# Integral Bridge Supports

Question:

Hi,

I have a few questions regarding the boundary supports for integral bridges:

1. When selecting the 'Pile Spring' soil spring type, a ground level input is required. Does this mean the ground level behind the abutment (at deck/road level) or the ground level in front of the abutment (underpass road level)?

2. Is there a recommended value for the 'Coeff. of Subgrade Reaction'?

3. If an abutment has an L shape, is the height taken from the top of the abutment to the very bottom of the section or would it be taken to the top of the horizontal section?

Thanks

Hello ,

Thanks for your query. Please see my comments to each of your questions below.

1. When selecting the 'Pile Spring' soil spring type, a ground level input is required. Does this mean the ground level behind the abutment (at deck/road level) or the ground level in front of the abutment (underpass road level)?
- The pile spring function in MIDAS Civil is developed based on a P-Y curve definition for a flat ground. The choice of ground level to be used should be based on engineering judgement and the aspect of upper and lower bound solution. If you specify the ground level behind the abutment (at deck level) then the pile spring will be stiffer and this can lead to higher forces in the structure due to temperature for example. On the other hand, specifying the ground level in front of the abutment will lead to lower stiffness of the pile springs which will result in larger movements but lower forces in the structure.

2. Is there a recommended value for the 'Coeff. of Subgrade Reaction'?
- The coefficient of subgrade reaction represents the stiffness of the soil and can very significantly, i.e. from clay to sand. There are typical values for each type of soil which you can find online, but in general this value should be based on site investigation and geotechnical report.

3. If an abutment has an L shape, is the height taken from the top of the abutment to the very bottom of the section or would it be taken to the top of the horizontal section?
- It is common to take the height as the full height of the abutment - top to bottom.

Kind regards,
MIDAS UK
Creation date: 8/21/2018 9:22 AM (MIDAS_UK_IM)      Updated: 8/24/2018 12:09 PM (MIDAS_UK_IM)