# Span information and effective flange width

Question:

I am not sure how span information is used and defined. Why need to define span information? How span information work in the model? If I have a four span bridge, how do I define the span information? Should I select Girder 1 span 1 elements, and assign as S1_Span 1, make the first and last node as support I, j respectively; select Girder 1 span 2 elements, and assign as S1_Span 2, make the first and last node as support I and J respectively? the same for span 3 and 4?

How do I define effective flange width? the girders in my model are splayed girders with some of the girders straight and some of the girders curved, and the spacing are different for each girder and keep changing along the span.

Thanks for writing to us.

1) Span Information is required and used for the variation of the section, reinforcement information, auto calculation of effective width, etc. Span Information contains the information about the number and location of end supports and interior supports, and the span length. Since the program does not acknowledge the intuitive information of the span and girder, the user should define the span information which contains the components of span and girder.

Span information is required for the program to distinguish the end and interior panes. Separate shear check formulae are needed for the panels depending upon their location. Span information is used for viewing the Composite Design Results and Design Result Diagram as per Span.

2) Effective width scale factors
Simplified consideration of shear-lag effect in the analysis is through consideration of effective flange width. (Reduce in properties).
Effective flange width concept: actual width of each flange is replaced by an appropriate reduced flange width.
Main factors affecting the effective flange width computations are span length and girder spacing (that's why we need span information).

A scale factor for moment of inertia (Iyy) about y-axis can be applied to check sectional stresses reflecting an effective width. Scale factors for the distances from the neutral axis to the top and bottom extreme fibers (z_top & z-bot) are also specified. The scale factors are applied only to stress calculations and do not affect the calculations for forces and deflections.

The boundary group of this effective width can be activated in Construction Stage definition and the final CS-stage factors will be also used for Post-CS analysis.

Regards,
Tech Support,
MIDAS
Creation date: 2/28/2018 6:08 AM      Updated: 11/6/2019 5:15 PM