Port Structures.pdf

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2003 by CRC Press LLC

27Port Structures

27.1 Introduction27.2 Seismic Response of Port Structures

Gravity Quay Walls Anchored Sheet Pile Walls

Pile-Supported Wharf Gantry Cranes Breakwaters

27.3 Current Seismic Provisions for Port StructuresTechnical Standards for Ports and Harbor Facilities in JapanU.S. Navy Seismic Design Guidelines Seismic Guidelines for

Ports, American Society of Civil EngineersTechnical Council

on Lifeline Earthquake Engineering (ASCETCLEE), Ports

Committee European Prestandard, Eurocode 8 Design

Provisions for Earthquake Resistance of Structures

27.4 Seismic Performance-Based Design27.5 Seismic Performance Evaluation and Analysis27.6 Methods for Analysis of Retaining/Earth Structures

Simplified Analysis Simplified Dynamic Analysis

Dynamic Analysis

27.7 Analysis Methods for Open Pile/Frame StructuresSimplified Analysis Simplified Dynamic AnalysisDynamic Analysis

ReferencesFurther Reading

27.1 Introduction

This chapter deals with the seismic performance and design of port structures. Typical port structures

are shown in Figure 27.1. Port structures have sustained major to catastrophic damage in a number of

earthquakes during the past few decades. This damage is not only costly in itself, but represents a major

impact on the regional economy, for which the port is the doorway.Figures 27.2to 27.8illustrate port

damage from earthquakes in Chile and Japan, for example.

27.2 Seismic Response of Port Structures

Following is a summary of modes of earthquake damage and deformation/failure for typical port

structures.

27.2.1 Gravity Quay Walls

A gravity quay wall is made of a caisson or other rigid wall put on the seabed, and maintains its stability

through friction at the bottom of the wall. Typical failure modes during earthquakes involve seawarddisplacement, settlement, and tilt. For a quay wall constructed on a firm foundation, an increase in earth

Susumu Iai

Port and Airport Research Institute

Yokosuka, Japan


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FIGURE 27.1 Typical port structures. (From PIANC. 2001. Seismic Design Guidelines for Port Structures, A.A. Balkema,

Rotterdam. With permission.)

2003 by C RC Press LLC


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pressure from the backfill plus the effect of an inertia force on the body of the wall result in the seaward

movement of the wall, as shown inFigure 27.9(a).If the width-to-height ratio of the wall is small, tilt

may also be involved. Case histories for gravity quay walls subjected to earthquake shaking often belong

in this category. When the subsoil below the gravity wall is loose and excess pore water pressure increases

in the subsoil, however, the movement of the wall is associated with significant deformation in thefoundation soil, resulting in a large seaward movement involving tilt and settlement, as shown in

Figure 27.9(b).The latter mode of failure is also shown inFigure 27.10,and has received wide attention

since the Kobe, Japan earthquake of 1995.

FIGURE 27.2 Collapse of crane due to quay failure, 1985 M 7.8 Chile earthquake. (Courtesy EQE International)

FIGURE 27.3 Destruction of Port of Aonae due to tsunami, Okushiri Island, 1993 M 7.8 Hokkaid Nansei (Japan)

earthquake. (Photo: C. Scawthorn)



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27.2.2 Anchored Sheet Pile Walls

An anchored sheet pile wall is composed of a wall, anchors, and tie-rods. Each structural component

contributes to the stability of the whole structure. In the ultimate state of stability, it should be decided

whether the wall or the anchor should be the first to yield. Excessive displacements of the anchor are

undesirable. A small movement of the anchor, however, contributes to reducing the tension in the tie-

rods and the bending moment in the wall. Well-balanced response of the wall and anchor is essential for

achieving a reasonable performance of the anchored sheet pile wall during earthquakes.

A variety of geotechnical conditions can result in a variety of failure modes of an anchored sheet pile

wall. In particular, three failure modes may be identified, depending on the extent of loose, saturated

sandy soils relative to the position and geometry of the wall. If the deformation of a loose deposit mainly

affects the stability of anchors as shown inFigure 27.11(a), the anchors will move toward the sea, resulting

in the seaward movement of the wall. This mode of deformation/failure has been the most frequently

FIGURE 27.4 Damage to container quay and gantry crane, Port of Kobe, 1995MW

6.9 Hanshin earthquake. (Photo:

C. Scawthorn)



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FIGURE 27.5 Detail ofFigure 27.4. (Photo: C. Scawthorn)

FIGURE 27.6 Detail of Figure 27.4. (Photo: C. Scawthorn)



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FIGURE 27.7 Failure of crane boom due to excessive accelerations, Port of Kobe, 1995MW6.9 Hanshin earthquake.

(Courtesy EQE International)

FIGURE 27.8 Failure of crane booms due to excessive accelerations, Port of Kobe, 1995MW

6.9 Hanshin earthquake.

(Courtesy EQE International)



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observed at waterfronts. If the deformation of the loose deposit mainly affects the backfill of the wall as

shown inFigure 27.11(b), the earth pressure increase will cause an excessively large bending moment in

the wall, resulting in yielding of the wall. This mode of failure has also been observed during past

earthquakes.

If the deformation of the loose sandy deposit mainly affects the stability of the embedment portion

of the wall, as shown inFigure 27.11(c), a gross instability of the wall at the embedment portion willexist. This mode of failure, however, can occur only when the anchor is strong and firmly embedded,

and both the wall and tie-rods are very strong. In current design practice, the wall is assumed to be

relatively firmly embedded, and thus is designed for a fraction of the bending moment induced at the

free-earth support conditions. If the conditions shown in Figure 27.11(c) are met, yielding of the wall

or failure of the anchor will most likely precede the instability of the embedment portion. This may be

the reason why there has not been a case history that fits the failure mode shown in Figure 27.11(c).

27.2.3 Pile-Supported Wharf

A pile-supported wharf is composed of a deck supported by a substructure consisting of piles and a dike,

often simply called a wharf. Because the dike is sloped, the piles between the deck and the dike will have

various unsupported lengths. Three causes of failure may be identified for a pile-supported wharf. For

a wharf constructed on a firm foundation having a rigid and stable dike, the seismic inertia force on the

deck will be the main cause of failure, as shown in Figure 27.12(a).The maximum bending moment

FIGURE 27.9 Cross section of caisson quay wall at Port of Kobe. (From PIANC. 2001. Seismic Design Guidelines

for Port Structures, A.A. Balkema, Rotterdam. With permission.)

(a) On firm foundation

(b) On loose sandy foundation

Loose sandy foundation



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occurs at the row of pile heads most landward because these piles have the shortest unsupported length.

If there is an excessively large displacement at the top of the dike or the retaining structures, the deck

will be pushed seaward, resulting in a similar mode of failure as shown inFigure 27.12(b). For a wharf

constructed on a loose foundation, the displacement in the dike will directly push the piles seaward, as

shown in Figure 27.12(c). The first cause of failure has been well taken into account in conventional

seismic design of pile-supported wharves. Increasing attention has been directed toward the effect of

displacement of dikes on pile-supported wharves since the Loma Prieta, CA earthquake of 1989, where

this behavior was observed at the Port of Oakland. The Kobe, Japan earthquake of 1995 again demon-

strated the importance of this mode.

27.2.4 Gantry Cranes

A crane consists of an upper structure for handling cargo and a supporting structure for holding in place

and transporting the upper structure, as shown in Figure 27.13. The crane is generally made of a steel

frame. The supporting structure is either of the rigid frame type or hinged leg type, with supporting

structure resting on rails through the wheels. A crane at rest is fixed to rails or to a quay wall with clamps

or anchors, whose strength provides the upper limit for the crane resistance against external forces.

However, clamps or anchors do not support a crane in operation, and the lateral resistance of the crane

against external forces is from friction and from the wheel flanges. Typical failure modes during earth-

quakes are derailment of wheels, detachment or pullout of vehicle, rupture of clamps and anchors,

buckling, and overturning. As shown inFigure 27.13(a),widening of a span between the legs due to the

deformation of the quay wall results in derailment or buckling of the legs. Conversely, as shown inFigure

27.13(b), narrowing of a leg span can also occur due to the rocking response of the crane. This is due

to alternating action of the horizontal component of resisting forces from the quay wall during rocking-

type response involving uplifting of one of the legs. Derailment and detachment of the wheel can also

occur due to rocking. As shown inFigure 27.13(c), when differential settlement occurs on a quay wall

below the crane, tilting or overturning of the crane may occur. If the crane has one-hinge type legs, thederailment can result in tilting and overturning of the crane, as shown in Figure 27.13(d). Though a

clamp or anchor will provide more resistance to motion under the action of external forces, the internal

stresses induced in the crane framework will become larger in comparison to the case with no clamp,

thus allowing for rocking responses. Crane rails are often directly supported either by a portion of a

FIGURE 27.10 Deformation/failure modes of gravity quay walls. (From PIANC. 2001. Seismic Design Guidelines for

Port Structures, A.A. Balkema, Rotterdam. With permission.)

Face

Line

Cran

eRail

Crane

Rail

Ground surface

after the earthquake

Concrete

Caisson

Rubble

Backfill

Backfill Soil

Compaction

Sand DrainBackfill Sand

for Replacing Clay Layer

Foundation Rubble

Alluvial Clay Layer

14.50

18.50

+4.0H.W.L.+1.7m

L.W.L.0.0m

4.25.2

3.04.01.5

2.2

34.00~ 36.0033.00~ 35.00

Unit (m)



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retaining wall or by the deck of a pile-supported wharf. When the width of the gravity wall is small, or

the quay wall is a sheet pile or cellular type, a separate foundation that often consists of piles is provided

to support the rails. In order to achieve desirable seismic performance of quay walls with cranes, special

consideration is required for the rail foundation, such as providing a dedicated and cross-tied upper

structure to support the rails.

FIGURE 27.11 Deformation/failure modes of sheet pile quay walls. (From PIANC. 2001. Seismic Design Guidelines

for Port Structures, A.A. Balkema, Rotterdam. With permission.)

(a) Deformation/failure at anchor

(b) Failure at sheet pile wall/tie-rod

(c) Failure at embedment



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27.2.5 BreakwatersA breakwater is usually made of a rubble mound, a massive structure such as a caisson, or a combination

of both placed on a seabed. Stability against a horizontal external load is maintained by shear resistance

of rubble, friction at the bottom of the caisson, and with associated resistance to overturning and bearing

FIGURE 27.12 Deformation/failure modes of pile-supported wharves. (From PIANC. 2001. Seismic Design Guide-

lines for Port Structures, A.A. Balkema, Rotterdam. With permission.)

(a) Deformation due to inertia force at deck

Loose Subsoil

Firm Layer

Firm Foundation

(c) Deformation due to lateral displacement of

loose subsoil

(b) Deformation due to horizontal force from

retaining wall



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capacity failure. Typical failure modes expected during earthquakes are shown inFigure 27.14. Break-

waters are generally designed to limit wave penetration and wave overtopping during specific design

storms, and at the same time are designed to resist the related wave actions. It is unlikely that a major

earthquake will occur simultaneously with the design sea state because the two events are typically not

related. Consequently, design storm wave action and an earthquake can be treated as two independentload situations. Only wave actions from a moderate sea state should be considered together with the

design earthquakes. Decision on this sea state has to be made based on the site-specific, long-term statistics

of the storm. Selection of the appropriate design criteria depends on the functions of the breakwater and

the type of earthquake-induced failure modes. However, for all breakwaters the main criterion is the

FIGURE 27.13 Deformation modes of gantry cranes: (a) widening of span between the legs, (b) narrowing span

between the legs due to rocking motion, (c) tilting of crane due to differential settlement of foundation,

(d) overturning of one-hinged leg crane due to rocking/sliding. (From PIANC. 2001. Seismic Design Guidelines for




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allowable settlement of the crest level because it determines the amount of overtopping and wave

transmission. For breakwaters carrying roads and installations, additional criteria for allowable differen-

tial settlement, tilting, and displacement of superstructures and caissons are needed. Shaking of the

breakwater may cause breakage of concrete armor units. Criteria have been proposed with regard to

maximum breakage in terms of number of broken units that may occur while the breakwater remains

FIGURE 27.14 Deformation/failure modes for breakwaters: (a) caisson resting on sea bed, (b) vertically composite

caisson breakwater, (c) horizontally compositecaisson breakwater, (d) rubble mound breakwater. (From PIANC.

2001. Seismic Design Guidelines for Port Structures, A.A. Balkema, Rotterdam. With permission.)



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serviceable [e.g., Zwamborn and Phelp, 1995]. The same criteria may be adopted for the earthquake-

related damage.

27.3 Current Seismic Provisions for Port Structures

The following existing codes and guidelines used at various ports are reviewed with regard to their seismic

design provisions.

27.3.1 Technical Standards for Ports and Harbor Facilities in Japan

A dual-level approach is employed for structures of Special Class of Importance. However, the single-level

approach is adopted for structures of Classes A, B, and C Importance. For structures of Special Class of

Importance, the performance level is specified as follows [Ministry of Transport, Japan, 1999]:

For Level 1 (L1): Minor or no damage, little or no loss of serviceability.

For Level 2 (L2): Minor or little damage, little or short-term loss of serviceability.

For retaining structures of Special Class of Importance: Criteria for structural damage and criteria

regarding serviceability are specified.

The seismic coefficient for use in retaining structures is defined as follows for Special Class structures:

(27.1)

For Class B structures (designed with importance factor of 1.0), the code-specified seismic coefficients

are about 60% of those given by Equation 27.1. For a pile-supported wharf with vertical piles, analysis

is performed based on a simplified procedure and pushover method. The ductility limits for use in the

simplified procedure (discussed later) for L1 earthquake motion are specified. Pushover analysis is

performed for Special Class structures and the strain limits prescribed are:

Level 1 motion: equivalent elastic

Level 2 motion: max= 0.44tp/Dp, for the embedded portion

Pile-supported wharves with vertical steel piles are designed using response spectra for L1 motion,

computed based on two-dimensional soilstructure interaction analysis for typical pile-supported wharf

cross sections. For L2 motion, time-history analysis should be performed and the results should meet

the ductility limits for L2 earthquake motion. Comprehensive guidelines are shown on liquefaction

potential assessment and implementation of remedial measures [PHRI, 1997].

27.3.2 U.S. Navy Seismic Design Guidelines

The U.S. Navy code [Ferritto, 1997a, 1997b] describes a dual level design and a performance level that

is serviceable under L1 and repairable under L2. The damage criteria are deformation limits for wharf

dikes and ductility limits for piles. The procedure requires a linear or nonlinear dynamic analysis.

California State design is similar to the U.S. Navy design in principle but the ductility requirements aremuch more detailed and specified by strain limits. This procedure is still under development and will be

finalized in the form of regulatory guidance.

ka

ga g

ka

ga g

h

h

= ( )

=

( )

max

max

max

max

.

.

0 2

1

30 2

1

3



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27.3.3 Seismic Guidelines for Ports, American Society of CivilEngineersTechnical Council on Lifeline Earthquake Engineering(ASCETCLEE), Ports Committee

This reference represents one of the first guideline documents developed specifically for the seismic

analysis and design of port structures and facilities in North America [Werner, 1998]. In addition tocomprehensive treatment of seismic hazards, seismic design, and analysis in North American engineering

practice, and guidelines for specific port components, this document presents pertinent information on

seismic risk reduction, and emergency response and recovery at ports. It should be noted that the ASCE-

TCLEE guidelines were developed with the primary objective of providing a framework for the estab-

lishment of improved seismic risk evaluation and reduction procedures for ports in the United States.

The recommendations outlined in the guideline document are not to be interpreted as codes, nor are

they intended to supercede local code requirements that may be applicable. The ASCE-TCLEE seismic

guidelines present a dual-level design, consistent with the current state of practice at major ports in the

United States. The multilevel design approach has been adopted at numerous ports in the form of two-

and occasionally three-level design procedures. An example of the two-level approach as applied in the

western United States follows.

Level 1. Under this first level of design, Operating Level Earthquake (OLE) ground motions are

established, which have a 50% probability of exceedance in 50 years (corresponding to an average

return period of about 72 years). Under this level of shaking, the structure is designed so that

operations are not interrupted and any damage that occurs will be repairable in a short time

(possibly less than 6 months).

Level 2. Under this second level of design, more severe Contingency Level Earthquake (CLE) ground

motions are established that have a 10% probability of exceedance in 50 years (consistent with

most building codes and corresponding to an average return period of about 475 years). Under

this level of shaking, the structure is designed to undergo damage that is controlled, economicallyrepairable, and not a threat to life safety.

It should be noted that the exposure times adopted for the L1 and L2 events in this example application

may vary regionally due to variations in the rate of seismicity, the type of facility, and economic

considerations. The damage criteria outlined in the guideline document are presented in the form of

general performance-based recommendations. As such, the recommendations address the evaluation

and mitigation of liquefaction hazards and ground failures, deformation limits for retaining structures,

earth structures, and other waterfront components, and ductility limits for piles. In order to evaluate

these earthquake-induced loads and associated deformations, pseudo-static methods of analysis must

often be supplemented with linear and nonlinear dynamic analysis, the level of analytical sophistication

being a function of the intensity of the ground motions, the anticipated soil behavior, and the complexityof the structure. General guidance on the level of analysis required for a variety of geotechnical and

structural applications is provided (including dynamic soilstructure interaction analyses).

27.3.4 European Prestandard, Eurocode 8 Design Provisions for EarthquakeResistance of Structures

The methodology of the Eurocode 8 describes in general a dual-level approach; however, in low seismicity

zones (adesign0.1g) and for well-defined structures in seismic zones with small design ground acceleration(adesign0.04g), a single-level approach can be sufficient [CEN, 1994]. The mentioned performance levels are:

No collapserequirement: Retain structural integrity and a residual bearing capacity.

Damage limitation requirement: No damage and associated limitations of use, the costs of which

would be disproportionately high compared with the cost of the structure itself.

Damage criteria in terms of maximum displacements and ductility levels are not specified. For piles,

it is stated that they shall be designed to remain elastic. When this is not feasible, guidance is given for



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the design of potential plastic hinging and the region it will cover. For the analytical procedure, the

design ground acceleration, adesign, tends to coincide with the actual peak acceleration for moderate- to

high-magnitude earthquakes in cases of medium to long source-to-site distances, which are characterized

(on firm ground) by a broad and approximately uniform frequency spectrum, while adesignwill be more

or less reduced relative to the actual peak for near-field, low-magnitude events. The adesign

corresponds

to a reference period of 475 years, or as specified by the national authority.

For retaining structures kh= adesign/rBCgand kv= 0.5kh, where rBC= 2 for free gravity walls with acceptable

displacements (mm) 300 adesign/g; rBC= 1.5 as above with displacements (mm) 200 adesign/g; and rBC= 1for the rest of the retaining structures.

For retaining structures 10 m or higher, a refined estimate of adesign can be obtained by a free-field

one-dimensional analysis of vertically propagating waves.

For a linear analysis design of pile-supported structures, design spectra are defined as:

(27.2)

where is design ground acceleration; 0is spectral acceleration amplification factor for 5% damping;qis damping correction factor with reference value q= 1 for 5% viscous damping. Values of the parameters

S, kd1, and kd2are given, depending on the subsoil class specified by shear wave velocity.

27.4 Seismic Performance-Based Design

Performance-based design is an emerging methodology born from the lessons learned from earth-

quakes in the 1990s. The goal is to overcome the limitations present in conventional seismic design.

Conventional building code seismic design is based on providing capacity to resist a design seismic force

but it does not provide information on the performance of a structure when the limit of the force-balanceis exceeded. If we demand that limit equilibrium is not exceeded in conventional design for the relatively

high intensity ground motions associated with a very rare seismic event, the construction or retrofitting

cost will most likely be too high. If force-balance design is based on a more frequent seismic event, then

it is difficult to estimate the seismic performance of the structure when subjected to ground motions

that are greater than those used in design.

In performance-based design, appropriate levels of design earthquake motions must be defined and

corresponding acceptable levels of structural damage must be clearly identified. Two levels of earthquake

motions are typically used as design reference motions, defined as follows:

Level 1: The level of earthquake motions that are likely to occur during the life span of the structure.

Level 2: The level of earthquake motions associated with infrequent rare events that typically involvevery strong ground shaking.

The acceptable level of damage is specified according to the specific needs of the users and owners of

the facilities and may be defined on the basis of the acceptable level of structural and operational damage

0 ( ) = +

( ) =

( )=

[ ]

( )=

[

T T S T ST

T

T T T S T Sq

T T T S T S

q

T

T

T T S T S

q

T

T

B A

B

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C D A

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D A

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:

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given in Table 27.1. The structural damage category in this table is directly related to the amount of work

needed to restore the full functional capacity of the structure and is often referred to as direct loss due to

earthquakes. The operational damage category is related to the amount of work needed to restore full or

partial serviceability. Economic losses associated with the loss of serviceability are often referred to as indirectlosses. In addition to the fundamental functions of servicing sea transport, the functions of port structures

may include protection of human life and property, functioning as an emergency base for transportation,

and as protection from spilling hazardous materials. If applicable, the effects on these issues should be

considered in defining the acceptable level of damage in addition to those shown inTable 27.1.

Once the design earthquake levels and acceptable damage levels have been properly defined, the

required performance ofa structure may be specified by the appropriate performance grade S, A, B, or

C, defined in Table 27.2. In performance-based design, a structure is designed to meet these performance

grades.

The principal steps taken in performance-based design are shown in the flowchart in Figure 27.15.

Choose a performance grade from S, A, B, or C: This step is typically done by referring to Table 27.1and Table 27.2, and selecting the damage level consistent with the needs of the users and owners.

Another procedure for choosing a performance grade is to base the grade on the importance of

the structure. Degrees of importance are defined in most seismic codes and standards. This

procedure is presented inTable 27.3.If applicable, a performance grade other than those of S, A,

B, or C may be introduced to meet specific needs of the users and owners.

Define damage criteria: Specify the level of acceptable damage in engineering parameters such as

displacements, limit stress states, or ductility factors. The details are addressed in the guidelines

[PIANC, 2001].

Evaluate seismic performance of a structure: Evaluation is typically done by comparing the

response parameters from a seismic analysis of the structure with the damage criteria. If the resultsof the analysis do not meet the damage criteria, the proposed design or existing structure should

be modified. Soil improvement, including remediation measures against liquefaction, may be

necessary at this stage. Details of liquefaction remediation can be found in the publication of the

Port and Harbour Research Institute, Japan [PHRI, 1997].

TABLE 27.1 Acceptable Level of Damage in Performance-Based Designa

Acceptable Level

of Damage Structural Operational

Degree I: Serviceable Minor or no damage Little or no loss of serviceability

Degree II: Repairable Controlled damageb Short-term loss of serviceabilityc

Degree III: Near collapse Extensive damage in near collapse Long-term or complete loss of serviceability

Degree IV: Collapsed Complete loss of structure Complete loss of serviceability

a Considerations: Protection of human life and property, functions as an emergency base for transportation, and

protection from spilling hazardous materials, if applicable, should be considered in defining the damage criteria in

addition to those shown in this table.b With limited inelastic response and residual deformation.c Structure out of service for short to moderate time for repairs.d Without significant effects on surroundings.

TABLE 27.2 Performance Grades S, A, B, and C

Design Earthquake

Performance Grade Level 1 (L1) Level 2 (L2)

Grade S Degree I: Serviceable Degree I: Serviceable

Grade A Degree I: Serviceable Degree II: Repairable

Grade B Degree I: Serviceable Degree III: Near collapse

Grade C Degree II: Repairable Degree IV: Collapse



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27.5 Seismic Performance Evaluation and Analysis

The objective of analysis in performance-based design is to evaluate the seismic response of the portstructure with respect to allowable limits (e.g., displacement, stress, ductility, and strain). Higher capa-

bility in analysis is generally required for a higher performance-grade facility. The selected analysis

methods should reflect the analytical capability required in the seismic performance evaluation.

FIGURE 27.15 Flowchart for seismic performance evaluation. (From PIANC. 2001. Seismic Design Guidelines for


Analysis type:

1. Simplified analysis

2. Simplified dynamic analysis

3. Dynamic analysis

Input:

Earthquake motions

Geotechnical conditions

Initial design or existing structure

Analysis

Output:

Displacements

Stresses

(Liquefaction potential)

Modification of

cross section/

soil improvement

Are damage criteria satisfied?No

Yes

End of performance evaluation

Acceptable damage:

I Serviceable

II Repairable

III Near Collapse

IV Collapse

Earthquake level:

Level 1 (L1)

Level 2 (L2)

Performance grade:

S, A, B, C

Damage criteria



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A variety of analysis methods is available for evaluating the local site effects, liquefaction potential,

and the seismic response of port structures. These analysis methods are broadly categorized based on a

level of sophistication and capability as follows:

Simplified analysis: Appropriate for evaluating approximate threshold limit for displacements and

elastic response limit, and an order-of-magnitude estimate for permanent displacements due to

seismic loading.

Simplified dynamic analysis: Possible to evaluate extent of displacement, stress, ductility, and strainbased on assumed failure modes.

Dynamic analysis: Possible to evaluate both failure modes and the extent of the displacement,

stress, ductility, and strain.

Table 27.4shows the type of analysis that may be most appropriate for each performance grade. The

principle applied here is that the structures of higher performance grade should be evaluated using more

sophisticated methods. As shown in Table 27.4, less sophisticated methods may be allowed for preliminary

design, screening purpose, or response analysis for low levels of excitation.

The methods for analysis of port structures may be broadly classified into those applicable to retaining/

earth structures, including quay walls, dikes/slopes, and breakwaters, or those applicable to open pile/

frame structures, including a pile/deck system of pile-supported wharves and cranes.

TABLE 27.3 Performance Grade Based on the Importance Category of Port Structures

Performance Grade Definition Based on Seismic Effects on Structures

Suggested Importance

Category of Port Structures

in Japanese Code

Grade S 1. Critical structures with potential for extensive loss ofhuman life and property upon seismic damage

2. Key structures that are required to be serviceable for

recovery from earthquake disaster

3. Critical structures that handle hazardous materials

4. Critical structures that, if disrupted, devastate economic

and social activities in the earthquake damage area

Special Class

Grade A Primary structures having less serious effects for 14 than

Grade S structures, or 5, structures that, if damaged, are

difficult to restore

Special Class or Class A

Grade B Ordinary structures other than those of Grades S, A, and C Class A or B

Grade C Small, easily restorable structures Class B or C

TABLE 27.4 Types of Analysis Related to Performance Grades

Performance Grade

Type of Analysis Grade C Grade B Grade A Grade S

Simplified analysis: Appropriate for evaluating approximate threshold

level and elastic limit and order-of-magnitude displacements.

Simplified dynamic analysis: Of broader scope and more reliable.

Possible to evaluate extent of displacement, stress, ductility, and strain

based on assumed failure modes.

Dynamic analysis: Most sophisticated. Possible to evaluate both failuremodes and extent of displacement, stress, ductility, and strain.

Note: Black area is standard/final design. Gray area is preliminary design or low level of excitations.



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27.6 Methods for Analysis of Retaining/Earth Structures

27.6.1 Simplified Analysis

Simplified analysis of retaining/earth structures is based on the conventional force-balance approach,

sometimes combined with statistical analyses of case history data. The methods in this category are often

those adopted in conventional seismic design codes and standards. In simplified analysis, retaining/earth

structures can be idealized as rigid blocks of soil and structural masses. The rigid block analysis is typically

applied for gravity, sheet pile, and cellular quay walls, and dike/slope/retaining walls for pile-supported

wharves and breakwaters.

Effects of earthquake motions in simplified analysis are represented by a peak ground acceleration or

an equivalent seismic coefficient for use in conventional pseudo-static design procedures. These param-

eters are obtained from the simplified analysis of local site effects discussed in the previous section. A

capacity to resist the seismic force is evaluated based on structural and geotechnical conditions, often in

terms of a threshold acceleration or a threshold seismic coefficient, beyond which the rigid blocks of soil

and structural masses begin to move. When soil liquefaction is an issue, the geometric extent of lique-faction must also be considered in the analysis.

27.6.2 Simplified Dynamic Analysis

Simplified dynamic analysis is similar to simplified analysis, idealizing a structure by a sliding rigid block.

In simplified dynamic analysis, displacement of the sliding block is computed by integrating the accel-

eration time history that exceeds the threshold limit for sliding over the duration until the block ceases

sliding.

Effects of earthquake motions are generally represented by a set of time histories of earthquake motion

at the base of a structure. The time histories of earthquake motion are obtained from the simpli fied

dynamic analysis of local site effects discussed in the previous section. In the sliding block analysis,structural and geotechnical conditions are represented by a threshold acceleration for sliding. A set of

empirical equations obtained from a statistical summary of sliding block analyses is available. In these

equations, peak ground acceleration and velocity are used to represent the effect of earthquake motion.

In more sophisticated analyses, structural and geotechnical conditions are idealized through a series

of parametric studies based on nonlinear Finite Element Method (FEM)/Finite Difference Method (FDM)

analyses of soilstructure systems. The results are compiled as simplified charts for use in evaluating

approximate displacements.

27.6.3 Dynamic Analysis

Dynamic analysis is based on soilstructure interaction, generally using FEM or FDM. In this category

of analysis, effects of earthquake motions are represented by a set of time histories of earthquake motion

at the base of the analysis domain chosen for the soilstructure system. A structure is idealized as either

linear or nonlinear, depending on the level of earthquake motion relative to the elastic limit of the

structure. Soil is idealized either by equivalent linear or by an effective stress model, depending on the

expected strain level in the soil deposit during the design earthquake.

Fairly comprehensive results are obtained from soilstructure interaction analysis, including failure

modes of the soilstructure system and the extent of the displacement, stress, and strain states. Because

this category of analysis is often sensitive to a number of factors, it is especially desirable to confirm the

applicability by using a suitable case history or a suitable model test result.



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27.7 Analysis Methods for Open Pile/Frame Structures

27.7.1 Simplified Analysis

Simplified analysis of open pile/frame structures is typically done by idealizing the pile/deck system of

pile-supported wharves or the frame of cranes by a single-degree-of-freedom (SDOF) or multidegree-

of-freedom (MDOF) system. In this analysis, earthquake motions are generally represented by the

response spectrum. Structural and geotechnical conditions are represented by a resonant frequency and

damping factor of the pile/deck system and the cranes. A ductility factor may also be introduced. The

movement of the dike/slope is generally assumed to be negligible. Results of the SDOF/MDOF analysis

are useful to evaluate approximate limit state response of a pile/deck system or a crane.

27.7.2 Simplified Dynamic Analysis

In simplified dynamic analysis of open pile/frame structures, the SDOF or MDOF analysis of pile/deck

structure or cranes is combined with pushover analysis for evaluating the ductility factor/strain limit.The movement of the dike/slope is often assumed to be negligible but sometimes is estimated by a sliding

block-type analysis. Movement of a pile-supported deck could thereby be estimated by summing up the

dike/slope movement and structural deformation. Soilstructure interaction effects are not taken into

account, and thus there is a limitation in this analysis. Interaction between the pile-supported wharves

and cranes can be taken into account by MDOF analysis. Displacement, ductility factor, strain, and

location of yielding or buckling in the structure are generally obtained as a result of the analysis of this

category. Failure modes with respect to sliding of retaining walls, dikes, and slopes are not evaluated but

assumed and, thus, there is another limitation in this type of analysis.

27.7.3 Dynamic Analysis

Dynamic analysis is based on soilstructure interaction, generally using FEM and FDM. Similar com-

ments to those related to the dynamic analysis of earth/retaining structures apply also to the open pile

structures and cranes.

References

CEN (European Committee for Standardization). 1994. Eurocode 8: Design Provisions for Earthquake

Resistance of Structures. Part l-l: General Rules Seismic Actions and General Requirements for

Structures (ENV-199811); Part 5: Foundations, Retaining Structures and Geotechnical Aspects

(ENV 19985).

Ferritto, J.M. 1997a. Design Criteria for Earthquake Hazard Mitigation of Navy Piers and Wharves,Technical report TR2069-SHR, Naval Facilities Engineering Service Center, Port Hueneme.

Ferritto, J.M. 1997b. Seismic Design Criteria for Soil Liquefaction, Technical report TR2077-SHR,

Naval Facilities Engineering Service Center, Port Hueneme.

Ministry of Transport, Japan, Ed. 1999. Design Standard for Port and Harbour Facilities and Commentaries

(in Japanese), Japan Port and Harbour Association (English edition [2001] by the Overseas Coastal

Area Development Institute of Japan), Yokosuka.

PHRI (Port and Harbour Research Institute). 1997. Handbook on Liquefaction Remediation of Reclaimed

Land(translated by Waterways Experiment Station, U.S. Army Corps of Engineers), A.A. Balkema,

Rotterdam.

PIANC (Permanent International Association for Navigation Congresses). 2001. Seismic Design Guidelinesfor Port Structures, A.A. Balkema, Rotterdam.



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Werner, S.D., Ed. 1998. Seismic Guidelines for Ports, Monograph No. 12, Technical Council on Lifeline

Earthquake Engineering, American Society of Civil Engineers, Reston, VA.

Zwamborn, J.A. and Phelp, D. 1995. When Must Breakwaters Be Rehabilitated/Repaired? in PORTS

95, American Society of Civil Engineers, Reston, VA, pp. 11831194.

Further Reading

Much of this section is based on the authors involvement in the development of the publication Seismic

Design Guidelines for Port Structures[PIANC, 2001], which is highly recommended to the reader, and

the use of material therefrom is gratefully acknowledged.

Documents

Port Structures.pdf