2015
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FINITE ELEMENT ANALYSIS USING MIXED FORCEDISPLACEMENT METHOD VIA SINGULAR VALUE DECOMPOSITION
2
2
The present approach is a combination of the force method and displacement approachto achieve the analysis using the substructuring technique. In this method, the inverse of thestiffness matrices of the substructures are constructed for the formation of the flexibility matrices.This part of the solution is equivalent to the stiffness approach. In the subsequent stage, the resultsof the analysis are assembled using the singular value decomposition (SVD) and the solution forthe entire structure is obtained. In fact, for assembling the structure, we need the flexibilitymatrices of the substructures which are obtained by the stiffness method.In this paper, a mixed forcedisplacement method is applied to finite element models forincreasing the speed of their solution. Each substructure is analyzed independently by singularvalue decomposition of the corresponding equilibrium matrix. Methods are then utilized fortransforming the substructures into regular forms whenever it is possible. The application of thismethod in finite element models with different substructures improves the process of analysis, andmakes the use of the existing solution techniques possible for regular systems.
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1
19
Mixed forcedisplacement method
substructuring
singular value decomposition of equilibrium matrix
regular forms
finite element analysis
OPTIMUM PARAMETERS OF TUNED MASS DAMPERS FOR SEISMIC APPLICATIONS USING CHARGED SYSTEM SEARCH
2
2
In this paper, optimum parameters of Tuned Mass Dampers (TMD) are determinedto minimize the dynamic response of multistory building systems under seismic excitations.Charged System Search (CSS), as an efficient optimization algorithm, is revised and applied fortuning passive mass dampers. A MATLAB program is developed for numerical optimization andtime domain simulation. Optimization criteria are the peak values of the first story displacementwith and without TMD, and the transfer function from input ground acceleration to the first storyacceleration response. An alternative formulation is also presented for solving state spaceequations. Compared to other populationbased metaheuristics, the charged system search has anumber of advantages distinguishing this algorithm from the others. However, for improvingexploitation (the fine search around a local optimum), it is hybridized with HS that utilizes chargedmemory (CM) to speed up its convergence. To ensure good performance of this approach, somenumerical considerations are conducted to verify the effectiveness and feasibility of the presentedapproach.
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21
40
Tuned mass damper
charged system search
structural control
state space equations of motion
PERFORMANCE OF RC BEAMS STRENGTHENED FOR SHEAR AND FLEXURE USING DIFFERENT SCHEMES OF USHAPED CFRP ANCHORAGES AND/OR STRIPS
2
2
Deficiencies of RC structures can be overcome by strengthening/retrofitting usingdifferent strengthening methodologies. This paper emphasises the effectiveness of externallyapplied Ushaped CFRP anchorages/strips on the performance of RC beams of relatively lowcompressive strengths (approximately 21 MPa). Three types of the beams were cast based on theshear reinforcement detailed as containing “no shear reinforcement”, “minimum shearreinforcement” and “adequate shear reinforcements” as suggested in ACI 31808. All beams wereprovided adequate flexural reinforcement as recommended by ACI 318 to fail the beams inflexure. Ushaped CFRP anchorages and strips were bonded to the beams in the predominant shearand flexural loading regions and tested under fourpoint bending condition by varying shear spantodepth ratio (a/d) as 2.46 and 3.38. Different strengthening schemes (including CFRP anchoragealone and in combination with CFRP strips) as well as the effect of Ushaped CFRP anchoragesapplied over full and partial applied beam depth was also the parameter of investigation in thecurrent study. Results showed that externally bonded Ushaped anchorages applied along the beamspan and at the ends together with CFRP strips improved the deformability, strength andperformance of RC beams by transforming failure manner from brittle to ductile. Moreover, use ofpartial depth anchorage is beneficial to attain higher load in comparison to the full depthanchorages, particularly anchorage height equal to 3/4 of the beam depth is found to be mostsuitable.
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41
51
Carbon fibre reinforced polymer
Reinforced concrete beams
Shear span to depth ratio
SHEAR STRENGTH OF REINFORCED CONCRETE BEAMS–RELATIONAL DATA BASE
2
2
Shear capacity of concrete (Vc) in reinforced concrete members depends on a numberof influencing parameters including compressive strength of concrete (ƒ), ratio of tensionreinforcement (), shear span to depth ratio (), size effect or depth factor (ξ), size of the aggregatein relation to the minimum size of the member (aggregate interlock aspects). Over the last severaldecades, researchers have tested reinforced concrete beams (without web reinforcement) to studythese parameters over a range limited by the breadth and depth of their experimental investigationsand, on the basis of their experimental results, proposed empirical equations for predicting theshear capacity of concrete in reinforced concrete beams.In this paper a relational database using ACCESS software is developed. The databasecontains experimental results of 2145 shear critical reinforced concrete beams without webreinforcement.Using the ACCESS shear database developed in this study, an evaluation was conducted toassess the predictive accuracy of shear design equation of Euro Code EC2. The results indicatethat the Euro Code EC2 design equations are found to be adequately conservative to predict theshear capacity of reinforced concrete beams over the range of variables considered in this study.
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53
63
Shear strength
concrete compressive strength
shear span to depth ratio empirical equations
database
EVALUATING TOPOLOGY DESIGN OF MATERIAL LAYOUT IN STEEL PLATE STRUCTURES WITH HIGH STIFFNESS AND EIGENFREQUENCY
2
2
This study presents optimal distributions of steel materials in steel thin plate structuresdetermined by using a classical elementwise and the present nodewise topology optimizationdesign methods for a dynamic problem. More specifically, the present article describes anapplication of a nodewise topology optimization technique to the problem of maximizingfundamental frequency for plane structure. The terms elementand nodewise indicate the use ofelement and node densities, respectively, as design parameters on a given design space. For adynamic free vibration problem, the objective function in general is to achieve maximumeigenfrequency with firstorder eigenmode subject to a given limited material, since structureswith a high fundamental frequency have a tendency to be reasonably stiff. For both static anddynamic problems SIMP (Solid Isotropic Microstructure with Penalization for IntermediateDensity) material artificially penalizing the relation between density and stiffness is used in thisstudy, and an implemented optimization technique is the method of moving asymptotes usuallyused for topology optimization. Numerical applications topologically maximizing the firstordereigenfrequency and depending on element or node densities as design parameters and variedboundary conditions to verify the present optimization design method provide appropriatemanufacturing information for optimally formfinding of steel materials with Poisson’s ratio of 0.3into thin plates.
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65
79
Topology optimization
material layout
stiffness
eigenfrequency
plate
SIMP
DETERMINATION OF MODAL DAMPING RATIOS FOR NONCLASSICALLY DAMPED REHABILITATED STEEL STRUCTURES
2
2
There are many reasons for rehabilitation of existing buildings. Adding stories is one ofthe most common reasons. When a steel building is retrofitted by concrete jacketing for addingstories, this system contains several structural systems. These systems are composite concrete andsteel systems in initial stories, welded steel system in middle stories and coldformed steel framesin upper stories. Dynamic analysis of hybrid structures is usually a complex procedure due tovarious dynamic characteristics of each part, i.e. stiffness, mass and especially damping.Availability of different damping factors causes a higher degree of complication for evaluatingseismic responses of hybrid systems. Due to using several structural systems, an existing buildingis changed to hybrid system. Damping matrix of these structures is nonclassical. Also, thenonlinear software is not able to analyze these structures precisely. In this study, a method andgraphs have been proposed to determine the equivalent modal damping ratios for rehabilitatedexisting steel buildings for adding stories.
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81
92
Hybrid buildings
damping ratio
rehabilitation
nonclassical damping
nonlinear analysis
STRENGTH AND FRACTURE PROPERTIES OF HYBRID FIBRE REINFORCED CONCRETE
2
2
This paper investigated the shear, impact and fracture strengths of highstrengthconcrete reinforced with two different industrial waste fibres. Locally available steel lathe wasteand nylon waste were used at different volume fractions as fibre cocktails in concrete. Steel lathewastes were used asreceived lengths and nylon fibres were chopped into 40 mm lengths in thisinvestigation. In total, 12 hybrid mixes were casted and tested at four different volume fractions(0.5%, 1.0%, 1.5% and 2.0%). The experimental programme was used the slump test and the aircontent test on the fresh concrete. The hardened concrete was tested for its shear and impactstrength. A flexural test on notched beams under threepoint bending was also carried outaccording to the RILEM 50FMC committee recommendations. Load vs. midspan deflection andload vs. crack mouth opening displacement were obtained and the fracture energy was evaluated.The best performance was obtained in hybrid which was enhanced due to the hybrid nature of thefibre cocktails of all the mixes, 2% volume fraction with a combination of steel ½ + nylon ½ fibresgives the best performance. The steel lathe waste fibres mainly contributed to limiting the crackinitiation and lightweight nonmetallic nylon fibres restricted the crack propagation. The combinedadvantages of these fibres provide high mechanical and fracture strength. Hence this hybrid fibrereinforced concrete with industrial waste fibres is doubly advantageous as it provides a superiorperformance without increasing the cost of the concrete.
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93
102
Fibre reinforcement
highstrength concrete
mechanical properties
fracture energy
industrial waste
SEISMIC PERFORMANCE OF RC FRAMES RETROFITTED BY FRP AT JOINTS USING A FLANGEBONDED SCHEME
2
2
A new, FRP flangebonded scheme, with practical application to 3D RC frames andwith the aim of relocating plastic hinges away from the joints is presented and its performance iscompared with that of the webbonded scheme. For this purpose, nonlinear pushover analyses ofdetailed Finite Element (FE) models of retrofitted joints of a benchmark RC frame are carried out.The optimal thicknesses of the Fibre Reinforced Polymer (FRP) sheets for relocating the plastichinges are first determined. The momentrotation curves of the joints are then utilised to create arepresenting model for the RC frame. Further, nonlinear pushover analyses are carried out on theretrofitted and the original frame to evaluate their capacity curves and seismic performanceparameters such as ductility, behaviour factor and performance points in relation to a specifieddemand earthquake. The results are then compared with those of the same frame when retrofittedwith the webbonded scheme as well as with steel bracing. Results point to the marked superiorityof the flangebonded scheme compared to the webbonded scheme in different aspects including,capacity, ductility and the performance level and cost. The performance of the FRP flangebondedscheme also compares well with that of the steel bracing method.
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103
123
Seismic retrofitting
RC frames
FRP
joint
nonlinear static (pushover) analysis
performance level
webbonded
flangebonded
steel bracing
A COMPARATIVE NUMERICAL STUDY OF A GEOSYNTHETICREINFORCED SOIL WALL USING THREE DIFFERENT CONSTITUTIVE SOIL MODELS
2
2
In this paper, three different soil constitutive models for granular soils wereimplemented in the numerical simulation of a fullscale reinforced soil segmental wall in order topredict the wall response during construction. The soil constitutive models in the order ofcomplexity are: linear elasticperfectly plastic MohrCoulomb, DuncanChang hyperbolic, and anonlinear elasticplastic hardening model. The latter, which can be regarded as a modified versionof the MohrCoulomb model, captures the nonlinear stressdependent soil response. The nonlinearmodel can consider soil dilative behavior. In this regard, it keeps the simplicity in the formulationtogether with the accuracy in the prediction of soil response. By comparing the results, in general,there is good and acceptable accordance between numerical simulations and field measurements. Itis seen that using a simple soil model can acceptably predict the performance of reinforced walls.However, the disadvantage relates to poorness in the prediction of wall facing displacement, whichis sensitive to proper consideration of deformation parameters in a soil model. The accuracy of theprediction can be augmented by adopting reasonable functions for elastic (stiffness) and plastic(dilatancy) parameters with respect to the stress condition within the soil backfill.
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125
141
Soil constitutive models
reinforced soil wall
response prediction
numerical analysis
geosynthetic reinforcements
soil dilatancy
PREDICTION OF SOILWATER CHARACTERISTIC CURVE USING GENE EXPRESSION PROGRAMMING
2
2
Soil–Water Characteristic Curve (SWCC) is one of the most important parts of anymodel that describes unsaturated soil behavior as it explains the variation of soil suction withchanges in water content. In this research, Gene Expression Programming (GEP) is employed asan artificial intelligence method for modelling of this curve. The principal advantage of the GEPapproach is its ability to generate powerful predictive equations without any prior assumption onthe possible form of the functional relationship. GEP can operate on large quantities of data inorder to capture nonlinear and complex relationships between variables of the system. The selectedinputs for modelling are the initial void ratio, initial gravimetric water content, logarithm ofsuction normalized with respect to atmospheric air pressure, clay content, and silt content. Themodel output is the gravimetric water content corresponding to the assigned input suction.Sensitivity and parametric analyses are conducted to verify the results. It is also shown that claycontent is the most influential parameter in the soil–water characteristic curve. The resultsillustrate that the advantages of the proposed approach are highlighted.
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143
165
Unsaturated soil
soil–water characteristic curve
artificial intelligence
gene expression programming
ANALYTICAL SOLUTION FOR CALCULATION OF BEARING CAPACITY OF SHALLOW FOUNDATIONS ON GEOGRIDREINFORCED SAND SLOPE
2
2
The bearing capacity of foundations resting on slopes is commonly calculated usingempirical equations. In recent years, it has been demonstrated that geosynthetic reinforced soil canenhance the foundation bearing capacity. In this paper, an analytical method for determination ofthe ultimate bearing capacity of surface strip footing on a sand slope reinforced with geogrid layersis presented. The angle of the slope with the horizontal direction is varied within 20o to 40o. In thisstudy, the Coulombtype lateral earth pressure theory has been used to compute the foundationbearing capacity. It is assumed that geogrid layers act such that the active earth pressures arereduced. The results obtained from the proposed method are compared with experimental andnumerical results. Parametric studies have also been performed to show the effects of contributingparameters such as number of geogrid layers, locations of reinforcement layers, soil properties andthe slope angle on the bearing capacity of strip foundations resting on the reinforced sand. Theresults indicate that the magnitude of bearing capacity of strip footings on the sand slope can besignificantly increased by using geogrid layers.
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167
182
Geogridreinforced slope
strip footing
Bearing capacity
shallow foundation
THE PROPERTIES OF SCALE EFFECT ON THE DENSITY OF ROCKFILL MATERIALS BASED ON FRACTAL THEORY
2
2
To study the scale effect on the density of rockfill materials, the relative density testswere carried out by physical tests and numerical tests. Fractal theory was drawn into the grading ofrockfill materials. Then, the fractal properties of scale effect on the density were studied byphysical tests and numerical tests. There are close relations between fractal dimension D anddensities of rockfill materials. The densities are largest when D is the critical value Dc. Further, Dcis independent of the relative density Dr and the maximum diameter dmax. Truncation error is oneof the main factors of scale effect of densities of rockfill materials. The existing four scale methodsin the standard can all be explained with fractal theory, and a unified formula was suggested. Theachievements in the paper lay a good foundation for further studying scale effect of rockfillmaterials with fractal theory.
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183
200
Scale effect
density
rockfill material
fractal theory
PFC2D (Particle Flow Code in 2 dimension)