Contact Information

• Philip Christensen

• Formation Design Systems

• philc@formsys.com

• www.formsys.com

• www.formsys.com/academic

• Password frog5cove

Tutorial Program

1. Introduction to Multiframe

2. Structural modeling & intro to Section Maker

3. Loads and load cases – sample problem

4. Understanding results – sample problem

5. Assignment

6. Assignment

Background to Multiframe

• What is Multiframe?

• Structural analysis and design software

• Linear 3D beam elements

• “Stick and Ball” model of primary structure

• Good for framed structures, less suited to

slab and wall structures

Using Multiframe

• Setup

– Units

– Size

• Basic Concepts

– Global axes

– Local axes

– Section Axes

• Frame, Load, Plot windows

Steps in structural analysis

1. Geometry

2. Connectivity

3. Materials/Section Properties

4. Member Types

5. Restraints

6. Loads

7. Analysis

8. Results

Frame Window

Load Window

Plot Window

Geometry

• Joint coordinates

• Member lengths

• Sketch in Frame window

• Modify by double click

• Modify in Data window

Connectivity

• Defines which members are

connected to which other

members

• Done automatically as you draw

in Frame window

• Can be reviewed in Member table

in Data window

Materials/Section properties

• Define size and materials of

structural members

• Sections are stored in Library

• Custom sections are possible

• Section Maker helps with

section property calcs

• Applied to members in the

Frame window

Member Types & Orientation

• Section Orientation

• Also known as “beta” angle

• Member releases define pins

at ends of members

• Applied to members in the

Frame window

Restraints

• Define how structure is “held down”

• Commonly pinned or rigid

• Apply to joints in Frame window

• Custom restraints are possible

Loads

• Automatic self weight

• Loads on joints

– Point loads or moments

• Loads on members

– Point or Distributed

• Consider a number of loading conditions or

cases

• Factored combinations of load cases

Analysis

• Static linear (1st order)

• Static nonlinear

– (2nd order, large deflection)

– P. and P.

• Dynamic modal

• Dynamic time history

Load

Deflection

1st Order

2nd Order

Results

• Deflections

• Actions

– Forces, moments

• Stresses

– Axial, bending, shear

• Diagrams in Plot window

• Tables in Results window

• NB Deflection diagram is exaggerated

Sample Problem

• 2D Truss to carry 1 x 20kN load at middle of a 10m span

• Goals are –

– Deflection not greater than 40mm

– Axial stress not greater than 100MPa

• How light can you make it?

– Use Data Window/Sections table to check weight

10m

20kN

Section Maker

• Utility for calculating properties of a

structural shape

• Weight, Area, Ix, Iy, J, E, G are required for

Multiframe

• Others are useful for stresses and design

Using Section Maker

• Placing Sections

• Placing Shapes

• Drawing Shapes

• Importing Shapes

• Properties

• Limitations

– No overlapping shapes

– J approximate in some cases

Structural Modeling

1. Use clipping and masking to manage

more complex models

2. Importing DXF

3. Modeling trusses

4. Modeling frames

5. Common errors

Data Import - DXF

• DXF - AutoCAD, Microstation etc

• Import 3D DXF from any CAD system

• Each LINE/POLYLINE segment

becomes a member in Multiframe

• No arcs in polylines

• Don’t use local extrusion axes

• Make sure any BLOCKs are exploded

prior to export

• Check units in DXF file are consistent

with Multiframe

• Use rotate command after import if

necessary

Modeling Trusses

• Trusses resist loads using axial

actions only

– bending

• Structure must be completely

triangulated

– Be careful in 3D

• Set joint types to pinned

• Usual to apply only joint loads

• Review deflections and axial

forces in results

– Tension and compression

Modeling Frames

• Frames resist loads using combination of

bending and axial forces

• Columns carry vertical loads as axial forces and

resist horizontal loads by bending

• Beams resist vertical loads by bending

• Braces resist transverse loads by axial tension

or compression

Common modelling errors

• Setting all joints to be restrained

– Only the joints at the foundations

should be restrained

• Drawing a member through a joint

– Every member must run from joint

to joint. Subdivide if

necessary.Check by selecting the

member.

• Duplicating members so they touch

but are not connected to other

members

– Check using animation

• Getting loading units wrong

Load Cases

• Common load cases

– Self weight (Permanent)

– Dead load (Permanent)

– Live load (Imposed)

– Wind load

– Load combinations

• Load magnitudes are determined using

AS1170 or from first principles

• Multiframe commands

– Add Self Weight

– Add Static Load Case

– Add Combined Load Case

Dead Load

• Loads which are permanently applied to the

structure

• For joint loads, consider area which will

contribute load to that joint

• For member loads, consider area which will

load that member

• For trusses its common to apply joint loads

L

P B

w

P (N) = B (m) x L (m) x w (Pa)

1 Pa = 1 N/m2

1 N = 1 kg x g

g = 9.8 (~10)

Live Load

• Loads which are temporarily applied to the

structure

• e.g. Pedestrians on the walkway

• w determined from no. of pedestrians per sq

metre and average weight per person

L

P B

w

P (N) = B (m) x L (m) x w (Pa)

1 Pa = 1 N/m2

1 N = 1 kg x g

g = 9.8 (~10)

Wind Load

• AS1170 prescribes wind load calculations

• q = 0.5 * * V2 * Cf

– q is design wind pressure Pa

– is air density = 1.2 kg/m3

– V is wind speed in m/s (assume 40 m/s)

– Cf is a shape factor (default to 1.0)

• Total load on member = L * D * q

• Load per unit length w = q * D

– D = depth of member perpendicular to air flow

• Direction of load is parallel to air flow

L

D

Loading Areas

• Tributary area

– Use to transfer pressure to a

member supporting an area

– Be careful with units

– More complicated patterns with

4-way supported slabs

W=P.d kN/m

where P is in kPa and d is in metres

Sample Problem Tree top walk

Tree top walk

Tree top walk

Tree top walk

Worked Example

• Tree Top Walk Truss, Walpole WA

• Length 60m, max depth 4m, max

width 3.0m, width at ends 1.0m

• Bottom chord 50mm rod, top

chords CHS168x4.8, transverse

members RHS150x50x4, bracing

CHS102x4

• www.donaldsonandwarn.com.au

Side Elevation

Plan

Worked Example Loads

• Consider self weight, dead weight, live load

and wind.

• Dead weight comes from 100mm thick jarrah

walkway

• Dead weight also comes from side railings at

70kg/m

• Live load comes from human traffic

• Wind load as per AS1170

• Self+Dead+Live+Wind

• Assume load is only applied at nodes of truss

Worked Example Dead Loads

• Self Weight using Add Self Weight load case

• Jarrah decking, 6m segment x 0.5m wide x

0.1m thick= 0.6m3

• Density of Jarrah is 800kg/m3 = 480kg = 4.8kN

• 6m handrail @ 70kg/m = 420kg = 4.2kN

• Total 9kN per node.

6m

9kN

9kN

Worked Example Live Loads

• People standing on deck

• 6m segment x 0.5m wide= 3m2

• Average person 70kg, one per square metre

• 3 x 70 = 210kg = 2.1kN per node

6m

2.1kN

2.1kN

Worked Example Wind Loads

• q = 0.5 * * V2 * Cf

– =0.5 x 1.2 * 40 x 40 = 960 Pa (~1kPa)

• Total load on member = L * D * q

• Load per unit on eg top chord

• w = q * D = 1 * 0.16 = 0.16 kN/m

• Repeat for each member of different depth

• Direction is perpendicular to length of truss

Analysis

• Static linear (1st order)

• Static nonlinear

– (2nd order, large deflection)

– P. and P.

• Dynamic modal

• Dynamic time history

Load

Deflection

1st Order

2nd Order

Results

• Deflections, forces, moments, stresses

• Diagrams in Plot window

• Tables in Results window

• Deflection diagram is exaggerated

Deflection Plots

• Exaggerated display of deflected shape

• Can exaggerate more or less using Scale

item in Plot dialog in Display menu

• Can set to true scale of displacement

using scale of -1

• Can overlay an action or stress as a color

on the diagram

• Can render the deflected shape

• Can animate the deflection shape and

save as an avi movie

Assignment

• Write the report as a self-contained

document

– Note any required external documents

• Use simple, annotated drawings to clarify

• Explain all assumptions

• Display intermediate as well as final working

of calculations and show all units

• Make sure units are consistent

• Use clear, simple, concise, professional

language

Student Models 1

Student Models 2

Student Models 3

Student Models 4

Student Models 5

Student Models 6

Student Work 1

Student Work 2

Student Work 3

Student Work 4

Student Work 5

Student Work 6

• © Formation Design Systems Pty Ltd

• PO Box 1293 Fremantle WA 6959

• Tel +61 8 9335 1522 Fax +61 8 9335 1526

• Email: philc@formsys.com

• Web Site: www.formsys.com