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Total characteristic shaft resistance = Rsk = 253.7kN

Rsk A

Total design shaft resistance Rsd --- 253.7 kNW

Design base resistance is Rbd =-= 315.6 kNU

Verification of compressive resistance Design values Vd = 1307 kN and Rd = 569 kN

Design is unacceptable if degree of utilization is > 100%

Degree of utilization

Design is unacceptable if degree of utilization is > 100%

If the model factor YRd = 1.5 had been omitted, then Rd = Rd x YRd = 853.9 kN

Degree of utilization

Vd aGEO,3 = -T- = 153% Rd

©

Design is unacceptable if degree of utilization is > 100%

© No value for the model factor is given in EN 1997-1 so we have arbitrarily chosen to use the one given in the Irish National Annex.

© The methods used to calculate shaft resistance in clay and sand and the end bearing resistance are standard methods taken from the literature.

© The characteristic resistance values are calculated by applying the model factor to the calculated resistance.

© To obtain design values for the shaft and end bearing resistance the characteristic values are divided by the appropriate partial factor.

© The resultant design is shown to be just satisfactory for DA1 but under-designed according to DA2 and DA3.

© DA2 applies partial factors greater than 1.0 to actions and resistance but not to material properties. The values of partial factors for shaft and base resistance are lower than those used in DA1-2 but greater than those used in DA1-1.

© DA3 applies partial factors to both the actions and the material properties but not to the resultant shaft and base resistance.

© It could be argued that the material partial factor of 1.25 should be applied to 9cv as well as to however ^cv already represents the lowest likely value for the material and for the purposes of assessing the shaft resistance through the sand it is acceptable to use the lower of ^cv and

® DA3 gives a much more conservative design than the other two approaches due to the large effect on Nq when = tan-1(tan ^k)/1.25 is used. Excluding the model factor improves the situation and it could be argued that it should be taken as 1.0 for DA3. Further, if actions were considered as geotechnical rather than structural, a more economical design would result.

13.14.2 Concrete pile from Example 13.1 to UK National Annex

Example 13.2 revisits the design of the concrete driven pile of Example 13.1 in view of the specific requirements of the UK National Annex to EN 1997-1.

The UK National Annex uses the model factor to account for increased confidence in the calculation model provided by static load testing. The resistance factors given in the National Annex are larger than those in Annex A to EN 1997-1. The partial factors aim to provide similar levels of reliability for Eurocode 7 and traditional UK designs, while allowing potential savings if a significant programme of pile testing is put in place.

Notes on Example 13.2

O For no pile tests the values of partial factors for DA1-2 are Yb = 1.7, Ys = 1.5 and YRd = 1.4.

© The resulting design is shown to be unsatisfactory.

© For proof load pile tests on 1% of working piles the values of partial factors for DA1-2 are Yb = 1.5, Ys = 1.3 and YRd = 1.4.

© The resulting design is shown to be unsatisfactory but only just and it is likely that a judgement would be made to accept the pile design provided proof load tests were carried out.

© For proof load pile tests on 1% of working piles the values of partial factors for DA1-2 are Yb = 1.5, Ys = 1.3 and YRd = 1.2.

© The resulting design is shown to be satisfactory provided preliminary pile tests are carried out. It could be argued that the design is too conservative and some economy could be made if preliminary tests to failure were carried out. It would be a matter of judgement to decide whether it was more economic to be less conservative in the pile design and carry out preliminary pile load tests, or limit the testing to proof loading of working piles.

Example 13.2

Concrete pile from Example 13.1 to UK National Annex Verification of strength (limit state GEO)

Design situation

Re-consider the design of the square concrete pile from the previous example, this time using the UK National Annex to BS EN 1997-1. Consider what size pile is needed if (a) no static pile load tests are scheduled, (b) tests on 1% of the working piles are scheduled to 1.5 times the characteristic imposed load, and (c) preliminary static pile load tests to the calculated ultimate imposed load are performed.

UK National Annex (Design Approach 1)

Actions, effects, and material properties f1307 ^

From previous calcuation: Vd v1015 j kN

Material properties are unchanged from the previous calculation. Resistance if no explicit SLS check is undertaken
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