Beirut Arab University

Faculty of Engineering

Civil and Environmental Department

Structural Modeling

CVLE 371

Chapter 2

3D Frames and Results Generation

Prepared by: Eng. Sandy Chaaban

Supervised by: Prof. Yehya Temsah

Chapter 2

3D Frames

Introduction

This chapter covers numerical 3D frames using Robot.

Before starting, keep in mind that the modeling tools used in 2D frames are the same when

working in 3D frames. However, there are certain tools special for space modeling.

Drawing 3D models

1. Start a new model with “Frame 3D Design” type and draw the following frame

(Don’t forget to modify the units)

X

Y

Z

N.B. In robot, the sections may be defined before drawing the structural skeleton i.e. start by

defining the different bar sections under “Bar sections” option then start drawing the bars and

choose their properties from the bars window as seen below.

(Apply the same loads and use the same sections you had in assignment 1)

Select the bar type

defined at the beginning

Select the bar section

corresponding to the

selected bar type

Assigning supports

In the previous chapter, you learnt that the support is defined by its degrees of freedom.

In 3D structures, supports have 6 degrees of freedom which are three translational (Ux, Uy

and Uz) and three rotational (Rx, Ry and Rz).

The procedure for defining supports in 3D is the same as that followed in 2D.

Defining the different types of supports in 3D:

Fixed support

Ux

Uy

Uz

Rx

Ry

Rz

Pin

Ux

Uy

Uz

Roller

Two way roller

o Horizontal roller

Ux

Uy

o Vertical roller

Uy

Uz

One way roller

o Vertical

UZ

The model should finally look like this

This is a 3D frame, so it is repeated in space (y-direction). (Assume here it is repeated

every 6 meters)

To perform this repetition, select the frame, launch the Edit toolbar and click on the

Move/Copy option.

Copying by translation copies all the defined supports, loads and section properties

Move/Copy

The translation box will open

Define the translational vector and the number of repetitions. The number of repetitions

excludes the existing frame i.e. if the structure consists n frames the number of repetitions

is n-1.

Clicking on the Drag option creates new members between new nodes and existing nodes

parallel to the translation vector. The last selected bar element in the sections dialog will

be the member created on drag.

2. To ease work while working in 3D, Robot has several options:

Global working plane

Local system definition

3D projection

Grouping

Global working plane

This option is found after launching the view toolbar from the standard toolbar.

Upon clicking on the global working plane option, the work plane box will open and

specify the coordinates either enter the coordinates in the boxes given or click on the

desired joint where a vertical or horizontal cut is to be performed.

Then, select the projection to which the cut will be done parallel to.

The different projections

Local system definition

This option enables performing cuts on inclined surfaces parallel to the different

projections XY, YZ, XZ by choosing three different joints which create a plane.

To perform this, launch the view toolbar and click on “Local System Definition” option

which will open the local system definition box select the joints (P1, P2 and P3) through

which the plane is drawn.

Local System Definition

Robot will open the local cut you performed in a new view which can be opened anytime.

3D projections

The 3D projections give a deep view of the structure, elements and joints parallel to the

three global projections XY, XZ and YZ.

“Exit” to close

the view

completely (the

view won’t be

available

anymore)

To switch between views

This will ease the selection of multiple structures, elements and joints. Moreover,

selected portions of the structure can be isolated for editing or results viewing by clicking

on the “View in new window” icon found in the selection toolbar. This doesn’t mean that

the selected portions are structurally isolated. They are only viewed independently i.e.

still connected to the whole structure.

Grouping/Making Selections

Making selections can operate on nodes and bar elements to create specific selection sets.

These sets are saved in the library of the file working in and can be picked for specific

and quick selections.

To perform this select the desired bar elements and go to “Bar Selection” option found in

the selection tool bar. The selection box will open click on define a new group option

which will open the group definition box.

View in New window

Define a new group

Now that the group is defined, the grouped elements can be selected directly from the list of “bar

selection” list.

Name of group

Remarks: I. In several cases, structural engineers may use tapered sections for columns for

several reasons:

Give the column a hinge behavior at the end of a column

High moment is generated at the joint level between the column and beam or

support level thus a larger section is required above to resist this moment leading

to the construction of a tapered section

In robot the tapered section is defined as a rectangular RC beam and by checking

the tapered section option box and giving the software the variable dimensions (h1

and h2).

Increased depth

(inertia) to drag

moment

Reduced section

to generate

hinge behavior

II. Defining lateral variable loads These loads are defined as trapezoidal uniform loads in Robot.

1. Type selector

2. Direction selection: the load will be aligned parallel to one of the shown axes

X, Y or Z according to the coordinate system chosen (local or global)

3. Define the magnitudes of the load at each point of interest.

4. Specify the location of each point of interest along the member length as

measured from the member start to the member end. This can be done by

giving relative coordinates (distance along the member/member length) (in

this case X2 is always 1) or by giving absolute coordinates along the member

length.

1

3

2

4

III. Diaphragm A rigid diaphragm ensures that all points in a plane have the same translational

and rotational movement upon subjection to horizontal forces.

Diaphragm in robot is defined as rigid link in two ways

a. Geometry/ additional attributes/ rigid links

b. Structure Model toolbar/ Structural Definition/ Rigid links

The rigid links window will open. A new rigid link is tobe defined called “diaphragm”

having the translations directions Ux and Uy and rotational direction Rz blocked.

Rigid Links

Structural Definition

The master node should be selected and then the other nodes (slave nodes) that shall be

connected to the master node should be selected as well.

IV. Releases When you apply a release to a member, this member is not taking moment at one

end (fixed-pinned or pinned-fixed) or both ends (pinned-pinned).

Open the release labels dialog using one of the following:

a. Geometry/ Releases

b. Structure Model toolbar/ Structural Definition/ Releases

This will open the Release Labels Dialog:

Press “New Release Definition” which will open the “New Release

Definition” dialog:

Label: each release must have a name.

Release directions: for each direction (Ux, Uy, Uz) or rotation (Rx, Ry, Rz) select

whether this direction/rotation is released at the start and/or end of the member. A

checked box indicates that this displacement/rotation is to be released and

unchecked means that it remains fixed.

After setting the name and release directions press “Add” to add it to the list of

available releases.

Upon applying the release to the selected bars the release codes will give you

exact information on which displacements and rotations have been released. The

codes use an “x” for a fixed and “f” for free (released/checked). There are 6 letter

codes for each end and are arranged in this order Ux, Uy, Uz, Rx, Ry, Rz

V. Results: There are two types of results generated in ROBOT:

a. Graphical

b. Tabulated

Before running the project, the model should be checked for errors and warnings

(instability, isolated joints, undefined materials, overlapped elements…). This is

performed either manually by clicking on “Analysis” icon on the tool bar and by

going to “verification” command or it is automatically performed by the software

upon clicking on “Analysis” from the tool bars and running the project by

launching the calculations (Analysis/Calculations).

Once calculations have been successfully run, you can view the analysis results.

Robot will give results for displacements, forces, reactions, stresses, etc. The

results can be gathered in two ways either from the results menu in the menu bar

(tabulated results) or from the results layouts from the layout selector (graphical

results).

The results diagrams allows you to view member force diagrams, structure

displacement, reactions, stresses and reinforcement requirements.

a. Graphical Results

For tabulated

results

For graphical

results

NTM (Normal Tangential Moment) tab:

The NTM is used to display diagrams on the bars which correspond to the force

components of the cross section. The forces are oriented according to the

member local axes.

Use the (+) or (-) tabs to increase to decrease the size of the diagrams

Z (Fz Shear)

X (Fx Axial)

Y (Fy Secondary Shear)

Y (My Main Moment)

Z (Mz Secondary Moment)

X (Mx Torsion)

Deformation Tab:

The deformation tab displays the structural deflection of the structure, and it

gives an animated view for the deflected shape.

Click on the start button to view the animation. The animation is an AVI file that

can be saved by clicking on the “Save” icon on the animation view controls which

open upon starting the animation.

Reactions Tab:

The main purpose of this tab is to display the reactions at the level of the supports.

Selecting reactions and moment components (FX, FY, FZ, MX, MY, MZ) will

display arrows and/or moment vectors showing the reactions on the supports.

Choose “descriptions” for tags showing the reaction values.

Parameters Tab:

It offers options for configuring the display of diagrams.

b. Tabulated Results

The graphical results determined above can also be determined as tabulated

results. There are different tables that robot can generate for the results:

reactions, displacements, stresses and forces.

None: doesn’t

display any value

on the diagram

Labels: displays

the values on

boxes

Text: gives the

values only

Reactions Table

Stresses Table

Forces Table

Displacements Table

The reactions table gives the reactions at the support due to the different

loading cases.

The forces and deflections/displacements tables give results for bar

elements. By default, then forces table displays the six force components

FX, FY, FZ, MX, MY, MZ and the deflections table shows the maximum

deflection values for each bar.

Forces table:

When robot opens the forces table, perform a right click and go to table

columns the following window will open

In the forces tab the information is straightforward with the additional

option of generating a new column to display the axial forces separately on

whether they are under compression or tension. (Fx as compression and

tension).

Under the division points tab you can configure which points along the

member Robot will display the results for.

N-points along the bar length: by default Robot gives the results at the

beginning and end of the bar (2), but this number can be changed to

multiple points distributed evenly along the bar.

N-points along calculation element: if a calculation node has been added

to a bar element, then you can have Robot display results at an even

number of points along the calculation element.

Relative point coordinate: Specify one single coordinate location along

the length pf the bar element relative to its length. Relative coordinates

are: desired position/length (0<x<1)

VI. Printout Composition Robot has a powerful report composition tool. Reports for all basic model data,

table information, views as well as calculation results and member design reports

can all be included in the printouts providing a very comprehensive reporting tool

for documenting your design.

Screen Captures: In any view of the model, notice the screen capture

Pressing this button will launch the Screen Capture dialog where you

can configure the parameters of the screen capture.

Add a label that will help you identify the capture when assembling the report.

In this dialog, we will select the elements of the report, order them and decide on

formats and spacing. There are several to access this dialog either from

File/Printout Composition or from the standard toolbar with the printout

composition button

Note that the screen captures taken will appear under the screen captures tab.

Standard: to choose the components (nodes, table, bar table)

Screen Captures: list of captures saved

Simplified printout: a report generator allowing quick access to standard

components with added filtering capabilities.

Adds one selected component

Adds all components to the report

Creates a Microsoft word file and launches it