DISTRIBUTION OF STRESSES AND STRAINS IN multilane pile grillage under columns

maya Vladimirovna Kochetkova

Displaying uneven load distribution between the piles in the grillage based on experience, compressive strain on supports, depending on the scheme and the percentage of reinforcement.

Keywords: grillage with piles in several rows, stress-strain state, physical experiment.

Grillage under the column rests on piles, the number of which may be 3 - 4 or multiple row arrangement of piles 5 - 12. Existing methods of calculation is not shared by the two groups grills under the column, assuming that all work in the same pile, and the total load is divided equally between them. Our experiment refutes this assumption.

Prototypes designed in the form of models in scale 1:3. Step piles longitudinally - 3 d, in cross - 4 d. (d - side cross-section of the pile, taking into account the scale - 100 mm). Height grills - 220 mm, size columns 200x300 mm has been assigned on the basis of the results of studies of regulatory calculation methods. Was used a different kind of reinforcement. Along with reinforcing mesh reinforcement was applied at a concentration of bars above the supports-piles. Figure 1 shows the dimensions of formwork and reinforcement of prototypes with the number of piles equal to eight, in table 1 provides a specification fittings.

Grillage loaded hydraulic jack through the metal plate that mimics the column. Were measured compressive strains on the supports using dial gauges and strain gauge transducer. Compressions set over supports are shown in Fig 2. The deformation amount varied depending on the reinforcement and the structural condition (before and after cracking).

Fig.1. Reinforcement scheme samples:
а – РК 1 (μ_s = 1,2 %); б – РК 2 (μ_s = 0,18 %); в – РК 5(μ_s =0,18 %);

Table 1

Specification fittings

The position number	Designation	Product Name	The Amount	Note
	РК-1	Grillage under column	2	n = 8 ms max
	C-1	Welded wire mesh
1		Æ10 АIII = 0,82	21
2		Æ12 АIII = 1,32	11
3		Æ10 АIII = 0,82	8
4		Æ10 АIII = 1,32	4
	РК-2 РК-5		1 1	n = 8 ms min
	С-2	Welded wire mesh
1		Æ4 Вр I = 0,82	21
2		Æ5 Вр I = 1,32	11
	РК-5		1	n = 8 ms min
	С-5	Welded wire mesh
1		Æ4 Вр I = 0,82	20
2		Æ5 Вр I = 1,32	11

The results of data processing make it possible to draw the following conclusions:

o Deformation in the grillage over supports with a large percentage of the reinforcement (m_s = max) is less than in the same raft foundation with a minimum percentage of reinforcement (m_s =min).

o If you compare options 2 and 3, it can be said that the concentration of reinforcement led to a more even distribution of load between the outer and middle supports and less deformation of supports in general.

o After the formation of cracks was observed slow growth deformations and their redistribution.

o Redistribution of efforts after cracking occurs as follows: In areas that are closer to the column, the deformation grew faster than in remote locations. Furthermore, remote locations are often observed a decrease in strain after the formation of cracks.

Fig.2. The average compressive strain on piles in the grillage depending on the type of reinforcement 1; 2; 3.

o Distant piles less loaded than the central pile. Voltage over the central and far the supports differ by 2-4 times. The quantitative ratio depends on the circuit and the percentage of reinforcement.

o Above each support a zone of compressive stresses. Stress intensity depends on the location of the pile. The area of the compressed area depends not only on the cross-sectional dimensions of the pile but also by the reinforcement (Figure 3). With increasing percentage of reinforcement increases the area of the compressed zone and reduces stress on the support.

Fig. 3. The formation of the area of the compressed zone of the pile - supported depending on the type of reinforcement

The findings should be taken into account in improving the methods of calculation and designing grills.

References

1. Kochetkova, M.V. Experimental evaluaton grillages / M.V. Kochetkova, N.I. Gusev, O.V. Snezhkina, K.S. Parshina // Regional architecture and engineering. – 2014. – No1 (18).

2. Kochetkova, M.V. Improving methods of calculation pile foundations under columns / M.V.Kochetkova, O.V.Snezhkina, A.V. Kornyuhin. – Penza: PGUAS, 2011. – 139 p.