1.1.1                            MATERIALS AND STRESSES

• General

Materials and stresses shall comply with the requirements of the Building (Construction) Regulations and the relevant codes of practice.

Where the permissible stress method is used in the structural design of foundation members, the working stress may be increased by not more than 25% where such increase is solely due to wind loads.

(2)                   Concrete

The concrete used for foundation elements shall comply with the Building (Construction) Regulations and the relevant codes of practice. Subject to the provisions of this Code, the design of the reinforced concrete elements of a foundation should be carried out in accordance with the Code of Practice for Structural Use of Concrete.

For cast-in-place concrete foundations, the concrete strength should be reduced by 20% where groundwater is likely to be encountered during concreting or where concrete is placed underwater.

The axial compressive stress on a driven precast concrete pile under working loads should not exceed 0.2f_cu.

For marine foundations, concrete should not be inferior to grade C45 as required in clause 2.6.4. All concrete should be cast in dry condition as far as

possible. Where the concrete is placed under water, the concrete should be assumed as grade C25 for design purpose.

(3)                   Grout

The requirements for concrete given in this Code shall equally apply to grout.

(4)                   Steel

For driven steel bearing piles with a design safety factor on driving resistance of 2, the axial stress in the steel at working load should not exceed 30% of the yield stress.

For steel bearing piles installed in pre-bored holes or jacked to the required depth, in which no peak stresses due to impact are set up, the axial stress in the steel at working loads may be increased to 50% of the yield stress.

Structural element design may be carried out in accordance with the Code of Practice for the Structural Use of Steel, provided that the condition under any possible load test is considered.

For steel piles, the allowable bond stress between steel and grout (with a minimum characteristic strength of 30 MPa) may be taken as 400 kPa (or 320 kPa when grouting under water).

Shear studs designed in accordance with the Code of Practice for the Structural Use of Steel may be used to enhance the allowable bond stress provided that the overall allowable bond stress does not exceed 600 kPa (or 480 kPa when grouting under water).

Steel sections or other means as substitute for shear studs may also be considered.

The surface area for calculation of allowable steel/grout bond stress should be the total external surface area of the steel section.

For steel piles relying on the bond between steel and grout to resist tension or compression loads, the pile surface should be clean and free from loose mill scale, loose rust or any substance that may reduce the bond.

For corrosion protection of marine foundations, the guidelines as given in clause 2.6.4 should be followed.