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Pit Test Setup

The procedure was based on the test procedures used for access chambers [AS4198 Appendix C and EN 1917 B.4.1 (AS4198 1994)]. The pit base with a 300 mm riser and lid were mounted on the loading frame as shown in Fig. 7.3. The load cell and hydraulic jack were positioned on the centre of the lid. Load was applied on a hard wood block of 240 x 240 x 100 mm. A rubber mat of 10-25 mm thickness was placed on the bottom of the pit base as Fig. 7.3. The load was increased at a rate 1-3 kN per second until it reached first crack, 80 kN (proof load) and 210 kN (ultimate load) as prescribed by the code. This test was conducted twice for each product design.

Results and Discussion

Since there was an initial crack already present in the Fibre Pit 1 before testing, the first crack of the pit happened on a lower load of 17 kN at the bottom of pit base, as shown in Table 7.2. The riser did not have initial cracks, so the first crack happened at a higher load of 67.5 kN. For the Fibre Pit 2, the first crack of both base and riser happened at 41.1 kN. The riser had two long cracks at 41.1 kN, while the base only

Vertical load test assembly

Fig. 7.3 Vertical load test assembly

Table 7.2 Vertical load testing results of Fibre and Control Pits

First crack of base (kN)

First crack of riser (kN)

Displacement of the loading point

Displacement at 80 kN (mm)

Displacement at 210 kN (mm)

Displacement at 330 kN (mm)

Fibre pit 1

17

67.5

6.93

9.84

13.47

Fibre pit 2

41.1

41.1

7.14

10.73

14.11

Control pit 1

26

43

9.4

12.51

15

Control pit 2

120

152

7.87

11.32

13.79

Vertical load testing results of fibre and control pits

Fig. 7.4 Vertical load testing results of fibre and control pits

had a short crack at the top right corner. For Control Pit 1 with steel reinforcement, the first crack of the base happened at 26 kN and the riser at 43 kN, which are similar to the first cracks of both the Fibre Pits. The first crack of the base of Control Pit 2, however, happened at a very high load of 120 kN, and the riser first cracked at 152 kN. At the proof load (80 kN), ultimate load (210 kN) and maximum load (330 kN), the steel reinforced pits showed slightly higher displacements at the loading point than those of the fibre reinforced pits.

As shown in Fig. 7.4, all the pits have similar load-displacement curves. Due to limited load cell capacity (400 kN), the pits were not crushed to obtain an ultimate load capacity. The pits were loaded up to a maximum load of 330 kN. According to AS 4198 (AS4198 1994), the ultimate strength requirement for the pits is 210 kN. Therefore, all the pits met the minimum strength requirement, indicating that the recycled PP fibre can be used to replace steel bars in the precast concrete pits.

Figure 7.5 shows the crack distributions of the pits after the loading tests. As can been seen, the Fibre Pits exhibited comparable crack distributions and amounts with those of the Control Pits. The maximum crack width was then measured by inserting the tip of feeler gauge along the crack. The maximum crack width of both fibre and steel mesh reinforced concrete pits was less than 0.05 mm. Except for the minor cracks, no residual deflection, dents, bulges, chips or spalls were found on the specimens.

Crack distributions of a Fibre pit 1, b Fibre pit 2, c Control pit 1 and d Control pit 2 at 330 kN vertical load

Fig. 7.5 Crack distributions of a Fibre pit 1, b Fibre pit 2, c Control pit 1 and d Control pit 2 at 330 kN vertical load

 
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