User talk:Kkolozvari

Element MVLEM

The MVLEM element command is used to generate a two-dimensional Multiple-Vertical-Line-Element-Model (MVLEM; Vulcano et al., 1988; Orakcal et al., 2004) for simulation of flexure-dominated RC wall behavior. A single model element incorporates six global degrees of freedom, three of each located at the center of rigid top and bottom beams, as illustrated in Figure 1a. The axial/flexural response of the MVLEM is simulated by a series of uniaxial elements (or macro-fibers) connected to the rigid beams at the top and bottom (e.g., floor) levels, whereas the shear response is described by a shear spring located at height ch from the bottom of the wall element. Shear and flexural responses of the model element are uncoupled. The relative rotation between top and bottom faces of the wall element occurs about the point located on the central axis of the element at height ch (Figure 1b). Rotations and resulting transverse displacements are calculated based on the wall curvature, derived from section and material properties, corresponding to the bending moment at height ch of each element (Figure 1b). A value of c=0.4 was recommended by Vulcano et al. (1988) based on comparison of the model response with experimental results.

Source: /usr/local/cvs/OpenSees/SRC/element/MVLEM/

Figure 1. a) MVLEM Element, b) MVLEM Rotations and Displacements

---

Input Format:

Element MVLEM $eleTag $Dens $iNode $jNode $m $c -thick {Thicknesses} -width {Widths} -rho {Reinforcing_ratios} -matConcrete {Concrete_tags} -matSteel {Steel_tags} -matShear {Shear_tag}

$eleTag	Unique element object tag
$Dens	Wall density
$iNode $jNode	End node tags
$m	Number of element macro-fibers
$c	Location of center of rotation with from the iNode, c = 0.4 (recommended)
{Thicknesses}	Array of m macro-fiber thicknesses
{Widths}	Array of m macro-fiber widths
{Reinforcing_ratios}	Array of m reinforcing ratios corresponding to macro-fibers; for each fiber: rho,i = As,i/Agross,i (1 < i < m)
{Concrete _tags}	Array of m uniaxialMaterial tags for concrete
{Steel_tags}	Array of m uniaxialMaterial tags for steel
{Shear_tag}	Tag of uniaxialMaterial for shear material

---

Element Recorders:

The following recorders are available with the MVLEM element:

globalForce	Element global forces
Curvature	Element curvature
Shear_Force_Deformation	Element shear force-deformation relationship
Fiber_Strain	Vertical strain in m fibers along the cross-section
Fiber_Stress_Concrete	Vertical concrete stress in m fibers along the cross-section
Fiber_Stress_Steel	Vertical steel stress in m fibers along the cross-section

---

Examples:

Element MVLEM 1 0.0 1 2 8 0.4 -thick 4 4 4 4 4 4 4 4 -width 7.5 1.5 7.5 7.5 7.5 7.5 1.5 7.5 -rho 0.0293 0.0 0.0033 0.0033

0.0033 0.0033 0.0 0.0293 -matConcrete 3 4 4 4 4 4 4 3 -matSteel 1 2 2 2 2 2 2 1 -matShear 5

Recorder Element -file MVLEM_Fgl.out -time -ele 1 globalForce

Recorder Element -file MVLEM_FiberStrain.out -time -ele 1 Fiber_Strain

---

References:

Developed and Implemented by:

Kristijan Kolozvari, California State University Fullerton

Kutay Orakcal, Bogazici University, Istanbul, Turkey

John Wallace, Univeristy of California, Los Angeles

1) Orakcal K., Conte J.P., and Wallace J.W. (2004). “Flexural Modeling of Reinforced Concrete Structural Walls - Model Attributes”, ACI Structural Journal, V. 101, No. 5, pp 688-698.

2) Vulcano A., Bertero V.V., and Colotti V. (1988). “Analytical Modeling of RC Structural Walls”, Proceedings, 9th World Conference on Earthquake Engineering, V. 6, Tokyo-Kyoto, Japan, pp. 41-46.

Element SFI_MVLEM

The SFI_MVLEM command is used to construct a Shear-Flexure Interaction Multiple-Vertical-Line-Element Model (SFI-MVLEM, Kolozvari et al., 2014a, b), which captures interaction between axial/flexural and shear behavior of RC structural walls and columns under cyclic loading. The SFI_MVLEM element (Figure 1) incorporates 2-D RC panel behavior described by the Fixed-Strut-Angle-Model (nDMaterial FSAM; Ulugtekin, 2010; Orakcal et al., 2012), into a 2-D macroscopic fiber-based model (MVLEM). The interaction between axial and shear behavior is captured at each RC panel (macro-fiber) level, which further incorporates interaction between shear and flexural behavior at the SFI_MVLEM element level.

Source: /usr/local/cvs/OpenSees/SRC/element/SFI_MVLEM/

Figure 1. a) SFI_MVLEM Element, b) RC Panel Element (nDMaterial FSAM)

---

Input Format:

Element SFI_MVLEM $eleTag $iNode $jNode $m $c -thick {Thicknesses} -width {Widths} -mat {Material_tags}

$eleTag	Unique element object tag
$iNode $jNode	End node tags
$m	Number of element macro-fibers
$c	Location of center of rotation with from the iNode, c = 0.4 (recommended)
{Thicknesses}	Array of m macro-fiber thicknesses
{Widths}	Array of m macro-fiber widths
{Material_tags}	Array of m macro-fiber nDMaterial1 tags

¹SFI_MVLEM element shall be used with nDMaterial FSAM, which is a 2-D plane-stress constitutive relationship representing reinforced concrete panel behavior.

---

Element Recorders:

The following recorders are available with the SFI_MVLEM element:

globalForce	Element global forces
Curvature	Element curvature
ShearDef	Element shear deformation
RCPanel $fibTag $Response	Returns RC panel (macro-fiber) $Response for a $fibTag-th panel (1 ≤ fibTag ≤ m). For available $Response-s refer to nDMaterial FSAM (LINK).

---

Examples:

Element SFI_MVLEM 1 1 2 5 0.4 -thick 6 6 6 6 6 -width 9 10 10 10 9 -mat 7 6 6 6 7

Recorder Element -file SFI_MVLEM_Fgl.out -time -ele 1 2 3 globalForce

Recorder Element -file SFI_MVLEM_panel_strain.out -time -ele 1 RCPanel 1 panel_strain

---

References:

Developed and Implemented by:

Kristijan Kolozvari, California State University Fullerton

Kutay Orakcal, Bogazici University, Istanbul, Turkey

John Wallace, Univeristy of California, Los Angeles

1) Kolozvari K., Orakcal K., and Wallace J. W. (2015). ”Modeling of Cyclic Shear-Flexure Interaction in Reinforced Concrete Structural Walls. I: Theory”, ASCE Journal of Structural Engineering, 141(5), 04014135 doi

2) Kolozvari K., Tran T., Orakcal K., and Wallace, J.W. (2015). ”Modeling of Cyclic Shear-Flexure Interaction in Reinforced Concrete Structural Walls. II: Experimental Validation”, ASCE Journal of Structural Engineering, 141(5), 04014136 doi

3) Kolozvari K. (2013). “Analytical Modeling of Cyclic Shear-Flexure Interaction in Reinforced Concrete Structural Walls”, PhD Dissertation, University of California, Los Angeles.

---

Example 1. Simulation of Shear-Flexural Behavior of a Medium-Rise RC Wall Specimen under Cyclic Loading using the SFI-MVLEM Model

Figure E1.1. Model discretization: a) Plan view, b) Cross-section

Figure E1.1. Wall responses: a) Load versus Top Displacement Behavior, b) Cracking Patterns

Figure E1.1. Load versus Deformation Behavior for: a) Flexure, b) Shear

Figure E1.1. Panel Total Stress vs. Strain Responses: a) Axial-Horizontal, b) Axial-Vertical, c) Shear

Figure E1.1. Predicted Stress-Strain Behavior for Concrete: a) Strut 1, b) Strut 2

Figure E1.1. Predicted Stress-Strain Behavior for Steel: a) Horizontal (X), b) Vertical (Y)

uniaxialMaterial SteelMPF

This command is used to construct a uniaxialMaterial SteelMPF, which represents the well-known uniaxial constitutive nonlinear hysteretic material model for steel proposed by Menegotto and Pinto (1973), and extended by Filippou et al. (1983) to include isotropic strain hardening effects. The relationship is in the form of curved transitions (Figure 1), each from a straight-line asymptote with slope E0 (modulus of elasticity) to another straight-line asymptote with slope E1 = bE0 (yield modulus) where b is the strain hardening ratio. The curvature of the transition curve between the two asymptotes is governed by a cyclic curvature parameter R, which permits the Bauschinger effect to be represented, and is dependent on the absolute strain difference between the current asymptote intersection point and the previous maximum or minimum strain reversal point depending on whether the current strain is increasing or decreasing, respectively. The strain and stress pairs (<math>\epsilon</math>_r,<math>\sigma</math>_r) and (<math>\epsilon</math>₀,<math>\sigma</math>₀) shown on Figure 1 are updated after each strain reversal.

Source: /usr/local/cvs/OpenSees/SRC/material/uniaxial/

Figure 1. Constitutive Model for Steel (Menegotto and Pinto, 1973)

---

Input Format:

uniaxialMaterial SteelMPF $mattag $fyp $fyn $E0 $bp $bn $R0 $a1 $a2 <$a3 $a4>

$mattag	Unique uniaxialMaterial tag
$fyp	Yield strength in tension (positive loading direction)
$fyn	Yield strength in compression (negative loading direction)
$E0	Initial tangent modulus
$bp	Strain hardening ratio in tension (positive loading direction)
$bn	Strain hardening ratio in compression (negative loading direction)
$R0	Initial value of the curvature parameter R (R0 = 20 recommended)
$a1	Curvature degradation parameter (a1 = 18.5 recommended)
$a2	Curvature degradation parameter (a2 = 0.15 or 0.0015 recommended)
$a3	Isotropic hardening parameter (optional, default = 0.01)
$a4	Isotropic hardening parameter (optional, default = 7.0)

---

Example:

uniaxialMaterial SteelMPF 1 60 60 29000 0.02 0.02 20.0 18.5 0.15

---

Discussion:

Although the Menegotto-Pinto model is already available in OpenSees (e.g., Steel02), the formulation of SteelMPF brings several distinctive features compared to existing models. For example, the model allows definition of different yield stress values and strain hardening ratios for tension and compression, and it considers degradation of cyclic curvature parameter R for strain reversals in both pre- and post- yielding regions, which could produce more accurate predictions of yield capacity for some RC wall specimens (see Example 1), whereas Steel02 considers the degradation in post-yielding region only. Strain-stress relationships obtained using SteelMPF and Steel02 are compared in Figure 2 for a strain history that includes strain reversals at strain values equal to one-half of the yield strain (e.i., <math>\epsilon</math>_r = ±0.001 = <math>\epsilon</math>_y/2). The model also allows calibration of isotropic hardening parameters through optional input variables a3 and a4, and uses default values of a3 = 0.01 and a4 = 7.0 as calibrated by Filippou et al. (1983) based on test results. To disregard isotropic strain hardening behavior in SteelMPF, parameter a3 needs to be assigned a zero value (a3 = 0.0).

Figure 2. Comparison of Steel02 and SteelMPF

---

References:

Developed and Implemented by:

Kristijan Kolozvari, California State University Fullerton

Kutay Orakcal, Bogazici University, Istanbul, Turkey

John Wallace, Univeristy of California, Los Angeles

1) Filippou F.C., Popov, E.P., and Bertero, V.V. (1983). "Effects of Bond Deterioration on Hysteretic Behavior of Reinforced Concrete Joints". Report EERC 83-19, Earthquake Engineering Research Center, University of California, Berkeley.

2) Menegotto, M., and Pinto, P.E. (1973). Method of analysis of cyclically loaded RC plane frames including changes in geometry and non-elastic behavior of elements under normal force and bending. Preliminary Report IABSE, vol 13.

uniaxialMaterial ConcreteCM

This command is used to construct a uniaxialMaterial ConcreteCM, which is a uniaxial hysteretic constitutive model for concrete developed by Chang and Mander (1994). This model is a refined, rule-based, generalized, and non-dimensional constitutive model that allows calibration of the monotonic and hysteretic material modeling parameters, and can simulate the hysteretic behavior of confined and unconfined, ordinary and high-strength concrete, in both cyclic compression and tension (Figure 1). The model addresses important behavioral features, such as continuous hysteretic behavior under cyclic compression and tension, progressive stiffness degradation associated with smooth unloading and reloading curves at increasing strain values, and gradual crack closure effects. Details of the model are available in the report by Chang and Mander (1994). Note that ConcreteCM incorporates the unloading/reloading rules defined originally by Chang and Mander (1994), as opposed to Concrete07, which adopts simplified hysteretic rules.

Figure 1. Hysteretic Constitutive Model for Concrete by Chang and Mander (1994)

The Chang and Mander (1994) model successfully generates continuous hysteretic stress-strain relationships with slope continuity for confined and unconfined concrete in both compression and tension. The compression envelope curve of the model is defined by the initial tangent slope, (Ec), the peak coordinate (epcc, fpcc), a parameter (rc) from Tsai’s (1988) equation defining the shape of the envelope curve, and a parameter (xcrn) to define normalized (with respect to epcc) strain where the envelope curve starts following a straight line, until zero compressive stress is reached at the spalling strain, <math>\epsilon</math>_sp. These parameters can be controlled based on specific experimental results for a refined calibration of the compression envelope (Figure 2). Chang and Mander (1994) proposed empirical relationships for parameters Ec, epcc, and rc for unconfined concrete with compressive strength fpcc, based on review of previous research. Parameters fpcc, epcc, Ec, rc, and xcrn can also be calibrated to represent the stress-strain behavior of confined concrete in compression, to follow the constitutive relationships for confined concrete proposed by Mander et al (1988) or similar.

Figure 2. Compression and Tension Envelope Curves

The shape of the tension envelope curve in the model is the same as that of the compression envelope; however, the tension envelope curve is shifted to a new origin that is based on the unloading strain from the compression envelope (Figure 2). As well, the strain ductility experienced previously on the compression envelope is also reflected on the tension envelope. The parameters associated with the tension envelope curve include the tensile strength of concrete (ft), the monotonic strain at tensile strength (et), a parameter (rt) from Tsai’s (1988) equation defining the shape of the tension envelope curve, and a parameter (xcrp) to define normalized (with respect to et) strain where the tension envelope curve starts following a straight line, until zero tensile stress is reached at a strain of <math>\epsilon</math>_crk. These parameters can also be controlled and calibrated based on specific experimental results or empirical relations proposed by other researchers (e.g., Belarbi and Hsu, 1994) to model the behavior of concrete in tension and the tension stiffening phenomenon. Concrete experiencing tension stiffening can be considered not to crack completely; that is, a large value for parameter xcrp (e.g., 10000) can be defined.

Source: /usr/local/cvs/OpenSees/SRC/material/uniaxial/

---

Input Format:

uniaxialMaterial ConcreteCM $mattag $fpcc $epcc $Ec $rc $xcrn $ft $et $rt $xcrp <-GapClose $gap>

$mattag	Unique uniaxialMaterial tag
$fpcc	Compressive strength
$epcc	Strain at compressive strength
$Ec	Initial tangent modulus
$rc	Shape parameter in Tsai’s equation defined for compression
$xcrn	Non-dimensional critical strain on compression envelope (where the envelope curve starts following a straight line)
$ft	Tensile strength
$rt	Shape parameter in Tsai’s equation defined for tension
$xcrp	Non-dimensional critical strain on tension envelope (where the envelope curve starts following a straight line – large value [e.g., 10000] recommended when tension stiffening is considered)
<-GapClose $gap>	gap = 0, less gradual gap closure (default); gap = 1, more gradual gap closure

---

Example:

uniaxialMaterial ConcreteCM 1 -6.2 -0.0021 4500 7 1.035 0.30 0.00008 1.2 10000

Example of hysteretic stress–strain history generated by the model code is illustrated in Figure 3.

Figure 3. Concrete Stress-Strain Behavior

---

Discussion:

An optional input parameter gap is introduced in the ConcreteCM model implemented in OpenSees for providing the users with the opportunity to control the intensity of gap closure in the stress-strain behavior of concrete, which in-turn influences the level of pinching in the lateral load-displacement behavior of a RC wall. The original Chang and Mander (1994) model adopts a non-zero tangent stiffness at zero stress level upon unloading from the tension envelope, which is represented by gap = 1 in ConcreteCM. Using gap = 0 (default) produces less gradual gap closure, since it assumes zero tangent stiffness at zero stress level upon unloading from the tension envelope, and is suitable for most analyses. Figure 4 illustrates the effect of plastic stiffness upon unloading from tension envelope (Epl+) on crack closure, i.e. use of more gradual (gap = 1) or less gradual (gap = 0) gap closure.

Figure 4. Effect of Plastic Stiffness upon Unloading from Tension Envelope (Epl+) on Crack Closure

---

References:

Developed and Implemented by:

Kristijan Kolozvari, California State University Fullerton

Kutay Orakcal, Bogazici University, Istanbul, Turkey

John Wallace, Univeristy of California, Los Angeles

1) Belarbi H. and Hsu T.C.C. (1994). “Constitutive Laws of Concrete in Tension and Reinforcing Bars Stiffened by Concrete”, ACI Structural Journal, V. 91, No. 4, pp. 465-474.

2) Chang, G.A. and Mander, J.B. (1994), “Seismic Energy Based Fatigue Damage Analysis of Bridge Columns: Part I – Evaluation of Seismic Capacity”, NCEER Technical Report No. NCEER-94-0006, State University of New York, Buffalo.

3) Mander J.B., Priestley M.J.N., and Park R. (1988). “Theoretical Stress-Strain Model for Confined Concrete”, ASCE Journal of Structural Engineering, V. 114, No. 8, pp. 1804-1826.

4) Orakcal K.(2004), "Nonlinear Modeling and Analysis of Slender Reinforced Concrete Walls", PhD Dissertation, Department of Civil and Environmental Engineering, University of California, Los Angeles.

NDMaterial FSAM

This command is used to construct a nDMaterial FSAM (Fixed-Strut-Angle-Model, Figure 1), which is a plane-stress constitutive model for simulating the behavior of RC panel elements under generalized, in-plane, reversed-cyclic loading conditions (Ulugtekin, 2010; Orakcal et al., 2012). In the FSAM constitutive model, the strain fields acting on concrete and reinforcing steel components of a RC panel are assumed to be equal to each other, implying perfect bond assumption between concrete and reinforcing steel bars. While the reinforcing steel bars develop uniaxial stresses under strains in their longitudinal direction, the behavior of concrete is defined using stress–strain relationships in biaxial directions, the orientation of which is governed by the state of cracking in concrete. Although the concrete stress–strain relationship used in the FSAM is fundamentally uniaxial in nature, it also incorporates biaxial softening effects including compression softening and biaxial damage. For transfer of shear stresses across the cracks, a friction-based elasto-plastic shear aggregate interlock model is adopted, together with a linear elastic model for representing dowel action on the reinforcing steel bars (Kolozvari, 2013).

Source: /usr/local/cvs/OpenSees/SRC/material/nD/reinforcedConcretePlaneStress/

Figure 1. FSAM for Converting In-Plane Strains to In-Plane Smeared Stresses on a RC Panel Element

---

Input Format:

nDMaterial FSAM $mattag $rho $sX $sY $conc $rouX $rouY $nu $alfadow

$mattag	Unique nDMaterial tag
$rho	Material density
$sX	Tag of uniaxialMaterial simulating horizontal (-X) reinforcement
$sY	Tag of uniaxialMaterial simulating vertical (-Y) reinforcement
$conc	Tag of uniaxialMaterial1 simulating concrete
$rouX	Reinforcing ratio in horizontal (-X) direction (rouX = AsX/AgrossX)
$rouY	Reinforcing ratio in vertical (-Y) direction (rouY = AsY/AgrossY)
$nu	Concrete friction coefficient (0.0 < $nu < 1.5)
$alfadow	Stiffness coefficient of reinf. dowel action (0.0 < $alfadow < 0.05)

¹nDMaterial FSAM shall be used with uniaxialMaterial ConcreteCM

Recommended values for parameter of a shear resisting mechanism (nu and alfadow, Figure 2) are provided above. Details about the sensitivity of analytical predictions using SFI_MVLEM to changes in these parameters are presented by Kolozvari (2013).

---

Material Recorders:

The following output is available from the FSAM RC panel model:

panel_strain	Strains <math>\epsilon</math>x, <math>\epsilon</math>y, <math>\epsilon</math>xy (Figure 4)
panel_stress	Resulting panel stresses <math>\epsilon</math>x, <math>\epsilon</math>y, <math>\tau</math>xy (concrete and steel, Figure 1)
panel_stress_concrete	Resulting panel concrete stresses xc, yc, xyc (Figure 2b)
panel_stress_steel	Resulting panel steel stresses xs, ys, xys (Figure 2d)
strain_stress_steelX	Uniaxial strain and stress of horizontal reinforcement x, xxs
strain_stress_steelY	Uniaxial strain and stress of vertical reinforcement y, yys
strain_stress_concrete1	Uniaxial strain and stress of concrete strut 1 c1, c1
strain_stress_concrete2	Uniaxial strain and stress of concrete strut 2 c2, c2
strain_stress_interlock1	Shear strain and stress in concrete along crack 1 cr1, cr1 (Figure 2c)
strain_stress_interlock2	Shear strain and stress in concrete along crack 2 cr2, cr2 (Figure 2c)
cracking_angles	Orientation of concrete cracks

Note that recorders for a RC panel (marco-fiber) are invoked as SFI_MVLEM element recorders using command RCPanel and one of the desired commands listed above. Currently, it is possible to output values only for one macro-fiber within one or multiple elements.

---

Example:

nDMaterial FSAM 1 0.0 1 2 4 0.0073 0.0606 0.1 0.01

Recorder Element -file MVLEM_panel_strain.out -time -ele 1 RCPanel 1 panel_strain

Figure 2. Behavior and Input/Output Parameters of the FSAM Constitutive Model

---

References:

Developed and Implemented by:

Kristijan Kolozvari, California State University Fullerton

Kutay Orakcal, Bogazici University, Istanbul, Turkey

John Wallace, Univeristy of California, Los Angeles

1) Kolozvari K. (2013). “Analytical Modeling of Cyclic Shear-Flexure Interaction in Reinforced Concrete Structural Walls”, PhD Dissertation, University of California, Los Angeles.

2) Orakcal K., Massone L.M., and Ulugtekin D. (2012). “Constitutive Modeling of Reinforced Concrete Panel Behavior under Cyclic Loading”, Proceedings, 15th World Conference on Earthquake Engineering, Lisbon, Portugal.

3) Ulugtekin D. (2010). “Analytical Modeling of Reinforced Concrete Panel Elements under Reversed Cyclic Loadings”, M.S. Thesis, Bogazici University, Istanbul, Turkey.