Live Load Design of Concrete Pipe

Transcription

1 Live Load Design of Concrete Pipe

2 Outline Critical Items Comparison of AASHTO Methods Testing and Research Latest Information

3 Live Load Distribution Factor A Critical Item AASHTO Standard Spec 1.75 AASHTO LRFD Initially 1.15 or 1.0 AASHTO LRFD Currently 1.15 up to 24 inch ID 1.75 for 96 inch ID and above Linear Interpolation in between these sizes

4 Distribution Through the Pipe A Critical Item Industry x OD AASHTO Previously No Comment Currently 0.06 x ID

5 Current Designs Based On: NCHRP Report 647, Recommended Design Specifications for Live Load Distribution to Buried Structures The results of the comparison of predictions from computer models with data from actual field test was often poor; extenuating circumstances are discussed in Section

6 Constant Change (D-Loads lbs/ft/ft) Type 2 Installation Depth (ft) Code Pipe Inside Diameter (in) Standard Spec LRFD LRFD Standard Spec LRFD LRFD

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9 Industry Testing Participants Forterra (formerly Hanson Precast Products) Rinker Materials Oldcastle Precast Forterra (formerly Cretex Companies Inc.) County Materials Corp. (formerly Independent Concrete Pipe Company) Scurlock Industries

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11 Distribution Through Pipe Coeff m = D o Coeff I = 242 D o

12 Moment from Live Load Bedding Factor Old/Proposed

13 Moment from Live Load Bedding Factor CURRENT

14 Comparison Table Type 2 Installation Depth (ft) Code Pipe Inside Diameter (in) LRFD LRFD Proposed LRFD LRFD Proposed

15 NCHRP 20-7, Task

16 NCHRP 20-07, Task 316 Moments at the Crown From a 24.7 kip wheel load Diameter (in) Depth (ft) LRFD 2007 (in-kips/ft) LRFD 2013 (in-kips/ft) Test (in-kips/ft)

17 Moments at the Crown From a 24.7 kip wheel load Diameter (in) Depth (ft) LRFD 2013 (in-kips/ft) Test (in-kips/ft) Proposed (in-kips/ft)

18 Standard LRFD H = 1 ft ll ww = ll tt HH ll ww = ll tt HH l w = 2.58 ft l w = 1.98 ft 18

19 Live Load 24 inch RCP at 1 foot LLDF = 1.75 and 1.15 Load Angle = 180 Bf = 2.2 Load Angle = 98 Bf = 1.9

20 Revised Live Load Bedding Factors Height of Fill Pipe Diameter (inches) feet

21 Using Revised Bedding Factors Moments at the Crown From a 24.7 kip wheel load Diameter (in) Depth (ft) LRFD 2013 (in-kips/ft) Test (in-kips/ft) Proposed (in-kips/ft)

22 L w C L value C L < 1 L w C L = 1 22

23 C L Value Plastic Pipe Metal Pipe 23

24 Box Culvert Shear Design For Fills Equal to or Greater Than 2 feet 24

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26 Equation for Beta

27 Crack Spacing Parameter

28 Moment at the Location Being Checked for Shear

29 Crack Spacing Parameter Add: s xe = the incorporation of the effect of maximum aggregate size into the crack spacing parameter. The requirement that s xe equal or exceed 12 inches need not apply to slabs.

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31 Limit s xe to 12 inches? 31

32 Moment at the Location Being Checked for Shear Add: In continuous slabs not containing prestressing, the value of M u for the location being analyzed may be utilized without consideration of the M u min = V u V p d v limitation.

33 Why the V u x d v requirement? Tension Face Compression Face If M v = 0, and N v = 0 Tension in the Entire Element

34 β versus Span 34

35 β versus ρ (depth limit removed) 35

36 β versus ρ (no limit) 36

37 Behavior and Strength in Shear of Beams and Frames Without Web Reinforcement Roger Diaz De Cossio and Chester P. Seiss A study of the test results in Table 3 and 4 reveals also that shear capacity is roughly a linear function of tensile steel percentage. 37

38 De Cossio Equation for Shear 38

39 Method 39

40 5.8.3 With No Restrictions 40

41 Minimum M u Required? 41

42 Why the Minimum M u? 42

43 What Has Been Implied? The minimum value of s x should be removed, or at least reduced to 5 inches. Relative Agreement The requirement that M u be not less than V u *d v should be removed, at least for frames/continuous members Additional discussion required 43

44 The End 44

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