Combination Type

Select the combination type from the Combination Type drop-down list. Some examples of combination types include LFD_GRP_I, SLD_GRP_I, STR_I, and SER_I. The type of a combination selected governs which specification checks and design activities the combination will be used for. For example, only service combinations are used in the calculation of minimum Pjack and only strength combinations are used for required As.

Gamma Factor

This factor is used in the formation of LFD group combinations. Define the gamma factor by entering the value in the Gamma field.

Overstress Factor

The Overstress Factor is used as a threshold value for stress capacity/demand ratios. If a stress capacity/demand ratio is less than the overstress factor, it is flagged with an asterisk on the stress check report. Define the overstress factor by entering the percentage in the Overstress % field.

Design Live Load Factor

This factor is used to factor responses due to design live loads as they are summed into a combination. For LFD projects, enter the value in the Design Live Load (LL) field. This factor is used to factor pedestrian responses for LFD.

Dead Load Factor

This factor is used to factor responses due to dead loads as they are summed into a combination. For LFD projects, enter the value in the Dead Load (DL) field.

Additional Dead Load (LFD) Factor

This factor is used to factor responses due to additional dead loads as they are summed into a combination. For LFD projects, enter the value in the Added Dead Load (ADL) field.

Uniform Temperature Factor

This factor is used to factor responses due to temperature loads as they are summed into a combination and should be entered in the Uniform Temperature (Tu) field.

Gradient Temperature Factor

This factor is used to factor responses due to gradient temperature loads as they are summed into a combination and should be entered in the Gradient Temperature (Tg) field. This is not normally used in an LFD design but CIP RC/PT Girder supports the use of a TG loading in a group combination.

Technical Discussion

Refer to the Technical Discussion on the Loads/Analysis tab for a discussion on how the various factors are used to compute LFD group combinations and LRFD limit states. CIP RC/PT Girder allows you to change any factor used in the formation of load combinations and therefore to include loads for a combination type that would normally not be part of that combination.

Some of the factors used for the generated combinations cannot be changed and are based on the factors in the combination from which they are derived. For example, for every SLD-IB combination in any analysis/design case, a combination of type PS+PERM is generated. Since this is a special combination, load factors for transient loads are set to zero (regardless what is specified in the Combinations Factors dialog box, but the factors for permanent and prestress loads are those specified in the Combinations Factors dialog box for the SLD-IB combination. Similarly, for every SLD-IB combination in any analysis/design case, a combination of type Half_PS+PERM+LL is generated. Temperature load factors are set to zero, live load factors are set to 1.0, and permanent and prestress load factors are set to 0.5 of the values specified in the Combination Factors dialog box.