Modeling of Reinforced Concrete Sub-frame Under Cyclic Load Reversals

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Journal of Earthquake Engineering, 11:215–230, 2007
Copyright © A.S. Elnashai & N.N. Ambraseys
ISSN: 1363-2469 print / 1559-808X online
DOI: 10.1080/13632460701221553
Journal of Earthquake Engineering, Vol. 11, No. 2, February 2007: pp. 1–25
Journal of Earthquake Engineering
Modeling of Reinforced Concrete Sub-frame Under
Cyclic Load Reversals
Modeling of Reinforced Concrete Sub-frameJ. H. Khoo and B. Li
Utraco Structural Systems Pte Ltd, Singapore
School of Civil and Environmental Engineering, Nanyang Technological
University, Singapore
A study of the strength and deformation characteristics of reinforced concrete structure under cyclic
load reversals by means of a computational model is presented in this article. A beam-column sub-
frame tested under reversed cyclic loading at NTU, Singapore was modeled and analyzed using
strut-and-tie method to capture its cyclic hysteretic responses and to explore the possible force flows
from beam and column to the joint core. The model was developed based on crack patterns observed
on the tested concrete specimen, and was analyzed using DRAIN-2DX. The modeling procedure for
different truss elements of the model is described herein. The analytical study reveals that the strut-
and-tie method is capable of modeling to a satisfactory accuracy the cyclic hysteretic response of a
reinforced concrete structure observed in the full-scale test.
Keywords Strut-and-tie; Modeling; Cyclic; Computer Analysis
The strut-and-tie approach is a physical method that involves modeling the reinforced
concrete member as a truss structure. The complex stress fields inside the structural mem-
bers when subjected to external forces are simplified into discrete compressive and tensile
force paths, which are represented, respectively, by compression struts and tension ties.
The longitudinal reinforcement in a member represents the chords of a truss while the
transverse reinforcement serves as transverse ties. Concrete in the flexural compression
zone can also be considered as part of the longitudinal compression chord member. The
diagonal concrete compression struts, which discretely simulate the concrete compressive
stress field, are placed to complete the static equilibrium of the truss. These struts and ties
are connected at rigid nodal points. With the aid of such a behavioral model, a better visu-
alization and understanding of the internal force distribution and force transfer mecha-
nisms are thus feasible.
The strut-and-tie modeling approach is not only capable of predicting the strength of a
localized region in a structure, but also equally applicable to predicting the strength of the
entire structure. This method is also appropriate and effective in the analysis and detailing
of complex structural regions. However, the utilization of this method to capture the non-
linear inelastic and cyclic hysteretic responses of a concrete structure is rather limited. To
Received 27 April 2005; accepted 10 January 2006.
Address correspondence to Bing Li, School of Civil and Environmental Engineering, Nanyang
Technological University, Singapore 639798;