Info

(Equations A1.12 and A1.15)

"s

Coefficient to describe development of shrinkage with time

"sc

Coefficient depending on type of cement

"(to)

Factor to allow for the effect of concrete age at loading on the notional creep coefficient

Ati

Number of days when a temperature T prevails

cso

Notional shrinkage coefficient

(cs(t — ts)

Shrinkage strain over period t - ts

(s(fcm)

Factor to allow for the effect of concrete strength on shrinkage

(o

A notional creep coefficient (Equation A1.2)

(RH

Factor to allow for RH on the notional creep coefficient

0(t,to)

Creep coefficient, defining creep between times to and t

A1.0 Data on time-dependent effects A1.1.1 General

(1) The information given below complements that given in 3.1.2.5.5 and is based on the assumptions in 2.5.5(5). It has been taken from material developed by CEB Commission VIII and GTG9. The same notation as in 2.5.5(7) is adopted.

(2) The following data refer to the average behaviour of a concrete member, not taking account of local rheological properties within the member, which are related to internal stresses, moisture states or local micro-cracking. The data are valid for ordinary structural concrete for classes between 12/15 and 50/60, subject to compressive or tensile stresses not exceeding 0.45 of the corresponding strength and exposed to mean relative humidities in the range 40 % to 100 % and to mean temperatures from 10 °C to 20 °C.

A1.1.2 Creep

(1) In Equation (2.21) of 2.5.5 the creep coefficient may be calculated from:

where

(o notional creep coefficient from Equation (A1.2)

"c coefficient to describe the development of creep with time after loading (Equation A1.7); t age of concrete in days at the moment considered; to age of concrete at loading in days; The notional creep coefficient may be estimated from:

with

where fcm mean compressive strength of concrete in N/mm2 at the age of 28 days; RH relative humidity of the ambient environment in %;

ho notional size of member in mm where Ac is the cross-section and u is the perimeter of the member in contact with the atmosphere. (rh a factor to allow for the effect of relative humidity on the notional creep coefficient " (fcm) a factor to allow for the effect of concrete strength on the notional creep coefficient " (to) a factor to allow for the effect of concrete age at loading on the notional creep coefficient

The coefficient for the development of creep with time may be estimated from:

"c(t - to) = [(t - to)/("H + t - to)]03 (A17)

where t - to is the non-adjusted duration of loading in days and "h is a coefficient depending on the relative humidity (RH in %) and the notional member size (ho in mm). "H may be estimated from:

"H = 1.5 [1 + (0.012RH)18] ho + 250 r 1 500 (A18)

(2) The effect of type of cement on the creep coefficient of concrete may be taken into account by modifying the age of loading to in Equation (A1.5) according to Equation (A1.9):

to = to ,t • (9/[2 + (to,T)12] + 1)! T 0.5 (A1.9)

where to,T temperature adjusted age of concrete at loading in days adjusted according to Equation (A1.10)

! power which depends on type of cement

(- 1 for slowly hardening cements, S; ! = (0 for normal or rapid hardening cements, N,R; (1 for rapid hardening high strength cements, RS.

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