Cross-Laminated Timber Rocking Walls with

Slip-Friction Connections (SFCs)

Dillon Fitzgerald (fitzgerd@oregonstate.edu); 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