Wood is strong in compression and tension (forces applied parallel to the primary axis of the grain) and weak when subjected to bending forces (forces applied perpendicular to the grain). For an elegant illustration of this principle, observe how easily a toothpick can be broken by folding it in half. Then see how much success you have trying to pull one apart by tugging the points in opposite directions parallel to its length.

The Tension Timber project explores the possibility of leveraging wood’s inherent tensile strength to achieve longer unsupported spans than would otherwise be possible with standard dimensional lumber. The project takes as its specific challenge the design of a shelter for Stick’s sawmill that provides clear access unimpeded by vertical supports along its entire 26-foot length.

Inspired by precedents such as the Hooke Park sawmill shelter, the structure employs a hyperbolic paraboloid (“saddle”) roof in which straight beams form a curved surface. The project began with a close site study, several scale models made of wood and string, and structural engineering consultation. Three beam designs were developed to test a variety of configurations and splice methods.

Using specialty shear rings & plates and fabrication tools purchased and donated by Rothoblaas and Portland Bolt, the final phase of the project saw the creation and testing of full-scale mockups of the three beam prototypes. This 1:1 construction provided valuable insights into installation workflow & efficiency, transportability, and performance under tension.