General guide

Time affect sets

At a glance: Descriptions of Time affect sets processes and definitions of terms here are applicable to all devices. For specific instructions on the use see the volumes specific to the Mac, PC or Android phone, iPhone & iPad devices.

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The need for Time affect sets

The information in the Time Affect Sets is not used by any of the main computation facilities in the methods in Load-cases nor by the Transformed Section Properties facility.
When the user applies a Time Affect Set the Other Distortion of the various components are affected and that in turn affects the main computations.

Note that a shrinkage represented by a positive number in a time affect set will cause a negative contribution to a strain when the set is applied.

The manual keying of shrinkage and creep directly into the Other Distortion numbers in the various component edit facilities might seem to be a trivial matter and that there is no need for time affect sets.
It is envisaged that the application of the time affects will be part of a sequence of computations and that sequence will be repeated many times as the design of a structure progresses from an initial concept to a final perfected design. The repeated use of a Time Affect Set makes it worthwhile.

Applying a Time Affect Set

A Time Affect Set pertains to a specific period of time in the life a structural member. The envisaged circumstances during that period and the duration length of the period would be important in determining the various coefficients and shrinkage values. Also important is the loading during that period.

In the physical model that is the basis of this facility the loading is assumed to be constant during the period. A load case describing that loading is required and that implies objective values for all three loading variables.

If there is a significant bending moment the Given Bending Moment should work. If however, the bending moment is small it may be necessary to resort to the Utility: Curvatures and Axial Load method and use manual trial and adjustment of the curvatures to find the distortion corresponding to the loading.

The procedure to apply a set is:

  1. Add a Load-case, give it a name indicating its purpose and set it up with the envisaged loading that would cause the creep.
  2. Add a Time Affect Set, give it a name indicating its purpose and fill in the appropriate values for the creep coefficients and shrinkage.
  3. In the Time Affect Set select the load case set up in step 1 as the creep load.
  4. Compute the Load-case set up in step 1.
  5. Apply the Time Affect Set.

Note that only steps 4 and 5 would be required in every cycle of a design process.

Note also that the application of a Time Affect Set makes a change in the cross-section description and thus makes all the Load-case results invalid.

In some circumstances creep and shrinkage affects the loading on a cross-section so that the assumption of constant loading is not true. This procedure is a compromise; an approximation. To reduce the error from this approximation divide the time interval into parts and do a sequence of computations for each part.

Time affects not included in the automatic facilities

The application of a Time affect set automatically affects the “other” distortion variables of all the components. With the use of these facilities there should never be a need to edit these variable directly in the component editing facilities.
Nevertheless those variables are editable in the component editing facilities.

Any affect can be included in a point component and any affect that obeys plane-sections-remain-plane within a shape component can be included in that shape component. For example concrete drying shrinkage that varies through the depth of a horizontal slab can be included as a curvature. Also thermal expansion and contraction can be included. For example the day to night change in the temperature of a bridge deck slab can be more at the top surface than the bottom which implies curvatures.