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Reinforcing Roof Truss Frames Under Load

by Timothy E. Donovan, (M.ASCE), Structural Engr.; Power Div., Charles T. Main, Inc., Engineers, Boston, Mass.,
Vytautas Izbickas, (M.ASCE), Chf. Engr.; Power Div. Charles T. Main, Inc., Engineers, Boston, Mass.,
Nicholas Mariani, (M.ASCE), Struct. Proj. Engr.; Industrial Div., Charles T. Main, Inc., Engineers, Boston, Mass.,


Serial Information: Civil Engineering—ASCE, 1984, Vol. 54, Issue 4, Pg. 48-51


Document Type: Feature article

Abstract:

Without altering the roof structure of an industrial boiler plant, a long-span steel truss frame was modified in place to support heavier loads. The owners of an industrial boiler plant in the Northeast were required to reduce particulate emission levels from coal fired boilers. The solution: replacement of a two-field electrostatic precipitator weighing 185 tons (168 mt) with a three-field precipitator weighing 450 tons (408 mt). Design considerations involved analyzing construction constraints to ensure structural integrity and to reduce the distortion of system components during construction. The location of the new precipitator was dependent on available space, and the turbine hall was to remain enclosed and operational during construction. The strengthening concept was based on keeping the existing riveted structure intact. The truss members and the columns were to be strengthened while in stressed condition with the building under load. The modified cross sections of the structural members with the additional material because of increased loading were designed on the assumption that no initial stress existed in the material of the parent member. Usually, the basis for calculating the additional load carrying capacity according to the concepts of elastic theory would be the difference between the allowable stress and the stress in the parent member at the time of structural modification. The assumption that the parent member had zero stress allowed reduction in steel weight, resulting in savings in construction cost and decreased plant downtime.

Subject Headings: Load factors | Maximum loads | Industrial facilities | Trusses | Steel frames | Structural strength | Steel structures

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