Full Terms & Conditions of access and use can be found at http://www .tandfonline.com/action/journalInformation?journ alCode=thie20 Download by: [University of Malaya] Date:14 January 2016, At: 22:56 HKIE Transactions ISSN: 1023-697X (Print) 2326-3733 (Online) Journal homepage: http://www .tandfonlin e.com/loi/thie20 Ductility design of reinforced concrete shear walls with the consideration of axial compression ratio J S Kuang & Y P Y uen T o cite this article: J S Kuang & Y P Yuen (2015) Ductility design of reinforced concrete shear walls with the consideration of axial compression ratio, HKIE Transaction s, 22:3, 123-133, DOI: 10.1080/1023697X.2015.1071027 T o link to this article: http://dx.doi.org/10.1080/1023697X.2015.1071027 Published online: 25 Sep 2015. Submit your article to this journal Article views: 52 View related articles View Crossmark data
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Ductility Design of Reinforced Concrete Shear Walls
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7/25/2019 Ductility Design of Reinforced Concrete Shear Walls
Ductility design of reinforced concrete shear walls with the consideration of axial compression
ratio
J S Kuanga∗ and Y P Yuen b
a Department of Civil and Environmental Engineering, the Hong Kong University of Science and Technology, Hong Kong, People’s Republic of China; b Department of Civil Engineering, Bursa Orhangazi University, Turkey
( Received 1 November 2013; accepted 9 December 2014 )
To evaluate and quantify the effect of the axial compression ratio on the seismic performance of reinforced concretewalls, a comprehensive statistical analysis with 474 sets of experimental data was conducted. Stipulated limits on theaxial compression ratio and their evaluation methods in various design codes were analysed and compared. Based on
the results of these analyses, methods for calculating the effective axial compression and the limiting value of the axialcompression ratio for reinforced concrete (RC) structural walls stipulated in the Code of Practice for Structural Useof Concrete 2013 may be amended and improved on a more scientific basis. Recommendations are made for possibleamendments to the provision of design or detailing for ductility of structural walls in Clause 9.9.3 of the Hong Kongstructural concrete code 2013.
Figure 1. Compression failure of a shear wall during the 2010Chile earthquake. (Courtesy of M Francisco; acquired from NISEE e-Library, EERC, University of California, Berkeley, theUSA).
To prevent undesirable brittle failures of RC walls,
many design codes of practice for RC structures,
including the Hong Kong structural concrete code
2013 (HKConcrete2013),[18] Chinese seismic code GB
50011–2010,[19] and Eurocode 8,[20] stipulated upper
limits for axial compression ratios and boundary-element
detailing requirements for various ranges of axial com-
pression ratios. Nonetheless, later it can be seen that the
provisions in different codes of practice have dissimilari-
ties, including the definitions and limiting values. In view
of this issue, this paper presented a comprehensive survey
and study on the suitability of various code provisions
on axial compression ratios. The detailed effect of axial
compression ratios on the seismic performance of RC
walls was firstly studied, followed by a comprehensive
comparison and discussion on the corresponding code
provisions. Based on an analysis of the results, methods
for calculating the effective axial compression and the
limiting value of axial compression ratio for RC structural
walls stipulated in the Code of Practice for Structural Use
of Concrete 2013 [18] may be amended and improved on
a more scientific basis. Recommendations were made for
possible amendments to the provision of design or detail-
ing for ductility of structural walls in Clause 9.9.3 of the
HKConcrete2013.
Definitions and effects of axial compression ratios
Effect on ductility of RC walls
Axial force has a crucial role in governing the drift
ductility of RC walls. An apparent and instant effect
with a higher axial compression is the reduction of the
curvature ductility µφ of walls,[5,21] which is directly
and inversely proportional to the natural axis depth c
and in turn is a monotonic increasing function of axial
compression, given as follows:
µφ =φu
φ y
=εcul w
2.00ε y c, (1)
where l w is the wall length. Hence, the curvature ductil-
ity, as well as the drift ductility µ, decreases with an
increase in axial compression. On the other hand, when
the strain penetration effect is deemed negligible and the
plastic hinge length is assumed to be l p ≈ 0.08l w, the
drift ductility of flexural-controlled wall segments can be
estimated as follows:
µ =u
y
≈φ y H 2/3 + (φu − φ y )l p H
φ y H 2/3
= 1 +1
αV
0.12εcu
ε y cαV
− 0.24
, (2)
where αV is the vertical aspect ratio ( H /l w) and H is the
wall height.
Equation (2) further indicates that the aspect ratio αV ,
concrete crushing strain εcu and steel yielding strain ε y arealso effective parameters of the drift ductility of a wall
segment, as well as the natural axis depth c as an influ-
ential parameter. This explains why confining boundary
elements for wall segments subjected to high axial forces
are required by various design codes to compensate for
the reduced ductility due to axial compression. The con-
fined concrete in the confining boundary elements can
attain a much higher ultimate crushing strain, εcu, than the
unconfined concrete; hence, the higher curvature ductil-
ity can be achieved in RC walls with confining boundary
elements.
In addition, strength and stiffness degradation of RC
members under cyclic loading is much more pronounced
under high axial compression, which is attributed to the
low cyclic fatigue effect.[22] High axial compression can
prompt pre-emptive buckling of thin RC walls, thus lead-
ing to a sudden and complete loss of axial force carrying
capacity in a brittle manner. Although on some occasions,
axial compression may be beneficial to the shear strength
of squat RC walls with potential shear failure modes such
as diagonal tension and sliding shear,[23] this benefit gen-
erally cannot compensate for the overall adverse effect.
It is thus widely recognised that RC walls subjected to
the high axial compression are more vulnerable to seismic
effects.
7/25/2019 Ductility Design of Reinforced Concrete Shear Walls
Table 2. Values of ψri for various imposed actions.
Specific use Storey Examples ψri
Areas for domestic and residential
activities, offices and places where people may congregate.
Roof 1.0
Storeys with correlated occupancies.
School, theatre, etc. 0.8
Independently occupied storeys. Dwelling area, restaurant, etc. 0.5
Areas in retail shops, departmentstores, storage, industrial use and accumulation of goods may occur.
Warehouse, library, mechanicalroom, etc.
1.0
By rewriting Equation (9) and taking f ck = 0.67 f cu,
then the axial compression ratio of RC structural walls
is given as follows:
ncr = N W , HK
f cu Ac
≤ 0.27. (10)
To preserve the clear physical meaning of the axial
compression ratio, it is not necessary for the factor of 0.45
to be included in the denominator (Equation (5)).
Conclusions
Excellent lateral stability and drift ductility of reinforced
concrete shear walls are important in the design of
medium-to-high-rise buildings to resist seismic actions
and other exceptional loads. However, shear walls in
modern buildings are often subjected to very high axial
compression, which has been pushing the limits of the
conventional design and analysis theories.
A comprehensive statistical analysis using 474 sets
of experimental data was conducted to investigate the
effect of the axial compression ratio on the structural per-
formance of various types of RC structural wall. It was
shown that the ductility of shear walls generally dimin-
ished with an increase in axial compression ratio, and
this trend was particularly noticeable for slender walls
with an aspect ratio greater than 1.5. Provisions on the
limits of the axial compression ratio stipulated in vari-
ous design codes of practice were then compared. The
expected attainable ductility of RC walls designed to
different codes was evaluated and compared with thestatistical analysis results.
Based on the analysis results, recommendations were
made for possible amendments to Clause 9.9.3 detail-
ing for ductility of walls in the HKConcrete2013 [18]
for calculation of the effective axial compression and
determination of the limiting value of the axial compres-
sion ratio. The suggested amendments include: (1) the
calculation of the effective axial compression in RC struc-
tural walls should be based on a realistic, representative
gravity action; and (2) the limiting value for the axial
compression ratio should guarantee that well-detailed RC
structural walls can attain moderate or at least restricted
ductility.
Funding
This work was supported by the Hong Kong Research GrantsCouncil [grant number 614011].
Notes on contributors
Ir Prof J S Kuang is a Professor of Civil and Environmental Engineering,the Hong Kong University of Scienceand Technology. His areas of exper-tise span seismic engineering, with anemphasis on seismic design and the behaviour of concrete structures, seis-mic vulnerability assessment of tall buildings, large-scale testing of struc-
tural concrete, and computational mechanics and simulationin structural engineering. Ir Prof Kuang’s awards include theTelford Premium and the TK Hsieh Award from the Institu-tion of Civil Engineers UK in 2014 and 2006, respectively, and
the HKIE Transactions Prize from the Hong Kong Institution of Engineers in 2007.
Dr Y P Yuen is currently an AssistantProfessor of the Department of CivilEngineering at the Bursa OrhangaziUniversity, Turkey. His research inter-ests include seismic analysis and engi-neering of building and bridge struc-tures, theoretical and computationalmechanics of materials, reinforced concrete and masonry structures, and
tall building structures. Dr Yuen is the recipient of the 2014Telford Premium from the Institution of Civil Engineers in theUK, presented for the best paper on engineering and computa-tional mechanics.
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