CONSIDERATIONS IN DESIGN 
WITH STRUCTURAL GLUED LAMINATED TIMBER 
Bridge, Church, Residence, School, Gymnasium, Pool, Park Shelter, Sound Barrier, Ship, Transmission or Antenna Tower, Restaurant, Bank, Lodge, Health Club, Arenas, Shopping Centers, or Chemical Storage. 

1.  Wood is our oldest construction material; it is a renewable and important economic resource. Wood gives us a wide range of properties from which to choose. Species are to wood what alloys are to metal. 

2.   The natural beauty of wood and its grain is unsurpassed. Enhanced with stain, almost any color is possible. Wood does change dimensions with changes in moisture content and this fact must be understood. Green or high moisture content wood can shrink 3/4" per foot from fiber saturation at 25-30% moisture content to zero percent moisture content. Large glued laminated timbers from kiln dried lumber may average 12% moisture content but can still exhibit wood checking if the surface is subjected to rapid lowering of moisture content. 

3.   Large structural timbers are an excellent fire risk. Wood withstands extremely cold temperatures and handles elevated temperatures all the way up to the high temperature at which large cross-sections will burn. 

4.   Very little energy is required to produce structural glued laminated timber. The process develops little waste and what does develop is an excellent fuel. Wood is easy to reuse, relocate or dispose of. It is light in weight for its strength, making large assemblies easy to transport and safe to erect. 

5.   Components for large timber assemblies can be fabricated in a plant, transported considerable distances and be reassembled at the jobsite. With prefitted steel and hardware, little or no field welding is required. 

6.   Almost any conceivable shape can be provided. Thinner laminations make sharper curves and end joints provide almost unlimited length to lumber. Species are available with a wide range of bending characteristics. 

7.   Conditions under which the wood will be in service determine whether it needs to be preservatively treated or can serve untreated. Covered by a roof a long life is assured when untreated. Fully exposed to the weather without roof cover it must be preservatively treated. In an enclosed interior space with wood moisture contents above about 20%, treatment is required. Ventilation of the space to keep the relative humidity below about 80% will assure that there will be a long service life even when untreated. 

8.   Wood is virtually unaffected by most chemicals. For highway bridge and sound barrier construction, when preservatively treated, the wood does not corrode or deteriorate. For storage of chemicals in fertilizer facilities, wood is the answer. 

9.   Lumber in the tension flange of large bending members must be graded for the tension parallel to grain stress at that location. A lumber bending grade is not adequate. The end supports for large members should use the good compression parallel or compression perpendicular to grain wood strength. Loads should not be supported from bolts in numerous holes drilled through the member depth nor in any other way should wood be loaded in tension perpendicular to grain for which there are no recognized design values. 

10.   It is not possible to tell everything about a structural glued laminated timber by merely observing its surfaces. A number of steps to check during the laminating process, physical tests from production members and visual inspection of the finished members are requirements of the current ANSI/AITC A190.1-02 Standard on Structural Glued Laminated Timber. History is the AITC Inspection Manual of 1955, CS253-63, PS56-73 ANSI/AITC A190.1-83, ANSI/AITC A190.1-92, and ANSI/AITC A190.1-02. 

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