Design and Deflection Loading Cases

The default behaviour of the steel design module is to carry out the member design checks contained within any design brief using the Ultimate Limit State design cases, while the deflection check is carried out using the based on the worst case serviceability load case. The software determines whether or not a load case is ultimate or serviceability by examining the applied load factors used in each load case. Where the software finds any load factor greater than or equal to 1.05, that load case is deemed to be an "ultimate" load case.

Note: The label (serviceability) or (ultimate) in the name of the load case does not determine whether or not the load case is seen as an ultimate limit state or serviceability limit state load case. These are a naming convention only, used for information.

The load factor does not need to be applied to a load that is included in the load case itself, or to even be used in the model itself. Therefore, in certain circumstances, it is possible to include a load factor greater than 1.05 on a load which is not used, simply to control whether or not the load case is used for the member design or for serviceability criteria. As an example, an accidental load case may have load factors of 1.0 or less, so automatically is used as a serviceability load case. However, to use this load case as part of the design checks, applying a load factor of 1.1 to some load will cause the software to automatically use it as part of the ultimate limit state and so check the member against the actions of that load case. The reason for applying the load factor of 1.1 on a load that isn't used is so the applied loads in that load case are not modified.

The default behaviour of the software in using specific load cases for ultimate or for serviceability design can be changed using the Design and Deflection Loading Cases brief. This allows specific load cases to be selected for use in the ultimate load cases and, conversely, specific load cases to be used for the serviceability design. The Design and Deflection Loading Cases brief also gives an additional level of control in that it can be applied to specific load cases. The Design and Deflection Loading cases only apply to the design of members which appear below it in the list of load cases. Therefore, by using the sort option, it is possible to determine different ultimate and serviceability load cases for selections of members.

The Design and Deflection Load case can be selected from the 'Integrated Design' menu at the top of the screen or using the following icon next to the design brief name.

When the Design and Deflection Load case is first selected, the screen layout is as shown below.

The upper area on the right hand side of the screen is the area where the Ultimate Design load cases are selected, while the lower area is where the Serviceability load cases are selected. In either area, a load case is selected by using the mouse pointer and left clicking to highlight the load case. When a load case is selected in either area, it will highlight in blue. A load case can only be highlighted in one area, that is, a load case cannot be set as both an ultimate and serviceability load case. When a load case is highlighted, the software will no longer use the load factors of that load case to determine whether it is used as part of the ultimate or serviceability load cases.

To view the list of current design briefs appended to members within a model, click on the  icon. This opens the Sort Steel Design Checks screen, which contains a list of the steel design briefs, arranged in brief number order. The list can be navigated by scrolling using the mouse wheel or using the scroll bar at the right hand side of the screen. Design briefs can be reposition by using the mouse pointer and pressing and holding the left mouse key. Once selected, a design brief can be reordered by using the mouse to move the selected brief to a new location in the list. In the case of the Design and Deflection Loading Case brief, this brief only applies to those design briefs which appear below it in the Sort Steel Design Checks screen. For example, to create a list of specific load cases for use in the ultimate and serviceability limit states that apply to all design briefs, then the Design and Deflection Loading Case brief would need to be moved to first in the list.

To create a set of ultimate and serviceability load cases to apply to specific members, it is necessary to move the design briefs for the members of interest, so as to group them such that a Design and Deflection Loading Cases set can be created and applied to them.

A Design and Deflection Load Cases brief will apply to all briefs which appear below it in the Sort Steel Design Checks until either (a) the end of the list of design briefs, or (b) the software encounters another Design and Deflection Load Cases brief, at which point that Deflection and Loading Cases brief controls. Thus it is possible to set up multiple Design and Deflection Loading Cases briefs for any model.