Konjengbam Darunkumar Singh

Stress intensity factors based fracture criteria for kinking and branching of interface crack: application to dams

In this paper, the application of contour integral method (J. Elast. 8 (1978) 21; On the marriage of fracture mechanics and mixed finite elements methods: an applications to concrete dams, Ph.D. Thesis, University of Colorado, 1993) for determination of bimaterial stress intensity factors in the case of crack lying between rock/concrete interface of gravity dam is shown using the concepts of linear elastic fracture mechanics. The kinking angle of the interface crack is computed based on the maximum circumferential stress criteria. Criteria for branching are proposed [Appendix].

Characteristic Properties of Cement-Stabilized Rammed Earth Blocks

AbstractThe paper presents an effort to study the properties of locally available soil and its suitability as a construction material. The properties of cement-stabilized and unstabilized rammed earth blocks were studied in terms of density, strength, compaction energy, and durability in both cured and uncured condition. All the test samples were produced using steel rammer and wooden mold, with an attempt to select and validate the block-making equipment and technique that can be used for construction of rammed earth structures. The detailed test results and analysis show that the cement-stabilized rammed earth (CSRE) blocks are consistent in terms of density with respect to standard Proctor value under the accurate control of parameters such as cement content, optimum moisture content (OMC), and compaction energy. The CSRE blocks meet the design criteria outlined in various standards.

Probabilistic seismic hazard estimation of Manipur, India

This paper deals with the estimation of spectral acceleration for Manipur based on probabilistic seismic hazard analysis (PSHA). The 500 km region surrounding Manipur is divided into seven tectonic zones and major faults located in these zones are used to estimate seismic hazard. The earthquake recurrence relations for the seven zones have been estimated from past seismicity data. Ground motion prediction equations proposed by Boore and Atkinson (2008 Earthq. Spectra 24 99–138) for shallow active regions and Atkinson and Boore (2003 Bull. Seismol. Soc. Am. 93 1703–29) for the Indo-Burma subduction zone are used for estimating ground motion. The uniform hazard response spectra for all the nine constituent districts of Manipur (Senapati, Tamenglong, Churachandpur, Chandel, Imphal east, Imphal west, Ukhrul, Thoubal and Bishnupur) at 100-, 500- and 2500-year return periods have been computed from PSHA. A contour map of peak ground acceleration over Manipur is also presented for 100-, 500-, and 2500-year return periods with variations of 0.075–0.225, 0.18–0.63 and 0.3–0.1.15 g, respectively, throughout the state. These results may be of use to planners and engineers for site selection, designing earthquake resistant structures and, further, may help the state administration in seismic hazard mitigation.

Surface level ground motion estimation for 1869 Cachar earthquake (Mw 7.5) at Imphal city

In this paper, the seismic susceptibility of Imphal city with respect to ten synthetically generated samples of the historic 1869 Cachar (Mw 7.5) earthquake that occurred in the Kopili fault is presented based on the finite-fault seismological model in conjunction with nonlinear site response analyses. For all the synthetic sample earthquake events, the mean and standard deviation of surface level spectral ground acceleration at peak ground acceleration (PGA) and natural periods of 0.3 and 1 s have been reported in the form of contour maps. These contour maps can serve as guidelines for engineers and planners to identify vulnerable areas for possible seismic disaster mitigation of Imphal city.

Thickness effects on maximum von-Mises stress of a cement mantle in total hip replacement - a finite element study.

AIM The present study seeks to increase the life term of fully cemented total hip replacements by minimizing the stress values within the cement mantle. METHODS Three-dimensional (3D) finite element analyses have been carried out to investigate the effects of varying cement thickness on the von-Mises stress of a cement mantle. The magnitude and location of maximum von-Mises stress within the cement mantle have been studied for both straight and tapered prosthetic stems. RESULTS For prosthetic stems having lower radii sizes, the maximum stress zone is found in the upper region of the cement mantle whilst for stems with higher radii sizes the maximum stress zone is found in the lower region of the cement mantle. For the same cement thickness, straight stems are found to produce lower maximum stress values in the cement when compared to tapered stems. Finally, for the straight models with the same cement thickness, maximum stress values are found to decrease with increasing stem radius. CONCLUSIONS It can be concluded that the maximum stress values in the cement mantle decrease with decreasing cement thickness.

Estimation of Seismic Site Coefficient and Seismic Microzonation of Imphal City, India, Using the Probabilistic Approach

Seismic site coefficients (Fs) for Imphal city have been estimated based on 700 synthetically generated earthquake time histories through stochastic finite fault method, considering various combinations of magnitudes and fault distances that may affect Imphal city. Seismic hazard curves and Uniform Hazard Response Spectra (UHRS) are presented for Imphal city. Fs have been estimated based on site response analyses through SHAKE-91 for a period range of engineering interest (PGA to 3.0 s), for 5% damping. Fs were multiplied by UHRS values to obtain surface level spectral acceleration with 2 and 10% probability of exceedance in 50 year (∼2500 and ∼500 year) return period. Comparison between predicted mean surface level response spectra and IS-1893 code shows that spectral acceleration value is higher for longer periods (i.e., >1.0 s), for ∼500 year return period, and lower for periods shorter than 0.2 s for ∼2500 year return period.

An investigation of plastic cell filled concrete block pavement (PCCBP) overlay

To explore the possibility of using plastic cell filled concrete block pavement (PCCBP) as overlay in pavement construction, an experimental investigation has been carried out by comparing the structural behaviour (layer elastic moduli) of a ∼ 50 mm thick PCCBP overlay and a conventional bituminous surface of similar thickness. To economise the cost of construction of PCCBP, an attempt has also been made to use waste stone dust in place of the traditional river sand as fine aggregates in concrete. Based on the investigation, it has been found that an increase of ∼ 235% in surface layer modulus is observed when PCCBP is used instead of bituminous layer (Overlay PCCBP layer modulus=1982 MPa). PCCBP as overlay construction on the existing bituminous pavement shows no significant distresses even after 62,000 ESAL load repetitions and can be rated ‘Excellent’ based on PCI (∼ 90) rating (ICPI, 2007).

Structural assessment of plastic cell-filled concrete block pavement (PCCBP): an experimental study

Experimental investigations into the structural behaviours of different thicknesses of plastic cell-filled concrete block pavement (PCCBP) over 100-mm thick water bound macadam sub-base course are presented. In this study, an attempt has been made to use waste stone dust in place of the traditional river sand as fine aggregates in concrete. Layer elastic moduli of different layers of PCCBP have been calculated using linear elastic theory-based backcalculation computer code BACKGA from the surface deflection data obtained through falling weight deflectometer. It has been observed that peak surface deflections decreased linearly with increasing PCCBP thickness; with 200% increase (from 50 to 150 mm) in thickness, a decrease of ∼48% in deflection was observed. Elastic layer modulus of PCCBP has been seen to increase linearly with increasing thickness (∼83% increase in elastic modulus was observed for 200% increase in thickness, with layer modulus value of ∼1995 MPa for 50-mm thick PCCBP). Furthermore, life cycle cost analysis showed that PCCBP is more economical than conventional pavements.

Numerical Study of the Effect of Boundary Conditions on Buckling Behaviour of Flat Oval LDSS Stub Column Under Axial Compression

This paper presents the effects of two support boundary conditions, viz. simply mounted and fixed on the buckling capacity of flat oval Lean Duplex Stainless Steel (LDSS) stub columns of two thicknesses (t = 20 mm and 5 mm, corresponding to Class 3 and 4 sections, respectively) under pure axial compression, analysed using Abaqus. It is observed that the ultimate load (Pu) capacity of both the boundary conditions (BCs) is similar for the Class 3 section, whereas simply mounted specimen showed lower value of Pu as compared to the fixed support boundary condition, for the Class 4 section considered. Further, in contrast to the Class 3 section, the Class 4 section with fixed BCs showed the formation of elephant foot near the end of column with denting located at the quarter height of column, while the simply mounted column showed mid-height denting only.

Semi-elliptical LDSS Hollow Stub Columns Under Axial Compression

In this paper, effect of thickness on the structural performance of concentrically loaded semi-elliptical lean duplex stainless steel (LDSS) hollow stub columns is presented via nonlinear finite element (FE) analysis by using ABAQUS. The modeling procedure has been validated against the LDSS stub column experimental results available in literature. The cross-sectional dimensions considered in this analysis conform to the commercially available semi-elliptical hollow sections from Ancofer Stahlhandel GMBH. Extensive parametric study was carried out to study the structural performance by varying the thickness from t = 5 to 14 mm. Based on the FE analyses, it has been found that, for the sections considered, a near linear increase (~+300%) in column resistance (Pu) is seen with increase (~+180%) in thickness from t = 5 to 14 mm. Further, an enhanced strain hardening effect on the load capacity can be observed for the thicker sections, i.e., t ≥ ~12.5 mm.