Browsing by Subject "Reinforced concrete columns"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item Assessment and strengthening of ASR and DEF affected concrete bridge columns(2009-08) Talley, Kimberly Grau; Breen, J. E. (John Edward), 1932-Alkali silica reaction (ASR) and delayed ettringite formation (DEF) are two causes of concrete deterioration. Both mechanisms cause expansion of concrete and thus extensive cracking. Most previous research on ASR and DEF focused on understanding the material science of the mechanisms. This dissertation adds to the smaller body of knowledge about ASR/DEF’s effect on the structural behavior of reinforced concrete columns. It compares the structural performance of ASR/DEF affected concrete columns to mechanically cracked columns, evaluates the relative performance of four different concrete repair methods for strengthening damaged columns, and describes how to model pre-existing cracks in the finite element program ATENA. Previous research on scaled columns used mechanically cracked concrete as an approximation of ASR/DEF cracking damage. These earlier column tests, by Kapitan, were compared to two columns affected by ASR/DEF. Due to a deficiency in original design of the actual columns modeled, all of these scaled column specimens failed in bearing during testing under biaxial bending. The ASR/DEF affected columns exhibited nearly identical performance (including bearing capacity) as Kapitan’s control specimen. Thus, with over one percent expansion due to ASR/DEF, there was no reduction in bearing capacity for these columns. Based on the bearing failure observed in these scaled column specimens, concrete repairs were designed to increase confinement of the column capital to address the bearing capacity deficiency. A series of bearing specimens was constructed, externally reinforced using four different strengthening schemes, and load tested. From this bearing specimen series, both an external post-tensioned repair and a concrete jacketing repair performed well beyond their designed capacities and are recommended for bearing zone confinement repair of similar ASR/DEF affected concrete columns. Further, this dissertation presents how Kapitan’s scaled column results were modeled using ATENA (a reinforced concrete finite element program). A technique for modeling the mechanical cracking was developed for ATENA. Once calibrated, a parametric study used the model to find that a 0.17-inch wide through-section crack in the scaled columnd (5/8 inches in the field) was the threshold that reduced capacity of the scaled column to the factored design load.Item Modeling the post shear failure behavior of reinforced concrete columns(2012-05) LeBorgne, Matthew Ronald; Ghannoum, Wassim M.; Wood, Sharon L.; Aggarwal, J K.; Bayrak, Oguzhan; Jirsa, James O.Numerous reinforced concrete buildings vulnerable to earthquake induced collapse have been constructed in seismic zones prior to the 1970s. A major contributor to building collapse is the loss of axial load carrying capacity in non-seismically detailed columns. Experimental investigations have shown that non-seismically detailed columns will only experience axial failure after shear failure and subsequent lateral shear strength degradation have occurred. Therefore, column shear failure and degrading behavior must be modeled accurately before axial collapse algorithms can be properly implemented. Furthermore, accurate modeling of the degrading lateral-load behavior of columns is needed if lateral load sharing between structural elements is to be assessed with reasonable accuracy during seismic analyses. A calibrated analytical model was developed that is capable of estimating the lateral strength degrading behavior of RC columns prone to shear failure. Existing analytical models poorly approximate nonlinear column behavior and require several nonphysical damage parameters to be defined. In contrast, the proposed calibrated model provides the engineering community with a valuable tool that only requires the input of column material and geometric properties to simulate column behavior up to loss of lateral strength. In developing the model, a database of RC columns was compiled. Parameters extracted from database column-tests were scrutinized for trends and regression models relating damage parameters to column physical properties and boundary conditions were produced. The regression models were implemented in the degrading analytical framework that was developed in this project. Two reinforced concrete columns exhibiting significant inelastic deformations prior to failing in shear were tested in support of the analytical work. A newly developed Vision System was used to track a grid of targets on the column face with a resolution of three-thousands of an inch. Surface column deformations were measured to further the understanding of the fundamental changes in column behavior that accompany shear and axial failure and validate the proposed analytical model. This research provides the engineering community with an analytical tool that can be used to perform nonlinear dynamic analysis of buildings that are at risk of collapse and help engineers improve retrofit techniques. Further insight into shear behavior attained through this project is an important step toward the development of better shear and axial degradation models for reinforced concrete columns.Item Non-linear modeling parameters for reinforced concrete columns with inadequate lap splices(2015-05) Al Aawar, Wiam; Ghannoum, Wassim M.; Clayton, PatriciaThe Structural Engineering Institute of the American Society of Civil Engineers (ASCE/SEI) publishes a Standard used across the United States and in many countries for Seismic Evaluation and Retrofit of Existing Buildings (ASCE/SEI 41-13). The Standard defines strength capacities of structural members, as well as deformation capacities through Modeling Parameters. The objective of this project was to collect and analyze needed data for updating the existing provisions in the Standard for concrete columns governed by splice failure. A database of 51 tests on columns with lap-spliced longitudinal reinforcement was assembled. Strength and deformation capacities were extracted from the test data and used to evaluate the splice failure triggers of ASCE/SEI 41-13. Deformation capacities of columns sustaining splice failures were extracted as nonlinear Modeling Parameters. The parameters were observed to increase with an increase in transverse reinforcement ratio. Additional trends between Modeling Parameters and various influential factors were also investigated and discussed.