Jian C. Lim

Lateral Strain-to-Axial Strain Relationship of Confined Concrete

The use of fiber-reinforced polymers (FRP) has become widely accepted engineering practice for strengthening reinforced concrete members. It is well established that lateral confinement of concrete with FRP composites can significantly enhance its strength and ductility. As the confinement pressure generated by FRP on the confined concrete depends on the lateral expansion of concrete, the mechanism of concrete expansion inside the FRP shell is of significant interest. A review of the existing stress-strain models of FRP-confined concrete revealed the need for a model that accurately predicts the dilation characteristic of confined concrete as it provides the essential link between the response of the concrete core and the passive confinement mechanism of the FRP shell. It is also understood that knowledge established from the research area of actively confined concrete can be employed in the development of a model applicable for both FRP-confined and actively confined concretes. Based on a large number of experimental test results of both FRP-confined and actively confined concretes, a generic model is proposed to describe the lateral strain-to-axial strain relationship of confined concrete. The instrumentation arrangements of the tested specimens have allowed for the lateral strain-axial strain relationships of confined concrete to be captured throughout the tests. The trend of the lateral strain-to-axial strain relationship of confined concrete is shown to be a function of the confining pressure, type of confining material and concrete strength. Assessment of models with the experimental databases showed that the predictions of the proposed model are well above existing models and in good agreement with the test results of both FRP-confined and actively confined concretes.

Unified Stress-Strain Model for FRP and Actively Confined Normal-Strength and High-Strength Concrete

AbstractAccurate modeling of the complete stress-strain relationship of confined and unconfined concrete is of vital importance in predicting the overall flexural behavior of reinforced concrete structures. The analysis-oriented models, which utilize the dilation characteristics of confined concretes for stress-strain relationship prediction, are well recognized for their versatility in such modeling applications. These models assume that at a given lateral strain, the axial compressive stress and strain of fiber-reinforced polymer (FRP)–confined concrete are the same as those of the same concrete when it is actively confined under a confining pressure equal to that supplied by the FRP jacket. However, this assumption has recently been demonstrated experimentally to be inaccurate for high-strength concrete (HSC). It was shown that at a given axial strain, lateral strains of actively confined and FRP-confined concretes of the same concrete strength correspond when they are subjected to the same lateral con...

Investigation of the Influence of the Application Path of Confining Pressure: Tests on Actively Confined and FRP-Confined Concretes

AbstractIt is often assumed that, at a given lateral strain, the axial compressive stress and strain of fiber reinforced polymer (FRP)–confined concrete are the same as those of the same concrete when it is actively confined under a confining pressure equal to that supplied by the FRP jacket. An experimental program was undertaken to assess the validity of this assumption, in which 63 actively confined and FRP-confined normal-strength (NSC) and high-strength concrete (HSC) specimens were tested under axial compression. The axial stress-strain and lateral strain-axial strain curves obtained from the two different confinement systems were assessed. The results indicate that, at a given axial strain, lateral strains of actively confined and FRP-confined concretes correspond when they are subjected to the same lateral confining pressure. At the points of intersection on the lateral strain-axial strain curves, FRP-confined NSC exhibits only slightly lower axial compressive stresses compared with those of activ...

Finite-Element Modeling of Actively Confined Normal-Strength and High-Strength Concrete under Uniaxial, Biaxial, and Triaxial Compression

AbstractA concrete strength-sensitive finite element (FE) model applicable to concrete subjected to various confining pressure levels and conditions is presented. This paper focuses primarily on the failure surface and flow rule of concrete in multiaxial compression, which were experimentally observed to vary with the unconfined concrete strength and level of confining pressure. To this end, a large experimental database, which consists of more than 1,700 results of concrete specimens tested under biaxial and triaxial compression, was assembled through an extensive review of the literature. This database was augmented with another test database of concrete in uniaxial compression that consists of more than 4,000 test results. Based on the test database results, it was observed that the tangential slope of the failure surface reduces with an increase in the unconfined concrete strength and confining pressure. The concrete dilation angle considered in the flow rule was observed to be nonlinear throughout lo...

Influence of Size and Slenderness on Compressive Strain Softening of Confined and Unconfined Concrete

AbstractIt is generally accepted that the postpeak strain-softening behavior of concrete in compression is a localized phenomenon that occurs mainly in the compression damage zone. Accurate quantification of the size and slenderness effects on the postpeak behavior of concrete, therefore, depends on the accurate quantification of the inelastic deformations that occur in the compression damage zone. In this study, a novel approach is proposed to separate the two inelastic deformation components, known as the localized crack deformation and the deformation caused by the inelastic strain in the compression damage zone, from experimental stress-strain curves. This new approach allows the utilization of existing test results in the published literature in the model development. Based on two comprehensive experimental databases of confined and unconfined concretes covering a wide range of concrete strengths, a constitutive model for predicting the strain-softening behavior of confined and unconfined concretes i...