CHAPTER 4 HEAVY TIMBER LAMINATED WOOD & SPECIAL COMPONENTS
A HEAVY TIMBER • Heavy timber is a diminishing industry. When the process flourished, that’s all there was. Plenty of material was available, but the process from tree to structure was long and tedious. Not much can be gained by an exhaustive study of heavy timber. • Heavy timber was limited by lack of transportation, finish of surfaces, methods of connection, and variety of appearance. • Spans were limited by the size of members, and the methods available to secure them in place.
Heavy timber construction still flourishes in regions where trees are plentiful and a desire for that venue exists. • But technology and mass production has far surpassed the antiquated methods of building and the demand for macho variety that heavy timber provides. • Heavy timber has been left behind by the industrial revolution that produced mill saws, planers, joiners, drills, and improved methods of fastening pieces, and made available a ready supply of material in parts of the country where no trees grow.
Consider the poetic statement in the margin of page 107,“The old country builder, when he has to get out a cambered beam or curved brace, goes round his yard and looks out the log that grew in the actual shape; and by taking off two outer slabs by handwork in the sawpit, chops it roughly to shape with his side-axe and works it to the finished face with the adze, so that the completed work shall forever bear evidence of his skill . . .” • Poignant certainly, but see when it was written. . . 1900. • To be sure, modern methods of building with wood are far greater in efficiency in use of materials. When heavy timber use was in its prime, there was a great amount of waste of material. Today, about the only part of a tree that is not used is its shadow.
With the exception of it’s aesthetic value, the use of heavy timber in construction today is actually a waste of material. Engineering technology shows us that to span long distances with heavy loads is not required by the engineering characteristics of a large square or rectangular cross section of material. • It can be shown that built up members of lesser volume of material can carry the same loads over the same span distance. That has been the result of advanced methods of manufacturing structural units and the conservation of materials.
THE MODERN ANSWER TO HEAVY TIMBER is LAMINATED WOOD CONSTRUCTION With the advent of adhesives that are stronger than wood, and the assembly and use of small and irregular pieces of material has allowed an industry to provide a variety of stronger structural shapes than members cut from original, solid wood.
Wood pieces that are laminated together and glued under high pressure can be made into most any shape desired, whether the shape is required by structural loading, or by aesthetic arrangement. The size of these shapes is practically limited by the method by which components are transported to the job site. Height and length of large components are often restricted by transportation through cities, roads, bridges, and utility lines, from the point of manufacture to the place of use.
Laminated Wood – called “glue-lam” • The Lamination Process involves assembling random size pieces of choice wood in a controlled pattern, shape, and atmosphere, then gluing them together under high pressure. • By laminating smaller parts together, one can create sizes not available naturally create shapes not available in nature, and with better quality of material
A SIMPLE 3 – HINGE ARCH STRUCTURE USED TO CLEAR SPAN LARGE AREAS
A CHURCH STRUCTURE IN RAPID CITY, SOUTH DAKOTA
A close up view of the haunch of a laminated arch to show that smaller pieces of wood are more readily formed into desired shapes. The pieces of this member were placed in a pre-arranged form, glued, then pressed together under high pressure to assume the desired shape. Units are then sanded to an acceptable surface – and can be pre finished or shipped to the job site unfinished. Waterproof glue is also available for use outdoors.
LAMINATED VENEER LUMBER is a by-product idea from the plywood industry. It is a process of making structural shapes by gluing together thin sheets of wood veneer, alternating the grain of each sheet. Where wood beams and headers in light wood construction had to be made of solid wood, LVL has replaced the requirement with stronger, straighter material that is not limited in length.
LAMINATED VENEER LUMBER BEAMS
Laminated Veneer Lumber in combination with Oriented Strand Board are used to make wood “I” joists. The top and bottom chords are made of LVL, and OSB is used for the web of the joists. Units are stronger and straighter than solid wood joists, and lengths are made to order. I joists are lighter, easier to install, and for a given depth and span, carry more load than solid wood joists.
LAMINATED VENEER LUMBER “I” JOISTS LVL TOP & BOTTOM CHORDS • OSB JOIST WEBS
WOOD TRUSSES are construction components to carry loads of roofs and floors where wood joists are not practical. Trusses are made so the perimeter members conform to the roof or floor cross section, and then installed at spaced intervals to accommodate roof or floor decking and ceiling configuration. Each truss is made up of members arranged in a triangular pattern of web members connected to top and bottom chord members. Wood trusses for light frame construction are generally made with dimension lumber, connected with toothed plates. Some types of floor trusses utilize steel bars for web members.
PARALLEL CHORD TRUSSES ARE USED FOR FLAT ROOFS OR FLOOR FRAMING IN MULTI-STORY BUILDINGS
“SCISSORS” TYPE TRUSS FOR SLOPING ROOF AND SLOPING CEILING
PARALLEL WOOD CHORD TRUSSES USING STEEL BARS FOR WEB MEMBERS CAN BE USED FOR FLOORS OR ROOFS
A SPECIAL DESIGN TRUSS USING TOOTHED PLATES FOR CONNECTIONS OF WEB MEMBERS WITH TOP AND BOTTOM CHORD
Pound for pound, trusses can carry more weight and span longer distances than wood “I” joists or solid wood joists. Trusses are made with top grade wood, and result in lighter weight members for a given span condition and a lesser volume of material compared to beams and joists. They are made in controlled conditions and are straight and easily handled, resulting in less labor cost to install.
WOOD IS A SUSTAINABLE MATERIAL Wood is the only major renewable construction material, a direct result of clear cutting in forests and replanting trees. Mill practice utilizes efficiency of material in that no materials are discarded, but recycled into other construction materials or usable byproduct. The wood construction industry overall, does not pollute, transportation of products is not complicated, and indoor air quality due to the industry and use of wood products is excellent.