Effects of Creep and Shrinkage on Time-dependent Strain and Curvature of R/C Members

Open Access
Author:
Karschner, Kyle Allan
Graduate Program:
Civil Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
February 01, 2012
Committee Members:
  • Andrew Scanlon, Thesis Advisor
Keywords:
  • creep
  • shrinkage
  • time-dependent
  • long-time multiplier
  • strain
  • curvature
  • deformation
  • deflection
Abstract:
The long-time deflection multiplier specified in the ACI Code is simple to use, but neglects the effects of several parameters such as age at loading and reinforcement ratio that are known to have significant effects on long-time slab deflections. Several authors including Branson (1977), Sbarounis (1984(a)), and Graham and Scanlon (1986) have made recommendations in the past to increase the long-time multiplier for application to two-way slabs, however, no systemic study has been found that would provide a sound theoretical basis to justify such recommendations. The research documented in this thesis examines the factors that influence long- time deflections from a theoretical viewpoint at the member section level using a time- step method of analysis developed from established principles. The time-step analysis traces the effects of creep and shrinkage on the time-dependent strain and curvature of various member sections. A parametric study is performed using the developed algorithm to evaluate the limitations of the existing ACI 318-11 long-time multiplier (λΔ) used in calculating two-way slab deflections. Results of the parametric study are used to provide designers with insight as to which factors have the most influence on long-term deflections and recommend methods of dealing with design problems engineers face.