• Registered: 2012-03-29
  • Posts: 9

Topic: Concrete Material (Creep problem)

Hello,

I'm modeling a prestressed I beam in ATENA-Creep.

The problem is the following: How can I define the concrete material?

The concrete material, with a design fc at 28 days=60 MPa, has to be 35 MPa at 1 day, when the prestressing action take place, and I want to study the beam behavior during a time of 1 year following to that moment (until day 366).

The material is now introduced into the .inp file as the equivalent concrete I used previously in ATENA2D-Engineering with fcu=60/0.85 (with the only parameter different from ATENA-Eng, fc0, calculated as suggested, 2.1 ft):

  MATERIAL ID 2
  NAME
   "Material #2 as USER name B3_Francisco"
  TYPE
   "CCModelB3"
   CONCRETE  1
   THICKNESS     6.190000e-02
   FCYL28        6.000000e+01
   E28           4.122000e+04
   HUMIDITY      7.500000e-01
   DENSITY       2.300000e-03
   AC            5.500000e+00
   WC            4.000000e-01
   SHAPE FACTOR 1.0
   AIR CURING
   End OF CURING TIME     1.000000e+00
BASE
   TYPE    "CC3DNonLinCementitious2"
// For base is used Cementitious2
        E     4.122000e+04
        MU     2.000000e-01
        RHO     2.500000e-03
        ALPHA     1.200000e-05
        FT     4.099000e+00
        FC    -6.000000e+01
        GF     1.025000e-04
        WD    -5.000000e-04
        EXC     5.200000e-01
        BETA     0.000000e+00       
        FC0    -6.000000e+00
        EPS_CP    -1.456000e-03
        FIXED     1.000000e+00

        FC_REDUCTION     2.000000e-01
        AGG_SIZE     2.000000e-02

But, it seems that at one day the concrete strength is still too low, in fact, I obtain a big deflection at middle span which is three times the expected one. How can I model the material in order to consider the time evolution of the material ?

Quote Post 1

  • dpryl
  • CC software developer
  • Offline
  • Registered: 2007-07-13
  • Posts: 1,107

Re: Concrete Material (Creep problem)

If you have some information about the material early aging, you can enter them at the "B3 Laboratory" tab. Define "Compliances" if you know the development of the elastic modulus.

dpryl's Website

Quote Post 2

  • Registered: 2012-03-29
  • Posts: 9

Re: Concrete Material (Creep problem)

Hi Dobromyl,

in reference to: "if you know the development of the elastic modulus..."

I know the development of the elastic modulus (at two times t=1,28) but..

"Compliances" is only the inverse of the elastic modulus? Or it comprises elastic+creep deformation?
Bazant reported in his paper "Creep and Shrinkage Prediction Model for Analysis and Design of
Concrete Structures: Model B3"

the compliance function = strain (creep plus elastic) at time t caused by a unit uniaxial constant stress applied at age t′,

Quote Post 3

  • dpryl
  • CC software developer
  • Offline
  • Registered: 2007-07-13
  • Posts: 1,107

Re: Concrete Material (Creep problem)

Once you define the compliances, it is a triangular table - one value for each combination of load time and observation time, i.e., one compliance value for loads applied day 7, deformations observed day 7, another for load day 7, observation day 14, yet another for load at day 14, observation day 14, ...

dpryl's Website

Quote Post 4

  • Registered: 2012-03-29
  • Posts: 9

Re: Concrete Material (Creep problem)

Hi,

I have defined the following values:
E(28)=41220 for t=28 days and fcd=60 MPa
E(t) =E(28)*(t/(4+0.85*t))^0.5 --> I found this formula in Bazant's paper
now, E(t0=1 day)=18717

I have defined the compliance function as:
J(t,t0)=1/E(t0)+fi(t,t0)/E(t28)
so, the starting value (at t0) is equal to 1/E(t0)=5.34*10^-5

Now, the question is:
How are calculated the value of fcd (and other concrete related parameters) throughout the time? How can I know these values at a specified time? Are indicated somewhere on a manual? I found the formulas for ATENA-Eng but I do not know how the Creep version works in this sense.

Quote Post 5

  • dpryl
  • CC software developer
  • Offline
  • Registered: 2007-07-13
  • Posts: 1,107

Re: Concrete Material (Creep problem)

Please see ATENA Theory, 5 CREEP AND SHRINKAGE ANALYSIS for details about the model and time integration used in ATENA.

dpryl's Website

Quote Post 6