The need for a journal in India, devoted exclusively to activities in the field of structural engineering with special emphasis on research and development had been felt since long. To meet this demand and to provide a medium for structural engineers in India and abroad and to document, discuss and debate current trends in design, research, and development relating to all areas of structural engineering, SERC decided to undertake the publication of a quarterly journal entitled Journal of Structural Engineering (JoSE). The first publication came out in April 1973. From 1993 onwards, the first issue in each Volume has been dedicated to a special topic of current R&D interest. From the year 2005 onwards, the JoSE has been converted in to a bi-monthly Journal to meet the enhanced responses received from the prospective authors, nationally and internationally.
CSIR-Structural Engineering Research Centre
Temperature rate dependent modeling of thermal ratcheting behavior
Material behavior under cyclic thermal load is highly nonlinear and requires the understanding of theories of deformation mechanics to perform calculations not only for life estimation but also to ensure safe functionality of the industrial components. The nonlinear cyclic behavior due to cyclic thermal load, as in case of the main vessel of Sodium cooled Fast Reactors (SFR), results into thermal ratcheting strain. Excessive thermal ratcheting strain is one of the critical failure modes of the main vessel of SFR. The accuracy of the thermal ratcheting strain prediction depends on the choice of constitutive model and numerical integration method. The present work discusses experimental and a numerical method employing a simplified semiimplicit integration procedure for predicting the thermal ratcheting behavior. Further, it is demonstrated that there is essential need of considering temperature rate dependence while predicting thermal ratcheting strain. It is also observed that the mode of deformation of the thin cylindrical specimen of SS 316 L material changed with the change in loading methods and the proposed constitutive model estimated the thermo-mechanical behavior appropriately.
Thermal ratcheting; viscoplastic model; temperature rate terms; low cycle fatigue; thermo-mechanical loading.
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A parametric study on defect sizing in plates using lamb wave reflection coefficients
In this paper, a parametric study is reported to examine whether a combination of reflection coefficients corresponding to ultrasonic mode converted S0 and A0 Lamb waves lead to a better estimation of the depth of defects in metal plates. The A0 reflection coefficient, when plotted as a function of the ratio between the crack depth and the plate thickness shows a dip, which results in an ambiguity related to the dimensioning of the crack depth. Our study shows that on the other hand the S0 reflection coefficient curve follows a more distinct trend with increasing crack depth and plate thickness ratio. Therefore, this information along with the A0 reflection coefficient information facilitates more accurate defect sizing.
Lamb waves; reflection coefficients; defect depth characterization; Ultrasonic testing; thin plates.
Analysis of thin walled composite box beam with and without piezoelectric actuators using ABAQUS
Nowadays, thin walled structural members are highly preferred over solid structural members. Thin walled composite box beam is such structural member which is extensively used in many engineering applications. In the present study a smart thin walled composite box beam model is developed using ABAQUS. The width and the height of the thin walled box beam are varied along the length of the beam to study the effect of different tapering ratio. The effects of piezoelectric actuators on deflection and twist of composite thin walled box beam with different ply orientations, loading conditions and boundary conditions has been investigated. Further, the optimal position of the piezoelectric patch is obtained. A good agreement in results is observed with the available experimental results for thin walled box beam with and without piezoelectric actuators. The results obtained show that due to piezoelectric actuation both vertical deflection and twist can be reduced significantly.
Thin walled; composite box beam; piezoelectric; actuators; tapered.
Estimating conical indentation load by numerical slip-line field technique
The present work describes the numerical generation of the slip-line field due to micro-indentation of a rigid conical wedge to a semi-infinite block. The work mainly compares the two shapes viz. linear and parabolic of the free surface of piled up material around the wedge. Previous studies in this area considered the shapes of the free surface material to be the linear one, but experimental investigations revealed that the shapes of the free surface are not exactly linear, but parabolic one when the semi-apex angle of the wedge is greater than 45°. The comparison of forces required for indentation, generated slip line fields, velocities of flow of material is made for linear and parabolic free surface profiles. The generation of the parabolic free surface profile is also verified by finite element method.
Micro-indentation; slip line field; parabolic lip profile; numerical technique; FEM.
Comparative study of delamination behavior of multidirectional carbon epoxy laminate
Presence of delamination causes reduction in strength and stiffness of laminated composite structure and detrimental to the safety and stability of structures made of composite materials. Determination of the residual strength and stiffness with respect to a finite size of delamination would be helpful in assessment of structures fitness to usage whenever the defects are identified by non-destructive procedures. Experiments of in-plane compression testing of multidirectional laminate (150mm × 100mm × 4.4mm) with an artificial delamination (Ø30 and Ø40mm) at the center are carried out. For the purpose of reference, tests of an ideal laminate with identical ply sequence and without delamination are carried out. Each experiment is performed till failure measuring strains and displacements. Simulation of the experiment are carried out by finite element analysis using cohesive zone material model assuming bonded contact with bilinear material behavior. Simulation is carried out to establish cohesive zone material parameters for further usage in analyzing real structures for the structural integrity assessment when identified with defects and testing is not probable. Significant reduction in strength is observed due to the defect. It is observed that failure load and strain at failure are decreasing from ideal to larger defect size. Strain data comparison with FEA is carried out and % error is below 10% in the case of ideal laminate whereas it is above 20% for the cases of defective laminates.
Delamination; cohesive zone material model; energy release rate; FRP composites; double cantilever beam; end notched flexure; compression testing.
Static analysis of thin walled composite and sandwich box beam
The static analysis of thin-walled laminated composite and sandwich box beam is presented. The one dimensional finite element method is used to predict the axial, vertical displacements and twist angle of thin walled box beam. Different types of loading such as axial, eccentric vertical tip load, and eccentric uniformly distributed load are taken. The results obtained are in good agreement with that available in literature for uniform cross-section. Numerical examples with different loading conditions, laminate stacking sequence and boundary conditions are taken into consideration. The effects of taper ratio along with different stacking sequence on flexural-torsional behaviour are also studied. The results show that with decrease in taper ratio, axial, flexural-torsional response increases for individual stacking sequence, however axial, flexural-torsional response decreases by changing ply orientation. Effect of core thickness, different stacking sequence in face sheet along with different types of loading and boundary condition for sandwich box beam are also studied in this paper. The improvement in flexural-torsional response of thin walled box beam is also observed when CNT is reinforced in laminated composite as well as in sandwich composite.
Thin-walled; box beams; composite structure; sandwich structure; finite element method; flexural-torsional response.
Predictive modeling of rubber-oil toughened epoxy resin using FEM
In the present investigation, an Epoxy Resin (ER) was first modified by varying concentrations of a novel liquid Rubber-Oil (RO). RO modified epoxy (ROE) was cast into dogbone shaped samples and tensile test was conducted on them. The RO Es were machined to Three -Point Bending (3PB) specimens and subjected to fracture toughness test. Fractured surfaces subjected to Field Emission Scanning Electron Microscopy (FESEM) exhibited biphasic morphology with phase-separated RO particles distributed in epoxy domain. Predictive modeling of the RO Es was then carried out through FEM by considering a Representative Volume Element (RVE) assuming Body-Centered Cubic (BCC) distribution of RO particles in epoxy domain. Effect of rubber-oil volume fraction (RO VF) on effective properties of RO Es was studied through a novel elastic stiffness tensor based homogenization scheme coupled with the FE model. Results show that, the effective Young’s and shear moduli decrease with ROVF with subsequent increase in bulk modulus and Poisson’s ratio. When subjected to stress analysis, the FE model revealed that high triaxiality associated with crack tip favours the cavitation of RO particles. Both the von-Mises as well as the hydrostatic stresses were observed to be unique functions of RO particle bulk modulus. The predicted values of Young’s modulus as a function of RO VF were observed to be in good agreement with experimentally obtained values.
FEM; ANSYS; rubber toughened epoxy; phase separation; predictive modeling; rubber-oil.
Dynamic analysis of functionally graded curved sandwich panels
Dynamic response of functionally graded singly and doubly curved sandwich panels on the rectangular plan-form, subjected to uniformly distributed transverse loading is presented in this work. Higher order shear deformation theory (HSDT) with a cubic variation of in-plane displacement and constant transverse displacement is used for mathematical formulation. Equations of motion are derived using dynamic version of the principle of virtual work and subjected to small deformation. Fast converging finite double Chebyshev series is used for the spatial discretization and Houbolt time marching scheme is used for the temporal discretization. Three types of sandwich panels are analyzed: FGM face-sheets and homogenous ceramic core, FGM core and homogeneous ceramic face-sheets and face-sheets and core both FGM. The results are obtained for cylindrical, hyperboloid, spherical sandwich panels subjected to uniform step, triangular, sine, half sine and exponential loading.
Analytical solution; sandwich panel; HSDT; functionally graded material; Chebyshev polynomial; dynamic analysis.
Dynamic buckling of laminated composite rectangular plates subjected to uni-axial compression loads
In this paper, the non-linear dynamic buckling of laminated composite rectangular plates is studied using finite element method. The laminated composite plates are subjected to in-plane dynamic compressive loads. The non-linear dynamic equations are solved using Abaqus/Explicit. Volmir’s criterion is used to calculate the dynamic buckling loads. In order to observe the actual phenomenon, imperfections are incorporated in the plate. The results are validated using results from the available literature. The effect of ply orientation, loading function and imperfections on the non-linear dynamic buckling loads are studied. Non-linear dynamic buckling loads for rectangular pulse loads are found to be critical when compared to sinusoidal loading function.
Dynamic pulse buckling; laminated composite plate; in-plane pulse loads.
Analysis and characterisation of a cantilever energy harvester
Harvesting the energy from base vibration through a Piezo-electric Transducer (PZT) is an adaptable and an emerging technique in recent years. The power output of piezoelectric energy harvester can be improved by an appropriate configuration of its geometry and positioning of additional mass. This paper presents a numerical study on a cantilever energy harvester to quantify the energy harvested from vibration having a single frequency harmonic excitation and discusses the effect of base acceleration on the energy output for different beam widths and proof masses. It focusses on the numerical simulation procedure necessary to develop a deeper understanding on the performance of the harvester. The methodology adopted to finalise the geometry and the proof mass is explained. The configuration of the cantilever energy harvesting structure includes structural steel cantilever beam sandwiched between two PZT layers. The beam is subjected to harmonic excitation. The results suggest that the bimorph configuration produces more energy output when the ratio of length to width of beam is more with large proof mass, provided the induced stress in the piezoelectric material is within the permissible limits. The studies demonstrated that the finalised harvester can deliver a maximum of 880mW of power to a matched resistive load of 12kΩ, when exposed to a base acceleration of 30g at the resonant frequency of 77.5Hz.
Energy harvesting; vibration; cantilever beam; piezoelectric transducer; FEA.
Vibration control of a glass fiber reinforced plastic beam with shape memory alloys
Vibration control of structures using smart materials has been an important topic of research in recent years. Among them, piezo electric materials have been used prominently due to the absence of mobile parts and their characteristics of light weight, high force generation with less power consumption. In spite of these advantages, they require high excitation voltages to control displacements in micro inch range. Shape memory alloys represent an attractive alternative as they require relatively lesser voltages to generate displacements in the neighbourhood of an inch. This paper demonstrates the usage of Shape Memory Alloy actuators in controlling the flexural vibrations of a flexible beam. The beam is made of Glass Fibre Reinforced Plastic with attached shape memory alloy wires on its top and bottom surfaces. The transient response of the beam subjected to harmonic excitation (with and without control by SMA wires) is determined theoretically using finite element method. An experimental apparatus involving a computer controlled setup is used to experimentally determine the same characteristics of the beam when subjected to same excitation. The results obtained from both the approaches are compared and are used to demonstrate the potential of shape memory alloys in controlling the vibrations of flexible structures.
Shape memory alloy; nitinol; GFRP; tanaka’s model; vibration testing.
Free vibration analysis of stiffened lock gate structure coupled with fluid
Free vibration analysis of rectangular stiffened lock gate structure is investigated to analyse the effect of fluid on the gate structure. Mindlin’s plate and Euler’s beam theories are used to formulate the isotropic plate and the stiffener, respectively. The fluid is assumed to be incompressible and inviscid resulting in an irrotational flow field. The far boundary of the fluid domain is truncated near the lock gate structure. The truncation of far boundary of the fluid domain is made by considering the Fourier half range cosine series expansion of Laplace equation. The theoretical formulation of the coupled problem of fluid-structure interaction is derived and it is transformed into a computer program. Similar study has been found in open literature for the lower order elements with unstiffened plate. In the present study, nine noded isoparametric plate element, three noded isoparametric beam element and twenty-seven noded isoparametric brick element have been used to discretise the plate, stiffener and fluid domain, respectively. The results obtained are compared with the reported one, which indicates the acceptance of the developed computer codes. The natural frequencies of stiffened lock gate coupled with and without fluid are evaluated by varying the dimensions of lock gate, stiffener and fluid domain.
Free vibration analysis; stiffened lock gate; undisturbed free surface; fluid structure interaction; FEM.
Comparison of modal parameters of isotropic shell structures using beam and shell models considering slenderness ratio with various boundary conditions
Modal parameters namely frequency, mode shape and generalized mass are required to determine the forced response of structures using mode summation method. The structure may be thin shell element of aircraft, rocket, submarine, pipeline and pressure vessel. The initial estimates are generally carried out using Euler-Bernoulli (EB) beam theory or classical beam theory since it provides reasonable engineering solution to the slender beams only as it introduces significant error for the calculation of modal parameters for short beams and also for higher modes. The predictions are improved by using Timoshenko Beam (TB) model which is based on First Order Shear Deformation Theory (FSD T). The accurate prediction of model parameters for thin isotropic shells shall be carried out by using shell equations based on Flügge formulations and Finite Element Analysis (FEA). The objective of the present paper is to compare the modal parameters of the first three beam type modes (n = 1) of thin isotropic shells using both beam and shell models considering the slenderness ratio for various boundary conditions. The results shall be useful for the selection of suitable model for the estimation of modal parameters of beam type modes for shell structures. The errors in modal parameters predicted by EB beam theory for the general assumption of slender beam (L/D = 10) is also reported.
Slenderness ratio; modal parameters; frequency; mode shape; generalized mass; beam type modes.
Earthquake-response of open ground storey reinforced concrete building retrofitted with and without yield type X shaped metallic elasto-plastic damper
A three-storey half scale Reinforced Concrete (RC) building frame model, fitted with yielding type X-shaped metallic elasto-plastic damper at the ground floor level, is designed and fabricated to study its seismic response characteristics. Experimental studies are carried out using the 4m × 4m tri-axial shake-table facility to evaluate the seismic response of a retrofitted RC frame building with Open Ground Storey (OGS) structure using yielding type X-shaped metallic elasto-plastic dampers (also called as Added Damping and Stiffness-ADAS elements) and repairing ground storey columns using Geopolymer concrete composites. In general, earthquake loading introduces large displacements in an OGS structure, and under such large displacements, a yielding type elasto-plastic device made of X-shaped metallic dampers is expected to perform better. The supporting steel frame of ADAS element is of chevron type, serially contributing stiffness to the ADAS element. Free vibration tests on RC frame building without and with yielding type X-shaped metallic damper are carried out. The natural frequencies and mode shapes of model without and with yielding type X-shaped metallic elasto-plastic damper are obtained. The reinforced concrete building is subjected to earthquake excitations. Further, seismic responses of the structure with metallic damper are evaluated with different earthquake excitations.
Open ground storey building; earthquake time history; RC building and yielding type X-shaped elasto-plastic metallic damper.
Comparative studies between Indian Standard codes IS 802 (part 1/ sec 1):2015 and IS 802 (part 1/ sec 1):1995 used for overhead transmission line towers
Transmission line towers are steel lattice structures and were generally analyzed and designed as per Indian Standards code IS 802 (Part 1):1995. A revised code IS 802 (Part 1/ Sec 1):2015 is introduced recently for transmission line towers with modified load combinations and material input provisions. So far no attempts have been made to compare the previous code with the revised code in terms of design, analysis efficiency and economy. The present study is aimed to compare the loading, axial forces, deflection and weight of the tower using the analysis and design procedure of previous and revised codes. Two transmission line towers of same geometry were analyzed and designed using STAAD.Pro V8i software using provisions of previous and revised codes. The conclusions drawn from the comparison shows that the axial forces at critical points as per IS 802 (Part 1/ Sec 1):2015 design is 25 to 40 %, 15 to 25% and 18 to 30% for 132kV, 400kV and 765 kV respectively less than design based on IS 802 (Part 1/ Sec 1): 1995. The difference in total weight of the tower material as per IS 802-2015 design is 6.24%, 5.92% and 5.72% for 132kV, 400kV and 765 kV respectively lesser in comparison to IS 802:1995 lesser in comparison to IS 802 (Part 1/ Sec 1): 1995 design.
Transmission line tower; IS 802 (Part 1/ Sec 1):2015; IS 802 (Part 1/ Sec 1):1995; STAAD.Pro. V8i; axial forces; deflection; economy; efficiency.
Improved confinement model for reinforced concrete circular bridge columns under static flexural loading
This study presents an improved analytical approach for the analysis of Reinforced Concrete (RC) circular bridge columns by proposing a new confinement model under static loading. Three widely used confinement models are examined and improvements are suggested. It is well known that the stress-strain behaviour of confined concrete is completely different from that of plain concrete. The level of confinement depends on amount of transverse reinforcement, amount of longitudinal reinforcement and spacing of rebars and level of axial load. The influence of these parameters on the section and member level behaviour is analysed and an improved model is proposed for the analysis of RC circular bridge columns under flexure. Predictions of the analytical model are compared with the experimental data of columns tested by the author and others from PEER DATABASE over a range of parameters. The comparisons indicate a very good agreement of the predictions of the proposed model with the test data.
RC columns; flexure; confinement; axial compression; transverse reinforcement ratio; longitudinal reinforcement ratio.
Mechanical behaviour of pre-stressed railway sleepers using geopolymer concrete
Geopolymer concrete can be considered as a green building technology which serves as alternatives for cement and fine aggregate by using Alkaline Activator Solutions (AAS) Fly Ash (FA) Granulated Blast Furnace Slag (GGBS) and Copper Slag (CS) in Geopolymer Concrete (GC). The High Strength Geopolymer Concrete (HSGC) M60 grade concrete was designed and used for the casting of Broad Gauge Pre-tensioned Pre-Stressed Concrete (PSC) sleepers as per Indian Railway Standard Specifications. Pre-tensioning wires of standard High Tensile Strength wire (HTS) were used with a pre-tensioning force of 50kN. Compaction was achieved through table vibrators and steam curing was adopted as per the standard manufacturing process of Indian Railways. The cured concrete sleepers were tested in the lab by stimulating the actual load transfer condones in the field called Rail Seat Centre Bottom (RSCB). Moment of Resistance (MR) and Moment of Failure (MF) of the sleeper was determined for either sides of the sleeper for a loading up to 230kN (MR) and 370kN (MF) as per the standard static bending test procedure. The test results proved that the Geopolymer concrete sleeper has high yield load and high ultimate load.
Geopolymer concrete; fly ash; GGBS; copper slag; pre-tensioning; pre-stressed; railway sleepers.
Flexural behaviour of reinforced fly ash and paper sludge ash-based geopolymer concrete beams
The present study aims at investigations of the flexural behaviour of reinforced Fly Ash (FA) Based Geopolymer Concrete (GPC) and fly ash and Paper Sludge Ash (PSA) based geopolymer concrete beams (FA-PSA-GPC) with 10% replacement of FA by PSA. The beams were made of M35 grade concrete and cured under three curing conditions viz., Ambient Curing (AC), External Exposure Curing (EEC) and Oven Curing (OC) at 60°C. The beams were tested at 28ᵗʰ day by conducting two-point loading flexural test. Performance aspects such as Load Carrying Capacity (LCC), First Crack Load (FCL), load-deflection behaviour, and moment–curvature behaviour of both types of beams were studied. The load-deflection and moment–curvature behaviours of two types of beams observed from the experimental results under different curing conditions were compared and it was concluded that GPC can be produced using PSA with FA.
Geopolymer concrete; fly ash; paper sludge ash; load deflection; curing; sodium hydroxide.
Shape memory alloy based smart link for aircraft wing structure:FE modelling and experiments
This article emphasizes on the development of Shape Memory Alloy (SMA) based smart link for the flight control system. SMA are the candidate material for the actuation of smart structures due to its Shape Memory Effect (SME). In this paper, Nitinol® is used as an SMA which is of 55% Titanium and 45% Nickel. Nitinol® in spring form, proposed in the present paper actuates the aileron which is a primary flight control system through a smart link system. The aileron facilitates the rolling motion of an aircraft. Due to symmetry, this paper addresses the actuation of aileron in one wing. Both experiments and finite element modelling are carried out. The finite element modelling of a cylindrical portion of SMA was performed so as to numerically exhibit the SME. The finite element simulation of the aileron actuation was performed by incorporating the effect of SMA spring. The finite element analysis reveals that as the temperature exceeds the phase transformation temperature (Tp), the material regain its original shape. The finite element analysis of SME was computed using ANSYS® Mechanical APDL 17.2 environment while the aileron actuation was simulated in ANSYS® 16.0 Rigid Dynamics environment. The SMA spring are actuated by heating to its phase transformation temperature. Analytical calculations are also presented for the detection of current value to be supplied into the SMA spring. Experiments are conducted in a Glass Fabric Reinforced Plastic (GFRP) wing model and the actuation of smart link has been investigated.
Nitinol®; shape memory alloy; GFRP; shape memory effect; ANSYS®; aileron.
Study on geopolymer mortar using hydrogen peroxide as foaming agent
A new arising technology called geopolymer with zero percentage of cement has been developed in order to protect our environment from harmful CO₂ emission and further to save energy in the world for future use. Several drawbacks of ordinary portland cement such as low tensile strength, unstable crack propagation and low fracture resistance have been overcome by geopolymer. Further to make geopolymer as a good thermal insulating material with adequate strength, some foaming agents are added to the geopolymer mix. Foaming agents intend to develop pores inside the specimen to make it as lightweight. In this work, hydrogen peroxide is preferred as foaming agent which is added in diluted as well as undiluted form in the range of 0.3-1.8% at an interval of 0.3% so as to find the best specimen which has low density and thermal conductivity with adequate compressive strength. From the result, it was found that the geopolymer mortar cured at 80°C for 24 hours in hot air oven with 0.9% hydrogen peroxide in diluted form gives the best result with compressive strength and density of 4.641MPa and 1209kg/m³. It also gives low thermal conductivity of 0.141W/mK when compared to normal geopolymer mortar.
Geopolymer foam mortar; fly ash; sodium hydroxide; sodium silicate; foaming agent; apparent porosity; water absorption; thermal conductivity.
Experimental and finite element analysis of tubular conveyor gallery
A conveyor system is a continuous system for haulage of the bulk materials. It enables us to haul anything from corn to iron ore in a continuous flow from one end of the plant to the other, feeding and reclaiming material through the different stages of the process. The tubular conveyor galleries consist of a tube, shop fabricated using steel plates forged to the required radius and welded at the longitudinal and circumferential joint section in a staggered pattern. This paper presents details of the finite element analysis (FEA) carried out to understand the behaviour of the tubular conveyer gallery systems subjected to concentrated load due to conveyer supporting system subjected to biaxial bending. Studies carried out to obtain the optimum size of the openings that can be provided for lighting and ventilation without affecting the stability of the structure to withstand dynamic loads are explained. Details of experimental investigations carried out on the scaled down model of the tubular conveyor gallery to compare the results of FEA is also presented in this paper.
Tubular conveyor gallery; experimental investigations; finite element analysis; load-deflection pattern; stress-strain pattern.
Comparison of behaviour between rebar and stud shear connectors under monotonic loading
In composite beams, shear connectors are commonly used to transfer longitudinal shear forces across the steel–concrete interface. The shear connectors also prevent relative displacement of concrete and steel elements at their interface and ensure composite action of the beam. Presently, the stud is the most widely used shear connector in composite constructions. However, the rebar can be used as a shear connector according to various international codes considering the fact that it can be fabricated to the required shape along with the reinforcement cage in the slab. This paper presents an experimental study of the behaviour of rebar shear connectors embedded in composite beam under monotonic load. Two different (8mm and 10mm) diameter rebar connectors of four different forms such as open link, closed stirrups, circular and rectangular spiral were used as shear connectors. Modified push-out tests were conducted to assess the ultimate strength, elastic stiffness, load-slip characteristics and failure pattern of the rebar shear connectors and the same are compared with conventional stud shear connectors. Rebar shear connector with circular spiral shows higher ultimate strength and superior ductile behaviour compared to conventional stud shear connector.
Composite structures; push-out test; rebar shear connector; circular spiral rebar connectors; load-slip characteristics; shear resistance.
Parametric study on seismic behaviour of slab-column junctions in flat slab system subjected to punching shear
Uplift capacity of plate anchors: application to transmission poles
A brief review of current research on uplift or pull-out capacity of plate anchors buried in various types of soils is presented. The definitions of shallow and deep foundations are examined with reference to direct embedded transmission poles. Classical uplift capacity models for plate anchors are discussed. Both cohesion-less (sand) and cohesive (clay) soils are considered. Procedures for computing approximate uplift capacity of transmission poles with base shoes and practical challenges are discussed. Numerical applications involving wood and steel poles embedded in soft clay and loose sand are provided. Results indicate that simplified approaches appear to agree well with classical theory for both the wood and steel poles, though the difference is more noticeable in soft clay.
Base shoes; clay; deep foundations; plate anchors; circular; sand; shallow foundations; steel; transmission poles; uplif tcapacity; wood.
Adjustment factors for direct-embedded transmission pole foundations
Current guidelines for determining direct embedment depths for tangent transmission poles are evaluated. Embedment depths from approaches based on pole stability as well as lateral resistance are compared. Numerical embedment calculations are performed in three different types of soils – moist sand, submerged sand and saturated clay – using two specific computer programs, for moderate ground line reactions. Based on the results, nominal adjustment factors for industry typical embedment depths are proposed for the three soil types. Suggestions for future extensions of the approach are made.
Adjustment factors; clay; embedment; foundation; soil; sand; transmission poles.
An experimental study on cracking mode in reinforced concrete structures using acoustic emission testing
This article presents an experimental study on cracking mode in Reinforced Concrete (RC) structures using Acoustic Emission (AE) testing. After few years of construction, it is necessary to assess damage status in RC structures. For rehabilitation of the RC structures, it is required to know whether the cracking in RC structures is due to shear failure or tensile failure. In this study, two known methods namely “relaxation ratio analysis of AE signals” which is based on earthquake phenomena for damage assessment and “Gaussian mixture modeling of AE signals”- a probabilistic method for crack classification in RC beams were used. In these days, these methods were used independently. But in this present study an attempt is made to combine these two methods. This could be interesting for structural health monitoring of RC structures. The differences in AE characteristics during tensile and shear failure in RC structures were emphasized. Relaxation ratio analysis of AE is a useful method to assess damage of the existing RC structures in-situ.
Reinforced concrete; acoustic emission; damage assessment; cyclic loading; structural health monitoring..
Multivariate adaptive regression splines model to predict strength characteristics of high performance concrete
Numerous advanced computational tools have emerged for the modelling and analysis of nonlinear multivariate engineering problems. During the recent years, a number of statistical tools are developed to predict the properties of concrete in which artificial neural networks are shown to offer a promising solution for the nonlinear relationship between the variables. This study proposes a Multivariate Adaptive Regression Splines (MARS ) model to predict the compressive strength, split tensile strength and flexural strength of high performance concrete. This model employs cement, silica fume, natural sand and manufactured sand as an input variable and compressive strength, split tensile strength and flexural strength as an output variable. Three individual MARS models have been developed and trained with about 70% of the total 36 data sets and tested with about 30% of the total data sets. The predicted values of compressive strength, split tensile strength and flexural strength are in good agreement with experimental values. It is concluded that MARS model is more reliable and computationally efficient for the prediction of compressive strength, split tensile strength and flexural strength of high performance concrete.
Compressive strength; high performance concrete; manufactured sand; multivariate adaptive regression splines (MARS); split tensile strength and flexural strength.
A numerical investigation on postbuckling behavior of composite cantilever columns at elevated temperature
Seismic fragility curves for old reinforced concrete building
This paper discusses effect of ductile design and effect of loss of material strength due to age of construction on Probabilistic Seismic Demand Model (PSDM) of reinforced concrete (RC) frame. A three-storey three-bay moment resisting RC building situated in Mumbai which was designed to gravity loads and which lack in ductility provisions is taken for present study. This RC building is further modified by redesigning it to Indian seismic design code (IS1893-2002 Part I) and detailing as per IS13920-1993 Indian code to investigate variability in confinement of concrete in frame elements and hence ductility on the PSDM. Sixteen ground motion records are used to study the ground motion variability. Incremental dynamic analysis is performed on numerical model, and the maximum interstorey drift is obtained as a response parameter for all simulations. The PSDM parameters are calculated using regression analysis for old and modified building. The variation in the PSDM parameters is studied. Finally, the effects of ductile design and effect of loss of material strength due to age of construction on the seismic fragilities are discussed.
Confined and unconfined concrete; ductility; demand; capacity uncertainties.
Behavior of concrete beams reinforced with low ratio of flexural steel reinforcement
Properties of high strength concrete other than compressive strength may not enhance in parallel with the compressive strength improve, and such properties need to be assessed carefully before wide practical applications of such type of concrete. Among the important properties one can consider the flexural behavior of concrete beams reinforced with low amount of steel bars. In this paper flexural strength and deformation of concrete beams made from different grades of concrete strengths, reinforced with steel bars close to minimum steel ratio given by codes of practice, were studied. For this purpose six reinforced concrete beams were cast and tested. According to the obtained results any HSC beam reinforced with low amount of steel reinforcement close to the minimum steel ratio provided by ACI code behaves like normal concrete beams except that beam made from concrete with compressive strength equal to 90 MPa. Load capacity and ductility of this type of beam was found to be normal, but fracture of reinforcement was occurred after excessive deflection. Such behavior should be considered in the design of high strength concrete beams with low amount of steel reinforcement.
Concrete beam; compressive strength; ductility; minimum steel ratio; mode of failure.