Load History / ECR tab

These are parameters that apply to RAM Concept 's load history calculations.

Calc options dialog, Load History / ECR tab

Load History Options

Setting

Description

Creep/Shrinkage Model

The design code model used to determine creep and shrinkage strains over time. Available selections include ACI 209R-92 (ECR Values), ACI 209.2R-08/GL 200, AS 3600-2018, and Eurocode 2-2004. See Creep and Shrinkage Models for additional information.

Initial Load Application

The time of application of the initial loads. This becomes the start time of the first load history step specified in the Load History Criteria page.

Cure Duration

The duration of the moist cure period. This is used in the calculation of shrinkage strains.

Ageing Coefficient

The coefficient that accounts for various behaviors in the calculation of sustained loads. See Load History Deflections for additional information.

External Shrinkage Restraint

A percentage of the free shrinkage strain to consider as externally restrained. The shrinkage restraint is used to calculate a hypothetical tension strain which is included in the tension stiffening calculations. The user may select one of the pre-set options mapped below or enter a specific value in the field box. See Load History Deflections for additional information.

Basic Creep Coefficient

(ACI 209.2-08/GL2000, AS 3600-2018, and Eurocode 2-2004 only). The unadjusted creep factor or coefficient as defined by the selected code model. When code is selected the coefficient is determined as outlined in Creep and Shrinkage Models. You may also enter a specific value in the field box.

Basic Shrinkage Strain

(ACI 209.2-08/GL2000 only). The unadjusted shrinkage strain as defined by the selected code model. When code is selected the coefficient is determined as outlined in Creep and Shrinkage Models. You may also enter a specific value in the field box.

Basic Autogenous Shrinkage Strain

(AS 3600-2018 and Eurocode 2-2004 only). The unadjusted autogenous shrinkage strain as defined by the selected code model.. When code is selected the coefficient is determined as outlined in Load History Deflections . You may also enter a specific value in the field box.

Basic Drying Shrinkage Strain

(AS 3600-2018 and Eurocode 2-2004 only). The unadjusted drying shrinkage strain as defined by the selected code model. When "code" is selected the coefficient is determined as outlined in Load History Deflections . The user may also enter a specific value in the field box.

Relative Humidity

(ACI 209.2-08/GL2000 and Eurocode 2-2004 only). The relative humidity as a percentage used to determine adjustment factors for the basic creep coefficient and/or basic shrinkage strain.

Environment

(AS 3600-2018 only). The environment classification used to determine adjustment factor k4 for the basic drying shrinkage strain that is defined in AS 3600-2018 3.1.7.2

Option	Description
Arid	k4 = 0.7
Interior	k4 = 0.65
Temperate Inland	k4 = 0.60
Tropical/Coastal	k4 = 0.50

Exposure

(ACI 209.2-08/GL2000, AS 3600-2018, and Eurocode 2-2004 only).Option to define the concrete surfaces subject to shrinkage, which is used as an adjustment factor for creep and shrinkage strain in some code models.

Options	Description
Top and Bottom	Both top and bottom of the cross section used to calculate surface area subject to shrinkage.
Top Only	Only the top of the cross section used to calculate surface area subject to shrinkage.
Bottom Only	Only the bottom of the cross section used to calculate surface area subject to shrinkage.

Cement Class

(ACI 209R-92 (ECR Values), ACI 209.2-08/GL2000, and Eurocode 2-2004 only). The cement type used to determine adjustment factors for various parameters in the creep and shrinkage models. Options for ACI 209R-92 (ECR Values) and ACI 209.2-08/GL2000 are Type I, Type II, and Type III. For ACI 209R-92 (ECR Values) Type II results is assumed equivalent to Type I. Options for Eurocode 2-2004 are Class S, Class N, and Class R.

ECR Options

RAM Concept calculates an effective curvature ratio (ECR) at every cross section:

ECR = C_e/C_g

where

C_e	=	the effective cross section curvature
C_g	=	the gross section curvature

RAM Concept calculates C_e by the approximate formula:

C_e = (k_c BSR C_g) + ((1 – BSR)C_ccs)

where

k _c	=	the concrete design creep factor (often 3.35) = total strain / elastic strain Note: Most standards utilize a creep coefficient which is the ratio of creep strain to initial strain. The creep factor in RAM Concept represents the ratio of total strain (initial strain plus creep strain) to initial strain. Before inputting into RAM Concept , a creep coefficient representing only the creep strain would need to be increased by 1.0 to transform to a creep factor representing the total strain. ACI 209 reports the value of 2.35 as an average creep coefficient, so the corresponding creep factor would be 3.35. RAM Concept files adopt this value as a default.
BSR	=	Branson's Stress Ratio
C_ccs	=	the cross section curvature considering cracking, creep and shrinkage

See Section Design Notes for further explanation.

Setting	Description
Creep factor, k_c	As defined above. The input value should represent the final ultimate creep value and should take into account concrete mix, environmental considerations, etc. and can reflect any considerations required by regional building codes.
Shrinkage strain	The design shrinkage value used to determine long-term curvature in cross sections. The input value should represent the final ultimate shrinkage and should take into account concrete mix, environmental considerations, etc. and can reflect any considerations required by regional building codes.

Load History Convergence Options

These parameters apply to RAM Concept 's load history calculations.

Setting	Description
Convergence Tolerance	The maximum specified difference in calculated deflection between iterations in order to consider RAM Concept to have converged upon the solution.