ISSN 0970-0137
Current Issue
December 2017 – January 2018 issue, Vol. 44 No. 5


Evaluation of specific fracture energy and the corresponding tension softening relation for the concrete made up of secondary aluminum slag

M. Satish Reddy and D. Neeraja



For the analysis and design of cracked concrete structures/components, the two important properties, namely, fracture energy and the corresponding tensile stress vs crack width are essentially required. To evaluate size independent fracture energy, two popular methods are available in the literature. They are (i) RILEM work of fracture method with tail correction for the load - deflection plot and (ii) back boundary effect method. The present study is aimed at on the evaluation of size independent fracture energy by using back boundary effect and the corresponding bi-linear stress vs crack width relation. Experiments have been conducted on notched concrete specimens made up of secondary aluminum slag with notch to depth ratio as 0.1 and 0.6. The percentage replacement of cement by secondary aluminum slag is 5, 10 and 15%. Bi-linear tension softening relation between stress and crack width has been derived for four concrete mixes based on inverse analysis by using load - crack mouth opening displacement.


Analysis and design of foundation systems to control the vibrations due to forging impact hammer

K. Rama Raju and B. Annesh



Forging impact hammer machines cause high impact loads on the foundation, resulting in propagation of vibrations to nearby buildings. A forging hammer foundation system is required to be designed to ensure long term efficient operation of the hammer with minimum disturbance to precision machines in the vicinity and adjoining structures. At present, elastomer below the anvil and spring casings below the foundation are used for vibration absorption. As per the present environmental specifications, the vibrations need to be reduced by providing elastomers with damping or spring damper casings below the anvil and foundation. Analytical and finite element methods to consider all these cases are developed to reduce the vibration levels as per present environmental standards.


Internal curing on high performance concrete with pre-soaked light weight aggregate to prevent shrinkage

P. Thamilselvi, A. Siva, N. Kabilan and Kinson Prabu



Concrete with low water-cement ratio has been encouraged in construction because of the improvement in strength and durability. However, higher shrinkage leads to early age cracking in the structures even though there is an increase in strength and reduction in permeability. The cracks due to shrinkage can be reduced by using internal curing agent. This can be achieved with the supply of required volume of water by using light weight aggregate as internal curing agent which nullifies the crack effect due to shrinkage. In the study a mix ratio of 1:1.76:2.52:0.36 was used to cast cubes, prisms and beams to investigate the strength properties of high performance concrete using silica fume and super plasticizer. The high performance concrete specimens were cast by replacement of cement with 12% of silica fume and addition of 6%, 12%, 20% light weight aggregate like vermiculite and saw dust. From the compression test result, optimum replacement percentage of light weight aggregate was found out and used for casting prisms and beams. The results of flexural tests conducted on beam specimens indicates that 6% replacement of saw dust gives higher strength in both water and internal curing conditions. Replacement of vermiculite (6%) as a Lightweight material reduced shrinkage significantly and prolonged the net-time to cracking considerably.


Interaction of in-plane and out-of-plane responses in unreinforced masonry walls under seismic loads

Jacob Alex Kollerathu and Arun Menon



Under seismic loading, a building is subject to simultaneous in-plane and out-of-plane actions. Existing simplified methods, such as the storey-shear mechanism, to determine the shear capacity of masonry structures neglect the interactions of out-of-plane actions. While neglecting the out-of-plane capacity can lead to a conservative estimate of global load carrying capacity, ignoring the interaction of in-plane and out-of-plane effects may lead to a non-conservative seismic assessment. In this paper, an analytical model is developed to evaluate the interaction of out-of-plane displacements with the in-plane shear capacities of unreinforced masonry (URM) walls under static loading. Results demonstrate that the out-of-plane displacements alter both the in-plane shear capacity and failure mechanism of a wall. The sensitivity of the interaction on the aspect ratio of, slenderness ratio of and axial load on the wall is also studied. Due to lack of experimental data specific to the phenomenon addressed, the proposed model is validated with non-linear finite element analysis. The model can be used to determine the reduced shear capacity of URM walls, if an estimate of the mid-height out-of-plane displacement is available. This interaction in URM walls are also studied under dynamic loading. The model is finally incorporated within the framework of the storey-shear mechanism to study the effect of out-of-plane displacements on the global shear capacity of a structure.


Investigation on the behaviour of electric power transmission line supports with a special reference to 8-meter long pre-stressed concrete pole

K. Gurunaathan and G.S. Thirugnanam



For pre-stressed concrete power transmission line pole, load test is nothing but the load-deflection test. It is a must quality control check in order to ensure the strength of structural elements. In this paper, the strength of pre-stressed concrete poles used as transmission line supports for low tension supply lines has been investigated by conducting the load-deflection test. The test has been carried out on 8-meter long pre-stressed concrete poles made of M42 grade, which were selected in random from the lots. Further, the load-deflection study has been conducted on pole with glass fiber mat wrapping using isophthalic resin (GFRP) for a height of 0.23 m on either side of the ground line. The ground line for the above poles is at a height of 1.5 m from the butt end of the pole. In this study, it is found that the pole with GFRP wrapping improves marginally compared to the conventional pole in terms of strength and durability. The aim of this investigation was to improve the failure pattern of the pole. The sudden failure of the pole is avoided to some extent and the failure location moves away from the bottom of the pole. Further, an analytical model for the pole has been developed to predict the pole deformation at tip and found that it almost matches with the actual load test results when the value of moment of inertia of the pole is taken at a section where the centroid lies for the portion of the pole between load point and the fixed end.


Prediction of SIFCON compressive strength using neural networks and curve fitting model

Gottapu Santosh Kumar and K. Rajasekhar



This paper presents the results of experimental investigation conducted to evaluate the possibilities of adopting Levenberg Marquardt (LM) based Artificial Neural Network (ANN) to predict the compressive strength of SIFCON (made with manufactured sand) with different percentage fibre fractions (8%, 10% and 12%) and different curing periods (7, 14, 21, 28, 35, 42, 49, 56, 63, 70, 77, 84, 91 and 98 days) as input vectors. The network has been trained with experimental data obtained from laboratory experimentation. The Artificial Neural Network learned the relationship for predicting the compressive strength of Slurry Infiltrated Fibrous concrete (SIFCON) in 400 training epochs. The input vector considered for the LM training phase includes curing periods of SIFCON concrete, fibre configuration, number of neurons, learning rate, momentum and activation functions. After successful learning, the LM based ANN models predicted the compressive strength satisfying all the constraints with an accuracy of about 95%. Results of LM algorithm are compared with the polynomial curve fitting method. Research results demonstrate that the proposed LM based ANN model is practical, predicts with high accuracy and beneficial. The various stages involved in the development of Levenberg Marquardt based Neural Network models are enumerated in brief in this paper.


Behaviour of RC interior beam column joints with diagonal bars under reverse cyclic loading

K.R. Bindhu, V. Vysakh and R.K. Vandana



In the design of reinforced concrete moment resisting frames, the beam column joint sub-assemblage is of great importance in Earthquake prone areas. The joints are designed based on ‘strong column weak beam’ behaviour so as to result in a ductile failure in the event of an earthquake. In this study, performance of interior beam column joints with cross inclined bars is assessed and compared with that of joints designed and detailed as per IS13920:1993. Three 1/3rd scaled joint specimens consisting of diagonal bars placed along column, diagonal bars placed along beam and conventional detailing were constructed and tested under reverse cyclic loading. The results of experiments indicate that non-conventional joint detailing involving use of diagonal bars is a better alternative for interior joint specimens with conventional reinforcement detailing. The specimen with diagonal bars along column exhibited better performance in terms of ultimate strength and energy dissipation capacity. Conventionally detailed specimens are good in providing sufficient displacement ductility.


3-D soil foundation structure interaction analysis for asyemmetrical buildings

Pallavi Badry and Neelima Satyam



The analysis and understanding of the integrated behavior of soil foundation and superstructure under the seismic excitation is very challenging and complicated. The various governing parameters including soil damping, soil nonlinearity, creation of a gap and penetration during vibration and soil stratifications makes the analysis more tedious. In this paper the seismic soil structure interaction analysis has been carried out for 11 storey RCC structure supported on a pile foundation with a homogenous soil condition.The analysis has been carried out by developing the program in C++ using finite element method which captures the soil nonlinear behavior and node to node interfaces between soil and pile. The building is investigated by simulating the building model using two different conditions: namely soil-structure interaction, and fixed-base behavior. The effect of asymmetry of the building has been investigated for L, C and T shapes and the effect is compared with the symmetrical building with the same stiffness and a foundation system under the same earthquake. The study reveals that the effect of interaction plays the vital role in the superstructure response. Also, it is noted that the asymmetrical building shows different behavior than the symmetrical building for the same building stiffness.


Confinement effect on strength of concrete columns by using cold-formed steel tubes

J. Kumar and V. Ramasamy



Enhancement of strength and ductility of weak concrete columns is continuously attempted and different methods are adopted. As the popular method, fiber reinforced polymer wrapping calls for precise quality control with skilled supervision, an alternate methods is being developed. Towards this, a methodology is proposed to confine concrete columns by using built-up tubes with cold-formed steel hat sections. This paper presents an experimental investigation on the confinement effect on axial strength of short concrete columns by using built-up. The performance of the columns is studied in terms of load-displacement behavior and failure modes and the results are compared with respective plain concrete columns. Critical failure modes; local crushing, vertical splitting of concrete followed by bulging of steel sections and rupture of the bolt are found out. The enhancement of the strength of the column is 38.64% to 56.61%. Based on the study, the existing expression for evaluating the confined strength of wall panels available in the literature is modified and validated with the results available in the literature. The modified expression predicts the axial strength of rectangular concrete columns confined with carbon fiber reinforced polymer wraps closer to the experimental results. It is inferred that the new method can be adopted as an alternative to the traditional methods for strengthening the weak columns.


Reliability indices for compression braces in eccentrically braced frames

Jaya Prakash Vemuri,



The Eccentrically Braced Frame (EBF) has been accepted by seismic codes as a major seismic load resisting system. EBFs are designed using the capacity design method where all structural members are proportioned for the maximum capacity of the ductile fuse element. Load and resistance factors for code provisions have historically been derived from the actions of external loads and have so far not been derived for capacity design provisions. The first order second moment method is used to derive reliability indices for compression braces in an EBF. Reliability indices derived using design code equation result are non-uniform. Alternatively, the use of a recently proposed statistical equation for computing link overstrength is observed to result in uniform reliability indices. Since the current design provisions are inconsistent and may lead to both conservative and insufficient designs, the proposed statistical equation may be adopted with a reduced value of resistance factor.


Seismic performance of asymmetrical building with VED and TMD

T. Naga Sai, P. Kamatchi and A.S. Santhi



Asymmetrical buildings on application of lateral loads are observed to be responding differently compared to symmetric building and the edge frames act as flexible or stiff based on the direction of eccentricity. Variations of the responses of the asymmetrical building at flexible edge and stiff edge are quantified in terms of peak displacements, drifts, shears and accelerations at different stories. In this paper, responses of a typical ten storey reinforced concrete (RC) asymmetrical building with and without passive energy dissipators are studied for four different earthquake ground motions. In the present study, different eccentricity ratios are considered by varying eccentricities in X direction of the building to be 0% to 30% and lateral loads are assumed to be acting in the Y-direction of the building. To bring down the peak seismic responses of the asymmetric building, applicability of designing two different passive dampers viz. Viscoelastic dampers (VED) and Tuned mass damper (TMD) are explored. Sensitivity of response ratio of peak displacements at roof level and ratio of peak base shear with and without VED and TMD are studied for different eccentricity ratios and torsional to translational frequency ratios. From the studies, the necessity to include the effect of asymmetry of the building in the design of VED and TMD are brought out.


Numerical modelling of glued laminated wood beams

Yashida Nadir, Praveen Nagarajan and Mohammed Ameen



Wood composite product or engineered wood product (EWP) is an important construction material which utilizes wood effectively and has structural applications. The process of manufacturing engineered wood products is an effective technique for reducing or eliminating the shortcomings of solid wood materials and for obtaining high performance materials. Studies on use of EWP for structural applications are uncommon in India. This study aims to assess numerically the load deflection behaviour of laminated and reinforced laminated wood beams, one among the EWPs, and compares the results with experimental findings. Good comparison was obtained between the numerical and experimental results for the flexural behaviour of laminated beams. Crack simulation in laminated wood beams was also carried out and the effect of different sizes and locations of cracks on the load carrying capacities of beams were investigated. Crack simulation and failure of the structure was given emphasis. For the cracked beam analysis, the ultimate load was found to decrease with increase in crack length for both edge cracked and inner cracked beams. Edge cracked beam has lesser load carrying capacity than inner cracked beam. Predominant value of energy release rate was found for mode II failure.


Numerical modelling of load-deflection behaviour of reinforced concrete beam-slabs

V.K. Mohamed Ameen, Bijily Balakrishnan, Swapnil Joshi and Devdas Menon



An efficient computational technique for nonlinear analysis of reinforced concrete (RC) beam-slab systems (rectangular grids) using grillage analogy is proposed. A load-controlled algorithm has been adopted for tracing the complete load-deflection response till the ultimate load, under monotonic loading. Material modelling of reinforced concrete in the present study includes nonlinear stress-strain behaviour such as cracking of concrete, yielding of steel and tension-stiffening effect. The proposed methodology has been validated against the test data reported in the literature as well as the experiments conducted for the present study. The numerically generated load-deflection curves are found to be in good agreement with the experimental results. The main advantages of this procedure is that it gives a more accurate estimation of short-term deflections under service loads, and a more realistic distribution of moments and shear forces at the limit state of collapse. Further, the algorithm can be conveniently used in reliability analysis of reinforced concrete beam-slab systems.


Thermal post-buckling of slender composite columns by using an equilibrium path method

VK. Sanjay Anand Rao G. Venkateswara Rao and R.K. Gupta



Thermal pre-buckling and post-buckling behavior of slender composite columns is studied by using an equilibrium path method. The von-Karman strain-displacement relations are used to account for moderately large transverse deflections. The ends of the column are axially immovable. A column subjected to severe thermal environment experiences axial compressive load which makes the column to buckle at critical temperature. The column is capable of carrying additional thermal load beyond critical temperature till it reaches material compressive strength limits. In highly optimized structures, generally used in weight sensitive structural applications, this additional thermal load carrying capability beyond critical temperature of columns can be used effectively. A finite element formulation is developed in this paper to obtain the pre- and post-buckling response of composite columns using equilibrium path method.


Non-linear behaviour of steel frame with aluminium shear-link

Aditi Pingle and K. Baskar



Experience through the years emphasizes the importance of further research to develop sustainable techniques to limit structural damages due to earthquake. Energy dissipation devices are known to be effective in reducing the structural response. Structural members yielding in shear are used in earthquake resistant systems in a conscious effort to concentrate the energy dissipation capacity of the structure in components that can be repaired or replaced after a major earthquake. A promising strategy for such damage control measure is the use of aluminium shear-link. An attempt is made to study the effectiveness of aluminium shear-link in concentrically and eccentrically braced steel frame system. An aluminium shear-link is proportioned to resist the maximum storey shear of the frame and introduced between the floor beam and top of the diagonal braces. The shear force is resisted by horizontal web area of the shear-link by yielding of the shear-link material or by tension field action depending upon its d/t ratio i.e. resistance to shear buckling. Using the finite element method, braced frame without shear-link is analyzed and compared to the behavior of the same frame with shear-link under non-linear static analysis. The failure mechanisms of both the frames are studied. The governing factors of the shear-link performance such as depth to thickness ratio and shear-link location (along the beam) are varied to study the variation in behavior. The numerical investigation is performed to study the shear carrying capacity, ductility and energy dissipation potential under the parametric variation.

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