Browsing by Subject "Reinforced Concrete"
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Item Effect of confinement on shear dominated reinforced concrete elements(Texas A&M University, 2005-02-17) Powanusorn, SuraphongIt has been demonstrated that transverse reinforcement not only provides the strength and stiffness for reinforced concrete (RC) members through direct resistance to external force demands, but also helps confine the inner core concrete. The confinement effect can lead to improved overall structural performance by delaying the onset of concrete fracture and allowing more inelastic energy dissipation through an increase in both strength and deformability of RC members. The objective of this research was to evaluate the effect of confinement due to the transverse reinforcement on enhancing the shear performance of RC members. A new constitutive model of RC members was proposed by extending the Modified Compression Field Theory (MCFT) to incorporate the effect of confinement due to transverse reinforcement by adjusting the peak stress and peak strain of confined concrete in compression. The peak stress of confined concrete was determined from the five-parameter failure surface for concrete developed by Willam and Warnke (1974). The peak strain adjustment was carried out using a relationship proposed by Mander et al. (1988). The proposed analytical model was compared with results from an experimental program on sixteen RC bent caps with varied longitudinal and transverse reinforcement details. Two-dimensional Finite Element Modeling (FEM) using the proposed constitutive model was conducted to numerically simulate the RC bent cap response. Results showed that the proposed analytical model yielded good results on the prediction of the strength but significantly overestimated the post-cracking stiffness of the RC bent cap specimens. The results also indicated that the confinement effect led to enhanced overall performance by increasing both the strength and deformability of the RC bent caps. Two potential causes of the discrepancy in the underestimation of the RC bent cap deformations, namely the effects of concrete shrinkage and interfacial bond-slip between the concrete and main flexural reinforcement in the bent caps, were discussed. Parametric studies showed that the tension-stiffening in the proposed constitutive models to implicitly take into account the bond-slip between the concrete and main flexural reinforcement was the major cause of the overestimation of the post-cracking stiffness of RC bent caps. The explicit use of bond-link elements with modified local bond stress-slip laws to simulate the slip between the concrete and main flexural reinforcement led to good predictions of both strength and deformation.Item Effects from Alkali-Silica Reacton and Delayed Ettringite Formation on Reinforced Concrete Column Lap Splices(2012-07-16) Eck, MaryReinforced concrete bridge columns can deteriorate prematurely due to the alkali-silica reaction (ASR) and/or delayed ettringite formation (DEF), causing internal expansion and cracking on the surface of the concrete. The performance of the longitudinal reinforcement lap splice in deteriorated concrete columns is the focus in this research. This thesis presents the results from the deterioration of large-scale specimens constructed and placed in an environment susceptible to ASR/DEF deterioration, the experimental results from four-point and three-point structural load tests, and an analytical model based on bending theory characterizing the specimen behavior during the structural load tests. Fourteen large-scale specimens were constructed, placed in an environment to accelerate the ASR/DEF deterioration mechanisms, and instrumented both internally and externally to measure the internal concrete expansions, and surface expansions and crack widths. In addition, two control specimens were constructed and kept in a laboratory, preventing ASR/DEF deterioration. Post-tensioning was used to simulate axial load on a bridge column. Structural load tests were performed on eight specimens with no ASR/DEF damage to late stage ASR and minimal DEF damage. Comparing the specimen behaviors during the loading testing, it was found that the yield strength increased about 5-15%, and post-cracking stiffness up to first yielding of the deteriorated specimens was about 25-35% stiffer than the control specimens. The increased specimen strength and stiffness likely occurred from volumetric expansion due to ASR/DEF damage which engaged the reinforcement, further confining the concrete and causing a beneficial increase in the axial post-tensioning load. The analytical model matched the control specimens well and matched the non-control specimens when the axial load was increased.Item Structural Assessment of D-Regions Affected by Alkali-Silica Reaction/Delayed Ettringite Formation(2012-11-12) Liu, Shih-Hsiang 1979-A combined experimental and analytical program was conducted to investigate the effects of Alkali-Silica Reaction (ASR) and Delayed Ettringite Formation (DEF) on D-regions in reinforced concrete (RC) bridge bents. Four large-scale RC specimens, which represent cantilever and straddle bents in Texas bridges in each specimen, were constructed. The first specimen represented the unexposed control specimen, while the other three were conditioned in the field with supplemental watering to promote ASR/DEF and served as the exposed specimens. The control and two exposed specimens with various levels of ASR/DEF, after eight months and two years of field conditioning, were load tested to failure. The last specimen remains in field with additional exposure to promote ASR/DEF and will be load tested in future studies. The width and length of preload-induced cracks and developing cracks that initiated in the exposed specimens and grew over time, indicating concrete expansion due to ASR/DEF mechanisms, were measured. Petrographic analysis results of concrete cores extracted from the exposed specimens after their load testing confirmed the formation of ASR gel and minimum accumulation of ettringite. The structural testing results showed that the failure mechanism in all three tested specimens was due to a brittle shear failure in the beam-column joint. However, slightly greater stiffness, strength, and ductility were observed in the exposed specimens as a result of the activation of the reinforcing steel in the specimens due to the expansion of the concrete primarily from ASR, which effectively prestressed and confined the core concrete. Sectional analysis and Strut-and-Tie Modeling (STM) of the experimental specimens were applied. Three-dimensional nonlinear Finite Element Analyses (FEA) were also conducted to numerically simulate the overall structural performance, internal response, and out-of-plane behavior of the experimental specimens. The effects of varying constitutive relations of the concrete in tension on models of the specimens were compared with the measured experimental response. A method to mimic ASR/DEF effects on exposed specimens was proposed and incorporated into the FEA approach. As a result, forces that prestress and confine the core concrete were effectively applied through the reinforcing steel prior to subsequent structural loading. The three-dimensional FEA approach was able to simulate the out-of-plane behavior of the beam-column joint and the proposed method yielded comparable results with the measured overall and internal behavior of specimens.Item Ultimate Limit State Response of Reinforced Concrete Columns for Use in Performance-Based Analysis and Design(2010-10-12) Urmson, Christopher R.The design of reinforced concrete structures for extreme events requires accurate predictions of the ultimate rotational capacity of critical sections, which is dictated by the failure mechanisms of shear, hoop fracture, low-cycle fatigue and longitudinal bar buckling. The purpose of this research is to develop a model for the full compressive behavior of longitudinal steel including the effects of bar buckling. A computational algorithm is developed whereby experimental data can be rigorously modeled. An analytical model is developed from rational mechanics for modeling the complete compressive stress-strain behavior of steel including local buckling effects. The global buckling phenomenon is then investigated in which trends are established using a rigorous computational analysis, and a limit analysis is used to derive simplified design and analysis equations. The derived buckling models are incorporated into wellestablished sectional analysis routines to predict full member behavior, and the application of these routines is demonstrated via an incremental dynamic analysis of a ten-storey reinforced concrete building. The buckling models and the sectional analysis routine compare favorably with experimental data. Design recommendations and topics for further research are presented.