Stress Laminated Deck

Stress laminated timber decks are typically constructed by compressing a series of wood laminations, placed edgewise, with post-tensioning bars, normal to the direction of the laminations. The post-tensioning bars are placed through holes in the laminations that must be predrilled. The diameters of the holes in the laminations for the post-tensioning bars must not be greater than 20 percent of the laminations depth, and the spacing of the holes shall not be less than 15 times the hole diameter nor less than 2.5 times the depth of the laminations (Article 9.9.5.4). A sketch of a stress laminated deck cross section is shown in Figure 16.

The compression created by the post-tensioning develops friction and load distribution between the laminations so that they act together as a large orthotropic plate (21). Per Article C9.9.5.6.3, the post-tensioning force per bar is based on a uniform compressive stress of 0.1 ksi between the laminations. Article 9.9.5.6.3 provides additional design requirements for stress laminated decks.

Stress laminated decks must be tied down at every girder with bolts or lag-screws to ensure proper contact of the deck with the top flanges of the girders. Stress laminated decks have a tendency to develop curvature perpendicular to the laminates when transversely stressed by posttensioning. Furthermore, past research and field experience has shown that it is necessary to restress a stress laminated deck system after initial stressing in order to offset long-term relaxation effects.