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JOURNAL OF STRUCTURAL ENGINEERING 467
Vol. 45, No. 5, DECEMBER 2018 - JANUARY 2019
Journal of Structural Engineering
Vol. 45, No. 5, December 2018 - January 2019 pp. 467-472 No. 45-SC
Detecting failures in temporary supporting structures used in construction
D. Kamalnataraj*, and V. Ramasamy**
Email: kamalnatarajsgi@gmail.com
*Department of Civil Engineering, Anna University, Chennai - 600 025, INDIA
**Department of Civil Engineering, Adhiparasakthi Engineering College, Melmaruvathur - 603 319, INDIA
Received: 13 May 2016; Accepted: 22 May 2018
The construction industry is signicantly more
hazardous
than most others economic sectors1. Trying
to reduce the incidence of construction failures is
a continuous process and organizations such as
Occupational Safety and Health Administration (OSHA)
and others are dedicated to this goal2. The European
foundation (1991) found that 60% of the accidents
it surveyed could have been eliminated, reduced, or
avoided with more thought during the design stage3. A
study on U.K. construction industry revealed that there
is a certain relationship between safety of construction
and decisions made in design process regarding the
accident causation4.
Temporary supporting structure fails persistently
due to decient design, substandard materials, worst
workmanship, poor supervision, combination of any
of these factors. These temporary structures are core
support in the formation of the main frame of the
building3,5. Recent studies have shown that these type
of failures results in minor to major losses and injuries
to human from casualty to fatality5,6. Such failures
are not instant and construction crews were unable to
identify these failures since these supports are huge
in volume7. The subject study attempted to design
and install a detector to distinguish any deection on
these temporary supporting structures from the time
of installation till dismantling on these temporary
supporting structures. Further the detection system will
notify such deections to the construction crew for
corrective action.
RESEARCH STUDY
General failures on temporary supporting structures
are due to loads which the structure could not bear.
These unexpected loads might cause minor damage to
complete collapse of the supporting frame. Supervising
the erection of each and every support of these structures
is mandatory. Thorough monitoring after installation
is also required. The key factors for these failures are
lack of testing each and every support for their rigidity.
The hesitance of the testing personnel in checking huge
number of supports lead to miserable accidents.
Hence an ideology of design and installation of a
device to detect all type of deection on these temporary
supporting structure and record the same to alert the
construction workers about the potential failures ahead
and urge them for corrective action.
Description of the device
This detector is mainly designed to predict the changes /
damages on the structural components of the temporary
supporting structure. This detector consists of many
components such as top plate, bottom plate, spring
and the circuit. The Fig. 2 shows the components of
the detector. The plates are made up of galvanized iron
to withstand heavy load. The springs are connected to
the top and bottom plate using the heavy duty bolts.
The circuit is placed in-between the top and the bottom
plates. The general working principle of this detector is,
“when the load is applied on the top plate, the detector
is subjected to a compressive force which activates the
468 JOURNAL OF STRUCTURAL ENGINEERING
Vol. 45, No. 5, DECEMBER 2018 - JANUARY 2019
switch followed by the alarm”. It predicts the structural
collapse and warns the humans about that collapse.
Fig. 1 Detector
MS angles Top load
bearing plate
Top enclosure
Alarm circuit
Heavy duty
springs enclosed
Heavy duty
galvanized rods
Central plastic piston
Bottom enclosure
Fig. 2 Components of the detector
The wires are extended outside the device to make
an external connection. This external connection is
made to place the alarm and the power source as per the
requirement. Using the external wires, the alarm can be
placed anywhere and the source of power can also be
changed. Backup power arrangement has to be done for
uninterrupted continuous operation. This detector has a
very simple circuit which consists of a power source, a
switch and an alarm only. The Fig. 3 shows the circuit
diagram of the detector.
Indicator installed in formwork
Fig. 3 Position of the detector in the formwork
The detector will work in two stages, the normal
stage and the activated stage. When the load is not
applied on the top plate, the detector is said to be in
normal stage. When the load is applied on the top plate,
the detector is said to be in the activated stage. In the
normal stage, the switch will be inactive which makes
the circuit open and hence there will be no current ow.
In the activated stage, the switch will be activated which
makes the circuit closed and thus the current ows from
the power source to the alarm through the switch.
PREDICTION OF TEMPORARY SUPPORTING
STRUCTURE COLLAPSE
The detector is designed to predict the collapse of
the temporary supporting structure mainly due to
unexpected / miscalculated load which may impact on
the supporting frames. The indicator is placed under
the sheathing of the formwork using jack, truss and
shores as shown in Figs. 3 and 4. A small space is left
between the sheathing of the formwork and the device
in order to nullify natural downward displacement of
the formwork during the application of the concrete.
The space to be provided depends upon the mass of the
concrete to be placed and the downward displacement
of the formwork. The inkling of the indicator will be
more accurate when the space between the sheathing
and the device decreases.
Indicator insert zoomed
Fig. 4 Zoom out of the indicator in the formwork
The indicator is placed at equal intervals (say 2
meters or 6 feet) to form a grid in the formwork as
shown in the Fig. 5. The interval in the grid may vary
depending upon many factors such as the dimension of
the roof slab, mass of the concrete to be placed and so
JOURNAL OF STRUCTURAL ENGINEERING 469
Vol. 45, No. 5, DECEMBER 2018 - JANUARY 2019
on. Deformation at any point of the formwork of the
roof slab can be monitored easily through the set of
indicators in the grid.
30′
30′
6′6′6′6′
Indicator
Roof slab
6′
6′
6′
6′
6′
6′
Fig. 5 Grid form of the detector in formwork
The indicator should be placed as a grid under the
sheathing of the formwork with small space in between
them. The alarm and the grid of indicators are connected
through electrical wiring. The alarms can be xed at
any place in any number at the site of the formwork and
the control room. When the indicator is in normal stage,
a minute space will exist between the indicator and the
sheathing which will endure until the deformation of
the formwork. The Fig. 6 shows the indicator in its
normal stage when placed in the formwork.
Concrete load
Concrete
Sheathing
Indicator
Alarm in the
control room
Jack
Shores
Fig. 6 Normal stage of the detector in the formwork
The formwork failure is caused due to many reasons
such as overloading of concrete, poor workmanship,
usage of low quality materials for formwork and so
on. When the formwork deforms at any place, the
excessive load is transferred to the nearby detector.
This load creates a compressive force in the detector
which contracts the springs in it and activates the
switch. The activated switch will further activate the
alarms which warn the humans in the formwork site
about the upcoming structural collapse. The prediction
stage of the detector in the formwork is shown in Fig. 7.
These detectors in the grid can be monitored and the
deformation of the formwork can be repaired instantly
which not only saves the human lives but also prevents
the great economic loss.
Compression
Alarm in the
control room
Fig. 7 Prediction stage of the detector in the formwork
ENHANCEMENT
This device can be developed further, by connecting
to a computer through a control panel which simplies
the monitoring of the detectors in the grid system.
The mobile alert system can also be enhanced with
this detector. The alert messages can be sent to the
required mobiles using zigbee chip. The Fig. 8 shows
the developed circuit of the detector.
In the building, the detectors in the grid should be
connected to a control panel through electrical wiring.
This control panel is used to monitor the inkling of
the detectors in the grid. The setup is computerized
by connecting the control panel to the computer. The
usage of the computer can serve various purposes such
as monitoring the detector, nding the cause of the
failure, measuring the total displacement and so on.
These computers can be further programmed to send
alert messages to the required mobile phones. The
Fig. 9 shows the developed grid in the building.
Building echanced
with damage
prediction device
Activation of device
due to failure of
substructure
Mobilization of
emergency
response team
Safe evacuation of
occupants
Initiation of
emergency alert
system
Central command
centre recievies
alert
Fig. 8 Enhanced device with its communication loop
470 JOURNAL OF STRUCTURAL ENGINEERING
Vol. 45, No. 5, DECEMBER 2018 - JANUARY 2019
EXPERIMENT
The detector is placed under the formwork in a
construction site as shown in Fig. 10. It is placed with a
small space in between the sheathing of the formwork
and the detector as shown in Fig. 11. The detector is
placed as a grid at every 2 meters in the construction
site.
Fig. 10 Detector in the formwork at the construction site
The concrete is lled upon the formwork and the
performance of the device in the grid is analyzed.
When concrete is placed upon the formwork, the
detector endures to be in normal stage when there is
no failure in the formwork. The formwork undergoes
some natural downward displacement due to the mass
of the concrete and the space between sheathing of the
formwork and the detector vanishes. When there is
further displacement of the sheathing due to failure of
the formwork, the load of the concrete is transferred to
the detector and it is subjected to a compressive force
which makes the detector to move on to the prediction
stage. In this stage, the springs in the device contracts
and the switch is activated. It further activates the alarm
which warns the humans in the construction site about
the failure of the formwork.
Fig. 11 Position of the detector in the formwork at the construction
site
OBSERVATION AND RESULTS
The detector is placed as a grid in the formwork at the
construction site and every placement is named with tag
as shown in the gure. Every position of the detector
is monitored and the observations are tabulated in
Table 1. Using tabulated information further action is
taken. The inkling of the detector at its each position is
checked. The detector showed inkling in the positions
A3, B2, C4, D1 and D3 which means that there is
30′
30′
6′
6′
6′
6′
6′
6′
6′6′6′6′
Indicator
System
Control
panel
Alarm
Project
manager
Project
engineer
Site
engineer
Site supervisor
Site foreman and
all site workers
Roof slab
Fig. 9 Schematic representation of detection and alert system
JOURNAL OF STRUCTURAL ENGINEERING 471
Vol. 45, No. 5, DECEMBER 2018 - JANUARY 2019
certain deformation / deection in the formwork at
those positions. Thus the damage of the formwork
at the detected positions were repaired. Also it was
found that the other positions in the formwork have no
failure since the detector showed no inklings on those
positions.
30′
6′6′6′6′
Indicator
A1 A2 A3 A4
B1 B2 B3 B4
C1 C2 C3 C4
D1 D2 D3 D4
6′
30′
6′
6′
6′
6′
6′
Roof slab
Fig. 12 Grid in the formwork at the construction site
CONCLUSION
Based on the results of the experiments, it is concluded
that this device is designed in such a way to detect
any minor / major deections on the temporary
supporting structures and alerting the site workers
for corrective action on immediate basis to avoid any
further deformation / collapses. This would facilitate
the site supervisory to monitor the performance of
material, installation crew and to save the possible
damages at site. The detector does not have any impact
on environment. The device should be maintained
periodically for its better performance. The device is
of simple design and can be fabricated personally. This
research attempted to predict the failures on temporary
structures prior to collapse and to repair the same for
acceptable conditions thus preventing major accidents
saving human life, property and time at a construction
site.
TABLE1
OBSERVATION OF THE DETECTOR IN THE FIELD
S.NO. Notation of the detector Indication of fall Cause for the fall Course of action
1 A1 NIL - NONE
2 A2 NIL - NONE
3 A3 YES Deformation of shuttering due to
poor supports
Repair the supports and reiterate
the shuttering back to its original
position
4 A4 NIL - NONE
5 B1 NIL - NONE
6 B2 YES
Deformation of shuttering base due
to over stocking of concrete at one
point
Distribute the stocked concretein
such away to forman uniform load
on top of the shuttering base
7 B3 NIL - NONE
8 B4 NIL - NONE
9 C1 NIL - NONE
10 C2 NIL - NONE
11 C3 NIL - NONE
12 C4 YES Failure of supports due to lack of
rm base slab
Ensure the supports are xed
properly on a rmbase slab.
13 D1 YES
Failure of connection between the
horizontal shuttering plate and its
vertical support
Ensure all the connection are made
as per the design and conrm the
bondage between them
14 D2 NIL - NONE
15 D3 YES
Deformation of shuttering base due
to over stocking of concrete at one
point
Distribute the stocked concretein
such away to forman uniform load
on top of the shuttering base
16 D4 NIL - NONE
472 JOURNAL OF STRUCTURAL ENGINEERING
Vol. 45, No. 5, DECEMBER 2018 - JANUARY 2019
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(Discussion on this article must reach the editor before
February 28, 2019)
