Mechanical Properties and Numerical Analysis of Long-term Deformations and Crack Widths in Prestressed Reinforced Concrete Members

1995 Fiscal Year Final Research Report Summary

• Project/Area Number: 06650495
• Research Category: Grant-in-Aid for General Scientific Research (C)
• Allocation Type: Single-year Grants
• Research Field: 土木材料・力学一般
• Research Institution: Utsunomiya University
• Principal Investigator: SATO Ryoiti Utsunomiya University, Faculty of Engineering, Associate Professor, 工学部, 助教授 (20016702)
• Co-Investigator(Kenkyū-buntansha): UJIKE Isao Ehime University, Faculty of Engineering, lecturer, 工学部, 講師 (90143669)
• Project Period (FY): 1994 – 1995
• Keywords: Prestressed Reinforced Concrete / Deformation / Crack / Tension stiffening / Long-term Behavior / Drying Shrinkage / Effective Flexural Stiffness / Principle of Superpositon

Research Abstract

This study presents the investigations on mechanical properties and numerical analysis of long-term deformations and crack widths in prestressed reinforced concrete (PRC) members under sustained load after prestressing. The results obtained from the investigations executed in 1994 and 1995 are summarized as followings :
(1) Based on the principle of superposition, the stress-strain relationship of concrete was formulated in considering effects of creep and drying shrinkage in concrete. By means of this formulation, creep analysis of cracked sections under long-term varying stresses from just inducing prestress was successfully carried out based on the assumption that"plane section remains plane after loading"for strains in concrete and reinforcement.
(2) Besides carrying out creep analysis of cracked sections, creep analysis for the full sections was also performed by means of the principle of superpositoin. Taking into account the effect of tension stiffening, the analysis method of def ormation was also proposed, which is applicable to PRC members sujected to varying load.
(3) As to applicability of existing typical models for tension stiffening, such as ACI,CEB Manual, CEB Model Code 90 (MC90), MC90 model underestmated tension stiffening effect as prestress becomes large and overestimated long-term average curvature more than CEB Manual and ACI models, which showed fairly good applicability.
(4) Modifying the above-mentioned method, effective flexural stiffness for the structural design of short and long-term deflection of PRC structures was proposed, which was quoted in JSCE Standard Specification for Design of Concrete Structures.
(5) It was cleared that the effect of drying shrinkage on the increase of crack widths of PRC members shared 65-80% at 180 days after loading and the share became smaller as the loading duration became longer. As prestress increase the spacing between cracks became larger due to the decrease of tension reinforcement ratio, which did not increase crack widths with time. It was also shown that effects of drying shrinkage on long-term deformation became week as prestress increase.