The document summarizes an experimental study on the seismic response of steel link beams coupling reinforced concrete walls. Two specimen walls were tested with short span steel beams connecting the walls. The steel beams were designed according to seismic standards to yield in shear and dissipate energy through hysteretic damping. Both specimen walls exhibited excellent ductility and energy absorption. The steel beams remained elastic with minor local buckling. The study demonstrated that steel link beams can provide ductile connections between reinforced concrete walls to resist seismic forces if properly designed and detailed.

1. SEISMIC RESPONSE OF STEEL BEAMS
COUPLING CONCRETE WALLS.
Presented by: Yahya Ali
Authors: Kent A. Harries, Denis
Mitchell, Member, ASCE, William D.
Cook and Richard G. Redwood.

2. Ductile coupled flexural walls are primary seismic load resisting
systems.
Their coupling beams must exhibit excellent ductility & energy
absorption.
Structural steel members with their ends embedded in concrete have
been used to provide connections for many
years in precast and cast-in-place construction.

3. In the following presentation we will expose the experimental
results for two specimen of RC flexural walls, coupled with steel
link beams and subjected to reversed cyclic-loading test.
Design and detailing of the system is also presented.

4. The experimented system has the following potential advantages:
1. Excellent ductility and energy absorption if the beam is properly detailed.
2. Elimination of a considerable amount of on-site labor due to the beam
prefabrication.
3. Simplification of formwork

5. DESIGN OF STEEL LINK BEAM
The beams for specimens 1 and 2 are designed in accordance
with the seismic design requirements for EBFs in the Canadian steel
design standard (Handbook 1989).
The design and detailing requirements are based on those of
recommended by the Structural Engineers Association of
California (Recommended 1988).
The coupling beam is the critical element  it must respond in a
ductile manner and exhibit significant energy absorbing
characteristics.

6. Steel link beams are more ductile than RC beams and are
able to dissipate greater amounts of energy if they are
designed and detailed to yield in shear.
The shear-to-moment ratio is large for short-span link beams
then:
 Ultimate shear capacity will be reached before the
flexural capacity.
 “Shear critical" design is frequently called for.
 The maximum amount of energy will be dissipated when
the link beam begins to exhibit plastic behavior.
In addition, the link beams were detailed to avoid local buckling of both the web and flange and lateral buckling of the link beam.

7. DESIGN OF REINFORCED CONCRETE EMBEDMENT REGIONS
At the faces of the walls, the link beam transmits a shear V and a moment of
Vl/2 to the reinforced concrete embedded region.
Shear and moment diagram of the beam:

8. Where the nominal shear capacity Vc of the concrete embedment is given by:
The embedment length le was chosen such that the vertical load capacity of the concrete embedment Vc exceeds
the plastic shear capacity of the link beam Vp which is equal to 1.25xVn
Vn: the nominal shear strength
Where:
e = eccentricity of resultant shear loads from the center of the embedment (i.e., e = l/2 + le/2);
f’c = compressive strength of concrete.

9. It is therefore necessary to provide sufficient vertical
reinforcing bars crossing the link beam-concrete
interface.
Under loading, a gap is created at the link beam flange-
concrete interface.
A larger proportion of reinforcement is concentrated near
the face of the wall.
Details of link beams of specimen 1 and 2:
Specimen 1:

10. Specimen 2:
Material
properties:

11. Details of reinforcing
cage of both
specimen:

12. Details of reinforcing cage and link beam of specimen1:`

15. Linear voltage differential transformers (LVDTs) recorded vertical displacements of both the
link beams and the concrete walls.
Electrical-resistance strain gages
recorded the strains in the link beam,
wall reinforcing bars, and on the face of
the concrete walls.
Load cells recorded the applied
forces.

16. Both steel link beam specimens exhibited great energy absorption.
Specimen 2 exhibited the largest levels of hysteretic
damping, with the least amount of decay with cycling.
This damping coefficient β is defined as:
Where:
A1 = area within the hysteresis loop of one half cycle
A2=area of the triangle defined by an equivalent elastic
stiffness to the peak load of each half cycle.
The decay of energy absorption occurring with cycling at each
ductility level is the width of the response band.
Experiment results:

17. Link Beams of Specimen 1 (a) and 2 (b) after removal
from Walls
Equivalent Elastic Damping Coefficients for
Specimens I and 2 and Reinforced Concrete
Coupling Beams

18. Specimens 1 and 2 after testing:
Specimen 1 Specimen 2

19. DESIGN STEPS OF LINK BEAM:
Step 1
Determine the web dimensions to resist the required shear strength Vu from:
Step 2
Determine the required moment resistance φbMn:
Step 3
Choose a beam section that satisfies the width-thickness ratios of Table 8.1 of AISC (Seismic 1992).
Provide full-depth intermediate stiffeners with details and spacing according to clause 10.3 of AISC (Seismic 1992).
Step 4
To control out of plane buckling, the maximum unsupported length Lp is given as:

20. Step 5
Provide full-depth stiffeners wide enough and having a thickness not less than 0.75tw or 10 mm.
Provide an additional full-depth intermediate stiffener on the embedded region of the web at a distance
equal to the cover inside the face of the wall.
Either provide additional intermediate stiffeners to obtain shear resistance >= Vp in clear
span or increase the web thickness in the embedment such that:
Step 6
Determine the required length of effective embedment leff such that:
Step 7
Choose the area of vertical reinforcing bars As, such that:

21. CONCLUSIONS:
The results of this experimental program have shown that:
It is possible to achieve excellent ductility and energy absorption characteristics by using this system.
Additional stiffeners are provided in the region of expected cover spalling
The embedment region must be designed for a shear and moment corresponding to the development of the full
capacity of the link beam.
Vertical reinforcing bars are placed near the inside face of the walls
The use of this system provides excellent quality and greatly simplifies the formwork and steel placement.
The use of steel link beams in RC walls is an alternative to traditionally or diagonally RC coupling beams.
The excellent performance of this structural system is well suited for structures designed for high levels of
ductility.

22. THANK YOU