LRFD AND POLICY UPDATE

By: Calvin E. Reed PE

State Bridge Design Engineer and Assistant Bureau Chief

October 9, 2015

OVERVIEW• KANSAS BRIDGE TRENDS

• NOTABLE CHANGES TO LRFD BRIDGE DESIGN

SPECIFICATIONS

• NOTABLE CHANGES TO KANSAS BRIDGE DESIGN

POLICY

• WHAT’S IN THE WORKS

BRIDGES IN KANSAS• Total Bridges in Kansas: 24,929

o 19,477 Owned by Local Entities

o 369 Owned by KTA

o 5,081 Owned by KDOT

• Average Age of a Kansas Bridge: 48 years

• Percent of Bridges > 50 years old: 44%

BRIDGES IN KANSAS BY DECADE BUILT

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500

1000

1500

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2500

3000

3500

4000

STATE LOCAL KTA OTHER

STATE OWNED BRIDGES

0

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• 51% of State System Built Prior to 1970

BRIDGE CONDITION OVER TIME

0%

2%

4%

6%

8%

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12%

14%

16%

18%

20%

State Owned System is currently at about 1.00% Structurally Deficient.

% Bridges Structurally Deficient

LRFD 2015 INTERIMS

• CONCRETE o Most changes came about by adopting guidelines from NCHRP Report

603

o General changes to account for higher strength concrete (up to 15 ksi)

o Development Length and Splices

o Basic Hooks

• STEELo Concrete Filled Steel Tube (CFST) Design

CONCRETE• Creep (5.4.2.3.2)

New Equation Old Equation

𝑘𝑡𝑑 =𝑡

12100−4𝑓′𝑐𝑖𝑓′𝑐𝑖+20

+𝑡𝑘𝑡𝑑 =

𝑡

61−4𝑓′𝑐𝑖+𝑡

CONCRETE• Modulus of Elasticity (5.4.2.4)

New Equations Old Equations

𝐸𝑐 = 120,000𝐾1𝑤𝑐2𝑓′𝑐

0.33𝐸𝑐 = 33,000𝐾1𝑤𝑐

1.5𝑓′𝑐0.5

𝐸𝑐 = 2,500𝑓′𝑐0.33

𝐸𝑐= 1,820𝑓′𝑐0.5

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6000

0 2 4 6 8 10 12

Ec

f‘c

Old New

CONCRETE• Development Length (5.11.2.1.1)

o Modified version of ACI method

o 𝑙𝑑 = 𝑙𝑑𝑏 𝜆𝑟𝑙 × 𝜆𝑐𝑓× 𝜆𝑙𝑤× 𝜆𝑟𝑐 × 𝜆𝑒𝑟

• 𝑙𝑑𝑏 = base development length

• 𝜆𝑟𝑙 = reinforcement location factor (+)

• 𝜆𝑐𝑓 = coating factor (+)

• 𝜆𝑙𝑤 = lightweight concrete factor (+)

• 𝜆𝑟𝑐 = reinforcement confinement factor (-)

• 𝜆𝑒𝑟 = excess reinforcement factor (-)

CONCRETE • Development Length (cont’d)

o 𝑙𝑑𝑏 = 2.4𝑑𝑏𝑓𝑦

𝑓′𝑐

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#3 #4 #5 #6 #7 #8 #9 #10 #11 #14 #18

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2015 Interims

2014

CONCRETE• Development Length (cont’d)

o Confinement Factor

o 0.4 ≤ 𝜆𝑐𝑟 =𝑑𝑏

𝑐𝑏+𝑘𝑡𝑟≤ 1.0

o Big benefit for proper confinement!

CONCRETE• SPLICES(5.11.5.3.1)

o Class A Splice: 1.0 ldo Class B Splice: 1.3 ldo Class C Splice: No longer Exists

• CLASS A: At least twice the area of reinforcement

required for the entire length of the splice

• CLASS B: Not Class A

CONCRETE• STANDARD HOOKS (5.11.2.4)

o Modified version of ACI method

o 𝑙ℎ = 𝑙ℎ𝑏 𝜆𝑐𝑓 × 𝜆𝑙𝑤× 𝜆𝑟𝑐 × 𝜆𝑒𝑟

• 𝑙ℎ𝑏 = base development length

• 𝜆𝑐𝑓 = coating factor (+)

• 𝜆𝑙𝑤 = lightweight concrete factor (+)

• 𝜆𝑟𝑐 = reinforcement confinement factor (-)

• 𝜆𝑒𝑟 = excess reinforcement factor (-)

STEEL• Concrete Filled Steel Tube Design

o Section 6.4.1

o Section 6.5.4.2

o Section 6.9.6

o Section 6.12.1.2.1

o Section 6.12.2.3.3

NOTABLE POLICY CHANGES

• Prestressed Girders

o Epoxy Coated Mild Reinforcing Under Joints

• Embedded Structures

o Call out Embedded Structures in Construct

Note

• RCB

o Allow precast on all RCB’s/RFB’s with less than

3 ft. rise

UPCOMING• NU Girders

o Verification Study by KSU

o Deck de-bonding research by KU

o Base Sheets

QUESTIONS?