Creep Coefficient

[cecil123]

For calculating the creep coefficient as per Eurocode2, I need the perimeter of the member in contact with the atmosphere(denoted by "u")

If the area of cross section of the member is "A".
Length of the member (member is a column)is "L", what should be the perimeter "u".Should it be "4 x L"
Please help!!

 

[271828]

Depends on the shape. Square, rectangular, circular, etc.

 

[cecil123]

It is a rectangular shape column, cross sectional area "A" and length "L"?

 

[271828]

Do you need the "perimeter" or the "surface area"? Surface area per meter of length?

Sorry for the lengthy interrogation, LOL.

 

[cecil123]

No, i need the perimeter.The code defines a variable "ho" , it says that "ho" is the notional size of the member and,

ho= (2Ac /u) , where, Ac is the cross sectional area of the member (the member is a column in my case) and "u" is the perimeter of the member in contact with the atmosphere.

The column is a composite column.

I want to know:

1)If the column is concrete encased I section, then, what will be the perimeter "u"?The concrete cross sectional area
may be taken as "Ac" as mentioned.Length of the column is "L"
2) If the member is a concrete filled circuar section,then what will be the perimeter "u"?The concrete cross sectional area
may be taken as "Ac" as mentioned.Length of the column is "L"


Please help!!

 

[rapt]

u is the perimeter of the cross section whose area is Ac. Some codes have an allowance for voids in the section but I do not think EC2 does but as your void is sealed by the steel section then I assume you would ignore it, so the perimeter is the outside perimeter if the column of area Ac.

 

[hokie66]

Your question seemed too simple for all these answers. For say 400 x 500 column, perimeter is 1800.

But now you say your column is a composite section. Are you sure the Eurocode2 provisions you are using apply to composite columns?

 

[cecil123]

Yes,very sure.For calculating the effective flexural stiffness considering long term effects we add the stiffnesses of the components i.e. the structural steel,concrete and reinforcing steel.

In case of concrete the code requires to modify "E" value in the expression.This "E" considering long term effects is also a function of creep coefficients