Bridge Building
2008 Bridge Building Contest FAQ
Each year, there are questions about the bridge specifications or the contest. Take a look at the following questions and answers, you might find your answer here. If you don't please don't hesitate to email us.

Q:
While I am waiting for my son to work through his school coordinator, I wanted to get some background work done. I have a few questions about the 2008 official wood kit. I assume that students will be building multiple versions for testing and development of their designs. Are the specifications of the official kit easy to duplicate? Or, will students be expecting multiple kits? I know that with the balsa, there were several grades available which made a difference in bridge performance. Are there grades or specifications beyond dimensions that are important to basswood? In rule 1b, how will the official basswood be identified? In past contests, the photos indicate many curved beams were used. How is this geometry achieved? Thanks for a hint.
A:
The official wood kit for the international contest contains enough bass wood to build two bridges. A student may build additional bridges with any wood, but the bridge entered in the contest must be made of official wood. The supplier of bass wood that we use distributes to many hobby shops across the nation. Bass wood comes in only one grade. This was a major factor in choosing it as the official wood for the contest. The official wood is treated with a special phosphorescent dye. All bridge are checked for the presence of this dye during the check in process. Wood may be bend by soaking it in water, bending it to the desired shape, and holding it in this shape until it dries.
Q:
Just want to confirm the UBolt size, since the one’s I bought look slightly different than your picture, even though it’s the same UPC code. UBolt for 3” pipe, approx 3.8” diameter at curve. Threaded ends 3.8” to 4” apart.
A:
The U-bolt is for a 3 inch diameter pipe. Here is other information I have gathered about it. Manufacturer: Crown Bolts Inc. Description: #334 U-bolt for 3" pipe ZP (zinc plated) Part Number: 09556 SKU: 118-128 Department: 25 Class: 3 Subclass: 2 Since the voids in the bridge that the legs of the U-bolt pass through are to be 100. mm apart, the legs of the U-bolt are approximately 3.937 inches apart.
Q:
1. It appears that the specifications for 2d has been changed since I printed out them on OCT 8, 2007, is that correct? Those specifications were “The loading plane (P) shall be horizontal and shall lie on the physical top of the bridge between 100. mm and 200. mm” Currently 2d reads “ The loading plane (P) shall be horizontal and shall lie no more than 50. mm above the support surfaces. The bridge may extend above the loading plane as long as clearance is provided for the U-bolt, loading plate and U-bolt nuts. This change appears to now allow for the loading rod to connect below the support plane. 2. Can it be assumed that the U-bolt and rectangular plate will be assembled on to the bridge to allow for members to pass underneath the rectangular plate and above the U-bolt? 3. Can members (lateral bracing) be above the loading plate as long as the rect. Plate can be maneuvered in to place, U-bolt inserted from below and nuts tightened.
A:
Here are the answers to your three questions. 1. Rule 2d was changed. 2. Yes. 3. Yes
Q:
One more question I hope you can answer. I see the specifications changed (the original paper we have stated the loading plane to be bet. 100 and 200 mm above the support surfaces and that it would also lie on the physical top of the bridge). With the new specs, 'loading plane shall be horizontal and shall lie no more than 50. mm above the support surfaces' can we still use the concept of the loading plane being the physical top of the bridge, i.e., a short bridge no taller than 50mm? Thank you again for your time,
A:
The bridge may extend above the loading plane but is not required to do so. Your concept of having the entire bridge below the loading plane is acceptable.
Q:
don’t see in the rules where there is anything preventing a student from making a bridge about 17 mm wide, with some strong shear wall sides, and simply placing the thin loading strip on top of the sides, so long as the height of the sides meets the rules for the height of the loading plane above the support surface. Is that a possible scenario? We are also trying to figure out how much loading distribution the thin 2 mm plate will provide. While you are loading at two principal points, until the thin plate “yields” or bends too much, it will apply load at more than the two end points. After a few tests, or maybe even one test, it may no longer be straight. I don’t know if you are worried about that issue at all or not (use a new plate for each test). We typically load from above and we can easily provide a two point loading, but it is more difficult to provide the “uniform” loading that the plate may provide with the flexibility of that 2 mm plate.
A:
These is no minimum width for a bridge. A student could make a narrow short bridge, allowing for the U-bolt and the 50mm maximum height of the loading plane. The scenario you describe should be possible. I do not think it would be the strongest bridge possible but it should be acceptable. Using the plate that comes with the U-bolt is new for this year. It has been several years since we used U-bolts. The last time they were used we specified our usual 40mm square loading plates.
Q:
A large portion of the U-Bolt is threaded. When loading the bridge, is there a specific position where the nuts will be on the bolt? The rules specify the cross-sectional clearance for the bolt, "two 12.7 mm (1/2 inch) holes," but not the height of this clearance area. I think this means that there is no significant clearance above the loading plane, except for the nuts that sit right above the plate, but I just wanted to be sure. Any help with this questing is appreciated.
A:
In the original rules the loading plane was the physical top of the bridge so clearance above the loading plane was not an issue. When the rules were modified it be came an issue but was not specifically mentioned in the modified rules. There is no required location of the nuts on the U-bolt. For safety purposes the nuts must be fully engaged on the U-bolt. This means that at least a fraction of a mm of the U-bolt must project above the nuts. If a student wants the nuts further down the threaded portions of the U-bolt this is acceptable. There is only the minimum requirement.
Q:
Regarding the term Laminated on the rules sheet. One of my students wants to know if two or more pieces of the basswood can be glued together side by side? Thanks for the help1
A:
Yes.
Q:
My daughter is confused on where the weight is going to be placed on the bridge. Should the plate be supported at the top of the bridge or at the bottom of the bridge, where the bolt will hang below? Thank You.
A:
The load will be applied to the bridge via the loading plate between the legs of the U-bolt. This plate will be placed on the bridge in a location known as the loading plane. The exact location of the loading plane is determined by the student, but there are some rules that limit the range of locations the student may choose. Also the loading plate will be centered on the bridge. The rules concerning the loading plane and the plate location are 2d, 3a, 3b, and 3c. Rule 2d states the loading plane shall lie no more than 50. mm above the support surface. This location may be the physical top of the bridge, but not necessarily so as the bridge may be a total of 200. mm in height above the support surface. A student may build a short bridge 50. mm or less in height and place the loading plane on the top of their bridge. Or a student may build a tall bridge, up to 200. mm above the support surface and have the loading plane near the bottom of the bridge, no more than 50. mm above the support surface. There is no one required height of bridge or location of the loading plane. Rules 3a, 3b, and 3c, deal with the horizontal location of the loading plate and its orientation. The loading plate shall be centered on the bridge and parallel to the bridge's longitudinal axis. This means the plate will be at the center between the support surfaces and aligned with the long axis of the bridge. No matter where the students decided to place the loading plane, the U-bolt will hang down from it. Thus the bridge must have open spaces to accommodate the U-bolt, the loading plate and the nuts which attach the loading plate to the U-bolt.
Q:
Where and how must the bridge support the U-bolt plate?
A:
A bridge may provide support for the U-bolt plate at any location or multiple locations along its length except for the two 12.5 mm holes, 50 mm each side of the center of the bridge. These holes provide openings for the legs of the U-bolt to hang down from the plate. It is envisioned that a bridge will provide support adjacent to these holes. A single support location at the center of the bridge would not be a violation of the rules. If the U-bolt plate is supported in only one location there can be a stability problem given the dynamic characteristics of the loading procedure. Imagine supporting a ruler using only one finger. This will work if your finger it exactly at the middle of the ruler. If you are off center just a fraction of an inch the ruler will fall. When a bridge is loaded, the loading rod often swings from side to side. This movement could cause the loading plate to move on a single support and become unstable. So we strongly recommend supporting the plate with more than one support.
Q:
Rule 1.b. indicates that official basswood may be laminated in any > manner. What is meant by the term laminate? Rule 1.a. indicates that no > material other than wood and glue may be used, so what might a student > use to laminate their bridge?
A:
In this context, lamination means "To make by uniting several layers". This means that beams can be made by gluing together several pieces of wood along their entire length.
Q:
The load will be applied on the longitudinal axis of the bridge with the loading plate centered on the 300. mm gap. The loading plane (P) shall be horizontal and shall lie no more than 50. mm above the support surfaces. So as long as the loading plate is 50mm or less than the support surfaces And the center of the plate is in the center of the bridge Am I correct?
A:
You appear to have left out the key work "above" in your description of the elevation of the loading plate relative to the support surface. The centering statement appears correct. The other aspects you missed are the plate being horizontal and parallel to the longitudinal axis of the bridge.
Q:
Can we have the “holes” for the U bolt to stick through the bridge “deck” as wide as we want As long as we can center the loading plate?
A:
The minimum size of the openings for the U-bolt legs to pass through the bridge is covered in rule 2e, and is 12.7 mm. Larger openings are allowed but not necessarily recommended.
Q:
It appears as though the only thing we have to stick through the deck Are the two ends of the u bolt such that the plate is centered correct and So that we can get the nuts on
A:
The above statement is correct but leaves out certain aspects. See my answer above for line and level requirements. Also clearance above the deck must be provided for the U-bolt legs, the plate and the nuts.
Q:
The loading plate's holes for the U-bolt are about 100mm apart. Today, a very insistent parent pointed out that the rule says "two 12.7mm(1/2inch)holes centered 50mm on the middle of the 300mm gap." He and his kid put the loading plate holes exactly 50mm apart centered at the middle of the span. Fortunately, they did not read the rest of the rules very well and are having a few other difficulties with their structure. The holes are actually 50mm on either side of the center line. Should the wording be changed to "centered 100mm on the middle of the gap"?
A:
Changing to "centered 100 mm on the center of the gap" may cause someone to space the holes 200 mm apart. A possibly clearer wording is as follows. Clearance for the U-bolt to hang vertically through the bridge will be provided by two 12.7 mm (1/2 inch) holes. These holes will be 100. mm apart and centered 50. mm on each side of the middle of the 300. mm gap. I am copying this e-mail to other rules committee members to ask their opinion if the specifications should be changed or thing clarification simply placed the FAQ section of the bridge contest web page.
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