proposed seismic design spec's for walls 5-16-11

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AASHTO Seismic Design AASHTO Seismic Design Specifications for Walls Specifications for Walls –– Key Key Changes Proposed for 2011Changes Proposed for 2011

by Tony M. Allenby Tony M. AllenWSDOTWSDOT

Motivations for ChangeMotivations for Change

Completion of NCHRP 611 ReportCompletion of NCHRP 611 ReportR t i ith ll f iR t i ith ll f iRecent experiences with wall performance in Recent experiences with wall performance in major earthquakes (e.g., Maule, Chile 2010 major earthquakes (e.g., Maule, Chile 2010 earthquake)earthquake)Frustration among designers with what appears Frustration among designers with what appears to be excessive conservatism in the wall seismic to be excessive conservatism in the wall seismic design considering past performance in walls indesign considering past performance in walls indesign, considering past performance in walls in design, considering past performance in walls in earthquakesearthquakes

Three Key Issues to Consider for Wall Three Key Issues to Consider for Wall Seismic Seismic Design with Regard to Proposed Design with Regard to Proposed

Specification Changes in Agenda ItemSpecification Changes in Agenda Item

Issue #1: Limits of no wall seismic analysis Issue #1: Limits of no wall seismic analysis provisionsprovisionsIssue #2: Dynamic earth pressure resultant Issue #2: Dynamic earth pressure resultant locationlocationIssue #3: Phase difference between wall mass Issue #3: Phase difference between wall mass inertial force and force due to dynamic earth inertial force and force due to dynamic earth pressure, Ppressure, PAEAE or or PPAEAE

Key Issue #1: Limits of “No Seismic Analysis” for WallsKey Issue #1: Limits of “No Seismic Analysis” for WallsCurrent specifications: seismic design of walls required in Current specifications: seismic design of walls required in all casesall casesProposal Proposal –– Seismic analysis for wall internal and external Seismic analysis for wall internal and external stability required only if:stability required only if:y q yy q y–– AAss > 0.4g or if in Seismic Zone 4 (SDC D)> 0.4g or if in Seismic Zone 4 (SDC D)–– Significant liquefaction can occur, or sensitive clays are present, that Significant liquefaction can occur, or sensitive clays are present, that

impact wall stability due to earthquakeimpact wall stability due to earthquake–– The wall supports another structure that, in accordance with the The wall supports another structure that, in accordance with the

applicable design specification, must be designed for seismic applicable design specification, must be designed for seismic loading, and poor seismic performance of the wall could impact the loading, and poor seismic performance of the wall could impact the seismic performance of the supported structureseismic performance of the supported structureseismic performance of the supported structureseismic performance of the supported structure

–– In addition, if in Seismic Zones 2 or 3, seismic analysis required if:In addition, if in Seismic Zones 2 or 3, seismic analysis required if:Exposed wall height plus average surcharge depth > 30 ftExposed wall height plus average surcharge depth > 30 ftThe wall has abrupt changes in its alignment (e.g., corners and short radius turns The wall has abrupt changes in its alignment (e.g., corners and short radius turns at an enclosed angle of 120at an enclosed angle of 120oo or less)or less)For gravity and semiFor gravity and semi--gravity walls, the backfill does not meet Article 7.3.6.3 of the gravity walls, the backfill does not meet Article 7.3.6.3 of the LRFD Bridge Construction Specifications and is not adequately drained to LRFD Bridge Construction Specifications and is not adequately drained to prevent water build upprevent water build up

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Observed Seismic Performance for WallsObserved Seismic Performance for WallsSignificant wall performance problems generally only occurred when Significant wall performance problems generally only occurred when AAss > 0.5g, and primarily when soils were liquefiable or otherwise poor. > 0.5g, and primarily when soils were liquefiable or otherwise poor. Examples include:Examples include:–– Floodway concrete cantilever walls in 1971 San Fernando EQ (AFloodway concrete cantilever walls in 1971 San Fernando EQ (Ass > 0.5g, > 0.5g, y (y ( ss g,g,

good soils, not specifically designed for seismic loads, some walls good soils, not specifically designed for seismic loads, some walls collapsed; below Acollapsed; below Ass of 0.5g, walls performed well)of 0.5g, walls performed well)

–– 1960 M1960 Mww 9.5 Great Chile EQ and 1964 Nigata EQ 9.5 Great Chile EQ and 1964 Nigata EQ –– gravity and anchored gravity and anchored sheet pile walls collapsed or had severe displacement sheet pile walls collapsed or had severe displacement –– may have been may have been due to liquefiable soils behind or below wallsdue to liquefiable soils behind or below walls

–– 1995 Kobe EQ 1995 Kobe EQ –– older (1920’s to 1960’s) masonry and concrete gravity older (1920’s to 1960’s) masonry and concrete gravity walls collapsed due to weak soils, heavy soil surcharges, or structural walls collapsed due to weak soils, heavy soil surcharges, or structural failure, mainly where Afailure, mainly where Ass > 0.6g; MSE walls had some damage but did not > 0.6g; MSE walls had some damage but did not , y, y ss g; gg; gcollapse, even up to 0.8gcollapse, even up to 0.8g

–– Marginally stable geogrid MSE wall (for static conditions) that used poorly Marginally stable geogrid MSE wall (for static conditions) that used poorly drained silt/clay backfill in 2001 Nisqually EQ (Adrained silt/clay backfill in 2001 Nisqually EQ (Ass approx. 0.15g) approx. 0.15g) –– facing facing blocks collapsed but reinforced soil remained intactblocks collapsed but reinforced soil remained intact

Based on lab research, seismic earth pressures appear to not develop Based on lab research, seismic earth pressures appear to not develop until Auntil Ass > 0.4g> 0.4g

Gravity Type Wall at Ishiyagawa Site – 1995 Kobe Earthquake

Original location

After 1995 Kobe Earthquake

5 m

+ ++

Original location


5 mOriginal location


5 m

+ ++

As = 0.6g+

EarthquakeEarthquakeEarthquake

〈重力式擁壁〉

Courtesy of Dr. F. Tatsuoka (Japan)

Leaning (Gravity) Type Wall at Sumiyoshi Site – 1995 Kobe Earthquake

As = 0.6g+


GRS Wall a week after the 1995 Kobe Earthquake

As = 0.6g+

24 Jan. 1995The wall survived!


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Tumwater Wall Failure Tumwater Wall Failure –– Pre Pre 2001 Nisqually 2001 Nisqually EQEQ

Poor backfill and drainage

Portion of wall replaced before earthquake

– portion of wall that had already failed was replaced

with better backfill and

stronger geogrid

99

geogridbefore EQ

Post Nisqually Post Nisqually 2001 EQ 2001 EQ –– Tumwater Wall Tumwater Wall Failure Failure –– Portion not Previously Repaired FailedPortion not Previously Repaired Failed

1010

Summary of Wall Performance in Maule Summary of Wall Performance in Maule Chile 2010 EarthquakeChile 2010 Earthquake

Magnitude 8.8, PGA ranged from 0.2g to 0.5g in central Magnitude 8.8, PGA ranged from 0.2g to 0.5g in central valley (Santiago to Talca), and 0.65g horizontal / 0.6gvalley (Santiago to Talca), and 0.65g horizontal / 0.6gvalley (Santiago to Talca), and 0.65g horizontal / 0.6g valley (Santiago to Talca), and 0.65g horizontal / 0.6g vertical in Concepcionvertical in ConcepcionWalls had very little damage, if any, even though bridges Walls had very little damage, if any, even though bridges adjacent to them had significant damage or even adjacent to them had significant damage or even collapsedcollapsedWall types evaluated include panel and block faced MSE Wall types evaluated include panel and block faced MSE walls concrete gravity and semiwalls concrete gravity and semi--gravity walls withgravity walls withwalls, concrete gravity and semiwalls, concrete gravity and semi--gravity walls, with gravity walls, with heights ranging to 12 m+ for all these wall typesheights ranging to 12 m+ for all these wall typesMost walls designed in accordance with AASHTO, but Most walls designed in accordance with AASHTO, but typically for ktypically for khh of 0.1g to 0.2g in central valley and 0.25g of 0.1g to 0.2g in central valley and 0.25g to 0.4g on coast, using good quality backfillto 0.4g on coast, using good quality backfill

Concepcion, Chile Ground Motion, EConcepcion, Chile Ground Motion, E--W DirectionW Direction(2010 Maule Earthquake, M(2010 Maule Earthquake, Mww = 8.8)= 8.8)

East-West DirectionPGA = 0.61gSignificant Duration = 76 sec.Bracketed Duration = 152 sec (A > 0 05g)

PGA = 0.61g Horiz.

2001 Nisqually Earthquake,

Bracketed Duration 152 sec. (A > 0.05g)

1212

at same scale as Chile ground motion, for comparison(E-W Direction, PGA = 0.26g, Significant Duration = 17 sec.Mw = 6.8)

0 60

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Retaining Wall Performance in Chile - 2010 Maule Chile EQ

Fallen top blocks – caused by inadequate lateralrestraint of the top few rows of blocks.

Modular block geogrid and precast concrete panel steel reinforced MSE walls supporting abutment fills, Americo Vespucio/Independencia Santiago area.

Precast concrete panel faced wall showed no signs of distress due to earthquake.

Bridge deck shifted150 to 200 mm towardacute skew angle

Top of wallmoved out0.3 m


Via Elevada bridge and walls (Concepcion) – First MSE wall in Chile (built in 2000). Shows deformation of wall top due to lack of connection between curtain wall and MSE wall panels, and due possibly to short reinforcements due to extreme skew angle restricting reinforcement length. Wall height approx. 10 m.

Panels in upper wall settled due to loss of soil in lower wall


32o

Soil spilled out from behind lowerwall, undermining upper wall facing, causing more soil loss

0.3 to 0.4 m

Via Elevada bridge and walls (Concepcion) showing deformation of wall and gap due to lack of connection between curtain wall and MSE wall panels, and loss of wall backfill through gap. Note angle of repose of sand is about 32o. Inset photo shows lower wall translational movement that allowed wall backfill to spill out.


Sand backfill spilled through gaps in wallthat opened up during

h ki

Via Elevada back side of wall shown in previous slide showing hole left due to gap caused by lack of connection between curtain wall and MSE wall panels, and loss of wall backfill through gap. Note uniformity of medium sand backfill.

shaking

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Block cracking in 45o shear bands

100 to 150 mm gap


Wall facedeformation(100 mm max.)

Muros Talca RR Xing with modular block geogrid walls, showing wall deformation and significant block cracking (located in central valley near Talca; 9 m high plus 2 m surcharge).

Block cracking in 45o shear zones

100 to 150 mm gap


Wall facedeformation(100 mm max.)

mm gap

Muros Talca RR Xing with modular block geogrid walls, showing wall deformation and significant block cracking, as seen from bridge deck.

Note gap in bridge railing(deck and railing on bridgespan is shifted toward nearend of abutment wall)


36 blocks high

RR X’ing west of Rt 5 between Santiago and Rancagua. Bridge foundation supported on top of geogrid wall. Longitudinally, bridge is sloping downhill away from the pictured (SW) abutment and has moved toward the near side of the abutment and downhill. Wall has no damage.

36 blocks high(7.4 m)

1960 M1960 Mww 9.5 Chile EQ 9.5 Chile EQ –– Sheet Pile Sea Wall Failure Sheet Pile Sea Wall Failure

Likely due to Liquefaction of backfill and 6 ft of soil below Likely due to Liquefaction of backfill and 6 ft of soil below MudlineMudline Line Line ––Built in 1930. Note: Modified Built in 1930. Note: Modified MercalliMercalli = VIII to IX, Est. PGA = 0.5g to 0.8g= VIII to IX, Est. PGA = 0.5g to 0.8g

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1960 M1960 Mww 9.5 Chile EQ 9.5 Chile EQ –– 18.5 m High Gravity Wall Failure 18.5 m High Gravity Wall Failure

Likely partially due to Liquefaction of retained fill. Foundation Soil was fairly Likely partially due to Liquefaction of retained fill. Foundation Soil was fairly dense, though. Note: Modified dense, though. Note: Modified MercalliMercalli = VIII to IX, Est. PGA = 0.5g to 0.8g= VIII to IX, Est. PGA = 0.5g to 0.8g

Gravity Wall Collapse in 1999 Taiwan Gravity Wall Collapse in 1999 Taiwan QiQi--QiQi EQEQ

PGA likely greater than 0.6g

Other Full Scale Wall Seismic ExperienceOther Full Scale Wall Seismic ExperienceSeed and Whitman (1970): Seed and Whitman (1970): Concluded that “many walls adequately designed for static earth pressures will automatically have the capacity to withstand earthquake ground motions of substantial magnitudes (up to 0.25g) and in many cases, special seismic provisions may not be needed.”GazetasGazetas, et al. (2004): Cantilever semi, et al. (2004): Cantilever semi--gravity walls with no gravity walls with no surcharge not explicitly design for seismic loads performed well up surcharge not explicitly design for seismic loads performed well up to almost 0.5g in 1999 Athens EQto almost 0.5g in 1999 Athens EQLew, et al. (1995): tied back shoring walls in 1994 Northridge EQ Lew, et al. (1995): tied back shoring walls in 1994 Northridge EQ performed well performed well –– no damageno damageVuceticVucetic, et al. (1998): Soil nail walls showed virtually no damage , et al. (1998): Soil nail walls showed virtually no damage after the Loma after the Loma PrietaPrieta EQ in 1989, even for PGA up to 0.4gEQ in 1989, even for PGA up to 0.4g

Clough and Clough and FragaszyFragaszy (1977) (1977) –– 1971 San Fernando EQ1971 San Fernando EQ

Floodway concrete cantilever walls Floodway concrete cantilever walls –– 1971 San Fernando EQ 1971 San Fernando EQ AAss > 0.5g, good soils, not specifically designed for seismic loads > 0.5g, good soils, not specifically designed for seismic loads ––some walls collapsedsome walls collapsedBelow ABelow Ass of 0.5g of 0.5g –– walls performed wellwalls performed well

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Clough and Clough and FragaszyFragaszy (1977) (1977) –– 1971 San Fernando EQ1971 San Fernando EQClough and Clough and FragaszyFragaszy (1977) (1977) –– 1971 San Fernando EQ1971 San Fernando EQ

Centrifuge Wall Modeling Results (Al Centrifuge Wall Modeling Results (Al AtikAtik and and Sitar, 2010, ASCE Geotech. Journal)Sitar, 2010, ASCE Geotech. Journal)

Centrifuge Wall Modeling Results (Al Centrifuge Wall Modeling Results (Al AtikAtik and and Sitar, 2010, ASCE Geotech. Journal)Sitar, 2010, ASCE Geotech. Journal)

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Areas Requiring Seismic Analysis for Walls Areas Requiring Seismic Analysis for Walls Using AUsing Ass = 0.4g Criteria= 0.4g Criteria

Areas Requiring Seismic Analysis for Walls Areas Requiring Seismic Analysis for Walls Using AUsing Ass = 0.4g Criteria= 0.4g Criteria

Areas Requiring Seismic Analysis for Walls Areas Requiring Seismic Analysis for Walls Using Zone 4, All Soil Classes A to E CriteriaUsing Zone 4, All Soil Classes A to E Criteria

Areas Requiring Seismic Analysis for Walls Areas Requiring Seismic Analysis for Walls Using Zone 4, All Soil Classes A to E CriteriaUsing Zone 4, All Soil Classes A to E Criteria

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Key Issue #2: Seismic Earth Pressure Key Issue #2: Seismic Earth Pressure Resultant LocationResultant Location

Current specification requirement:Current specification requirement:0 5h for total earth pressure (static plus seismic)0 5h for total earth pressure (static plus seismic)–– 0.5h for total earth pressure (static plus seismic)0.5h for total earth pressure (static plus seismic)

–– 0.6h for seismic increment of earth pressure0.6h for seismic increment of earth pressureProposed requirement:Proposed requirement:–– At same location as static earth pressure resultant, At same location as static earth pressure resultant,

but no less than h/3 above wall basebut no less than h/3 above wall base–– Should consider higher resultant for walls in whichShould consider higher resultant for walls in whichShould consider higher resultant for walls in which Should consider higher resultant for walls in which

impact of failure is especially highimpact of failure is especially high

Seismic Earth Pressure Resultant Location Seismic Earth Pressure Resultant Location –– the Evidencethe Evidence

Original proposal by Original proposal by MononobeMononobe and Matsuo (1932) and Matsuo (1932) –– resultant at h/3resultant at h/3Theoretical considerations by Wood (1973) Theoretical considerations by Wood (1973) –– resultant at h/2resultant at h/2Model studies reported by Seed and Whitman (1970) Model studies reported by Seed and Whitman (1970) –– dynamic dynamic ode s ud es epo ed by Seed a d a ( 9 0)ode s ud es epo ed by Seed a d a ( 9 0) dy a cdy a cincrement increment PPAEAE at 0.6hat 0.6hFull scale walls in 1971 San Fernando EQ from back analysis Full scale walls in 1971 San Fernando EQ from back analysis –– indicated indicated resultant location at h/3 needed to match observed performance (Clough resultant location at h/3 needed to match observed performance (Clough and and FragaszyFragaszy, 1977), 1977)Centrifuge model tests on gravity walls indicate resultant should be at h/3 Centrifuge model tests on gravity walls indicate resultant should be at h/3 (Al (Al AtikAtik and Sitar, 2010, Bray, et al., 2010, and Lew, et al. 2010)and Sitar, 2010, Bray, et al., 2010, and Lew, et al. 2010)Centrifuge model tests by Nakamura (2006) on gravity walls indicateCentrifuge model tests by Nakamura (2006) on gravity walls indicateCentrifuge model tests by Nakamura (2006) on gravity walls indicate Centrifuge model tests by Nakamura (2006) on gravity walls indicate resultant could be a little higher than h/3 depending on ground motion resultant could be a little higher than h/3 depending on ground motion and wall detailsand wall detailsFull scale shake table study of MSE wall (3 m high) indicated pressure Full scale shake table study of MSE wall (3 m high) indicated pressure distribution behind facing was consistent with static earth pressure distribution behind facing was consistent with static earth pressure distribution (Ling, et al., 2005, ASCE)distribution (Ling, et al., 2005, ASCE)

Static and Seismic Earth Pressure Distributions Static and Seismic Earth Pressure Distributions Obtained from 0.3 m High Model Tests by Matsuo Obtained from 0.3 m High Model Tests by Matsuo (1941) as Reported in Seed and Whitman (1970)(1941) as Reported in Seed and Whitman (1970)

Seismic Earth Pressure Resultant Location Seismic Earth Pressure Resultant Location –– Al Al AtikAtik and Sitar, 2010 ASCE Geotech. Journaland Sitar, 2010 ASCE Geotech. Journal

Shows earth pressure distribution is triangular, indicating resultant at h/3,Shows earth pressure distribution is triangular, indicating resultant at h/3,and less than 65% of Mand less than 65% of M--O earth pressureO earth pressure

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Seismic Earth Pressure Resultant Location Seismic Earth Pressure Resultant Location –– Nakamura, 2006, Soils and FoundationsNakamura, 2006, Soils and Foundations

Shows earth pressure resultant location varies from h/3 to almost h/2 in some cases.Shows earth pressure resultant location varies from h/3 to almost h/2 in some cases.

Seismic Earth Pressure Seismic Earth Pressure Resultant Location from Resultant Location from Full Scale Shake Table Full Scale Shake Table

Studies (Ling, et al. Studies (Ling, et al. 2005, ASCE)2005, ASCE)

Wall 1 Layout

2005, ASCE)2005, ASCE)Static and seismic earth pressures have similar distributions – represent earth pressure at wall face

Key Issue #3: Seismic Earth Pressure Phase Key Issue #3: Seismic Earth Pressure Phase Difference between Wall Mass Inertial Force and Difference between Wall Mass Inertial Force and

Dynamic Earth PressureDynamic Earth PressureCurrent specification requirement:Current specification requirement:–– Assume these two dynamic forces are in phase (concurrent) forAssume these two dynamic forces are in phase (concurrent) forAssume these two dynamic forces are in phase (concurrent) for Assume these two dynamic forces are in phase (concurrent) for

gravity walls, though the current specifications are not clear gravity walls, though the current specifications are not clear about this about this –– the specifications and commentary simply say that the specifications and commentary simply say that the wall mass inertial force should not be neglectedthe wall mass inertial force should not be neglected

–– Assume for MSE walls the wall mass inertial force is combined Assume for MSE walls the wall mass inertial force is combined with 100% of the static earth pressure plus 50% of the dynamic with 100% of the static earth pressure plus 50% of the dynamic earth pressure incrementearth pressure increment

Proposed specification requirement:Proposed specification requirement:Proposed specification requirement:Proposed specification requirement:–– Combine 100% of total earth pressure PCombine 100% of total earth pressure PAEAE with 50% of wall with 50% of wall

mass inertial force Pmass inertial force PIRIR, and compare to:, and compare to:–– 50% of P50% of PAEAE (but no less than 100% of static earth pressure) (but no less than 100% of static earth pressure)

combined with 100% of wall inertial force Pcombined with 100% of wall inertial force PIRIR

–– Use most conservative resultUse most conservative result

Seismic Earth Pressure Phase Difference between Wall Seismic Earth Pressure Phase Difference between Wall Mass Inertial Force and Dynamic Earth Pressure Mass Inertial Force and Dynamic Earth Pressure ––

Nakamura, 2006, Soils and FoundationsNakamura, 2006, Soils and Foundations

Dynamic earth pressure increment near zero or minimum (negative) value

Wall mass inertial force near maximum value at same time step

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Seismic Earth Seismic Earth Pressure Phase Pressure Phase

Difference between Difference between Wall Mass Inertial Wall Mass Inertial

Force and DynamicForce and DynamicForce and Dynamic Force and Dynamic Earth Pressure Earth Pressure -- Al Al AtikAtik and Sitar, ASCE and Sitar, ASCE

(2010)(2010)

Dynamic earth pressure y pnear maximum

Wall mass inertial force near zero or negative

Similar behavior as shown in figure, which represents stiff wall, was also observed for flexible wall.

Other AASHTO Wall Seismic Design Provision Other AASHTO Wall Seismic Design Provision ChangesChanges

For nonFor non--yielding walls, kyielding walls, khh is proposed to be reduced to 1.0Ais proposed to be reduced to 1.0Ass

Guidance on taking advantage of soil cohesionGuidance on taking advantage of soil cohesionNew article summarizing good details to improve seismic performance New article summarizing good details to improve seismic performance f llf llof wallsof walls

Better guidance on application of static and seismic load factors for Better guidance on application of static and seismic load factors for wall seismic designwall seismic designDistribution of seismic loads to the soil reinforcement in MSE walls has Distribution of seismic loads to the soil reinforcement in MSE walls has been revised based on new researchbeen revised based on new researchImproved specifications and commentary guidance for all wall typesImproved specifications and commentary guidance for all wall typesAppendix A11 has been rewritten and updatedAppendix A11 has been rewritten and updated–– A 1 page long summary of past wall performance in earthquakes, and a A 1 page long summary of past wall performance in earthquakes, and a

summary of key laboratory testing findings, is providedsummary of key laboratory testing findings, is provided–– Details of how to calculate seismic active and passive earth pressuresDetails of how to calculate seismic active and passive earth pressures–– Details of three options on how to account for lateral wall deformation and Details of three options on how to account for lateral wall deformation and

wave scatteringwave scattering

Concluding RemarksConcluding RemarksThis is the first major change to seismic design of This is the first major change to seismic design of walls in many yearswalls in many yearsThe no seismic analysis option proposed will likelyThe no seismic analysis option proposed will likelyThe no seismic analysis option proposed will likely The no seismic analysis option proposed will likely eliminate the need to do seismic design of walls eliminate the need to do seismic design of walls except for the most seismically active areas in the except for the most seismically active areas in the US US –– Primarily along the extreme west US coast, Hawaii, Alaska, a small Primarily along the extreme west US coast, Hawaii, Alaska, a small

area in the center of the New Madrid area, and a small area in area in the center of the New Madrid area, and a small area in South Carolina) andSouth Carolina) andSouth Carolina), and South Carolina), and

–– Other specific high risk situations (e.g., when supporting other Other specific high risk situations (e.g., when supporting other structures, liquefaction, very tall walls)structures, liquefaction, very tall walls)

Improvements are provided to calculate more Improvements are provided to calculate more realistic seismic earth pressuresrealistic seismic earth pressures

proposed seismic design spec's for walls 5-16-11

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