Smitha Gopinath

Behaviour of reinforced concrete beams strengthened with basalt textile reinforced concrete

Experimental investigations were carried out to determine the flexural behaviour of reinforced concrete beams strengthened with basalt textile-reinforced concrete under monotonic and low-cycle fatigue load. Reinforced concrete beams strengthened with basalt textile-reinforced concrete were tested under four-point bending. The behaviour of the strengthened beam was compared with that of un-strengthened reinforced concrete beam. It is observed that there is an enhancement in energy absorption for reinforced concrete beams strengthened with basalt reinforced concrete even though there is no considerable increase in load carrying capacity. It is observed that when the strengthened beams are subjected to monotonic loading, the increase in ultimate load carrying capacity is marginal but the increase in ductility is 84.5% and the increase in energy absorption is 162% compared with un-strengthened beam. Reinforced concrete beams strengthened with basalt reinforced concrete were also tested under low-cycle fatigue load. It is observed that there is about 20% reduction in ultimate load carrying capacity and 27% reduction in ductility compared to monotonic case. But the cracking and failure patterns are similar in both the cases.

Nonlinear analysis of RC shell structures using multilevel modelling techniques

Purpose – The purpose of this paper is to present integrated methodologies based on multilevel modelling concepts for finite element analysis (FEA) of reinforced concrete (RC) shell structures, with specific reference to account for the nonlinear behaviour of cracked concrete and the other associated features.Design/methodology/approach – Geometric representation of the shell is enabled through multiple concrete layers. Composite characteristic of concrete is accounted by assigning different material properties to the layers. Steel reinforcement is smeared into selected concrete layers according to its position in the RC shell. The integrated model concurrently accounts for nonlinear effects due to tensile cracking, bond slip and nonlinear stress‐strain relation of concrete in compression. Smeared crack model having crack rotation capability is used to include the influence of tensile cracking of concrete. Propagation and change in direction of crack along thickness of shell with increase in load and defo...

Optimised mix design for normal strength and high performance concrete using particle packing method

Abstract This paper presents the details of optimized mix design for normal strength and high performance concrete using particle packing method. A critical review of mix design methods have been carried out for normal strength concrete using American Concrete Institute (ACI) and Bureau of Indian Standards (BIS) methods highlighting the similarities and differences towards attaining a particular design compressive strength. Mix design for M30 and M40 grades of concrete have been carried out using ACI, BIS and particle packing methods. Optimization of concrete mix has been carried out by means of particle packing method using EMMA software, which employs modified Anderson curve to adjust the main proportions. Compressive strength is evaluated for the adjusted proportions and it is observed that the mixes designed by particle packing method estimates compressive strength closer to design compressive strength. Further, particle packing method has been employed to optimize the ingredients of high performance concrete and experiments have been carried out to check the design adequacy of the desired concrete compressive strength.

Probabilistic modelling of fatigue crack initiation from pits and pit clusters in aluminium alloys

Abstract A numerical model of crack initiation under high cycle fatigue loading from pits is investigated in this paper. A probability based pit growth model, which takes into account the influence of mechanical cyclic load and particle clusters present in alloys, is used for investigations. Critical pit sizes, calculated using linear elastic fracture mechanics principles, are used to determine the probability of crack initiation for different conditions. The results are critically compared to extract an insight on the parameters that control the pit growth behaviour and thereby the fatigue crack initiation.

Nonlinear Analysis of rc Structures Using Isotropic Damage Model

This article proposes a simple isotropic damage model within damage mechanics framework to represent the behavior of concrete in tension. Macroscopic evolution of tensile crack is considered as damage and is mathematically defined using an exponential function of tensile strain. A damage evolution law is formulated by applying strain equivalence principle to hyperbolic tension-softening curve. Value of damage variable is assumed theoretically to vary between ‘0’ and ‘1’ to denote uncracked and ruptured states, respectively. A smeared rotating crack model is coupled with damage formulation to simulate crack propagation effects in nonlinear finite element analysis of reinforced concrete (RC) structures. Many deficiencies of smeared crack model such as stress locking, mesh-induced directional bias, and instability in response computation for near-ultimate load are overcome using the coupled model. To verify the proposed model, nonlinear static response behavior of a RC beam is computed and compared with experimental and analytical results reported in literature. Effectiveness and applicability of the model to analyze practical structures are proved by analyzing a RC chimney. Nonlinear response of RC chimney is reviewed at global level while damage states of finite elements are studied at local level.

Structural Performance of Precast and Cast-in-situ UltraHigh Strength Concrete Sandwich Panel

This paper investigates the flexural performance of a sandwich panel made up of ultra high strength concrete (UHSC) as top and bottom skin and cold formed steel as sandwich. A novel sandwich panel has been designed such a way that bottom skin of UHSC is of precast in nature and top skin of UHSC is cast-insitu and cold formed steel (profiled sheet) as sandwich. The connection between top skin of UHSC and cold formed steel is made with self tapping screws. Flexural performance of UHSC sandwich panel has been tested under flexural loading and it is found that the post peak response of the panel is significant in terms of more energy absorption. It is observed that the final failure of the specimen is occurred by forming a dominant crack on the bottom face of the skin apart formation of many multiple cracks with increase of load. Numerical investigations have been carried out by simulating the experimental conditions and found that the response obtained through simulation is in good agreement with the corresponding experimental values. From the studies, it can be concluded that UHSC steel sandwich panels can be employed for structural and non structural applications.

Experimental Investigations on the Glass Fabrics for Confinement of Concrete Specimens

This paper deals with the performance of concrete specimens confined with different glass fabric reinforcement in organic binder consisting of resins. Three varieties of glass fabrics such as woven roving (WR), chopped strand mat (CSM), and textile reinforcement have been studied in the investigation. Experiments have been conducted on unconfined and confined concrete cylindrical specimens under compression. The effect of number of layers on confinement has been studied for specific cases. Specimens have been tested under displacement control. It is observed from the experiments that there is an increase in load carrying capacity as well as energy absorption capacity for specimens confined with different glass fabrics, and these materials can be used for retrofitting applications. It is observed that, in the case of specimens confined with textile reinforcement, failure is less abrupt compared to WR and CSM. The experimental findings will help the designer to choose the appropriate material towards confinement for practical applications.

An Improved Concrete Damage Model for ImpactAnalysis of Concrete Structural Components by usingFinite Element Method

This paper presents the development of an improved concrete damage model for projectile impact on concrete structural components. The improvement is in terms of reduction of input material parameters for nonlinear transient dynamic impact analysis by employing concrete damage model. The experimental data such as pressure vs volumetric strain, triaxial compression failure and pressure vs stress difference have been used for evaluation of the important parameters of concrete damage model. Various contact algorithms have been outlined briefly to model the interface between the projectile and target. The nonlinear explicit transient dynamic analysis has been carried out by using finite element method to compute the responses. It is observed that the computed penetration depth obtained in the present study is in good agreement with those values of corresponding experimental studies and LS-DYNA.

Fracture Analysis of Concrete Structural Components Accounting for Tension Softening Effect

This paper presents methodologies for fracture analysis of concrete structural components with and without considering tension softening effect. Stress intensity factor (SIF) is computed by using analytical approach and finite element analysis. In the analytical approach, SW accounting for tension softening effect has been obtained as the difference of SIP obtained using linear elastic fracture mechanics (LEFM) principles and SIP due to closing pressure. Superposition principle has been used by accounting for non-linearity in incremental form. SW due to crack closing force applied on the effective crack face inside the process zone has been computed using Greens function approach. In finite element analysis, the domain integral method has been used for computation of SIR The domain integral method is used to calculate the strain energy release rate and SIF when a crack grows. Numerical studies have been conducted on notched 3-point bending concrete specimen with and without considering the cohesive stresses. It is observed from the studies that SW obtained from the finite element analysis with and without considering the cohesive stresses is in good agreement with the corresponding analytical value. The effect of cohesive stress on SW decreases with increase of crack length. Further, studies have been conducted on geometrically similar structures and observed that (i) the effect of cohesive stress on SW is significant with increase of load for a particular crack length and (iii) SW values decreases with increase of tensile strength for a particular crack length and load.