Box structures have been commonly used underneath highways. They are installed at grade or atgreat depths. When a box culvert is buried at a shallow depth, vertical pressure and impact due totraffic load transferred onto the roof of the culvert can induce deflections of the culvert. Theeffect of traffic load on the response of the culvert depends not only on the magnitude, pattern,and speed of the traffic load but also on the pavement structure. To investigate these factors, areinforced concrete box culvert under three roadway sections (concrete pavement, concreteshoulder, and unsurfaced fill) was tested under static and traffic loads. The total thickness ofpavement layers was 26 inches within the pavement section and decreased gradually towards theend of the culvert through the shoulder and the unsurfaced section. The culvert was instrumentedwith displacement transducers and strain gauges under the roof and pressure cells on top of theroof within the unsurfaced fill. A low-boy truck with a known axle configuration and load wasused to apply seven static load combinations and traffic loads at different speeds. Deflectionsunder the roof and pressures on the roof were measured. Measured strains were too small to bemeaningful for analysis. The test results show that the magnitudes of the deflections of theculvert roof under static loads were in the small to large order from the concrete pavement, theconcrete shoulder, to the unsurfaced fill. The truck at a higher speed generally induced moredeflections than that at a lower speed or stopped.
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