Chronological sequences

General

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Chronological Sequences

At a glance: The use of the application to follows a chronological sequence of events is described here. Various procedures specific to the Android phone, iPhone & iPad and Mac and PC are set out in the user guide volumes specific to those various platforms. Those volumes include a procedure for adopting a stage load and setting up an initial state.

The chronological sequence

A sequence of computations that follows the chronological sequence of events in the life of a structural member is envisaged. This provides a framework for the description of some of the facilities in this application. It is also envisaged that such a sequence will be repeated many times as a design progresses from an initial concept to a final perfected design.

Load cases with all three loading variable as objectives

Both the adoption of a stage load and also the computation of creep require a load case where all three loading variables are objectives. This is one of the purposes of the “Given bending moment” method. This method will not work however in situations where the bending moment is small. An example to illustrate this is a pretensioned member immediately after the tendons are released. The method “Utility: Curvatures and axial load” is provided for this situation. In the case of the pretensioned member immediately after the tendons are released the axial load is zero. With the curvatures also set to zero this method will compute the bending moment if the member stays flat on the pretensioning bed. That bending moment can be compared with the bending moment from the self weight if the member were to lift itself off the pretensioning bed. A bending moment with zero curvature that is greater indicates the member would lift off the bed. In this case the curvature can be adjusted manually to find the curvature where the bending moments are equal.

Time affects

For the steps to apply a Time Affect Set that includes creep computation see General – Time Affect Sets, Applying a Time Affect Set.

Adopting a stage load

The initial state and stage distortion facilities have a purpose illustrated by two parallel structural members in close association but structurally independent; each having a loading and corresponding distortions. At a particular instant in the construction process these two members are joined so they act as one structural member. Immediately after that instant the resulting member has a loading that is the combined affect of the two loadings before and each component has the same distortion as before that instant. Those distortions are referred to as the stage distortions (if adopted as such), and the combined member is said to be in an initial state.

The facilities use three XSF files; one for each of the contributing members cross-sections, and one for the resulting member cross-section. A procedure is set out the user guide sections for the specific platforms.

Those descriptions of the procedure have been devised to cope with the most complicated design. In practice often the procedure is less complicated. For example the setting of wet concrete can be perceived as the instant of joining; the newly set concrete and any mild steel embedded in it being one of the contributing members. That contributing member has no loading and no distortion (it would be reasonable to assume). In these cases the XSF file for the other contributing member can be used for the resulting member. In effect the new concrete is added.

At the beginning of the next cycle in the design process that concrete and the steel embedded in it can be deleted.