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1. Flat Slabs
The trial bay simulated a 26ft x 20ft internal panel of a
11in thick flat floor slab for a six-story building. The floor was designed
to take a typical imposed office loading of 100 psf , plus self weight.
Trials were carried out using
- A traditional loose
bar layout
- A hand-laid mat layout
using single-directional mats
- A crane-handled mat
layout using two-directional mats
Crane:
18 ton capacity mobile crane with a jib height of 121ft and a maximum
horizontal reach of 72ft when carrying a one ton load.
Prior to the trials, the bay area was marked out and column starter bars
drilled into concrete base at the column positions. The reinforcement for all
the speed trials was stored in a designated area outside the footprint of the
mock building, with the crane positioned centrally.
Work was “theoretically” carried out at level 5, some 49ft above ground
level, by hoisting reinforcement from the storage area to a height of 59ft
before landing it in the work area.
Strictly regulated working hours:
Start 8:30
Break 10:00 – 10:15 am
Lunch 12:30 – 1:30 pm
Break 3:00 – 3:15 pm
End at completion, but no later than 6:30 pm
The time was noted at the start of operations, with the laying of spacer
strips. Work was considered complete when the last bar was fixed in position
and shear links placed over the column supports.
a. Rebar Trial:
The crane was used to pick up reinforcement bundles from the storage area
and place them near to the working zone. The time trial commenced after a
dummy run to familiarize the team with the identification and handling, so
that the recorded trial run represents an efficient working cycle.
Work sequence:
- Cover spacer strips
for the bottom reinforcement layer were laid out uniformly over the area.
- A single bar for the
26ft span was positioned and spacings for
similar bars chalked out.
- Bottom layer bars were
identified in the reinforcement bundles and laid out to the chalk marked
spacings.
- A single bar in the
opposite (20ft span) direction was positioned and the centers for the
top layer of the bottom reinforcement chalked out.
- The remaining bottom
bars were located and fixed in position.
- The bottom bars were
tied at every other crossover to keep the assembly rigid.
- Steel chairs to
support the top reinforcement were placed over the area and tied to the
bottom reinforcement.
- Bars for the lower
layer of top reinforcement were identified, their positions chalked out,
and the bars placed and tied. Bars for the upper layer were then
extracted from the reinforcement bundles and positioned to finish the
top reinforcement.
- Loose bars were
threaded through to complete the reinforcement over the columns.
- All top bars were tied
at every other crossover to fix the assembly.
- The shear links were
sleeved-in and tied.
Results:
Fixing the loose bar reinforcement started at 8:30am and was completed at 3:45pm , when the last shear link was in position. Over
this period 298 single bars were fixed with a total weight of 1.8 tons. This
required 5.75 hours.
b. Single Direction Mat:
For the second trial on the flat slab, traditional reinforcement was
replaced by single-directional fabric mats, light enough to be manhandled.
The sizes were approximate varying from 30ft x 10ft down to 10ft x 6.5ft.
Each mat at the main reinforcement running in one direction, with traverse
wires welded on to keep the assembly rigid. A second mat was overlaid at
right angles to provide the main reinforcement in the other direction.
All mats were machine-fabricated and scheduled in accordance with sheet
size, using standard dimensions. Loose bars were used for continuity over the
columns and for shear links. The mats were stacked in the designated storage
area and lifted by crane to the working area, with the bottom and top mats
arranged in the required order for handling.
Work sequence:
- Cover spacer strips
for the bottom mats were laid out uniformly over the area.
- Bottom mats in the
longitudinal direction (26ft span) were located and placed in position
by hand. Four mats were laid.
- Bottom mats in the
transverse direction (20ft. span) were laid over the first layer and the
two bottom mats tied together.
- Steel chairs to
support the top reinforcement were positioned.
- The first layer of top
mats was placed over the support chairs in the 26ft direction.
- The remaining top mats
were positioned and tied down to secure both layers.
- Single bars were fixed
over the column supports to provide continuity steel, and shear links
positioned to complete the assembly.
Results:
The trial commenced at 8:30 am and finished at 10:00am ,
when the last shear link was fixed. In all, 40 reinforcement mats were fixed,
with a total weight of 2.0 tons. The time required was 1.5 hours.
c. Two Directional Mat:
For the third trial, two-directional fabric reinforcement mats were
substituted for the single-directional mats. The mats were prefabricated in
the largest possible sizes, limited only by the dimensions of the transport
and the crane capacity. The reinforcement for the bottom layer was fabricated
in three mats, each 29.5ft x 10ft and the top layer was fabricated in four
mats, two of 29.5ft x 10ft and two of 20ft x 10ft. Reinforcement over and
around the columns was provided by loose bars, as were the shear links.
The two-directional mats were stacked in the designated storage area and
lifted by crane directly into position.
Working sequence:
- Cover spacer strips
for the bottom mats were laid uniformly over the 26ft x 20ft bay area.
- One mat for the bottom
reinforcement was craned directly into position within the area. The
remaining two mats were craned in together. The lower mat was unhooked
in position, then the upper mat was craned into
place.
- Steel spacer chairs
were laid over the bottom mats and secured before landing the top
reinforcement mats.
- The two 29.5ft x 10ft
mats of top reinforcement were craned in together. The lower mat was
unhooked before the crane lifted the top mat into position on the
opposite side of the bay.
- The two smaller top
mats, running in the 20ft direction, were then craned into position.
- A minimum amount of
tying was carried out to secure the mats to the support chairs. The
weight of the mats was sufficient to keep the assembly rigidly in place.
- Continuity
reinforcement, using loose bars, was positioned over the four columns
and shear links were inserted and tied.
Results:
The trial commenced at 12:15 pm and by 12:45 pm the last mast for the top
reinforcement was in position. By 12:51 all the shear links and continuity
reinforcement over the column positions had been fixed. Seven mats were fixed
with a total weight of 2.2 tons. The time required was 0.5 hours.
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