Displacement recovery and energy dissipation of crimped NiTi SMA fibers during cyclic pullout test

다국어 초록 (Multilingual Abstract)

This study investigated the cyclic pullout behaviors of cold-drawn paddled and crimped fibers; two diameters of 1.0 mm and 0.7 mm were considered. All fibers presented displacement recovery and energy dissipation, which were not shown in previous studies of straight, L-, and N- shaped SE SMA fibers. Thus, these cold-drawn fibers could produce re-centering and dissipated energy capacity for the reinforced concrete/mortar.
The experimental cyclic pullout results showed that the deep crimped fiber produced higher maximum pullout stress than the shallow crimped fiber. When heating, the shallow crimped fiber increased diameter more significantly than the deep crimped fiber, whereas the fiber wave depth decreased more for the deep crimped fiber. Thus, the maximum pullout stress increased for heated shallow crimped fiber and decreased for heated deep crimped fiber. The heating was more effective for 0.7 mm diameter crimped fibers than for 1.0 mm diameter crimped fiber because of the thinner shape and lower flexural stiffness. The cold-drawn fiber presented displacement recovery at each cycle loading, and the displacement recovery ratio (DRR) decreased after each cycle because of reduced friction due to the damaged mortar duct. The DRR reduction was significant for the fiber with a low anchoring bond. The high anchoring bond fiber also introduced a higher average DRR than the fiber with a relatively low anchoring bond. The thicker fiber showed a little higher average DRR than the thinner fiber. Under heating treatment, the average DRR increased due to the prestressing in the fiber caused by the shape memory effect; however, the anchoring bond of fiber much be enough to produce prestressing in the fiber. The anchoring bond of fiber and the prestressing also influenced energy dissipation (ED). The higher anchoring bond introduced a higher ED value, and the prestressing in fiber contributed more to the increased ED values.

목차 (Table of Contents)

• CHAPTER Ⅰ INTRODUCTION 1
• 1.1 Problem Description 1
• 1.2 Objective of study 4
• 1.3 Outline of Thesis 7
• CHAPTER Ⅱ REVIEW FOR PREVIOUS STUDY 8
• 2.1 Shape Memory Alloys(SMA) 8
• 2.1.1 Superelastic characteristics 8
• 2.1.2 Shape Memory Effect 10
• 2.2 Literature review 12
• 2.2.1 Effect of steel fiber geometry on the pullout response 12
• 2.2.2 Pullout behavior of superelastic SMA fibers 14
• 2.2.3 Investigating stress distribution of crimped SMA fibers during pullout behavior 16
• 2.2.4 Pullout resistance of crimped reinforcing fibers using cold-drawn NiTi SMA wires 20
• CHAPTER Ⅲ SPECIMENS AND PULLOUT TEST 24
• 3.1 SMA fibers and specimens 24
• 3.1.1 SMA fibers 24
• 3.1.2 Specimens 29
• 3.2 Test set-up and cyclic load method 31
• 3.3 Heating method 32
• CHAPTER Ⅳ RESULT 34
• 4.1 Hysteretic slip-displacement curves 34
• 4.2 Maximum pullout stress 48
• 4.3 Displacement recovery ratio (DRR) 51
• 4.4 Energy dissipation(ED) during loading and unloading cyclic 57
• CHAPTER Ⅵ CONCLUSIONS 60
• REFERENCE 63
• 국 문 요 약 68