Incorporation of Foundation Deformations in AASHTO LRFD Bridge Design Process, Naresh C

17 Pages·2017·2.27 MB·English

Incorporation of Foundation Deformations
inAASHTO LRFDBridge Design Process
Incorporation of Foundation Deformations in
AASHTO LRFDBridge Design Process
Naresh C. Samtani, PhD, PE, D.GE, F.ASCE
NCS GeoResources, LLC
May 3, 2017
SHRP2 at a Glance
SHRP2 Solutions–63 products
Solution Development– 430
processes, software, testing
procedures, and specifications
SHRP2 projects nationwide
Field Testing–refined in the field
Implementation–More than 430
transportation projects; adopt as
standard practice
R19B Product Page
SHRP2 Education Connection–
http://shrp2.transportation.org/Pages/R19B
connecting next-generation
_ServiceLimitStateDesignforBridges.aspx
professionals with next-generation
innovations
| 2
42nd Southwest Geotechnical Engineers Conferences May 03, 2017
May 1 –4, 2017, Phoenix, AZ Page 1of 17
Incorporation of Foundation Deformations
inAASHTO LRFDBridge Design Process
Initial SHRP2-TRB Research
Team for R19B
(cid:127) Modjeskiand Masters (M&M) Report S2-R19B-RW-1
– John M. Kulicki(Principal Investigator)
– WagdyG. Wassef (formerly M&M)
(cid:127) University of Delaware (UD)
– Dennis R. Mertz
(cid:127) University of Nebraska –Lincoln (UNL)
– Andrzej S. Nowak (now at Auburn)
(cid:127) NCS Consultants, LLC (NCS)
– Naresh C. Samtani
| 3
History of Work Related to
Foundation Deformations
(cid:127) Project R19B work started in 2009 Authors: Naresh C. Samtani
– Final Report published in 2015 and John M. Kulicki
(cid:127) Presentations at AASHTO SCOBS
Annual T-15 Committee Meetings
– 2012, New Orleans, LA
– 2014, Columbus, OH
– 2015, Saratoga Springs, NY
– 2016, Minneapolis, MN
(cid:127) Presentation at AASHTO SCOBS Mid
Year Joint Meeting of T-15 and T-5
committees on October 28, 2015, in
Chicago, IL; included a flow chart
(cid:127) Development of examples, draft agenda
items for T-15 and T-5 committees, a
white paper, and a training course
| 4
42nd Southwest Geotechnical Engineers Conferences May 03, 2017
May 1 –4, 2017, Phoenix, AZ Page 2of 17
Incorporation of Foundation Deformations
inAASHTO LRFDBridge Design Process
Bridge Configuration and
Foundation Types
Reference: Nielson (2005)
Foundation Deformations
(cid:127) Vertical (Settlement)
(cid:127) Lateral (Horizontal)
(cid:127) Rotation
| 5
AASHTO Table 3.4.1-1
Superimposed
Deformations
| 6
42nd Southwest Geotechnical Engineers Conferences May 03, 2017
May 1 –4, 2017, Phoenix, AZ Page 3of 17
Incorporation of Foundation Deformations
inAASHTO LRFDBridge Design Process
Superimposed Deformations
Article 3.12.6 – Settlement
(cid:127) “Force effects due to extreme
values of differential settlement
among substructures and within
individual substructure units shall
be considered.”
Commentary
(cid:127) “Force effects due to settlement may be reduced by
considering creep. Analysis for the load combinations in
Tables 3.4.1-1 and 3.1.4-2 which include settlement
should be repeated for settlement of each possible
substructure unit settling individually, as well as
combinations of substructure units settling, that could
create critical force effects in the structure.”
| 7
Standard Specifications
– 17th Edition (2002)
(cid:127) Article 3.3 – DEAD LOAD
3.3.2.1 “If differential settlement is
anticipated in a structure,
consideration should be given to
stresses resulting from this
settlement.”
(cid:127) Since the above stipulation is under the parent article
(3.3, Dead Load), it implies that settlement effects
should be considered wherever dead load appears in
the allowable stress design (ASD) or load factor design
(LFD) load combinations.
| 8
42nd Southwest Geotechnical Engineers Conferences May 03, 2017
May 1 –4, 2017, Phoenix, AZ Page 4of 17
Incorporation of Foundation Deformations
inAASHTO LRFDBridge Design Process
Key Points
(cid:127) Evaluation of differential deformation is mandated by
AASHTO bridge design specifications regardless of design
platform (ASD, LFD, or LRFD)
– It is not a new requirement
(cid:127) In LRFD platform,
– Category of superimposed deformations
– Theg load factor appears in both strength and service
SE
limit state load combinations
(cid:127) The uncertainty of predicted deformations needs to be
calibrated for the g load factor within the overall framework
SE
of limit state design
| 9
Differential Settlement, D
d
D
S d
L
S
(cid:127) Differential settlement, D , induces force effects
d
within superstructure
(cid:127) Differential settlement, D , when normalized by span
d
length, L , is an expression of angular distortion
S
| 10
42nd Southwest Geotechnical Engineers Conferences May 03, 2017
May 1 –4, 2017, Phoenix, AZ Page 5of 17
Incorporation of Foundation Deformations
inAASHTO LRFDBridge Design Process
Concept of Differential Settlement
and Angular Distortion
| 11
Induced Moments in
Continuous-Span Bridges
EXAMPLE
(cid:230) (cid:246)(cid:230) (cid:246)
6EID EI D
M = d =6(cid:231) (cid:247)(cid:231) d (cid:247)
D
L2S (cid:231)ŁLS(cid:247)ł(cid:231)Ł LS (cid:247)ł
(cid:230) (cid:246)
M = func(cid:231)EI ,Dd (cid:247)
D
(cid:231)L L (cid:247)
Ł S S ł
EI/L is a representation of Structure Stiffness
S
D /L is Angular Distortion (dimensionless)
d S
| 12
42nd Southwest Geotechnical Engineers Conferences May 03, 2017
May 1 –4, 2017, Phoenix, AZ Page 6of 17
Incorporation of Foundation Deformations
inAASHTO LRFDBridge Design Process
Limiting (Tolerable) Angular
Distortion
(cid:127) Moulton et al. (1985) – For FHWA
(cid:127) AASHTO – Standard (ASD) and LRFD Specifications
Type of Limiting Angular Distortion,D /L
d S
Bridge Moulton et al. (1985) AASHTO
Continuous 0.004 0.004
Span (4.8" in 100') (4.8" in 100')
Simple 0.005 0.008
Span (6.0" in 100') (9.6" in 100')
For rigid frames, perform case-specific analysis
| 13
Arbitrary Use of AASHTO
Limiting Values
Examples of arbitrary (inconsistent) application
(cid:127) 0.004(cid:224)0.0004 or 0.008(cid:224)0.0008
(cid:127) I-25/I-40 TI (BIG-I), NM: 0.004(cid:224) 0.002, 0.008(cid:224)0.004
(cid:127) WSDOT (From Chapter 8 of Geotech Design Manual)
Total Differential Settlement over 100 ft within
Settlement, d, Pier or Abutments and Differential
Action
at Pier or Settlement Between Piers [Implied Limiting
Abutment Angular Distortion, radians]
d≤ 1" D ≤ 0.75"[0.000625] Design& construct
d100’
Ensurestructure can
1" <d≤ 4" 0.75" <D ≤ 3"[0.000625-0.0025]
d100’ tolerate settlement
d> 4" D > 3"[> 0.0025] Need Dept approval
d100’
(cid:127) Arizona DOT: “The bridge designer should limit the settlement of
a foundation per 100 ftspan to 0.75 in. Linear interpolation
should be used for other span lengths.”
| 14
42nd Southwest Geotechnical Engineers Conferences May 03, 2017
May 1 –4, 2017, Phoenix, AZ Page 7of 17
Incorporation of Foundation Deformations
inAASHTO LRFDBridge Design Process
Settlement, S, and Angular
Distortion, A = D /L
d d S
(cid:127) What is a tolerable value of D /L ?
d S
(cid:127) How reliable is the value of S ?
| 15
Many Methods to Estimate
Foundation Movements
(cid:127) Vertical
– Immediate settlement
(cid:127) Elastic method
(cid:127) Hough method
(cid:127) Schmertmann
(cid:127) Others
– Long-term settlement
(cid:127) Based on 1-D consolidation theory
(cid:127) Lateral
– P-y analysis
– Strain Wedge Method (SWM)
– Others
(cid:127) Are all methods equally reliable?
(cid:127) What is the uncertainty in predicted values?
| 16
42nd Southwest Geotechnical Engineers Conferences May 03, 2017
May 1 –4, 2017, Phoenix, AZ Page 8of 17
Incorporation of Foundation Deformations
inAASHTO LRFDBridge Design Process
When is a Bridge Structure
Affected?
CONSTRUCTION POINT CONCEPT
ad Factored Load
o (Strength Limit) F
L
During
construction
Z S Long –term settlement
Y (if applicable)
Service Load
X (Service Limit)
W
Vertical
d d d d Displacement
W X Y Z
Foundation could be shallow (spread footings) or deep (piles, shafts, etc.)
| 17
When is a Bridge Structure
Affected?
Construction-
Point Concept
0.8
(in)0.6
ment
Settle0.4
Average0.2
Reference: Sargand, et al., (1999); Ohio DOT
| 18
42nd Southwest Geotechnical Engineers Conferences May 03, 2017
May 1 –4, 2017, Phoenix, AZ Page 9of 17
Incorporation of Foundation Deformations
inAASHTO LRFDBridge Design Process
Calibration Process
for Load Factor g
SE
(cid:127)What is the uncertainty in
estimated values of
foundation deformation?
(cid:127)Need to expressg in terms
SE
of probability of exceedance
(or reliability index)
| 19
Concept of Reversible-Irreversible
Limit States
(cid:127) Reversible-irreversible limit state is one where the effect
of an irreversible limit state may be reversed by
intervention.
(cid:127) Example: Foundation deformation,
which is an irreversible limit state
with respect to foundation
elements but may be reversible in
)
terms of its effect on the bridge 06
0
superstructure through 2
(
A
intervention, e.g., through use of W
H
shims or jacking F
(cid:127) Target reliability index is a function of reversible,
irreversible, and reversible-irreversible limit states
| 20
42nd Southwest Geotechnical Engineers Conferences May 03, 2017
May 1 –4, 2017, Phoenix, AZ Page 10 of 17