Non Obtrusive Rehabilitation of Small Bridges and Large Culverts Using Corrugated Steel Pipe (CSP) Structures, Innovations in Bridge Engineering, Rehabilitation David J. Penny B.E.S. Marketing Manager Corrugated Steel Pipe Institute 652 Bishop Street Unit 2A, Cambridge Ontario N3H 4V6 djpenny@cspi.ca Many bridges and culverts in Canada are in a serious state of disrepair or are structurally inadequate for modern operating conditions. The estimated cost to replace these structures is staggering. Materials and construction costs are often minor when compared to the social, environmental, heritage and economic impact costs of a bridge replacement. Relining or building a structure within a structure is a solution that can minimize costs at all levels. As excavation and demolition of the old structure are avoided or more easily staged to manage detours, the costs and public impact are minimized. The construction techniques used for relining require a smaller access area, lower quantities of building materials and smaller construction equipment. This paper will outline a number of techniques used to reline small bridges and larger culverts providing alternatives for consideration. It will be presented as a series of case studies of Ontario installations both recent and revisited. Methods and materials will be discussed as will significant site factors that influenced the decision to reline versus rebuild. The Saint Paul Street Bridge, Brockville, an historic stone arch from the 1840s relined in 1976 using a closely fitting corrugated steel structural plate arch and grouting. (Case study was published September 2004 Environmental Science & Engineering Magazine). The Gosling Lake / HWY 35, Dorset, an invert reline of twin corrugated steel structural plate pipe arches (CSSPA) using cast in place reinforced concrete, completed March 2004. HWY 401 / 38, Kingston, a reinforced concrete railway underpass replacement using a deep corrugated steel box culvert erected and backfilled inside the original box, February 2005. HWY 417, Limoges, a reline of long twin CSSPA using a close fit, slip lined polymer laminated corrugated steel pipe arch with internal couplers and grouting. The project is significant due to the high traffic volumes and the challenging soil conditions making bridge alternatives prohibitively expensive. Summer 2005.