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Author: Qian Li (Writer on transportation) Publisher: ISBN: Category : Columns, Concrete Languages : en Pages : 11
Book Description
During earthquake excitations, reinforced concrete bridge columns can be subjected to a combination of axial load, shear force, flexural moments, and torsional moments. The torsional moment can be much more significant in columns of bridges that are skewed, curved, have unequal spans, or unequal column heights. Combined loading including torsion can result in complex flexural and shear failure of these bridge columns. This paper presents an experimental study on the seismic behavior of square reinforced concrete columns under combined cyclic flexural and torsional moments. The columns in this study were designed with an aspect ratio of six and tested under various loading conditions: cyclic flexural moment and shear force, cyclic pure torsion, and combined cyclic shear force, bending, and torsional moments. Test results reveal that (1) the flexural and torsional capacity is decreased due to the effect of combined loading, (2) the failure modes and deformation characteristics are changed, and (3) the damage zone tends to move upwards from the typical flexural plastic hinge zone due to the effect of additional torsional moment. The effects of combined loading on the hysteretic loading-displacement response, and damage characteristics are discussed.
Author: Qian Li (Writer on transportation) Publisher: ISBN: Category : Columns, Concrete Languages : en Pages : 11
Book Description
During earthquake excitations, reinforced concrete bridge columns can be subjected to a combination of axial load, shear force, flexural moments, and torsional moments. The torsional moment can be much more significant in columns of bridges that are skewed, curved, have unequal spans, or unequal column heights. Combined loading including torsion can result in complex flexural and shear failure of these bridge columns. This paper presents an experimental study on the seismic behavior of square reinforced concrete columns under combined cyclic flexural and torsional moments. The columns in this study were designed with an aspect ratio of six and tested under various loading conditions: cyclic flexural moment and shear force, cyclic pure torsion, and combined cyclic shear force, bending, and torsional moments. Test results reveal that (1) the flexural and torsional capacity is decreased due to the effect of combined loading, (2) the failure modes and deformation characteristics are changed, and (3) the damage zone tends to move upwards from the typical flexural plastic hinge zone due to the effect of additional torsional moment. The effects of combined loading on the hysteretic loading-displacement response, and damage characteristics are discussed.
Author: Suriya Prakash Shanmugam Publisher: ISBN: Category : Bridges Languages : en Pages : 634
Book Description
"Reinforced concrete (RC) columns of skewed and curved bridges with unequal spans and column heights can be subjected to combined loading including axial, flexure, shear, and torsion loads during earthquakes. The combination of axial loads, shear force, and flexural and torsional moments can result in complex failure modes of RC bridge columns. This study carried out experimental and analytical studies to investigate the seismic performance of circular RC columns under combined loading including torsion. The main variables considered here were (i) the ratio of torsion-to-bending moment (T/M), (ii) the ratio of bending moment-to-shear (M/V) or shear span (H/D), and (iii) the level of detailing for high and moderate seismicity (high or low spiral ratio). In particular, the effects of the spiral reinforcement ratio and shear span on strength and ductility of circular RC columns under combined loading were addressed. In addition, the effects of torsional loading on the bending moment-curvature, ductility, and energy dissipation characteristics were also considered. The analytical investigation examined the development of existing models for flexure and pure torsion. Interaction diagrams between bending, shear and torsional loads were established from a semi-empirical approach. A damage-based design approach for circular RC columns under combined loads was proposed by decoupling damage index models for flexure and torsion. Experimental and analytical results showed that the progression of damage was amplified by an increase in torsional moment. An increase in the transverse spiral reinforcement ratio delayed the progression of damage and changed the torsional-dominated behavior to flexural-dominated behavior under combined flexural and torsional moments"--Abstract, leaf iii.
Author: Qian Li Publisher: ISBN: Category : Civil engineering Languages : en Pages :
Book Description
Reinforced concrete (RC) bridge columns, specifically in the skewed and horizontally curved bridges, the bridges with unequal spans or column heights, and the bridges with outrigger bents, can be subjected to cyclic combined loading including axial, flexure, shear, and torsion loads during earthquakes. This combined loading condition would affect the performance of RC bridge columns with respect to strength, stiffness, deformation and progression of damage, and cause complex failure modes and in turn influence the overall behavior of the bridge system. This study performed experimental and analytical studies in order to investigate the performance of RC bridge columns under cyclic combined loading including torsion. The main variables considered here were (i) the ratio of torsion-to-bending moment (T/M), (ii) cross sectional shape, and (iii) transverse reinforcement configurations. The torsional and flexural hysteretic responses, plastic hinge formation, strength and stiffness degradation, rotation and displacement ductility limits, energy dissipation characteristics, and damage progression for these columns are discussed in this dissertation. A unified damage assessment approach was proposed to assess the damage limit states for RC columns under combined loading by unifying the decoupled damage index models for flexure and torsion. Moreover, a semi-empirical model was established to predict the interaction between bending, shear and torsional loads. It was found that the strength and stiffness degradation and progression of damage were amplified by an increase in torsional moment. The damage distribution and failure modes were affected by the combined loading effect. Also the square columns experienced more localized damage due to cross sectional shape and the transverse reinforcement configuration effect.
Author: Yang Yang Publisher: ISBN: Category : Columns, Concrete Languages : en Pages : 458
Book Description
"During earthquakes, reinforced concrete (RC) bridge columns may experience different levels of damage such as cracking, spalling, or crushing of concrete and yielding, buckling, or fracture of reinforcing bars. This study developed and assessed permanent and emergency methods to repair damaged bridge columns with fractured longitudinal reinforcement through experimental and modeling work. The permanent repair method involved replacement of the plastic hinge region by removal of spirals, replacement of longitudinal bar segments by mechanically splicing with new bars segments attached with mechanical couplers, replacement of concrete, and installation of an externally bonded carbon fiber reinforced polymer (CFRP) jacket. The emergency repair method involved removal of damaged concrete, bonding and embedding CFRP strips for flexural reinforcement, building a jacket from a prefabricated CFRP laminate, and repair of the footing with CFRP fabric. The repair methods were evaluated by large-scale component tests on RC column specimens subjected to constant axial loading and slow cyclic loading resulting in combined flexure, shear, and torsion. Test results showed that the repair methods developed in this study are capable of restoring the seismic performance of the repaired columns to that of the undamaged columns in terms of lateral load and deformation capacity, as well as torsional load and twist capacity. However, both repair methods resulted in lower lateral and torsional stiffness as well as lower energy dissipation capacity. Three-dimensional truss models were developed to simulate the as-built and repaired columns and showed efficiency and accuracy in predicting the response of columns under combined cyclic loading including torsion"--Abstract, page iii.
Author: Shannon D. Paboojian Publisher: ISBN: Category : Columns Languages : en Pages : 454
Book Description
Abstract: "An experimental study was undertaken to investigate the cyclic strength and ductility of composite columns subjected to simulatedseismic loading conditions. Eight two-thirds scale specimens were tested, each consisting of a structural steel shape encased in reinforcedconcrete. Parameters studied in the test program included: the degree of concrete confinement required to achieve adequate ductility; the effectiveness of shear studs for developing flexural stiffness and capacity under combined loading; the distribution of transverse shear resistance among the elements of the composite column; and concrete compressive strength. The results of the test program indicate that composite columns possess exceptional ductility and strength under cyclic loading if the buckling of longitudinal reinforcement is inhibited. Furthermore, the steel shape provides the primary resistance to transverse shear during overloading, and shear studs are not effective in enhancing the resistance against lateral loading. The elastic secant stiffness of the composite section corresponding to initial yielding of the longitudinal reinforcement was found to be well approximated by using one-half the gross moment of inertia (0.5I[subscript g]) in conjunction with Young's modulus for concrete. A prediction method based on superimposing the individual strengths of the reinforced concrete and structural steel shape was found to provide good agreement with test results. Current AISC LRFD provisions were determined to grossly underestimate the flexural capacity of the test specimens, which were axially loaded to 20% of their nominal pure axial load capacity [sic]."
Author: Ruili He Publisher: ISBN: Category : Columns, Concrete Languages : en Pages : 333
Book Description
"This research aimed to develop a technique to rapidly repair reinforced concrete (RC) bridge columns for emergency service restoration after severe earthquake damage has occurred. Experimental and analytical studies were conducted to study the performance and effectiveness of the proposed repair method. The experimental study included a series of 1/2-scale RC square bridge columns originally tested to failure under constant axial and increasing cyclic lateral loadings resulting in combined flexure, shear, and torsion with different torsional-to-flexural moment ratios. Using externally bonded carbon fiber reinforced polymer (CFRP) sheets, each column was repaired over a 3-day period and then retested under the same combined loading as the corresponding original column. Ruptured and/or buckled longitudinal reinforcing bars were not treated during the repair. A strength-based methodology was used to design the CFRP strengthening system to compensate for the strength loss due to the damage observed after the original test. Results indicated that the severely damaged columns were successfully repaired using the developed technique, with the exception of one column with fractured longitudinal reinforcing bars near the joint, which was only partially restored. The response of a prototype bridge structure was analyzed under earthquake loadings using OpenSees software considering different numbers and locations of repaired columns in the model. A technique was developed to model the response of the repaired column that accounted for the different damage and repair conditions along the column. The bridge models with one or more of the repaired columns were found to be capable of resisting the base shear and drift demand by the 40 ground motion records selected according to the target design spectrum, which confirmed the effectiveness of the repair"--Abstract, page iv.
Author: Mahmoud M. Hachem Publisher: ISBN: Category : Bridges, Concrete Languages : en Pages : 496
Book Description
Describes the dynamic testing of 4 circular reinforced concrete bridge columns. The specimens were divided into 2 pairs, with each pair subjected to a different ground motion. Within each pair, one specimen was subjected to one component of the ground motion, while the other was subjected to 2 components. Two analytical studies were carried out for a wide array of column heights, diameters, and axial load intensities. The columns were subjected to large suites of ground motions scaled to match on average the design response spectrum.
Author: Qian Li (Writer on transportation)
Author: Qian Li (Writer on transportation)
Author: Suriya Prakash Shanmugam
Author: Qian Li
Author: Yang Yang
Author: Shannon D. Paboojian
Author: Mahmoud Mohamad Hachem
Author: Juan F. Correal
Author: Ruili He
Author: Nadim I. Wehbe
Author: Mahmoud M. Hachem