General Mechanical

Mechanical APDL Model Error?

• Billy Lovell
Subscriber

Hi,

I've carried out a simple model of a static monotonically loaded reinforced concrete beam using a script. The model runs successfully, however it appears the load carrying capacity of the beam is excessively high, when compared with the experiment. For context, the experimental beam failed at 29kN & 50mm displacement. I have modelled one quarter of the beam due to double symmetry.

My script uses the legacy solid65, link180 (rebar) and solid 45 (steel support/loading plates). It also utilises the CONCR model, with crack shear coefficients of 0.1 & 0.4 for open & closed cracks, respectively. The script also uses the MELAS curve for the concrete. I've also played around with the stress-strain curve for the concrete, using a idealised curve that stops at the ultimate compressive strength. Use of a full curve with the descending branch makes the model fail prematurely (around 18mm) before the reaction loads turn to a negative value i.e. fail.

I've attached the script here and wondered if there was anything blatently obvious error wise? I've double & triple checked various parameters...

Even with use of the idealised stress-strain curve, my highest load is around 8-10kN too high, with the load-displacement curves being quite far apart.

The script is as follows:

! B Lovell
! December 2022
! RC Beam - Hughes & Speirs 1982
! RC Beam Run

!
fini
/prep7
/title,Hughes & Speirs RC Beam Analysis
!!! ELEMENT TYPES !!!
!
ET,1,SOLID65
!*
KEYOPT,1,1,0
KEYOPT,1,3,0
KEYOPT,1,5,1
KEYOPT,1,6,3
KEYOPT,1,7,1
KEYOPT,1,8,0
!*
!*
!*
KEYOPT,2,2,0
KEYOPT,2,10,0
!*
!*
ET,3,SOLID45
!*
!*
KEYOPT,3,1,0
KEYOPT,3,2,0
KEYOPT,3,4,0
KEYOPT,3,5,0
KEYOPT,3,6,0
!*
!*
!!! MATERIALS!!!
!
!
!Concrete
mp,dens,1,2400      !2400kg/m3 for concrete
mp,ex,1,3.431e+10      !Youngs modulus
mp,prxy,1,0.2       !Poissons Ratio
TB,CONCR,1,1,9,
TBDATA,,0.1,0.4,3.27e6,-1, !Concrete Non-metal plasticity model
TBDATA,5,,,,,0.6,
!
TB,MELAS,1,1,17,    !Concrete multilinear elasticity model
TBTEMP,0
TBPT,,0,0
TBPT,,0.0005129,1.76E+007
TBPT,,0.0008,2.46E+07
TBPT,,0.001,2.93E+07
TBPT,,0.0012,3.35E+07
TBPT,,0.0014,3.70E+07
TBPT,,0.0016,3.98E+07
TBPT,,0.0018,4.19E+07
TBPT,,0.0020,4.33E+07
TBPT,,0.0022,4.40E+07
!
!
!Reinforcement
mp,dens,2,7850      !Density 7850kg/m3 for steel rebars
MP,EX,2,2.06E+011  !Youngs modulus
MP,PRXY,2,0.3     !Poissons Ratio
TB,MISO,2,1,4,0   ! 2 x 4 array
TBTEMP,0
TBPT,,0.0017864,3.68E+008
TBPT,,0.0042464,4.6E+008
TBPT,,0.15,5.6E+008
!
!
mp,dens,3,7850      !Density 7850kg/m3 for steel plates
MP,EX,3,2.06E+011  !Youngs modulus
MP,PRXY,3,0.3     !Poissons Ratio
!
!
! Rigid Concrete element for support
mp,dens,4,2400      !2400kg/m3 for concrete
mp,ex,4,3.2e10      !Youngs modulus
mp,prxy,4,0.2       !Poissons Ratio
!
!
!
!
!
!!! ELEMENT REAL CONSTANTS !!!!
!
!
R,1,0, , , ,0, ,

R,2,1.13097e-4, ,   (For 12mm tension rebar)
!*
!
!R,2,5.02655e-5,,   (For 8mm, thicker first shear link)
!
!*
R,3,2.82743e-5,, (For 6mm compression + remaining shear links)
!*
!*
!*
!!! COMPONENT VOLUMES METHOD !!!
!
!
BLOCK,0,0.2,-0.1,0.1,-0.05,0,       ! Generate vol for concrete beam (200mm links)
BLOCK,0,0.2,-0.075,0.075,-0.025,0,  ! Generate vol for rebar area (200mm links)
VGEN,6,ALL, , ,0.2, , , ,0          ! Mirror vols for 6 instances (for 200mm spacing links)
BLOCK,1.2,1.35,-0.1,0.1,-0.05,0,    ! Generate vol for concrete beam (150mm links)
BLOCK,1.2,1.35,-0.075,0.075,-0.025,0, ! Generate vol for rebar area (200mm links)
BLOCK,1.35,1.5,-0.1,0.1,-0.05,0,      ! Generate vol for concrete beam (150mm links)
BLOCK,1.35,1.5,-0.075,0.075,-0.025,0, ! Generate vol for rebar area (150mm links)
BLOCK,1.3,1.4,-0.125,-0.1,-0.05,0,    ! Generate vol for support pad
VOVLAP,ALL                            ! Overlap/connect various volumes
!
VSEL,S,LOC,Y,-0.1,0.1                 ! Assign S65 element, concrete mat, section 1 to outer volume
TYPE,   1
MAT,       1
REAL,
ESYS,       0
SECNUM,
!*
ESIZE,0.025,0,                        ! Mesh 25mm sizing
VSWEEP,ALL
!
!
VSEL,NONE,ALL
VSEL,S,LOC,Y,-0.125,-0.1              ! Assign S45 element, rigid conc mat, to bottom support plate
TYPE, 3                               !solid45
MAT, 3                                !rigid Steel plate
REAL,
ESYS, 0
!*
ESIZE,0.025,0,                        ! Mesh 25mm sizing
VSWEEP,ALL
!
!
VSEL,NONE,ALL
!
VSEL,S,LOC,Y,0.1,0.125                ! Assign S45 element, rigid steel mat, to top loading plate
TYPE, 3                               ! Solid45
MAT, 3                                ! Original code says concrete? error? changed to rigid steel plate?
REAL,
ESYS, 0
ESIZE,0.025,0,
VSWEEP,ALL
!
VSEL,NONE,ALL
LSEL,NONE,ALL
!
!
LSEL,S,LOC,Y,-0.075                   ! Select lines that make up bottom tensile reinforcement (D12 bars)
LSEL,R,LOC,Z,-0.025
TYPE, 2                               ! Apply LINK180 elem
MAT, 2                                ! Apply rebar material
REAL, 2
ESYS, 0                            ! Apply 12mm diameter section
LMESH,ALL
!
LSEL,NONE,ALL
!
LSEL,S,LOC,Y,0.075                    ! Select lines that make up top compression reinforcement (D6 bars)
LSEL,R,LOC,Z,-0.025
TYPE,   2                             ! Apply LINK180 elem
MAT,       2                          ! Apply rebar mat
REAL,   3
ESYS,       0                         ! Apply 6mm diameter section
LMESH,ALL
!
LSEL,NONE,ALL
LSEL,S,LOC,Z,-0.025                   ! Select & mesh shear links
LSEL,U,LOC,Y,-0.075
LSEL,U,LOC,Y,0.075
LSEL,A,LOC,Z,-0.0125
LSEL,R,LOC,Y,-0.075,0.075
LSEL,U,LOC,X,0
TYPE, 2                               ! Apply LINK180 elem
MAT, 2                                ! Apply rebar mat
REAL, 3
ESYS, 0
LMESH,ALL
!
LSEL,NONE,ALL
!
LSEL,S,LOC,Z,-0.025                   ! Change REAL constant of fit, thicker shear link to 4
LSEL,U,LOC,Y,-0.075
LSEL,U,LOC,Y,0.075
LSEL,A,LOC,Z,-0.0125
LSEL,R,LOC,Y,-0.075,0.075
LSEL,R,LOC,X,0
TYPE,   2
MAT,       2
REAL,   3
ESYS,       0
LMESH,ALL
!
!
/GRAPHICS,POWER
!*
/TYPE,1,0
/CPLANE,0
/HBC,1,0
/REPLOT
ALLSEL,ALL
VPLOT
!
!
!
!!! Constraints !!!
!
!
!
ALLSEL,ALL
NSEL,S,LOC,Y,0.125
D,ALL, ,-0.05, , , ,UY, , , , ,  ! Apply Y Displacement to loading pad area nodes
!
! RHS Support Plate
ALLSEL,ALL                  ! Apply support constraints at RHS of beam along support plate
NSEL,S,LOC,X,1.35           ! Select centre-line of support
NSEL,R,LOC,Y,-0.125
D,ALL, , , , , ,UY, , , , , ! Restrain beam along 'Y' axis (Down)
!
! Symmetry condition on LHS face in X plane
ALLSEL,ALL                  ! Apply symmetry constraints along LHS side (where remainder of beam length would be)
NSEL,S,LOC,X,0              ! Select nodes on LHS of beam
NSEL,U,LOC,Y,0.125
D,ALL, , , , , ,UX, , , , , ! Restrain beam along 'X' axis (Across)
!
! Symmetry condition on front face in Z plane
ALLSEL,ALL                  ! Apply symmetry BC to nodes at 0 Z position (half-width of actual beam)
NSEL,R,LOC,Z,0
NSEL,U,LOC,Y,0.125
D,ALL, , , , , ,UZ, , , ,
!
ESEL,S,MAT,,1
CM,CM_conc,ELEM
/color,CM,GREE,CM_conc
ESEL,S,MAT,,3
CM,CM_plates,ELEM
/color,CM,YELL,CM_plates
ESEL,S,MAT,,2
CM,CM_rebar,ELEM
/color,CM,RED,CM_rebar
ALLSEL,ALL
ESEL,S,MAT,,4
CM,CM_stiffconc,ELEM
/color,CM,BLUE,CM_stiffconc
ALLSEL,ALL
EPLOT
!
!
!
!
!!! SOLUTION !!!
!
!
ALLSEL,ALL  ! Select all
CNVTOL,F, ,0.05,0, ,        ! Apply convergance tolerance values for NL solution
!*
DELTIM,5e-004,5e-005,5e-004
!
!
ANTYPE,0
NSUBST,1000,100000,1000
AUTOTS,1
TIME,1.0000
OUTRES,ALL,ALL

Many thanks if anyone has the time to read - would be greatly appreciated.

• Erik Kostson
Ansys Employee

Hi

Even though I cannot comment on this (results and apdl snippet - perhaps some other forum users that use this element can), I would like to suggest the current elements (solid187) and using the Menetrey-Wilam or DP concrete models, for modelling this type of structure and failure.

Menetrey-Willam (ansys.com)

(Solid65 is an old legacy which is mesh sensitive and can produce different results for different meshes)

There are many posts in this forum on using this approach and I have written it in an old post (it does not exist anymore as it was in the old forum) a small tutorial on how to do a punching shear example.

Also in help we can find some examples tech demo 49 and 52

49.1. Introduction (ansys.com)

For reinforcement use the reinforcement element/option in workbench.

https://forum.ansys.com/forums/topic/reinforced-concrete-with-shear-reinforcement/

Hope this helps and all the best

Erik