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Any increase in legal truck weight would shorten the time for repair or replacement of many bridges. Five steel girder bridges and three prestressed concrete I-girder bridges were instrumented, load tested, and modeled. The results were used to assess the effects of a 10 or 20% increase in truck weight on bridges on a few key routes through the state. Essentially all prestressed girders, modern steel girders, and most bridge decks could tolerate a 20% increase in truck weight with no reduction in life. Unfortunately, most Minnesota steel girder bridges were designed before fatigue-design specifications were improved in the 1970's and 1980's. Typically, an increase in truck weight of 20% would lead to a reduction in the remaining life in these older steel bridges of up to 42% (a 10% increase would lead to a 25% reduction in fatigue life). Bridge decks are affected by axle weights rather than overall truck weights. Transverse cracks in bridge decks are primarily caused by shrinkage soon after construction and are not affected by increasing axle weight. However, decks with thickness less than 9 inches or with girder spacing greater than 10 ft may be susceptible to longitudinal flexural cracking which could decrease life.

An appendix to report 2003-16, "Effects of Increasing Truck Weight on Steel and Prestressed Bridges." Chapter A1 - Introduction Chapter A2- Background Chapter A3 - Field Testing and Analytical Modeling Chapter A4 - Effect of Increasing Truck Weight on Tested Bridges Chapter A5 - Effect of Increasing Truck Weight on Other Minnesota Bridges Chapter A6 - Summary and Conclusions

An appendix to Report 2003-16, "Effects of Increasing Truck Weight on Steel and Prestressed Bridges." Chapter B1 - Introduction Chapter B2 - Background Chapter B3 - Field Testing and Analytical Modeling Chapter B4 - Effect of Increasing Truck Weight on Steel Bridges Chapter B5 - Summary and Conclusions

An appendix to Report 2003-16, "Effects of Increasing Truck Weight on Steel and Prestressed Bridges." Chapter C1 - Introduction and Research Approach Chapter C2 - Background Chapter C3 - Field Testing Chapter C4 - Fatigue in Bridge Decks Chapter C5 - Overstressing in Bridge Decks Chapter C6 - Extension of the Results to the Bridge System Chapter C7 - Summary, Conclusions and Recommendations