Bond-slip Model to Capture Strain
Penetration Effects in OpenSees

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Sponsors:
National Science Foundation

Graduate Students:
Jonathan D Waugh 

    Well-designed flexural concrete members experience rotations at the fixed end(s) due to slip of longitudinal bars fully anchored into the adjoining concrete members. The slip results from strain penetration along a portion of the fully anchored bar. A zero-length section element placed between a fiber-based flexural element and an adjacent member is used to model the bond slip rotation. Focusing on column and wall longitudinal bars anchored in footings and bridge joints, a constitutive model that expresses the bar stress vs. loaded-end slip response has been developed for the steel fibers in the zero-length section element. The adequacy of the proposed monotonic response for the steel fibers has been illustrated using suitable experimental data reported in the literature. Hysteretic rules for the bar stress vs. loaded-end slip response have been established using the available test data and observed responses of concrete members under cyclic loading.
    Advantages of the proposed method to improve fiber-based analysis of concrete structures have been demonstrated by simulating cyclic response of two concrete cantilever columns and a bridge tee-joint system. Simulated responses have been compared with the observed responses at both global and local levels. Based on the observations, it is concluded that 1) the strain penetration effects should not be ignored in the analysis of concrete members, and 2) the zero-length section element incorporating the proposed constitutive model for the steel fibers can be used in nonlinear fiber-based analysis to accurately capture the strain penetration effects and thus the global and local responses of concrete flexural members. The proposed method is versatile in that it can be used for modeling concrete flexural members without limiting cross-sectional shapes or direction of the lateral load. In addition, the proposed constitutive model for the bar stress vs. slip response can be employed to capture the strain penetration effects in models of concrete structures developed using other types of elements.

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• Referred Papers in Journals

Zhao, J., and S. Sritharan. Modeling of strain penetration effects in fiber-based analysis of reinforced concrete structures. ACI Structural Journal. (Accepted for publication in 2006). (Bond_SP01_ACI.pdf)

• Papers in Conference Proceedings

Zhao, J., and S. Sritharan. Nonlinear analysis of RC structures with strain penetration effects. proceedings of 8th  National Conference on Earthquake Engineering. (Bond_SP01_8NCEE.pdf)

• Theses and Technical Reports