Live-load-design-on-concrete-pipe.pdf

Live Load Design of Concrete Pipe

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

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

Distribution Through the Pipe – A Critical Item • Industry

• 1.3125 x OD

• AASHTO

• Previously

• No Comment

• Currently

• 0.06 x ID

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 2.1.3.”

Constant Change (D-Loads – lbs/ft/ft) Type 2 Installation Depth (ft)

1

2

Code

Pipe Inside Diameter (in) 12

36

60

Standard Spec

1161

761

671

LRFD 1998

1700

850

800

LRFD 2014

1492

1244

948

Standard Spec

667

557

530

LRFD 1998

1050

700

675

LRFD 2014

1322

1137

875

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 • • • • •

10

Rigid Rugged Resilient

Distribution Through Pipe

Coeffm = 14500 Do-1.58+0.755 CoeffI = 242 Do-1.97+0.855

Moment from Live Load – Bedding Factor Old/Proposed

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Moment from Live Load – Bedding Factor CURRENT

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Comparison Table

Type 2 Installation

Depth (ft)

1

2

Code

Pipe Inside Diameter (in) 12

36

60

LRFD 1998

1700

850

800

LRFD 2014

1492

1244

948

Proposed

1659

920

998

LRFD 1998

1050

700

675

LRFD 2014

1322

1137

875

Proposed

993

749

717

NCHRP 20-7, Task 316

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Rigid Rugged Resilient

NCHRP 20-07, Task 316 Moments at the Crown From a 24.7 kip wheel load

16

Diameter (in)

Depth (ft)

LRFD 2007 (in-kips/ft)

LRFD 2013 (in-kips/ft)

Test (in-kips/ft)

24

4

5.8

5.8

2.3

24

2

17.0

17.0

6.0

24

1

29.4

29.4

10.1

48

4

18.9

16.8

5.3

48

2

36.9

33.5

11.6

48

1

56.9

53.1

18.5

Rigid Rugged Resilient

Moments at the Crown From a 24.7 kip wheel load

17

Diameter (in)

Depth (ft)

LRFD 2013 (in-kips/ft)

Test (in-kips/ft)

Proposed (in-kips/ft)

24

4

5.7

2.3

5.1

24

2

9.9

6.0

7.3

24

1

17.5

10.1

9.1

48

4

20.3

5.3

17.2

48

2

26.0

11.6

18.3

48

1

46.5

18.5

22.6

Rigid Rugged Resilient

LRFD

Standard

H = 1 ft

𝑙𝑙𝑤𝑤 =

𝑙𝑙𝑡𝑡 + 1.75𝐻𝐻 12

lw = 2.58 ft

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Rigid Rugged Resilient

𝑙𝑙𝑤𝑤 =

𝑙𝑙𝑡𝑡 + 1.15𝐻𝐻 12

lw = 1.98 ft

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

Revised Live Load Bedding Factors Height of Fill feet 0.5

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Pipe Diameter (inches) 12 2.2

24 2.1

36 1.6

1.7

48 1.4

60 1.3

72 1.2

1.1

1.1

1.4

1.3

1.3

1.5

1.4

1.4

1.5

1.5

1.3

1.0

2.2

1.5

2.2

2.2

2.0

2.2

2.2

2.5

2.2

2.2

2.2

3.0

2.2

2.2

2.2

2.2

3.5

2.2

2.2

2.2

2.2

2.2

4.0

2.2

2.2

2.2

2.2

2.2

Rigid Rugged Resilient

1.9

2.2

1.6

1.7

1.8

2.1

2.0

2.2

1.5 1.7

1.8

1.8

2.0

2.0

2.2

84

1.7

1.8

1.8

2.0

2.0

2.2

1.8 2.2 2.2 2.2

1.7

1.7

1.8

1.8

2.0

1.9

2.1

2.1

2.0

Using Revised Bedding Factors Moments at the Crown From a 24.7 kip wheel load

21

Diameter (in)

Depth (ft)

LRFD 2013 (in-kips/ft)

Test (in-kips/ft)

Proposed (in-kips/ft)

24

4

5.7

2.3

5.1

24

2

9.9

6.0

7.3

24

1

17.5

10.1

10.4

48

4

20.3

5.3

17.2

48

2

26.0

11.6

18.3

48

1

46.5

18.5

22.6

Rigid Rugged Resilient

Lw

CL value

CL < 1 Lw

CL = 1 22

Rigid Rugged Resilient

CL Value • Plastic Pipe

23

Rigid Rugged Resilient

• Metal Pipe

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

24

Rigid Rugged Resilient

25

Rigid Rugged Resilient

Equation for Beta

Crack Spacing Parameter

Moment at the Location Being Checked for Shear

Crack Spacing Parameter

Add: sxe =

the incorporation of the effect of maximum aggregate size into the crack spacing parameter. The requirement that sxe equal or exceed 12 inches need not apply to slabs.

Limit sxe to 12 inches?

31

Rigid Rugged Resilient

Moment at the Location Being Checked for Shear • Add: • In continuous slabs not containing prestressing, the value of |Mu| for the location being analyzed may be utilized without consideration of the |Mu|min = |Vu – Vp|dv limitation.

Why the Vu x dv requirement? Tension Face

Compression Face

If Mv = 0, and Nv = 0 Tension in the Entire Element www.concrete-pipe.org

β versus Span

34

Rigid Rugged Resilient

β versus ρ (depth limit removed)

35

Rigid Rugged Resilient

β versus ρ (no limit)

36

Rigid Rugged Resilient

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

Rigid Rugged Resilient

De Cossio Equation for Shear

38

Rigid Rugged Resilient

5.14.5.3 Method

39

Rigid Rugged Resilient

5.8.3 With No Restrictions

40

Rigid Rugged Resilient

Minimum Mu Required?

41

Rigid Rugged Resilient

Why the Minimum Mu?

42

Rigid Rugged Resilient

What Has Been Implied? • The minimum value of sx should be removed, or at least reduced to 5 inches. • Relative Agreement

• The requirement that Mu be not less than Vu*dv should be removed, at least for frames/continuous members • Additional discussion required

43

Rigid Rugged Resilient

The End [email protected]

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Rigid Rugged Resilient

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