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IBRACON Structures and Materials Journal • 2013 • vol. 6 • nº 1
J. E. CAMPUZANO | R. DE CASTRO
|
S. ÁVILA
|
G. DOZ
W type, with their respective U-type shear connectors and the steel
U-type profiles of four inches, closing the top frame and thereby,
providing greater rigidity to the structure.
The third step in constructing the platform was the installation of
wood and metal bracing in order to withstand the shape of the
concrete slab. All this temporary shoring structure was built on
the same level of vertical pillars and horizontal beams levels and
wood forms.
The fourth step was the installation of the armor with steel bars
type ASTM A 572 Grade 50. For positive reinforcement toward
the slab length (X direction) were placed 39 bars 5.0 m length
and gauge of 6.5 mm spaced every 15 cm. For the armor in
the perpendicular direction (Y direction), were placed 41 bars
of 6,1m length and gauge of 12.5 mm spaced every 11.8 cm.
Furthermore, It was performed the installment of the negative
armor in the region of the flexible collet, which consisted in 25
bars in each board, resting on the steel gauge profiles of 12.5
mm and 1.82 m length.
The fifth step consisted in the concreting of the slab until it
achieved a thickness of 10 cm using concrete pumped with
f
ck
of 25 MPa.
The sixth step was the process of curing the slab, which was done
during 30 days. In the first 7 days, water was putted on the slab
within regular intervals of 2 hours. On the other 23 days, the cure
was done every couple days, always checking that the cloths that
covered remained moist. Throughout the process the cloths were
covered with plastic.
At last, the steel and wood shoring was removed after 35 days of
concreting. Figure 8 shows photographs of different stages of the
construction of the dynamic tests platform construction.
3.4 Experimental tests
To obtain the natural frequencies of the platform of dynamic tests,
it was stimulated with impacts through the use of a steel sledge-
hammer and a rubber placed on the surface of the slab. The re-
sponse was measured using a mobile accelerometer which was
been displayed at different points of the slab (see figure 9), using
metal plates. The piezoelectric accelerometer used is the 4366 type,
manufactured by Brüel & Kjaer, with mass approximately equal to
10 grams and sensitivity of 4.80 pC/ms-2, connected to a system of
data acquisition comprised by a module ADS2000, manufactured
by Linx Tecnologia Eletrônica, containing two conditioned plates of
AI-2164 type, each with 16 channels of data acquisition. Data were
monitored and recorded using the software AqDados 7. The acquisi-
tion system is configured to acquire records from a channel (channel
0) corresponding to the accelerometer was placed on the platform
slab at time instants of 5x10-3 s resulting in a sampling frequency
of 200 Hz (1/Δt) . In this case, the cutoff frequency or the Nyquist
frequency was 100 Hz (1/2Δt) and the test duration was 15 seconds.
Data were monitored and recorded using the software AqDados 7.
The acquisition system was configured to acquire records from a
channel (channel 0) corresponding to the accelerometer placed on
the platform slab, at time instants of 5x10-3 s, resulting in a sam-
pling frequency of 200 Hz (1/Δt) . In this case, the cutoff frequency
or the Nyquist frequency was 100 Hz (1/2Δt) and the test duration
was of 15 seconds.
It was noted that the two first natural frequencies of the platform,
obtained experimentally in the different tests were close to the fre-
quencies numerically obtained with the element model type Sol-
id65 and Solid45 and, as shown in Table 4.
Table 3 – Displacement, speed and acceleration in Z direction (vertical), for the analyzed nodes in transient analysis
Node
number
Maximum value
Displacement in Z
Uz (mm)
Speed in Z
Vz (m/s)
Acceleration in Z
2
Az (m/s )
8512
↓
16,780
↓
0,218
↑
4,430
8586
↓
19,356
↑
0,255
↑
5,060
8660
↓
19,331
↑
0,254
↑
5,055
8734
↓
16,747
↓
0,217
↑
4,432
26272
↓
41,972
↓
0,543
↓
10,982
26346
↓
42,053
↑
0,543
↓
11,277
26420
↓
42,043
↑
0,543
↓
11,266
26494
↓
41,980
↓
0,544
↓
10,968
43792
↓
42,877
↓
0,555
↓
11,232
43866
↓
42,877
↑
0,555
↓
11,528
43940
↓
42,866
↑
0,553
↓
11,516
44014
↓
42,886
↓
0,555
↓
11,217
61552
↓
19,024
↓
0,247
↑
5,018
61626
↓
21,359
↑
0,280
↓
5,556
61700
↓
21,334
↑
0,280
↓
5,550
61774
↓
18,995
↓
0,247
↑
5,021