Messages from Departments and Centers of NILIM

Performance Verification Act of Harbor Structure
towards Further Streamlining
NAGAO Takashi
Director of the Port and Harbor Department(Keywords ) Reliaibility, Action, Proof stress
1. Importance of Design Engineering View
Designing is an act to determine cross-section surface
element that gives structure stability for assumed action.
Margin is set with consideration such as various
uncertain factors and variation to secure necessary safety.
Indicators that indicate margin are various such as safetyrate, proof stress action ratio, reliability indicator andfracture probability (for comparison, safety rate is not
used for the harbor performance verification). In
designing, it is needed to set margin along withassessment of action and assessment of response ofstructure for action. These assessments and setting all
should reasonably be done.
Assessment of action and assessment of response ofstructure have been improved by a pile of engineeringresearch. In port and harbor field, regarding input
earthquake motion traditionally, the measure below hasbeen adopted. level 1 earthquake motion is assessed ascoefficient which is dived 5 block from all parts of thecountry, and level 2 earthquake motion, representative
example is selected from past earthquake motion records,
and acceleration is adjusted in response to assumed
earthquake size. Today, based on the way of thinking ofearthquake-resistant design guideline of civil structure ofSociety of Civil Engineers, time history crimp withconsideration of amplification characteristic by source
property, propagation path characteristic, deep layer
ground in each port and harbor are set in both level 1 andlevel 2).
Research for response of structure has been improved.
In earthquake-resistant design of quay, the following
measure has adopted. For level 1, performanceverification is done by setting intensity for verificationthat responds to deformation amount of quay 2). For
level 2, effective stress analysis by 2D finite element
procedure is normally used.
Research regarding action and response has beenproceeded, but setting of margin ratio is the one thateventually determines reliability of structure, and settingof margin is needed to be done carefully in considerationof technical level of action and response in a standpointof design engineering. Traditionally, it may have been alack of view of the design engineering.
Chart-1 is a comparison of system reliability indicator
for wave action of each breakwater 3). Reliability
indicator is the indicator that indicates indirectly fracture
probability of structure, and the relationship of them isindicated in graphic-1.Difference as reliability indicator
between the lowest reliability indicator 2.04 and thehighest reliability indicator is 30%. However actual
stability of structure is assessed in fracture probability.

Fracture probability is 0.021 / 0.004 referring chart-1,and the difference is 5 times.
Structure format

Average ofreliability
indicator
2.11

Caisson typecompound bankWave-dissipating
block cleading bankSuperior slope bankUpstand vanishingwave bank
Vanishing wave
caisson bank

2.64
2.16
2.04
2.05

0.1

Fracture
probability

0.01

1 1032

2.2

2.4

2.6

2.8

3

Reliablity indicator
Graphic-1 Relationship between reliability andfracture probability
Required performance for breakwater is to maintainquiet in harbor, in this regard, there is no difference forrequired safety level for each structure format. However,there is actually a difference of safety level as above.
The difference comes of the way of thinking of theproposer of wave power calculation formula for eachstructure. It occurred, because it was a different way ofthinking, but it was used for the same performanceverification calculation. Effort will be needed in thefuture to resolve such mismatch.

Messages from Departments and Centers of NILIM(a) Quay No.3(b) Otsurugi quay
10
spectral ratio

2.Further streamlining of action assessment
Regarding further streamlining of assessment of action
and response, it will also be needed to proceed. Due to a
space constraint, it’s stated regarding action is asfollows; The 2011 off the Pacific coast of Tohoku
Earthquake occurred in 2011, a lot of damaged not only
by tsunami, but also by the action of earthquake motion.
Especially, situation of damage by district in the sameharbor was very different, and it was the feature of theseismic damage. It is thought that because amplification
characteristic in sedimentary layers from seismic
basement to ground level is different in points that havealmost same distance from seismic center.
For example, in Onahama harbor, a great damage
occurred at No. 3 quay, but at Otsurugi quay, there was
not damage (picture-1). Microtremor H/V spectrum(Ratio of horizontal component and vertical componentof microtremor H/V spectrum amplitude) is indicated ingraphic-2. Peak frequency of microtremor H/V spectrum
responds to frequency that earthquake motion isamplified. Therefore if the frequency is less than 2Hz
and has a great impact on deformation of quay, it issaid that damage usually occurs during earthquake. The
peak, at the quay no.3 less than 2Hz and at Otsurugi
quay more than 2Hz, is approved, and it responds to thedifference of damage. Based on the results, in Onahama
harbor, zoning of input earthquake motion has been done,
and it has reflected to designing. High assessment ofaccuracy of amplification characteristic of earthquake
motion is very important to structure a strong country,
and research will be needed to proceed in the future.

10.1

1

Takeshiandother:

10

Probabilistic

earthquake hazard analysis focused on fourier amplitude
and group delay time. Japan Society of Civil Engineerscollection of papers, No.801 ， Ⅰ -73 ， pp.141-158 ，

spectral ratio

NAGAO

10frequency(Hz)Reference1)

Quay No.3

2

2005

motion and setting measure of earthquake resistantOtsurugi quay

10.12)NAGAO TAkeshi: Gravity formula for earthquake

21

10frequency(Hz)performance verification intensity of sheet pile quay wall.
TECHNICAL NOTE of NILIM No.310, 2006
3)YOSHIOKA Ken, NAGAO Takeshi: Proposal oflevel 1 reliability designing method regarding externallystable of gravity formula breakwater. RESEARCHREPORT of NILIM No. 20, 2005

Graphic-2 Onahama harbor microtremor H/V
spectrum