(1) In a general manner, imperfections in the geometry of the structure and of structural members should be considered for the most critical design situations during execution. These imperfections should be defined in the project specification.
Note 1 : Guidance may be found in design Eurocodes.
Note 2 : For concrete structures, see European Standards established by CEN/TC/229 "Precast Concrete Products".
(2) Any transient design situation should be associated with a nominal duration to be generally chosen among the following ones, this nominal duration being equal to or greater than the probable duration of the execution phase corresponding to the design situation under consideration:
- three months;
Note : A nominal duration of three days, to be chosen for very short execution phases like lifting by crane of a structure, corresponds to the extent in time of reliable meteorological predictions. This choice may be kept for a little longer execution phase if appropriate organizational measures are taken. For a nominal duration of three months, seasonal effects may be, for certain actions, identified. For example, the flood magnitude of a river depends on the period of the year under consideration.
(3) For some climatic actions where characteristic values for persistent situations are defined on the basis of return periods, the characteristic values during execution may be chosen smaller than those for persistent situations if at least one of the following conditions apply:
- the nominal duration of the transient situation is equal to or less than one year, and can be controlled;
- in case of unforeseen events, protective measures can be provided to secure the structure.
(4) Where a transient design situation is associated with a nominal duration of one year, the mean return period of the characteristic values of climatic actions should not be less than  years.
Note 1 : For nominal durations of 3 months or 3 days, the concept of mean reteurn period is generally not appropriate and the reduction should depend on the available seasonal and meteorological information.
Note 2 : Some phenomena like creep and shrinkage effects in concrete construction works should generally be assessed on the basis of the expected dates and duration associated with the design situations.
(5) For design situations corresponding to execution phases where the structure or parts of it are subjected to accelerations that may give rise to significant mass effects, these effects should be taken into account for the verification of the various limit states.
Note : Significant accelerations may be excluded where possible movements are strictly controlled. In such a case, the controlling devices should be designed in accordance with the combinations of actions corresponding to the relevant design situations which may be transient or accidental.
(6) Where relevant, water actions should be assessed in conjunction with water levels corresponding to specified or identified design situations.
Note : These actions may commonly be assessed in the same manner as specified in (2) and (3) above.
(7) Where relevant, design situations should be defined taking account of scour effects in current water.
Note : For long construction phases, accidental scour situations may have to be considered for the design of permanent or auxiliary structures immersed in current water.
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