Open bottom fiber reinforced precast concrete arch unit

Abstract

A one-piece open bottom fiber reinforced precast concrete arch unit is buried in compacted soil and has an arcuate top wall portion integrally connecting arcuate side wall portions. The fiber reinforced wall portions have a configuration which provides ductility and flexure strength for effectively utilizing the surrounding compacted soil to resist deflection of the unit in response to a load and to redistribute stresses in the unit. Each of the side wall portions of the unit has a reducing wall thickness towards its bottom and has a radius of curvature greater than the rise of the unit and at least twice the radius of curvature of the top wall portion. Bands of continuous fibers may be attached by adhesive resin to the outer surface of the arcuate side and top wall portions of the unit near opposite ends of the unit to increase the load carrying capacity of the unit.

1 . An underground open bottom precast concrete arch unit adapted to be buried in compacted soil, said arch unit comprising a one-piece inverted U-shaped wall structure having a predetermined length and arcuate opposite side wall portions integrally connected by an arcuate top wall portion, a predetermined volume of reinforcing fibers dispersed throughout said wall structure and providing said side wall portions and said top wall portion with a predetermined ductility and flexure strength adapted to utilize the resistance of the surrounding compacted soil to increase the load capacity of the unit, said wall structure having a rise defined between bottom surfaces of said side wall portions and an inner top surface of said top wall portion, said arcuate top wall portion having a radius of curvature substantially smaller than said rise, and said arcuate side wall portions each having a radius of curvature greater than said rise.  
     
     
         2 . A precast concrete arch unit as defined in  claim 1  wherein said arcuate top wall portion has a radius of curvature less than one-half of said radius of curvature of said arcuate side wall portions.  
     
     
         3 . A precast concrete arch unit as defined in  claim 2  wherein said top wall portion has an arcuate length generally the same as the arcuate length of each of said side wall portions.  
     
     
         4 . A precast concrete arch unit as defined in  claim 1  wherein each of said arcuate side wall portions has inner and outer curved surfaces converging together toward said bottom surface of said side wall portion and providing said side wall portion with a tapered wall configuration.  
     
     
         5 . A precast concrete arch unit as defined in  claim 4  wherein each of said side wall portions has a bottom thickness less than ninety percent of the thickness of said top wall portion.  
     
     
         6 . A precast concrete arch unit as defined in  claim 1  wherein said volume of reinforcing fibers within said wall structure is within a range of 0.25 and 2.0 percent by volume of said wall structure.  
     
     
         7 . A precast concrete arch unit as defined in  claim 1  wherein said arcuate top wall portion has a radius of curvature greater than twenty percent of the span of said unit as defined between inner bottom surfaces of said side wall portions and less than forty percent of said span.  
     
     
         8 . A precast concrete arch unit as defined in  claim 1  wherein said reinforcing fibers within said wall structure comprise steel fibers having a length within a range of 0.25 inch and 3 inches.  
     
     
         9 . A precast concrete arch unit as defined in  claim 1  wherein each of said reinforcing fibers within said wall structure has a length at least fifty times the cross-sectional thickness of said fiber.  
     
     
         10 . A precast concrete arch unit as defined in  claim 1  wherein each of said wall portions of said wall structure has a bottom thickness within a range of 1.5 percent to 3.5 percent of the span of said wall structure as defined between bottom inner surfaces of said side wall portions.  
     
     
         11 . A precast concrete arch unit as defined in  claim 1  and including at least one elongated band of longitudinally extending reinforcing fibers connected to peripheral portions of said arcuate top and side wall portions.  
     
     
         12 . A precast concrete arch unit as defined in  claim 11  wherein said band of reinforcing fibers extends across an area where said top wall portion integrally connects with at least one of said side wall portions.  
     
     
         13 . A precast concrete arch unit as defined in  claim 11  wherein a plurality of parallel spaced said bands are adhesively bonded to an outer surface of said arcuate top and side wall portions adjacent opposite ends of said wall structure.  
     
     
         14 . A precast concrete arch unit as defined in  claim 11  and including a second said band overlying and adhesively bonded to at least a portion of the first said band.  
     
     
         15 . An underground open bottom precast concrete arch unit adapted to be buried in compacted soil, said arch unit comprising a one-piece inverted U-shaped wall structure having a predetermined length and arcuate opposite side wall portions integrally connected by an arcuate top wall portion, a predetermined volume of reinforcing fibers dispersed throughout said wall structure and providing said side wall portions and said top wall portion with a predetermined ductility and flexure strength adapted to utilize the resistance of the surrounding compacted soil to increase the load capacity of the unit, said wall structure having a rise defined between bottom surfaces of said side wall portions and an inner top surface of said top wall portion, said arcuate top wall portion having a radius of curvature substantially smaller than said rise and between twenty percent and forty five percent of the span of said unit as defined between inner bottom surfaces of said side wall portions, and said arcuate side wall portions each having a radius of curvature greater than said rise.  
     
     
         16 . A precast concrete arch unit as defined in  claim 15  wherein said arcuate top wall portion has a radius of curvature less than one-half of said radius of curvature of said arcuate side wall portions.  
     
     
         17 . A precast concrete arch unit as defined in  claim 15  wherein each of said arcuate side wall portions has inner and outer curved surfaces converging together toward said bottom surface of said side wall portion and providing said side wall portion with a tapered wall configuration.  
     
     
         18 . A precast concrete arch unit as defined in  claim 15  wherein said volume of reinforcing fibers within said wall structure is within a range of 0.25 and 2.0 percent by volume of said wall structure.  
     
     
         19 . An underground open bottom precast concrete arch unit adapted to be buried in compacted soil, said arch unit comprising a one-piece inverted U-shaped wall structure having a predetermined length and arcuate opposite side wall portions integrally connected by an arcuate top wall portion, said side wall portions and said top wall portion having ductility and flexure strength adapted to utilize the resistance of the surrounding compacted soil to increase the load capacity of the unit, said wall structure having a rise defined between bottom surfaces of said side wall portions and an inner top surface of said top wall portion, and at least one elongated band of longitudinally extending reinforcing fibers connected to an outer surface of said arcuate top and side wall portions and extending across an area where said top wall portion integrally connects with at least one of said side wall portions.  
     
     
         20 . A precast concrete arch unit as defined in  claim 19  wherein a plurality of parallel spaced said bands are adhesively bonded to an outer surface of said arcuate top and side wall portions adjacent opposite ends of said wall structure.  
     
     
         21 . A precast concrete arch unit as defined in  claim 19  and including a second said band overlying and adhesively bonded to at least a portion of the first said band.  
     
     
         22 . An underground open bottom precast concrete arch unit adapted to be buried in compacted soil, said arch unit comprising a one-piece inverted U-shaped wall structure having a predetermined length and arcuate opposite side wall portions integrally connected by an arcuate top wall portion, a predetermined volume of reinforcing fibers dispersed throughout said wall structure, said volume of reinforcing fibers within a range of 0.25 and 2.0 percent by volume of said wall structure with said fibers having a length within a range of 0.25 inch and 3 inches to provide said side wall portions and said top wall portion with a predetermined ductility and flexure strength adapted to utilize the resistance of the surrounding compacted soil to increase the load capacity of the unit, said wall structure having a rise defined between bottom surfaces of said side wall portions and an inner top surface of said top wall portion, and said arcuate top wall portion having a radius of curvature substantially smaller than a radius of curvature of each of said side wall portions.