lab 8 predicting strength of trusses approximate running time – 20 minutes

© 2006 Baylor University

EGR 1301

Lab 8Predicting Strength of Trusses

Approximate Running Time – 20 minutesDistance Learning / Online Instructional Presentation

Presented byDepartment of Mechanical Engineering

Baylor University

Procedures:

1. Select “Slide Show” with the menu: Slide Show|View Show (F5 key), and hit “Enter”

2. You will hear “CHIMES” at the completion of the audio portion of each slide; hit the “Enter” key, or the “Page Down” key, or “Left Click”

3. You may exit the slide show at any time with the “Esc” key; and you may select and replay any slide, by navigating with the “Page Up/Down” keys, and then hitting “Shift+F5”.


EGR 1301

Introduction

Dr. Carolyn Skurla

Speaking


EGR 1301

F

Notes on Tensile Strength

Ft

w• Tensile Strength

– Material property– Measure cross-

sectional area– Load to failure in

tension– Calculate tensile

strength

AF

TS


EGR 1301

Notes on Compressive Strength

• Long, thin members– Buckling will occur– Member fails in bending instead

of in compression

2

2

LEI

Pcr


EGR 1301

Notes on Shear Strengthof Glue

• Standard method for testing adhesive strength– Shear the glue joint

A

Fxy

xyA 2

F

F


EGR 1301

How to Use ModelSmart

• Add Joints– On Menu, select “Joints” and make sure that “Add” has

a next to it (i.e., Add is selected).– Place your truss joints on the grid.


EGR 1301


• Add Joints– The cursor will point to a red dot as you move it around.

– When you click to place the joint, a blue dot will appear.


EGR 1301


• Select Size/Grade of Wood– On Menu, select “Members” / “Default Material Type” /

“Balsa Wood” / “1/4” Balsa – BAL8D3”


EGR 1301


• Add Members– On Menu, select “Members” and make sure that “Add” has a next

to it (i.e., Add is selected).– Place your truss joints on the grid by clicking on one joint and

dragging to the other joint.


EGR 1301


• Add Members– Construct your truss bridge by adding all the truss

members.


EGR 1301


• Add Supports– On Menu, select “Supports” and select the fixed support. Place a

fixed support on one end of the truss.– On Menu, select “Supports” and select and place a horizontal

rolling support.


EGR 1301


• Add Loads– On Menu, select “Loads” and select “Vertical Down.”– The cursor will change to a down-pointing arrow.


EGR 1301


• Add Loads– Place a “Vertical Down” load on the joints at each end

of the top horizontal member.


EGR 1301


• Analyze your truss.– On Menu, select “Analysis” / “Analysis Options”.

– Select “Show Displacements”, “Show Broken Members”, and “Show Stress Levels.”


EGR 1301


• Understanding analysis results– Red Broken– Blue Compression– Green Tension


EGR 1301


• Understanding analysis results– On Menu, select “Member” / “Show Member Numbers”

to see the assigned member number for each truss member.


EGR 1301


• Understanding analysis results– On Menu, select “Analysis” / “Show Results” to see the

loading, strength, and efficiency ratio data for each truss member.


EGR 1301


• To Change Material Type– On Menu, select “Members” / “Default Material Type” /

“Balsa Wood” / new grade & size of wood

– On Menu, select “Members” / “Change Material Type”


EGR 1301


• To Change Material Type– Click on the truss member that you want to change– The changed truss member will change in size and/or color,

depending on the size and class of balsa wood chosen


EGR 1301


• To Double Truss Members – On Menu, select “Members” / “Double Members”

– Click on truss members that you want to double

– The truss member number background for doubled members is blue


EGR 1301

This Concludes the Lab 4 Lecture

lab 8 predicting strength of trusses approximate running time – 20 minutes

Documents