One of the most important tests from a practical standpoint is that of built-up structures such as compounded beams composed of small pieces bolted together, mortised joints, wooden trusses, etc.  Tests of this kind can best be worked out according to the specific requirements in each case.

APPENDIX

SAMPLE WORKING PLAN OF THE U.S.  FOREST SERVICE

MECHANICAL PROPERTIES OF WOODS GROWN IN THE UNITED STATES

Working Plan No. 124

PURPOSE OF WORK

It is the general purpose of the work here outlined to provide: 

(a) Reliable data for comparing the mechanical properties of various species;

(b) Data for the establishment of correct strength functions or working stresses;

(c) Data upon which may be based analyses of the influence on the mechanical properties of such factors as: 

Locality;

Distance of timber from the pith of the tree;

Height of timber in the tree;

Change from the green to the air-dried condition, etc.

The mechanical properties which will be considered and the principal tests used to determine them are as follows: 

Strength and stiffness—­
  Static bending;
  Compression parallel to grain;
  Compression perpendicular to grain;
  Shear.

Toughness—­
  Impact bending;
  Static bending;
  Work to maximum load and total work.

Cleavability—­
  Cleavage test.

Hardness—­
  Modification of Janka ball test for surface hardness.

MATERIAL

Selection and Number of Trees

The material will be from trees selected in the forest by one qualified to determine the species.  From each locality, three to five dominant trees of merchantable size and approximately average age will be so chosen as to be representative of the dominant trees of the species.  Each species will eventually be represented by trees from five to ten localities.  These localities will be so chosen as to be representative of the commercial range of the species.  Trees from one to three localities will be used to represent each species until most of the important species have been tested.

The 16-foot butt log will be taken from each tree selected and the entire merchantable hole of one average tree for each species.

Field Notes and Shipping Instructions

Field notes as outlined in Form—­a Shipment Description, Manual of the Branch of Products, will be fully and carefully made by the collector.  The age of each tree selected will be recorded and any other information likely to be of interest or importance will also be made a part of these field notes.  Each log will have the bark left on.  It will be plainly marked in accordance with directions given under Detailed Instructions.  All material will be shipped to the laboratory immediately after being cut.  No trees will be cut until the collector is notified that the laboratory is ready to receive the material.