Ultimate compressive resistance from static load tests

If static load tests are performed on several piles with similar characteristics, the characteristic compressive resistance may be computed as:

where £, and £2 are correlation factors applied to the mean and the lowest of the measured resistances, Rc;m, respectively. The objective of these correlation factors is to introduce the variability of the ground conditions into the analysis. Their recommended values are presented in Table 7.11.

Ultimate compressive resistance from ground test results

Two approaches may be adopted: the “model pile” and the “alternative” or “ground model” approach. In the “model pile” approach, a pile compressive resistance is calculated for each

Table 7.11 Correlation factors £ to derive characteristic values from static pile load tests (EN 1997-1:2004).

/

2

3

4

>5

1.40

1.30

1.20

1.10

1.00

1.40

1.20

1.05

1.00

1.00

n = number of tests

test profile, using a semi-empirical method based on in situ or laboratory test results. After calculating one resistance, Rc.cah per profile, the characteristic value is computed as:

where £s and are correlation factors applied to the mean and the lowest of the calculated resistances, Rc.cai, respectively, and depend on the number of test profiles, n, and are applied, respectively:

• to the mean values:

• to the lowest values:

The values of the proposed correlation factors are given in Table 7.12.

In the “alternative” or “ground model” procedure, the characteristic values of the base and shaft resistances are computed, based on ground parameters:

Note that, for calculation of the characteristic values of the unit base and shaft resistances, no partial factor is applied to the ground parameters (except for Design Approach 3) and no correlation factors £ are applied to the resistances. In this “ground model” alternative procedure, a model factor, yRd, greater than 1, defined in the National Annex, is used to

Table 7.12 Correlation factors £ to derive characteristic values from ground test results (EN 1997-1:2004).

/

2

3

4

5

7

10

1.40

1.35

1.33

1.31

1.29

1.27

1.25

1.40

1.27

1.23

1.20

1.15

1.12

1.08

n = number of test profiles increase the partial factors for base and shaft resistances. In this case, Equation 7.100 can be rewritten as:

Ultimate compressive resistance from dynamic impact tests

When dynamic impact tests are used to determine pile resistance, the characteristic value is given by:

The correlation factors £s and £6 are listed in Table 7.13.

Table 7.13 Correlation factors g to derive characteristic values from dynamic impact tests (EN 1997-1:2004).

>2

>5

>10

>15

>20

1.60

1.50

1.45

1.42

1.40

1.50

1.35

1.30

1.25

1.25

  • * n = number of tested piles
  • 1 The ^-values in the table are valid for dynamic impact tests.

b The ^-values may be multiplied by a model factor of 0.8S, when using dynamic impact tests with signal matching.

c The ^-values should be multiplied by a model factor of 1.10, when using a pile driving formula with measurements of the quasi-elastic pile head displacement during the impact.

d The ^-values should be multiplied by a model factor of 1.20, when using a pile driving formula without measurements of the quasi-elastic pile head displacement during the impact.

' If different piles exist in the foundation, groups of similar piles should be considered separately when selecting the number n of test piles.

Load and Resistance-Factored Design (LRFD)

The Load and Resistance-Factored Design has been presented in Chapter 3. The verification of safety is performed under the following conditions:

where Pu is the factored normal load, computed as the sum of factored overall load effects, for a given load combination, Ф is the resistance factor, and R„ is the nominal normal load capacity.

 
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