Creep coefficient calculation

 

The creep coefficient calculation is done according to Annex B.1 of EN1992-1-1.

 

The creep coefficient ϕ (t,t0) may be calculated from: ϕ (t,t0) = ϕ0×βc (t,t0)

where ϕ0 is the notional creep coefficient and may be estimated from: ϕ0 = ϕRH× β (fcm) × β (t0)

where ϕRH is a factor to allow for the effect of relative humidity on the notional creep coefficient:

 

ϕRH is a factor

 

where RH is the relative humidity of the ambient environment in %.

This parameter can be defined in the General Design dialog, Creep section:

 

relative humidity

Design Assumptions – General Design dialog, Relative Humidity

 

RH = 50%

fcm is the mean compressive strength of concrete in MPa at the age of 28 days

Reinforced Concrete dialog

Design Assumptions – Reinforced Concrete dialog, fck

 

fck = 25 mPa

fcm = fck + 8 = 25 + 8 = 33 MPa

h0 is the notional size of the member in mm, where:

h0

Ac is the cross-sectional area

u is the perimeter of the member in contact with the atmosphere

 

Geometry Geometry dialog Width

Geometry – Geometry dialog, Width

 

 

h0

 

β(fcm) is a factor to allow for the effect of concrete strength on the notional creep coefficient:

 

β(fcm)

 

β(t0) is a factor to allow for the effect of concrete age at loading on the notional creep coefficient:

β(t0)

 

The effect of the type of cement on the concrete creep coefficient may be taken into account by modifying the age of loading, t0, in the expression above, according to the following expression:

 

t0

This parameter can be defined in the Design Assumptions dialog, Creep section.

 

Concrete loading age (t0)

Design Assumptions – General Design dialog, Concrete loading age (t0)

 

 

t= 28 days

α is a power that depends on the type of cement:

α = -1 for slowly hardening cement, S:

α = 0 for normal or rapid hardening cement, N

α = 1 for rapid hardening high strength cement, R

=> α = 0

βc(t, t0) is a coefficient describing the development of creep overtime after loading, and maybe estimated considering the following situations:

1. if the creep ϕ(, t0) option is checked in the Design Assumptions dialog, the age of concrete at the considered instance (t) is infinite and βc(t, t0) = 1 (not calculated)

 

creep ϕ(∞, t0)

 

2. if the creep ϕ(t, t0) option is checked in the Design Assumptions dialog, the age of concrete at the considered instance (t) is imposed by the user and  βc(t, t0) is calculated as follows:

 

creep ϕ(t, t0)

 

High Strength concrete

Design Assumptions – Reinforced Concrete dialog, High Strength concrete

 

 

βc(t, t0)

 

where

a = 0.37 and b = 2.8, if the Concrete with silica fume option is selected

 

Concrete with silica fume

 

a = 0.4  and b = 3.1, if the Concrete with silica fume option is not selected

High strength concrete

 

where t is the age of concrete in days at the moment considered

This parameter can be defined in the Design Assumptions dialog, Creep section:

 

Concrete age (t)

Design Assumptions – General Design dialog, Concrete age (t)

 

 

t = 365 days

t - tis the non-adjusted duration of loading in days

βis a coefficient depending on the relative humidity (RH in %) and the notional member size (h0 in mm). It may be estimated from:

 

βH