ACPA 2014 Pipe School – Houston, TX Direct Design Hugh Martin, P.E. Hanson Pipe & Precast www.concrete-pipe.org

Direct Design Approach 2 Direct Design Approach Direct Design vs. Indirect Design Concrete Design vs. D-Load Design www.concrete-pipe.org

Indirect Design Method 3 Indirect Design Method Analyze Pipe Installation and Support Conditions Calculate Total Load on Pipe Calculate and Apply Bedding Factors Determine Pipe Class / D-Load www.concrete-pipe.org

Direct Design Method Define Pipe Material Properties 4 Direct Design Method Define Pipe Material Properties Specify Installation Conditions Calculate Total Load on Pipe Calculate Design Forces Design Pipe to Resist Design Forces www.concrete-pipe.org

References AASHTO LRFD Bridge Design Specifications, 6th Ed., American Association of State Highway and Transportation Officials, 2012. Standard Practice for Direct Design of Buried Precast Concrete Pipe Using Standard Installations (SIDD), ASCE 15-98, American Society of Civil Engineers, 2000. Concrete Pipe Technology Handbook, American Concrete Pipe Association, 2001.

Installation Methods Trench Embankment Tunnel

AASHTO LRFD 12.10.2.1 “Standard installations for both embankments and trenches shall be designed for positive projection, embankment loading conditions where Fe shall be taken as the vertical arching factor, VAF, specified in Table 12.10.2.1-3 for each type of standard installation.” www.concrete-pipe.org

Loads Earth Load Internal Fluid Load Pipe Weight Surcharge Load Live Load

Earth Load Final Grade WE = PL x Fe Prism Load (PL) H Where: ( ) c B 8 π 4 H w PL ú û ù ê ë é ÷ ø ö ç è æ - + = Bc (O.D.) WE = w x Bc x H x Fe (AASHTO LRFD 12.10.2.1-1)

Fluid Load Effects are of little significance in small diameter pipe. Fluid weight is calculated as:

Pipe Weight Always included in direct design. Pipe weight is given by:

Live Loads Highway Live Load Railroad Live Load Aircraft Live Load

AASHTO HL-93 Live Load H20 vs. HS20

Tire Contact Area LRFD (3.6.1.2.5) 10”x20” Footprint LFD 6.4.2: “When the depth of fill is less than 2 feet, the wheel load shall be distributed as in slabs with concentrated loads.”

Live Load Distribution “Live load shall be distributed to…concrete pipe with less than 2.0 ft. of fill as specified in Article 4.6.2.10.” – LRFD 3.6.1.2.6a E = 96 + 1.44S (for Axle Load) E = in. S = Span (ft.) ‘l’ = 0” or 1” per LFD’s reference to “concentrated loads”. ‘l’ = 10” + 1.15H per LRFD For skewed culverts???

Live Load Distribution Factor (LLDF) 2 ft. of Cover or Greater Structure Type Transverse to Span Parallel to Span Concrete Pipe with Depth 2 ft. or Greater 1.15 for Diameter 2 ft. or Less 1.75 for Diameter 8 ft. or Greater Linearly Interpolate for LLDF Between 2 ft. and 8 ft. Same as Transverse All Other Culverts and Buried Structures 1.15 www.concrete-pipe.org

Live Load Distribution – LRFD 3.6.1.2.6b Live Load Applied From “Interacting Wheels” As Opposed to Axles. Axle Load Interaction Depth

Live Load Distribution Previously: Le = L + 1.75(¾ Bc) For 36” RCP, Le = L + 4.8125’ Currently: Le = L + 0.06 Di For 36” RCP, Le = L + 0.18’

Live Load Distribution For single-span culverts, the effects of live load may be neglected where the depth of fill is more than 8.0 ft and exceeds the span length;” – LRFD 3.6.1.2.6a

AASHTO LRFD – Lane Load “Where the slab spans primarily in the transverse direction…[and] where the slab spans primarily in the longitudinal direction…only the axle loads of the design truck or design tandem of Articles 3.6.1.2.2 and 3.6.1.2.3, respectively, shall be applied.” – LRFD Article 3.6.1.3.3

Calculate Design Forces Uniform Load System Radial Load System SIDD Pressure Distribution

Uniform Load System Rational Approximation Also Allowed per LRFD 12.10.4.2.1 Uniformly distributed vertical and horizontal components of pressure. First proposed by J.M. Paris in the early 1920’s.

Radial Load System Pressures act normal to the pipe surface and vary as a trigonometric function. First presented by H.C. Olander in 1950.

SIDD Pressure Distribution Resulted from a long range research program initiated by the ACPA in the 1970’s. Commonly referred to as the Heger Pressure Distribution.

Vertical Arching Factors (SIDD) INSTALLATION Fe TYPE 1 1.35 TYPE 2 1.40 TYPE 3 1.40 TYPE 4 1.45

SIDD Pressure Distribution The following equations are used to calculate the internal pipe moments, thrusts, and shears:

SIDD Pressure Distribution Type 1 Installation

SIDD Pressure Distribution Type 2 Installation -.437

SIDD Pressure Distribution Type 3 Installation

SIDD Pressure Distribution Type 4 Installation

SPIDA Finite Element Analysis Soil Pipe Interaction Design Analysis

Pipe Wall Design “The procedures for analysis and design are similar to those used for other reinforced concrete structures.” – LRFD C12.10.4.2.1 Design procedure is based on “limit states” criteria to ensure adequate pipe strength and serviceability.

Direct Design – Articles 12.5.3 & 12.10.4.1 Flexure & Thrust Steel Concrete Crack Control Diagonal Tension (Shear) 7 ksi Max. Conc. Comp. Strength Radial Tension

Radial Tension

Pipe Wall Design Steps: Determine required reinforcement areas based on the tensile yield strength limit. Check radial tension. Check compressive strains. Check shear. Modify design if any strength limit is exceeded. Design stirrup reinforcement (if req’d.). Check crack width.

Example:

Same Procedure for Outer Cage

Same Procedure for Crown

www.concrete-pipe.org