1,721,142 research outputs found
Case-based Reasoning for Contractor Pre-qualification
No full textThe contractor prequalification process is characterised by the lack of an universally accepted system and appropriate quantitative and qualitative information. This has led to the development of a number of proprietary prequalification systems together with an over-reliance on human judgement for assessment in practice. To improve the reliability and objectiveness of decisions being made, prequalification needs to be carried out on a more rational basis. An emerging technology in artificial intelligence, namely case based reasoning (CBR), appears to have high potential to satisfy the specific characteristics of the prequalification domain. The aim of this paper is to demonstrate, through the development of a prototype system, the practicality and suitability of CBR approach for prequalification
Response of a buried tunnel to surface blast using different numerical techniques
No full textThis paper presents a comparative study on the response of a buried tunnel to surface blast using the arbitrary Lagrangian-Eulerian (ALE) and smooth particle hydrodynamics (SPH) techniques. Since explosive tests with real physical models are extremely risky and expensive, the results of a centrifuge test were used to validate the numerical techniques. The numerical study shows that the ALE predictions were faster and closer to the experimental results than those from the SPH simulations which over predicted the strains. The findings of this research demonstrate the superiority of the ALE modelling techniques for the present study. They also provide a comprehensive understanding of the preferred ALE modelling techniques which can be used to investigate the surface blast response of underground tunnels
Development of an Innovative Hybrid-Composite Floor System
No full textThis paper discusses the research carried out towards the development of a hybrid-composite floor plate systems (HCFPS) using polyurethane (PU), glass-fibre reinforced cement (GRC) and thin perforated steel laminate. HCFPS is configured in such a way where positive inherent properties of individual component materials are combined to offset any weakness and achieve the optimum performance. Finite Element modeling of HCFPS with ABAQUS 6.9-1, comparative studies of HCFPS with the steel deck composite system and experimental investigations which will be carried out are briefly described in the paper
Simplified nonlinear analysis: application to damper-braced structures
No full textThis paper investigates the design of new or existing structures equipped with hysteretic dissipation devices by using simplified nonlinear analysis based on the definition of the strength reduction factor. In this paper a plane reinforced concrete frame retrofitted by means of properly designed dissipative braces is analysed. In particular, two different conditions are considered: when the bare frame behaves elastically or inelastically. The bare frame and the strengthened frame are subjected to nonlinear static analysis in order to obtain the corresponding strength reduction factor. This simple study is repeated varying the brace mechanical properties in order to investigate the effects on the strength reduction factor. The N2 method is employed to propose a procedure to follow in order to perform strength and ductile checks of the braced system. Finally some hints are given with respect to the possibility of design with equivalent damping and stiffness, according to the American guidelines FEMA 273 and 274
A design procedure in state-space representation for seismic retrofit of existing buildings with viscous dampers
No full textThe present paper proposes a non-iterative design procedure for the design of the seismic retrofit of existing buildings with viscous dampers supported by elasticdeformable braces. For taking into account the brace-damper compliance, dampers are arranged together with the supporting brace in a viscous-elastic assembly that needs to be represented by the Maxwell visco-elastic model. The force deformation relationship of such dampers is described by a first-order differential equation. Herein, a symmetric system of equations for structures installed with Maxwell dampers has been developed by means of state-space representation. This new formulation, together with the control theory is used to select design parameters of both dampers and supporting braces to achieve the preselected target overall structural damping, once mass and stiffness properties of the bare structure are known. The procedure is applied for seismic retrofit of an existing moment resisting steel frame
Lateral impact response and parametric studies of axially loaded square concrete filled steel tube columns
No full textThis paper presents a numerical study on the response of axially loaded slender square concrete filled steel tube (CFST) columns under low velocity lateral impact loading. A finite element analysis (FEA) model was developed using the explicit dynamic nonlinear finite element code LS -DYNA in which the strain rate effects of both steel and concrete, contact between steel tube and concrete and confinement effect provided by the steel tube for the concrete were considered. The model also benefited from a relatively recent feature of LS-DYNA for applying a pre-loading in the explicit solver. The developed numerical model was verified for its accuracy and adequacy by comparing the results with experimental results available in the literature. The verified model was then employed to conduct a parametric study to investigate the influence of axial load level, impact location, support conditions, and slenderness ratio on the response of the CFST columns. A good agreement between the numerical and experimental results was achieved. The model could reasonably predict the impact load-deflection history and deformed shape of the column at the end of the impact event. The results of the parametric study showed that whilst impact location, axial load level and slenderness ratio can have a significant effect on the peak impact force, residual lateral deflection and maximum lateral deflection, the influence of support fixity is minimal. With an increase of axial load to up to a certain level, the peak force increases; however, a further increase in the axial load causes a decrease in the peak force. Both residual lateral deflection and maximum lateral deflection increase as axial load level increases. Shifting the impact location towards the supports increases the peak force and reduces both residual and maximum lateral deflections. A rise in slenderness ratio decreases the peak force and increases the residual and maximum lateral deflections
Finite element model updating of a highway bridge based on operational modal analysis
No full textThis paper deals with the dynamic identification and finite element model updating of Magaz bridge, located in Spain. It is a three span continuous bridge with composite steel-concrete cross section. Operational modal analysis was performed from ambient vibration data by the covariance driven stochastic subspace identification algorithm. A very accurate three-dimensional finite element model was built using SAP2000 assuming geometrical and mechanical properties from the original drawings. At the first step of the calibration process, a parametric study was performed to identify the most sensitive parameters affecting the finite element model-computed modal frequencies and mode shapes. The automated finite element model updating problem has then been formulated as an optimization problem. The uncertainty on some physical parameters has been adjusted through an iterative process that aims at minimizing the objective function, hence to solve a nonlinear least squares problem which has as its subject the residuals of the relative difference from the numerical and experimental eigenfrequencies and eigenvectors. The outcome of the optimization is a significantly improved finite element model with very good agreement in terms of frequencies and modal assurance criteria values on the first modes
Optimization of tuned mass dampers subject to non-stationary random excitation
No full textThis paper presents a stochastic approach for the optimum design of a single tuned mass damper (TMD) protecting a linear mechanical system. The optimum strategy is directed towards maximizing the effectiveness of the TMD in reducing the vibration level in the system to be protected. This performance is evaluated on the basis of the reduction of the root-mean-square displacement and acceleration of the main system. Several numerical analyses are carried out for assessing the influence of the system and the excitation characteristics of the optimum TMD. In particular, a comparison between the TMD optimum designs for a system excited by stationary and nonstationary filtered white noise is presented. Finally, the advantages of modelling the seismic excitation as non-stationary filtered white noise for the optimum TMD design are clearly stated
An Object-Oriented Framework for Programming Iterative Solution Algorithms
No full textAn object-oriented approach is used to develop classes and frameworks for the implementation of distributed iterative equation solution. The software is implemented using the .NET framework, and builds upon previous work by the author. Development of the framework for iterative solution makes good use of interfaces. The framework is used for three different solution scenarios (i) conjugate gradient iteration on a single matrix; (ii) conjugate gradient iteration when domain decomposition is used; and (iii) using the Schur complement approach. Moreover, the framework is used for both local and remote objects. The .NET framework makes it very straightforward to program distributed applications, and the object-oriented approach greatly facilitates the software development. The framework was used in a finite element program and the speed-up results are shown.</p
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