International Journal of Civil and Structural Engineering Research ISSN 2348-7607 (Online) Vol. 6, Issue 2, pp: (270-286), Month: October 2018 - March 2019, Available at: www.researchpublish.com
Strain Based Approach to the Modeling of Concrete under Uniaxial Tension-Tension Fatigue Loading Indra Narayan Yadav1, Dr. Kamal Bahadur Thapa2 1
Ph.D. Scholar, Department of Civil Engineering, Pulchowk Campus, Institute of Engineering, Tribhuvan University, Nepal 2 Associate Professor, Department of Civil Engineering, Pulchowk Campus, Institute of Engineering, Tribhuvan University, Nepal Corresponding emails: 1eecconsultant@gmail.com, 2kamal.thapa@ioe.edu.np
Abstract: Strain based Approach to the Modeling of Concrete under Uniaxial Tension-Tension Fatigue Loading is briefly described regarding Stiffness degradation and inelastic deformation which are the essential features of concrete that develop due to the formation of multitude of microcracks in the fatigue environment. Microcracking, which is anisotropic in nature, destroys the bond between material grains, and affects the elastic properties resulting in the reduction of material stiffness. This paper presents Strain based Approach to the Modeling of Concrete under Uniaxial Tension-Tension Fatigue Loading. The model is developed, in strain space, using the general framework of internal variable theory of continuum thermodynamics. It is argued that within the damage surface of given strain states the unloading-reloading cycles (fatigue loading) stimulate the nucleation and growth microcracks in concrete, which will result in stiffness degradation and inelastic deformation, and hence material is termed as damaged. Damage is reflected through the fourth-order stiffness tensor involving a damage parameter whose increment is governed by the consistency equation associated with a cycle dependent damage surface in strain space. The model is capable of predicting stiffness degradation, inelastic deformation and strength reduction under fatigue loading and compared against experimental results. Keywords: Fatigue; uniaxial; damage; Concrete; Thermodynamics; stiffness; microcracks, response tensors.
1. INTRODUCTION In recent times, concrete has become the bedrock of infrastructural civilization in Nepal. Statistics has shown that over 75% of the infrastructures in Nepal have to do with concrete. Thus, it is important to study and understand every aspect of concrete from the production, transportation, placing and eventually maintenance of concrete. Concrete today has a very wide range of applications. Virtually every civil engineering work in Nepal today is directly or indirectly involving the use of concrete. The use of concrete in civil engineering works includes: construction of residential houses, industrial warehouses, roads pavement construction, Shore Protection works, piles, domes, bridges, culverts, drainages, canals, dams etc. (Shetty, 2005; Neville, 2011; Edward and David, 2009; Duggal, 2009; Gambhir, 2005). In Nepal, the cases of failure of structures and roads (concrete related failure) occur on a yearly basis. Concrete is one of the most widely used materials in numerous civil engineering applications due to its workability and formability into various structural components. Except cement all ingredients of concrete are commonly available local materials like aggregate and water so concrete is getting more popular. Concrete is a composite material consisting of three components: the cement matrix, the aggregate and the interface between the matrix and aggregate. The cementmatrix is the weakest zone of the composite. It contains voids and micro cracks even before any load has been applied. A material or a component exposed to cyclic loading leads to increase of stress concentration around the micro cracks and
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