1) The date for the competition has been set for the Schools Carnival Day on Saturday 3 October 2009 at the Amphitheatre.
2) Parents and students must please attend the testing demonstration at 8.00am
3) Testing commences from 8.15 - 11.45
4) Students book their testing times after the demonstration and return when it is time to test.
5) No testing will be done during the grade 8 derby
Our sponsors
A big hearty thank you to CHC parent and general goodfellow Mr Jan van der Merwe from PG BISON who has kindly offered to picked up the quite hefty bill of 5000 sticks specially made to order for the competition!
Testing your bridge
On the day of the event:
a) The bridges will be checked for compliance with the competition requirements as laid out in specification diagrams. (figures 1 – 6)
b) Bridges that do not comply will be tested as far as possible but will suffer a 25%, 50% or 75% deduction depending on the severity of the non-compliance and the effect of the unfair advantage on the bridges load bearing capacity. If the loading harness does not fit on the day of the competition you will be asked to remove parts of your bridge to enable the harness to fit. If the harness then cannot fit Mr. Buys will make an estimation of what your bridge would probably have held subject to the same rules as if your bridge accidentally broke on testing day.
c) Non-compliant bridges will also not qualify for medals.
e) In the unlikely event of two winning bridges that carry exactly the same load amount the lighter bridge will be the winner.
f) Bridges will be weighed to check if pupils have used more than the required 25 sticks and 1 set of epoxy resin glue.
g) The load that will count for marks is the load that the bridge was able to stand before total destruction. If a weight is put onto the loading harness and the bridge fails immediately, the previous load will be the counted load.
Testing recommendations:
a) Do not let the harness swing at all.
b) Do not "slam" or drop the weight onto the harness, not even for 1mm.
c) Use bigger weights in the beginning and smaller weights towards the end.
d) Ensure that the stem of the weight harness, which hooks onto the loading harness, sits in the middle of the peg at the bottom of the loading harness.
e) Ensure that your bridge sits evenly on each side of the desk.
f) Ensure that the loading harness is positioned in the middle of your bridge in both in lateral and longitudinal positioning.
a) The bridges will be checked for compliance with the competition requirements as laid out in specification diagrams. (figures 1 – 6)
b) Bridges that do not comply will be tested as far as possible but will suffer a 25%, 50% or 75% deduction depending on the severity of the non-compliance and the effect of the unfair advantage on the bridges load bearing capacity. If the loading harness does not fit on the day of the competition you will be asked to remove parts of your bridge to enable the harness to fit. If the harness then cannot fit Mr. Buys will make an estimation of what your bridge would probably have held subject to the same rules as if your bridge accidentally broke on testing day.
c) Non-compliant bridges will also not qualify for medals.
e) In the unlikely event of two winning bridges that carry exactly the same load amount the lighter bridge will be the winner.
f) Bridges will be weighed to check if pupils have used more than the required 25 sticks and 1 set of epoxy resin glue.
g) The load that will count for marks is the load that the bridge was able to stand before total destruction. If a weight is put onto the loading harness and the bridge fails immediately, the previous load will be the counted load.
Testing recommendations:
a) Do not let the harness swing at all.
b) Do not "slam" or drop the weight onto the harness, not even for 1mm.
c) Use bigger weights in the beginning and smaller weights towards the end.
d) Ensure that the stem of the weight harness, which hooks onto the loading harness, sits in the middle of the peg at the bottom of the loading harness.
e) Ensure that your bridge sits evenly on each side of the desk.
f) Ensure that the loading harness is positioned in the middle of your bridge in both in lateral and longitudinal positioning.
West Point Bridge Designer
Finding the right shape:
You can experiment with the shape of your design by trying different options in the West Point Bridge Designer Computer Aided Design (CAD) program.The CAD program can be downloaded from the Internet as freeware and is male ware free.
West Point Bridge Designer Link: http://bridgecontest.usma.edu/download.htm
A new bridge design with a span of 16m and no piers works very well to determine the rough shape of your bridge.
Faults of West Point Bridge Designer CAD program:
a) The competition loading harness does not fit through the sidewall of the bridge at the middle because of the placing of the joints in the CAD program at the level plane. That means you cannot use the design exactly as it is in the CAD program and have to adapt your design for the real bridge.
b)The software of the CAD program does not allow the structure to "sit" on supports beyond the abutments and the designer must make sure that at least 50mm of each side of the real structure is flat from the level plane downwards.
c)The bridge will only exhibit how it will perform if the truck used to represent a dynamic load on the CAD design is stopped in the middle of the bridge and the members in tension and compression are examined whilst there is a static force acting on the CAD design.
d)Double members in CAD can only be represented as members with double the material size thus a steel beam of 160mm must be changed to a steel beam of 320mm for the structure to behave realistically under test conditions.
You can experiment with the shape of your design by trying different options in the West Point Bridge Designer Computer Aided Design (CAD) program.The CAD program can be downloaded from the Internet as freeware and is male ware free.
West Point Bridge Designer Link: http://bridgecontest.usma.edu/download.htm
A new bridge design with a span of 16m and no piers works very well to determine the rough shape of your bridge.
Faults of West Point Bridge Designer CAD program:
a) The competition loading harness does not fit through the sidewall of the bridge at the middle because of the placing of the joints in the CAD program at the level plane. That means you cannot use the design exactly as it is in the CAD program and have to adapt your design for the real bridge.
b)The software of the CAD program does not allow the structure to "sit" on supports beyond the abutments and the designer must make sure that at least 50mm of each side of the real structure is flat from the level plane downwards.
c)The bridge will only exhibit how it will perform if the truck used to represent a dynamic load on the CAD design is stopped in the middle of the bridge and the members in tension and compression are examined whilst there is a static force acting on the CAD design.
d)Double members in CAD can only be represented as members with double the material size thus a steel beam of 160mm must be changed to a steel beam of 320mm for the structure to behave realistically under test conditions.
Building tips
a) Glue and work slowly, carefully and according to a design.
b) The total wood that you will have to complete your bridge is 15000mm. In general each truss takes 7000mm and the cross bracing and extras take about 1000mm.
c) Use cross bracing and diagonal cross bracing to prevent the bridge from failing due to sideways movement.
d) Wood is strong in tension, weak in compression and even weaker in bending.
e) Transfer the load into the strengthened top compression member via tension members. The compression member must then transfer the load from the top centre of the structure away into the supports.
f) Mix the 2 halves of the epoxy resin in small and equal amounts as the glue gets it strength from a chemical reaction and dries quickly.
g) Use West Point Bridge designed to give you an idea of where the stress in your design occurs. Blue members are undergoing tension and red members compression. The darker the colour the more the stress.
h) Remember that wood under compression wants to buckle and snap and wood under tension wants to dislodge itself from its joint.
i) Use all your material but make sure you use it in the correct place.
j) Transference, dissipation and the material properties of the wood and glue must be intelligently applied not to focus the stress that the loading harness applies back into the bridge.
k) Oil on your hands cause glue failure.
l) Look at the photographs of previous winners and competition participants to get an idea of what good bridges look like.
m) Use clothing pegs or masking tape to hold the glued wood in place while drying.
n) Use Lions matches to mix and apply small dabs of glue to the wood.
o) Use cutting pliers to easily snip the wood.
p) Use A 4 typing paper to mix the epoxy resin glue on.
q) A Tape measure, calculator and a piece of string that is 6500 long will make measuring the length of the wood you have used in one truss easy.
r) Build your truss from the 1:1 cut and build template to make sure both trusses are exactly equal.
b) The total wood that you will have to complete your bridge is 15000mm. In general each truss takes 7000mm and the cross bracing and extras take about 1000mm.
c) Use cross bracing and diagonal cross bracing to prevent the bridge from failing due to sideways movement.
d) Wood is strong in tension, weak in compression and even weaker in bending.
e) Transfer the load into the strengthened top compression member via tension members. The compression member must then transfer the load from the top centre of the structure away into the supports.
f) Mix the 2 halves of the epoxy resin in small and equal amounts as the glue gets it strength from a chemical reaction and dries quickly.
g) Use West Point Bridge designed to give you an idea of where the stress in your design occurs. Blue members are undergoing tension and red members compression. The darker the colour the more the stress.
h) Remember that wood under compression wants to buckle and snap and wood under tension wants to dislodge itself from its joint.
i) Use all your material but make sure you use it in the correct place.
j) Transference, dissipation and the material properties of the wood and glue must be intelligently applied not to focus the stress that the loading harness applies back into the bridge.
k) Oil on your hands cause glue failure.
l) Look at the photographs of previous winners and competition participants to get an idea of what good bridges look like.
m) Use clothing pegs or masking tape to hold the glued wood in place while drying.
n) Use Lions matches to mix and apply small dabs of glue to the wood.
o) Use cutting pliers to easily snip the wood.
p) Use A 4 typing paper to mix the epoxy resin glue on.
q) A Tape measure, calculator and a piece of string that is 6500 long will make measuring the length of the wood you have used in one truss easy.
r) Build your truss from the 1:1 cut and build template to make sure both trusses are exactly equal.
Letter to Parents and Pupils
Dear Grade 8 Parent and Pupil
It is my pleasure to invite you and your child to the Annual Grade 8 Bridge Building Competition at Cornwall Hill School.
The event will be governed by the rules of the School of Civil Engineering's Bridge Building Competition at the University of the Witwatersrand and falls under the auspices of the South African Institute of Civil Engineers. The bridges are to be designed and built by father and child.
A - PURPOSE OF THE COMPETITION:
The competition will function on the following levels:
i) Social -
As a pupil and parent bonding exercise, please excuse the pun! I thought that the competition would be a good stimulus to team up dad and child in the form of a focused practical task to experience the joy of structural design. It will basically function as an alternate group work exercize.
ii) Academic -
For the pupil to learn about: applied structural theory; material properties of wood and epoxy glue; computer aided design; elementary project planning; interpretation of a complex brief; optimal use of material; presicion building by means of a cutting template.
iii) Scholastic-
The competition functions as the terms major project for each pupil in grade 8 and the attained mark for the bridge will form half of the term 3 CASS mark together with the standardised test. The mark for the competition will be awarded in two parts as follows:
Part A -
Pupils receive 50% before the bridge gets load tested if they have built the bridge to specification.
5% will be deducted for every specification not met.
and
Part B -
To make up the remaining 50% the bridge then gets load tested.
Each kilogram that the bridge holds will count for 1%.
Bridges that were not compliant with specifications will receive a 25%-75% deduction from the load that the bridge bears in accordance with the level of advantage gained by the non compliance. Adding extra wood and glue and building a shorter bridge makes the bridge unfairly strong on an exponential level and will receive the more severe % deductions on the load beared.
Bridges normally hold an average of 20kg - 30kg but can hold as much as 170kg for pupils that apply the theory correctly. It is therefore quite attainable to get a mark of 80% for a specification compliant bridge that bears a 30kg load.
iv) Competitive -
The competition also doubles up as the schools inter-house bridge building competition and as trials to select the six best bridge builders that will represent the school at the Regional Civil Engineering competition which takes place in “The Great Hall" at Wits in middle March 2010.
B - ORDER OF EVENTS:
i) Lessons, discussions and demonstrations - term 2
In the second term pupils are lectured on structural theory and shown demonstrations of an actual model bridge and loading harness as used in the competition. They are also shown Dvd's on structural design, talked through the bridge building brief and the frequently asked question section of the blog site is gone through in some detail.
ii) A dedicated blog site - all year
The competition blog site has been established to deal with any queries; update information; provide a gallery of helpful diagrams and photos; store essential competition documentation; and field frequently asked questions. All queries are addressed and suggestion on how to improve the competition are most welcome.
iii) Talk shop and information evening - 15 June 2009
After an initial period of immersement into the competition rules and structural theory participants are invited to an evening talk shop in the schools auditorium where any issues are addressed which might need clarification. For 2010 a guest lecturer is envisaged.
iv) Standardised test - 17 June 2009
The structural knowledge of the pupils are tested formally, amongst other work covered in the term in the terms standardised test.
v) Submission of West Point Bridge (Computer Aided) Design plan - 25 June 2009
Pupils experiment with various designs and attempt to build the cheapest bridge on West Point bridge designer(WPBD), a specialized software program for bridge design.
vi) Exam - 23 July 2009
The structural knowledge of the pupils are tested formally, amongst other work covered in the term in the school's end of term exam.
vii) Submission of the cut and build template on Technology day - 30 July 2009
Final approval of the cut and build template to receive wood (Normally in the week after exams)
Pupils are given the entire school day to use the basic shape of the WPBD program and adapt it to the specifications of the competitions bridge building brief.
They need to submit and have approved a 1:1 cutting template in order to receive their wood. The template ensures that the essential design elements of the bridge has been met in terms of the competition specifications and prevents heartaches on the day of the competition if any major parts of the brief has been misinterpreted. The pupils normally get it right on the thrid attempt.
viii) Comment report - 31 July 2009
The pupils are given a comment report that details their assessed state of readiness for the competition.
ix) Bridge building afternoon - 9 September 2009
Pupils bring their bridges to school and iron out any problems during the afternoon. (Compulsory for pupils who have not had their cutting templates approved but voluntary to pupils who have started building.)
x) Main event at the school pavilion - 3 October 2009 (Carnival day)
The bridges are finally tested. Parents are encouraged to take photos during the competition as there is normally not much left of the bridge after testing. Pupils must ensure that their own bridge is ready for testing and then test the bridge with the assisatnce of their dad sometime during the allocated time period. Participants need not attend the event start to finish but are required to be present for the testing demonstartion and medal ceremony.
Carnival programme - times and order of events (to be finalised)
* Registration and checking of basic compliance for specifications as per brief.
* Demonstration on how to use the loading apparatus and test the bridge to teams.
* Bridge testing commences by parent and pupil overseen by judges.
* Bronze medals awarded by the headmaster position 20 - 14
* Silver medals awarded by the headmatser for position 15 - 2
* Gold medal and permanent trophy awarded by the headmaster to the position 1.
* Inter-house winners with the highest load average are announced.
xi) Wits Civil Engineering Competition in the Wits Great Hall - Middle March 2010
The top six pupils designers receive new wood and glue and rebuild their bridge. On the day of the competition Mr Buys leaves at 11am by 22 school bus and the pupils have lunch at the University of Witwatersrand with the compliments of the school.
Pupils pre-enter their bridges in the hall and parents are invited to watch a usually very informative and entertaining Dr Luka, who heads the Universities' Civil Engineering Department, test the bridges with the help of the staff from the engineering department. The top 5 bridges are kept for closer inspection. Pupils can win cash prizes for the first 3 places which normally range from R1000 - R250. The competition normally finishes around 4pm.
xii) SAICE National Competition - Late to middle August 2010 (optional)
The designers may opt to attend this one day event where a single bridge is built by the group in one day. There rules are very similar to the schools competition but is strictly voluntary as the event is normally held over the Cornwall Hill holiday period and only done when the pupils feel that they would like yet another shot at being top dogs in the pin jointed truss community.
C - OTHER CLARIFICATIONS:
i) Tools -
The only essential tool that is needed is a pair of pliers to cut the wooden sticks with. There are also other aids such as clothing pegs and masking tape to hold the sticks in place while they dry; matches to mix and apply small dabs of glue and old newspaper to cover and protect the desk surface being worked on.
ii) The role of the parent -
The role of the parent is purely that of assistance and positive motivation during the design, building and testing of the bridge. Parents are not suddenly required to be engineers and, to build the bridge for their children, is not within the spirit of the competition. Some enthusiastic parents may choose to immerse themselves in the theory and building, but such behaviour is certainly not a requirement.
Parents can rest assured that pupils receive enough instruction and practical know how from the classes at school. Parents are to please understand that the intention of the project was to create an opportunity for parent and child to work together on something that is socially and acdemically rewarding and the intent is certainly not cause any friction or tension between parent, child and school.
iii) Problem solving and feedback -
Please feel free to submit any questions, concerns, suggestions and observations to Mr. Buys via the contact information below. All contributions are welcomed no matter how small or trivial they may seem.
Yours in Technology
Marius Buys
Cell: 076 800 698 83 ( Working hours)
Blog site - http://grade8bridgebuilding.blogspot.com/
E Mail - m.buys@cornwall.co.za (School term)
E Mail - mariusbuys@gmail.com (School holidays and weekends)
It is my pleasure to invite you and your child to the Annual Grade 8 Bridge Building Competition at Cornwall Hill School.
The event will be governed by the rules of the School of Civil Engineering's Bridge Building Competition at the University of the Witwatersrand and falls under the auspices of the South African Institute of Civil Engineers. The bridges are to be designed and built by father and child.
A - PURPOSE OF THE COMPETITION:
The competition will function on the following levels:
i) Social -
As a pupil and parent bonding exercise, please excuse the pun! I thought that the competition would be a good stimulus to team up dad and child in the form of a focused practical task to experience the joy of structural design. It will basically function as an alternate group work exercize.
ii) Academic -
For the pupil to learn about: applied structural theory; material properties of wood and epoxy glue; computer aided design; elementary project planning; interpretation of a complex brief; optimal use of material; presicion building by means of a cutting template.
iii) Scholastic-
The competition functions as the terms major project for each pupil in grade 8 and the attained mark for the bridge will form half of the term 3 CASS mark together with the standardised test. The mark for the competition will be awarded in two parts as follows:
Part A -
Pupils receive 50% before the bridge gets load tested if they have built the bridge to specification.
5% will be deducted for every specification not met.
and
Part B -
To make up the remaining 50% the bridge then gets load tested.
Each kilogram that the bridge holds will count for 1%.
Bridges that were not compliant with specifications will receive a 25%-75% deduction from the load that the bridge bears in accordance with the level of advantage gained by the non compliance. Adding extra wood and glue and building a shorter bridge makes the bridge unfairly strong on an exponential level and will receive the more severe % deductions on the load beared.
Bridges normally hold an average of 20kg - 30kg but can hold as much as 170kg for pupils that apply the theory correctly. It is therefore quite attainable to get a mark of 80% for a specification compliant bridge that bears a 30kg load.
iv) Competitive -
The competition also doubles up as the schools inter-house bridge building competition and as trials to select the six best bridge builders that will represent the school at the Regional Civil Engineering competition which takes place in “The Great Hall" at Wits in middle March 2010.
B - ORDER OF EVENTS:
i) Lessons, discussions and demonstrations - term 2
In the second term pupils are lectured on structural theory and shown demonstrations of an actual model bridge and loading harness as used in the competition. They are also shown Dvd's on structural design, talked through the bridge building brief and the frequently asked question section of the blog site is gone through in some detail.
ii) A dedicated blog site - all year
The competition blog site has been established to deal with any queries; update information; provide a gallery of helpful diagrams and photos; store essential competition documentation; and field frequently asked questions. All queries are addressed and suggestion on how to improve the competition are most welcome.
iii) Talk shop and information evening - 15 June 2009
After an initial period of immersement into the competition rules and structural theory participants are invited to an evening talk shop in the schools auditorium where any issues are addressed which might need clarification. For 2010 a guest lecturer is envisaged.
iv) Standardised test - 17 June 2009
The structural knowledge of the pupils are tested formally, amongst other work covered in the term in the terms standardised test.
v) Submission of West Point Bridge (Computer Aided) Design plan - 25 June 2009
Pupils experiment with various designs and attempt to build the cheapest bridge on West Point bridge designer(WPBD), a specialized software program for bridge design.
vi) Exam - 23 July 2009
The structural knowledge of the pupils are tested formally, amongst other work covered in the term in the school's end of term exam.
vii) Submission of the cut and build template on Technology day - 30 July 2009
Final approval of the cut and build template to receive wood (Normally in the week after exams)
Pupils are given the entire school day to use the basic shape of the WPBD program and adapt it to the specifications of the competitions bridge building brief.
They need to submit and have approved a 1:1 cutting template in order to receive their wood. The template ensures that the essential design elements of the bridge has been met in terms of the competition specifications and prevents heartaches on the day of the competition if any major parts of the brief has been misinterpreted. The pupils normally get it right on the thrid attempt.
viii) Comment report - 31 July 2009
The pupils are given a comment report that details their assessed state of readiness for the competition.
ix) Bridge building afternoon - 9 September 2009
Pupils bring their bridges to school and iron out any problems during the afternoon. (Compulsory for pupils who have not had their cutting templates approved but voluntary to pupils who have started building.)
x) Main event at the school pavilion - 3 October 2009 (Carnival day)
The bridges are finally tested. Parents are encouraged to take photos during the competition as there is normally not much left of the bridge after testing. Pupils must ensure that their own bridge is ready for testing and then test the bridge with the assisatnce of their dad sometime during the allocated time period. Participants need not attend the event start to finish but are required to be present for the testing demonstartion and medal ceremony.
Carnival programme - times and order of events (to be finalised)
* Registration and checking of basic compliance for specifications as per brief.
* Demonstration on how to use the loading apparatus and test the bridge to teams.
* Bridge testing commences by parent and pupil overseen by judges.
* Bronze medals awarded by the headmaster position 20 - 14
* Silver medals awarded by the headmatser for position 15 - 2
* Gold medal and permanent trophy awarded by the headmaster to the position 1.
* Inter-house winners with the highest load average are announced.
xi) Wits Civil Engineering Competition in the Wits Great Hall - Middle March 2010
The top six pupils designers receive new wood and glue and rebuild their bridge. On the day of the competition Mr Buys leaves at 11am by 22 school bus and the pupils have lunch at the University of Witwatersrand with the compliments of the school.
Pupils pre-enter their bridges in the hall and parents are invited to watch a usually very informative and entertaining Dr Luka, who heads the Universities' Civil Engineering Department, test the bridges with the help of the staff from the engineering department. The top 5 bridges are kept for closer inspection. Pupils can win cash prizes for the first 3 places which normally range from R1000 - R250. The competition normally finishes around 4pm.
xii) SAICE National Competition - Late to middle August 2010 (optional)
The designers may opt to attend this one day event where a single bridge is built by the group in one day. There rules are very similar to the schools competition but is strictly voluntary as the event is normally held over the Cornwall Hill holiday period and only done when the pupils feel that they would like yet another shot at being top dogs in the pin jointed truss community.
C - OTHER CLARIFICATIONS:
i) Tools -
The only essential tool that is needed is a pair of pliers to cut the wooden sticks with. There are also other aids such as clothing pegs and masking tape to hold the sticks in place while they dry; matches to mix and apply small dabs of glue and old newspaper to cover and protect the desk surface being worked on.
ii) The role of the parent -
The role of the parent is purely that of assistance and positive motivation during the design, building and testing of the bridge. Parents are not suddenly required to be engineers and, to build the bridge for their children, is not within the spirit of the competition. Some enthusiastic parents may choose to immerse themselves in the theory and building, but such behaviour is certainly not a requirement.
Parents can rest assured that pupils receive enough instruction and practical know how from the classes at school. Parents are to please understand that the intention of the project was to create an opportunity for parent and child to work together on something that is socially and acdemically rewarding and the intent is certainly not cause any friction or tension between parent, child and school.
iii) Problem solving and feedback -
Please feel free to submit any questions, concerns, suggestions and observations to Mr. Buys via the contact information below. All contributions are welcomed no matter how small or trivial they may seem.
Yours in Technology
Marius Buys
Cell: 076 800 698 83 ( Working hours)
Blog site - http://grade8bridgebuilding.blogspot.com/
E Mail - m.buys@cornwall.co.za (School term)
E Mail - mariusbuys@gmail.com (School holidays and weekends)
Making the cut and build template
Building it right the first time:
The cutting template is used to cut and join your wood with precision and ensures that the amount of wood received is used optimally to only a small amount of wood left after the completion of the bridge. Pupils normally get the cut and build template right after their second or third attempt.
Pupils who want to have their design approved first time round must be prepared to put in the required effort to combine the competition specifications, their CAD shape, basic structural theory of force transference and member reinforcement as well as the measurement of the trusses total length in mm to not exceed 6500mm - 6900mm.
Step by step:
1) Paste the 8 typing sheets together with Cello tape in two rows of four sheets by slightly overlapping each sheet with the other and taping the overlapped section on the back. Pritt can also be used.
2) Draw a horizontal line 210mm from the bottom edge of the template. This line will be known as the "level plane" and will indicate the imaginary line between the desktops.
3) Find the middle of the level plane line and mark it with a small cross. This will be the exact middle of your bridge.
4) Draw two vertical dotted lines 375mm left and right from the cross in the middle of the line on the level plane to indicate the actual total length of the bridge that needs to be built.(750mm long and resting on the desks.)
5) Indicate the area of where your bridge legs will sit on each desk with light cross hatching at the point of contact between desk and bridge. (This is done to know where to reinforce the 50mm area on each side of the bridge where the top compression member transfers the load into the desk "abutment")
6) Draw two vertical dotted lines to indicate the "gap" of 650mm of clear space that needs to be crossed between the desks. (This is to show the designer the area that may be used to reinforce the bottom section from the level plane downward as the loading harness exerts a bending force on the level plane and is similar to what a ravine would be for a real bridge.)
7) Draw a dotted line 80mm below the level plane. (To indicate the maximum depth that you may build below the level plane.)
8) Draw a dotted line 250mm above the level plane. (To indicate the maximum height you may build above the level plane.)
9) Draw in the two Drums (turned down D shapes) of the loading harness as indicated on the loading harness diagram. The two drums are 50mm wide, 50mm apart and 30mm high. The drums are drawn in to ensure that diagonal members do not obstruct the drums of the loading harness when crossing over the harness and that the harness will physically fit through the sidewall of the bridge.
10) Draw your bridge exactly as you plan to build it after Mr. Buys has discussed its shape with you. (Draw each member to its actual size i.e. 4mm) (Double or strengthened members must be drawn as double members separated by 10mm spacers every 50mm apart in between the double members. See the specification diagrams.)
11) Measure the length of the members in mm, it should not exceed 6500mm - 6900mm as you still need to leave wood to use as spacers for the double / reinforced members as well as wood for cross bracing and diagonal cross bracing between the trusses.
12) Check that you have reinforced the top compression members; the level plane and the area directly below where the loading harness fits.
13) Ask Mr Buys to check your cutting template for obvious and key mistakes with regards to shape and design. He will approve your design to in terms of some basic things such as the length of the structure (750mm), that the structure will sit flat on the testing desks, that the height above the level plane does not exceed 250mm, that you have drawn the members to their actual with of 4mm, that the distance below the level plane does not exceed 85mm, that the top compression member is reinforced all the way to the desk abutment, that you have physically measured the total length of wood used for one truss and that it does not exceed 6500mm - 6900mm.
14) After your template has been approved you may use your approved template to receive your wood for the competition from Mr. Buys who will sign it off on your template.
The cutting template is used to cut and join your wood with precision and ensures that the amount of wood received is used optimally to only a small amount of wood left after the completion of the bridge. Pupils normally get the cut and build template right after their second or third attempt.
Pupils who want to have their design approved first time round must be prepared to put in the required effort to combine the competition specifications, their CAD shape, basic structural theory of force transference and member reinforcement as well as the measurement of the trusses total length in mm to not exceed 6500mm - 6900mm.
Step by step:
1) Paste the 8 typing sheets together with Cello tape in two rows of four sheets by slightly overlapping each sheet with the other and taping the overlapped section on the back. Pritt can also be used.
2) Draw a horizontal line 210mm from the bottom edge of the template. This line will be known as the "level plane" and will indicate the imaginary line between the desktops.
3) Find the middle of the level plane line and mark it with a small cross. This will be the exact middle of your bridge.
4) Draw two vertical dotted lines 375mm left and right from the cross in the middle of the line on the level plane to indicate the actual total length of the bridge that needs to be built.(750mm long and resting on the desks.)
5) Indicate the area of where your bridge legs will sit on each desk with light cross hatching at the point of contact between desk and bridge. (This is done to know where to reinforce the 50mm area on each side of the bridge where the top compression member transfers the load into the desk "abutment")
6) Draw two vertical dotted lines to indicate the "gap" of 650mm of clear space that needs to be crossed between the desks. (This is to show the designer the area that may be used to reinforce the bottom section from the level plane downward as the loading harness exerts a bending force on the level plane and is similar to what a ravine would be for a real bridge.)
7) Draw a dotted line 80mm below the level plane. (To indicate the maximum depth that you may build below the level plane.)
8) Draw a dotted line 250mm above the level plane. (To indicate the maximum height you may build above the level plane.)
9) Draw in the two Drums (turned down D shapes) of the loading harness as indicated on the loading harness diagram. The two drums are 50mm wide, 50mm apart and 30mm high. The drums are drawn in to ensure that diagonal members do not obstruct the drums of the loading harness when crossing over the harness and that the harness will physically fit through the sidewall of the bridge.
10) Draw your bridge exactly as you plan to build it after Mr. Buys has discussed its shape with you. (Draw each member to its actual size i.e. 4mm) (Double or strengthened members must be drawn as double members separated by 10mm spacers every 50mm apart in between the double members. See the specification diagrams.)
11) Measure the length of the members in mm, it should not exceed 6500mm - 6900mm as you still need to leave wood to use as spacers for the double / reinforced members as well as wood for cross bracing and diagonal cross bracing between the trusses.
12) Check that you have reinforced the top compression members; the level plane and the area directly below where the loading harness fits.
13) Ask Mr Buys to check your cutting template for obvious and key mistakes with regards to shape and design. He will approve your design to in terms of some basic things such as the length of the structure (750mm), that the structure will sit flat on the testing desks, that the height above the level plane does not exceed 250mm, that you have drawn the members to their actual with of 4mm, that the distance below the level plane does not exceed 85mm, that the top compression member is reinforced all the way to the desk abutment, that you have physically measured the total length of wood used for one truss and that it does not exceed 6500mm - 6900mm.
14) After your template has been approved you may use your approved template to receive your wood for the competition from Mr. Buys who will sign it off on your template.
Gallery 1 - Joining and strengthening members
DIAGRAM A: A STRENGTHENED MEMBER
DIAGRAM B: A SPLICE JOINT
DIAGRAM C1: A BUTT JOINT (weak and not recommended if not reinforced)
DIAGRAM C2: A STRENGTHENED BUTT JOINT
DIAGRAM D: OVERLAPPING MEMBERS
DIAGRAM E: BUILDING UP COMPRESSION MEMBERS
The design brief
Brief:
Design and build a pin jointed truss structure, IE: bridge with 25 units of 4mm x 4mm x 600mm Pine sticks and Pratley Quickset Clear Epoxy Resin to take maximum load applied from a loading harness that is fitted in the middle of the bridge. The structure must comply with the supplied specifications, constraints and specification diagrams.
Specifications:
a) The bridge must be 750mm long with 50mm of each side of the bridge sitting on the support/table.See figure 2
b) The loading harness must fit the bridge and allow the apparatus to pass through the sidewall of the bridge on the level plane. See figure 1a and 1b, 2 and 3.
c) The bridge must be between 70mm and 135mm wide.See figure 3.
Constraints (limitations):
d) The height of the top truss may not be higher than 250mm from the line of where the bridge feet touch the supports that the bridge rests on. In this case two school desks.See figure 2.
e) The depth of the bottom truss may not be deeper than 80mm from the line of where the bridge feet touch the supports that the bridge rests on to allow the loading harness to fit through the wall of the bridge.See figure 2.
f) No members may be laminated together for their full length. The only allowable lamination is for a maximum of 10mm long with a distance of at least 50mm clear space before the start of the next cross member spacer.See figure 5.
g) Bracing against the desk supports is not allowed.See figure 4.
h) Glue fillets against the outside of a joint may not exceed 1.8 mm in height and width.See figure 6.
i) No continuous lamination of wood may be used. That means you may not just glue two sticks together in their length.
j) Glue fillets must not be larger than 1.8mm in size.
k) You may use only the supplied 25 sticks.
l) You may only use one set of Pritley Pratley quickset clear epoxy resin glue tubes.
Design and build a pin jointed truss structure, IE: bridge with 25 units of 4mm x 4mm x 600mm Pine sticks and Pratley Quickset Clear Epoxy Resin to take maximum load applied from a loading harness that is fitted in the middle of the bridge. The structure must comply with the supplied specifications, constraints and specification diagrams.
Specifications:
a) The bridge must be 750mm long with 50mm of each side of the bridge sitting on the support/table.See figure 2
b) The loading harness must fit the bridge and allow the apparatus to pass through the sidewall of the bridge on the level plane. See figure 1a and 1b, 2 and 3.
c) The bridge must be between 70mm and 135mm wide.See figure 3.
Constraints (limitations):
d) The height of the top truss may not be higher than 250mm from the line of where the bridge feet touch the supports that the bridge rests on. In this case two school desks.See figure 2.
e) The depth of the bottom truss may not be deeper than 80mm from the line of where the bridge feet touch the supports that the bridge rests on to allow the loading harness to fit through the wall of the bridge.See figure 2.
f) No members may be laminated together for their full length. The only allowable lamination is for a maximum of 10mm long with a distance of at least 50mm clear space before the start of the next cross member spacer.See figure 5.
g) Bracing against the desk supports is not allowed.See figure 4.
h) Glue fillets against the outside of a joint may not exceed 1.8 mm in height and width.See figure 6.
i) No continuous lamination of wood may be used. That means you may not just glue two sticks together in their length.
j) Glue fillets must not be larger than 1.8mm in size.
k) You may use only the supplied 25 sticks.
l) You may only use one set of Pritley Pratley quickset clear epoxy resin glue tubes.
Gallery 2 - A winning bridge
Front view: (load tested at 170kg - unbroken)
.jpg)
Top compression member:
.jpg)
Left side view:
.jpg)
Top compression member joint:
.jpg)
Loading device area:
.jpg)
Top compression member:Left side view:.jpg)
Top compression member joint:.jpg)
Loading device area:.jpg)
Abutment area:
Contact us
Mr. MARIUS BUYS:
Cellular: 076-800-6983
E Mail: m.buys@cornwall.co.za (School term)
E Mail: mariusbuys@gmail.com (Holidays and weekends)
Cellular: 076-800-6983
E Mail: m.buys@cornwall.co.za (School term)
E Mail: mariusbuys@gmail.com (Holidays and weekends)
Frequently asked questions
Please check back every now and then to see if the answer to any more questions have been added.
1) When is the date of the competition?
We would probably have the event early in the 3rd term, it looks like it will be Carnival day, to allow boarders and busy parents to do some work with their children. The dates have been inserted into the letter to parents and pupils.
2) Can I use winning designs from previous years?
Yes
3) Can I use outside help such as advice from a actual civil engineer with the design of my bridge?
Yes
4) May any other person except me and my parent build the bridge?
No
5) I do not like the material handed to me, may I ask a carpenter to cut my own material form A grade pine? (twenty five sticks of 4mm x 4mm x 600mm)
Yes
6) Does the project count for marks?
Yes
7) I cannot get my Westpoint bridge designer to work on my computer. Is it absolutely neccesary to do the design for the shape of my bridge on Westpoint?
No
8) Will I loose marks if I do not use Westpoint Bridge Designer?
No
9) Approximately how many hours do I have to set aside for the making of my bridge?
About 30 hours of work in total.
10) What safety gear will I use when I test my bridge?
Safety Glasses, some form of protection to prevent the glue from damaging furniture and clothing. The glue cannot be removed once it has touched another surface.
11) Do I keep my trophy/medal if I win?
Yes, you keep it permanently.
12) Can I use extra wood or glue on my bridge?
No
13) Can I use another type of glue or wood?
No
14) Can I build more than one bridge?
Yes, but I only provide material for one, if you want more material you would need to pay for it.
15) Where do I buy the Pritley Pratley Quickset Clear - Epoxy Resin?
Any hardware shop at about R30
16) Where can you buy extra wood?
The wood for the competition is very hard to get hold of. You will have to find a friendly carpenter to cut the wood for you from A Grade SA Pine, or so called clear Pine. Expect to be charged in the region of R180 (The school supplies it at R30)
17) May I use a partner from school?
No
18) May I ask other teachers and specialists such as architects and civil engineers for help?
Yes
19) What happens if my PC at home does not have Westpoint bridge designer or I have no internet?
The computers in the Media / Library resource centre have been loaded with Westpoint. You can work at break or after school.
20) Will there be a lecture to explain some basics to our parents?
Yes
21) When and where will the parent lecture / talkshop take place?
Monday evening the 15th of June, in the school hall from 17h00 - 18h00 and both parent and student may attend. Attendance is not compulsory but strongly advised.
22) How do I calculate what length of wood to use for 1 truss?
a) You are provided with 15000 mm of wood which comes in lengths of 600mm at a time.
b) You have to leave wood for diagonal cross bracing, supports, cross bracing between the 2 trusses.
c) Because there are 2 trusses, in most cases, you would need about 6000mm - 7000mm for each truss.
d) Therefore you will probably use about 10 sticks for each truss.
e) You count the actual length of wood you will use for your truss by measuring it off your first 1:1 design template.
23) Where can I see examples of good /winning bridges?Photos will be posted to the Blogsite gallery.
24) How will my bridge be tested to make sure I have used the legal amount of wood and glue?
The bridge will be weighed on the day of the competition.
25) Whats the distance from desk to desk that my bridge has to cover?
The "gap" is 650mm the actual required length is 750mm.26) How many sticks do we get?You get twenty five (25) sticks that are 600mm long.
27) Will I be given the epoxy glue or will I have to buy it myself?
No, you must buy the epoxy glue yourself.
28) Can I check to see if the loading harness fits my bridge before the competition?
Yes
29) What tools will I need to make the bridge?
All the tools you need are listed in the project overview
a) Plastic clothing pegs to hold the glued wood in place while drying.
b) Lions matches to mix and apply small dabs of glue to the wood.
c) Cutting pliers to easily snip the wood.
d) A 4 typing paper to mix the epoxy resin glue on.
e) Tape measure and calculator
f) Surgical gloves to avoid the oil from your hands soaking into the wood. (optional)
30) Does the loading harness have to fit into my bridge in a specific place?
Yes, the loading harness must fit through the side of your bridge in the middle of your bridge.NB! It must also be more or less on the level plane which runs at desk level.
31) Can I ask Mr. Buys to buy the glue for me and give him the cash?
Yes, but only if you have tried to buy it yourself first.
32) How many other schools compete in the regional final?
About 25 other schools which include entries from grade 11 and matric pupils from St Stithians College, KES, Roedean School, St John's College, St David's Marist Inanda.
33) What happens if one of my sticks break?
You use the stick for the shorter parts / members of the truss.
34) How will the final weight that the bridge can hold be recorded?T
he weight that the bridge held before it broke will be the weight that will be taken as the final weight.
35) Will the weight of the loading harness be added to the final weight?
Yes, but Mr. Buys will add it after the competition to avoid counting the weight from the loading harness twice. Thus you will record and hand in ONLY the weight that was loaded ONTO the harness.
36) What happens if my bridge accidentally breaks on the day of testing before it has been tested?
Mr. Buys will award an approximate weight that he thinks the bridge would have held.
37) What happens if my bridge broke and I do not agree with the weight that Mr. Buys estimates my bridge would have held?
You will be given 2 days to fix your bridge and it will be tested in the normal way. You have to make sure that Mr. buys tests your bridge as after 2 days all results will stand as they are with no exeptions.
38) Can I take pictures of the sample bridge?
Yes
39) Can I take the sample bridge home?
No
40) If I have fixed my broken bridge and my weight tests out lower than Mr. Buys's estimation, can I get the weight of the estimation?
Yes, because the wood would have been fatigued by the break and will not perform in the original intended manner.
41) May I take part in the competition at school even if I am not in grade 8?
Yes, you will just be required to pay for a bundle of wood and we would need to order an extra medal for you if you place in the top finishers. You may then also go on to take part in the prestige group which represents the school at the University of Witwatersrands Civil Engineering competition the following term.
42) What happens if my bridge is not built to specifications?
a) If your bridge has too much material or incorrect dimensions you will suffer a 25% - 75% deduction on the weight it can hold as shortening the bridge or using extra wood or glue exponentially increases its loading capacity.
b) Your 50% for building the bridge will be deducted by 5% for every specification it cannot hold.
43) What happens if the loading harness does not fit my bridge on the day of testing?
You will be asked to remove parts of your bridge to enable the harness to fit. If the harness then cannot fit Mr. Buys will make an estimation of what your bridge would probably have held subject to the same rules as if your bridge accidentally broke on testing day.
44) What happens if I am sick on the testing day?
You have the option of sending someone to test the bridge for you or you can test it at school when you are better. If you are in the medal group we will order an extra medal for you.
45) Do I test the bridge alone?
No, you test it with your parent.
46) Will the testing happen on the school stage?
No, because of the spring effect of the stage boards sending a so called L-shock wave / pulse through someones feet when they walk on the stage which travels into your bridge though the tables legs. The wave/pulse bounces the bridge up and down which has the same effect of a person jumping up and down on a plank of wood that is leaning against a rock at an angle.
47) What is the best way to put the weights onto the harness?
a) Do not let the harness swing at all.
b) Do not "slam" or drop the weight onto the harness, not even for 1mm.
c) Use bigger weights in the beginning and smaller weights towards the end.
d) Make sure the stem of the weight harness sits in the middle of the peg at the bottom of the loading harness.
e) Make sure that your bridge sits evenly on each side of the desk.
f) make sure that the harness is positioned in the middle of your bridge both in lateral and longitidue positioning.
48) Will we work in pairs like previous years, and if not, why?
No, the objective of the project is different and the learning experience is set out is in the letter to the parents.
49) Do we get the wood through the school?
Yes
50) Where do we build the bridge?We start at school with demonstartions but the bridge is largely built at home.
51) How much do we pay for the wood, and how is the payment made?
An amount of about R35 will be added to your school fee account for the wood.
52) If I break a stick in half does it count as one or two sticks?
You may cut up the 25 sticks of 600mm long as many times as you want.
53) When I test my bridge, and one stick breaks, do I have to stop testing or can I carry on if I want to?
You do not have to stop if your bridge is still holding the weights in the air. Your final weight will be taken as the weight that was held by your bridge before it breaks.
54) Where will my bridge be tested?
On the floor area of the school hall.
55) Why are we doing this project?
To learn about structures, material properties of epoxy resin and wood and to work with your parent in a testing/difficult situation that requires you and your parent to cooperate.
56) What if I never plan on becoming an engineer?
You will still be able to use the theory in much more ways than what an engineer would use the theory for and the theory is prescribed in your Technology syllabus.
57) How do I get marked for my bridge?Y
ou get 50% for just building the bridge and then you add 1% for every 1kg. your bridge holds.There are however some deductions if your bridge is not built correctly:
a) 5% deducted from your original 50% for every specification not met.
b) 25% -75% deducted from the weight your bridge holds if the bridge was not built to specifications.
58) What happens if my bridge holds 60kg and is built to specifications without any deductions?
50% plus 60% will equal 110% but you can only get a maximum of 100% for the project. Your reward for achieving a higher weight will be awarded a higher placing in the top 20 medals.
59) Can I keep my bridge if it survives?
Yes
60) How much will this project count for my term mark?
50% for term 2 and 50% for term 3
61) Do I have to pay for the wood if I am a bursary student?
No, the school pays for bursary students. You will however have to tell Mr. Buys that if you are.
62) Can I spraypaint or decorate my bridge?
No, the paint and decorations adds extra strength and also throws off the weight calibration.
63) How much must the bridge weigh?
That information is not revealed.
64) Do I need to steam the wood to bend the members?
Yes, but be carefull as pre-bending a member pre-stresses your bridge member as well. If you are not exactly sure of what you are doing you can end up making the bridge much weaker rather than stronger.
65) Do I loose any marks if my bridge breaks?
No, the idea is to test it to just before it breaks or untill it breaks. The focus is on building a design that is strong and the bridge would need to fail for you to know its strength.
66) Whats the highest one of these bridges have held?
In 2009 Mr. Buys's top students at his previous school attained 156kg, 143kg and 137kg. Enough to place first, second and third at the Wits Civil Engineering Competition.
67) What are the common mistakes that students make with regards to specifications?
They use too much wood and glue, make their fillets too big and build their bridge too short.
68) If the sticks are shorter than the length that the bridge should be, how do I get the bridge to be longer?
You may join the sticks with inserts which are 50mm apart.
69) Does my bridge have to look like my template?
Yes
70) What is the most important part of the bridge?
The top compression member which is allways a strengthened/double member
71) May I use a Butt joint to join members together?
Yes, but I would reccommend that you use a Lap joint or Splice joint before you use a Butt joint as they are much stronger.
72) How do I find out about joints?
Internet research.
73) Is there any other way to make sure that a joint is strong?
Yes, by overlapping the joint with other sticks or inserting small pieces of wood to act as gusset plates.
74) Approximately how much glue do I use for 1 single joint of wood?
The size of two match stick heads.
75) Must there be a clear space "inside" the length of my bridge as if a car would drive through the bridge?
No, you must use the space in the middle.
a) It is vital that you put in diagonal cross bracing to prevent the bridge from becoming a parralelogram. Remember that these structures are actually called "Pin jointed truss structures" and that the word bridge is not an accurate description of what you are building.
b) The bridge is also not tested / loaded with a dynamic force. (A force that moves from the one end of the bridge to the other end)
c) The way that the bridge is tested is with a static force through the use of a loading harness.
76) What do I do if my dad is unable to help me?
You may ask any other member of your family. It would however be unfortunate as working with your dad is part of the goal of the competition. Please inform your dad that Mr. Buys would very much like him to be involved and that he should read the letter to the parent and pupil on the website.
77) Can I use cellotape or duct tape on my bridge?
Only during construction to keep members/pieces in place. When you test the bridge the bridge may ONLY consist of the allocated wood and glue.
78) The gap is only 650mm why do I have to build my bridge 750mm long?
Valid question with a simple answer, because its the rule of the competition. You bridge is in effect stronger if you build it to 700mm and nothing stops you from building the bridge to 700mm and cosmetically extending the length of the bridge to 750mm on each side with a single 25mm member to come in under the competition specificastions.In life there is often a compromise between what is the optimum and what is the specification requirement. In this case the optimum is not to build the bridge to the specified length as the longer your bridge is the more your top compression members undergo a bending force. The purpose of the competition, however is for the bridge to carry the most load whilst still being built to specification. The trick is thus to comply with both requirements with the focus on the strength of the bridge.
79) If I have a double member can I fit another member into or running through the required clear space of the 50mm between the spacers?
Yes
1) When is the date of the competition?
We would probably have the event early in the 3rd term, it looks like it will be Carnival day, to allow boarders and busy parents to do some work with their children. The dates have been inserted into the letter to parents and pupils.
2) Can I use winning designs from previous years?
Yes
3) Can I use outside help such as advice from a actual civil engineer with the design of my bridge?
Yes
4) May any other person except me and my parent build the bridge?
No
5) I do not like the material handed to me, may I ask a carpenter to cut my own material form A grade pine? (twenty five sticks of 4mm x 4mm x 600mm)
Yes
6) Does the project count for marks?
Yes
7) I cannot get my Westpoint bridge designer to work on my computer. Is it absolutely neccesary to do the design for the shape of my bridge on Westpoint?
No
8) Will I loose marks if I do not use Westpoint Bridge Designer?
No
9) Approximately how many hours do I have to set aside for the making of my bridge?
About 30 hours of work in total.
10) What safety gear will I use when I test my bridge?
Safety Glasses, some form of protection to prevent the glue from damaging furniture and clothing. The glue cannot be removed once it has touched another surface.
11) Do I keep my trophy/medal if I win?
Yes, you keep it permanently.
12) Can I use extra wood or glue on my bridge?
No
13) Can I use another type of glue or wood?
No
14) Can I build more than one bridge?
Yes, but I only provide material for one, if you want more material you would need to pay for it.
15) Where do I buy the Pritley Pratley Quickset Clear - Epoxy Resin?
Any hardware shop at about R30
16) Where can you buy extra wood?
The wood for the competition is very hard to get hold of. You will have to find a friendly carpenter to cut the wood for you from A Grade SA Pine, or so called clear Pine. Expect to be charged in the region of R180 (The school supplies it at R30)
17) May I use a partner from school?
No
18) May I ask other teachers and specialists such as architects and civil engineers for help?
Yes
19) What happens if my PC at home does not have Westpoint bridge designer or I have no internet?
The computers in the Media / Library resource centre have been loaded with Westpoint. You can work at break or after school.
20) Will there be a lecture to explain some basics to our parents?
Yes
21) When and where will the parent lecture / talkshop take place?
Monday evening the 15th of June, in the school hall from 17h00 - 18h00 and both parent and student may attend. Attendance is not compulsory but strongly advised.
22) How do I calculate what length of wood to use for 1 truss?
a) You are provided with 15000 mm of wood which comes in lengths of 600mm at a time.
b) You have to leave wood for diagonal cross bracing, supports, cross bracing between the 2 trusses.
c) Because there are 2 trusses, in most cases, you would need about 6000mm - 7000mm for each truss.
d) Therefore you will probably use about 10 sticks for each truss.
e) You count the actual length of wood you will use for your truss by measuring it off your first 1:1 design template.
23) Where can I see examples of good /winning bridges?Photos will be posted to the Blogsite gallery.
24) How will my bridge be tested to make sure I have used the legal amount of wood and glue?
The bridge will be weighed on the day of the competition.
25) Whats the distance from desk to desk that my bridge has to cover?
The "gap" is 650mm the actual required length is 750mm.26) How many sticks do we get?You get twenty five (25) sticks that are 600mm long.
27) Will I be given the epoxy glue or will I have to buy it myself?
No, you must buy the epoxy glue yourself.
28) Can I check to see if the loading harness fits my bridge before the competition?
Yes
29) What tools will I need to make the bridge?
All the tools you need are listed in the project overview
a) Plastic clothing pegs to hold the glued wood in place while drying.
b) Lions matches to mix and apply small dabs of glue to the wood.
c) Cutting pliers to easily snip the wood.
d) A 4 typing paper to mix the epoxy resin glue on.
e) Tape measure and calculator
f) Surgical gloves to avoid the oil from your hands soaking into the wood. (optional)
30) Does the loading harness have to fit into my bridge in a specific place?
Yes, the loading harness must fit through the side of your bridge in the middle of your bridge.NB! It must also be more or less on the level plane which runs at desk level.
31) Can I ask Mr. Buys to buy the glue for me and give him the cash?
Yes, but only if you have tried to buy it yourself first.
32) How many other schools compete in the regional final?
About 25 other schools which include entries from grade 11 and matric pupils from St Stithians College, KES, Roedean School, St John's College, St David's Marist Inanda.
33) What happens if one of my sticks break?
You use the stick for the shorter parts / members of the truss.
34) How will the final weight that the bridge can hold be recorded?T
he weight that the bridge held before it broke will be the weight that will be taken as the final weight.
35) Will the weight of the loading harness be added to the final weight?
Yes, but Mr. Buys will add it after the competition to avoid counting the weight from the loading harness twice. Thus you will record and hand in ONLY the weight that was loaded ONTO the harness.
36) What happens if my bridge accidentally breaks on the day of testing before it has been tested?
Mr. Buys will award an approximate weight that he thinks the bridge would have held.
37) What happens if my bridge broke and I do not agree with the weight that Mr. Buys estimates my bridge would have held?
You will be given 2 days to fix your bridge and it will be tested in the normal way. You have to make sure that Mr. buys tests your bridge as after 2 days all results will stand as they are with no exeptions.
38) Can I take pictures of the sample bridge?
Yes
39) Can I take the sample bridge home?
No
40) If I have fixed my broken bridge and my weight tests out lower than Mr. Buys's estimation, can I get the weight of the estimation?
Yes, because the wood would have been fatigued by the break and will not perform in the original intended manner.
41) May I take part in the competition at school even if I am not in grade 8?
Yes, you will just be required to pay for a bundle of wood and we would need to order an extra medal for you if you place in the top finishers. You may then also go on to take part in the prestige group which represents the school at the University of Witwatersrands Civil Engineering competition the following term.
42) What happens if my bridge is not built to specifications?
a) If your bridge has too much material or incorrect dimensions you will suffer a 25% - 75% deduction on the weight it can hold as shortening the bridge or using extra wood or glue exponentially increases its loading capacity.
b) Your 50% for building the bridge will be deducted by 5% for every specification it cannot hold.
43) What happens if the loading harness does not fit my bridge on the day of testing?
You will be asked to remove parts of your bridge to enable the harness to fit. If the harness then cannot fit Mr. Buys will make an estimation of what your bridge would probably have held subject to the same rules as if your bridge accidentally broke on testing day.
44) What happens if I am sick on the testing day?
You have the option of sending someone to test the bridge for you or you can test it at school when you are better. If you are in the medal group we will order an extra medal for you.
45) Do I test the bridge alone?
No, you test it with your parent.
46) Will the testing happen on the school stage?
No, because of the spring effect of the stage boards sending a so called L-shock wave / pulse through someones feet when they walk on the stage which travels into your bridge though the tables legs. The wave/pulse bounces the bridge up and down which has the same effect of a person jumping up and down on a plank of wood that is leaning against a rock at an angle.
47) What is the best way to put the weights onto the harness?
a) Do not let the harness swing at all.
b) Do not "slam" or drop the weight onto the harness, not even for 1mm.
c) Use bigger weights in the beginning and smaller weights towards the end.
d) Make sure the stem of the weight harness sits in the middle of the peg at the bottom of the loading harness.
e) Make sure that your bridge sits evenly on each side of the desk.
f) make sure that the harness is positioned in the middle of your bridge both in lateral and longitidue positioning.
48) Will we work in pairs like previous years, and if not, why?
No, the objective of the project is different and the learning experience is set out is in the letter to the parents.
49) Do we get the wood through the school?
Yes
50) Where do we build the bridge?We start at school with demonstartions but the bridge is largely built at home.
51) How much do we pay for the wood, and how is the payment made?
An amount of about R35 will be added to your school fee account for the wood.
52) If I break a stick in half does it count as one or two sticks?
You may cut up the 25 sticks of 600mm long as many times as you want.
53) When I test my bridge, and one stick breaks, do I have to stop testing or can I carry on if I want to?
You do not have to stop if your bridge is still holding the weights in the air. Your final weight will be taken as the weight that was held by your bridge before it breaks.
54) Where will my bridge be tested?
On the floor area of the school hall.
55) Why are we doing this project?
To learn about structures, material properties of epoxy resin and wood and to work with your parent in a testing/difficult situation that requires you and your parent to cooperate.
56) What if I never plan on becoming an engineer?
You will still be able to use the theory in much more ways than what an engineer would use the theory for and the theory is prescribed in your Technology syllabus.
57) How do I get marked for my bridge?Y
ou get 50% for just building the bridge and then you add 1% for every 1kg. your bridge holds.There are however some deductions if your bridge is not built correctly:
a) 5% deducted from your original 50% for every specification not met.
b) 25% -75% deducted from the weight your bridge holds if the bridge was not built to specifications.
58) What happens if my bridge holds 60kg and is built to specifications without any deductions?
50% plus 60% will equal 110% but you can only get a maximum of 100% for the project. Your reward for achieving a higher weight will be awarded a higher placing in the top 20 medals.
59) Can I keep my bridge if it survives?
Yes
60) How much will this project count for my term mark?
50% for term 2 and 50% for term 3
61) Do I have to pay for the wood if I am a bursary student?
No, the school pays for bursary students. You will however have to tell Mr. Buys that if you are.
62) Can I spraypaint or decorate my bridge?
No, the paint and decorations adds extra strength and also throws off the weight calibration.
63) How much must the bridge weigh?
That information is not revealed.
64) Do I need to steam the wood to bend the members?
Yes, but be carefull as pre-bending a member pre-stresses your bridge member as well. If you are not exactly sure of what you are doing you can end up making the bridge much weaker rather than stronger.
65) Do I loose any marks if my bridge breaks?
No, the idea is to test it to just before it breaks or untill it breaks. The focus is on building a design that is strong and the bridge would need to fail for you to know its strength.
66) Whats the highest one of these bridges have held?
In 2009 Mr. Buys's top students at his previous school attained 156kg, 143kg and 137kg. Enough to place first, second and third at the Wits Civil Engineering Competition.
67) What are the common mistakes that students make with regards to specifications?
They use too much wood and glue, make their fillets too big and build their bridge too short.
68) If the sticks are shorter than the length that the bridge should be, how do I get the bridge to be longer?
You may join the sticks with inserts which are 50mm apart.
69) Does my bridge have to look like my template?
Yes
70) What is the most important part of the bridge?
The top compression member which is allways a strengthened/double member
71) May I use a Butt joint to join members together?
Yes, but I would reccommend that you use a Lap joint or Splice joint before you use a Butt joint as they are much stronger.
72) How do I find out about joints?
Internet research.
73) Is there any other way to make sure that a joint is strong?
Yes, by overlapping the joint with other sticks or inserting small pieces of wood to act as gusset plates.
74) Approximately how much glue do I use for 1 single joint of wood?
The size of two match stick heads.
75) Must there be a clear space "inside" the length of my bridge as if a car would drive through the bridge?
No, you must use the space in the middle.
a) It is vital that you put in diagonal cross bracing to prevent the bridge from becoming a parralelogram. Remember that these structures are actually called "Pin jointed truss structures" and that the word bridge is not an accurate description of what you are building.
b) The bridge is also not tested / loaded with a dynamic force. (A force that moves from the one end of the bridge to the other end)
c) The way that the bridge is tested is with a static force through the use of a loading harness.
76) What do I do if my dad is unable to help me?
You may ask any other member of your family. It would however be unfortunate as working with your dad is part of the goal of the competition. Please inform your dad that Mr. Buys would very much like him to be involved and that he should read the letter to the parent and pupil on the website.
77) Can I use cellotape or duct tape on my bridge?
Only during construction to keep members/pieces in place. When you test the bridge the bridge may ONLY consist of the allocated wood and glue.
78) The gap is only 650mm why do I have to build my bridge 750mm long?
Valid question with a simple answer, because its the rule of the competition. You bridge is in effect stronger if you build it to 700mm and nothing stops you from building the bridge to 700mm and cosmetically extending the length of the bridge to 750mm on each side with a single 25mm member to come in under the competition specificastions.In life there is often a compromise between what is the optimum and what is the specification requirement. In this case the optimum is not to build the bridge to the specified length as the longer your bridge is the more your top compression members undergo a bending force. The purpose of the competition, however is for the bridge to carry the most load whilst still being built to specification. The trick is thus to comply with both requirements with the focus on the strength of the bridge.
79) If I have a double member can I fit another member into or running through the required clear space of the 50mm between the spacers?
Yes
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