BRIDGE REPAIR/REHABILITATION FEASIBILITY STUDY

Photo 5 - Stringer and Diaphragms
Repair Scope: Although the timber stringers currently do not exhibit significant deterioration,
the size and depth of the current splits and checks, the limited remaining preservatives in the
wood, and the current exposure introduce conditions conducive for fungal decay. As such, the
remaining service life of the existing timber stringers may be limited without corrective action.
There are options for in-place preservative treatment of large timber members including both
internal treatments and surface treatments (see Appendix D.) Internal treatments include use of
liquid and solid fumigant or fungicide chemicals inserted into drilled holes in the timber
members. Surface treatments include application of preservative chemicals to the exterior face
of the members. However, there are limitations and concerns with each treatment that reduces
their effectiveness or makes the treatment undesirable for use.
Internal in-place preservative treatments on heavy timber beams typically consist of drilling
holes (pairs of holes typically 3/8 inch to 7/8 inch in diameter at a spacing of no greater than 4
feet) from the top to nearly the bottom of the beam, installing the liquid (e.g. chloropicrin) or
solid (e.g. methylisothiocyanate) chemical fumigants into the holes in the members, and capping
the drilled holes with timber dowels. The chemicals then spread throughout the member by way
of gaseous diffusion. Solid fumigants typically require a minimum amount of moisture for the
diffusion to take place.
Surface in-place preservative treatments consist of saturating the surface of the timber with
liquid oil-based preservative chemicals (e.g. penta or copper naphthenate) by brush or spray
application so that all surfaces, cracks and crevices are thoroughly treated.
Repair/Rehab. Feasibility Study March 10, 2011
Bridge No. C-07-001 (437) 23 Final Report