Embed Size (px)
Citation preview
Additional Considerations for
Superstructure Evaluation
CG Gilbertson
March 22nd, 2011
Additional Considerations
• Structural steel
• Reinforced concrete
• Prestressed concrete
• Timber
• Truss bridges
Additional Considerations for LRFR
Structural Steel
US-141, Menominee River, Dickinson CO.
Ford Exit Dr. US-12, Ypsilanti Co.
Structural Steel
• Non-specification metals
• Coupon testing is needed
• Take yield as mean test value minus 1.65
standard deviations
• Unavailable specifications
• Estimate according to year built using the
following table:
• (6B.5.2.1 – The Manual for Bridge Evaluation)
Structural Steel (LFR)
• For beams consider overload
requirements of AASHTO Standard
Spec. 10.57
• Operating rating of welds, bolts, and
rivets use max strength from Table
10.56A AASHTO Standard Spec.
• For friction joint fasteners (A325 bolts)
use a stress of 21 ksi and 1.0 for A1 &
A2
Structural Steel (LRFR)
Applicable Limit States (6A.4.2.2-1):
Strength I
Strength II
Service II
Fatigue
Resistance factors
LRFD Design Article 6.5.4.2
Reinforced Concrete
Muskegon River, MI: Oldest Surviving
Concrete Girder Bridge (1900)
US-12, St. Joseph River, Berrien Co.
Reinforced Concrete
• Use the following table for minimum concrete compressive strength:
Year of Construction F’c (ksi)
Prior to 1959 2.5
1959 and later 3.0
Ref: The Manual for Bridge Evaluation
Reinforced Concrete • Use the following table for reinforcement yield strength:
Reinforcing steel Yield Point Fy
(ksi)
Unknown Steel (prior to 1954) 33
Structural Grade 36
Billet or Intermediate Grade
and unknown after 1954 (Grade 40) 40
Rail or Hard Grade (Grade 50) 50
Grade 60 60
Ref: Manual for Condition Evaluation of Bridges
Reinforced Concrete (LFR)
• Area of tension steel at yield for determining
ultimate moment capacity shall not:
• Exceed that available in the section
• Exceed 75% of reinforcement required for
balanced conditions
Reinforced Concrete (LRFR)
Applicable Limit States (6A.4.2.2-1):
Strength I
Strength II
Service I
Resistance factors for concrete
members for strength limit state as
specified in LRFD Design Article 5.5.4.2
Reinforced Concrete (LRFR)
Shear should be checked for permit
loads, however, if no signs of shear
distress in service, then there is no need
to check for shear when rating design or
legal loads.
Prestressed Concrete
M-13/Saganing Creek, Arenac Co.
Prestressed Concrete (LFR)
• Allowable stresses at inventory must be
checked (AASHTO 9.15.2.2)
(Summarized in upcoming slides)
• In cases of unusual design with
dispersed tendons, operating stresses
not to exceed 0.9 yield stress of
tendons.
Prestressed Concrete (LFR)
• If minimum
reinforcement was not
used, the bridge owner
may opt to limit live load
to preserve relationship
between ФMn and Mcr. If
this is done, kФMn
should be used in the
flexural strength
equations.
1.2
n
cr
Mk
M
1.33
n
u
Mk
M
or
When ФMn<1.2Mcr
Prestressed Concrete (LFR)
• Federal Level Inventory (HS-20 Truck) • Concrete Tension • Concrete Compression (2 equations) • Prestress Steel Tension • Flexural Strength • Shear Strength
Prestressed Concrete (LFR)
Inventory Rating Equations:
l
spdc
F
FFFfRF
)('6
l
spdc
F
FFFfRF
)('6.0
l
spdc
F
FFFf
RF
)(2
1'4.0
Concrete Tension
Concrete Compression
Concrete Compression
Prestressed Concrete (LFR)
Inventory Rating Equations (Cont.):
l
spdy
F
FFFfRF
)(8.0 *
)1(17.2
)3.1(
IL
SDRRF n
Prestressing Steel Tension
Flexural and Shear Strength
Prestressed Concrete (LFR)
• Federal Level Operating (HS-20 Truck) • Flexural Strength • Shear Strength • Prestressing Steel Tension
• Michigan Level Operating (1,2, & 3-unit trucks)
• Flexural Strength • Shear Strength • Prestressing Steel Tension
Prestressed Concrete (LFR)
Operating Rating Equations:
l
spdy
F
FFFfRF
)(9.0 *
)1(3.1
)3.1(
IL
SDRRF n
Prestressing Steel Tension
Flexural and Shear Strength
Prestressed Concrete (LFR)
RF = Rating factor
f’c = concrete compressive strength
6√f’c = allowable concrete tensile stress. A factor of 3√f’c
may be applicable, or this allowable stress may
be zero, as provided in AASHTO 9.15
Fd = unfactored dead load
Fp = unfactored stress due to prestress force after all losses
Fs = unfactored stress due to secondary prestress forces
Fl = unfactored live load stress including impact
Prestressed Concrete (LFR)
ΦRn = nominal strength of section satisfying the
ductility limitations of AASHTO 9.18 & 9.20
Includes both ΦMn and ΦVn
D = unfactored dead load moment or shear
S = unfactored prestress secondary moment or shear
L = unfactored live load moment or shear
f*y = prestressing steel yield stress
I = impact factor
Prestressed Concrete (LFR)
Note: In the rating equations, effects of dead
load, prestress force and secondary prestress
forces are subtracted from the allowable stress
or capacity. The actual effects of each load
relative to the allowable stress or capacity
should be considered in the rating equations
through using appropriate signs.
Prestressed Concrete (LRFR)
Applicable Limit States (6A.4.2.2-1):
Strength I
Strength II
Service I
Service III
Resistance factors for concrete
members for strength limit state as
specified in LRFD Design Specifications,
5.5.4.2
Prestressed Concrete (LRFR)
Shear should be checked for permit
loads, however, if no signs of shear
distress in service, then there is no need
to check for shear when rating design or
legal loads.
Prestressed Concrete (LRFR)
Special considerations for rating of
segmental prestressed concrete
bridges:
6A.5.11
Timber Superstructures
Wagners Bridge, N. Fork Snoqualmie River,
King Co. WA
Eagle River Bridge, M-26, Keweenaw Co.
Timber (LRFR)
Applicable Limit States (6A.4.2.2-1):
Strength I
Strength II
Resistance factors
LRFD Design Article 8.5.2.2
Timber (ASR)
• ASR
• Inventory unit stress = allowable stress for stress-grade lumber given in AASHTO Standard Specs.
• Operating unit stress = 1.33 times allowable stress for stress-grade lumber, then reduced for grade and condition based on inspection
Timber (ASR)
Allowable operating stress for long columns (11<l/d<50), psi
2
0.40
( / )
P E
A l d
2
4.8
( / )
P E
A l r
All columns: Square or rectangular columns:
P = total load, lb
A = x-sect area, sq. in.
E = modulus of elasticity
l = unsupported length between points of
lateral support of simple columns, in
r = least radius of gyration of section, in
d = dimension of narrowest face, in
Truss Bridges
US-2 / Cut River, Mackinac Co.
M-86, Prairie River, St. Joseph Co.
Truss Bridges
McMillin Bridge, Pierce County , WA
Trusses
• During inspection:
• All corrosion/section loss should be recorded and
subtracted from the gross cross-section area.
• Tension Members
• Find size, number, and location of all bolts/rivets (to determine
net area)
• Check condition of threaded rods at turnbuckles
• Compression Members
• Check for misalignments, bends, or kinks
• Check connections for eccentricities
References:
Bridge Analysis Guide, 2005 Edition with 2009 Interim Update. MDOT Construction and Technology Support Area
The Manual for Bridge Evaluation, Second Edition, AASHTO, Washington DC. (2011)
Michigan Historic Bridge Webpage:
http://www.michigan.gov/mdot/0,1607,7-151-9620_11154_11188---,00.html
