ROLLING CHRACTERISTICS OF WEDGE LOCKSCAFFOLDDINGS DURING USE
Noriyuki Horii , Masao Suzuki, and Kazuhiko Takeishi
Scaffolding and Construction Equipment Association of Japan,
General Incorporated Association.
5-26-20 Shiba, Minato-ku, Tokyo, Japan 108-0014

Leading handrail frames for scaffoldings have recently been used in construction
work sites in Japan. Since then, the Ministry of Health, Labour, and Welfare hasrecommended the adoption of this safety method to prevent falling accidents.
Meanwhile, wedge lock scaffolding has been increasingly used because of its versatile
range of applications. Wedge lock scaffolding systems are considered more flexible
structures than frame-type scaffoldings. To elucidate the advantages offered by theformer, we compared the rolling characteristics of wedge lock scaffoldings equippedwith different leading handrail frames during workers walked on catwalks. The test
results show that the perception of rolling effects is influenced not only by rolling
amplitude, but also by worker’s walking speed and manner of walking (i.e., type ofsteps taken). On a scaffolding with ledgers (longitudinal struts) on both sides,
rolling occurs synchronously with the movement of the entire scaffolding. Onscaffoldings with pre-installed handrails on both sides, the rolling amplitude inindividual scaffoldings is high but the movement of each scaffolding does notextend to the adjacent scaffolding because of the looseness of the connecting
mechanism.

Introduction
Leading handrail frames for scaffoldings (denoted as scaffold) have recently been used inconstruction work sites in Japan to prevent falling accidents. Wedge lock scaffolds, approved assafe by the Scaffolding and Construction Equipment Association of Japan (SCEA), have gradually
been used as attachments to pre-installed handrails. Typical wedge lock scaffolds equipped withleading handrail frames are shown in Figure 1. According to the SCEA’s technical standards,
wedge lock scaffolds should be equipped with wedge lock ledgers on both sides of longitudinalplanes. Scaffolds with pre-installed handrails on one side and wedge lock ledgers on another areused because of easy handling in situ. However, in this case, these scaffolds should be verified inconfirmation tests as being as strong as ordinary scaffold systems. Workers have increasinglydemanded the use of scaffolds with pre-installed handrails on both sides of longitudinal planes
given the flexible application that these scaffolds offer. The SCEA experimentally validated that theaforementioned scaffold systems have sufficient strength for different construction needs. Thisdevelopment prompted the organization to revise its technical standards to include the use ofscaffolds with pre-installed handrails on both sides of longitudinal planes. During the review of theSCEA standards, construction workers indicated that the aforementioned scaffolds exhibit higher
rolling than do scaffolds with wedge lock ledgers on both sides. To verify these observations, we
carried out an experiments intended to determine the rolling characteristics of wedge lock scaffolds
during use.

- 195 -Measurement of the rolling movements of scaffolds in use
Specimens

The tested scaffolds were equipped with four different connecting
mechanisms (Figure 2). Four types of scaffold systems were selected,
in which the deformations measured during a horizontal bending
resistance test were considered. The test shows that the A-type, B-type,C-type scaffolds exhibit maximum, moderate, and minimal
deformation, respectively. The D-type was that wedge connecting
mechanisms are located on uprights outside the longitudinal planes.

Test procedure

1. Tested scaffolds
Scaffolds consisting of 2 stages and 3 spans were tested. Targets(‫=׎‬15cm, painted yellow and black) were attached to the scaffolds tomeasure their rolling movements. The movements of these targets
were recorded using a video camera while a worker walked along thetop catwalk (Figure 3). The movements were measured by the image
processing method using the Dipp-Motion Pro 2D program. The
displacements of the targets were compared to determine the rollingcharacteristics of the tested scaffolds.

A-typeFigure 1. Scaffoldings withboth pre-installed handrails

B-typeC-typeD- typeFigure 2. Four types of wedge connecting mechanism

2. Walking patterns used in the test
Three walking patterns were used: slow, normal, and fast. Two workers made one round trip
each on the 3-span catwalk. Details on the height, weight, and experience of the workers arelisted in Table 1.
Table 1. Worker profile
WorkerA
B

Age
2427

GenderMale
Male

Height(cm)175
171

Weight(kg)6270Experience (years)
14

3. Structures of the tested Scaffolds
The structures of scaffolds were 2 stages and 3 spans. Each scaffold was set up using
prefabricated scaffold elements produced by the same manufacturer. The scaffolds were test
under conditions (a), (b), and (c):(a) Pre-installed handrails were attached on both sides of scaffolds (denoted as PH+PH)
 (Figure 4);(b) A pre-installed handrail was attached on one side and a wedge lock ledger was attached
on another (denoted as PH+LS) (Figure 5);(c) Wedge lock ledgers were attached on both sides of scaffolds (denoted as LS+LS);
The SCEA standards stipulate that wall-anchored ties must be attached within 5 m in the verticaldirection and near the putlog (transverse strut). Thus, wall-anchored ties need not be attached on
the 2-stage scaffold (whose height is about 4 m). This condition is considered the most flexible,
because only bases of scaffolds are anchored.
Here after, PH and LS represents pre-installed handrails and wedge lock ledgers, respectively.

- 196 -Rolling direction

Videocamera

Position of measured targets

Walking pattern

Start & end point

Walking direction

1800

900

Video
camera1800

Rolling direction

Base plate
1800

1800

1800

900

Figure 3. Schematic diagram of rolling test

Figure 4. Both side were preinstalled Handrail

Figure 5. One side was pre-installed handrail
and another side was ledge

Test results

The test results are shown in Table 2 and Figure 6. The vertical and horizontal axes represent thehorizontal displacement (mm) of the targets and elapsed time (sec), respectively. After thewalking test, worker A revealed that the scaffold exhibiting the strongest rolling is the A-type
scaffold with LS+LS. By contrast, worker B pointed out the D-type scaffold with PH+PH shows
the strongest rolling. The analysis of the test results on rolling amplitude indicates that eventhough a worker detects strong rolling, such assessment does not necessarily translate to a highrolling amplitude.
For example, the worker evaluated the A-type scaffolds with PH+PH and LS+LS as “steady” and“having the strongest rolling”, respectively. However, minimal difference was found in therolling amplitude of both scaffolds, as shown in the analysis (the scaffold with LS+LS exhibits amaximum rolling amplitude of 8 mm; the scaffold with PH-PH shows a maximum rolling
amplitude of 7 mm). Numerous irregularities were observed in the rolling movements of thescaffolds with LS+LS. This irregular rolling drove worker A to assess the scaffolds thus: “It was
not easy to walk because it is rolling". The rolling amplitudes of scaffolds do not always
correspond with the assessments of workers. Worker B, who is more skilled than worker A,walked fast along the scaffolds by taking wide steps.

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A typeB typeC typeD typePH + PH

PH + LS

LS + LS

PH + PH

PH + LS

PH + PH

PH + LSD♫

PH + PHD♫୧㠃ඛ⾜42-4-60
ᨭᰕ2-10-8

PH + LS

ඛ ⾜ +ᕸ ᮦ

64-22-40

ᨭᰕ2-1 0-6-8

8D♫LS୧㠃ᕸᮦ+ LS

642-40ᨭᰕ2-10-6-8Figure 6. Shapes of rolling at walking test

- 198 -

Table 2. Maximum rolling amplitudes scaffolds at walking test
Combination
PH + PH
PH + LS
LS + LSof leading handrails
A type (flange type)
7.0
8.0
8.0
B type (pocket type)
13.0
21.0
--C type (flange type)
11.5
9.5--D type (pocket type, outside)
15.0
8.5
17.0
Consequently, the rolling becomes to increase. Worker B assess the scaffolds was not difficult towalk even though high rolling of scaffold, because he has considerable experience walking on
catwalks and high rolling occurred relatively constant pitch. Most of the pre-handrails wereattached by inserting a wedge into the pocket of an upright for flexibility during work. Therefore,
scaffolds essentially have low resistance to rolling because of the looseness of the connecting
mechanism. This looseness of locking affects the manner by which worker’s walk along such
structures. These results indicate that the workers assessed the scaffolds as rolling because theirregular rolling movements disturbed the worker’s walking pitch. The graph of each scaffold
shows clear and undisturbed waves, indicating relatively high rolling amplitudes. Conversely,
unclear and disturbed waves demonstrate the tendency of the scaffolds to generate low rolling
amplitudes.

Discussion

A number of human factors influence the rolling of the scaffolds.
(1) The speed with which unskilled workers walk is slow, in which case a worker attempts towalk in accordance with the rolling pitch of a scaffold.
(2) The steps taken by unskilled workers are narrow, a situation that a worker tries to rectify
by walking also in accordance with the rolling pitch of a scaffold.
(3) A worker’s skill level influences characteristics 1 and 2; thus, an unskilled worker slows
down his pace to walk carefully. The differences in walking speed and steps taken arereflected by a worker’s skill level.
From a structural,(4) Pre-installed handrails are attached on both sides of a scaffold, so that the strength of awedge lock component affects scaffold rolling.
(5) A wedge lock can be strike or insert type. The former exhibits a small rolling width.
If the structure and strength of scaffolds are more rigid, then the rolling amplitudes of such
scaffolds would be reduced. Nevertheless, the perception of rolling effects is influenced not only
by rolling amplitude, but also by walking speed and steps taken, among other similar factors.

Displacement of scaffolds due to horizontal loading
Specimens

The tested scaffold systems were the B-type and D-type scaffolds, which have high rolling
amplitudes.

Test Procedure

A horizontal load test was conducted (Figure 7). In the test, a horizontal load acted on uprightno.2 at the height of upper catwalk surface, and the horizontal displacement at the horizontal load
reaches 489 N (50 kgf). The horizontal displacements of the uprights at the opposite side of aloaded upright were measured by LVDT. For the scaffolds with PH+LS, the loading point wasapplied on the pre-installed handrail side.

Test result

The scaffolds with PH+PH are characterized by large displacements and the scaffolds withPH+PH exhibit stiffness smaller than that generated by the other types of scaffolds. To compare- 199 -Upright
LVDT

Uprightno.2

Loading point

Upright
no.3

Dead load
489 NCatwalk

B-type: 3100 mm
D-type: 2900 mm

Upright
no.1

LVDT
Upright
no.4

Deadload
100 mmBaseplateFigure 7. Schematic diagram of horizontal load test  Table 3. Horizontal displacements of B-type and D-type scaffoldings (mm)Upright no.
1234
Upright no.
123
PH + PH
7.6
24.912.2
3.1
PH + PH14.2 30.7
13.4
PH + LS
16.6
21.8
10.4
4.2
PH + LS
17.6 24.3
12.5
LS + LS
16.9
17.1
10.4
4.9
LS + LS
17.6 17.9
12.0
B type (Pocket type)

D type (Pocket type)

4
3.6
6.1
6.3

the stiffness of entire scaffold structures, the displacements of each upright were also compared(Table 3). In both LS types of scaffolds, the loaded upright and adjacent uprights exhibit a small
difference in displacement. Conversely, both PH type scaffolds show a considerably large
difference in displacement. The stiffness of the connecting mechanism in the LS type scaffolds islarger than that in PH type scaffolds. In the LS type scaffolds, the stiffness of the entire structures
increases because the connecting wedges were placed in position using a hammer.

Discussion

In both LS type scaffolds, rolling occurs synchronously with scaffold movement because evenunder high rolling, workers experience difficulty traversing across such components. In both PH
type scaffolds, the amplitude of individual scaffolds is high but the movement of one scaffold
does not extend to the adjacent scaffolds because of the looseness of the connecting mechanism.
The uneasiness that the workers felt as they walked across the scaffolds may be attributed to theirmisassumption that small rolling waves occur along the ledgers.

Conclusions
The conclusions derived from the experiment are summarized as follows.
(1) If the structure and strength of scaffolds are more rigid, then the rolling amplitudes ofscaffolds would be expected to reduce. Nonetheless, the perception of rolling effects isinfluenced not only by rolling amplitude, but also by walking speed and steps taken.
(2) On scaffolds with ledgers on both sides, rolling occurs synchronous with an entire
scaffold‘s movement.
(3) On scaffolds with pre-installed handrails on both sides, the amplitude of individual
scaffolds is high but the movement of each scaffold does not extend to the adjacentscaffolds because of the looseness of the connecting mechanism.

Reference
Yoshida, I (1956). Wooden scaffolding and metal tubular scaffolding. Tokyo: Maki Shoten- 200 -