Modelling and Analysis of Concrete & Steel Structures Lecture No4 - Modelling... · Rigid End Offsets • Rigid End connections to model large joints • Automated end offset evaluation

CSE E13 - 2018

Certificate Program in Structural Engineering

Course Coordinator:

Armin Bebamzadeh, Ph.D.

Instructor:

Armin Bebamzadeh, Ph.D.

E13 – COMPUTER SOFTWARE

APPLICATIONS IN STRUCTURAL

ENGINEERING

Modelling and Analysis of Concrete

& Steel Structures

Certificate Program in Structural Engineering – E13

Instructor: Armin Bebamzadeh, Ph.D.

Insertion Point

• The insertion point relates the actual position of an object

to the line drawn to represent that object in a model.

• By default, prismatic objects are positioned such that their

centroid and analytical properties align with the line shown in

the computational model.

No. 2

../../../Documents and Settings/Dr. C.E. Ventura/Local Settings/CIVIL230/contents.ppt



Insertion Point

No. 3




Insertion Point

No. 4

Connecting

lines

Top surface of

beam is located at

connecting line




Insertion Point

No. 5

Bending

moment on

tension side

Bending

moment with

insertion point

top center

24’

1.5k/ft

Both supports are pinned to fix axial load.




Insertion Point

No. 6

Centroid to centroid

24’

12’




Insertion Point for Columns

No. 7

Cardinal Point:

Top Center

Cardinal Point:

Bottom Center




Insertion Point

No. 8

Larger moment

M33




Insertion Point for Beams

No. 9

Cardinal Point:

Top Center




Insertion Point for Beams

No. 10




Rigid End Offsets

• Rigid End connections to model

large joints

• Automated end offset evaluation

and assignment




Rigid Zone Factor

• Rigid Zone Factor

No. 12

Rigid Zone Factor = 0 Rigid Zone Factor = 1

Rigid Zone Factor = 0.5

Half of the joint link is rigid,

Concrete frame usually have RGF = 0.5




Panel Zone

• Panel zone creates rotational springs connects beam to the

column

No. 13




Offset and Panel Zone

No. 14

Rigid Zone

Factor = 1 is

applied to

columns and

beams

Beams insertion point top

center, left columns bottom

center and right columns top

surface

Panel zone,

same property

of columns




Offset and Panel Zone

No. 15




Adding Braces

No. 16

Chose section

Choose type of brace

Choose connection




Add Braces

No. 17

Released at both ends no moments




Braces

No. 18

6’

6’

2’2’

Continuous Beam




Braces

No. 19

X Braces

Concentric

Inverted V

EccentricV

Eccentric

Tension – Compression only

Backward Forward

Don’t forget this

support




Braces

No. 20




Area Section

No. 21




Area Section

• The Shell element is a type of area object

that is used to model membrane, plate,

and shell behavior in planar and three-

dimensional structures.

• The Plane element is used to model

plane-stress and plane-strain behavior in

two dimensional solids.

• The Asolid element is used to model

axisymmetric sol ids un der axisymmetric

loading.

No. 22




Shell

No. 23




Mesh Examples Using the Quadrilateral Area Element

No. 24




Membrane and Plate Behavior

No. 25

1

2

3F11

F22

F12

M11

V13

V23M22

M12




Membrane and Plate Behavior

No. 26

1

2

3

F22




Shell Behavior

• Shell = Membrane (in-plane) +

Plate(Bending and out-of-plane shear)

Plate : (both have the transverse shear forces) but

– Thin : thin-plate formulation follows a Kirchhoff application, which

neglects transverse shear deformation

– Thick: thick-plate formulation follows Mindlin/Reissner, which

does account for shear deformation.

Shear deformation tends to be important when shell thickness is greater than

approximately 1/5 to 1/10 of the span of plate-bending curvature.

No. 27




Shell Section Data

No. 28

To apply cracked values,

….




Example – Diaphragm

No. 29

10m

10m

100mm thickness

under 5kN/m2 load

including dead load




Meshing Shell

No. 30




Meshing Shell

No. 31




Assigning Load to Shell

No. 32

Two options for

uniform load




Shell Results

No. 33

Forces

Stresses




Shell Results – Two Way Slab

No. 34

M11 V13




One Way Slab

No. 35

One Way along 1 – about 2




Shell Results – One Way Slab

No. 36

M11 V13




Shell Results – One Way Slab

No. 37

Rotate local axis, 90o




Shell to Beam Connection

• By default, ETABS and SAP2000 automatically add joints to

beam/frame elements for connectivity whenever adjacent

area elements are meshed.

No. 38




Shell to Beam Connection

• Turning off the auto mesh, separate the beam from slab

No. 39




Reduced bending stiffness of shell to make it behave

like a membrane. Shell will still transfer load only at

meshed joint locations.

Meshing as long strips forces 1-way load distribution with shell type areas

Area meshing - Users have the option to mesh shell area elements to make them distribute load one-way as demonstrated below left using

Edit>Edit areas in SAP2000 (Edit>Mesh areas in ETABS). In addition, users can use the modifier option to reduce stiffness in any

direction. The modifier option can be used to specify reduced section for cracking, and/or reduced membrane stiffness if the engineer does

not want to take credit for the slab or deck in-plane resistance to lateral loads.

Shell Modifier




Add gridlines to help you mesh precisely where needed. Select area(s) to be meshed

Edit menu>Edit areas in SAP2000. Similar options in ETABS

SAP2000 and ETABS offer several meshing tools. In addition to the 4X4, 2X8, etc. type of meshing, users can add gridlines or draw

lines to help them more easily mesh area elements. In the example below, gridlines are added and then Edit>Edit areas in SAP2000

to mesh by Intersections of Visible gridlines as shown below right. With ETABS, when meshing floors, use “cookie cut” mesh options

Meshing Shell




Use Set View options to activate Fill Objects to view mesh. Similar options in SAP2000, ETABS and SAFE

In this example below, only 1 shell area is meshed. Joints are automatically added to perimeter

beams, but adjacent area shells need to be meshed in order to transfer loads at mesh points

Select 2 adjacent shell areas

Use Edit menu again to mesh by gridlines




In order to assign different loads to different areas, to create openings, to assign a joint load or support, or transfer floor load to

a beam or wall or column, you need to mesh for connectivity. One exception is with floor openings in ETABS. Floor openings in

ETABS are drawn as an area with property “Opening” as shown below and ETABS will automesh. In SAP, floor openings are

created by meshing and deleting areas. Wall openings are created by mesh and delete in both SAP2000 and ETABS

With ETABS, floor openings are drawn with this property

Select a meshed

area and press

Del key on

keyboard to create

opening

With ETABS, use Edit menu to add reference planes and

reference lines to help mesh vertical shear walls by

gridline. With SAP2000, just add gridlines Mesh by gridlines

Select and delete for openings




SAP2000 default

ETABS default

Edge/Line constraint would solve this problem

One important issue to note with regards to meshing is the application of the line constraint (called ‘edge constraint’ in SAP2000). The line constraint

“zips” together adjacent elements which do not share common mesh points using a displacement interpolation numerical technique. By default, the

line constraint is activated in ETABS, but in SAP2000 the edge constraint must be manually assigned. In the example below, we have a wall with a

mismatched mesh. Select adjacent area elements and Assign>Area to activate or deactivate line/edge constraints. If joints of adjacent elements are

reasonably close together, use of these constraints can be a huge time saver compared to manually adjusting the meshes, and it can save users from

having to model transitions using less accurate triangular elements. Conversely, use of line constraints also gives results in a poorly meshed model

which may be misleading, so use engineering judgment.




Constraints

• Body Constraint

– A Body Constraint causes all of its constrained joints to move together as a three-

dimensional rigid body. By default, all degrees of freedom at each connected joint

participate. However, you can select a subset of the degrees of freedom to be

constrained.

• Diaphragm Constraint

– A Diaphragm Constraint causes all of its constrained joints to move together as a

planar diaphragm that is rigid against membrane deformation. Effectively, all

constrained joints are connected to each other by links that are rigid in the plane, but

do not affect out-of-plane (plate) deformation.

This Constraint can be used to:

– Model concrete floors (or concrete-filled decks) in building structures, which typically have very

high in-plane stiffness

– Model diaphragms in bridge super structures

No. 45




Diaphragm Constraint

No. 46




Constraints

• Plate Constraint– A Plate Constraint causes all of its constrained joints to move together as a flat

plate that is rigid against bending deformation. Effectively, all constrained joints are

connected to each other by links that are rigid for out-of-plane bending, but do not

affect in-plane (mem brane) deformation.


– Connect structural-type elements (Frame and Shell) to solid-type elements (Plane and Solid);

the rotation in the structural element can be converted to a pair of equal and opposite

translations in the solid element by the Constraint

– Enforce the assumption that “plane sections remain plane” in detailed models of beam

bending

No. 47




Constraints

• Rod Constraint– A Rod Constraint causes all of its constrained joints to move together as a

straight rod that is rigid against axial deformation. Effectively, all constrained

joints maintain a fixed distance from each other in the direction parallel to the

axis of the rod, but translations normal to the axis and all rotations are

unaffected.


– Prevent axial deformation in Frame elements

– Model rigid truss-like links

• Beam Constraint– A Beam Constraint causes all of its constrained joints to move together as a

straight beam that is rigid against bending deformation.

No. 48




Constraints

• Equal Constraint– An Equal Constraint causes all of its con strained joints to move together with the

same displacements for each selected degree of freedom, taken in the constraint

local coordinate system. The other degrees of freedom are unaffected.

– This Constraint can be used to partially connect together different parts of the structural

model, such as at expansion joints and hinges

• Local Constraint– A Local Constraint causes all of its constrained joints to move together with the

same displacements for each selected degree of freedom, taken in the separate

joint local coordinate systems. The other degrees of freedom are unaffected.


– Model symmetry conditions with respect to a line or a point

– Model dis placements con strained by mechanisms

No. 49




Weld

• Welds– A Weld can be used to connect together different parts of the structural

model that were de fined using separate meshes. A Weld is not a single

Constraint, but rather is a set of joints from which the program will

automatically generate multiple Body Constraints to connect together

coincident joints. Joints are considered to be coincident if the distance

between them is less than or equal to a tolerance, tol, that you specify.

Setting the tolerance to zero is permissible but is not recommended.

No. 50




References and Acknowledgements

• SAP2000 , CSi Analysis Reference Manual

No. 51
