stresses and delaying the time to cracking. However, limited data are available concerning tensile creep of concrete and the magnitude and rate of development of the early-age shrinkage of Australian concrete. As a consequence, tensile creep is often poorly modelled in predictions of early-age cracking. The current method to calculate creep in the Australian Standard AS3600 is based on compressive creep data obtained from specimens loaded at ages generally greater than 14 days and cannot be used to predict very early-age creep confidently. In order to accurately quantify the early-age shrinkage and creep of concrete, a comprehensive experimental programme is being conducted at the UNSW Centre for Infrastructure Engineering and Safety. Creep and shrinkage strains were measured on different specimens subjected to sustained loading. Tests were conducted on two different concrete mixes of normal strength concrete (32 and 45 MPa). Restrained ring specimens were tested to observe the cracking age of concrete. A model is proposed to predict the early-age tensile creep of concrete.

Application of SAP2000 API and .NET Framework for Reliability Assessment of RC Structures

Based on the results of integral structure analysis, a practical program for the reliability analysis of the members is introduced for engineering application. The .NET framework and SAP2000 API were combined to develop this program. The probability distribution parameters of the load and the material are the input parameters and then based on the integral structure analysis results, by combining the Monte Carlo simulation methods and the JC methods, the probability distribution of the load effects and the resistance of the members can be calculated, thus the reliability indices of each member could be obtained. Furthermore, an example was introduced and the comparative study between this proposed method and the conventional method for evaluation of a structure was carried out. The results show that it is a feasible method to evaluate the bearing capacity of a structure by exploiting reliability indices directly and this method can offer more quantitative reliability indicators of the structures.