ISSN 0970-0137
Current Issue
October 2017 issue
Vol. 44 No. 4


Studies on fracture behaviour of lightly reinforced concrete beams using digital image correlation

G. Appa Rao and H.E. Nagesh



Lightly reinforced concrete (RC) beams are fracture sensitive, which can be analysed with accuracy using fracture mechanics principles. This paper describes fracture behaviour of lightly reinforced concrete beams using digital image correlation (DIC) and also discusses short comings related to prediction of minimum tension reinforcement, as per IS 456-2000, in beams made of high strength concrete. The images acquired using two dimensional (2D)-DIC technique are correlated with undeformed image for capturing full field displacements, horizontal strain, crack width and crack length. The crack mouth opening displacement (CMOD) and mid-span deflection recorded using DIC have been compared with those measured from linear variable differential transducer (LVDT), are found to be in good agreement. Overall, DIC technique has been observed to be effective for predicting the fracture parameters of lightly RC beams. An experimental study has been carried out to understand the influence of beam size and compressive strength of concrete on behaviour of lightly RC beams. It has been found that tensile cracking stress in concrete decreases with increase in beam depth. The minimum tension reinforcement as per IS 456-2000 cannot ensure stable behaviour and hence unsafe for high strength concrete beams. Thus, the provision for minimum reinforcement needs modification incorporating compressive strength of concrete and beam size.


Experimental investigations on behaviour of cold formed steel stub uprights

Vimal Mohan, Arul Jayachandran and M.S. Kallapa



Uprights act as a column member in the rack system. In pallet racking systems, all upright sections are perforated to accept the hooks of the beam end connector and are the heart of the structural system. The perforations not only play an important role in the rack industry (for holding component in place), but are prone to more problems compared to any other form of structural member without perforation. The present study focuses on the behavior of perforated uprights under axial concentric loading. For better understanding, experiments were conducted on four specimens of steel rack uprights, by varying the thickness of sections as 1.6 and 1.8 mm with limitation on the slenderness ratio 10 and 18. Experimental investigations on the cold formed upright sections were studied for different type of configuration and their results are presented. Stress distribution across the specimen is also presented.


Development of seismic fragility curves for mid-rise masonry infilled reinforced concrete building by incremental dynamic analysis

V.S. Patil, and S.N. Tande



The present work is to study the effect of Brick Masonry Infill (BMI) in reinforced concrete (RC) building on seismic fragility curves using Incremental Dynamic Analysis (IDA). Multiple IDA curves which capture the ground motion uncertainties and which govern the shape of fragility curves are developed for twenty real ground motions. Spectral acceleration-based fragility curves and damage probability matrix under various damage states are developed for midrise RC frames with and without BMI. The comparative fragility curves for buildings with and without BMI are presented. It is concluded that the BMI frame have shown superior performance during earthquake in all modes of different damage states and the dispersion of Damage Measures (DM) and Intensity Measures (IM) in IDA analysis are less in the case of BMI thus improve robustness of the building response results in predictability in design.


Effect of soil structure interaction on response of G+3 building

Maheswara Varma, V.A. Sawant and V.K. Chandaluri



In conventional analysis, superstructures are generally analysed considering their bases as either totally fixed or hinged. But in reality the superstructure, is connected to compressible soil-foundation system. Hence, there is a need of considering the compressibility of soil and flexibility of foundation for the analysis of superstructure. The effect of Soil-Structure Interaction (SSI) on a G+3 storey building frame with 2 bay resting on pile foundation is studied in the present paper wherein the pile foundations are embedded in Cohesive Soil. A FORTRAN 90 code is developed using three dimensional finite element method for the analysis to be more realistic. An uncoupled analysis is employed to demonstrate the effect of SSI. The results obtained by considering the effect of SSI are compared to that of building with fixed supports (neglecting underlying soil and foundation). A parametric study is conducted by varying pile length, pile diameter, pile spacing and configuration of the piles in the pile group along with the modulus of elasticity of soil. The effect of change in these parameters is observed by analysing the top displacements of the building frame as well as bending moments in both beams and columns. It is observed that these values have increased by a considerable factor when SSI is taken into consideration for the analysis.


Strength and erodibility characteristics of compressed stabilised earth blocks using rice husk ash and lime

R. Sathish Kumar, Maganti Janardhana and N. Darga Kumar



Construction of building requires various building materials including burnt clay bricks. When compared to burnt clay bricks, Compressed Stabilised Earth Blocks (CSEBs) have certain advantages as the blocks can be manufactured without burning and by making use of locally available materials and hence reduces the transportation cost as the production can be done at the site. CSEB is considered to be energy efficient and environmental friendly building material. This investigation has evaluated the erodibility characteristics and the effect of varying exposure conditions on the wet compressive strength of CSEBs stabilized with rice husk ash and lime. The CSEBs were sprayed with water at a constant pressure of 1.5 kg/cm2 for a period of two hours and the depth of erosion was measured for every 15 minutes. The results of the weathering spray test clearly satisfy the Indian standard code provisions for soil based blocks which reflect the excellent performance of CSEBs stabilised with rice husk ash and lime.


Experimental and numerical studies on the performance of light gauge steel-concrete composite channel section beams

T. Valsa Ipe and H. Sharada Bai



Experimental studies are carried out to investigate the performance of light gauge steel-concrete composite channel section beams having different depth to thickness ratios and compared with that of non-composite channel section beams. FEM analysis using ANSYS is carried out to develop a numerical model to study the nonlinear behaviour of composite beams and a comparative study between experimental and numerical results is also carried out. Ultimate loads obtained from the FE analysis for composite beams are found to be close to the experimental results. Experimental investigation reveals that limiting the flat width ratio to 60 when simple lip is provided, as recommended by codes of practice for non-composite beams, is not a barrier for composite beams.


Development of lightweight concrete for structural applications

R.S. Muralitharan and V. Ramasamy



Lightweight concretes are widely accepted in the construction industry mainly due to its low density. Pumice lightweight aggregate (PLA) is a volcanic-origin natural aggregate of very low specific gravity. It is possible to develop light weight concrete of density up to 1450 kg/m3 using pumice having a dry density of 1200 kg/m3 and sound insulation properties, higher strength/weight ratio, better fire resistance and durability properties. The advantages of lightweight concrete are: reduced mass, improved thermal Performance of pumice lightweight aggregate concrete (PLAC) under cyclic loading, which is predominantly encountered during an earthquake, is of prime importance. In the present study, cyclic behaviour of reinforced PLAC beams of M30 grade with length (L) 1500 mm, breadth (B) 100 mm and depth (D) 150 mm have been studied in the laboratory along with control beams.


Stability and free vibration of functionally graded tapered Timoshenko beam-columns on two parameter elastic foundation

S. Rajasekaran



In this paper, the effect of two parametric elastic foundations on the stability and free vibration behaviour of functionally graded (FG) Euler (EB) and Timoshenko beams (TB) in the presence of conservative axial loads is examined. In Timoshenko beam, both shear deformation and rotary inertia effects are taken into account. The governing equations and boundary conditions are derived using the variational principles and presented in a matrix form. Differential Quadrature Element Method of fist order (DQEM) is used to solve the equations. Many examples and comparisons are presented in order to emphasize the influence of elastic foundation, beam taper, boundary conditions and the material properties. Finally the results are compared with the results given by the other authors using the closed form and other numerical techniques.


An experimental investigation of fly ash – ggbs based high strength geopolymer concrete incorporating copper slag

S. Imran Khan, D. Brindha and K.L. Muthuramu



Geopolymer concrete can be considered as a Green building technology that serves as an alternative for cement and river sand by using Alkaline Activator Solutions (AAS) and Copper Slag (CS). To attain High Strength Geopolymer Concrete (HSGC) trial tests were carried out by creating eleven different mix proportions with replacement of binder material fly ash by Ground Granulated Blast Furnace Slag (GGBS) from 0% to 100% by weight at increments of 10%. Alkaline activator solutions (14 molar Sodium Hydroxide and Sodium Silicate) were used in this study for polymerization. In each different mix proportion, specimens were cast and heat curing was done by maintaining 70 degree Celsius for 24 hours. The specimens were tested for strength parameters like compressive strength, split tensile strength and flexural strength. From the test results, combination of 60% GGBS and 40% fly ash produced high compressive strength of 71 N/mm2. Further, an attempt was made with the same proportion of binder material and by replacement of river sand with Copper slag from 0% to 100% by weight at increments of 10%, eleven different mix proportions were made. It is understood from the strength test results, substitution of 50% copper slag by sand yielded a high compressive strength of 77 N/mm2. Thus, the above mix combination resulted in high strength geopolymer concrete.


Numerical and experimental simulation of liquefaction for scenario earthquake

P. Kamatchi, M. Gayathri and M. Dilna



In this paper, numerical simulation of liquefaction has been done and comparisons are made with the results from experiment on shake table. Properties of river sand sample which are required for numerical simulations are obtained through laboratory tests. Scenario earthquake is artificially generated with seismological parameters of Mw 7.6 Bhuj earthquake January 2001 and numerical simulations are carried out using OpenSeesPL computer program. The excess pore pressure ratios, shear stress-strain histories and stress paths are studied. River sand sample passing through 1.18 mm sieve is filled in Perspex glass box for a dimension of 1.15 m × 1 m × 0.54 m and tested on shake table. A model frame of 7 storey building is placed in the soil specimen and instrumented for the observation of settlement. The time of occurrence of liquefaction observed from numerical simulation is 4.8s and found to be in agreement with the observation from the experiment on shake table. Further, the acceleration response at 110 mm from base observed in the experiment and numerical simulation are compared and are found to be in good agreement. This study, demonstrates the applicability of numerical simulations in prediction of liquefaction phenomenon and dynamic response analysis of typical soil sites for scenario earthquakes.


Vibration control of structures and structural components with magnetorheological elastomers

K. Rama Raju and D. Vineeth Varma



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