International Journal of Structural Engineering (12 papers in press)
Single Variable-based Unified Numerical Model for Plane Elastic Problems of Stress Analysis in Cartesian and Polar Coordinate Systems
by Abhishek Kumar Ghosh, Shaikh Reaz Ahmed, Partha Modak
Abstract: This paper presents a scalar potential function-based unified numerical model for stress analysis of plane elastic problems in Cartesian and Polar coordinate systems. The potential function is defined in terms of the components of displacement, which reduces the two-variable problem of stress analysis to a single-variable problem. The resulting mathematical formulations for the Cartesian and the polar coordinate systems differ significantly in terms of the derivatives and coefficients present in the corresponding differential equations. However, they are discretized in a fashion so that the obtained sets of difference equations differ in terms of coefficients only and, therefore, can be expressed as a single set of difference equations applicable to both the coordinate systems. Consequently, the resulting unified numerical model handles straight and curved geometries using Cartesian and polar coordinate systems, respectively, and thus avoids the interpolation-extrapolation related inaccuracies associated with the models based on a single coordinate system. The model is validated against the analytical solutions of both ends fixed straight beam under uniformly distributed normal loading in the Cartesian coordinate system and curved beam under pure bending moments in the polar coordinate system. Finally, the application of the model is demonstrated by analyzing the effects of the initial curvature on stresses and displacements in both ends fixed beams with and without intermediate supports.
Keywords: unified numerical model; stress analysis; plane problems of elasticity; finite-difference method; effect of curvature; both ends fixed beam; intermediate support.
Seismic performance of bridges with variable friction pendulum system
by V.R. Panchal, R.S. Jangid, Bhargav B. Shobhana
Abstract: In this paper, the effectiveness of a variable friction pendulum system (VFPS) is studied and compared with friction pendulum system (FPS) for the three span continuous deck bridge which is subjected to six different near-fault ground excitations and trigonometric cycloidal pulses. For studying seismic performance of the bridge, the piers and the deck are considered as flexible and rigid respectively. Newmarks iterative method was used to evaluate governing equations of motion assuming linear change of acceleration for relatively small-time step. Additionally, a detailed parametric study was carried out to study the seismic performance of isolated bridge with VFPS system. From the analyses carried out, it is established that the seismic response of the bridge under near-fault ground excitations is significantly reduced when equipped with VFPS. A good comparison has been done on the bridge system considered, to investigate the response of near-fault ground excitations with corresponding response due to trigonometric cycloidal pulses.
Keywords: variable friction pendulum system; VFPS; base isolation of bridges; friction pendulum system; FPS; near-fault motions; trigonometric cycloidal pulses; seismic performance of bridges.
Impact Resistance of Waste Tyre Rubber and Silica Fume based Concrete Mixes
by Satnam Singh, Gurpreet Kaur
Abstract: In this paper, the feasibility of using waste tyre rubber and silica fume based concrete mix is tested for designing non-structural applications that can bear a sudden impact of specified limit. The compressive strength and impact resistance is tested for 10 different concrete design mixes (as per Indian Standard Codes) in which coarse aggregates, fine aggregates and cement is replaced with varying proportions of chipper rubber (10%, 15%, 20%, 30%), crumbed rubber (10%, 20%, 30%) and silica fume (5%, 10%, 15%) respectively. The mechanism used for repeated-impact testing is manually designed using drop-weight method. The comparative analysis of compressive strength & impact resistive of proposed concrete mix is performed with conventional M20 grade concrete mix. It is observed that the compressive strength of waste tyre rubber and silica fume based concrete mixes is lower than the conventional (M20) concrete, while the impact resistance is higher.
Keywords: Compressive Strength; Impact Resistance; Impact Testing; Indian Standard Codes; Rubberized Concrete; Silica Fume.
A study on existing masonry heritage building to explosive-induced blast loading and its response
by S.M. Anas, Md. I. Ansari, Mehtab Alam
Abstract: In the present study, explicit dynamic analysis has been conducted to investigate the blast response of the masonry heritage building, located in the southern part of Asia, subjected to peak overpressures generated from the TNT charges at different standoff distances and locations. The explosive-induced blast wave pressure-time history has been modelled using the modified Friedlanders equation for different scaled distances. For safety and security purpose varying explosive charges have been concealed in this investigation. A sophisticated material model available in the ABAQUS/CAE program has been utilised to compute damage dissipation energy and distribution of damage for the considered locations of the varying explosive charges. The stress analysis results have been compared with the provisions of the Indian Standard Code of Practice for Structural Use of Unreinforced Masonry, IS 1905(1987). This study shall open a new vista for engineers and researchers working in the field of blast engineering.
Keywords: heritage masonry buildings; blast loading; finite element analysis; FEA; explicit solver; concrete damaged plasticity; CDP; stresses; damage; damage dissipation energy.
DAMAGE INTEGRITY ASSESSMENT FOR BEAMS USING STRUCTURAL HEALTH MONITORING TECHNIQUE
by VANAPALLI POORNIMA, VENKAT LUTE
Abstract: Structures get deteriorated as its service life increases. Structural health assessment of critical structure is one of the essential safety requirements. Three levels of structural health assessment are performed in this paper i.e., damage identification, localisation and quantification. Among all the computational tools available in civil engineering for damage detection, Artificial Neural Network (ANN) and Support Vector Machine (SVM) are aimed to detect damage in beams. Cantilever I and hollow beams are modelled using finite element software and modal parameters are extracted. An attempt is made to demonstrate that parameters such as mode shapes and frequency are adequate for detection of structural damage using three classical techniques namely Frequency based damage detection method (FBDD), Mode shape based damage detection method (MBDD), Mode shape curvature square (MSCS) damage detection techniques. Damage scenarios are created in the beam with various severities and locations along the beam. The modal parameters thus extracted from ANSYS for damaged beams are used as input for ANN and SVM algorithms for damage assessment. Thus, it is observed from the results that both the algorithms are reliable for damage detection of cantilever beam but ANN performed better than SVM
Keywords: Damage Assessment; Mode shape based assessment; Artificial Neural Network; Support Vector Machine.
Tensile stress limits for high strength concrete prestressed structures
by Fayez Moutassem, Mohammad I. Hossain
Abstract: High strength concrete (HSC) is regularly used in precast prestressed concrete structures. The allowable tensile stresses in various codes do not account for high early strength HSC exceeding 10,000 psi (69 MPa). In this study, design equations are developed for the tensile stress limits at the time of initial prestress and at service. An experimental program is developed and it involved the use of mineral admixtures and subjecting fresh concrete to 24 hours of accelerated heat curing to mimic actual field conditions. Comparison between various design codes (ACI 318, AASHTO, LRFD) has revealed that all the code equations significantly underestimated the allowable tensile stresses at service and are therefore too conservative. The proposed tensile stress limits would ensure a more economical design of high strength prestressed concrete members.
Keywords: concrete; high-strength; prestressed; precast; compression; flexure; allowable stresses; heat-curing; tensile limits.
Prediction of crack width and intermediate-crackdebonding strain of FRP bonded two-way RC slabs a comparative and novel approach
by G. Balamurugan, T.S. Viswanathan
Abstract: This paper presents the confirmation study for the suitability of existing models to forecast the maximum crack width (MCW) and intermitted-crack-debonding (ICD) strain of fibre-reinforced polymer (FRP) bonded two-way reinforced concrete (RC) slabs. The experimental results of MCW and ICD strain of FRP bonded two-way RC slabs compared with predicted values, which shows the higher coefficient of variation. This variation indicates that the additional factors need to consider to determine the MCW, and ICD strain of FRP bonded two-way RC slabs. Subsequently, the new prediction models proposed for MCW and ICD strain of FRP bonded two-way RC slabs based on the random forest (RF) classification algorithms and multiple linear regressions. The numerical factors revealed that the proposed RF and regression based-models are the finest to predict the MCW, and ICD strain of FRP bonded two-way RC slabs.
Keywords: two-way slabs; fibre-reinforced polymers; FRP; crack width; intermediate-crack-debonding strain; ICD strain; random forest; comparison.
Imperialist competitive algorithm approach to solve structural fuzzy random reliability
by Mohammad Haranji, Mehdi Yazdani
Abstract: In the presence of aleatory and epistemic uncertainties, the reliability index is a fuzzy number, instead of an ordinary (single-valued) one. A well-known approach to determine the fuzzy reliability is -cut. The fuzzy random variable is transformed into an interval random variable for each membership degree . In this method, the maximum and minimum of the reliability index corresponding to the membership degree must be obtained. The proposed fuzzy random reliability is more accurate in comparison with the classical reliability. This article applies a metaheuristic algorithm, imperialist competitive algorithm (ICA), to search the maximum and minimum of the reliability index. The obtained results using the proposed algorithm are compared with outputs of a genetic algorithm. Results show the high performance of the ICA in obtaining desirable solutions. Considering the method applied and the algorithm hybridised to obtain reliability index, this is a new issue in structural reliability.
Keywords: imperialist competitive algorithm; ICA; structural reliability; fuzzy reliability index; fuzzy sets; uncertainty.
Optimal residual subspace model for structural damage diagnosis: an approach independent of operational and environmental variations
by Kundan Kumar, Sumanshu Agarwal
Abstract: Several machine learning algorithms have been proposed to detect damage in civil structures that implicitly learn changes in dynamic characteristics of structures due to varying operational and environmental conditions. However, despite the intensive computational load, the methods were not able to completely mitigate the said variations. In contrast to that, here, we introduce a new methodology based on percentage of total variance (PTV) criterion for damage detection to overcome the influence of varying operational and environmental conditions on the vibration-based
damage sensitive features. Using PTV criterion, an optimal residual subspace (ORS) is modelled which is applied to Mahalanobis squared distance (MSD) and singular value decomposition (SVD)-based damage detection methods. Interestingly, we find that in comparison with similar machine learning-based damage detection approaches, the proposed approach outperforms in terms of false positive reduction and overall accuracy.
Keywords: structural health monitoring; damage detection; outlier detection; optimal residual space; percentage of total variance; PTV; eigenspace; Mahalanobis squared distance; MSD; singular value decomposition; SVD.
Prediction of axial capacity of octagonal concrete-filled steel tube columns considering confinement effect
by Nazar J. Abbas, Ammar A. Ali
Abstract: The present research presents both detailed and simplified formulae on the octagonal concrete-filled steel tube (CFST) columns to define the ultimate strength of this type of column. These formulae have been validated and proved to be accurate through comparisons with experimental tests and with other available methods proposed by other researchers. On the other hand, employing the new formula in the constitutive model of core concrete in the finite element analsis (FEA) has shown to be of adequate accuracy to predict the behaviour of octagonal CFST columns. The effects of variation in both concrete-steel strength ratio (f'c/fy)and depth-to-thickness of the tube (D/t) (D/t) were studied. It is found that by decreasing the depth-to-thickness ratio of steel tube (D/t) the confining pressure will be increased. Also, decreasing the ratio of compressive strength of concrete to yield strength of
steel (f'c/ fy)the confining pressure will be decreased.
Keywords: axial capacity; octagonal CFST; concrete-filled tube; confinement effect; composite columns; steel tube; concrete core; finite element; constitutive model; concrete-steel strength; FE modelling; column behaviour; nonlinear FEA.
Performance of simply supported concrete beams reinforced with high-strength polymer re-bars under blast-induced impulsive loading
by S.M. Anas, Mehtab Alam
Abstract: A finite element model is developed in ABAQUS/CAE to simulate the dynamic response of the reinforced concrete (RC) beam under close-in air-blast loading. The model is subjected to different blast pressures at different scaled distances in free air. The values of the blast pressure have been taken from the blast tests conducted on four RC beams of size 1,700 mm x 150 mm x 150 mm by the State Key Laboratory of Explosion Science and Technology (China). The finite element predictions and available test results, including maximum mid-span displacements and damage to the beams, are presented and contrasted. The validated ABAQUS/CAE model is used to investigate the behaviour of the beams with replacement of the mild steel re-bars by the polymer re-bars of equivalent tensile strength on both compression and tension sides of the beam under air-blast loading.
Keywords: reinforced concrete; beams; air-blast; explosion; fibre-reinforced polymer; FRP; re-bars; blast pressure; displacement; CDP model; damage; cracks.
Review of buckling restrained braces for earthquake resistant design of industrial structures in India
by Bhavinkumar S. Shah, Vijay R. Panchal
Abstract: India had already witnessed devastating earthquakes in past and may witness even higher intensity of earthquakes in the future. The industrial structures are highly irregular structures and hence they are more vulnerable to earthquakes. The earthquake resistant design related codal provisions are revised recently in India. The conventional structural systems of moment resisting frame and conventional brace are not the most efficient systems for earthquake resistant design. In this paper, buckling restrained braces (BRB) are reviewed for the industrial structures in India. In the study, heavy silo supporting structure is analysed using conventional braces and BRBs. Total six nos. of analytical models are generated and response reduction factor are evaluated using pushover analysis. BRB is not yet codified in the Indian Standards. For implementation of the system in the country, codification is required for standardisation. The more research is required to eliminate the full scale testing requirements of BRB.
Keywords: buckling restrained braces; earthquake resistant design; industrial structures in India; seismic design; earthquake engineering; response reduction factor; retrofitting; India.