Optimized Forms of Bracket Frames
Tseng-Hsing Hsu1*, Chi-Chie Chang2, and Chen-Hua Lin1
1
Department of Civil Engineering and Engineering Informatics, Chung Hua University
707, Sec.2, WuFu Rd., Hsinchu, Taiwan 30012, R.O.C.
E-mail: thsu@chu.edu.tw
Tel.: +886-3-5186720 Fax.: +886-3-5372188
2
Institute of Occupational Safety and Health
No. 99, Lane 407, Hengke Rd., Sijhih City, Taipei County 22143, Taiwan (R.O.C.)
E-mail: chngc@mail.iosh.gov.tw
Abstract
The safety performance and stability of the scaffolds are highly dependent on the strength of the bracket frames
they erected on. If these bracket frames lack sufficient strength, it is possible to cause the collapse of the scaffolds.
There are various factors that can affect the strength of the bracket frames. The cross sections, internal stress,
distribution of these stresses, and the anchorages can all have effects on the strengths. The construction industries in
Taiwan usually use the cheapest frames and ignore the possible consequence. The current research performed finite
element analysis on various types of bracket frames. These results are then used to explore the optimized designs of
the bracket frames. These designs can then be used by the industry to manufacture better products.
Keywords: Loading capacity, bracket frame, finite element analysis, optimized form.
1. Introduction
In densely populated urban area, the space for
construction work is severely limited. It is very
important for the industry to utilize a measure that
requires less space without affecting the progress and
safety of the project. One way to circumvent the
problem is to use bracket frames and erect scaffold
system from the second floor up [1]. It can reduce the
space required and shorten the work period which in
turns save time and budget. As a result, the bracket
frames are one of the most often used equipments on
construction sites [2, 3]. Because the bracket frames
of appropriate bracket frame strength may cause
possible collapse of the scaffold system [7, 8]. Most
researches explore the strength of the scaffold system
[9, 10, 11, 12]. The inspection and test focus on the
scaffold systems as well [13, 14]. In light of this, this
research
will
optimization
study
of
the
the
loading
bracket
capacity
frame.
and
Numerical
simulations were utilized to analyze the mechanical
behaviors of the bracket frames. Tests were also
performed on the bracket frames to verify the numerical
model. The optimized form for the frame was explored
based on results of numerical simulation.
provide platforms for the scaffold systems, the safety
and stability of the scaffold systems depend on the
2. Finite Element Model
loading capacities of the frames. Safety of working
Numerical simulation was used to explore the
crews demands reliable bracket frames [4, 5, 6]. Lack
optimized form of the bracket frame. This approach can
save
time
and
expense
for
manufacturing
the
the industry is to weld two single frames together to
experiment specimen and actually perform the tests. For
form a more robust bracket frame. This research also
this research, the program ANSYS was used. The
considered these types of frames (type E, F, G, H). The
dimension of the reference bracket frame is shown in
results in this section are all obtained through numerical
fig. 1. The dimension used here is the same as the frame
simulations. To simplify the modeling process, the
bracket used in actual test. The element used was 3D
dimension of the basic configuration is slightly different
solid element (Solid92). The material used is CNS-
from that in fig. 1. The dimensions and configurations
SS400 steel. The Poisson ratio is 0.3 (  0.3 ) and the
for types A, B, C, and D single frames are shown in fig.
Young’s modulus is set to be 2.03×106 kgf/cm2
2 to fig. 5. Type E, F, G, and H double-frames combine
( E  2.03  106 kgf/cm 2 ). The frame was assumed to be
two type A, B, C, and D single frames respectively.
fixed at two elliptical holes shown in the figure. The
point loads were applied equally at 30cm and 106cm
from the left side.
A linear elastic buckling analysis was performed on
this numerical model. The total load at buckling is
approximately 1.07 ton.
To verify the numerical model, a actual test was
performed on a frame with the same dimension and
loading condition. The test results showed that the
ultimate load of the bracket frame is approximately 1.2
ton. There was difference between simulation and test
results because the simulation gave the load at first
yielding while the test result was the ultimate load. This
result indicated that the finite element analysis can
reasonably predict the loading capacity of the bracket
frame.
In the finite element analysis, Solid92 elements
were used in all cases. The material used was CNSSS400 steel. All frames were fixed at the two
intermediate points on the left side as shown in figures.
The results of the linear elastic buckling analysis
were shown in table 1. From these results, it is clear that
the type of reinforcement will affect the loading
capacities of the bracket frames. The loading capacity
of type A is the best among the four single frames while
type D is the worst. The loading capacities for double
frames (type E, F, G, and H) have the same trend.
Other than the type of the bracket frame, the
results indicate other factors to be considered. The first
thing to take into consideration is the effect of
combining two single frames into one double-frame
bracket. At first thought, the loading capacity should be
doubled because there are two frames to support the
3. Analysis of Optimized Form of Bracket
Frame
After verifying the validity of the finite element
analysis, different types of bracket frames were
analyzed to find out the best form of the frame. In order
to compare the effects among various types of
reinforcements, all frames used the same basic frame.
Different kinds of reinforcements were then added to
the basic frame (type A, B, C, D). A usual practice in
load. The results of finite element analysis indicate that
the effect is more than that. It can be seen in table 1 that
the effects are always more than double the capacities.
One possible explanation can be seen in figure 6 and
figure 7. Figure 6 and 7 are the top views of the
deformations of two bracket frames. In figure 6, the
single frame deformed sideway because of the torsion
effect of the loading. The frame in figure 7 does not
have this effect due to the symmetric configuration of
the double frame setup. This torsion reduces the
capacity of the single frame bracket. It suggests that the
2.
For single frame bracket, type A has the
industry practice of combining two single frames into a
highest loading capacity, followed by type C
larger double-frame bracket has its merit. But the
and type B. Type D (without reinforcement)
configuration of the two frames in the double-frame
has the lowest loading capacity. Type E, F, G,
configuration should be such that the effect of torsion
and H combine two type A, B, C, and D frames
can cancel out.
respectively. The order of their capacities is the
The other thing worth noting is the effect of
loading on the anchoring point of the bracket frame.
same as that of their components.
3.
Double-frame brackets have more than twice
Usually the frames are installed using screws. As a
the capacities than those of single frames due
result, the stress around the anchoring point is very
to the asymmetric nature of single frames. The
large. The results of finite element analysis clearly show
torsion effect reduces the loading capacity of
this effect. Figure 8 is the stress distribution of a bracket
the single frame bracket. The manufacturers
frame under loading. The maximum stress (in red circle)
should use double-frame design if possible.
occurs at the anchoring point. Figure 9 shows the
4.
The anchoring point sustains very large stress.
deformation around the anchoring point. To study this
Use of double-frame bracket can alleviate the
effect, another set of simulations are performed by
situation. Reduce the distance between the
varying the distance between the edge of the frame and
anchoring point and the edge of the frame can
the anchoring point (distance
reduce the stress as well.
d in figure 10). The
results showed that the loading capacity of the bracket
frame will change when distance
d varied. Figure 11 is
the figure of the relationship between loading capacities
of frame type A, B, C, and D and the distance
5.
Based on the results of this research, the users
should choose double-frame bracket with
vertical reinforcements if possible.
d . The
figure shows that the capacities increase as the distance
5. Acknowledgement
decreases.
This work is supported by the Institute of Occupational
Safety and Health under grant IOSH94-S304.
4. Conclusions
From the results of this research, the following
conclusions can be drawn:
1.
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Unit: cm
Figure 1: Dimension of the Reference frame
Figure 2: Type A Bracket Frame
Figure 3: Type B Bracket Frame
Figure 4: Type C Bracket Frame
Figure 5: Type D Bracket Frame
Figure 6: Top View of the Deformation of a Single Frame Bracket
Figure 7: Top View of the Deformation of a Double-Frame Bracket
Figure 8: Stress Distribution for a Bracket Frame under Loading
Figure 9: Deformation around the Anchoring Point for a Bracket Frame under Loading
Figure 10: Definition of the Distance
d
Loading Capacity ( kgf)
1900
1700
1500
Type D
Type C
1300
Type B
1100
Type A
900
700
500
4
6
8
10
d ( cm )
Figure 11: Relationship between Loading Capacity and Distance
d
Table 1: Loading Capacities of Bracket frames
Type
Illustration
Loading Capacity (kgf)
A
1050
B
780
C
880
D
640
E
2862
F
1727
G
1696
H
1083