This document summarizes a study on ductile reinforced-concrete beam-column joints with alternative detailing. It discusses test results from a full-scale precast beam-column subassembly specimen (Specimen #2) incorporating ductile thread rod connectors and post-tensioning. The specimen exhibited stable hysteretic behavior with little strength degradation or post-yield deterioration up to 7% drift, comparable to monolithic cast-in-place results. While beam rebar fractured at high drifts, overall the test supported using precast construction for beam-column joints.

1. Ductile Reinforced-Concrete Beam-
Column Joints with Alternative Detailing
EERI Annual Meeting
February 13, 2009
by Barbara Chang
University of California, San Diego

2. Acknowledgements
• EERI, FEMA, and NEHRP Graduate
Fellowship
• Charles Pankow Foundation,
Englekirk Partners, Dywidag
Systems International USA, Inc
(DSI), Morley Contractors, MMFX
Tech Corp, Baumann Eng, and Clark
Pacific.
• TC Hutchinson, RE Englekirk, R Chen
• Powell Laboratory Staff: A
Gundthardt, C Latham, R Parks

3. Seismic Design Philosophy
• Provide minimum standards to
maintain public safety in an extreme
earthquake
• Safeguard against major failures and
loss of life
– Do not necessarily limit damage, maintain
function, or provide for easy repair
• Design assumes significant amount of
inelastic behavior will occur in the
structure during a design earthquake
– Design forces much lower than if structure
assumed elastic

4. Result!
Building survival in a large earthquake
depends on the ability of its lateral
resisting system to dissipate energy
hysteretically while undergoing large
inelastic deformations
Public misconception: Buildings will not
be damaged during earthquakes.

5. What does dissipated energy
look like in a structure?

6. Code-conforming joints

7. Joint Failures

8. Use of ductile joints
Δ, small
Stiff and Strong Foundation
Small
displacements
protect frame
from damage
High forces
cause shear
wall damage Δ,large
Flexible and Weak Foundation
Large
displacements
cause frame
damage
Foundation
yielding and
rocking protects
shear wall
Δ, smallΔ, small
Stiff and Strong Foundation
Small
displacements
protect frame
from damage
High forces
cause shear
wall damage
High forces
cause shear
wall damage Δ,largeΔ,large
Flexible and Weak Foundation
Large
displacements
cause frame
damage
Large
displacements
cause frame
damage
Foundation
yielding and
rocking protects
shear wall
(ATC 40, 1996)

9. Warcholik & Priestley, 1997
γ = 6.7%
Comparable specimen
- Full scale
- Reduced joint reinforcing

10. Warcholik & Priestley, 1997

11. Test Program Design
• Four full-scale specimens
– Interior beam-column subassemblies
– Experimentally assess various innovative
alternatives
• Re-evaluate previous hybrid system @ full-scale
• Combine previously successful attributes of
hybrid and ductile connector subassembly
• High strength & strain capacity steels
• Extensive input & consultation from
Industry – what do they want/need!
• Performance, constructability, & cost

12. Test Set-up Design

13. Specimen #2
Full-Scale
Building Beam-
Column
Subassembly
Slow reversed cyclic displacement loading
Controlled evaluation of physical damage
> 100 analog sensors internal/external monitoring
23’

14. Ductile System – Enhancement (#2)
Dywidag Ductile Connector
• Attributes
– Precast assembly
– Yielding within
column, minimal
damage to beam
– Recentering/elastic
restoring force

16. Details: #2
= Cast-in-Place
= Precast
Beam stopped short (North) Flush beam (South)

17. Precast Details
Flush beam (South)
Beam stopped short (North)
(dowels extended for slab)
= Cast-in-Place
= Precast

18. Slab details
• North beam has no
cut-out in slab.
Only DDRs with
Threadrod used.
• South beam
has cut-out in
slab. Both DDRs
and DDC used.

19. P#2: Damage Observations
γ = 1.77%

20. P#2: Damage Observations
γ = 2.65%

21. P#2: Damage Observations
γ = 2.65%
(2nd cycle)

22. P#2: Damage Observations
γ = 5.25%

23. P#2: Damage Observations
γ = 5.25%

24. P#2: Damage Observations
γ = 7%

25. P#2: Damage Observations
γ = 7%

26. P#2: Damage Observations
γ = -7.1%
End of test

27. Videos of #2
DDR, DDC, & post-tensioned subassembly
Overall View Joint Region

28. P#2: PT + DDC (‘super hybrid’)
γ = 7.0%
Salient features:
-Stable hysteresis
-Asymmetric behavior
-No post-yield degradation

29. Design versus experimental
• Reasonable results from predicted
values.
Predicted Experimental
Δy (in) 0.87” 1.41”
Vy (kips) 113 110
My (kip-in) 13600 13560
Ky (kip/%) 157 92
EIeff (kip-
in2)
9.5*107 11.1*107

30. Popov et al. (1972)
CIP, Cantilever
specimen, conv
reinforced

31. CIP vs Precast

32. Secant Stiffness
-8 -4 0 4 8
Average Drift Ratio γ (%)
0
50
100
150
200
250Stiffness(kip/%γ)
Pankow 2
Popov

33. Hysteretic energy/cycle

34. Equiv viscous damping/cycle

35. Remarks
• Specimens exhibited stable hysteresis
response
– Little-no strength degradation post-yield
– Reasonably full hysteresis
– Fairly symmetric hysteresis
– Theoretical strengths & yield deformation
comparative
• Fracture of longitudinal beam rebar requires
consideration (but – for demands > 7% drift)
• Results are consistent with CIP specimen
behavior, support use of precast in practice