Experimental and analytical research has been conducted to investigate the degradation of shear performance of beams due to bond deterioration and longitudinal bar cutoffs.
To achieve the controlled rate of bond degradation, the method of adjustment of the rib height by machining was adopted. Bond behaviour of the milled bars were measured in tension stiffening tests with internally installed strain gauges. Maximum bond stresses for the milled bars were reduced by up to 50% compared to those for normal deformed bar.
The bond behaviour of the milled bars were compared with those of the bars subjected to accelerated corrosion. It was confirmed that the stripped bar had the possibility to simulate corroded bars to some extent. Based on the calculations of average tensile stresses in the cracked concrete for each specimen, appropriate tension stiffening factors for each type of bar were suggested and then verified with the 2-dimensional nonlinear finite element analysis program VecTor2.
Next, eight simply supported beams were tested. In four of them half of the longitudinal bars were cut off near the supports. Various combinations of normal and machined reinforcing bars were selected for both longitudinal and transverse reinforcement.
The predicted shear failure load for the cutoff beam based on the general method for shear design in CSA A23.3-04 was unconservatively estimated. Cutoffs of longitudinal reinforcement resulted in much more significant drops of shear resistance than did bond deterioration of reinforcement. The inclinations of diagonal cracks for the cutoff series were larger than those for the no-cutoff series due to significant concentrations of longitudinal strains near the cutoff locations.
Finally modifications to the general shear design method in CSA A23.3-04 were proposed based on the results of VecTor2 analyses for the beam tests. It was found that the influence of bond deterioration on the shear strength of reinforced concrete member can be accounted for by adjusting the tension stiffening factor applied to the equation for β. With respect to bar cutoffs, its influence on shear strength can be expressed by the strain concentration factor applied to the equation for ε_x.
| Identifer | oai:union.ndltd.org:TORONTO/oai:tspace.library.utoronto.ca:1807/32767 |
| Date | 30 August 2012 |
| Creators | Masukawa, Junji |
| Contributors | Collins, Michael P., Bentz, Evan |
| Source Sets | University of Toronto |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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