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American
<br />Concrete Pipe
<br />Association
<br />Highway Live Loads on Concrete Pipe
<br />FOREWORD
<br />Thick, high -strength pavements designed for heavy
<br />truck traffic substantially reduce the pressure transmitted
<br />through a wheel to the subgrade and, consequently, to
<br />the underlying concrete pipe. The pressure reduction is
<br />so great that generally the live load can be neglected. In
<br />1926,1Nestergaard presented a paper summarizing the
<br />results of an extensive study of Ine effects of loading
<br />conditions, subgrade support, and boundary conditions
<br />on concrete pavements(1). These results formed the
<br />basis by which Weslergaard developed a method to
<br />calculate the stresses in concrete slabs. Based upon the
<br />work of Westergaard and others, the Portland Cement
<br />Association, (PCA), developed a method to determine
<br />the vertical pressure on buried pipe due to wheel loads
<br />applied to concrete pavements(2). The PCA method is
<br />presented in the American Concrete Pipe Association,
<br />ACPA, "Concrete Pipe Handbook'(3) and "Concrete Pipe
<br />Design Manual"(4).
<br />Intermediate and thin thicknesses of asphalt or
<br />flexible pavements do not reduce the pressure
<br />transmitted from a wheel to the pavement subgrade to
<br />any significant degree. For these pavements, there is
<br />no generally accepted theory for estimating load
<br />distribution effects, and, therefore, these pavements
<br />should be considered as unsurfaced roadways.
<br />Historically, the American Association of State
<br />Highway and Transportation Officials, AASHTO, criteria
<br />for transmission Of loads through soil have been
<br />published in "Standard Specifications for Highway
<br />Bridges"(5). The AASHTO Standard criteria was the
<br />primary basis for the method of determining live load
<br />pressure intensity on buried concrete pipe presented in
<br />IheACPA Handbook(3) and IheACPA Design Manual(4),
<br />with the exception that the ACPA assumes a wheel load
<br />is applied as a footptint(Figure 1), whereas theAASHTO
<br />Standard assumes a wheel load is applied as a point
<br />load. For the past decade, AASHTO has been
<br />developing a different approach to design criteria in a
<br />new publication, "Load Resistance Factor nae;(!o R,r;i• I,
<br />Design Specifications"(6), Ll.—
<br />,IVJN"III:I:I
<br />load Is applied as a footprint(Figure 1). In the future
<br />AASHTO will require all designs to be performed in
<br />accordance with the LRFD, and has stopped accepting
<br />proposed revisions to the "Standard Specifications for
<br />Highway Bridges".
<br />This Design Data addresses the method of
<br />determining the live load pressure transmitted through
<br />unsurlaced roadways to circular, elliptical and arch
<br />concrete pipe in accordance with the criteria of the
<br />AASHTO LRFD Bridge Desigh Specifications .
<br />INTRODUCTION
<br />To determine the required supporting strength of
<br />concrete pipe installed under intermediate and thin
<br />thicknesses of asphalt or flexible pavements, or relatively
<br />shallow earth cover, it is necessary to evaluate the effect
<br />of live loads, such as highway truck loads, in addition to
<br />dead loads imposed by the soil and surcharge loads.
<br />LIVE LOADS
<br />If a rigid pavement or a thick flexible pavement
<br />designed for heavy duty traffic Is provided with a sufficient
<br />buffer between the pipe and pavement, than the live load
<br />transmitted through the pavement to the buried concrete
<br />pipe is usually negligible at any depth. If any culvert or
<br />sewer pipe is within the heavy duty traffic highway right-
<br />of-way, but not under the pavement structure, then such
<br />pipe should be analyzed for the effect of live toad
<br />transmission from an unsurfaced roadway, because of
<br />the possibility of trucks leaving the pavement.
<br />DEAD LOADS
<br />Various methods for analyzing soil dead loF.ds, which
<br />have been developed over the years, are presented in
<br />the ACPA"Concrete Pipe Technology Handb,3ok"(7).
<br />SURCHARGELOADS
<br />A common type of surcharge load is additional soil
<br />fill placed after the pipe has been installed for a period of
<br />time. If the surcharge load is a building or other surface
<br />load, the resultant uniformly distributed load can be
<br />converted to an equivalent height of fill, and then
<br />evaluated as an additional soil load. When concrete pipe
<br />has been installed underground, the soil -structure system
<br />tail contivially show an increase in load capauty. Data
<br />un wuu dRd pipe, whicn have been removed from service
<br />and tested, indicate an increase in concrete strength and
<br />an increase in load carrying capacity of 10 to 40 percent.
<br />Settlement and consolidation will improve the soil
<br />structure surrounding the pipe, which also improves load
<br />carrying capacity.
<br />American Concrete Pipe Associalion • 222 W. Las Colinas Blvd., Suite 641 • Irving, TX 75039 • (972) 506.7216 • FAX (972) 506-7682 1
<br />0201 ACPA Design Data 1
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