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									 ACI STRUCTURAL JOURNAL                                                                                   TECHNICAL PAPER
Title no. 105-S71

Probabilistic Joint Shear Strength Models for Design of RC
Beam-Column Connections
by Jaehong Kim and James M. LaFave

An extensive experimental database is constructed for diverse types         has recommended design guidelines for RC beam-column
of reinforced concrete (RC) beam-column connections subjected to            connections based in part on bench-marking studies such as
quasistatic cyclic lateral loading, with all included test subassemblies    those previously described, and the committee has updated
having eventually experienced joint shear failure. RC joint shear           its design guidelines a number of times (currently to ACI
strength models are developed using the experimental database
                                                                            352R-023) based on extensive additional experimental and
(after removing those subassemblies having inadequate confinement
within the joint panel) in conjunction with a Bayesian parameter            analytical studies. Throughout this process, Joint ACI-ASCE
estimation method. The improved performance of the developed                Committee 352 has tried to keep a simple and safe joint shear
joint shear strength models is evaluated by comparison with other           strength model for use in design, primarily by considering
deterministic RC joint shear strength models (of both the code-             the concrete strut mechanism. ACI 318-054 has also generally
based and the research variety). Finally, the ACI 352R-02 joint             accepted a similar joint shear design philosophy to that of
shear strength definition for design is modified for greater consistency,   ACI 352R-02.3
by following the general ACI 352R-02 approach but with adjusted                More recently, Kim and LaFave5 have qualitatively
joint shear strength factors.                                               assessed the key influence parameters on RC joint shear
                                                                            stress versus joint shear strain behavior based on collected
Keywords: Bayesian parameter estimation; lateral loading; shear failure.    experimental subassembly results. In those previously
                                                                            collected test results, all specimens experienced joint shear
                      INTRODUCTION                                          failure (either in conjunction with or without yielding of beam
   Since the mid-1960s, numerous experimental tests and                     reinforcement), had equal to or above 70% of the recommended
analytical studies have been conducted to investigate the                   joint transverse reinforcement per ACI 352R-02,3 and had
performance of reinforced concrete (RC) beam-column                         no out-of-plane members or eccentricity between the beams
connections subjected to lateral earthquake loading. When                   and the column. Kim et al.6 then established a procedural
only the flexural strength of well-detailed longitudinal beams              framework to develop more reliable joint shear strength
limits overall response, RC beam-column connections typically               models using the collected experimental specimens in
display ductile behavior (with the joint panel region                       conjunction with a Bayesian parameter estimation method.
remaining elastic). This beam-hinging governing failure                     Based on experimental observation, a number of possible
mode is usually considered to be the most desirable for                     influence parameters on RC joint shear strength were
maintaining good global energy-dissipation without severe                   selected, and the most significant were identified. Finally,
degradation of capacity at the connections. On the other                    Kim et al.6 proposed a preliminary joint shear strength model
hand, RC beam-column connections can exhibit less robust                    and briefly confirmed its improved reliability in comparison
behavior when severe damage is concentrated within the                      with the ACI 352R-023 joint shear strength model.
joint panel. Therefore, understanding joint shear behavior is                  The previous research conducted by Kim and LaFave5 and
important in controlling the overall performance of RC                      by Kim et al.6 motivated the desire to further develop simple
beam-column connections and frames.                                         and reliable joint shear strength models for design that can be
   The general terminology of RC beam-column connections                    broadly applied to many different types of RC beam-column
is dependent on in-plane geometry: an interior connection                   connections (considering the effects of out-of-plane members
has two longitudinal beams with a continuous column, an                     and eccentricity between the beams and the column, as well
exterior connection has one longitudinal beam with a                        as other important effects such as joint type). In this current
continuous column, and a knee connection has one longitudinal               research, then, an expanded experimental database has been
beam with a discontinuous column. For such beam-column                      constructed that includes all types of RC beam-column
connections, Hanson and Connor1 first suggested a definition                connections found in the literature to have experimental joint
of RC joint shear, which is determined from a free-body                     shear failure. By applying the procedures established by Kim
diagram at the midheight of the joint panel. Paulay et al.2                 et al.6 to this new database, three kinds of joint shear strength
described concrete struts and/or trusses as possible joint                  models (for diverse types of modern RC beam-column
shear resistance mechanism(s); the concrete strut comes                     connections) have been developed using the Bayesian
from force transfer to the joint panel by bearing from                      parameter estimation method. The first model considers
concrete compression zones of adjacent beam(s) and column(s),               many possible influence parameters on RC joint shear strength.
whereas the concrete truss results from force transfer
through the joint panel via bond between the reinforcement                    ACI Structural Journal, V. 105, No. 6, November-December 2008.
and surrounding concrete.                                                     MS No. S-2007-180.R1 received May 18, 2007, and reviewed under Institute
                                                                            publication policies. Copyright © 2008, American Concrete Institute. All rights reserved,
   From 1976 to the present, Joint ACI-ASCE Committee 352,                  including the making of copies unless permission is obtained from the copyright proprietors.
                                                                            Pertinent discussion including author’s closure, if any, will be published in the September-
Joints and Connections in Monolithic Concrete Structures,                   October 2009 ACI Structural Journal if the discussion is received by May 1, 2009.

770                                                                                ACI Structural Journal/November-December 2008
                                                                                        story shear, the experimental joint shear demand is calculated
ACI member Jaehong Kim is a Structural Consultant at S.K. Ghosh Associates, Inc.,
in Palatine, IL. He is a member of Joint ACI-ASCE Committee 352, Joints and             from force equilibrium and a free-body diagram at the
Connections in Monolithic Concrete Structures. He received his BS and MS from           midheight of the joint panel.5 (For knee joints, the experimental
Yeungnam Un
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