Result Extraction [SIG]

This object serves multiple purposes, including defining unfactored result cases for AASHTO-based combinations, filtering staged construction results by load type, extracting incremental/cumulative results from staged construction analysis, and combining transient loads such as wind loads, live loads to identify the most critical load effects.

The main purpose of this section is to prepare Staged Construction Analysis results for AASHTO-based combinations. Most of the auto-generated transient loads, such as wind load on the structure, wind load on live load, and live load definitions, automatically generate their result extraction cases and can be directly used in limit states. However, for other loads, such as construction loads or temperature loads, the user must define a case here.

The Result Extraction Cases generated through this process will be utilized in the "Limit States" section.

When selecting result cases from a Staged Construction Analysis, there are several options available to extract results :

1.Result Extraction Method from Stages[Cumulative/Incremental]: Users can choose either 'Cumulative' or 'Incremental'. When the 'Cumulative' option is chosen, the 'Filter by Load Type' column will be activated, allowing cumulative results to be filtered based on load types. This will include all prior stages as well as the results of the selected stage.

For example, if you are analyzing a structure that has been loaded in multiple stages—say, first with dead loads and then with wearing surface loads—choosing 'Cumulative' will give you the total effect of all these loads combined up to the current stage. In contrast, selecting 'Incremental' would show only the effect of the wearing surface load applied in the current stage, without considering the dead loads applied in previous stages.

2.Filter By Load Type[None/Dead Load/Imposed Dead ….]: Since different load types may exist in a particular stage, narrowing down the results by load type may be necessary. If the "Filter By Load Type" option is set to "None," the component will extract the incremental or cumulative results from the selected stage without filtering them by load types. However, if it is set to "Dead Load," the component will extract only the incremental or cumulative dead load results and exclude other load types, such as imposed dead or wearing surface loads, from the selected stage. This option filters the results by load type, making it crucial to correctly assign load types to the stages for accurate result extraction.

For example, consider a structure that has been loaded in four stages. In the first stage, a dead load is applied; in the second stage, an additional dead load is applied; in the third stage, an imposed dead load is added; and in the fourth stage, a wearing surface load is applied.

If you set the 'Filter By Load Type' option to 'None' and choose 'Cumulative,' and then select the fourth stage, the results will show the combined effect of all the loads (dead loads from stages one and two, imposed dead load from stage three, and wearing surface load from stage four) up to and including the fourth stage.

Now, if you select the fourth stage and filter by 'Dead Load,' the results will display the cumulative effect of the dead loads applied across the first and second stages while excluding the imposed dead load and wearing surface load. This means that although the imposed dead load and wearing surface load are present in the third and fourth stages, they won’t be reflected in the filtered results. Instead, you will see only the cumulative impact of the dead loads from the first and second stages up to the final stage.

This filtering process allows you to specifically get the cumulative effect of the dead loads over multiple stages, even when other load types are applied in subsequent stages.

Once results are extracted from a staged construction analysis using the incremental and filter by load type options, the Transient/Permanent Loads and Combination Method columns can be used to further define the combination of results.

3.Transient/Permanent Loads: For permanent loads, this column’s input should be set to ‘Permanent’. However, for transient loads, such as temperature effects, wind on the structure, wind on live loads, live load, braking, or centrifugal forces, this parameter should be set to ‘Transient’.
Selecting this option as ‘Transient’ will neglect the selected result case from the combination if its value in the enveloped column is positive results for minimum envelopes or negative results for maximum envelopes. For example, if a live load produces a positive moment in a beam, and the ‘Transient’ setting is applied, this result could be excluded from the minimum moment combination.

4.Stages | Factors: By clicking the three dots and selecting 'Edit,' another spreadsheet opens, allowing the user to determine the stage(s) that will be used in the extraction cases. Additionally, factors to modify the FEA results can be defined.

5.Combination Method[Linear/Envelope(Critical)]: This option can only be selected when two or more stages are involved in the ‘Stages Factors’ column. If multiple stages are involved, you can set this to either "Envelope (Critical)" or "Linear."

If the "Envelope (Critical)" option is selected, the component will find the critical case from the cases specified in the "Stages and Factors" column for each extracted result.

Example:

Suppose you are analyzing a structure with multiple stations along its length, each subjected to various loading conditions.

• At Station 10, Case 1 might produce the highest bending moment, making it the critical case for bending moment at that location.

• At Station 20, however, Case 2 might generate the highest axial force, making it the critical case for axial force at that station.

• Furthermore, within the same station:

  • Case 1 could be critical for axial force.

  • Case 2 could be critical for bending moment.

When the "Envelope (Critical)" option is selected, the component automatically determines the most critical case for each result type (e.g., bending moment, axial force) at each station. This ensures that the most significant effects are captured and used in the combinations, regardless of which case produces them.

Consider the following scenarios:

• Temperature Loads: Typically, temperature loads involve two cases—expansion and contraction. The user can add these cases to a single result extraction case and choose the "Envelope" option as "Yes" to find the critical case.

• Deck Pouring Sequence for Constructability Checks: The deck pouring process may consist of multiple stages, with some stages exhibiting a maximum bending moment greater than that of the final stage. To capture these maximum values, the user can combine all deck pouring stages into a single result extraction case and select the "Envelope" option as "Yes" to determine and utilize the critical stage.

Important Note: If you are combining deck pouring results with live load cases for strength and serviceability checks, choosing the envelope option for each deck pouring stage is not appropriate. You should choose the final deck pouring stage for these checks. The envelope option is more suited for constructability checks, such as those involving wind loads.

Both examples are illustrated in the screenshot below.

If the "Combination Method" is set to "Linear," the linear result combinations will operate by summing the results of multiple cases specified in the "Stages Factors" column. Factors can be applied to the cases to achieve a weighted linear combination, but it is recommended to increase the loads according to the factors defined in AASHTO under the Limit States section. These factors should only be used if any increase is needed to compute the unfactored loads.