Outline

  • Keywords
  • 1. Introduction
  • 2. Research Significance
  • 3. Experimental Program
  • 3.1. Test Specimens
  • 3.2. Materials
  • 3.3. Test Setup and Instrumentation
  • 4. Experimental Results
  • 4.1. Specimen Jbc-1
  • 4.2. Specimen Jbc-2
  • 4.3. Load-Story Drift Envelope
  • 4.4. Cumulative Energy Dissipation
  • 4.5. Beam Rotations
  • 4.6. Measured Strains in Rebars
  • 5. Discussion
  • 6. Conclusions
  • Acknowledgment
  • References

رئوس مطالب

  • 1.مقدمه
  • 2. اهمیت تحقیقاتی
  • 3. برنامه آزمایشی
  • 3.1 نمونه های تست
  • 3.2 منابع
  • 3.3 آماده سازی آزمایش و بکارگیری ابزارها
  • 4. نتایج آزمایشی
  • 4.1 نمونه 1. JBC
  • 4.2 نمونه 2. JBC
  • 4.3 پوشش رانش طبقه بار
  • 4.4 پراکندگی انرژی انباشته
  • 4.5 چرخشهای تیر
  • 4.6 کرنشهای اندازه گیری شده در میلگردهای آجدار
  • 5. بحث
  • 6. نتیجه گیری ها

Abstract

Superelastic Shape Memory Alloys (SE SMAs) are unique alloys that have the ability to undergo large deformations and return to their undeformed shape by removal of stresses. This study aims at assessing the seismic behavior of beam-column joints reinforced with SE SMAs. Two large-scale beam-column joints were tested under reversed cyclic loading. While the first joint was reinforced with regular steel rebars, SE SMA rebars were used in the second one. Both joints were selected from a Reinforced Concrete (RC) building located in the high seismic region of western Canada and designed and detailed according to current Canadian standards. The behavior of the two specimens under reversed cyclic loading, including their drifts, rotations, and ability to dissipate energy, were compared. The results showed that the SMA-reinforced beam-column joint specimen was able to recover most of its post-yield deformation. Thus, it would require a minimum amount of repair even after a strong earthquake.

Keywords: - - - -

Conclusions

The use of SE SMA rebars in the plastic hinge region of a BCJ has been examined under reversed cyclic loading. The experimental investigation described in the present article provides an insight into the potential for developing a new type of RC structures with hybrid steel-SMA reinforcement. Based on the experimental observations and analysis of test results, the following conclusions can be drawn.

1. The flag-shaped hysteretic stress-strain curve of SE SMA rebar produced a flagshaped force-displacement hysteretic shape for JBC-2. This resulted in very small residual displacements in the SE SMA-RC beam-column joint JBC-2 compared to that of the conventional steel-RC beam-column joint JBC-1. This extraordinary characteristic of SE SMA-RC beam-column joints could have a great benefit in highly seismic areas, where such RC joints would remain functional even after a strong earthquake.

2. In the case of steel-RC beam-column joint specimen JBC-1, the plastic hinge developed at the face of the column. On the other hand, the use of SE SMA in the joint region of JBC-2 successfully relocated the plastic hinge region away from the column face to a distance of approximately half of the beam-depth.

3. Specimen JBC-2 dissipated lesser amount of energy compared to that of JBC-1. However, it could dissipate equivalent amount of energy of JBC-1 at an expense of relatively larger story drift. Larger hysteretic loop of steel and extensive cracking in concrete in the beam hinge region of JBC-1 resulted in higher amount of energy dissipation compared to that of SE SMA-RC BCJ specimen JBC-2.

4. The beam moment rotation relationship of JBC-2 was found different than that of JBC-1 because of the low modulus of elasticity of SMA, which led to delayed yielding of the Ni-Ti rebar compared to that of steel. This also caused higher beam rotation in JBC-2 than that of JBC-1 at equivalent beam-tip displacements.

5. The strains in the longitudinal SMA rebar of specimen JBC-2 experienced negligible residual strain, while longitudinal steel rebar of specimen JBC-1 suffered much larger residual strain. The transverse reinforcements inside the joint of specimen JBC-1 also experienced larger strains compared to that of JBC-2.

The study mainly focused on observing the performance of subassemblies and their level of damage during reversed cyclic loading. It should assist in developing a numerical model, which will be able to simulate the performance of SE SMA-RC beam column joints. Such a model can be used to assess the performance of SE SMA-RC multi-story frames under dynamic loading, allowing predicting their capacities and meeting seismic resistance requirements. It is also important that the design code provisions for seismic design of steel-RC structures are re-examined for SMA-RC structures considering its low modulus of elasticity, low-energy dissipation capacity, large deformation capability, negligible residual strain, and recentering capability.

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