A Study of Seismic Design of 1st Story Vertical Boundary Elements in Multi-Story Steel Plate Shear Walls.

Steel plate shear walls (SPSWs) have been recognized as a high lateral stiffness
and ductility system for building structures. It has gained significant acceptance in the
U.S and Canada in recent years. However, it has not been adopted in Taiwan for
practical use so far. This could be due to the following two reasons: (1) the capacity
design of boundary elements must be checked by using the strip model which may be
complicated and time-consuming; (2) according to the AISC seismic provisions for
structural steel buildings, the plastic hinge in the 1st story column is allowed to form
only at the bottom end. Therefor the design of the 1st story column may be quite
conservative and uneconomic. Unlike the low-rise SPSWs most past researches have
investigated, large overturning moment-to-shear ratios may develop in the 1st story in
a high rise SPSW. For the purpose of developing an effective capacity design
methodology for the 1st story column in multi-story SPSWs, this study considers large
shear and overturning moment exist in the 1st story column. Equivalent brace model is
incorporated into a simplified design procedure to estimate the force demand in the 1st
story column. Allowing the in-span plastic hinge to form approximately at the
0.3-height of the 1st story column, this study proposed the minimum requirements of a
capacity design to prevent the shear and flexural yielding forming at the top of the 1st
story column.
In order to design the test specimen, pushover analyses on ABAQUS FEM
models for a 12-story SPSW full system and substructure are conducted. Analytical
results confirm that the overall and local inelastic responses of the lower two stories
of the 12-story SPSW model can be accurately represented using a two-story
substructure model. Significant analysis time can be saved by using proper boundary
condition and applied loads.
In order to verify the effectiveness of the proposed capacity design method, two
0.4-scale single-bay 2-story SPSW specimens were tested using the multi-axial
testing system (MATS) in National Center for Research on Earthquake Engineering
(NCREE). Each specimen is 2.4-meter wide, 2.0-meter and 1.6-meter high for the 1st
and 2nd stories, respectively, representing the lower two stories of the 12-story
prototype SPSWs. The 2.65mm-thick low yield strength steel plates and the same
VI
boundary beams are adopted for both specimens. The two specimens, NC and SC are
designed to go into the inelastic range with or without the shear yielding forming at
the top of 1st story column under cyclic increasing lateral displacements.
The test and ABAQUS analytical results show that the proposed capacity design
method could predict the in-span plastic flexural hinge location accurately. As
predicted, the in-span plastic flexural hinge of specimen NC first developed near the
0.3-height of the 1st story column. Although the plastic zone are spread out widely
along the 1st story column height, the force versus displacement relationships of
specimen NC show that the system still have excellent load carrying capacity when
the total drift reached 5.0% radians. Shear yielding at the top of 1st story column in
specimen SC was observed when the total drift reached 2.5% radians. Soft story
mechanism was never observed in either NC or SC when the story drift reached 5.0%
radians. Although the total steel weight of NC is 5.7% more than SC, but the
maximum lateral strength of NC is 12% greater than SC. However, specimen SC may
not be desirable as severe local buckling and minor out-of-plane buckling occurred
when the total drift reached 4.0% radians.