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
Determination of the energy release rate function for an eccentrically notched center-loaded beam using elastic fracture analysis
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.
Linear elastic fracture mechanics; finite element analysis; non-planar cracking; mixed-mode fracture
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Strength and stiffness characteristics of self-drilling screw lap-joints
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.
Self-drilling screw; bearing and tilting; lap-joint; shear fracture and net-section failure.
Failure analysis of 3D sandwich beams under transverse shear
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, IS 456-2000 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.
Shear strength; shear ductility; serviceability; 3D sandwich panels.
Experimental investigation on structural behavior of micro and macro fibre reinforced concrete beams subjected to cyclic loading
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 100x150mm 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.
Micro and macro steel fibre; cyclic loading; toughness; ductility; stiffness degradation.
Experimental investigations of fatigue crack growth and behaviour on stainless steel elbows
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.
Fatigue; crack initiation; crack growth; SS elbow; leak before break; surface crack; healthy elbow.
Non-local theory of buckling of tapered nano columns under self weight and an axial tip load using matrix based Chebyshev spectral collocation (MBCSC)
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.
Carbon nano tubes; Euler Bernoulli column; buckling; Chebyshev polynomial; non-local theory; small scale effect.
State-of-the-art review on cold-formed steel channel sections under compression
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.
Cold-formed steel; experimental investigations; theoretical investigations; numerical investigations; analytical investigations.
Deflection analysis of a multistage hydraulic cylinder
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.
Hydraulic cylinder; deflection; buckling; conjugate beam; telescopic cylinder; finite element analysis.
Influence of longitudinal rebars and boundary elements on the performance of 3D sandwich walls in direct compression
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.
3d sandwich walls; longitudinal reinforcement; boundary elements; axial compression; slenderness ratio.
Estimation of spectral velocity at long periods for application in velocity dependant seismic energy management devices
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.
Spectral velocity; psudo spectral velocity; longer period; damping; seismic energy dissipation devices.
Studies on cold-formed steel battened box columns under axial compression
Details of experimental, theoretical and numerical investigations of pin-ended cold-formed steel battened box columns subjected to axial compression is presented in this paper. A finite element model was developed by using finite element analysis (FEA) software ABAQUS 6.10. It is proved that the results correlate well with the experimental results. Based on the limitation provided by AISI S100-2007, prequalified sections of single lipped channel sections are chosen for the study. Two different cross-sections of cold-formed steel lipped channel sections with different batten widths oriented to form a box section are chosen for this study. For these sections, spacing between the channels are formed such that Iᵧᵧ=2Iₓₓ. A parametric study, which involves the change in the slenderness ratio from 20 to 120, change in the batten width and in the number of battens is carried out for 44 columns. The theoretical analysis is based on the Direct Strength Method [DSM] and the results are compared with that of FEA. Based on the study, a design recommendation is proposed for DSM to find out the ultimate capacity of box battened columns.
Built-up columns; battened columns; cold-formed steel; direct strength method; finite element method.
Design of semi-rigid steel-concrete composite frames for seismic performance
In general practice, composite beams are designed with either simple connections or fully rigid moment connections due to lack of information on semi-rigid connections. But, semi-rigid composite connections will offer several advantages like strength, stiffness and economy to the system when compared to simple or moment connection. Although, several researchers have reported the advantages of semi-rigid frames, information for their optimal design is currently not available. In this study, 4, 8 and 12 storey composite plane frames in different seismic zones are designed and their capacity curve is compared with corresponding curves for rigid frames to study the limitations and economy of semi-rigid frames. It is shown that semi-rigid frames perform better in low to moderate seismic zones but may not be advantageous in severe seismic zones.
Steel-concrete composite construction; semi-rigid connections; seismic performance; pushover analysis.
Performance of glass fiber reinforced geopolymer concrete composites
Experimental studies on flexural behavior of self compacting hybrid steel fiber reinforced concrete beams
Self compacting concrete (SCC) is the special concrete which is a lead significant step towards effectiveness at building site. By addition of fiber to SCC it helps in improvement of performance of concrete structures. Self compacting fibers reinforce concrete (SCFRC) combines the benefits of SCC and fiber reinforced concrete (FRC). Fibers are used to enhance harden properties of concrete. Steel fibers plays an important role in arresting initial cracks and prolongs the failure than all other fiber. The objective of this study is to evaluate the fresh and harden properties SCFRC with and without fibers. Depending upon the aspect ratio steel fiber the flexural behavior varies, hence in this work two steel fiber with aspect ratio 50 and 60 with different combination ratio were used to test SCFRC beams. Beams were casted and tested under cyclic loading to study the ductile and energy dissipation of properties of beams. The effect of using steel fiber reinforced self compacting concrete (SFRSCC) in place of SCC was studied. The properties of ultimate strength, ductility, energy dissipation and stiffness were compared with different aspect ratio combination of steel fiber.
Hybrid fibers; reinforced; ultimate strength; ductility; energy dissipation.
Moment-rotation curves for semi-rigid top and seat angle connections
Beam-to-column connections are vital components whose behavior affects the overall structural response of moment resisting steel frames. During the frame analysis and design step, connections are assumed as pinned or rigid type, but it has been observed that in actual practice most of the connections fall under the semi-rigid category. Though the analysis procedures for semi-rigid connections are more tedious, the final design proves to be more economical. The top and seat angle connection which has been traditionally considered as a pinned connection for simplifying frame analysis, is found to exhibit semi-rigid behaviour. In the present paper, all-bolted top and seat angle connections are investigated in detail by finite element analysis. The effect of geometric parameters of the connection on the monotonic moment-rotation relationship is ascertained by parametric studies. Equations to generate the M-θ curve for connection using the three parameter power model is also developed for the bolted top and seat angle connection.
Semi-rigid; connection; finite element; parametric; three parameter power model.
Experimental investigation on high volume fly ash based autoclaved aerated concrete reinforced with synthetic fibers
Fly ash is being used as a cement replacement material in recent years. Studies on the recent past demonstrated that it can also be used as sand replacement material because of certain advantages like lower density, degree of permeability and manufacturing cost, better durability, Strength to Weight Ratio and Strength to Energy Ratio, than those of conventional river sand based cement concrete. An experimental study on mechanical properties of high volume fly ash based autoclaved aerated concrete (HVFAAC), reinforced with synthetic fibers was carried out in this research work. High volume fly ash was used instead of river sand with minimized cement content, in order to overcome environmental impact and cost related factors. Different types of fibers such as glass, nylon, polyester and polypropylene were incorporated to study their performance in HVFAAC. From the studies it was observed that the overall performance of 0.5% polyester and 1% polypropylene fibers in aerated concrete is found to be good when compared to that of glass and nylon fiber. High volume fly ash based fibrous autoclaved aerated concrete (HVFFAAC) reduces brittle fracture. It was also observed that the wastage of specimens, due to the formation of cracks arising during handling is also less when compared to that of conventional HVFAAC.
Autoclaved aerated concrete; light weight concrete; high volume fly ash; synthetic fibers; mechanical properties.
An experimental study on structural behaviour of reinforced cement concrete and pre-tensioned slab panels using high strength hybrid fiber self compacting concrete
An experimental program is carried out to evaluate the effect of hybrid fibers on the structural behavior of high strength hybrid fiber reinforced self-compacting concrete (HSHFSCC) slab panels. For the present experimental work, 1200mm x 1200mm and 100mm thick slab panel specimens were cast with addition of hybrid fibers (steel and glass fibers) and the high strength self-compacting concrete (HSSCC) mix developed by complete replacement of river sand with quartz sand and by using micro silica and quartz powder as mineral admixture. The hybrid fibers i.e., glass fibers and steel fibers are varied from 0% to 1.5% of weight of powder content in mix. The slab panels with HSSCC mixes for reinforced cement concrete slabs (RCCS) are designed as per IS: 456 (2000) and pre-tensioned slabs (PTS) are designed as per IS: 1343 (2012). The slab panels are tested under loading frame to obtain the load and deflection characteristics, first crack load, ultimate load and comparative analysis is made between RCCS and PTS panels using the obtained results for various HSSCC mixes. Addition of hybrid fibers enhanced the first crack load and post cracking behavior. A marginal improvement in the ultimate load carrying capacity is observed. It is observed that the load carrying capacity of slab panels with hybrid fibers (1.0% steel fibers + 0.75% glass fibers) showed improved load carrying capacity compared to all other slab panels.
Self compacting concrete; hybrid fibers (steel and glass fibers); reinforced cement concrete slabs; pre-tensioned slab panels; ultimate load.
Response of framed machine supporting structures using modified contribution factor
Framed machine foundations are used for installing heavy machineries such as turbo generators. In this study, the response of framed machine foundation is determined incorporating modified contribution factor (CFm‎). The proposed CFm accounts for the combined effect of dynamic magnification factor and contribution factor. The proposed method accounts for a wide range of modal frequencies in the response prediction. Unlike in the existing approaches, the necessity of considering wide range of modal frequencies is demonstrated in this paper.
Dynamics; machine foundation; framed foundation; mode participation factor.
Flexural behavior of lightweight precast concrete sandwich one-way slabs
Ten one-way prototype precast concrete sandwich panels are tested in this investigation to study the effect of variables such as panel thickness, grid size of wire mesh used as wythe reinforcement and presence of reinforced edge ribs and/or rebars in bottom wythe together with wire mesh on their failure mode, failure load, load-deflection behavior and load-strain behavior. Truss-shaped shear connectors made of wires are found to be effective until failure of the panels. Test results indicate that, presence of reinforced edge ribs and/or rebars in bottom wythe significantly affect the flexural behavior and cracking behavior, and are found to increase the flexural load carrying capacity of the panels. The behavior of concrete sandwich panels with edge ribs is found to be similar to conventional RC slabs. Test results also indicate that, reinforced edge ribs are required to preclude shear failure of the panels when rebars are present in bottom wythe of the panels. Cracking behavior such as crack spacing and number of cracks are found to be significantly affected by mesh size and volume ratio of tensile reinforcement in bottom wythe similar to ferrocement.
Composites; precast; insulated structural panel; one-way slabs; flexural behavior; EPS.
Linear response of pre-stressed concrete skewed box beam bridge girder using CFRP tendons
Hermite model based estimation of peak factors for tall buildings subjected to wind induced pressures
The peak factor for non-Gaussian fluctuating pressures occurring in the flow separated regions of a rectangular tall building has been evaluated based on three translation based Hermite methods, basic Hermite Model (HM), Revised Hermite Model (RHM) and Modified Hermite Model, with parameters evaluated from Yang (MHM-Yang). The evaluated peak factors have been compared with observed values from the data and other Hermite based models of peak factors available in literature. The relative performance of the models towards evaluation of peak factors, especially in the regions of flow separation have been assessed. It has been observed that use of data driven Hermite based models could provide a better and realistic estimate of peak factor, as compared to that offered by Gaussian framework.
Pressures; Gaussanity; peak factor; tall building; Hermite models; skewness; kurtosis.
Modal identification and damage detection in structures using non-linear and non-stationary vibration response
Vibration based method for Structural Health Monitoring (SHM) utilizes the dynamic response of a structure measured using a set of sensors to identify the modal properties and potential damage in the structure. Signal processing tools are widely used for analyzing these response signals. Change in the dynamic characteristics of a structure can provide an indication of damage. However, a direct comparison of the vibration signals at different periods of time may not be sufficient to identify the modal properties and the damages. Therefore, it is important to analyze the vibration signals to extract the modal properties and the morphologies of the changes in these response-signals and correlate them with the types, location and magnitude of structural damage. This present article presents a set of novel techniques for system identification and damage detection in structures based on their vibration signals. The modal parameters are estimated using Frequency Domain Decomposition (FDD) and the response signals are decomposed into intrinsic mode functions (IMF) using empirical mode decomposition (EMD) technique. Those IMFs are then processed with Hilbert-Huang transform (HHT) to obtain their corresponding Hilbert spectra, which allows the estimation of the time-varying instantaneous properties of those response signals. Then a marginal Hilbert spectrum (MHS)-based technique has been applied on the Hilbert spectrum coefficients to calculate associated Damage Indices (DI). The proposed method was tested using experimental tests conducted on a cantilever steel beam prototype at the CBRI laboratory, Roorkee, India, and a three-storey steel frame at Concordia University, Canada. Modal parameters were identified from system identification and the damage locations were determined by comparing the DIs of the damaged steel beam and frame with that of the corresponding baseline (undamaged) structures.
Structural health monitoring (SHM); damage detection; frequency domain decomposition (FDD); intrinsic mode functions (IMF); empirical mode decomposition (EMD); marginal hilbert spectrum (MHS); damage indices (DI).
A study on compressive strength and corrosion behaviour of reinforcing steel in chloride contaminated fly ash based geopolymer concrete
This paper investigates the effect of alkali concentration on compressive strength and corrosion behaviour of reinforcing steel in chloride contaminated geopolymer concrete (GPC) mixes. In this work, fly ash based GPC mixes were prepared with different concentrations of NaOH solution i.e. 8 M and 10 M. Chloride was admixed to GPC mixes at the time of preparation in the form of sodium chloride. Sodium chloride concentrations used were 0%, 1.5% and 3% by mass of geopolymer solids content. Cube specimens and prismatic reinforced concrete specimens were prepared from GPC mixes for determining 7-days compressive strength and corrosion parameters respectively. Potential measurement and corrosion current density by linear polarization resistance (LPR) measurement were carried out on prismatic reinforced concrete specimens at different testing ages. From the results, it is observed that the compressive strength of GPC specimens increased with increase in molarity of NaOH solution. The potential values of steel reinforcement in chloride contaminated GPC specimens were more negative than -270 mV (SCE) for both molarity of NaOH solution, indicating greater probability of occurrence of steel reinforcement corrosion. Further, the corrosion current density of steel reinforcement increased with increase in admixed sodium chloride concentration for both concentrations of NaOH solution. There was an increase in corrosion current density with increase in molarity of NaOH solution i.e. from 8 M to 10 M at all testing ages till 180 days.
Geopolymer concrete (GPC); fly ash; admixed chloride; alkaline solution; corrosion.
Nonlinear system identification using empirical slow flow model
Most of the existing SHM damage detection methodologies are based on the changes in the system parameters estimated by the linear model fitted to the structure. However, real-life structures exhibit nonlinearity even in their healthy state due to complex joints and interfaces etc. Nonlinear identification and damage detection is a very challenging inverse engineering problem. In this paper, we present a nonlinear system identification methodology using empirical slow flow model. This nonlinear system identification technique using empirical slow flow model requires only input-output measurement and need not know about the type of nonlinearity present in the system. Numerical simulation studies have been conducted on Duffing oscillator and a beam with breathing crack to demonstrate the effectiveness of the proposed algorithm.
Nonlinear system identification; slow flow model; Hilbert transform; breathing crack; Duffing oscillator; complexification-averaging; least square.
Performance of compliant liquid column damper for seismically excited structures
The Compliant Liquid Column Damper (CLCD) is a variation of the conventional Liquid Column Damper (LCD) that is applicable for the vibration control of relatively short period structures. Along with the long period structures short period structures are also highly vulnerable to the seismic excitation, as the frequency content of earthquake excitation is generally more broad-banded and richer in high frequency as compared to that of wind excitation. In the present study the equations of motion of the SDOF structural system with attached CLCD are formulated and a time domain parametric study with real earthquake input data is carried out. For a short period model structure the sensitivity of the design damper parameters are investigated and optimum values of the same are identified. Further, an experimental study on a base-excited stiff scaled structural model with CLCD is carried out for white noise and random loading. Identification of designed structural model followed by an experimental sensitivity study of the CLCD design parameters are presented. The optimal values of design parameters are identified and the performance of the optimally designed CLCD is examined for random base excitation. The efficacy of the CLCD for vibration mitigation of short period structures is thereby validated.
Compliant LCD; parametric study in time domain; earthquake; experimental study; random excitation.
Experimental estimation of time variant structural reliability via intelligent sampling
This paper presents a testing protocol developed using the idea of subset simulations, for estimating time variant reliability of dynamical systems subjected to random excitations. The developed testing protocol does not require any prior information about the mathematical model of the test structure, and hence, can be employed in a wide range of contexts. However, this protocol requires that, the metric, which is used in defining the performance function, should be measureable with the help of a set of suitable sensors. The subset simulation method is employed to sample the random excitations in such a way that the reliability estimation is carried out with reduced sampling variance and hence, with reduced test times. The main challenge in the study is to interface the code developed on the Matlab platform (which is used for sampling the random excitations) with the software controlling the actuators, so that the entire test can run in an uninterrupted manner. This method is shown to be well suited for treating linear and a class of nonlinear problems. Illustrative example consists of reliability estimation of an earthquake driven, two-story, geometrically nonlinear steel frame. This frame is tested on a reaction wall based system under excitations specified via random process models. A limited amount of direct ensemble testing is also performed to assess the results obtained using the experimental subset simulations.
Subset simulation; variance reduction; structural dynamic testing; time variant reliability; random excitations.
Dynamic hybrid simulation using an electromagnetic shaker
This paper discusses a controller design strategy for the dynamic hybrid simulation using an electromagnetic shaker. A two-storey shear building is adopted as the system whose response is emulated using hybrid simulation. The bottom storey is taken as the physical subsystem while the top storey is taken as the virtual subsystem. A control law is derived such that the mechanical impedance of the electromagnetic shaker matches to that of the virtual subsystem. The control law is validated by comparing the frequency responses of the virtual subsystem and the electromagnetic shaker from the physical subsystem acceleration to the force transferred. Finally, the experimental validation of the controller design strategy is carried out by the dynamic hybrid simulation of the two storey structure. The frequency response obtained from the experiment and emulated system are found to be in good agreement with each other.
hybrid simulation; controller; electromagnetic shaker; impedance; real-time; substructuring.
Adaptive metamodel based efficient robust design optimization of offshore structure under stochastic wave loading
The present study deals with Robust Design Optimization (RDO) of an offshore steel structure under stochastic wave loading considering parameter uncertainty. An adaptive Moving Least Squares Method (MLSM) based metamodeling strategy has been adopted in place of direct MCS to evade extensive computational time requirement. The optimization problem is formulated to minimize the weight of an offshore deck supporting structure under maximum lateral displacement constraint. The random wave load is modelled by two approaches i.e.1) a spectral representation method with stochastic weighted amplitude wave superposition technique and 2) a simplified approach considering uncertainty in load related parameters. The RDO is formulated by simultaneously optimizing the expected value and variance of the performance function. The robustness in constraint is ensured by adding suitable penalty term to attain a specified target reliability index. The results indicate that by compromising a small increment in structural weight designer can have robust and reliable design solution within affordable computational time by the proposed RDO approach.
Robust design optimization; offshore structure; parameter uncertainty; stochastic wave load; moving least squares method; response surface method.
Numerical and experimental simulation of liquefaction for scenario earthquake
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.
Liquefaction; experiment on shake table; numerical simulation; scenario earthquake.
Vibration control of structures and structural components with magnetorheological elastomers