Experimental and Analytical Studies on Reinf. Conc. Buildings w/ Seismically Vul

[asim99]

Experimental and Analytical Studies on Reinf. Concrete Buildings with Seismically Vulnerable Beam-Column Joints

Author: Sangjoon Park, Khalid M. Mosalam | Size: 33.1 MB | Format: PDF | Quality: Unspecified | Publisher: PEER | Year: 2012 | pages: 224

Existing reinforced concrete (RC) buildings designed prior to the 1970s are vulnerable to shear
failure of beam-column joints under earthquake excitations because of insufficient transverse
reinforcement in the joint region. The failure of such “unreinforced” joints, especially corner
joints, has played a crucial role in building collapses in past earthquakes. The accurate prediction
of shear strength and flexibility for these unreinforced beam-column joints is therefore essential
to assess the seismic risk of older-type RC buildings characterized by having unreinforced beamcolumn
joints. To predict shear strength, two shear-strength models were developed previously,
as a part of this larger study. A practical shear-strength model combining the two previously
developed models is presented in this report.
To validate the shear strength models and to develop a moment-rotation relationship
(backbone relationship) of unreinforced corner beam-column joint, four full-scale unreinforced
corner beam-column joint specimens with two orthogonal beams and floor slab were tested
under quasi-static cyclic load reversals simulating earthquake loading. The test results show that
the joint shear strengths decrease with increase of the joint aspect ratio, and for a certain joint
aspect ratio, the joint shear strengths are proportional to the beam longitudinal reinforcement
ratio within the range of variables investigated in the test matrix. The proposed three models
accurately predicted the shear strengths of the tested specimens. Based on the measured joint
responses and visual observations of the tested four corner joint specimens, a backbone
relationship was developed for nonlinear joint macro-modeling. Furthermore, the proposed
backbone relationship was modified to be applicable to interior and roof beam-column joints.
The strength parameters in the backbone relationships were defined using the proposed joint
shear strength models. These backbone relationships were validated by accurate reproduction of
the force-drift responses of the tested four corner joint specimens in this study and eight other
exterior and interior joint specimens taken from the literature. Using these backbone
relationships, nonlinear dynamic simulations were performed on three hypothetical prototype RC
building frames. These simulations indicate that consideration of the flexibilities for unreinforced
joints is important for seismic assessment of older-type RC buildings characterized by having
unreinforced joints.

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