THESIS
2017
xxvi, 245 pages : illustrations (some color) ; 30 cm
Abstract
Over the last three decades, the discipline of earthquake engineering has witnessed
tremendous improvements and innovations in the seismic design of reinforced
concrete (RC) frame structures. Notable advances have been achieved in the seismic
behaviour and design of RC beam-column connections, in particular conventional
interior and exterior beam-column joints. However, during the past two decades few
investigations have been conducted on the seismic performance of knee connections,
which are normally seen at the roof level of frame buildings and pier bents of an RC
bridge.
The structural response of RC knee joints subjected to earthquake-induced loading is
presently giving a lot of concern to engineers as a result of their questionable
performance. Presently, codes of practic...[
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Over the last three decades, the discipline of earthquake engineering has witnessed
tremendous improvements and innovations in the seismic design of reinforced
concrete (RC) frame structures. Notable advances have been achieved in the seismic
behaviour and design of RC beam-column connections, in particular conventional
interior and exterior beam-column joints. However, during the past two decades few
investigations have been conducted on the seismic performance of knee connections,
which are normally seen at the roof level of frame buildings and pier bents of an RC
bridge.
The structural response of RC knee joints subjected to earthquake-induced loading is
presently giving a lot of concern to engineers as a result of their questionable
performance. Presently, codes of practice (EC2&8, ACI 318-14, etc.) specify rules for
the design of beam-column joints, where the guidelines provided are only for
conventional interior and exterior joints, with little or no mention of the knee joints.
An increasing number of failures of knee joints before the corresponding inter-storey
beam-column joints have been perceived under earthquakes. Therefore, it is
imperative to re-consider the validity of designing knee joints directly as conventional
beam-column connections as per current design methods.
This thesis presents a combined experimental and theoretical study on the seismic
performance and shear strength of reinforced concrete beam-column knee joints. The
experimental study consists of a series of reinforced concrete (RC) beam-column knee
joints with different configurations including the different detailing techniques of joint
reinforcement and the dimensions of the joint region. A Total of 10 large-scale beam-column
knee joint specimens, which are fabricated to simulate those in as-built RC frame buildings designed in accordance to the provisions of ACI 318-14 and ACI-ASCE 352R-02, were tested under reversed cyclic loading. It was shown that the area of transverse reinforcement and member sizing of connecting beam and column had a significant effect on the shear strength and the ductility of the joints.
However, none of these specimens had shown sufficient ductility energy dissipation
capacity. Tested results are also compared with those predicted by five seismic codes
of practice, namely, ACI 318, EC8, NZS 3101, GB50010, and AIJ. In general, the
present seismic design codes cannot accurately predict the shear strength of beam-column
knee joints under earthquake-type loading.
Finally, an analytical model is also presented for analysing the shear performance and
predicting shear resistance of reinforced concrete (RC) knee joints. The proposed
method, termed as Modified Soften Strut-and-Tie Model (MS-STM), is partly derived
from the experimental observations of knee joint specimens and partly modified from
the soften strut-and-tie model. In the proposed methodology, the new strut-and-tie
model satisfies different equilibrium conditions including all force components (axial
forces, shear forces and moments) transferred from the beam and column framing into
the joint, as well as the compatibility and the constitutive relationships of cracked
reinforced concrete. The proposed model not only revealed the different mechanisms
on resisting the input forces but also quantified the shear strength of knee joints under
both closing and opening actions. The accuracy of the proposed model is validated by
comparing the calculated shear strength with the experimental data available in the
previous literature and a good agreement was observed. The proposed model can
provide crucial insights in to the shear performance of knee joints under seismic loadings.
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