Investigation on Effect of Transverse Reinforcement on Performance of Diagonally Reinforced Coupling Beams by ProQuest


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									 ACI STRUCTURAL JOURNAL                                                                                   TECHNICAL PAPER
Title no. 105-S72

Investigation on Effect of Transverse Reinforcement on
Performance of Diagonally Reinforced Coupling Beams
by Patrick J. Fortney, Gian A. Rassati, and Bahram M. Shahrooz

The response of coupled core wall systems is governed by the                crossties. The study presented in this paper investigates the
performance of their coupling beams. Moreover, coupling beam                influence of the amount of transverse reinforcement provided in
design is controlled by the post-elastic behavior of the entire             a diagonally-reinforced coupling beam on its overall response,
coupled system. This paper presents the results of an experimental          in terms of available ductility and hysteretic stability.
investigation dealing with the effects that transverse reinforcement
ratios have on the post-elastic performance of diagonally-reinforced
coupling beams. Two coupled wall subassemblages, with two                                   RESEARCH SIGNIFICANCE
different transverse reinforcement detailings, were designed and               The matter of transverse reinforcement detailing is being
tested under cyclic reversed loads. The design philosophy for both          actively discussed within both ACI Committees 318H and
specimens is presented and discussed, and the detailing is                  374 and among practitioners. Due to the fact that current
compared with what is required by ACI 318-05. The experimental              provisions are open to interpretation, practitioners often do
results are presented, with particular attention to the post-elastic        not have full confidence that the transverse reinforcement
performance of the specimens tested. Overall performance
comparisons are made. It is concluded that providing a higher
                                                                            they design will provide the necessary deformation capacity
transverse reinforcement ratio greatly benefits ductility and hysteretic    and ductility. This paper presents a study that compares the
stability of diagonally-reinforced coupling beams.                          response of two diagonally-reinforced coupling beams with
                                                                            different transverse reinforcement detailing. This research
Keywords: coupling beams; reinforcement detailing; seismic design; walls.   will clarify the effect of transverse reinforcement and illustrate
                                                                            the positive impact of an increase in transverse reinforcement
                                                                            ratios with respect to ACI 318-05 specifications. Additionally,
                                                                            the manner in which the transverse reinforcement is distributed
   Coupled core wall systems (CCWs) are advantageous
                                                                            is equally crucial.
lateral force-resisting (LFR) systems that combine the large
shear and axial stiffness of shear walls with the ductility of
the coupling beams. Many studies in literature amply                                       DESIGN PHILOSOPHY
demonstrate the desirable attributes of CCWs as a whole as                    The shear strength of a diagonally-reinforced concrete
well as the issues and advantages related to the components                 coupling beam as given by ACI 318-05 is shown in Eq. (1).
within the system: some examples include Fortney (2005),
Harries et al. (2005), Shahrooz et al. (1992, 1993), and                            V n = 2A vd fy sin α ≤ 0.83 f c ′A cw (f c ′ in MPa)
Aristizabal-Ochoa (1982). The overall lateral stiffness                                                                                                            (1)
largely depends on the type and detailing of the coupling                              V n = 2A vd fy sin α ≤ 10 f c ′A cw (f c ′ in psi)
beams used. Previous work by the authors (Fortney et al.
[2004a,b]; Fortney [2005]; Harries et al. [2005]; Shahrooz et
al. [1992, 1993]) highlighted the difference in response                       Note that Eq. (1) relies solely on the strength provided by
between steel, steel-concrete, and diagonally-reinforced                    the diagonal bar groups and ignores the contribution of the
concrete coupling beams. Traditionally, the coupling beam                   concrete (Vc) or stirrups (Vs) to shear resistance (that is, Vc
typology chosen for CCWs is represented by diagonally-                      and Vs are taken as zero). Furthermore, the limit on the shear
reinforced concrete beams. These beams, if properly detailed,               strength is 0.83 f c ′ Acw (10 f c ′ Acw) and is a function of the
can provide considerable stiffness, strength, and ductility;                compressive strength of the concrete. In Eq. (1), Avd is the
but sometimes they can be very complicated, if not impossible,              cross-sectional area of one diagonal bar group, fy is the yield
to fabricate and construct. Harries et al. (2005) clearly                   strength of the diagonal bars, α is the angle of inclination of
showed that diagonally-reinforced coupling beams with                       the diagonal bar groups from the horizontal, fc′ is the specified
practical span-depth ratios cannot practically be built when                
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