Browsing by Subject "Prestress"
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Item Analysis of Short and Long Term Deformations in a Continuous Precast Prestressed Concrete Girder(2014-12-09) Sarremejane, TristanA precast prestressed concrete girder using in-span splices to extend the span length is constructed to investigate performance under service and ultimate load conditions. Continuity is provided through the splices by a combination of mild steel reinforcement plus post-tensioned prestress. The thesis focuses on the study of short and long term deformations in the test specimen between the time the pretensioned prestressed segments were first cast, through splicing, deck construction and curing, and then initial testing. To support these observations, three creep frames are set up and shrinkage readings are taken. Previous research is reviewed to determine what models should be used for the analysis of the experimental results. A time-dependent Matlab program based on AAASHTO recommendations is developed to predict the prestress losses due to the short and long-term deformations. Experimental observations from the test specimen are compared to those predictions. The predictions by most models available for assessing long-term deformations due to creep and shrinkage are overestimated when compared to the experimental observations. Unreliable predictions of prestress losses due to long-term deformations may have significant repercussions on a long-span structure; an over-estimation may lead to a design being too conservative, while an under-estimation may lead to cracking and thereby excessive deflections under service loading. It appears that the over-estimation is, in part, due to the girder units being constructed with self-consolidating concrete (SCC). It is concluded that improved estimates of deformations for such structures composed of SCC girders can be achieved if a correction factor of 0.6 is applied to the AASHTO recommendations.Item Effects of prestress on strains and deflections in pretensioned beams(2013-12) Koutrouvelis, Stergios; Tassoulas, John LambrosIn this research, nonlinear structural analysis along with finite element analysis were carried out for a pretensioned concrete beam at different levels of pretension in order to examine the effect of the change in the tendon force on the geometric stiffness of the beam. Several results were obtained for deflection, horizontal displacement and surface strains to investigate how they are affected by the level of pretension under the application of the same load in each case. These computations were compared with the tendon force to conclude whether they can be used to estimate the pretension level by means of simple measurements. The purpose was to develop a methodology for quantifying the prestress losses by taking advantage of the dependence of the prestressed concrete beam stiffness on the tendon force.Item Mechanics of prestressed and inhomogeneous bodies(Texas A&M University, 2006-10-30) Umakanthan, SaravananIn finite elasticity, while developing representation for stress, it is customary to require the reference configuration to be stress free. This study relaxes this requirement and develops representations for stress from a stressed reference configuration. Using the fact that the value of Cauchy stress in the current configuration is independent of the choice of the reference configuration, even though the formula used to compute it depends on the choice of the reference configuration, the sought representation is obtained. It is then assumed that there exists a piecewise smooth mapping between a configuration with prestresses and a configuration that is stress free, and the representation obtained above is used to study the mechanical response of prestressed bodies. The prestress fields are obtained by directly integrating the balance of linear momentum along with the traction free boundary condition. Then, different classes of boundary value problems for the type of inhomogeneous and prestressed bodies of interest are formulated and studied. For the cases studied, it is found that even the global measures like axial-load required to engender a given stretch ratio for a prestressed body vary from the homogeneous stress free bodies, though not significantly. The local measures - stress and deformation - in a prestressed body differ considerably from their homogeneous stress free counterparts. The above gained knowledge is applied to understand the mechanics of circumflex arteries obtained from normotensive and hypertensive micro-mini pigs. It is found that the deformation of these arteries when subjected to inflation and axial extension is not of the form r = r(R), ???? = ????, z = Z. Comparison is also made between the response of an artery at various levels of smooth muscle activation and stretch ratio as well as normotensive and hypertensive specimens, using statistical methods.