BARSLIP Material

This command is used to construct a uniaxial material that simulates the bar force versus slip response of a reinforcing bar anchored in a beam-column joint. The model exhibits degradation under cyclic loading. Cyclic degradation of strength and stiffness occurs in three ways: unloading stiffness degradation, reloading stiffness degradation, strength degradation.

uniaxialMaterial BarSlip $matTag $fc $fy $Es $fu $Eh $db $ld $nb $depth $height <$ancLratio> $bsFlag $type <$damage $unit>

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$matTag	unique material object integer tag
$fc	positive floating point value defining the compressive strength of the concrete in which the reinforcing bar is anchored
$fy	positive floating point value defining the yield strength of the reinforcing steel
$Es	floating point value defining the modulus of elasticity of the reinforcing steel
$fu	positive floating point value defining the ultimate strength of the reinforcing steel
$Eh	floating point value defining the hardening modulus of the reinforcing steel
$ld	floating point value defining the development length of the reinforcing steel
$db	point value defining the diameter of reinforcing steel
$nb	an integer defining the number of anchored bars
$depth	floating point value defining the dimension of the member (beam or column) perpendicular to the dimension of the plane of the paper
$height	floating point value defining the height of the flexural member, perpendicular to direction in which the reinforcing steel is placed, but in the plane of the paper
$ancLratio	floating point value defining the ratio of anchorage length used for the reinforcing bar to the dimension of the joint in the direction of the reinforcing bar (optional, default: 1.0)
$bsFlag	string indicating relative bond strength for the anchored reinforcing bar (options: "Strong" or "Weak")
$type	string indicating where the reinforcing bar is placed. (options: "beamtop", "beambot" or "column")
$damage	string indicating whether there is full damage in the material or no damage (optional, options: "Damage", "NoDamage" ; default: Damage)
$unit	string indicating the type of unit system used (optional, options: "psi", "MPa", "Pa", "psf", "ksi", "ksf") (default: "psi" / "MPa")*

NOTES

1. Model Characteristics:

The uniaxial material model uses the Pinching4 material model (Ref. Pinching4 material model). The response envelope for the bar-slip springs does not represent strength deterioration, but once the slip demand exceeds 3mm (0.12 in), strength deterioration due to cyclic loading initiates. As a result the bond-slip springs always exhibit positive stiffness, but strength deterioration upon reloading to a previously observed slip demand. Reloading and Unloading Stiffness deterioration are also simulated.

The damage index for unloading and reloading stiffness degradation is evaluated the same say as the Pinching4 material (ref. Pinching4 material doc.) but the index for strength degradation is specified as

With degradation model parameters gF*. It should be noted in here that the deterioration parameters for unloading, reloading stiffness and strength degradation cannot be modified by the user and are defined to represent observed behavior.

1. The model includes predefined bond strengths, so there is the necessity to include in Units in this material model. For default one can specify units in psi (i.e. pounds/inch2) or in MPa (i.e. N/mm2). The code detects units in psi if the compressive strength of concrete is greater than 1000 otherwise it takes it as MPa system. The optional variable $unit will help the user to specify other different types of unit systems according to one's choice, but currently it is limited to the unit systems as specified above. The user should also take care to specify the units of length in the corresponding matching units. (note: Pa = N/m2; ksf = kilo-pound/ft2)

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Code Developed by: Nilanjan Mitra, CalPoly State University