Direct Design and Indirect Design of Concrete Pipe Part 2 Josh Beakley March 2011

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1 Direct Design and Indirect Design of Concrete Pipe Part 2 Josh Beakley March 2011

2 Latest in Design Methods? AASHTO LRFD Bridge Design Specifications 2010 Direct Design Method for Concrete Pipe 1993?

3 LRFD5732FlexuralResistance Flexural Resistance

4 Assumptions for Strength and Extreme Event Limit States Section Factored resistance of concrete components shall be based on conditions of equilibrium and strain compatibility 2 Strain is directly proportional to distance from neutral axis 3 Maximum compression strain at the extreme concrete compression fiber is 0.003

5 Assumptions for Strength and Extreme Event Limit States Section Stress in the reinforcement is based on a stress-strain strain curve representative of the steel or on an approved mathematical representation 5 The tensile strength of the concrete is neglected 6 The concrete compressive stress-strain strain distribution is assumed to be rectangular, parabolic

6 Assumptions for Strength and Extreme Event Limit States Section The net tensile strain in the extreme tension steel is determined from a linear strain distribution 8 The use of compression reinforcement in conjunction with additional tension reinforcement is permitted to increase the strength of flexural members.

7 What do we have in Section 12 for Pipe?

8 c = s =? = y Strain compatibility -1 Strain is directly proportional to distance from neutral axis 2 Maximum compression strain = Tensile strain determined from a linear strain distribution - 7

9 085*f` 0.85 c *b*a ba a = 1 *C Nu Mu A s f y Equilibrium -1 Tensile strength of concrete is neglected 5 Concrete stress-strain strain distribution is rectangular 6

10 Was Anything Missed? 4 Stress in the reinforcement is based on a stress-strain strain curve representative of the steel or on an approved mathematical representation 8 The use of compression reinforcement in conjunction with additional tension reinforcement is permitted to increase the strength of flexural members.

11 Review Some Factors for Difference Reinforcement Proportions Size Factor Steel Reinforcement Properties Double Reinforcement

12 B - Wall Pipe Class III in Type 2 16 ft. Advanced Steel Properties and Combined Moments 27 inch Pipe Advanced Steel Properties H f (ft) H r (ft) H cr (ft) H s (ft) Section 12

13 B - Wall Pipe Class III in Type 2 16 ft. Advanced DR and Steel Mod 42 inch Pipe Double Reinforced H f (ft) H r (ft) H cr (ft) 18 H s (ft) 17 Section 12

14 B - Wall Pipe Class III in Type 2 16 ft. Advanced DR and Steel Mod 54 inch Pipe Double Reinforced H f (ft) H r (ft) H cr (ft) H s (ft) 15 Min Section 12

15 B - Wall Pipe Class III in Type 2 16 ft. 66 inch Pipe H f (ft) Advanced DR and Steel Mod Double Reinforced Section 12 H r (ft) H cr (ft) H s (ft)

16 Where are the Benefits? Size Factor - < 36 inches Steel Reinf. Properties - < 54 inches Double Reinforcement - < 60 inches

17 PIPE DESIGN PROGRAMS

18 18 inch Pipe Class III

19 Class III 18 Inch Pipe Per ASTM C 76

20 PIPECAR Direct Design 18 inch B-Wall Pipe at 16 Feet

21 PIPECAR 3.E.B. Design 18 inch B-Wall Pipe Class III

22 How Does PIPECAR 3EB Calculate Flexural Steel?

23 M = Pr X

24 How Does PIPECAR 3EB Calculate Flexural Steel? A s f y (d-a/2) = PrX

25 How Does PIPECAR 3EB Calculate Flexural Steel? A s f y (d-a/2) = PrX

26 How Does PIPECAR 3EB Calculate Flexural Steel? PrX α α = lbs/ft/ft P = lbs/ft P = S i x α where S i is in feet r = (S i + h)/2 where S i is in inches

27 How Does PIPECAR 3EB Calculate Flexural Steel? X = X = (2) (12) 85 x C m x C mp C m x C mp C m = 1.0 for circular pipes (shape factor) C mp = coefficient for increased bending strength based on plastic behavior

28 X = 0.282/Cmp

29 The C mp Factor C s = coefficient for flexural reinforcement at springlines based on ASTM Specifications C mp = for a 18 inch B-wall pipe with C s =

30 X = 0.282/C mp X = 0.255

31 We calculate the moment at a specific location without any consideration of moment distribution as a result of the pipe size or reinforcement proportions

32 How Does PIPECAR 3EB Calculate Flexural Steel? A si = A si = if C s = were used

33 42 inch Pipe Class III

34 PipePac 42 Inch Pipe

35 ASTM C inch Class III, B- Wall A si = 0.21

36 42 inch Pipe at 16 feet of Fill

37 42 inch Pipe at 16 feet of Fill

38 42 Inch Class III Pipe in the Three-Edge Bearing Module

39 How Does PIPECAR 3EB Calculate Flexural Steel?

How Does PIPECAR 3EB Calculate Flexural Steel? A si = 0.

40 How Does PIPECAR 3EB Calculate Flexural Steel? A si = Not accounting for: Plastic behavior, steel stress passed yield, and double reinforcement. A si = Not accounting for: steel stress passed yield and double reinforcement - Not accounting for double reinforcement

41 HAVE WE KNOWN ABOUT THIS FOR A LONG TIME AND JUST NEVER ADDRESSED IT?

42 Shear

Calculating Shear in Concrete Research presented in (15) has shown

subject to a distributed loading, such as buried pipe, pe, is not

reduced by the presence and severity of flexural cracking.

is a significant consideration in the evaluation of the adequacy

43 Calculating Shear in Concrete Research presented in (15) has shown that the critical internal shear force in a flexural component subject to a distributed loading, such as buried pipe, pe, is not necessarily the maximum shear force, because shear strength is reduced by the presence and severity of flexural cracking. Because of this, the nondimensional ratio of moment to shear, M/Vd is a significant consideration in the evaluation of the adequacy of shear strength of a buried pipe. ACPA Concrete Pipe Technology Handbook Pipe

44 Section 12 Shear (Pipe)

45 Strain & Shear

46 Section 5 Shear (Concrete Design)

47 Proposed Change for Shear Design of V c 2 v b d Concrete Pipe (ASTM C 361 and ASCE) f' c F d F x F c F x x u Based on the Shear Design Method in the CHBDC and LRFD Codes. x u M u v 0.9d.5V u v cot v E s A si 0.4 N u ve 0.5 N u p

48 Summary The Direct Design Method is more conservative than the Indirect Design Method for pipes governed by flexure. The Direct Design is more conservative than the Indirect Design Method for small diameter pipes evaluated for shear. The Direct Design Method is a valuable tool for the simplified design of large diameter pipe, which h was its intended d use.

49 Summary Some of the conservatisms result from: Reinforcement Proportions Size Factor Steel Reinforcement Properties Double Reinforcement A concrete pipe could be more accurately designed following the prescribed assumptions in Section 5 on Concrete Design than it can following the required equations in Section 12 of the LRFD Code.

50 Summary The concrete pipe pp industry should not be punished in smaller size pipe simply because it made an effort to provide a simplified design process for large diameter pipe pp to make the design engineers life easier.

51 HDPE Indirect Design Method Stub Compression Test

52 AASHTO 2011 Section As an alternate to determining the effective area by the calculation procedure presented above, the results of the stub compression test, AASHTO T , 10, may be used

53 The End

Why are We Here? AASHTO LRFD Bridge Design Specifications Metal Pipe Section 12.7 Concrete Pipe Section Plastic Pipe Section 12.12

Direct Design and Indirect Design of Concrete Pipe Part 1 Josh Beakley March 2011 Why are We Here? AASHTO LRFD Bridge Design Specifications Metal Pipe Section 12.7 Concrete Pipe Section 12.10 Plastic Pipe