# Application of temp gradient load.

Question:

Hi,

I need to understand how midas is calculating temperature gradient stress for box girder bridges with inclined deck (super elevation) in cross section.

Answer:Hello,

To clearly understand the load application for temperature gradient, I am dividing the calculation process into 2 parts.
1. Load Calculations:
Based of the input by user like H1, T1, B, etc., the software calculates the resultant axial force and moment due to the temperature gradient. To calculate the axial force as well as the moment, the section properties are not used. So, for calculating the acting axial stress/force, the area used is derived from user input of B and difference between H (Say H1 & H2) for each part with non-linear temperature. Similarly for calculating the moment as well, the user input is used.
2. Sectional stress calculations:
Now, once this axial force and its eccentricity is obtained, this force is applied to the said structure and once this is done, the stress output are provided at point 1, 2, 3 and 4 of the cross-section. These points of the cross section could be noted from the section property. This stress calculations is nothing but P/A (+/-) M/Zi, where P is the axial force calculated before, A is C/s Area of section, M is moment as calculated before and Zi is the I/yt, where I is Iyy of section and yt is distance of the fiber where stress is being measured from the centroid.
A sample calculation for temperature gradient at point 1 for one such section is attached for review. The method used is as recommended in Bridge Deck Behavior by E.C. Hambly.
Creation date: 10/27/2017 6:27 AM      Updated: 10/27/2017 3:59 PM