ISSN 0970-0137
Current Issue
October – November 2016 Vol. 43 no. 4


Influence of longitudinal rebars and boundary elements on the performance of 3D sandwich walls in direct compression

G. Appa Rao and P. Poluraju



3D sandwich precast concrete walls are often used in building construction due to their superior performance, thermal efficiency, and speed of fabrication. An extensive literature review on the behaviour of solid walls has been reported. This paper reports on experimental investigations on 3D sandwich walls of 150mm thickness, formed with interior and exterior layers of concrete, separated by 50mm thick layer of insulation material. The performance of 3D sandwich walls under axial compression vis-a-vis influence of longitudinal reinforcement and boundary elements is discussed. Eight full-scale and one-third scale wall classified as slender and squat walls were tested to study the behavior and ultimate axial compressive strength. The structural properties including load-deformation response, crack initiation, and crack propagation under axial line loading have been discussed. It has been observed that the 3D sandwich walls exhibited composite behavior under axial compression up to ultimate stage. The ultimate load carrying capacity of 3D sandwich walls has been observed to be reduced gradually with increase in slenderness ratio. The experimental observations have been compared with the provisions of various codes of practice. The Indian and ACI code provisions along with other empirical expressions developed for estimating the carrying capacity of solid walls are compared for their applicability to 3D sandwich walls.


Estimation of spectral velocity at long periods for application in velocity dependant seismic energy management devices

R.S. Desai and S.N. Tande



In response spectrum method of structural analysis spectral displacement (SD), spectral velocity obtained by undamped natural frequency times SD called pseudo spectral velocity (PSV), and pseudo spectral acceleration (PSA) are the response quantities used in general. FEMA356 classifies energy dissipation devices in different categories and specifies four distinct methods of analysis and design of structures installed with these devices. Pseudo spectral velocity is recommended by it to estimate damping forces in the velocity responding devices and subsequent structural response. As reported in literature, for accurate seismic response analysis of longer period structures using such devices, peak relative velocity (SV) value is more appropriate to be used in place of PSV, which is able to capture true forces in the devices. In view of this, new methodology of approximating SV values from PSV is proposed in this study which is useful for structures using velocity responding energy dissipation devices. Ensemble of several earthquake records with wide variations in their characteristics from all over the world are used to derive the proposed estimation of SV from PSV and to verify its accuracy. It is shown that proposed approximation rule performs better than other available approximations at longer periods. It is suggested to use combined approximation which yields reasonably accurate SV values for short, intermediate and long periods.


State-of-the-art review on cold-formed steel channel sections under compression

G. Beulah Gnana Ananthi



This paper presents a detailed review on cold-formed steel channel sections, which are subjected to both axial and eccentric compressive forces. Different cross-sections with single and built-up configurations are presented in this paper. Literature pertaining to experimental, theoretical and numerical investigations are reviewed in detail. The main objective of this literature survey is to study the available literature and to propose the required research work for the development of various other single and compound cold-formed steel sections. Research in cold-formed steel channel sections subjected to compressive forces shows the importance of channel sections and compares with other possible sections.


Non-local theory of buckling of tapered nano columns under self weight and an axial tip load using matrix based Chebyshev spectral collocation (mbcsc)

S. Rajasekaran



In this paper, elastic buckling of tapered Euler Bernoulli nano columns for tip load and self weight using non-local theory of elasticity is studied using matrix based Chebyshev spectral collocation method (MBCSC). The size effect is taken into consideration using Eringen’s non-local elasticity theory. Detailed numerical analyses about the effects of boundary conditions and load types are conducted and the influence of non-local parameter on the static buckling response of tapered or uniform nano tubes and rods is discussed. It is hoped that the results in this paper may present a bench mark in the study of buckling of tapered nano rods and tubes.


Deflection analysis of a multistage hydraulic cylinder

V. Ramasamy and A.M. Junaid Basha



The deflection of a multistage hydraulic cylinder is an important factor which reduces the critical buckling load of the cylinder and it is necessary to limit the deflections in the cylinder to avoid failure before reaching the critical load. In the present research work the deflections in multistage hydraulic cylinders due to self weight, oil weight and frictional moments are analyzed by classical methods and finite element methods and their effect in buckling with hinged and cantilever mounting conditions are studied. Deflection of three stage multistage telescopic hydraulic cylinder used in tippers are computed by a new set of simple programmable equations using the conjugate beam method and verified by ANSYS finite element method. The results are discussed.


Strength and stiffness characteristics of self-drilling screw lap-joints

V. Marimuthu, G.S. Palani and S. Kumar



Self-drilling screws (SDS) are generally used to connect secondary structural elements such as purlin, roofing sheets, wall and side claddings etc, in which the screw head is in contact with thin sheets. Attempts have been made to use these fasteners to connect primary structural members made up of cold-formed steel (CFS) sections, where it is expected that screw heads will be in contact with thick sheets, for which guidelines are not available. The existing guidelines addresses the configuration, where the screw head is in contact with thin sheets. As these fasteners are used to connect primary load carrying members, the performance of SDS joints (SDSJ) play a major role in analysis and design of such structures. In view of this, experimental studies have been conducted on SDS lap-joints (SDSLJ) under tensile shear loading with different combinations of plate thicknesses and number of screws. The performance of the SDSLJ has been studied in terms of load-displacement behavior and failure modes. The specimens failed by bearing and tilting, shearing of screws and net-section fracture. The obtained failure mode and strength of specimens are used to validate the existing guidelines and to evaluate the stiffness of SDSJ. It is found that the existing guidelines predict the failure mode and strength closer to that of the experiment. This paper presents the details of the experiments, methodology for evaluation of strength and stiffness of SDSJ and the comparative studies.


Experimental investigation on structural behavior of micro and macro fibre reinforced concrete beams subjected to cyclic loading

M. Kalaivani and G.Vennila



The structural performance of concrete made with commercially available steel fibres has been investigated. Two types of steel fibres, short crimped of length 15mm and aspect ratio of 37.5, another of long hooked ends of length 30 mm and aspect ratio of 60 were used in the present study. The overall volume fraction of steel fibres were restricted to 1 percent by the volume of concrete. M30 grade of concrete was used to cast the specimens. Reinforced concrete beams of 1.5 m length and 100 X 150mm in cross section were cast with different percentages of micro and macro steel fibres and the specimens were tested under two point forward cyclic loading after 28 days of curing. The various parameters such as stiffness, ductility and energy absorption capacity or toughness were evaluated and compared with the conventional RC beam. The short crimped fibre delays the initial crack when compared to all the specimens. The combination of micro and macro steel fibre increases the stiffness, ductility and energy absorption capacity significantly. The optimum fibre proportion of long hooked and short crimped for hybrid fibre reinforced concrete beam was found to be 0.8:0.2 for overall better performance as compared to that of the conventional beam.


Failure analysis of 3D sandwich beams under transverse shear

G. Appa Rao and J. Leon Raj



In this paper, an experimental investigation on the behaviour of 3D sandwich beams under transverse loading is reported. In order to study the shear strength, modes of failure, ductility and service ability, eight sandwich beams were tested at low shear span-to-depth ratio. Since the width and span are the primary variables, two different span-to-depth ratios, (Ln/D), 1.73 and 4.07, and four different depth-to-breadth ratios 1.13, 1.44, 1.62 and 1.92 were adopted at constant depth. In addition, the concrete cover on either face (vertical) of the polystyrene was kept constant with varying thickness of polystyrene inner layer. All the beams failed due to either flexure or diagonal splitting. Since the beams in this study were not provided with additional longitudinal tension reinforcement, only a major flexural crack was propagated which predominantly tended to split the beam into two. From the ratio of measured-to-predicted shear strength, it is concluded that ACI 318-08, IS456-2000 and Eurocode 2 overestimate the shear capacity of sandwich beams. By incorporating the influencing parameters, ACI building code shear strength expression has been modified, which showed good agreement with the experimental results.


Determination of the energy release rate function for an eccentrically notched center-loaded beam using elastic fracture analysis

Víctor Óscar García-Álvarez, Ravindra Gettu and Ignacio Carol



The center-loaded beam with an eccentric notch is a simple test setup for studying non-planar fracture, which is a common cracking mode in structural elements. This work presents a methodology for obtaining the relations between the energy release rate and crack extension for this geometry, considering two different notch eccentricities. The finite element analysis is based on linear elastic fracture mechanics and the method of virtual crack extension, and can be applied to other geometries and notch eccentricities. Using the energy release rate and the crack path, the mode I and mode II components of the stress intensity factor have been obtained. The crack paths used in the analysis have been obtained from tests of concrete and polymethylmethacrylate beams, in order to study the effect of both tortuous and smooth cracks on the mode II fracture component.


Experimental investigations of fatigue crack growth and behaviour on stainless steel elbows

DM. Pukazhendhi, K.C. Pazhani and S. Parivallal



Straight pipes, Tees and elbows form the primary heat transport piping system of nuclear power plants. Leak-before-break (LBB) design philosophy is used in the design of such piping systems. Leak-before-break analyses assume that the flaw becomes a through-wall crack, and that the through-wall crack can be detected by leakage at normal operating loads in advance of a catastrophic failure. Hence, systematic experimental investigations were carried out to study the fatigue crack initiation and growth behaviour of healthy (without notch) elbows and notched elbows having circumferential outer surface notch at one crown, extrados and intrados used in primary heat transport systems of nuclear power plants. Tests have been carried out on eight numbers of 90 degrees radius, 168 mm outer diameter and 15.1 mm nominal thickness elbows made of SA403 type 304LN stainless steel. The aspect ratios 2C/a (notch length to notch depth) and a/t (notch depth to thickness) of the notches were 1.5 to 4.5 and 0.18 to 0.28. The initial notch depth was varied from 3 to 4 mm. The fatigue tests were conducted at stress ratio (R) of 0.1 under load and displacement control. Fatigue crack detection and sizing were carried out using alternating current potential difference (ACPD) and Ultrasonic techniques. Fatigue crack growth curves and crack profile development curves were generated based on experimental data. Number of cycles to crack initiation and through-wall crack under in-plane bending moment were determined. Multiple cracks were observed in the elbow at various locations during fatigue crack growth studies. The two elbows with axial notch at crown location have shown less fatigue life compared to that of one elbow with circumferential notch at extrados and one elbow with circumferential notch at intrados.


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