Global ETD Search

1	INVESTIGATION OF RECTANGULAR CONCRETE COLUMNS REINFORCED OR PRESTRESSED WITH FIBER REINFORCED POLYMER (FRP) BARS OR TENDONS Choo, Ching Chiaw 01 January 2005 (has links) Fiber reinforced polymer (FRP) composites have been increasingly used inconcrete construction. This research focused on the behavior of concrete columnsreinforced with FRP bars, or prestressed with FRP tendons. The methodology was basedthe ultimate strength approach where stress and strain compatibility conditions andmaterial constitutive laws were applied.Axial strength-moment (P-M) interaction relations of reinforced or prestressedconcrete columns with FRP, a linearly-elastic material, were examined. The analyticalresults identified the possibility of premature compression and/or brittle-tension failureoccurring in FRP reinforced and prestressed concrete columns where sudden andexplosive type failures were expected. These failures were related to the rupture of FRPrebars or tendons in compression and/or in tension prior to concrete reaching its ultimatestrain and strength. The study also concluded that brittle-tension failure was more likelyto occur due to the low ultimate tensile strain of FRP bars or tendons as compared to steel.In addition, the failures were more prevalent when long term effects such as creep andshrinkage of concrete, and creep rupture of FRP were considered. Barring FRP failure,concrete columns reinforced with FRP, in some instances, gained significant momentresistance. As expected the strength interaction of slender steel or FRP reinforcedconcrete columns were dependent more on column length rather than material differencesbetween steel and FRP.Current ACI minimum reinforcement ratio for steel (pmin) reinforced concretecolumns may not be adequate for use in FRP reinforced concrete columns. Design aidswere developed in this study to determine the minimum reinforcement ratio (pf,min)required for rectangular reinforced concrete columns by averting brittle-tension failure toa failure controlled by concrete crushing which in nature was a less catastrophic and moregradual type failure. The proposed method using pf,min enabled the analysis of FRPreinforced concrete columns to be carried out in a manner similar to steel reinforcedconcrete columns since similar provisions in ACI 318 were consistently used indeveloping these aids. The design aids produced accurate estimates of pf,min. Whencreep and shrinkage effects of concrete were considered, conservative pf,min values wereobtained in order to preserve an adequate margin of safety due to their unpredictability.
2	Detaljstudie av tryckbrott i betongsliprar : Samband mellan tryckprovsresultat och val av dimensioneringsmetod / Detail study of compression failure in concrete sleepers : Correlation between pressure test results and choice of design method Bülow Angeling, Jenny, Wikell, Sebastian January 2016 (has links) En jämförelse av Abetongs beräkningsunderlag och statistik från tryckprov visar att sliprarna klarar mycket mer belastning än vad beräkningarna visar. I den här studien har en utvärdering av använda beräkningsmetoder gjorts, samt en jämförelse mellan olika dimensioneringsprinciper för att komma så nära resultaten vid tryckprov som möjligt. Beräkningar med förenklat tryckblock och idealiserad-rektangulär parabolisk arbetskurva visade att det senare alternativet gav ett något högre värde på sliprarnas momentkapacitet, men förändringen förklarade inte varför den verkliga momentkapaciteten är så mycket högre än den framräknade. Den faktor som enligt den här undersökningen påverkar betongens tryckhållfasthet och i sin tur ger en större momentkapacitet än vad tidigare beräkningar visar är förhindrad tvärutvidgning. Studien visar att hänsyn till förhindrad tvärutvidgning bör tas med i beräkningar på betongsliprars hållfasthet. Detta medför att det finns utrymme att minska betongklass på Abetongs slipermodell A26 från C58/70 till C50/60. / A comparison of the calculation data from Abetong and statistics from pressure tests shows that the sleepers can handle more load than the calculations show. In this study, an evaluation of used calculation methods has been made and a comparison between different principles of dimensioning to get as close to the result from the pressure tests as possible. Calculations with rectangular stress distribution and idealized parabola-rectangle diagram showed that the second alternative gave a bit higher value on the sleeper bending moment capacity, but the difference did not explain why the real bending moment capacity is so much higher than the calculated one. According to this study confined concrete gave a larger capacity than the previous calculations. With regards to that effect the compressive strength of the concrete almost doubled, which together with an increased critical strain gave a bending moment capacity very close the one obtained from the pressure tests. This study concludes that the confined concrete effect should be considered when calculating the concrete strength. This also means that there is a possibility to reduce the concrete strength of Abetong’s sleeper model A26 from C58/70 to C50/60. Concrete sleeper compression failure design method testing cross section dimension rectangular stress distribution idealized parabola-rectangle diagram confined concrete concrete strength pressure strength Betongsliper tryckbrott dimensionering provning tvärsnittsdimensionering förenklat tryckblock parabolisk-rektangulär arbetskurva tvärutvidgning betongklass tryckhållfasthet
3	Rehabilitation of Exterior RC Beam-Column Joints using Web-Bonded FRP Sheets Mahini, Seyed Saeid Unknown Date (has links) In a Reinforced Concrete (RC) building subjected to lateral loads such as earthquake and wind pressure, the beam to column joints constitute one of the critical regions, especially the exterior ones, and they must be designed and detailed to dissipate large amounts of energy without a significant loss of, strength, stiffness and ductility. This would be achieved when the beam-column joints are designed in such a way that the plastic hinges form at a distance away from the column face and the joint region remain elastic. In existing frames, an easy and practical way to implement this behaviour following the accepted design philosophy of the strong-column weak-beam concept is the use a Fibre Reinforced Plastic (FRP) retrofitting system. In the case of damaged buildings, this can be achieved through a FRP repairing system. In the experimental part of this study, seven scaled down exterior subassemblies were tested under monotonic or cyclic loads. All specimens were designed following the strong-column weak-beam principal. The three categories selected for this investigation included the FRP-repaired and FRP-retrofitted specimens under monotonic loads and FRP-retrofitted specimen under cyclic loads. All repairing/retrofitting was performed using a new technique called a web-bonded FRP system, which was developed for the first time in the current study. On the basis of test results, it was concluded that the FRP repairing/retrofitting system can restore/upgrade the integrity of the joint, keeping/upgrading its strength, stiffness and ductility, and shifting the plastic hinges from the column face toward the beam in such a way that the joint remains elastic. In the analytical part of this study, a closed-form solution was developed in order to predict the physical behaviour of the repaired/retrofitted specimens. Firstly, an analytical model was developed to calculate the ultimate moment capacity of the web-bonded FRP sections considering two failure modes, FRP rupture and tension failure, followed by an extended formulation for estimating the beam-tip displacement. Based on the analytical model and the extended formulation, failure mechanisms of the test specimens were implemented into a computer program to facilitate the calculations. All seven subassemblies were analysed using this program, and the results were found to be in good agreement with those obtained from experimental study. Design curves were also developed to be used by practicing engineers. In the numerical part of this study, all specimens were analysed by a nonlinear finite element method using ANSYS software. Numerical analysis was performed for three purposes: to calculate the first yield load of the specimens in order to manage the tests; to investigate the ability of the web-bonded FRP system to relocate the plastic hinge from the column face toward the beam; and to calibrate and confirm the results obtained from the experiments. It was concluded that numerical analysis using ANSYS could be considered as a practical tool in the design of the web-bonded FRP beam-column joints. Reinforced concrete Reinforcement Bar strong-column weak-beam principal Exterior Beam-Column Joints Core Small scale modelling Experimental Test set-up Control Plain specimen Rehabilitation Retrofitting retrofitted Repair Repaired Repairing Strengthening Controlling Relocating Plastic hinge Pre-cracking Cracking Crushing Post-cracking Crack Cracked Penetration Damaged Pre-cracked Web-Bonded Wrapping De-bonding Fibre Reinforced Plastic FRP Sheets Composite Confinement Monotonic loads Cyclic loading Loads Displacement control Load control Regime Phase Loading sequence Procedure Available ductility factor Curvature ductility factor Ultimate First yield Flexural yielding Strength Moment Stiffness Failure mechanism Modes Sudden Brittle failure Measured beam-tip displacement Deflection Numerical analysis ANSYS Solid65 Solid45 Link8 Non-linear Finite Element (FE) Convergence criteria Analytical Closed from FRP rupture tension failure Compression failure Minimum thickness Maximum thickness Compressive Tensile Steel Ratio Design charts Effective Moment of Inertia Compatibility Strain Stress

1

Page generated in 0.1296 seconds