HIGH-CAPACITY HYPERELASTIC HOLD-DOWN FOR CROSS-LAMINATED
TIMBER SHEAR WALLS

By

Oyawoye Abubakar Ajibola

B.Sc., University of Portsmouth, Portsmouth, United Kingdom, 2009
M.Sc., University of Sheffield, Sheffield, United Kingdom, 2012

PROJECT REPORT SUBMITTED IN PARTIAL FULFILLMENT OF
THE REQUIREMENTS FOR THE DEGREE OF
MASTER
OF
NATURAL RESOURCES AND ENVIRONMENTAL STUDIES

UNIVERSITY OF NORTHERN BRITISH COLUMBIA
August 2021
© Oyawoye Abubakar Ajibola, 2021

Abstract
Cross-laminated timber (CLT) continues to establish a stronger footing in the Canadian
construction industry, also as an option for lateral load resisting systems, such as shear walls.
Recent modifications to the Canadian Standard for Engineering Design in Wood (CSA O8619) allow only rocking kinematics as energy dissipative mechanics for CLT shear walls,
whereby hold-down must remain elastic. These provisions necessitate the development of
novel hold-down solutions. In this report, the performance of a hyper-elastic high-capacity
hold-down was investigated at the component level through tests on: (1) hold-down steel rod,
(2) CLT housing, and (3) hold-down assemblies with different sizes of rubber pads. The tests
demonstrated that: i) the rubber hold-down can remain elastic under a rocking kinematics
provided that the elastic limit of the steel rod is not exceeded; ii) failure of the rod is the
subsequent desired ductile mode; iii) the CLT width influences the failure mode; iv) the shape
factor influences the achievable deformation of the rubber pad; v) increasing the rubber pad
thickness reduces the hold-down stiffness; and vi) increasing the rubber pad width increases
the hold-down stiffness. Numerical modelling and optimization suggested that using an
intermediate steel laminate between layers of rubber pads could improve its performance.
Based on the results of the investigations presented herein, a capacity-design procedure for the
hyper-elastic hold-downs was proposed.

ii

Table of Contents
Abstract..................................................................................................................................... ii
Table of Contents..................................................................................................................... iii
List of Figures ............................................................................................................................ v
List of Tables .......................................................................................................................... vii
List of Symbols...................................................................................................................... viii
Acknowledgements ..................................................................................................................ix
Chapter 1:

Introduction ....................................................................................................... 1

Background ................................................................................................................ 1
Problem statement ..................................................................................................... 1
Objective, scope and limitations................................................................................ 3
Chapter 2:

Literature Review .............................................................................................. 4

Cross-laminated timber.............................................................................................. 4
CLT shearwalls and connections ............................................................................... 5
Hyper-elastic rubber hold-down ................................................................................ 9
Summary .................................................................................................................. 11
Chapter 3:

Experimental investigations ............................................................................ 12

Overview ................................................................................................................. 12
Materials – steel rods ............................................................................................... 13
Materials – CLT....................................................................................................... 14
Materials – rubber .................................................................................................... 15
Materials: top and bottom plate ............................................................................... 18
Steel rod tests ........................................................................................................... 19

iii

CLT tests .................................................................................................................. 21
Hold-down tests ....................................................................................................... 22
Chapter 4:

Experimental results and discussion ................................................................ 26

Steel rod test results ................................................................................................. 26
CLT test results ........................................................................................................ 27
Hold-down test results ............................................................................................. 28
Discussion rod tests ................................................................................................. 31
Discussion CLT tests ............................................................................................... 33
Discussion hold-down tests ..................................................................................... 35
Chapter 5:

Finite element analysis .................................................................................... 41

Modell development ................................................................................................ 41
FEA results and discussion ...................................................................................... 44
Verification .............................................................................................................. 46
Chapter 6:

Conclusions and outlook ................................................................................. 47

Appendix: All hold-down test result ....................................................................................... 53

iv

List of Figures
Figure 1-1: Layout of hyper-elastic hold-down in a CLT shear wall ........................................ 3
Figure 2-1: Typical CLT shear wall layouts .............................................................................. 7
Figure 2-2: Coupled panel kinematic behavior ......................................................................... 7
Figure 3-1: Capacity-based design principle ........................................................................... 12
Figure 3-2: Steel rod samples .................................................................................................. 14
Figure 3-3: Geometry parameters for CLT housing ................................................................ 15
Figure 3-4: Geometry parameters of rubber pad ..................................................................... 17
Figure 3-5 Masticord rubber pad a) 90mm pad b) 140mm pad............................................... 17
Figure 3-6: Steel top and bottom plates ................................................................................... 19
Figure 3-7: Layout for hold-down steel rod tests .................................................................... 20
Figure 3-8: Modified CUREE cyclic loading .......................................................................... 21
Figure 3-9: CLT test setup ....................................................................................................... 21
Figure 3-10: Rubber hold-down component level test setups ................................................. 24
Figure 4-1: Load-displacement of a) full and b) section reduced rod under monotonic loading;
c) preliminary test carried and d) hold-down rod quasi-static monotonic and cyclic test ....... 26
Figure 4-2: CLT test load-displacement curve ........................................................................ 28
Figure 4-3: Hold-down load-displacement: a) 90mm and b) 140mm wide rubber hold-down
................................................................................................................................................. 29
Figure 4-4: Failed rod after testing .......................................................................................... 31
v

Figure 4-5: CLT failure patterns .............................................................................................. 34
Figure 4-6: CLT failed specimens, part 1 ................................................................................ 34
Figure 4-7: CLT failed specimens, part 2 ................................................................................ 35
Figure 4-8: a) CLT failure of outer lamella using configuration A; b) CLT intact after multiple
tests using configuration B ...................................................................................................... 36
Figure 4-9: Deformation of hold-down at 120 kN load ........................................................... 38
Figure 4-10: Hold-down deformation vs. shape factor under monotonic loading for a) 90mm
and b) 140mm wide hold-downs ............................................................................................. 39
Figure 4-11: Hold-down deformation at 120kN vs shape function and width of rubber pad . 40
Figure 5-1: Maximum allowable load vs. shape factor ........................................................... 41
Figure 5-2: Sketch of the model with dimension definition .................................................... 42
Figure 5-3: Finite element models a) P4 b) NP4 ..................................................................... 43
Figure 5-4: Model contact interaction and boundary condition .............................................. 43
Figure 5-5: Simulated compression of the rubber pad of a) NP4, b) P4 ................................. 44
Figure 5-6: Simulated load-displacements .............................................................................. 45
Figure 5-7: Deformation at 120kN based on numerical model ............................................... 45
Figure 5-8: Numerical result verification ................................................................................ 46

vi

List of Tables
Table 3-1: The material property of the CLT sample .............................................................. 14
Table 3-2: Dimension of CLT samples ................................................................................... 15
Table 3-3: Relevant mechanical properties of Masticord [33] ................................................ 16
Table 3-4: Rubber test samples dimension .............................................................................. 18
Table 3-5: Labels and dimensions for the CLT test sample .................................................... 22
Table 3-6: The label, discretion and loading rate for the hold-down test. ............................... 25
Table 4-1: Result of preliminary steel rod test ........................................................................ 27
Table 4-2: Results of hold-down rod quasi-static monotonic and cyclic tests ........................ 27
Table 4-3: CLT test results ...................................................................................................... 28
Table 4-4: Hold-down deformation under quasi-static monotonic loading ............................ 30
Table 4-5: Design peak load Fload and yield load Fy,Rod ........................................................... 32
Table 5-1: The parametric data of the simulated sample ......................................................... 42
Table 5-2: Yeoh 3rd model parameters ................................................................................... 44

vii

List of Symbols
ac
al
h
hs
r
w

Edge distance
Loaded end distance
Height of CLT panel
Height of the slot
Rounded corner radius
Width of the CLT panel

ws
t
t1
tt
wlam
wR

Width of the slot
Thickness of the CLT panel
Thickness of longitudinal layers
Thickness of transverse layers
Width of lamellas
Width of rubber pads

wst

Width of steel plates

dR

Depth of rubber pads

dst

Depth of steel plates

tR

Thickness of rubber pads

tst

Thickness of steel plates

φ

Diameter of the centric hole

NR
CLT
Fy,rod
Fd,max
Fpeak
FU,rod
FU,rubber
FU,CLT
FTarget
Ro
Rd
SF
σc

Number of rubber layer
Cross laminated timber
Hold-down rod yield load
Hold-down rod maximum elastic design load
Hold-down rod peak load
Hold-down rod ultimate load
Load in rubber at 40% strain (ultimate load)
CLT Ultimate load
Elastic design load or Experiment target load
Reduction factor due to overstrength
Reduction factor due to ductility
Shape factor
Compressive stress in rubber pad
Compressive strain in rubber pad

ec
Vnr

Compressive Load in rubber pad

viii

Acknowledgements
Glory be to God for the completion of this report.
The completion of this study could not have been possible without the expertise and support
of Dr. Thomas Tannert, a remarkable supervisor and mentor. It was a great honor to work with
him. His wealth of knowledge provides valuable suggestion for the experiment and review of
the report. He is a wonderful person to work with. Many thanks to Dr. Asif Iqbal and Dr.
Cristiano Loss for their contribution as co-supervisors and role as committee member. In
addition to this, I would like to offer a special thanks to Dr. Asif Iqbal. Without his offer of
admission to the program, I would not have a chance to work with Dr. Thomas Tannert.
Many thanks to Hosain Asgari; this study was built on the extensive foundation inherited from
his thesis work. Finite element analysis studies carried out was built on parameters derived
from his material level testing.
I owe a debt of gratitude to my fellow graduate student, there review and suggestions on my
academic writings contributed immensely. I would also like to thank the technical staff at the
Wood Innovation Research Laboratory; Michael Billups, Ryan Stern and James Andal, their
supports are greatly appreciated. A special gratitude to Claudia Barreira and Mr. Niyi Bankole
for their moral support, it was useful throughout my studies.
A final big thank you to my parents, Prof. and Mrs. Oyawoye, my wife, Aisha Nwakego
Oyawoye, and children, the contribution of your bravery, patience and mental support is a
major part of this success that cannot be understated.

ix

Chapter 1: Introduction
Background
Environmental concerns around the world have driven the need for sustainable substitutes to
steel and concrete multi-storey construction. Cross-laminated timber (CLT) has been proven
to be environmentally friendly and sustainable; it acts as a carbon storage and requires less
energy to manufacture [1]. CLT has structural properties that makes it suitable for multi-story
applications and tackling earthquake-related challenges [2, 3, 4]. When compared with steel
and concrete, CLT is lighter and has a higher strength to weight ratio, which results in a smaller
foundation and consequently saving project cost and construction time. CLT has gained
popularity as a building material in Canada because of these advantages [5]. Many CLT
Structures have been erected around Canada in the past decade; examples include the Wood
Innovation and Design Centre (WIDC), a 29.5m high 6-storey building in Prince George,
British Columbia, the Origine building in Quebec City which is 41m high; and the 18 story
UBC Brock Commons Tall Wood House in Vancouver, which is 54m high [6].
Problem statement
Since wood when loaded in tension or shear is a brittle material, wood structures typically rely
on their connections for ductility to avoid brittle failure [7, 8]. Consequently, recent research
and development efforts have given more attention to innovation and the manufacture of
proprietary connector kits for mass timber construction. Contemporary connectors are usually
made of cold-formed steel with various fastener types that can provide the ductility needed in
structural design [9, 10]. However, dissipative connections suffer degradation in stiffness and
strength during earthquake action, a phenomenon known as pinching action [11].

Page 1

In any CLT shear wall, the function of the hold-down is to resist uplift from overturning
moments caused by lateral forces. Recent modifications in the Canadian Standard for
Engineering Design in Wood (CSA O86-19) dictate that hold-downs in CLT shearwall remain
elastic, even though hold-downs have been widely proven to act as dissipative connections.
The standard also dictates that rocking should be the only form of allowable kinematics [12,
13]. Most of the existing hold-downs cannot accommodate such kinematics and remain elastic
at the same time [14]. Therefore, there is a need for innovative hold-down solutions that can
meet these new standard requirements.
A hyperelastic hold-down system was developed and investigated by Asgari et al. [15]. Even
though the concept is still in its early stage of development, the tests demonstrated that the
rubber hold-downs exhibited high strength and deformation capacity without any residual
deformation after unloading. Shape factor and loaded area of rubber layers were the main
factors that contribute to the response of the rubber hold-down.
The layout of the hold-down in a shear system is as described in Figure 1-1. The concept
consists of a coupled shearwall connected by a vertical joint for energy dissipation. The rubber
hold-down itself consists of an opening inside the CLT panel with a rubber pad and
compression plate, connected to the floor beneath through a steel rod that passes through a
drilled hole in the middle of all of the hold-down assembly’s members. Rocking kinematics is
ensured in the shearwall through a supporting non-dissipative shear connector. When the shear
wall rocks, the rod is loaded in tension, compressing the rubber pad as a result.

Page 2

Figure 1-1: Layout of hyper-elastic hold-down in a CLT shear wall

Objective, scope and limitations
The work presented in this report studied the hyper-elastic rubber hold-down on the component
level based on its role in full-scale shearwall system. To achieve this objective, first the yield
and ultimate strength of the steel rods were verified. Then, the hold-down system without the
rubber pad was tested to failure. Subsequently, the CLT housing was tested to failure to
evaluate its brittle failure strength. Conclusively, tensile tests were performed on the hyperelastic rubber hold-down setup with various rubber thicknesses for a targeted load at various
load rates. To complement the experimental study, numerical simulations were carried out to
model and optimize the hyper-elastic behavior of different thicknesses of rubber. The result
from the numerical analysis was then validated using experimental data.
The study of the full-scale shearwall system was beyond the scope of this study, this research
focuses on the behavior and optimization of the hold-down on a component level.

Page 3

Chapter 2: Literature Review
Cross-laminated timber
Cross-laminated timber (CLT) is an engineered wood panel product that consists of several
layers of lumber boards stacked orthogonally and glued together. Its cross-section has at least
three glued layers of boards placed in orthogonally alternating orientation to the neighboring
layers. CLT products are usually made up of an odd number of layers with a minimum of three
layers and up to seven layers or more. CLT usually comes in a size of up to 3 m in width, with
a length of up to 18m. In most cases, its size is limited by transportation regulations. The layers
in the minor direction are usually produced using lower-grade lumber. Which can be either
visually stress-graded lumber (V grades) or machine stress-rated (MSR) lumber (E grades)
[16]. The CLT panel stress grading is usually in line with the stress grades provided in the
ANSI/APA PRG 320 standard for performance rated CLT (ANSI/APA, 2018).
CLT has some advantages over other engineering wood products. Its orthogonal cross
lamination offers it an improved dimensional stability. This offers the room for prefabrication
of wide floor slabs, long single-story walls in platform construction, and tall plate height
conditions as in multi-storey balloon-framed configurations. Also, CLT has relatively high inplane and out-of-plane strength and stiffness properties. This allows the product to be used in
a two-way action for floors, similar to that of reinforced concrete slabs [17]. The reinforcement
from its cross lamination also offers CLT considerably higher splitting resistance in some types
of connection systems. CLT has good thermal insulation and acoustic performance. It also has
better performance under various fire conditions, because it can form a thick char cover during
a fire for protection. This allows tall mass timber structures to meet building code fire
requirements [16].
Page 4

Structures made up of CLT are usually put together on-site. Prefabricated panels are brought
to the site, lifted using cranes and fastened together using mechanical fasteners such as bolts,
dowels, self-tapping screws or steel brackets and so on [18]. Its prefabricated nature offers the
ability for high precision and fast construction which increased safety and less demand for
skilled workers on-site, less noise, less wastage, timesaving, and cost-saving [16]. For
example, the 8-storey The Murray Grove, built in London in 2010, was completed by four
people in 27 days [19].
CLT also has a high strength to weight ratio compared to steel or concrete. This results in a
lighter superstructure, which means that foundations can be smaller when compared with
concrete or steel structure, which consequently saves cost [20]. CLTs are used in construction
mostly in the form of wall and floor panels. For wall panels, CLT is usually erected so that the
major axis is in the vertical orientation to take vertical loading. As for floor application, CLT
can be one-way spanning or two-way spanning depending on its thickness. There are two ways
in which CLT multi-structures can be constructed. They are platform-type construction and
balloon framing [21]. The provisions provided in the CSA O86 and National Building Code of
Canada (NBCC) are tailored for Platform-type constructed CLT Structures.
CLT shearwalls and connections
In order to achieve taller wood structures, efforts are being devoted towards developing new
innovative wood applications, and construction methods that can facilitate engineering design
solutions that ensure reliability within capacity-based design method. In the past decade, most
attention has been focused on the mechanical performance of timber structures, even though
there is insufficient data on its performance in an actual earthquake scenario. Full-scale CLT
multi-story shake table test has shown that that midrise CLT structures will perform well under
Page 5

seismic instances. For example, the 7-story SOFIE project conducted in 2007 at the Hyogo
Earthquake Engineering Research Center in Miki, Japan. There, a 13.5 m x 7.5 m and 23.5 m
high CLT building designed in accordance with the equivalent static force procedure in the
Eurocode 8 was tested. The structure was subjected to different three-dimensional ground
motions of various intensities. The earthquake produced a maximum interstorey drift of 1.3%.
However, studies have suggested adding ductile elements to CLT building design may further
improve building performance [5]. Also, a three-story CLT house shake table test conducted
at the NIED laboratory in Tsukuba, showed that CLT can withstand multiple earthquakes with
minimal damage [3, 4, 18, 21].
When a platform-type CLT building is subjected to an earthquake loading, the response of the
building transfers load through the floor diaphragm and is distributed to the shearwalls. The
shearwall is responsible for resistance and energy dissipation in the structure [4]. Full-scale
shearwall test and full-scale shearwall numerical analysis carried out by Popovski et al. and
Izzi et al., respectively, demonstrated that kinematics is crucial for energy dissipation to occur
in CLT shearwall [22, 18]. For a coupled CLT shearwall system described in Figure 2-1,
typically comprises two CLT panels connected by a vertical joint, horizontal shear resisting
connectors, and hold-downs. CLT panels are considered rigid in a CLT shearwall system.
Therefore, lateral stiffness, strength and kinematics in the structure are determined by the
properties of connections.

Page 6

Figure 2-1: Typical CLT shear wall layouts

Coupled CLT shearwall can behave either like a single wall or coupled walls depending on the
stiffness of the hold-down in relation to the vertical joint as described in figure 2-2 [22, 23, 24,
25]. Studies have shown that inter-panel connections did not compromise the performance of
the building in terms of resistance, however, it increased the overall building deformability [4,
12, 26]. The studies by Izzi et al. and Casagrande et al. and Shahnewaz et al., showed that
aspect ratio contributes significantly to the kinematic behavior of the panels and subsequently
the amount of force that goes into hold-down [18, 24, 27]. The kinematics interaction of the
panels as a single or couple wall behavior is highly influenced by the stiffness of the holddown and the vertical joint, relative to one another and the aspect ratio of the panels [24, 28].

Figure 2-2: Coupled panel kinematic behavior

Page 7

When an earthquake occurs, damage is inevitable; it provides supplementary energy
dissipation. To ensure adequate performance in a building, capacity design is usually
employed. Specific connecting elements in the system are required to have enough ductility
and deformability for dissipation of energy (dissipative connection), while the remaining
connections and structural components are designed with sufficient overstrength to remain
elastic (non-dissipative connection) under the rocking as the predominant kinematic behaviour
of the shearwall [6]. For CLT shearwalls, the CLT panels are considered rigid, ductility and
dissipation are designated to connections in the form of yielding and bending of metal fasteners
and connector plates, and wood crushing due to nail embedment [29, 30].
As a requirement for dissipative connections in accordance with CSA O86-19; dissipative
connection should be designed such that yielding mode governs the resistance. It should also
be at least moderately ductile in the directions associated with the rocking rigid body motions
of CLT panels. Finally, such types of connections should possess sufficient deformation
capacity under the force and displacement demands that are induced in them to allow for the
CLT panels to develop rocking motion [21].
Non-dissipative connections on the other hand are usually provided with sufficient capacity to
remain elastic when the dissipative connection reaches ultimate resistance. In the CSA O8619, the force exerted in the non-dissipative connection when the 95th percentile of ultimate
resistance of the dissipative is attained must be less than the 5th percentile elastic limit of the
non-dissipative connection. For the CLT panel, the seismic design force may be determined
using Rd Ro = 1.3 [6, 16, 21, 24, 31].
Prior to the recent update of the O86-19 on CLT shearwall design, non-dissipative connections
included floor to wall connection (hold-downs), floor to floor panel and vertical joints between
Page 8

octagonal panel. In the CSA O86-19, hold-down connections were included as a nondissipative connection, therefore required to remain elastic throughout an earthquake action.
The role of the hold-downs is to resist uplift resulting from an overturning moment. Previous
studies have shown that proprietary connectors such as Simson and MiTicon brackets and other
innovations such as HSK can easily meet the amount of load demand elastic [9, 10, 22, 31,
32]. However, such connections deform non-elastically and suffer pinching action under cyclic
loading because they do not have the required elastic deformability. Nevertheless, ductility
provided by such hold-downs has been proven to satisfy structural performance criteria, as
shown by e.g. Popovski et al., on a 3-D system behavior of CLT structures under lateral loads
using a two-story full-scale of a CLT structure, a 2-storey structure of 6.0 m by 4.8 m in plan
and with a total height of 4.9 m. The study concluded that the presence of additional holddowns lowered the uplift deformations of the walls but did not increase the building’s
resistance [18].
Hyper-elastic rubber hold-down
A hyperelastic hold-down system was developed and investigated by Asgari et al. [15]. It
consists of Masticord elastomeric rubber (MER), compression plate(s) and steel rod. Masticord
rubber is a composite material consisting of an elastomer with random-oriented synthetic
fibers. It is an isotropic material that behaves in a non-linear manner. For a shearwall system
that uses such type of hold-down, the tension force that occurs in the hold-down when the
shearwall rocks is translated into a compression load exerted by the top plate on the rubber
pad. This causes the rubber pad edges to bulge, and its surface area increases. The hold-down
boundary restriction allows only two opposite faces to bulge due to its assembly position in
the CLT housing compartment.

Page 9

The shape factor (SF) has been shown to contribute significantly to the strength and stiffness
of the MER pad. The size, and boundary condition influences the shape factor. The SF for a
rectangular pad with a cylindrical hole at the middle can be estimated using the following
formula provided in the MER manufacturers design guide [33]:

=

(

)

,

(2-1)

Where dR wR tR,t and Φ are Depth of rubber pads, Width of rubber pads, Thickness of rubber
pads and Diameter of the center hole at the middle of the rubber respectively.
In rubber hold-down applications, the role of the rubber pad is to resist compression only. The
synthetic fibers in the rubber pad strengthen the elastomer [15, 33]. Based on the manufacturer,
Masticord rubber is assumed to reach its ultimate load at 40% compressive strain deformation.
Based on the manufacturer's guide, at 40% compressive strain, the reinforcement fibers debond
and pull away from the exterior surface of the pad. The voids left by the de-bonded fiber start
to experience tears in the elastomer. A tear may also occur in the fibers leading to permanent
deformation. At this stage, the edges are where most damage is concentrated for the pad,
depending on the amount of strain in such instances. Further deformation beyond this limit will
typically extend from the situation of the previous damage to areas having the highest strain.
However, unlike other materials, the rubber pad will continue to transfer and distribute load
after it is damaged [33].
Asgari et al. [15] tested the rubber hold-down concept with a thickness of 1” and 2” enclosed
in a CLT opening. A total of 53 quasi-static monotonic and cyclic tests were performed and
demonstrated that rubber hold-downs exhibited high strength and deformation capacity

Page 10

without any residual deformation after unloading. The shape factor and loaded area of rubber
layers were found as the main factors that contributed to the response of the rubber hold-down.
It was shown that openings wider than the lamellas’ width weakens the CLT and will leave the
panel susceptible to brittle failure. The need for further research using a thicker rubber pad in
the hold-down was suggested. The study also suggested using laminated rubber bearings in
between the pad layer rather than the plain rubber. The study claimed that rubber bearing can
provide higher stiffness in the rubber Hold-down.
Summary
While CLT has been proven to be an efficient and sustainable material for wood structures, the
concerns around recent modification in CSA O86-19 for hold-downs to remain fully elastic
during earthquake action calls for more research on CLT hold-down design. This is to provide
a solution that satisfies the new requirement because studies have shown that proprietary holddowns cannot facilitate rocking and remain elastic. The hyper-elastic rubber hold-down
concept has shown significant potential as a feasible solution to address this problem but more
research is deemed necessary to improve its performance and develop capacity-design
principles.

Page 11

Chapter 3: Experimental investigations
Overview
Even though CSA 086-19 recommends that hold-downs in CLT shearwalls should remain
elastic during dynamic action, it is good practice that failure after overloading is ductile. This
will provide energy dissipation and avoid sudden brittle failure that may be catastrophic.
Consequently, it is essential that the failure of the system occurs in the steel rod and not the
rubber or CLT panel which should both have a higher load-bearing capacity than the holddown steel rod, so that the failure of the system will occur in the hold-down rod.
The completed tests provided a stage-by-stage guidance for the component level capacity
design of the rubber hold-down in a shearwall system. In other to demonstrate how brittle
failure can be avoided in the hold-down even if failure were to occur. For this study, two levels
of protection were considered (see Figure 3-1).

Figure 3-1: Capacity-based design principle

Page 12

The first protection avoids failure of the CLT and prevents the rubber pad from exceeding its
ultimate strain capacity of 40%. This was achieved by ensuring sufficient brittle failure safety
margin between the peak load of the steel rod Fpeak, and the failure load of the CLT FU,CLT and
rubber pad FU, rubber. The second protection applies an overstrength factor RdRo of 1.3 to ensure
that the hold-down remain elastic throughout the experiment.
In order to achieve the study objective, a series of quasi-static monotonic tensile tests were
first carried out on a sample of three (3) different rod diameters; 4/3” (full cross section),
10/16” and 9/16”. The objective of these tests was to identify a suitable elastic limit for the
hold-down test by defining the 5th percentile and 95 th of the yield and ultimate strengths. Then,
quasi-static monotonic and a modified CUREE cyclic test was carried out on a total of six (6)
samples of the selected hold-down rod to study its fatigue resilience. Subsequently, the CLT
housing was loaded in tension to study the brittle failure of the panel under a quasi-static
monotonic loading. This is to ensure the CLT housing is well protected above the 95th
percentile of the steel rod ultimate tension strength. Finally, a comprehensive test series was
carried out on the full hold-down system using ten different sizes of Masticord rubber pad.
Each test sample subjected to a monotonic tensile target load at various loading rates.
Materials – steel rods
Steel rods, grade 8 was used, the yield and ultimate strengths of the steel rod was determined
in a preliminary test carried out. A diameter of 19.1 mm (¾”) was chosen. For the preliminary
tests, four samples of the full ¾” rod, and four samples each of lathed dog bone sample of
diameter 10/16” and 9/16” were tested on 300mm long specimens. Subsequently, a hold-down
steel rod tests were carried out on a 600mm full rod of the same diameter. Full size sample of
the rods used in the study is illustrated in Figure 3-2.
Page 13

Figure 3-2: Steel rod samples

Materials – CLT
The CLT samples were 5-ply 139mm E1M4 grade by Structurlam, with 35mm MSR E-rated
lumber in all major strength direction layers and 17mm SPF #2& Btr lumber in the minor axis.
The CLT used was manufactured in accordance with PRG 320-2012 requirements. The
material property of the CLT is described in Table 3-2.

Table 3-1: The material property of the CLT sample

CLT

Grade

Longitudinal layers
E

139E

E1M4

ft

12400 17.7

fc

Transverse layers
fcp

fs

E

19.9 6.5 0.5 9000

ft

fc

fcp

fs

3.2

9

5.3 0.5

The CLT is the main housing compartment for all other members in the setup for the
experiment. The CLT panel sample was prepared with a rectangular opening large enough to
accommodate symmetrical assembly setup for the hold-down experiment. The opening was
also prepared with rounded edges with a radius r on all corners to prevent concentrated stress.
A hole was drilled through the center of each panel on the face perpendicular to the grain
direction of the outermost layer, linking the end side of the panel of the rectangular opening
prepared in its middle. This provided the passage for fixity on both sides. The geometry of the
CLT housing is provided in Figure 3-3 and in Table 3-3. These can be categorized into group
A and group B.

Page 14

Figure 3-3: Geometry parameters for CLT housing

Table 3-2: Dimension of CLT samples

Group
A
B

Slot
dimension

CLT panel dimension

al

ac

dc

wlam

r

h

w

t

tl

tt

hs

ws

1000

500

139

35

17

350 90

500

205

22

130

5

1000

500

139

35

17

350 140

500

180

22

130

5

1200

400

139

35

17

400 90

600

155

22

130

25

1200

400

139

35

17

400 140

600

130

22

130

25

Materials – rubber
Masticord elastomeric rubber (MER) pads were used for the study (Figure 3-3). The chosen
widths of the rubber pad determine the dimension of the prepared CLT opening. Masticord
elastomeric rubber is a composite material consisting of elastomer (made up of carbon black,
zinc oxide, sulphur, rubber processing oils, and other chemicals encapsulated in the rubber
crumb) with random oriented synthetic fibres. It was selected for its high compressive strength,
cost-effectiveness, and commercial availability in comparison to other elastomeric rubber
materials. Its role in the setup of the rubber pad is used to resist uplift through compression as
later demonstrated. Relevant mechanical properties of Masticord are listed in Table 3-4. The

Page 15

stress-strain relationship for the rubber pad can be predicted using an empirical formula based
on MER manufacturers design guide [33]:
= 0.00689(0.6

+ 2)

.

(3-1)

Where, sc and ec are the vertical compressive stress and strain on the rubber pad without any
rotation or horizontal displacement. The maximum allowable load Vnr and compressive stress
σc for all samples are hereby listed in Table 3-4. This is based on a maximum strain value of
40% as recommended by the manufacturer.

Table 3-3: Relevant mechanical properties of Masticord [33]

Compression emax

40% maximum compressive strain

Shear

75% maximum compressive strain

Creep

irrelevant after application of load

Shape factor

Limited by 40% maximum compressive strength

Slip friction

coefficient 0.7 - 0.9 (by static incline plane)

Maximum compressive stress

55.16MPa

Tensile Strength
(ASTM D 412, Die B)

6.89 MPa

Rubber pads of thickness one, two, three and four inch were produced by gluing multiple layers
of the 1” (tR) MER pad. A fifth thickness was later included by combining 1” and the build-up
glued 4” MER pad. NR represents the total number of Layers (Figure 3-4). Figure 3-4
demonstrates the bulging behavior of the rubber pad under compression. For the setup that was
used, the breath of the sample dR was restricted from bulging by the CLT enclosure. A 22mm
diameter hole was drilled at the middle of each pad for support fixity. A total of 10 different
sample types were prepared by cutting out a 90 x 140 mm2 (see Figure 3-5a) and a 140 x 140
Page 16

mm2 (see Figure 3-5b) rectangular cuboid of each of the buildup MER pad types. The
geometrical details and SF of each sample is listed in Table 3-5.

Figure 3-4: Geometry parameters of rubber pad

Where, dR, wR, and tR,t = tR x NR are the depth, width, and thickness of rubber pads, respectively.

a)

b)
Figure 3-5 Masticord rubber pad a) 90mm pad b) 140mm pad

Page 17

Table 3-4: Rubber test samples dimension

Thickness
[inch]
1"
2"
3"
4"
5"
1"
2"
3"
4"
5"

dR
[mm]
140
140
140
140
140
140
140
140
140
140

wR
[mm]
90
90
90
90
90
140
140
140
140
140

tR
[mm]
25.4
25.4
25.4
25.4
25.4
25.4
25.4
25.4
25.4
25.4

NR
[mm]
1
2
3
4
5
1
2
3
4
5

tR,t
[mm]
25.4
50.8
76.2
101.6
127.0
25.4
50.8
76.2
101.6
127.0

φ
[mm]
22
22
22
22
22
22
22
22
22
22

SF
1.9
1.0
0.6
0.5
0.4
2.2
1.1
0.7
0.5
0.4

Vnr
KN
209.9
171.4
158.6
152.2
148.3
341.2
274.0
251.6
240.4
233.7

σc
MPa
17.18
14.03
12.98
12.45
12.14
17.75
14.26
13.09
12.51
12.16

Materials: top and bottom plate
The dimensions of the top and bottom plates are illustrated in Figure 3-6. The top plate was
over-designed with a thickness of 2” to ensure that no local deformation occurred. The bottom
plate was trimmed with a rounded edge of the same radius as the rounded corner of the CLT
housing, this is to allow an even stress transfer to the corners of the CLT panel housing. Both
top and bottom plates were fabricated with a hole of 22mm in diameter at the center to allow
room for fixity.

Page 18

Figure 3-6: Steel top and bottom plates

Steel rod tests
A preliminary monotonic tensile test was first carried out on the high strength and high yield
threaded 3/4” steel rods to be used as the hold-down steel rod. For the test, a total of 12 samples
consisting of 3 different diameter sizes were tested. Each specimen first was measured with a
vernier digital caliper before being testing. Specimens were attached to hydraulic collett grips
of a UTM machine and loaded in tension at 10mm/min till failure was achieved. All
deformation was recorded relative to the actuator position.
Since the hold-down steel rod may also be susceptible to strength degeneration due cyclic
loading, the fatigue behavior of the hold-down system without any rubber pad was tested. To
carry out this test, the 22mm hole drilled into the CLT samples was widened to 30mm. The
holes in the bottom plates were also widened to 1” to ensure free passage. A high strength 1”
steel rod was used to secure the CLT to the UTM machine on one end, while the proposed
hold-down rod was secured to the other end of the CLT housing. The test setup is illustrated
in Figure 3-7.

Page 19

Figure 3-7: Layout for hold-down steel rod tests

Quasi-static monotonic and cyclic tests were conducted on a total of six (6) samples. Three (3)
of the hold-down rod specimens were first tested to failure using a displacement controlled
monotonic tensile loading protocol at a loading rate of 10mm/min. After that, a tensile cyclic
load test was conducted using the remaining three (3) specimens. A modified version of
CUREE method C in accordance with ASTM E2126 was used [34], see Figure 3-8. The target
displacement was calculated based on the initial monotonic test as 35mm. It is worth
mentioning that deformation was acquired straight from machine-reading and not an LVDT.
Therefore, the acquired deformation is the overall deformation of the hold-down system
without the rubber pad.

Page 20

Figure 3-8: Modified CUREE cyclic loading

CLT tests
Quasi-static monotonic tensile tests were carried out on the CLT housing samples. Each sample
was loaded to failure, at a loading rate of 5mm/min. The setup of the test is similar to the holddown steel rod test setup, but with a 1” threaded steel rod used on both sides as shown in Figure
3-9 and summarized in Table 3-6.

Figure 3-9: CLT test setup

Page 21

Table 3-5: Labels and dimensions for the CLT test sample

Label

ws

m

90-350-1

90

350

90-350-2

90

350

90-370-1

90

370

90-400-1

90

400

90-400-2

90

400

120-450-1

120 450

120-450-2

120 450

140-370-1

140 370

140-400-1

140 400

Hold-down tests
The different layout configurations used in the experiment are described in Figure 3-10. The
first Layout, cf. A, uses only a top plate that compresses the rubber pad to the CLT support.
This leaves the CLT outer layer vulnerable to delamination from the bulging, leading to
premature failure of the CLT compartment. The second Layout, cf. B, used a bottom plate
solely to protect the CLT compartment. The third Layout, cf. C, used only one hold-down with
the 5” thick rubber pad. Average relative deformation in the rubber pad sample was recorded
in reference to the top plate during each test using Linear Variable Differential Transformers
(LVDT) devices. The LVDT were secured to the CLT and labeled as described in the Figure
3-10 below for each layout.
The hold-down test was set up to isolate the behavior of the rubber hold-down to study how
certain parameters influence the performance. The parameters of interest were: 1) the rubber
Page 22

thickness; 2) the rubber width; and 3) the loading rate. Thus, ten rubber samples were tested
using the setups described in Figure 3-10. Tension load was applied using a displacement
control universal testing machine (UTM) with a capacity of 500kN. A tensile monotonic
displacement-controlled target load FTarget of 120kN was applied to each specimen at a loading
rate of 10mm/min. It is worth noting that an initial preload of 5kN was introduced to the setup
system by applying a torque of 35lbs on the nut on the inside of the CLT opening before each
test. This is to ensure a consistency in the tightening of the all sample. Deformation of the
MER pad due to the compression load applied on the MER pad was recorded at 120kN. The
target load was decided based on the preliminary steel rod tests so that the applied load was
less than a factored average yield load with a RdRo factor of 1.3 to ensure that the steel rod
remained elastic throughout the test. All tests were repeated three (3) times for each
experiment. The label for each test is detailed in Table 3-7.

Page 23

Figure 3-10: Rubber hold-down component level test setups

Page 24

Table 3-6: The label, discretion and loading rate for the hold-down test.

Depth
[mm]

Width
[mm]

Thickness
[inch]
1"

2"

90

3"

4"

5"
140
1"

2"

140

3"

4"

5"

Page 25

Rate of loading
[mm/min]
10
50
250
10
50
250
10
50
250
10
50
250
10
50
250
10
50
250
10
50
250
10
50
250
10
50
250
10
50
250

Label
90-1-10
90-1-50
90-1-250
90-2-10
90-2-50
90-2-250
90-3-10
90-3-50
90-3-250
90-4-10
90-4-50
90-4-250
90-5-10
90-5-50
90-5-250
140-1-10
140-1-50
140-1-250
140-2-10
140-2-50
140-2-250
140-3-10
140-3-50
140-3-250
140-4-10
140-4-50
140-4-250
140-5-10
140-5-50
140-5-250

Chapter 4: Experimental results and discussion
Steel rod test results
The load-deformation curves from the steel rod tests are presented in the Figure 4-1. Figure 41a and Figure 4-1b show the curves of the monotonic test from the preliminary tests and Figure
4-1c and Figure 4-1d illustrate the curves of the fatigue test carried out. The result of the
preliminary test is presented in Table 4-1. Also shown in Table 4-2, are the peak loads FPeak,
yield loads Fy, rod, yield elongations dy,Rod, and fracture elongation dult,Rod, generated from the
fatigue test carried out. Ductility μRod was calculated in accordance with ASTM E2126 [30].

A-Full

200

150

Load (kN)

Load (kN)

150
100
50
0

0

10

20

30

40

50

30

40

50

60

Displacement (mm)

Load (kN)

50

20
30
40
Displacement (mm)

20

200

100

10

10

Cyclic Rod Test

150

0

0

b)

Monotonic Rod Test

200

Load (kN)

50

60

Displacement (mm)

c)

100

0

a)

0

10/16 and 9/16

200

50

60

150
100
50
0

d)

0

10

20
30
40
Displacement (mm)

50

60

Figure 4-1: Load-displacement of a) full and b) section reduced rod under monotonic loading; c)
preliminary test carried and d) hold-down rod quasi-static monotonic and cyclic test

Page 26

Table 4-1: Result of preliminary steel rod test

Diameter (mm)
Specimen
A-full
B-full
C-full
D-full
A-10/16
B-10/16
C-10/16
D-10/16
A-9/16
B-9/16
C-9/16
D-9/16

Top
18.9
18.9
18.8
18.9
15.9
15.9
15.9
15.9
14.0
14.3
14.3
14.3

Middle
18.9
18.9
18.9
19.2
15.9
16.0
15.9
15.9
13.8
14.3
14.3
14.3

Yield
strength
Bottom Average KN
18.9
18.9
162.0
18.9
18.9
171.4
18.8
18.8
163.5
18.7
18.9
170.9
15.9
15.9
153.1
16.0
16.0
156.5
15.9
15.9
158.9
15.9
15.9
168.1
13.9
13.9
138.0
14.3
14.3
129.0
14.1
14.3
134.8
14.3
14.3
137.2

Yield
stress
MPa
1297
1285
1250
1181
1100
1245
1192
1171

Peak
strength
KN
183.8
193.3
186.3
196.8
173.0
178.7
181.8
192.0
154.8
143.3
150.0
154.0

Table 4-2: Results of hold-down rod quasi-static monotonic and cyclic tests

Loading

FPeak
[kN]
Monotonic 196.3
Monotonic 194.0
Monotonic 192.0
Cyclic
194.2
Cyclic
195.1
Cyclic
194.6

Fy,Rod
[kN]
170.5
170.7
167.5
170.0
169.8
168.6

0.8Fpeak
[kN]
157.1
155.2
153.6
155.3
156.0
155.7

dy,Rod
[mm]
6.9
6.5
6.3
7.1
7.1
8.2

dult,Rod
[mm]
51.0
49.5
39.0
54.0
43.5
58.6

μRod
7.4
7.6
6.2
7.6
6.1
7.1

CLT test results
From the monotonic tensile test carried out to study the strength of the CLT housing, the loaddeformation curve from the study is shown in Figure 4-2. Table 4-3 presents the peak load
FCLT,peak and deformation at peak load dCLT,ult.

Page 27

CLT Test

350

140-400-1
140-370-1
120-450-2-2
120-450-2-2
90-400-2
90-400-1
90-370-1
90-350-2
90-350-1
90-350-2

Load (kN)

300
250
200
150
100
50
0

0

5

10

15

Deformation (mm)

20

25

30

Figure 4-2: CLT test load-displacement curve

Table 4-3: CLT test results

ws

al

FCLT,peak dCLT,ult

kCLT

[mm]
370
400
400
450
450
370
400

[kN]

[mm]

[N/mm]

90-370-1
90-400-1
90-400-2
120-450-1
120-450-2
140-370-1
140-400-1

[mm]
90
90
90
120
120
140
140

90-350-1

90

350

291.5
304.7
308.6
303.6
308.7
280.7
292.5
177.8

20
24
25
22
20
18
23
13

16405
14984
14445
15680
16522
16376
16819
14390

90-350-2

90

350

219.5

16

15413

Label

Hold-down test results
Figure 4-3a and Figure 4-3b shows the load-deformation curve of the 90mm and 140mm wide
rubber hold-down. The average deformations recorded in the rubber pad from the two LVDTs
attached to both sides for the top and bottom sample at the target load (Ftar = 120kN) are shown
in Table 4-4.
Page 28

90mm Ruber Hold-down
140
120

Load (kN)

100
80
60
40
20

a)

0

0

5

10

15

20

25

Displacement (mm)
90-1-10

90-1-50

90-1-250

90-2-10

90-2-50

90-2-250

90-3-10

90-3-250

90-3-50

90-4-10

90-4-50

90-4-250

90-5-50

90-5-10

90-5-250

140mm Ruber Hold-down
140
120

Load (kN)

100
80
60
40
20

b)

0

0

5

10

15

20

Displacement (mm)
140-1-10

140-1-50

140-1-250

140-2-10

140-2-50

140-2-250

140-3-10

140-3-50

140-3-250

140-5-10

140-5-50

140-5-250

140-4-10

140-4-50

140-4-250

Figure 4-3: Hold-down load-displacement: a) 90mm and b) 140mm wide rubber hold-down

Page 29

Table 4-4: Hold-down deformation under quasi-static monotonic loading

Width Thickness Speed
[mm] [inch]
[mm/min]
10
1"
50
250
10
2"
50
250
10
90
3"
50
250
10
4"
50
250
10
5"
50
250
10
1"
50
250
10
2"
50
250
10
140
3"
50
250
10
4"
50
250
10
5"
50
250

Page 30

A top
[mm]
3.8
4.1
2.9
9.4
7.0
7.4
16.0
15.3
14.5
20.1
18.6
17.9
24.3
23.9
23.7
2.7
2.4
2.1
8.3
7.3
7.0
10.7
9.8
9.4
11.2
13.2
11.2
18.8
17.3
17.1

A bot
[mm]
4.0
3.5
2.4
9.5
6.6
10.3
15.7
14.4
13.7
19.8
18.9
18.2
24.7
24.0
23.8
2.5
2.2
2.0
7.5
6.7
6.5
10.4
9.2
8.7
12.3
12.9
11.1
17.6
17.3
17.2

B top
[mm]
4.0
3.3
3.2
9.3
9.0
8.8
14.8
12.9
12.5
19.6
19.0
18.9
23.7
24.1
23.9
2.7
2.3
2.0
8.7
8.1
7.7
9.1
9.1
8.7
11.2
12.5
11.3
17.5
17.3
17.3

B bot
[mm]
4.4
3.4
3.3
9.5
9.2
9.3
15.5
13.2
12.8
20.3
19.7
19.4
24.0
24.3
24.0
2.6
2.4
2.9
8.8
8.1
7.6
9.3
9.0
8.8
14.0
11.7
11.2
17.7
17.5
17.1

Strain
16%
14%
11%
19%
16%
18%
20%
18%
18%
20%
19%
18%
19%
19%
19%
10%
9%
9%
16%
15%
14%
13%
12%
12%
12%
12%
11%
14%
14%
14%

Discussion rod tests
The load-displacement curve for all quasi-static monotonic and cyclic tests follows a typical
ductile steel path, see Figure 4-1. The cyclic curves match relatively well with the monotonic
curves, showing no evidence of deteriorations or drop in the achievable peak load because of
the cyclic loading. Image of the failed rod samples are presented Figure 4-4, the reduction in
diameter at failure region signifies plastic necking, which is an evidence of ductile failure.

Figure 4-4: Failed rod after testing

The results, summarized in Table 4-5, show a consistent peak load FPeak and yield load Fy, rod,
across all tested samples. A coefficient of variation (COV) of 2% was obtained. For design
purposes using the full diameter samples, 95th percentile of 197kN was determined for peak
load FPeak and a 5th percentile of 162kN was calculated for yield load Fy,Rod from the normal
distribution of tested sample as shown Table 4-5.
As for the difference between the monotonic and cyclic test, the only difference worth
mentioning is the elastic deformation. Samples tested under cyclic loading experienced a
slightly larger deformation than samples tested under quasi-static monotonic loading in the
elastic region. The peak load and deformation of results acquired from both tests showed no
evidence a pinching. Therefore, the rod test shows no evidence of fatigue base on the result

Page 31

attained. It is worth mentioning the performance of CLT. During the test, cracking sound from
the CLT can be heard louder as the tensile load in the system increases, however, no visible
crack was observed on the sample after the test. The steel rod had the ability to provide the
necessary ductility. Across all tests, a ductility higher than 6 was achieved even though all
samples failed at different elongations. Which signifies a highly ducting hold-down rod.
To ensure the rod remains elastic during the hold-down test, an estimated 5th percentile normal
distribution of yield strength hold-down rod from Table 4-5 was factor by a RdRo value of 1.3
to ensure the test remains elastic at targeted load as described in equation 4-1. Base on the
result, a target load of 120 was concluded.
≤

=

.

.

(4-1)

= 125.15

Table 4-5: Design peak load Fload and yield load Fy,Rod

Page 32

Label

FPeak

Fy,Rod

ROD TEST 1
ROD TEST 2
ROD TEST 3
F-ROD-140-1
F-ROD-140-2
F-ROD-140-3
A-full
B-full
C-full
D-full
5th Percentile
95th Percentile
COV

[kN]
196.3
194.0
192.0
194.2
195.1
194.6
183.8
193.3
186.3
196.8
196.6
2%

[kN]
170.5
170.7
167.5
170.0
169.8
168.6
162.0
171.4
163.5
170.9
162.7
2%

Discussion CLT tests
According to Figure 4-2, the load-displacement curve for all tested samples shows a linear
behavior. Sudden load drop at peak load indicates brittle failure of the CLT. Various brittle
failure modes were observed on all CLT samples. Figure 4-5 shows the failure pattern observed
and photos of these failure modes are shown in Figure 4-6 and Figure 4-7.
The panels with 140 mm wide openings failed along the entire five layers of the sample.
However, failure in the panel with 120mm and 90mm wide openings failed mostly on the first
two layers on either side. Failure load for most samples was above 290kN, except for the 90350-1 and 90-350-2 that failed at 177.8kN and 219.5kN respectively. This due to the smallest
longitudinal edge distance al (see Figure 3-2). The result demonstrated that panel opening
width do have an influence on load carrying capacity of the CLT, this is similar to the finding
of Asgari et al. in his study [15]. Panel with opening width smaller than the width of the
lamella, performed better that the wither sample with a less brittle failure mode.
Generally, to ensure the desired ductile failure for the hold-down, all other components was
well capacity protected from the hold-down rod. From Table 3-5, it can be observed that the
load bearing capacity of the rubber pad reduces as the thickness of the pad increases. For the
140mm rubber pad, the highest value of 341kN was estimated for the 1” thick pad, while the
lowest load bearing capacity of 234kN was estimated in the 5” rubber pad. For the 90mm
rubber pad, an estimate of 210kN and 148kN was recommended for the 1” and 5” rubber pad
respectively. In deduction, one could argue that the 140mm MER hold-down is a more suitable
solution because the estimated load bearing capacity of the 5” pad is higher than the normal
distribution 95th percentile for the peak load of the steel rod (see equation 4-2). For the CLT
panel a minimum edge distance of 400mm was concluded as a result.

Page 33

<

,

(4-2)

,

Figure 4-5: CLT failure patterns

Figure 4-6: CLT failed specimens, part 1

Page 34

Figure 4-7: CLT failed specimens, part 2

Discussion hold-down tests
As for the performance of the CLT housing, the layout A form the hold-down layout causes
early cracks on the CLT panel region beneath the rubber pad. This propagates as the number
of tests carried out increases. Which subsequently lead to a premature failure of the outer
lamellar of the CLT housing after three to four tests (see Figure 4-8a). The introduction of a
base plate in layouts B and C resolved the issue completely. No visible cracks were observed
Page 35

in all tests carried out using configuration B and C (see Figure 4-8b). All tests were completed
using one CLT housing in either 90mm or 140mm rubber pad case. All hold-down layouts A,
B and C (see Figure 3-10) produced similar results for the average load-displacement from the
LVDTs attached to both sides of the CLT panel.

a)

b)
Figure 4-8: a) CLT failure of outer lamella using configuration A; b) CLT intact after multiple tests
using configuration B

Page 36

The load-deformation curves presented in Figure 4-3 follow a non-linear path to the targeted
load as anticipated. The result also showed that rubber hold-down has low stiffness at the early
loading stage, but its stiffness increases exponentially as the load increases. Rubber pad
stiffness increases as the width of the rubber pad increases. The 90mm rubber pad deforms a
lot more than the 140mm pad for any of the pad thicknesses. This demonstrated that pad width
is a major contributing factor to the stiffness of rubber hold-down.
In Table 4-4, the average deformation for LVDT on both sides of each rubber pad is calculated
for both top and bottom deformations and plotted in Figure 4-9. Overall, both 90mm and
140mm wide rubber pads exhibit an increase in horizontal deformation as the thickness of the
rubber pad increases, which implies that using thicker rubber pad will reduce the stiffness of
the hold-down. For individual rubber pad thickness, results demonstrate a slight decrease in
average deformation as the loading rate increases. Its influence, however, is consistent for any
rubber pad thickness. A difference of approximately 1mm was observed on an average for all
loading rate irrespective of the rubber thickness. In translation, especially for high aspect ratio
shearwall, the influence of loading rate on the story drift will be less than 1mm. This
demonstrates that the influence of loading rate is negligible. The result in the Table also shows
that at 120kN, the deformation achieved is less than 50% of the allowable recommended strain
of 40% by the manufacturer’s design guide specification. For example, it can be observed that
the 90mm wide 5” thick rubber pad, produced strain deformation is less than 20% in
experiment at target load, the estimated ultimate load capacity at 40% strain is 145kN.

Page 37

17.2

23.9

17.4

24.2
17.9

18.6
11.2

12.6

19.1

12.2

8.9

13.4

9.3

13.9

15.5
9.9

2.2
2.9

7.2
9.0

2.3
3.6

7.6
8.0

8.3
9.4
2.6
4.0

5-250

4-250

3-250

4-50

3-50

4-10

3-10

2-10

1-250

0.0

1-50

5.0

2-250

10.0

2-50

15.0

5-50

20.0

5-10

20.0

25.0

1-10

Horizontal Deformation (mm)

30.0

24.1

Deformation of Rubber Hold-down at 120kN Load

Thickness (inches) - Loading Rate (mm/min)
140 90

Figure 4-9: Deformation of hold-down at 120 kN load

In Figure 4-10, the relationship between mean deformation of the rubber pad at target load and
shape factor (SF) of the rubber pad is illustrated. It demonstrated that shape factor is a major
contributing factor to the stiffness of the rubber pad. As the SF increases, the attained
deformation increases. This agrees with the findings of Asgari et al [15]. One must keep in
mind that the SF is determined from the geometry of the rubber pad. When Figures 4-10a and
Figure 4-10b are compared, it can be observed the, even though the SF trend looks similar, the
deformation attained for the target load the 90mm wide rubber pad is higher than the 140mm
wide rubber pad. This shows that surface area plays an explicit role in the relationship between
the deformation of the rubber pad at target load, outside its relationship with SF. The curve
fitting expression for rubber pad is illustrated in Equation 4-3. In addition to this, it is worth
mentioning that the loading rate does not significantly contribute to the relation between
deformation of the rubber pad and shape factor of the rubber pad.

Page 38

90mm Rubber Pad
30
25

dmean (mm)

20
15
10
5
0

0

0.5

10 [mm/min]

50 [mm/min]

a)

1
Shape factor
250 [mm/min]

1.5

2

Power (50 [mm/min])

Dmean (mm)

140mm Rubber Pad

b)

20
18
16
14
12
10
8
6
4
2
0

0

10 [mm/min]

0.5

1

50 [mm/min]

1.5
Shape factor
250 [mm/min]

2

2.5

Power (50 [mm/min])

Figure 4-10: Hold-down deformation vs. shape factor under monotonic loading for a) 90mm and b)
140mm wide hold-downs

Page 39

Figure 4-11: Hold-down deformation at 120kN vs shape function and width of rubber pad

The curve fitting expression for the relationship between shape function, dmean and width of
rubber pad at 120kN with a goodness of fit of R2 = 0.95
@ 120

= −0.0941

+ 0.02228

+ 15.57

Where wR is width of rubber and SF is the shape factor.

Page 40

.

(4-3)

Chapter 5: Finite element analysis
Modell development
The shape factor (SF) has a significant influence on the stiffness of the hold-down [15]. The
SF also has an influence on the allowable load bearing capacity of the rubber pad based on the
empirical formula provided by the MER manufacturers design guide [33]. Figure 5-1 shows
the contribution of shape factor on the allowable load bearing capacity of rubber pads based
on estimation. One of the ways to improve the stiffness and load bearing capacity is to alter its
SF. Since SF can be attributed to influencing the bulging behavior of a rubber pad, by altering
the bulging behavior of the rubber to maintain a high shape factor, consequently improving the

Max allowable load (kN)

stiffness, and loaded bearing capacity of the rubber pad.

Recommended load bearing vs shape factor

400
300
200
100
0

90
0

0.5

1

1.5

140
2

2.5

Shape factor

Figure 5-1: Maximum allowable load vs. shape factor

In the aim to optimize the hold-down system, a finite element model was developed using the
hyperplastic properties developed by Asgari et al. [15]. A total of seven (7) simulations were
carried out to produce a matching model of the tested sample and an optimized model of the
existing hold-down concept. Two types of models were studied. The parametric data of the
simulated tested sample is described in Figure 5-2 Table 5-1. In group 1, labeled NP2, NP3

Page 41

and NP4, a full rectangular prism hyper-elastic rubber pad mode with no plate (NP = no plate)
was modeled. In group 2, labeled P2, P3 and P4, include stacks of 1” rubber model with thin
plate in-between each pad of the model to restrict bulging those that regions.

a)

b)
Figure 5-2: Sketch of the model with dimension definition

Table 5-1: The parametric data of the simulated sample

Label
S1"

N/A

dR

wR

tR

NR

[mm]

[mm]

[inch] [mm] [mm]

140

90

1

1

tR,t
25.4

SF

Vnr
KN

1.9

209.9

Group 1: hyper-elastic rubber pads with No plate glued between each pad
NP2

No

140

90

2

1

50.8

1

171.4

NP3

No

140

90

3

1

76.2

0.6

158.6

NP4

No

140

90

4

1

101.6

0.5

152.2

Group 2: hyper-elastic rubber pads with plate glued between each pad
P2"

yes

140

90

1

2

2”

1.9

209.9

P3"

yes

140

90

1

3

3”

1.9

209.9

P4"

yes

140

90

1

4

4”

1.9

209.9

The rubber pad was simulated using a Yeoh 3rd model with the parameter provided in Table 52. The model of P4 and NP4 are illustrated in Figure 5-5. Figure 5-4 on the other hand
illustrates the contact interaction and boundary condition applied on the P4 and NP4 model. In

Page 42

the models, deformation at the top was avoided, therefore, it was modeled as a fully rigid
element. The middle plate, however, was modeled as linear elastic. Interaction between all
members was assumed to be fully bonded. In other to avoid complexity of modelling frictional
interaction with other members on the two long sides and at the middle hole of the rubber pad
model, both regions were modeled as a frictionless support region. This also prevents bulging
on the sides and on the middle hole. The bottom part of the model was modelled as a fully
fixed in those regions. A nonlinear analysis was carried out on the model by applying a load
of 120kN on the top plate.

a)

b)
Figure 5-3: Finite element models a) P4 b) NP4

Figure 5-4: Model contact interaction and boundary condition

Page 43

Table 5-2: Yeoh 3rd model parameters

Yeoh 3rd Order
Material Constant

Incompressibility Parameter

C10

C20

C30

D1

D2

D3

Pa

Pa

Pa

Pa-1

Pa-2

Pa-3

1.36E+06

-2.27E+06

5.61E+06 2.90E-06

-1.71E-11

5.17E-11

FEA results and discussion
Based on the ANSYS simulation of the rubber pad. Figure 5-3a shows the deformed shape of
the rubber pad after a load of 120kN is applied. Figure 5-3b on the other hand shows the
deformed shape of the optimized 4-layer pad after being loaded. The result generated from that
analysis is illustrated in Figure 5-4 to Figure 5-6.

a)

b)
Figure 5-5: Simulated compression of the rubber pad of a) NP4, b) P4

Figure 5-6 shows the load-displacement curves of the numerical simulations. The curves
follow a nonlinear path that is similar to the laboratory test results. An improved stiffness in
the optimized model was achieved, P4 is stiffer than NP4 by approx. 40%. Figure 5-7 shows
the relationship between the maximum displacement of both models at 120kN. The result
shows a lower deformation in the pad model with lamellar when compared to the model with
Page 44

laminated steel plate. The bulging pattern, when both types of samples are placed side by side
shows that the shape factor of the steel plate laminated rubber pad is a lot closer to a 1” rubber
pad shape factor irrespective of its thicknesses when this boundary condition is applied in each
layer. Which in return means, an improved stiffness can be achieved by introducing a steel
plate lamellar in between each rubber pad layer and also, using thinner rubber layer.

Numerical result: Load-displacement curve

Load (kN)

160
120
80
40
0

0

5

P2

P4

10
15
Deformation (mm)
P3

NP4

S1

20

NP2

25

NP3

Figure 5-6: Simulated load-displacements

Numerical Result: Deformation at 120kN
Deformation (mm)

25
20
15
10
5
0

1 inch

2 inch
3 inch
Rubber pad thickness
no plate lameller

plate laminated

Figure 5-7: Deformation at 120kN based on numerical model

Page 45

4 inch

Verification
Model and experimental data are compared in Figure 5-8 to further verify the accuracy of the
model. Based on comparison of the model with the experimental result; the model only worked
for 1” (S1) and 2” (NP2) rubber pads, as the thickness of the rubber pad increased, the model
began to lose its accuracy for the rubber pad simulation with no plate in between. This is
because the frictionless contact applied on the sides of the mode is not an accurate model of
rubber pad contact. In the experiment samples that the models are compared to, there is a
frictional contact interaction between restricted long side of the rubber pad and the inner
surface of the CLT wood panel. This was modeled as frictionless contact in the models to avoid
numerical convergence problem. The margin of error carried becomes more pronounce as the
thickness of the rubber pad increases due to shape factor. Although S1 and the 1” pad
experimental data match more accurately, it is tough to tell how accurate the optimized rubber
pad model simulation will be until an actual laboratory experiment is carried out.

Experimental Verification
140
120

Load kN

100
80
60
40
20
0

0

5
90-1-250
NP2

10
15
Deformation (mm)
90-2-250
S1

NP4
90-4-10

Figure 5-8: Numerical result verification

Page 46

20

25
NP3
90-3-10

Chapter 6: Conclusions and outlook
The performance of a hyper-elastic high-capacity hold-down was investigated at the
component level through tests on: i) hold-down steel rod; ii) CLT housing; and iii) hold-down
assemblies with different sizes of rubber pads. These demonstrated that the hold-down
assembly can achieve the performance as desired for CLT shearwall according to CSA 08619. The hold-down system can remain elastic at 120kN without degrading and ductile failure
can be achieved as long as the steel rod is the weakest link in the setup. The strength of the rod
provided sufficient tolerance for elastic behavior of the hold-down even at higher load. For
higher utilization of the concept, it is recommended that a stronger hold-down rod may be
considered. However, all other members must be capacity protected to avoid brittle failure.
The tests further showed that the edge distance and the opening width are contributing factors
to the CLT housing failure modes and ultimate load-carrying resistance. A precautionary
minimum edge distance of 400mm or greater is recommended for the CLT housing. Further
studies are required to fully understand individual parameter’s significance.
The stiffness of shearwalls equipped with such hold-down will depend on the rubber pad
dimensions and the resulting shape factor. Using thinner rubber increases the shape factor and
consequently the hold-down stiffness. The rubber pad empirical formula provided in the
manufacturer’s design guide is highly conservative. Loading rate add minimal contributing
factor to deformation based on result generated. The loaded surface area of the rubber pad is a
major contributing factor in the load bearing capacity. But one must keep in mind that, the use
of wider pad can weaken the CLT, thereby leaving it vulnerable to brittle failure.

Page 47

The finite element simulations showed that, by introducing a middle plate glued between each
rubber pad layer, the amount of deformation in the rubber pad can be highly reduced.
Based on findings, the following design approach is proposed: First, determine peak load Fpeak
and yield load Fy,rod either through manufacturer guide or experiment. Second, calculate target
elastic load limit FTarget by apply a reduction factor RdRo of 1.3 to the yield load Fy,rod. Third,
ensure ultimate CLT load FU,CLT and Frubber is greater than peak load Fpeak.
The high-capacity hyper-elastic rubber hold-down has shown remarkable performance on the
component level based on the test all carried out. A full scale shearwall is appropriate to fully
understand the feasibility and performance of the concept.

Page 48

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Page 52

Appendix: All hold-down test result
90-1-10

140
120

Load kN

100
80
60
40
20
0

0

1

2
3
Deformation mm

4

5

4

5

90-1-50

140
120

Load kN

100
80
60
40
20
0

Page 53

0

1

2
3
Deformation mm

90-1-250

140
120

Load kN

100
80
60
40
20
0

0

0.5

1

1.5
2
2.5
Deformation mm

3

3.5

4

90-2-10

140
120

Load kN

100
80
60
40
20
0

Page 54

0

2

4

6
Deformation mm

8

10

12

90-2-50

140
120

Load kN

100
80
60
40
20
0

0

2

4

6
Deformation mm

8

10

12

8

10

12

90-2-250

140
120

Load kN

100
80
60
40
20
0

Page 55

0

2

4

6
Deformation mm

90-3-10

140
120

Load kN

100
80
60
40
20
0

0

5

10
Deformation mm

15

20

15

20

90-3-50

140
120

Load kN

100
80
60
40
20
0

Page 56

0

5

10
Deformation mm

90-3-250

140
120

Load kN

100
80
60
40
20
0

0

2

4

6
8
Deformation mm

10

12

14

90-4-10

140
120

Load kN

100
80
60
40
20
0

Page 57

0

5

10
15
Deformation mm

20

25

90-4-50

140
120

Load kN

100
80
60
40
20
0

0

5

10
15
Deformation mm

20

25

20

25

90-4-250

140
120

Load kN

100
80
60
40
20
0

Page 58

0

5

10
15
Deformation mm

90-5-10-4

140
120

Load kN

100
80
60
40
20
0

0

5

10
15
Deformation mm

20

25

20

25

90-5-50

140
120

Load kN

100
80
60
40
20
0

Page 59

0

5

10
15
Deformation mm

90-5-250

140
120

Load kN

100
80
60
40
20
0

0

5

10
15
Deformation mm

20

25

140-1-10

140
120

Load kN

100
80
60
40
20
0

Page 60

0

0.5

1

1.5
Deformation mm

2

2.5

3

140-1-50

140
120

Load kN

100
80
60
40
20
0

0

0.5

1

1.5
Deformation mm

2

2.5

3

3

3.5

140-1-250

140
120

Load kN

100
80
60
40
20
0

Page 61

0

0.5

1

1.5
2
Deformation mm

2.5

140-2-10

140
120

Load kN

100
80
60
40
20
0

0

2

4
6
Deformation mm

8

10

8

10

140-2-50

140
120

Load kN

100
80
60
40
20
0

Page 62

0

2

4
6
Deformation mm

140-2-250

140
120

Load kN

100
80
60
40
20
0

0

2

4
6
Deformation mm

8

10

140-3-10

140
120

Load kN

100
80
60
40
20
0

Page 63

0

2

4

6
Deformation mm

8

10

12

140-3-50

140
120

Load kN

100
80
60
40
20
0

0

2

4

6
Deformation mm

8

10

12

140-3-250
140
120

Load KN

100
80
60
40
20
0

Page 64

0

2

4
6
Deformation mm

8

10

140-4-10

140
120

Load kN

100
80
60
40
20
0

0

2

4

6

8
10
Deformation mm

12

14

16

140-4-50

140
120

Load kN

100
80
60
40
20
0

Page 65

0

2

4

6
8
Deformation mm

10

12

14

140-4-250

140
120

Load kN

100
80
60
40
20
0

0

2

4

6
Deformation mm

8

10

12

140-5-10

140
120

Load kN

100
80
60
40
20
0

Page 66

0

5

10
Deformation mm

15

20

140-5-50

140
120

Load kN

100
80
60
40
20
0

0

5

10
Deformation mm

15

20

15

20

140-5-250

140
120

Load kN

100
80
60
40
20
0

Page 67

0

5

10
Deformation mm