wassef presentation

7/28/2019 Wassef Presentation

1/78

DESIGN SPECIFICATION AS N EXAMPLE OF

PROBABILISTIC-BASED SPECIFICATIONS

State University of New York at Buffalo,

Presented ByWagdy G. Wassef, P.E., Ph.D.

Modjeski and Masters, Inc.


2/78

A Brief Histor 1931 First printed version of AASHO Standard

Structures 1970s AASHO becomes AASHTO (1990s AREA becomes

AREMA)

Early 1970s AASHTO adopts LFD Late 1970s OMTC starts work on limit-states based

OHBDC


3/78

Technically state-of-the-art specification.

. Readable and easy to use. Keep specification-type wording do not develop

a textbook. Encourage a multi-disciplinary approach to bridge

desi n.


4/78

A new philosophy of safety - LRFD

The relationship of the chosen reliability level, theload and resistance factors, and load models

roug e process o ca ra on new load factors new resistance factors


5/78

-


6/78

Some Algebra

2Q

2 RQ)-(R + =

2Q

2 R +

- =

x 1

= R = + + Q = R ii2Q

2 R

ii x

=

Q R + +


7/78

Load and Resistance Factor Desi n

Q R = R in which: i = D R I 0.95 for loads for max = I D R . or oa s or m n where: = load factor: a statisticall based multi lier on

force effects = resistance factor: a statistically based


8/78

i = load modifier =

R = a factor relating toredundancy

I = a ac or re a ng oimportance

Q i = nominal force effect: adeformation stress, or stressresultant

=n

R r = factored resistance: Rn


9/78

Reliabilit Calcs Done for M and V Simulated Bridges Based on Real Ones

-with spans of 30,60,90,120,and 200 ft, andspacings of 4,6,8,10,and 12 ft.

Composite steel girder bridges having the sameparameters identified above.

P/C I-beam brid es with the same arameters identified above.

R/C T-beam bridges with spans of 30,60,90,and

, .


10/78

Reliabilit of Std S ec vs. LRFD 175 Data Points


11/78

Major Changes Revised calculation of load distribution

K S S + 0.075 = g g0.10.20.6

t s

Circa


12/78

Combine plain, reinforced and prestressed concrete.

. Limit state-based provisions for foundation design. Expanded coverage on hydraulics and scour. The introduction of the isotropic deck design. Expanded coverage on bridge rails. Inclusion of lar e ortions of the AASHTO/FHWA

Specification for ship collision.


13/78

Changes to the earthquake provisions to eliminate

making the method of analysis a function of theimportance of the structure.

Guidance on the design of segmental concretebridges from Guide Spec.

The develo ment of a arallel commentar . New Live Load Model HL93 Continuation of a long story


14/78

1923 AREA Specification

4k6k

16k24k

10-Ton15-Ton

8k14'

32k5.5 '

20-Ton

VERY CLOSE!!


15/78

1928-1929 Conference Specification

6k14'

24k30'

6k14'

24k30'

8k14'

32k30'

6k14'

24k30'

6k14'

24k

15-Ton 15-Ton 20-Ton 15-Ton 15-Ton

640 lb/ft

18,000 lb for Moment26,000 lb for Shear


16/78

1944 HS 20 Design Truck Added


17/78

Live Load Continued to be Debated Late 60s H40, HS25 and HS30 discussed

increasing weight of design truck wastefulobsolescence of existing bridges

1978 HS25 proposed again 1979 HS25 again commentary

need for heavier desi n load seems unavoidable HS25 best present solution 5% cost penalty


18/78

xc us on oa s ase onSpecial Report 225, 1990


19/78

EXCL/HS20 Truck or Lane or 2 25kips Axles @ 4 ft (110 kN @ 1.2 m)


20/78

HL-93


21/78


22/78

-

-

Second Draft - 1991 workable Third Draft - 1992 rett close Fourth Draft - 1993 ADOPTED!!

12,000 comments Reviewed by hundreds Printed and available - 1994


23/78

Upgrades and Changes to 1990ec no ogy

.

New wall provisions ongoing upgrade. 2002 upgraded to ASBI LFRD Segmental Guide

Specs. MCF shear in concrete simplified and clarified several

times ma or u date in 2002. Load distribution application limits expanded several

time in 1990s due to requests to liberalize.

.


24/78

2004 major change in steel girder design in

2005 seamless integration of curved steel bridgesending three decade quest


25/78


26/78

Where Do We Go From Here?


27/78

The original AASHTO LRFD live load

s u y was ase on oa measuremen smade in the 1970s in Ontario. How thisre a es o o ay s oa s


28/78

The specifications was calibrated for the

s reng m s a e w ere e e n on ofailure is relatively simple: if the factoredoa s excee e ac ore res s ance,

failure, i.e. severe distress or collapse, willa e p ace.What about service limit state and what is

failure under service limit states?


29/78

Two Current Projects of Special Note:

SHRP R19 B - Bridge for Service LifeBeyond 100 Years: Service Limit StateDesign (SLS)

NCHRP 12-83 Calibration of Service LimitState for Concrete


30/78

Modjeski and Masters, Inc.: John Kulicki, Ph.D., P.E.Wagdy Wassef, Ph.D., P.E.

University of Delaware: Dennis Mertz, Ph.D., P.E.University of Nebraska: Andy Nowak, Ph.D.NCS Consultants: Naresh Samtani, Ph.D., P.E.

NCHRP 12-83 Research TeamSame except that NCS Consultants are replaced with

Rutgers University: Hani Nasif, Ph.D., P.E.


31/78

Live load deflections

Bearings-movements and service forces Settlement of foundations and walls


32/78

Permanent deformations in compact steel

componen s Fatigue of structural steel, steel

reinforcement and concrete (through its

own limit state) Slip of slip-critical bolted connections


33/78

Stresses in prestressed concrete under

Crack control reinforcement

- Shrinkage and temperature reinforcement

p ng re n orcemen


34/78

s an mean ng u an ecalibrated?

Does it really relate to service---or

something else? Can (should) aging and deterioration be

incorporated? Can it reflect interventions?


35/78

Survey of owners se o a a

Calibration process


36/78

Crack control in reinforced concrete Load induced fatigue in steel and concrete - -


37/78

SLS Live Load live load model Finite Life fati ue load model Infinite Life fatigue load model

P/s beams)

Work on compiling info on joints and


38/78

Service and Fatigue LL has been achallenge

Truck WIM was obtained from the FHWA

and NCHRP Project 12-76 o a num er o recor s a ou m on

about 35 million used


39/78

Initial Filtering Criteria For Non-FatigueSLS (FHWA Unless Noted)

Individual axle weight > 70kips -

7 >Total length >200 ft

First axle s acin Speed > 100 mph

GVW +/- the sum of the axle weights by more than 7%. FHWA Classes 3 14


40/78

Filter #1 Questionable Records1 - Truck length > 120 ft2 sum of axle spacing > length of truck.3 - any axle < 2 Kips

- - 5 - GVW < 12 Kips

Filter #2 Presumed Permit Trucks 6 - Total # of axles < 3 AND GVW >50 kips7 - Steering axle > 35 k

8 individual axle weight > 45 kipsFilter #3 Traditional Fatigue Population

9 - Vehicles with GVW


41/78

Vehicles Passing Filters #1 & #2 will be

use or ca ra on o a m s a esexcept for Fatigue, the limit state for permitve c es an poss y reng .

Vehicles filtered by Filter #2 will beconsidered Permit vehicles and will bereviewed and may be filtered further.

Vehicles passing all three filters will beused for the fati ue limit state


42/78

WIM Data - FHWA

14 sites 4

5

of traffic at most sites The maximum 23

r i a

b l e Arizona(SPS-1) Arizona(SPS-2) Arkansas(SPS-2)

recorded GVW is 220kips

0

1

N

o r m a

l V Colorado(SPS-2)

Illinois(SPS-6)Indiana(SPS-6)Kansas(SPS-2)Louisiana(SPS-1)Maine(SPS-5)

from 20 to 65 kips-3

-2

-

S t a n

d a r Minnesota(SPS-5)

New Mexico(SPS-1)NewMexico(SPS-5)Tennessee(SPS-6)Virginia(SPS-1)Wisconsin SPS-1

0 50 100 150 200 250-5

-4

Delaware(SPS-1)Maryland(SPS-5)Ontario


43/78

Anal sis of the WIM Data

shear , ,

90, 120 and 200 ft ruc s caus ng momen s or s ears

< 0.15 (HL93) were removed


44/78

Removal of the Heav Vehicles for SLS

6New York 8382 Span 90ft

Filter trucks causing moments

4

or s ears more an .

live load effect) were removed

2

m a

l V a r i a

b l e

1,551,454

Number of trucks after filtering

-2

0

t a n

d a r d

N o r, ,

Number of removed trucks 540

-4

No Trucks Removed

0.03%

0 0.5 1 1.5 2 2.5 3-6

Truck Moment / HL93 Moment

0.03% Trucks Removed


45/78


46/78

Correlation Criteria

axles

GVW of the trucks is within +/- 5% All corresponding spacings between

axles are within +/- 10%


47/78

Ad acent Lanes - Florida140

100

120

y

record accuracy 1second

60

80

F r e q u e n

Number of Trucks :

1,654,004

20

40 Number of FullyCorrelated Trucks:

0 20 40 60 80 100 1200

Gross Vehicle Weight - Trucks in Adjacent Lanes

,

Max GVW = 102 kips


48/78

Adjacent Lanes Florida

, o , ,4

5

2

3

b l e

0

1

N o r m a

l V a r i

-2

-1

S t a n

d a r d

-5

-4

-

Florida I10 - 1259 Correlated Trucks - Side by SideFlorida I10 - All Trucks

Gross Vehicle Weight


49/78

One Lane Florida

, o , ,5

2

3

4

l e

0

1

o r m a l

V a r

i a b

-2

-1

S t a n d a r

d

-4

-3

Florida I10 - 4190 Correlated Trucks In One LaneFlorida I10 - All Trucks

0 50 100 150 200 250-

Gross Vehicle Weight


50/78

Conclusions for Multi le Presence

tails of the CDFs need not becons ere o occur s mu aneous y n

multiple lanes.

, - -load model need be considered.


51/78

-

ADTT = I,000, Project Bias on HL 93 = 1.4 ADTT = 5 000 Pro ect Bias on HL 93 = 1.45

COV = 12%

Project Bias varies with time interval which will

Not strongly influenced by span length


52/78

Span 60 ft

1.40

1.60

0.80

1.00

.

B i a s ADTT 250

ADTT 1000

0.40

0.60ADTT 2500

ADTT 5000

ADTT 10000

0.00

0.20

1 10 100 1000 10000 100 years


53/78

-

expected to be exceeded occasionally

enforcement may have to have additional

load)

- a ap a e as na ona no onalive load model


54/78

- ,

plus 1.5 standard deviations tabulated with

5 ADTTs = 250, 1,000, 2500, 5000 and 10,000

10 Time eriods = 1 da 2 weeks 1 month 2 months, 6 months, 1 year, 5 years, 50 years, 75 yearsand 100 years

pans = , , , , With and w/o DLA


55/78

Fatigue SLS LL Model


56/78

Live Load For Fati ue II finite fati ue life6

NCHRP Data - Indiana

0

2

o r m a

l V a

r i a

b l e

-4

-2

S t a n

d a r d

Station - 9511Station - 9512Station - 9532Station - 9534

Station - 9552

0 50 100 150 200 250 300-6

GVW [kips]

Rainflow counting yields cycles per truckVariety of spans and locations yields Mean, bias and COV


57/78

3*

n

1eq i i

i

eff

30 ft (-184)* 60 ft (-360)* 90 ft (-530)* 120 ft (-762)* 200 ft (-1342)*

90 -215 -300 -452 -896

- - - -

* Values in parentheses= current AASHTO fatigue moment

Example Using FHWA WIM Data 3


58/78

Example Using FHWA WIM Data 3sites

/ Fat Trk eq M M Fatigue II Load Factors for 3 sites

30 ft 60 ft 90 ft 120 ft 200 ft

0.45 0.56 0.51 0.54 0.63

0.48 0.60 0.57 0.59 0.67

0.47 0.60 0.55 0.58 0.68

,Passage and compare to current


59/78

C cles Per Passa e

4.00 Arizona (SPS1)

3.00

3.50 Arizona (SPS2)

Arkansas (SPS2)Colorado (SPS2)C

2.00

2.50 e aware

Illinois (SPS6)Kansas (SPS2)

cl 33% damage increase

1.00

1.50

Continuous Bridges

Maine (SPS5)Maryland (SPS5)Virginia (SPS1)

es

0.00

.

30 80 130 180

Middle Support

Wisconsin (SPS1)


60/78

- rc

30 ft 60 ft 90 ft 120 ft 200 ft

3.13 3.03 3.38 3.02 2.36

3.09 2.85 3.00 2.76 2.38

3.30 3.30 3.52 3.04 2.44


61/78

3/ rcFat Trk e

n M M

Current =0.75

AASHTOn

30 ft 60 ft 90 ft 120 ft 200 ft

0.52 0.71 0.66 0.68 0.73

0.57 0.74 0.71 .73 0.78

. . . . .

Hi h = 0.87 or 116% of current


62/78

the time stamps Not individual trucks one at a time

8 hypothetical trucks 49 axles

963 ft 843,000 lbs


63/78

MM Cobbled together existing pieces: Variation of program MM used in early 1990s truck

study that resulted in HL93 Loading modified to

Used rainflow counting algorithm based on ASTM E

1049 85 reviousl develo ed to rocessinstrumentation data for repair of in-service bridge tocalculate cycles per truck; and

ner s aw o ca cu a e eq.


64/78

Results:

n y a ew ssues nego a e

Final results damage factors same for simple span,ver close for Ne moment at ier of continuous.

Sometimes intermediate results varied seemed todepend maximum magnitude of small cycles (noise)

a was gnore --- e a a smoo ng

Common sense check MM found that

equ va en s ng e cyc e amage ac or or the 8 truck train could be used as acompar son c ec wor e we .

Does This Increase Make Sense?


65/78

Does This Increase Make Sense?2,500,000

t i o n s

1,500,000

, ,

C o m

b i n

1,000,000

r

o f T r u c

0

,

5 0 5 0 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8

N u m b

1 9

1 9

1 9

1 9

1 9

1 9

1 9

1 9

1 9

1 9

1 9

1 9

1 9

1 9

1 9

2 0

2 0

2 0

2 0

2 0

2 0

2 0

2 0

2 0

Year


66/78

120.0%

140.0% 1992 19971992 2002

60.0%80.0%

100.0%

n t C h a n g

20.0%

0.0%

20.0%

.

P e r c e

Truck Weight



67/78



68/78


69/78

-

LRFD article

5.7.3.4 Control of cracking bydistribution of reinforcement

Service I A:Crack control of R C

9.7.2.5Reinforcement requirementsfor concrete deck designed

Service I B:Crack control of R/C concrete deck

Stresses check at service IIIService IIIA: DecompressionService IIIB: Uncracked section (max

. . . m s a e a er osses u yprestressed components

ens e s ressService IIIC: Cracked section (specified crack width)


70/78

.

Bridges

Service III Limit State

Reliability Indices of Existing P/S Conc.


71/78

r ges3

4

5

e x 345

e x

-2

-1

0

1

2

R e l

i a l b i t y

I n

ave=0

-2-1012

R e

l i a l

b i t y

I n

ave=0.2

Decompression Max. Allowable TensionSpan Length (ft.) Span Length (ft.)

4

5

Reliability index of existing bridgesAssuming ADTT 5000-1

0

1

2

3

R e l

i a l b i t y

I n d e x ave=2

Max. Allowable Crack Width (0.016 in., 1 year return period)

-0 20 40 60 80 100 120 140 160

Span Length (ft.)

Reliability Indices of Existing P/S Conc.


72/78

r gesReliability index (return Period 1 year)

ADTTDecompression

Maximum

Allowable Tensile Stress

Maximum

Allowable Crack Width

1000 0.2 0.4 2.35

2500 0.1 0.3 2.20

. . .10000 0.15 0.1 1.88

Proposed Target *Beta

. . .

In any one year period the limit state will be exceeded in:500 of 1000 brid es for reliabilit index of 0.023 of 1000 bridges for reliability index of 2.0

Reliability Indices of Bridges Designed to


73/78

urren pec ca ons234

e x 234

e x

-4-3-2-101

0 20 40 60 80 100 120 140 160

R e l

i a l b i t y

I n ave= 0.15

-4-3-2

-101

R

e l i a

l b i t y

I n ave= 0.06

Decompression Max. Allowable TensionSpan Length (ft.) Span Length (ft.)

3

4 ave=1.9

Same existing bridges except No. of strands determined using current

specifications-4

-3

-2

-1

0

1

2

R e l

i a l b i t y

I n d e x

Max. Allowable Crack Width (0.016 in., 1 year return period)

Reliability IndexAssuming ADTT 5000

0 20 40 60 80 100 120 140 160Span Length (ft.)

Reliability Indices of Bridges Designed to


74/78

urren pec ca onsPerformance Level

ADTTDecompression

Maximum

Allowable Tensile Stress

Maximum

Allowable Crack Width

1000 0.05 0.26 2.20

2500 0.05 0.11 2.06

. . .10000 0.35 0.21 1.80

660 of 1000 bridges for reliability index of -0.1529 of 1000 bridges for reliability index of 1.90


75/78

Bridges designed with various spacing,,

Bridges designed with different spaneng s an sec on ypes u same g r er spacing

Bridges designed with different spanlengths and girder spacing but samesection types.


76/78

4.0

5.0

n d e x

4.0

5.0

I n d e x

1.0

2.0

3.0

R e l i a

l b i t y

1.0

2.0

.

R e l i a

l b i t y

Existin Brid es Redesi ned Brid es

0.030.0 60.0 80.0 100 120 140

Span Length (ft.)

0.030.0 60.0 80.0 100 120 140

Span Length (ft.)

Various girder spacing, section types, and.

ADTT = 5000 ax a owe crac w

Conclusions Related to SLS for Concrete


77/78

ruc ures

target reliability index to maintain current

Bluewater Brid e #2


78/78

First LRFD Major Bridge

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