Effect of Differential Movement of Straight Reinforcing Bars During Early Age Curing on the Bond Strength

Author

Tyler Andrews, Clemson UniversityFollow

Date of Award

8-2013

Document Type

Thesis

Degree Name

Master of Science (MS)

Committee Chair/Advisor

Schiff, Scott D

Committee Member

Nielson , Bryant G

Committee Member

Rangaraju , Prasad R

Abstract

As the nation's infrastructure continues to age, the number of structural deficiencies is rising. Accordingly, there is a great need and desire to replace these failing components in a quick and efficient fashion. Prefabricated elements for structures such as bridges and parking decks are commonly implemented in this process in order to save both time and money. These prefabricated elements are often subjected to moving live loads during construction and repair which, consequently, result in differential movements occurring across the joints connecting the elements of these structures. Potential reductions in joint capacity, joint stiffness, and structural durability are the byproducts of these differential movements. The research presented in this paper seeks to address one issue related to differential movements. In particular, the bond capacity of straight reinforcing bars placed in structural connections is examined.
To implement this research, differential movements were applied to deformed reinforcing bars embedded 6 inches into 6' by 12' cylindrical specimens. Two types of rebar motion - linear translation and angular rotation - were considered for all tests. Varying amplitudes of differential movement, mimicking those experienced in the field, were applied to the rebar ranging from 0.015 to 0.047 inches. Additionally, multiple time sequences were employed which applied differential movements for different lengths of time during the setting process of the grout.
The findings of this study indicate the potential impact these parameters may have on bond strength. The larger the amplitude, the larger the reduction will be in bond strength for both types of rebar motion. Nearly 22 percent bond loss was observed when 0.044 inches of angular rotation movement was applied throughout the entire setting process. For amplitudes as small as 0.016 inches applied during the full setting process for translation, bond loss of about 10 percent was measured. Furthermore, results indicate that there was a critical window of time during which differential movements, when applied, will cause a notable reduction in bond. This critical time window was observed in both types of rebar movement. For Quikrete¨ Non-Shrink Precision grout, which was the joint material used throughout this study, the critical time window appeared to be bounded by the initial and final set times of the material which were approximately 30 and 60 minutes after initial mixing, respectively. This time window will be different depending on the cementitious material used.
Based on these findings, it is clear that the effects of differential movements on bond loss need to be further and more thoroughly investigated. The testing apparatus and test methods used also demonstrate that tests can be done investigating several parameters and using multiple specimens in a cost effective manner. Also, potential restrictions in construction practices during the curing process or revisions to design code regarding development length can be supported.

Recommended Citation

Andrews, Tyler, "Effect of Differential Movement of Straight Reinforcing Bars During Early Age Curing on the Bond Strength" (2013). All Theses. 1690.
https://open.clemson.edu/all_theses/1690