Cross-Laminated Timber Rocking Walls with
Slip-Friction Connections (SFCs)
Dillon Fitzgerald ([email protected]); Arijit Sinha; Thomas H. Miller; John Nairn
Cap Plate
Bearing Cog
Base Plate
Ledge
Belleville Springs
Slotted Plate
Brass Shims
MOTIVATION
OBJECTIVES METHODS
RESULTS
Cross-laminated timber panels are very strong and stiff in-
plane, requiring carefully designed connections to dissipate
energy and transfer large forces. As taller wood buildings
are constructed, stronger, stiffer, and more resilient lateral
performance is required for connections. The presented
slip-friction connection (SFC) is a novel application of a time
tested passive energy dissipator and the presented research
focuses on full-scale testing of CLT rocking walls.
Fig. 1. Assembled CLT rocking wall with slip-friction connections at the corners and a centered restoring rod.
Fig. 2. Parts of the slip-friction connection Fig. 3. Notch in CLT wall panel with one of two SFCs and polymer bearing pad installed (top-left). Partially-threaded screws with wedge washers and a cut away of tested screw holes (top-right). Bent screws after tests (bottom-left). Sliding surfaces after all connection and wall tests (bottom-right).
1. Develop and test a stiff, strong, and elastic connection
between CLT and the slip-friction connection (Fig. 1 and
2).
2. Determine the damping capacity of the slip friction
connection and the entire rocking wall assembly (Fig. 1).
3. Detail a simple to install supplemental restoring force
system and a method to control wall base sliding.
4. Protect the CLT wall from damage under loads
significantly above allowable loads.
5. Create a fixed rocking point system for modeling
simplicity.
6. Determine the repeatability of slip forces.
• CLT walls were 1.52x3.04 m (5x10 ft) V1 Douglas-fir
(Fig. 1).
• Conducted connection and full-scale wall tests using
monotonic and various pseudo-static cyclic loads.
• Belleville washers (Fig. 2) and a torque wrench were used
to develop repeatable and predictable slip loads.
• 10x140 mm ASSY Ecofast screws with 45 degree
washers were used to transfer load from the SFC to the
CLT wall (Fig. 3. top-right).
• Screws were installed at 45-degrees in two different
loading directions to create a wood connection that was
proof loaded to 668 kN (150 kip) in tension and
compression.
• 70 connection and 30 wall tests were conducted.
The tested slip-friction connections performed very well
during the 100 overall tests with no significant damage to
the system. The SFC could be implemented into multistory
timber buildings in high seismicity regions. Further
observations are:
• The inclined screw connection achieved a stiffness of
570 kN/mm (3200 kip/in).
• The ASSY Ecofast screws failed at 24.7 kN (5.5 kip) per
screw in withdrawal when cyclically loaded.
• The inclined screws exhibited a long linear elastic region
and yielded near 85% of their peak load.
• The equivalent viscous damping of the slip-friction
connection, including the deformation from the screw to
SFC, was found to be 0.56, 87% of the dissipation of an
idealized friction system.
• The bearing cog controlled lateral base sliding, rotated
with the rocking wall, and slid freely on the bearing
pads.
• The restoring rods were able to provide complete self-
centering of the system and predictable lateral
resistance (Fig. 5).
• Intentional bolt hole slack was easy to identify and
model. Indicating easy system improvement with tighter
fabrication tolerances (Fig. 4 and Fig. 5).
• No damage occurred to the CLT wall until the test was
adjusted to force a screw withdrawal failure. With no
screws removed, the SFC cap plates began to fail in steel
bearing.
• Slip forces were highly repeatable with variation
averaging 5%.
• Screw roping noticeably improved the stiffness and
strength of the connection.
Fig. 4. Slip-friction connection extension at both North (N) and South (S) wall corners during cyclic testing. The “chipping” in the N SFC is due to bolt hole oversizing. The stiffening of the envelop is due to the restoring rod compressing the springs.
Fig. 5. Top-of-wall actuator displacement and force with “chipping” from bolt hole slack. High self-centering is present as evident by the symmetric flag shape returning to zero.
Slip-friction connection
(SFC)
Restoring rod with
stacked Belleville
springs
