One of the fundamental rules of wood design is that there is no such thing as a wood moment frame. Two pieces of wood joined together with nails, screws or other available fasteners simply cannot be joined together in a way to adequately and consistently transfer forces form one direction (horizontal) to another (vertical). The reason is that wood is too soft to create a rigid enough connection between the members. The more fasteners that are added, the weaker the members themselves become.
A fairly new technology in wood construction is a family of manufactured wood structural members including I-joists, laminated veneer lumber (LVL), micro-lams, and paralams. These products consist of plywood and oriented strand lumber products designed to replace traditional wood joists, rafters, headers, beams, studs, and posts. As older and larger trees have become harder to find and harvest, not to mention environmentally sensitive, this new category of engineered wood products has become a very desirable alternative as they are made of wood from smaller and younger trees.
Production
The AVAVA Systems building begins as an idea based on the intended purpose and specific location. The purpose will dictate the most efficient size and layout of the building along with anticipated occupancy and loads it will accommodate. The site will determine how to best support the critical corners of the building and how the building will be situated for most efficient use of light, views, and access.
The idea then becomes the design and is put onto drawings that can be organized into the layers such as floors, roof, wall elevations, and sections. The layers are visualized in three-dimensions so that the geometry of the wall and floor intersections can be exactly located. Because the interlocking corner connections ultimately determine the geometry of the structure it is critical that the design be dimensionally correct. The three-dimensioned drawings allow the framing members, corner blocks, plywood skin, and tension rods to be tabulated into a final bill of materials.
The bill of materials is used to order the materials and keep the materials in order for proper assembly once they are delivered to the site. The blocks, I-joists, plywood, and tension rods can be ordered cut and shaped to match the plans within very fine tolerances. This eliminates waste and provides for very easy assembly, much like a kit or prefabricated structure.
Construction
The site requires very little work to prepare for construction beyond the installation of corner supports, either concrete footings, drilled piers, or driven piles. Once the supports are constructed temporary beams are laid between with temporary intermediate supports for the assembly process. The assembly requires scaffolding, powered screw drivers, basic hand tools, and little else.
The I-joists used in our building-related products are intended to replace the 2x joists and rafters used for roof and floor systems with similar properties to 2xs of similar depths. I-joists weigh less than their 2x counterparts, can span slightly longer distances with simply supported end connections, and are made of plywood, a much more renewable resource than dimension lumber. The blocks used in our corner connections are made of LVL beam material and the exterior and interior surfaces consist of plywood, thus our entire building system, with the exception of the tension members and fasteners, is entirely made of engineered wood.
The I-joist shape consists of two flanges with a web spanning between and connecting each flange at the midsection of each flange. The name is very descriptive of the shape of the typical cross section of the member. In a vertically oriented I-joist with a horizontal span that is carrying a vertical (gravity) load the bottom flange will typically be in tension, the top flange will be in compression, and the web will transfer the forces between the two flanges continuously along the length of the member. The I-joist shape also lends itself to some sort of locking device that can be fitted into the web between the two flanges, which is where AVAVA Systems comes into the picture.
With a locking block wedged between the flanges and pressed into the opposing webs of parallel members, the flanges will create leverage from one member to the next. The block will be resisting the moment forces at the ends of the members through torsion, a force that resists rotation. The third element of the new connection idea is a rod or cable inserted in a perpendicular or normal direction to the adjoining members and pulled tight to place the connection in compression.
Take a long series of these connections and configure them such that you create a series of four or more intersections, and you will have a rectangular or other geometric shape that is open at each end, much like a tube. By adding plywood or similar panels over the framing members, the structure becomes very stiff and resistant to horizontal forces in the direction parallel to the tube. The corner elements, by their nature, create resistance to both vertical and horizontal forces and eliminate the need for shear walls or special moment-resisting steel frames.
The sides of this tube, combined with continuous tension elements at the top and bottom of each side, convert the structure into a very large and extremely strong horizontal beam. Thus the shape and form of the structure become the structure itself. Imagine a building large enough to comfortably house two or more families supported on just four small foundations or legs. With a little more imagination you may also picture this same structure designed to float harmlessly up and down in the event of a sudden flood or other natural disaster.
Testing
Testing of assemblies is recommended for each new building design. Loads for test should be two to three times the anticipated live loads for the building.
For large scale projects where many buildings of similar type and nature are to be used, testing should be carried out by an approved testing agency or laboratory.