Vibration criteria in EC5 are limited to the vibration behaviour of residential floors, and the design loading conditions producing the design value at the SLS are as follows:

(a) The mass of the floor - to be used to determine the lowest natural frequency of the floor structure.

(b) The application of a 1 kN vertical force at the point on the floor that will result in the maximum vertical deflection - to be used to determine the maximum instantaneous vertical deflection due to foot force effect.

(c) The application of a 1N s impulse at the point of maximum instantaneous vertical deflection referred to in item (b) - to be used to determine the maximum initial value of the vertical floor vibration velocity due to heel impact effect. Deflection

The combinations of actions associated with the deflection states at the SLS that will result in the design value of the displacement are given in EC0 under the following headings:

• Characteristic combination

• Frequent combination

• Quasi-permanent combination.

Using the symbols defined in 2.2.24, these combinations are determined as follows:

(a) Characteristic combination

J2 Gk. j + Qk,i + J210,i Qk,i (EC0, equation (6.14b)) (2.24)

This combination is normally used for irreversible limit states (i.e. states where the SLS will be permanently infringed even when the actions that caused the exceedance are removed) and is the combination used in EC5, 2.2.3. It will be noted that equation (2.24) equates to equation (2.13) when the partial factors (Yg and yq ) in equation (2.13) are set equal to unity.

(b) Frequent combination

J2 Gk, j + fh1 Qk,1 + Qk.i (EC0, equation (6.15b)) (2.25)

This combination is normally used for reversible limit states (i.e. where an infringement of a state disappears when the action causing the exceedance is removed). Although this option is not referred to in EC5, provided an agreement can be established with the client on those situations that will fall into this category together with a frequency of occurrence that will be acceptable, the combination can be used.

(c) Quasi-permanent combination

This is the combination that is used for the assessment of long-term (creep) effects.

To determine the design value, the characteristic combination is applied with each variable action acting as the leading variable, from which the maximum loading condition will be obtained. If a reversible limit state condition has been accepted for the deformation criteria, the frequent rather than the characteristic combination will be used.

The design displacement, Efd, arising from the application of the design load case will be an instantaneous deformation, i.e. the displacement that will immediately arise due to elastic deformation of the structure as well as any deformation arising from joint movements in the structure.

Assuming all of the members, components and connections have the same creep behaviour, and on the assumption that there is a linear relation between actions and their associated displacements, to obtain the displacement caused solely by creep the quasi-permanent load combination is used.

The final deformation is obtained by combining the instantaneous and the creep displacement.

Where the structure comprises members with different time-dependent properties, the final deformation requirements are discussed in 2.3.2(b).

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