Updates for beam-column joints reinforced with high-strengthreinforcement
Hung-Jen LeeAssociate Professor
National Yunlin University of Science and Technology
Moment-resisting frame joints
Interior joint
Exterior joint
Nominal joint shear strength Joint confinementDevelopment and Anchorage
Steel bar stress
fs = αo fyfs'
hc
Excessive slip
db
Crushed concrete
Crushed concrete Q
θ
Typical cyclic loading response
Very pinched hysteresis loops
Very low stiffness at small drift
Degraded strength in repeated cycles
fs = αo fyfs'= καo fy
hc
db =Beam bar diameterAverage bond focres
Steel bar stress
fs = αo fyfs'= καo fy
Can HSR be properly anchored in the joint?
Design Criteria for Minimum Joint Depth ACI 318-14
20≥b
c
dh
⋅≥
MPa420 20 y
b
c fdh
ACI 352-02 26 420
55020 =
⋅≥
b
c
dh
33 420
69020 =
⋅≥
b
c
dh
ℎ𝑐𝑐𝑑𝑑𝑏𝑏
≥𝑓𝑓𝑦𝑦
3.2 𝑓𝑓𝑐𝑐′MPa =
𝑓𝑓𝑦𝑦38.4 𝑓𝑓𝑐𝑐′
psi
We proposed
0 2 4 6 8 10 12 14Concrete compressive strength, fc
' (ksi)
0.50
0.75
1.00
1.25
1.50
1.75
2.00
Re l
a tiv
e min
. colu
mn di
men
s ion
0 10 20 30 40 50 60 70 80 90 100Concrete compressive strength, fc
' (MPa)
10
15
20
25
30
35
40
13
20
26
33
39
46
52
16
25
33
41
49
57
66
Brooke and Ingham
(2013)
Li and
Leong
(2014)
Eurocode (2004)
NZS 3101
(2006)
AIJ Guideline (1999)
ACI 352R
(2002)
hc
db
420
550
690 MPa
Steel Grade
Steel
Grade
60
80
100 ksi
As,bot / As,top=
0.75P
= 0.2Ag
fc'
Proposed
Design Criteria for Minimum Joint Depth
Q
θ
Evaluation of hysteresis loop at the 2nd or 3rd cycle of 4% drift ratio
Energy dissipation
𝑄𝑄 ≥ 0.75𝑄𝑄𝑚𝑚
𝐾𝐾𝑜𝑜 ≥ 0.05𝐾𝐾𝑖𝑖
⁄𝐸𝐸𝐷𝐷 𝐸𝐸𝑃𝑃𝑃𝑃 ≥ 0.125
ACI 374.1-05Strength
Stiffness 𝐾𝐾𝑖𝑖 𝑄𝑄𝑚𝑚
𝐸𝐸𝐷𝐷
𝐸𝐸𝑃𝑃𝑃𝑃
20 30 40 50 60 70 80 90 100 110 120Concrete
compressive strength, fc' (MPa)
10
15
20
25
30
35
40
ℎ𝑐𝑐𝑑𝑑𝑏𝑏
Beam-Column Joints with Grade 490 beam bars
23 420
49020 =
⋅≥
b
c
dh
ℎ𝑐𝑐𝑑𝑑𝑏𝑏
≥𝑓𝑓𝑦𝑦
3.2 𝑓𝑓𝑐𝑐′
26 data
20 40 60 80 100 120 140 160Concrete
compressive strength, fc' (MPa)
10
15
20
25
30
Beam-Column Joints with Grade 590 beam bars
ℎ𝑐𝑐𝑑𝑑𝑏𝑏
28 420
59020 =
⋅≥
b
c
dh
13 data
ℎ𝑐𝑐𝑑𝑑𝑏𝑏
≥𝑓𝑓𝑦𝑦
3.2 𝑓𝑓𝑐𝑐′
Beam-Column Joints with Grade 690 beam bars 15 data
20 40 60 80 100 120 140 160 180 200Concrete
compressive strength, fc' (MPa)
10
15
20
25
30
35
ℎ𝑐𝑐𝑑𝑑𝑏𝑏
33 420
69020 =
⋅≥
b
c
dh
ℎ𝑐𝑐𝑑𝑑𝑏𝑏
≥𝑓𝑓𝑦𝑦
3.2 𝑓𝑓𝑐𝑐′
Seismic Testing for Interior Beam-Column Joints, Lee et al. (2014) A24
𝐴𝐴𝑠𝑠,𝑏𝑏𝑜𝑜𝑏𝑏
𝐴𝐴𝑠𝑠,𝑏𝑏𝑜𝑜𝑡𝑡= 0.75
24 mm 25mm 600
==b
c
dh
𝑓𝑓𝑐𝑐′ = 100 𝑀𝑀𝑀𝑀𝑀𝑀𝑓𝑓𝑦𝑦 = 690 𝑀𝑀𝑀𝑀𝑀𝑀
Test results
Qn
-918kN
918kN
-8 -6 -4 -2 0 2 4 6 8
Story Drift
(%)
-1500
-1200
-900
-600
-300
0
300
600
900
1200
1500
Sto
r y S
hear
, Q (k
N)
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
Q/ Q
n3 2 1
1 2 3
μ
μBJ-typeA24
33
𝑓𝑓𝑐𝑐′ = 100(116) 𝑀𝑀𝑀𝑀𝑀𝑀
𝑓𝑓𝑦𝑦 = 690(725) 𝑀𝑀𝑀𝑀𝑀𝑀
𝑀𝑀 = 0.05𝐴𝐴𝑔𝑔𝑓𝑓𝑐𝑐′
𝛼𝛼𝑜𝑜 = 1.15
Simplified equation
24 mm 25mm 600
==b
c
dh
Provided
4%-drift cycle Performance Rating = 3 Acceptable 𝐴𝐴𝑠𝑠,𝑏𝑏𝑜𝑜𝑏𝑏
𝐴𝐴𝑠𝑠,𝑏𝑏𝑜𝑜𝑡𝑡= 0.75
0.93, =n
mjh
VV
ℎ𝑐𝑐𝑑𝑑𝑏𝑏
≥690
3.2 100= 22
30 40 50 60 70 80 90 100 110 120Concrete
compressive strength, fc'
(MPa)
15
20
25
30
35
Min
imum
Co l
umn D
e pt h
, h c (d
b)
420 560 700 840 980 1120Concrete
compressive strength, fc
(kgf/cm2)
ℎ𝑐𝑐 ≥𝑓𝑓𝑦𝑦
3.2 𝑓𝑓𝑐𝑐′𝑑𝑑𝑏𝑏 𝑀𝑀𝑎𝑎𝑑𝑑 20𝑑𝑑𝑏𝑏
-6 -4 -2 0 2 4 6
Drift Ratio
, θ (%)
-400
-300
-200
-100
0
100
200
300
400
Stor
y Shea
r , Q
(kN
)Brooke-2006Unit-3B
Bond or anchorage failure (BJa failure)
Brooke, N. J.; Megget, L. M.; and Ingham, J. M., (2006) "Bond Performance of Interior Beam-Column Joints with High-Strength Reinforcement," ACI Structural Journal, V. 103, No. 4, Jul-Aug,
Beam hinging but no bar buckling
Unit 3B
Robust hysteresis behavior
-6 -4 -2 0 2 4 6
Drift Ratio
, θ (%)
-400
-300
-200
-100
0
100
200
300
400
Stor
y Shea
r , Q
(kN
)Brooke-2006Unit-3B 2725/675/
537/45/0.75/,
==
=′
=
bc
yac
nmjh
dhff
VV
Bond failure at 4.4% drift ratio
Bond or anchorage failure along beam bars in the joint (BJa failure)
Hwang H-J, Park H-G, Choi W-S, et al. (2014) Cyclic Loading Test for Beam-Column Connections with 600 MPa (87 ksi) Beam Flexural Reinforcing Bars. ACI Structural Journal 111 (4)
Pinching behavior
Low residual stiffness at small displacement
Unlikely to repair
2225/055/635/30/
0.79/,
==
=′
=
bc
yac
nmjh
dhff
VV
Concrete crushing at beam ends
-250
-200
-150
-100
-500
50100150200250
Stor
y Shea
r, Q
(kN
)
-6 -4 -2 0 2 4 6Story
Drift Ratio
(%)
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
Q / Q
y
(d) Specimen
EW0
BJa-failure
-600
-450
-300
-1500
150300450600
Stor
y Shea
r, Q
(kN
)
-6 -4 -2 0 2 4 6Story
Drift Ratio
(%)
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
Q / Q
y
(c) Specimen
B1BJ-failure
“BJ” failure versus “BJa” failure
2025/005/470/56/
08.1/,
==
=′
=
bc
yac
nmjh
dhff
VV
2019/004/347/31/
78.0/,
==
=′
=
bc
yac
nmjh
dhff
VV
06.0/ =′cg fAP 10.0/ =′cg fAP
Lee et al. (2017) Lee et al. (2007)
Concluding remarks
G.L
Plastic Hinge
chbd
Pinching effect
Strength and stiffness degradation, poor hysteresis behavior
Low residual stiffness at small displacement
Unlikely to repair
Bond failure
ℎ𝑐𝑐 ≥𝑓𝑓𝑦𝑦
3.2 𝑓𝑓𝑐𝑐′𝑑𝑑𝑏𝑏 𝑀𝑀𝑎𝑎𝑑𝑑 20𝑑𝑑𝑏𝑏
SD685-D25 Bar tensile tests
20
Grade, Size
Yield Strength(N/mm2)
Tensile Strength(N/mm2)
Elongation(%) TS/YS Yield
Pleatau
Criteria 685~785 ≧860 ≧10 ≧1.25 ≧0.014
SD685,D25 703 907 16 1.29 0.022
SD685,D25(Retest) 713 932 15 1.31 0.0216
SD685 D25Tensile tests0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16
Strain
0
150
300
450
600
750
900
1050St
ress
(N/m
m2 )
D25-SD685
fya=703 N/mm2
fya=713 N/mm2
fua=907 N/mm2
fua=932 N/mm2
0 0.005 0.01 0.015 0.02Strain
0
150
300
450
600
750
900
1050
Stre
ss (N
/mm
2 )
E=223,369 N/mm2
E=196,481 N/mm2
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