1. E NGINEERING D ESIGN L AB II ENGR-102 W INTER 2015 W EEK 4 L ECTURE – B RIDGE M ODULE Pramod Abichandani, Ph.D. Richard Primerano, Ph.D. 1 L AB W EEK 4 – CAD AND S IMULATION T OOLS U SING D ATA F ROM S OFTWARE T OOLS

2. T EAMWORK E VALUATIONS Due this week This is meant mainly to help us identify potential teamwork issues and is not the only factor in deriving teamwork scores If you are having any issues with team members, please let us know ASAP (don’t wait for evaluations). 2

3. D UE N EXT W EEK Design Proposal See proposal template Signoff sheets Lab notebook pages from weeks 1-4 See journal guidelines 3

4. B RIDGE D ESIGN M ODULE W EEK 4 I TERATIVE K’NEX T RUSS B RIDGE D ESIGN Often, engineers rely on a combination of (pen and paper) calculation, simulation, and testing to arrive at final designs. In this lab, we will simulate then build and test several K’NEX structures to compare simulation and experimental results. 4

5. B RIDGE D ESIGN W ORKFLOW 5 CAD Design Simulation Build and Test

6. I NTERPRETING S OFTWARE TOOL O UTPUT Software tools often handle the computations that would be tedious (or impossible) for us to do by hand. They should never be relied upon without understanding the underlying theory or without qualitatively understanding the results. It is easy to set up a simulation problem incorrectly Simulation models always contain a certain amount of uncertainty Simulation tools never capture everything Approximations are made to simplify analysis 6

7. I NTERPRETING S OFTWARE TOOL O UTPUT Within Visual Analysis you must specify the constraints and applied load It will calculate the relevant equations and determine the tension/compression in each member Blue = tension, Red = compression 7

8. S CALING OF F ORCES WITHIN A S TRUCTURE Under the assumption that the structure is operating in its linear elastic range, changes in applied load lead to proportional changes in internal and reaction forces. 8 100 lb 28.9 lb (t) 57.7 lb (c) 50 lb 200 lb 57.8 lb (t) 115 lb (c) 100 lb

9. D ETERMINE W HERE THE B RIDGE W ILL F AIL Different joint types fail at different loads Joints are stronger in compression than tension 9 weak in tension stronger in tension strongest in tension

10. L OAD A MPLIFICATION Be aware that certain geometries can lead to amplification of internal loads 10 100 lb 28.9 lb (t) 57.7 lb (c) 50 lb 60˚ 100 lb 86.6 lb 100 lb 50 lb 30˚ 100 lb 186 lb 193 lb 50 lb 15˚

11. O RIENTATION OF C ROSS B RACING The orientation of cross bracing will effect whether it is in tension or compression. k’NEX joints are generally stronger in compression 11 tension Applied load compression Applied load

12. D ETERMINING W HEN THE B RIDGE W ILL F AIL If we assume the bridge is linear elastic, it is simple to determine approximately when it will fail. The analysis is complicated by the fact that different joint types fail at different strengths 12

13. D ETERMINING W HEN THE B RIDGE W ILL F AIL The bridge does not necessarily fail at its weakest joint. e.g. a very weak joint that has zero tension/compression The bridge does not necessarily fail at in the member with the largest scaling factor e.g. the member’s joints could be much stronger than all other joints 13

14. D ESIGN P ROPOSAL Should contain the following Summary of the design constraints under which you must design your bridge Detailed description of your intended bridge design Truss type, experimental and simulation results Include any sketches, pictures, calculations relevant to your design 14

15. D UE N EXT W EEK ! Preliminary Design Proposal First notebook check You should have a minimum of 15 pages by the end of the quarter Document all experimental data, mechanism sketches, pseudo code, etc… 15