Balsa Wood Bridges
High School/Grades 9 - 12
Each student will be required to have on file with the MESA office one short diversity statement (one paragraph), either as a team member or an individual, by February 28, 2008 to be eligible to compete at MESA Day. (One statement per student not per activity.) Each statement should explain the diversity of their team or various teams or, for individuals, be a short statement on the value of diversity.
MaterialsTen 3 ft. strips of ¼" x ¼" square balsa wood and water soluble Elmer's white glue. This is usually sufficient. More can be used.Rules for SizeBridge Dimensions
Rules for Construction
Acceptable Joints:  Unacceptable Joints:  Specifications Check
Judging
AwardsAwards are given in each of the following three categories:
SafetyAppropriate safety measures will be used during testing. JournalingThis should be judged by the teacher. We suggest that it include a plan sheet showing the proposed bridge and an explanation of why a particular design was chosen. On construction projects, we keep daily diaries that include a description of the work being performed on a bridge each day (footings, abutments, columns, crossbeams, deck, etc.), along with a description of any problems encountered along with the solution to that problem. Clarification of LaminationThe spirit of the lamination rule is to allow bridges made of balsa wood ONE LAYER thick. Since the balsa may need to be overlapped at the joints, the bridge may need to be more than one layer thick at the joints. Rules for Construction #1 & #2 state: "No lamination (lamination is defined as the gluing of two pieces of wood along their longitudinal length (i.e. no part of a stick may be glued to another stick except where at the joints as specified in rule #2))" and "joints must be at or within ¼" of the end surface of the one of the members." Since dry glue is nearly invisible and it is impossible to tell what part of overlapping members is glued and what part is not, judges must assume that the entire length of overlapping members is glued. Therefore, no two members anywhere on the bridge may overlap by more than ¼". ¼" long pieces of balsa may be used as "spacers." A spacer is defined as a piece whose sole role is to separate structural members (such as the corners of the bridge). Wholly glued pieces which appear to strengthen, reinforce, serve a purpose other than separating, or are placed too closely together will be considered lamination, not spacers. Determination of what is a spacer and what is lamination will be left solely to the judges. Since this may be a "gray area," with disqualification as a possible result, students are encouraged to avoid the use of spacers. Please remember that the purpose of this contest is to use creativity to build the best structure within the framework of the rules. The purpose is not to break the rules and see if you can get away with it. Steel Bridge TerminologyAngleStructural steel shape that has a cross section resembling L. Legs may be equal or unequal (shown). Used in trusses and built-up girders. C-Shape or Channel Structural steel shape that has a cross section resembling [. A channel is similar to a W-Shape but has half width flanges on one side. Used in trusses and built-up girders. Flange On structural steel shapes, like C-Shapes and W-shapes, a flange is the horizontal portion at the top and bottom that are perpendicular to the web. I-Beam Structural steel shape that has a cross section resembling an I. I-Beam is the common name for an S-Shape (standard) steel beam. W-Shape Structural steel shape that has a cross section resembling an H. A W-Shape beam is different from an I-Shape beam because the flanges are wide and flat. W-shape beams are also called Wide Flange beams. Web On structural beams, like C-shapes and W-shapes, the web is the flat portion in the center of the beam between the two flanges. General Bridge TerminologyProfile View A plan sheet showing the bridge along the longest side. Also known as the longitudinal section. If you were driving across the bridge the profile would be perpendicular to the direction that you were driving. Elevation View A plan sheet showing the bridge along the shortest side. Also known as the transverse section. Substructure The portion of the bridge below the roadway. This can include footings, abutments, grade beams, columns, and crossbeams. Superstructure The portion of the bridge above the substructure. This includes the roadway deck and any structures above the deck. Pier The sections of the bridge that transfer the load to the ground. At the ends of bridges these piers are also called bridge abutments. Piers can also be referred to as bents. Footing The section of the bridge that is below the ground line. Footings can be drilled shafts (deep foundations) or spread footings (a large block of concrete - sometimes these spread footings have piling beneath them). Grade Beam A block of concrete at ground level. The long side of the block is parallel to the transverse direction of the bridge. Column The section of bridge that connects the footing to underside of the bridge deck. Columns are usually round, square, or rectangular. Crossbeam A rectangular section of concrete between the columns and the roadway deck. The long side of the block is parallel to the transverse direction of the bridge. Girders typically set on crossbeams. Crossbeams are also called cap beams. Girder A beam section that spans the longitudinal distance from one pier to the next. |
Implement engineering concepts in the design and
construction of a model balsa wood bridge from a plan while using as
little wood as possible, and to develop neatness, craftsmanship and
creativity.