Calculate General Stress/Strain
Description
A comprehensive series of data checks are carried out before the calculations are performed and the results displayed.
The program uses the material property stress/strain data to calculate the section's internal forces and iterates to modify the strain plane so that these internal forces are modified to balance the applied load effects.
The fields labeled 'internal forces' are the out of balance forces, (i.e. the difference between applied loads and internal loads). If the 'Resistance' is set, these fields will display the value of this load.
If the iteration process fails to converge the option is given to edit the iteration parameters via the Control Iterations panel. This panel can also be shown via the Control Iterations button.
Form Graphic
Field Help
Loadcase
This field contains a drop-down list of all the loadcases that have been defined in the Define Loads form for LRFD or the Define Loads form for Standard 17th. Select one for analysis. The first option is always '* None *' for use with the 'Resistance' option.
Resistance
The program may be used to find the maximum load resistance for the load effect (or pair of effects) specified in this field.
' Moment - Positive' for example will find the bending moment about the x axis in the positive direction which, in addition to any other specified load effects included on this form, will cause the section to reach its limiting capacity. (Limiting strain in concrete for ULS, or limiting stress in any element or bar for SLS).
For the options that are combinations of two effects (X Moment & Y Moment, X Moment & Axial, and Y Moment & Axial) the limiting capacity of the section is found in the same manner, with the two effects maintained in the ratio specified in the field labelled 'ratio 1.0:'.
ratio 1.0 :
This field will be available when the 'Resistance' option has been set to find a pair of effects (i.e. X Moment & Y Moment, X Moment & Axial, and Y Moment & Axial). The limiting capacity of the section will be found with the two effects maintained in the ratio specified in this field.
Analysis type
For the 'General Stress/Strain' option there are no other types available here.
Neutral Axis angle
For a section which is symmetrical about its y axis, and which has no applied moment about the y axis, the neutral axis (NA) will be horizontal. For all other cases it will not be horizontal.
Sometimes it may be advantageous to force the NA to be horizontal (e.g. modelling an edge beam which is rigidly connected to a stiff bridge deck, or modelling half of a symmetrical structure). This field enables that to be done, by selecting the option 'Fixed horizontal'. The neutral axis will then be set to either 0 degrees or 180 degrees depending on the sign of the bending moments in the loading data.
The NA may be fixed to any angle by selecting the third option. This will make the next field (angle) available.
(angle)
Access to this field indicates that 'Set angle to' has been selected in the previous field.
The angle required is the angle from the x axis to the neutral axis measured clockwise in degrees. The value must be in the range -180 to +180.
When a value is entered the display of the section will rotate so that the Neutral Axis appears horizontal on the display.
Resistance Factor
The Resistance Factor is specified in this field. On completion of the analysis the Resistance Factor will be assessed in accordance with Article 5.5.4.2 of AASHTO LRFD 9 (based on the applied load effects), and displayed in the adjacent field. If this value varies from the value used in the analysis, the application will issue a prompt and reanalyze with the revised value if requested. There may in certain circumstances be more than one iteration before the two values match.
The application allows any value from 0 to 1.0 to be entered, although the range of LRFD values is from 0.65 to 1.0. Initially the value is set to 0.8, which is an arbitrary value.