muelle lo rojas guidoppoo

7/28/2019 Muelle Lo Rojas Guidoppoo

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Summary

The earthquake of 27 February in Chile had a great effect on structures all over the

country and in

particular in the region of Concepcion. The structure treated in this article is one of

the pile

supported wharfs of the fisheries in city of Coronel. The structure consists of a

walkway, which

connects the land with a mooring platform. The walkway is divided into two partsby dilatations.

Unknown is why the wharf was so heavily damaged and what was the main

cause of the damage. Two cases are considered. Either the wharf was designed to

sustain an earthquake with an

acceleration of 0.40g, while the maximum acceleration of the earthquake in

Coronel was

approximately 0.65g, or the damage is a consequence of improper design or

manufacturing.

Damage to the pierThe damage to the pier manifests itself in a number of ways. The platform adjacent part of the

walkway shows large

vertical deformations

accompanied with

plastic hinges in-

between the concrete slab and beams of the superstructure. The land adjacent part

of the walkway shows large horizontal displacements and the tear out of diagonal

piles. The mooring platform had very little damage. The emphasis of the analyses

will be on the platform adjacent part of the walkway.

Threecommon cases are known, which can cause such damage to the pile supported structure:

1. An inertia force at the deck of the structure2.Liquefaction

of the soil

3. Acombination of the

two above

In thecase of

an

inertia

force,

the earthquake load working on the mass of the structure is the cause

of the damage. In the case of liquefaction the loss of the stiffness due to the

increase of effective pile


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length is the cause. Liquefaction is a significant strength loss in loose saturated

granular soils as a

result of the shaking of ground. As saturated soil deposits are sheared rapidly back

and forth by the

shaking motion, the water pressure in the pores starts to rise. The soil loses its

strength and stiffness.

Hereafter a description is given of the model, which has been developed to analyze

the failure mode.

The Lp modelThe walkway is modeled as a rigid floor slab, supported by two beams on piles. All connections

between slab, beam and pile are rigid. The important part of this case is modeling the soil-pile

interaction. The so-called Lp-model is used. In the Lp-model, after some depth in the

soil the position

of the pile is fixed. This point is the position of the maximum moment in the pile.

The penetration

depth into the bearing sand layer, which necessary to reach the fixing point, is

represented by the

length Lp. In order to obtain the fixation the total penetration into the bearing sand

layer should be3Lp. In the case of liquefaction the bearing sand layer is positioned deeper. In case

the bearing layer

is too deep to obtain 3Lp, the support may act as a hinge or

not at all. Lp formula.

1 E s

is defined by the following

Lp= with: = 4 4EI

EI = flexural rigidity of the pile


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Es = the soil elastic modulus

Response spectrum

The earthquake load can be put in the model using the acceleration response spectrum of the

structure. Two spectra are considered: the spectrum of the Chilean code Nch2369

and the actual

spectrum of the 27 February earthquake. When both spectra are plotted in one

graph, one of the

main questions of the research is almost instantly answered. Except for a small

peak in the lower

period-range, the design response spectrum of the code is larger than the response

spectrum of the

27 February earthquake.

The Eigen period of the structure in the stiffest case (no liquefaction and fixed supports)

corresponds with 0.44s.The critical range where the 27 February earthquake

spectrum exceeds the design spectrum is approximately 0.17s - 0.25s. For caseswhere the structure is less stiff, the Eigen period become larger. Thus can be

concluded that, despite of the lower maximum acceleration, the design code is well

fit for this structure.

Results of the Lp calculation

The structure can be modeled using the Lp-model with Finite Element software. In

this analysis the program RAM Advance is used. Using the average of the properties

of the sand soil layers, the length Lp can be calculated to be approximately 2

meters. Thus a 6 meter penetration of the piles is

necessary to obtain fixation. All the piles ought to have a penetration depth of 17meters, but this is not exactly known. Nevertheless without liquefaction of the soil,

the pile penetration is sufficient.

A ground research indicates that the top 11 meter of the sand layers are

susceptible to

liquefaction. This means that when the whole length of 11 meter truly liquefy,

exactly 6 meters of

pile penetration are left to ensure the fixation. However the calculation used to

determine this

length is merely a rough representation of the reality, the 6 meters may not be

sufficient to ensure fixation, and the true penetration depth is unknown.Assuming that fixation of all the piles is ensured, the structure performs pretty

well both in case with and without liquefaction. Two indicators of performance are

use for comparison with the capacity of the structure: the maximum moment in

axial direction in the cross section of the

superstructure and maximum axial displacement.

Failure mechanism

Because the structure performs very well in the model when all the piles are still

fixed, there must be

an additional effect. The assumption is made that several piles loose all bearingcapacity and have no

support, due to liquefaction of the soil. This assumption is supported by the before

mentioned fact

that the bearing soil penetration may not be sufficient. Based on the real

deformations of the


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structure, other schemes are proposed. By one of them, the outer pile rows and one

row of the

diagonal axial piles keep their fixed supports (+ 3 fixed rows), the other piles lose

their support. Only

for this scheme the axial maximum moment in the concrete deck exceeds the cross

section capacity.

The exceeding of cross section capacity occurs at two places, both above the

diagonal piles. Here

plastic hinges are formed. When the deformation of the 3 fixed rows model is

compared with realdeformation of the structure, the similarities are abundant. With probability close to

certainty, it can

be said that this is the failure mechanism, which occurred during the 27 February

earthquake.

Due to the loss of bearing capacity of several piles, the structure was unable to

bear its own

weight. The contribution of the inertia load on the deck is minor, because in this

unstable state, the

Eigen period of the structure is very high. Thus can be concluded that liquefaction of

the soil is the

main cause of the occurred damage.

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1 Report introduction

The earthquake of 27 February in Chile has caused damage all over the country and

in particular in

the region of Concepcion. Engineering experts from universities, companies and

from abroad are

analyzing damaged structures. In this report one of the damaged structures will be

analyzed. The

structure in question is the fishing pier of the city of Coronel. The pier was designed

to sustain an

earthquake with 0.40g acceleration; the acceleration of the earthquake in coronel

was approximately

0.65g. Unknown is why the pier was so heavily damaged and what was the main cause of the

damage. The high maximum accelerations, significantly higher than the design

accelerations, could be the reason, but maybe the structure could not resist the

design acceleration itself. The

government plans to rebuild the pier using old piles, although no research hasbeen done, whether this is the best way.

In this report a damage investigation and structural analyses on the pier are performed. The

objective is to trace the origin of the damage and under which minimum

conditions the pier would have collapsed.

Before the structural analyses and the damage investigation there are introductory

chapters. The

introductory chapters give background information and structural information, such

as dimensions

and design criteria. Chapter 2 gives a area description, the chapter zooms in fromthe country to the

fishing pier. Chapter 3 explains the basics of subduction earthquakes: the

earthquakes that emerge in

Chile. The chapter forms the basis of the up following chapter. That chapter is about

the Earthquake

of 27 February. The total picture of the earthquake will be put out. Later in the

analyses significant

characteristics of the earthquake will be used. In chapter 5 the structural lay-out of

the pier is

discussed. The emphasis is on the part of the structure that will be analyzed in the

structural

analyses.

The damage investigation is described in chapter 6. This chapter consists of two

parts. The first part is a list of all the damages. The damages are summed up

supplemented with pictures and comments. In the second part the possible origins

of the damage are put out. Three standard deformation cases of piers due to

earthquakes will be treated.

The actual structural analyses is treated in the last three chapters. Chapter 7 laysout the principles

and the method of analyses. This mainly concerns the conversion of reality to a

usable computer

model. In Chapter 8 all the necessary input parameters of the model are

determined. This includes


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soil properties, liquefiable soil layers and response spectra. Chapter 9 is the

chapter where its all

about, the structural analyses. First the use of failure indicators is explained. Next

different models

are compared with each other and with the real damage. The results of the design

and the 27

February earthquake are compared with each other. And the results of the analyses of the two

walkway parts are viewed in relation with the real damage. The chapter finishes

with a sketch of the failure mechanism of one of the walkways and some firm

conclusions.

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2 Area description from country to fishing pier

2.1 Description of Chile

Chile is a peculiar county in the southern part of South-America. With a coastline of

4630 km Chile is the longest country in the world, in north-south direction. The

country is bordered by two natural barriers. In the north is the Atacama desert, a

very dry and uninhabitable desert. And in the east over the full length of the country

is the Andes mountain range. These two barriers make that Chile is

dependent on its ports for any large goods to enter.

The country can be divided in three parts. The

northern part of Chile which mainly consists of

the

desert is thinly populated. The middle part of

Chile,

which is the engine of the economy is

relatively dense

populated. Over 80 percent of the people live

in the

area. The area approximately extends from

Coquimbo

to Puerto Mont. The southern part of Chile is

rather

cold and just like the north thinly populated.The total

population of Chile is 17 million people. 5

million live in

the capital Santiago.

The living standard of the people is high in

comparison

with other Latin American countries. The

average

income per capita is $14.300. In 2010 Chilebecame a

member of the OECD, which is basically an

organization of counties with a high income.

Because of the isolated position, 88% of the

international commercial exchange is carried

out via

maritime transport. The main sea ports of

Chile are

San Antonio and Valparaiso. Because of thelong

coastline, the presence rocky coast and many

bays, a

lot of small ports emerged at the coast of Chile

as well.

The bays give good sheltering conditions and


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possibilities for small economic activity such

as fishing.

2.2 Description of Coronel Bay

Coronel Bay is situated 30 km south of

Concepcin.

The bay is a part of the Gulf of Arauco, the

bay south

of the line Isla Santa Maria - Coronel. Coronel

Bay is indicated in the highlighted yellow box.

The bay is well sheltered from waves. The

northwestern wave heights are reduced by

the Coronel Land end, the south-

western waves by Isla Santa Maria, the largeisland.

Figure 2.1: Map of Chile (Wikipedia)

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Figure 2.2: Map of the area around Coronel Bay (Google Earth)

Coronel Bay houses Port Coronel, Cabo Froward and fisheries. Port Coronel is an

important port in

the region for the export of wooden products and industrial products. The Port is

indicated in the red

highlighted part in figure 3. Cabo Froward is a port with two conveyor belts and is

mainly used for the

import of wood chips and coal. It is indicated in the green highlighted part in the

figure. The fishing

area is indicated with the blue highlighted box and will be discussed in the next

paragraph.

Figure 2.3: Partition of Coronel Harbor (Google Earth)


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2.3 Description of the Fishing Wharf

The fisheries are an important part of the coronel industry. The fishery area contains six fishing

companies. Together the companies used to produce 1.3 million ton fish per year.

There are up to

7000 workers active in the industry. Two types of ships are used: big ships with adraught of 2-3

meters and small ships. The six companies all have their own conveyer: two piers

and four flexible

conveyers. For years the Coronel Bay suffers from sedimentation problems inside

the bay. Because of this extensions of the piers had to be realized. Other companies

use flexible conveyer belts, so the

mooring location can be moved.

The largest fishing pier was heavily damaged by the earthquake of 27 February. The

investigation andanalyses of the damage of this pier is the subject of this report. The pier in question

is highlighted

with a yellow box in figure 3. General information and structural details of the pier

will be elaborated

in chapter 5.


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3 Earthquakes in Chile

3.1 The emergence of a subduction earthquake

Earthquakes are the result of movement of land masses on the earth. Due to a

convection process in

the core of the earth, different tectonic plates at the surface of the earth move in

the direction of the

underlying convection current. In this slow process the plates move in different

directions. The

meeting point of two tectonic plates is called a fault line. Plates can move towards

and from each

other and they can shear against each other. The first and the last type of

movement can cause

major earthquakes. Within a sort of movement there is more than one type ofearthquake. From this

point I will focus on the type of earthquake present in Chile, the subduction

earthquake.

In Chile two plates move towards each other, the Nazca plate and the South-America plate. The

Nazca plate is an Ocean plate and moves eastwards. The South-America plate is a

continental plate and moves westwards. At the fault line the Nazca plate sub ducts

the South-America plate and goes in the depth of the earth. This movement has

average relative velocity of 80 mm per year, but the largest part of the movement

is caused by the Nazca plate (see Figure 3.1). Rupture zones extend to a depth of50 km and their lengths could reach over 1000 km. This convergence is responsible

for strong earthquakes, even the strongest earthquakes we know in the world.

In the most southern part the situation is different. Here the Antarctic plate is sub

ducted under

the South-America plate, this happens at a slower rate. In this region the

earthquakes are mediocre.


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Figure 3.1: Tectonic movement of continental plates (Vigney, 2003)

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In the contact region the convergence is not constant, because of the subduction process. The

convergence of two plates is determined with two stable points on the plates, for

example with GPS, with the points on Easter Island and Buenos Aires. The relative

movement in the contact region is

close zero for a long time. This process is the offset of an earthquake. The process is

graphicallyexplained in Figure 3.2.

While the sub-ducting plate sub ducts the overriding plate, the overriding plate

sticks to the subducting plate. In this process the plates deforms elastically. The

elastic deformation continues to accumulate over a time span of years, but at a

certain time the stress between the two plates

become too high. The deformation accumulates up to the ignition of the fault and

the generation of an earthquake. Ultimately the plates are back in their original

positions; the position of the beginning of a seismic cycle. Dependent on the time

between two major earthquakes in one area in a fewminutes the overriding plate can move 5 to 10 meters during an earthquake.

Figure 3.2: The genesis of an earthquake in case of subduction (Terremonto Cauquenes 27 Febrero 2010)

The intensity of an earthquake is different per

region. In Figure 3.2 can be seen that the

earthquake motion for the most part takes

place in the coastal region. The most effected

part of the country is located from the coast

up to 50-100 kilometers inland, approximately

200 kilometers from the trench. Next to

scientific knowledge also earthquake records

confirm the diminishing effect of earthquakes

inland.

The Chilean building norm uses three

distinct earthquake risk zones. Zone 1

mostly in the Andes, with low risk, and

zone 3 close to the coast with high

risk.

Several design criteria depend on the risk area

where a structure is built. Criteria such as the

design acceleration of an earthquake and

modification design load factors. In figure 6

the risk zones for middle Chile are shown. The

majority of the cities are situated in risk area 2

or 3.

Figure 3.3: Risk zones used in the Chileanbuilding norms (NCh0433-1996)


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3.2 The effects on nature and on structures as a result of earthquakes

The effect on land structures

An earthquake is a dynamic load on the land and on the buildings atop of the land. A good

representation is the maximum acceleration in vertical and in horizontal direction. The load is

temporary, but can cause a lot of damage to structures that are not properlybuilt. Not properly in this case, means: not properly to withstand the earthquake.

The structure can still agree with national building codes.

Additional to the risk area, the magnitude of earthquake load on a structure, is dependent on

more aspects. One aspect is local side effects, such as the properties of the subsoil

and the thickness of the subsoil layers. Another aspect is the fault orientation. The

progressive rupture process

determines the directivity of the ground motion. The orientation of a structure is of

importance here. In their stiffest direction, structures develop the largest forces.

The principle of soil liquefactionLiquefaction is a significant strength loss in loose saturated granular soils. It is a

result of the shaking

of ground. As saturated soil deposits are sheared rapidly back and forth by the

shaking motion, the

water pressure in the pores starts to rise. In loose cohesionless soil, the water

pressure rises rapidly

and a level can be reached where the particles float apart and the strength of the

soil is temporarily

lost altogether. A possible effect of liquefaction is the occurrence of water sprouts

and large ground

movements. After liquefaction the conditions of the soil, such as the density, are

permanently

changed. As strength is reduced, deformations can occur due to a driving static

shear stress such as sloping ground, embankment loads and building loads,

amongst others.


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Figure 3.4: The mechanism of liquefaction (PIANC wg34)

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The particle size and relative density of the granular soils play the key role in the occurrence of

liquefaction. As the rivers travel from east to west, the slope and therefore the energy for

transporting particles decrease. The soils close to the Andes are primarily composed

of gravels. As the rivers approach the coast, smaller particle size are present.

Excess pore pressures or water

sprouts arise more readily in finer granular material than in coarser granular

material, because of the permeability of the material with respect to the rate of

floating. For this matter liquefaction is more common in coastal regions, especially

at or near river banks.

Tsunami waves

A possible effect of an earthquake is a tsunami. In Figure 3.2 a representation is included of the

emergence of a tsunami. The sudden horizontal and vertical movement of the land

is taken over by

the water in the form of a wave. Tsunami waves can reach heights up to 5 meter in

coastal areas and

inundation heights have been measured from up to 30 meters. Total villages have

been wiped out in

the past.

Permanent vertical uplift of the coastline

In addition to temporary effects, there is also a more permanent effect, the

displacement of the land. As mentioned earlier the land can move 5 to 10 meters

in horizontal direction. Also a vertical displacement takes place. The vertical

displacement can be noticed with easy practical methods at the coast. In figure 7

you can see vegetation of litho amnion coralline algae. These algae have a red

color and lose their color when they are not in their natural salt environment. The

white color is a marker for the natural coastal uplift. In this case there was an uplift

of 1.1 meter.

Figure 3.5: Uplift of the coastline visual due to vegetation (Barrientos, April 18, 2010)

3.3 History of earthquakes in Chile

No recorded human generation in Chile has escaped the damaging consequences of a large

earthquake. More than ten events with magnitudes greater then magnitudes 8 on

the Richter scale have taken place during the 20 th century alone. Since the settling

of the Spanish in Chile earthquakes have been recorded. Among these, the event of

1960 is the largest earthquake ever measured, with a magnitude of 9.5.

The return period for a magnitude 8 event for Chile considered as a whole is 15

years. The return period for any given region in Chile on itself for a magnitude 8

event is 80 to 130 years. Mega trust earthquakes like the one of 27 February have a

much longer return period. The last large earthquake in Concepcion was in 1835, a


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period of 175 years. Logically large and very large earthquakes are not independent

events. When the a return period of a magnitude 8 earthquake is long past since

the last earthquake, a much larger earthquake may be expected.

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4 The Earthquake of 27 February 2010

4.1 Properties and effects of the earthquake

Before the earthquake, Chilean geotechnical scientist indentified the Concepcion

area as a mature seismic gap, since no large subduction earthquake has occurred

there since 1835. They noted that the convergence of 75mm/year would have

accumulated up to more than 10 meter displacement, and predicted a magnitude

8.5 event should the earthquake happen in the near future. The time of an event is

unpredictable; however the magnitude if an event would happen can be predicted

pretty well. In this case as well, the prediction was good.

On February 27, 2010 the earthquake occurred off the coast of Maule, near

Concepcion. The epic

centre was located at the coordinates S36.027, W72.834 at a depth of 35 km

(see Figure 4.1). The

earthquake had magnitude of Mw 8.8 in Richter scale and a seismic moment of

1.8 1022 Nm. The

main shock occurred at 3.34 am local time and had duration of approximately 2

minutes. The effects of the earthquake were observed from Valparaiso to Temuco.

Apart from the immediate

consequences, the earthquake resulted in a tsunami that affected a significant

portion of Chile coast. The tsunami has wiped out total villages. Inundation in some

villages was 6 meters. At cliffs and near coastal islands inundation of over 10 meters

has been measured.

Figure 4.1: Intensity radius of the 27 February earthquake (Terremonto Cauquenes 27 Febrero 2010)


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Maximal ground accelerations

A network of ground motion station, monitor the ground motion accelerations continuously. The

outputs the stations give are digital acceleration files and response spectra. From these datathe

maximum accelerations can be subtracted. In Table 4.1 Table 4.1a number of

maximum accelerations measured by ground stations are given. Here g is thegravitational acceleration of 10 m/s2

Accelerations are an important quantity, used in the design codes, to determine the

forces exerted by an earthquake. Striking is the high vertical acceleration in

Concepcion. Both in relative a absolute value Concepcion had the highest vertical

acceleration.

Table 4.1: Accelerations measured by several Chilean ground motion stations (Terremonto Cauquenes27F)

Resulting vertical and horizontal displacements

Due to earthquake the large horizontal and vertical displacement of the land

occurred. In Figure 4.2

the deformation of the land is shown. The figure shows maximum uplift at the coast

of 1.5 to 2 meter

and subsidence inland. The horizontal deformations have maximum levels of 5 to 6

meters on the

coast. These figures however are based on seismic data. From GPS measurements isknown,

horizontal deformations of 8.5 meters have occurred at the coast near Concepcion.

For the vertical

deformation, the model produces are more accurate, based on comparisons with

measurements.

These uplift/subsidence are estimated from the upper growth limits of marine

intertidal organisms,

as explained in paragraph 3.2.


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Figure 4.2: Left: the fault slip inverted form seismic data; Right: the coseismic verticaldeformation (color in m) and the horizontal displacement (arrows). {Terremonto Cauquenes27 Febrero 2010}

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Liquefaction due to the 27 February earthquakeLiquefaction was observed to have occurred over a large area around Coronel. The widespread

presence of river sediments and the long duration of the event contributed to the number of

liquefaction observations. Areas of high spatial density soils susceptible to liquefaction, were

observed to have liquefied. In areas of low spatial density there was intermittent liquefaction of

susceptible soils. Observations indicate that the central region east of the epicenterexperienced less

intense ground shaking, which agrees with the lesser amount of damage of

structures in that region.

Significant properties for Coronel Bay

In this paragraph four earthquake properties/effects are discussed. In this research

ultimately only

the data of Coronel are of interest, particularly of the pier. Table 4.2 is a summary of

the

properties/effects of the earthquake in Coronel. First: The maximum acceleration in

Coronel is similar

to the maximum acceleration in Concepcion, 0.65g. Second: The vertical en

horizontal displacements

are considerable, however not as large as the displacements north of Coronel. Third:

Liquefaction

frequently occurred in the area of Coronel. Coronel is on build on not densely

stacked river soil.

Table 4.2: Properties/effects in Coronel of the 27 February earthquake

distance to epic centre 85km southmaximum acceleration 0.65g North - South

displacements ver. +1.3m Hor. 5.5m west

liquefaction frequently occurred

4.2 Aftershocks of the earthquake

After the occurrence of an earthquake,

aftershocks are expected to occur.

Aftershocks occur mainly in the area that hasbeen fractured and at the ends of the rupture

zones. The change of activation of a similar

major earthquake however is negligible.

Figure 2.2 shows all the (after)shocks with a

magnitude greater than 4.8. The number of

earthquakes and the magnitude decrease

with time. Both seem to decrease

exponential.

For a long period after the major event,earthquakes that matter occur. In the

building and analyses of structures

this long

and intense period of aftershocks

should be


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accounted for. For example when a

structure

is built such that damage is expected

after a

major event. The aftershocks could

hinder

the repair for a long time.Figure 4.3: Distribution of aftershocks of the earthquake ()

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5 The Muelle lo Rojas fishing pier

The Muelle lo Rojas fishing pier is a pile supported pier. The pier is 98m long and has

a walkway and a mooring platform at the end. The walkway is 4.0 meters wide; the

mooring platform is 6.0m wide and 14.0m long. The water depth varies from 0meters at the coast to 10 meters at the end of the mooring platform. The average

penetration length of the piles is 30m. The total length of the piles is the penetration

length plus the length in and above the water.

The mooring platform has the most important function of the pier. The platform

functions both as mooring structure and loading/unloading platform. Mooring is

possible on both long sides of the

platform. The mooring defense consists of 3 meter long wooden fenders, connected

to the platform. Also the platform contains stairs on one side that go all the way

down to the waterline. Both

walkway and mooring platform are 4.25m above sea level (N.R.S.). The pier ismainly used by big

fishing ships with maximum sizes of 20 by 10m and a draft of approximately 3m.

Pictures of the pier before the earthquake are shown in Figure 5.1.

Figure 5.1: Photos of the Muelle lo Rojas before the 27 February earthquake


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5.1 The layout of the structure

Anticipating on the damage of the pier and the pier analyses beforehand, only the

dimensions of the walkway will be discussed in this chapter. In the investigation of

the damage will become clear that the mooring platform only suffered minor

damage. Further the mooring platform and the walkway are not connected witheach other. Hence the mooring platform is of less interest for the analyses of the

structure and will not be discussed.

5.1.1 Dimensions of the structure

In Annex 1 the original drawings of the fishing pier can be found. On the first page a

top view and a

side view are shown. In the top view very nicely the distribution of the piles can be

seen. Piles are

placed every 6 meter and at several row on one or on both sides the piles are

placed diagonal. Thediagonal pile are always in pares. There are two different pares used in the

structure; pares oriented

in the axial direction of the walkway and pares oriented in the lateral direction. Two

cross sections

are of interest, a standard cross section (c.s. B-B), and a cross section with lateral

diagonal piles (c.s.

A-A). Further between row 8 and 9 and between the walkway and the platform,

next to row 16, are

expansions joints.

Piles of the walkway

The foundation of the structure consists of hollow steel piles. The piles are filled

with sea sand up to

the pile cape. The upper 45 mm of the pile is filled with concrete, as part of the pile

cap connection.

The profile of the piles is 123/4x61.7: the diameter is 324mm and the wall

thickness is 8mm. Final

the piles have different lengths, dependent on the water depth. In Table 5.1 the

length of the piles

for each row is shown. The column diagonal length contains the length of only the

diagonal piles.

The column vertical length contains the vertical length of both diagonal as

orthogonal piles.

Pile profile: 123/4x61.7 (d=324mm / t=8mm)

Table 5.1: length piles of the walkway

row pile length vertical pile length Seabed Embedded

orthogonal length diagonal depth (m) verticalpiles (m) diagonals (m) piles (m) length (m)

1 33.6 - - -0.00 30.02 34.0 33.0 34.7 -0.42 30.0 / 29.0

3 35.5 - - -0.85 30.0

4 - 33.9 35.0 -1.33 29.0

5 35.4 34.4 35.6 -1.80 30.0 / 29.0


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6 36.0 - - -2.38 30.0

7 36.6 35.6 36.8 -2.96 30.0 / 29.0

8 38.9 - - -5.30 30.0

9 39.3 - - -5.70 30.0

10 41.2 40.2 41.7 -7.61 30.0 / 29.0

11 - 40.8 42.3 -8.16 30.0

12 42.0 - - -8.44 19.0 / 29.0

13 - 41.3 42.8 -8.72 29.0

14 42.6 41.6 43.1 -9.00 30.0 / 29.0

15 42.9 - - -9.25 30.0

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Cross section of the walkway

The upper structure consists of a concrete floor that is supported by two longitudinal concrete

beams. The floor has a thickness of 200mm and is 4000mm wide. The beams have size h x w =

450x350mm, and a centre to centre distance of 2500mm. The beams and piles are

connected with

pile caps of 90x70x70mm. The top of the pile in the centre of the pile cap. The

system consisting of

the three types of elements is poured in one piece. Also the inner part of the steel

hollow pile at the

connection is filled with concrete. Further the walkway is supplemented with railing

and lampposts,

which have no structural purpose. In Figure 5.2 a cross section is shown with only

orthogonal piles.

Figure 5.2: Cross section of the walkway with two orthogonal piles (dimensions in m and cm)

However the majority of the pile rows have a cross section that deviates, with one

diagonal pare of piles in lateral direction, or two diagonal pares in the axial

direction. The piles stand under an angle of 18, with the vertical position. In case of

the lateral pare, the pile on the outside is connected with the beam. The pile on the

inside is only connected with the system through the block. The block has a

different size, in order to make the connection with both diagonal piles able. The

size of the block here is 90x170x80. In case of the axial pares both pile are


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connected to the beam. From a structural point of view, the floor height is part of

the beam and pile cap height.

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Figure 5.3: Cross section of the walkway with one orthogonal and two diagonal piles (dimensions in m andcm)

Expansion joints

In the introduction of this paragraph the presence of two extension joints was

mentioned. Figure 5.4

shows such a joint. The dilatation of the joint is 30mm. There are no materials

connecting the two

ends together in any way. So structural the dilatation separated parts are

completely independent.

Figure 5.4: Detail of a dilatation in the structure (dimensions in cm an mm)


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5.1.2 Layout of floor and beam reinforcement

The concrete floor, beams and pile caps all contain reinforcement steel. The

reinforcement lay-out can be found in on the second page of Annex 1. In this

paragraph I will lay out the reinforcement of the different elements, with help of

drawings. However it should be noted that the drawings in this paragraph dont give

the complete reinforcement lay-out. For the complete set of drawings I refer to thebefore mentioned annexes.

Floor reinforcement

The floor is reinforced with a mesh of orthogonal bars in the top and bottom of the floor. In the

longitudinal direction are 10 bars, c.t.c. 200 or 220mm, see Figure 5.5. There are

5 additional bars

16 at the supports. The length of the additional bars is 3.2m for intermediate

supports and 2.15m

for end supports. In the transversal direction are 10 bars c.t.c. 200mm. Between

two top/bottombars is an additional bar that crosses diagonally from top to bottom between the

beams, see Figure

5.5, the middle bar. This means that above the beams in the top of the floor the

bars have a c.t.c. 100mm, and similar for the bottom of the floor between the

beams.

Figure 5.5: Transversal cross section of the floor reinforcement (dimensions in m and cm)

Beam reinforcement

The beams are reinforced with a reinforcement cage in the transversal direction and bars in the

longitudinal direction. The cage 10, with has a c.t.c. distance of 250mm in the field and a

150mmc.t.c. distance above the support. The lay-out of the longitudinal bars is somewhat

more complicated. I will suffice with the explanation of the two lay-outs of Figure 5.6.

Over the whole length of the

beam there are four corner and two intermediate bars. The corner bars in the

bottom are 18, the four above are 12. An individual bar has a length of 12m, and


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between bars a weld length of

500mm exists. In the field are an extra 3 bars in the bottom of the beam 3 22. At

the support are an extra 6 bars in the top of the beam 6 22. The transfer of forces

of bottom and top additional bars can be seen well in Annex 1, in the longitudinal

beam reinforcement figure.

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Figure 5.6: Transversal cross section of the beam reinforcement: right - at a support; left - in the field (allin mm)

5.1.3 Structural details and layout of the reinforcement of the pile caps

The pile caps are reinforced with an reinforcement cage. The cage contains of 20 vertical bars12 @

11 and 10 horizontal rectangles 12 @10; see Figure 5.8 and

Figure 5.7. In addition the top of the pile has to the surface welded spiral

reinforcement. The pile top also has elongated cuttings, which are connected to the

inside of the pile and reach to the floor. The spiral reinforcement is 10 and thecuttings 4 16. From the reinforcement lay-out of the structural drawings does not

become clear how the reinforcement of the blocks, beams and floor collaborate in

the joined structural parts. Supposedly the reinforcements are braid together,

obeying maximum reinforcement standards for reinforced concrete.

Figure 5.7: Top view of the pile - block connection reinforcement (dimensions in mm and cm)

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Figure 5.8: Longitudinal cross section of the pile - block reinforcement (dimensions in cm and mm)

The connection of the structure with two diagonal piles is off course different. The

principle of the

spiral reinforcement, cuttings and the reinforcement cage however, is the same.

The difference is in

the amount of bars and the extreme measures of the pile cap. The lay-out can be

found in Annex 1.

5.1.4 Properties of the pier materials

In the structure of the walkway three different materials are used: A36 steel for

the piles, FeB500 steel for the reinforcement and H20 concrete for the

superstructure. The properties of these materials presented below, are the

properties that will be used in the analyses.

Steel of the piles

The piles have steel quality ASTM A36, which is an American standard for steel.

This steel quality close to the European standard S235, but is slightly different.

fs = 250 N/mm2 yield stress

ft = 400 N/mm2 ultimate tensile strength

E = 2.1 105 N/mm2 Youngs modulus

= 7800 kg/m density

Reinforcement steel

The reinforcement quality unfortunately is unknown. Because of this I assume the moststandard

reinforcement quality FeB 500. FeB is a reinforcement quality used all over the

world. This quality is used for all bars.

fs = 435 N/mm2 yield stress

E = 2.1 105 N/mm2 Youngs modulus

= 7800 kg/m density


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Concrete upper structure

In the upper structure H20 (Hormign 20) is used. H20 is quite similar to the

European C20/25. The Youngs modulus is calculated using fck. For the density I

assumed the typical density of concrete, 2400 kg/m, a legitimate assumption for

normal concrete. The design compressive and tensile

strength are the characteristic material strength divided by a material factor.

fcd = 20 N/mm2 design compressive strength

fcd = 1.15 N/mm2 design tensile strength

Ec = 21.4 103 N/mm2 Youngs modulus

= 2400 kg/m density

5.2 Conditions and properties of the structure and the earthquake

In order to determine the design response spectrum and the true response

spectrum, several design need to be known. Within the design conditions are threeimportant subjects, the sort of structure, the area conditions, and the risk area. The

sort of structure influences the design response spectrum through factors. The area

conditions contain soil properties. The soil type is also of importance for

determining the response spectrum. The risk area is discussed before in paragraph

3.1. Coronel is situated in risk area III. Earthquake load conditions depend on the

risk area.

Structural design conditions

In dynamic analyses two structural properties are of importance; the correction factor I and the

damping coefficient . The correction factor is a structure type dependent factor.Structures in the Chilean code are subdivided in the three categories, C1 to C3. The

Muelle de Rojas pier is a category C2 structure. For category C2 structures a factor

of I=1.0 is taken into account. Further every

structure has a typical damping coefficient; the Chilean code gives an estimate for

several structures. For welded steel structures a coefficient is given of = 0.02.

Structure factor I = 1.0

Damping coefficient = 0.02

Further Coronel Bay has minor tidal movements. The difference between the tides isapproximately

0.5m. Loads due to currents are negligible. The extreme wave height in the bay is measured Hs=

1.5m with Tp = 13s. However it is not realistic to account for the extreme

values during the earthquake. The flow and wave loads are not taken into

account in this analyses.

Properties of the design earthquake load

With Chilean code a design earthquake can be determined. This earthquake load is

determined by a formula containing several parameters. The parameters are lay

out here.

Earthquake induced vibrations are modeled with a acceleration. In Chile each

earthquake risk

zone has its own acceleration. Coronel lies in risk zone III; for this zone the

design acceleration is

0.40g. The other risk zones have lower design acceleration. At this acceleration


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the structure is supposed to stay fully intact.

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Figure 5.9: maximum acceleration for seismic design in the Chilean code (NCh2369)

In the Chilean code, soil is divided in four types. Type I being a solid and hard, e.g.

gravel. And Type IV

being soft and flexible, e.g. clay. The soil of Coronel bay and specifically the soil near

the pier is a

saturated sandy soil with fine sand and silt; the relative density DR is between 55%

and 75% and the

blow count N between 20 and 40 for the larger part of the soil. The soil can beclassified as an Type III soil. Soil properties Dr and N are determined in Chapter 8.1.

In Table 5.2 two soil dependent

properties can be found. The definition of these properties is not given by the code.

Both entities are properties of the response spectrum.

Table 5.2: Soil dependent properties of the response spectrum in the Chilean code (NCh2369)

Further in the structural analyses the following modifications factors are used in the

analyses; R the

reaction modification factor; and the seismic coefficient Cmax. Factor R is an empirical

value that takes

the type of structure into account. It is selected from a list with all types of building

withcorresponding R-values. Coefficient Cmax determines the maximal spectrum value in

the design

acceleration response spectrum. The coefficient is dependent on the damping

coefficient and the modification factor R. It is selected from a table.

Table 5.3: The table necessary to determine Cmax

in the Chilean code (NCh2369)


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The pier in relation with the earthquake

Next to properties that apply for the area of Concepcion Bay, there is a property

that is specific for the pier; namely the orientation of the pier in relation to the fault

orientation. The horizontal

acceleration of the earthquake concentrates in one direction. The simplest

approach to obtain this direction is drawing a line from the epic centre of theearthquake to the place of interest. Parallel to this line is the direction of

acceleration. This method is physically not correct, but it delivers a good

approximation of the direction.

In case of the pier: the fault orientation was in the longitudinal direction. This

fault direction was, given the orientation of the axial diagonal piles, in the stiffer

direction of the pier.

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6 Damage report of the fishing pier

As a result of the 27th February earthquake the Muelle lo Rojas fishing pier has suffered severe

damage. In Figure 6.1 and Figure 6.2 you can see some extraordinary displacements both

horizontaland vertical. Most of the piles are out of their original position and are skewed.

Because of the large

displacements the concrete is cracked and burst at critical positions. Striking is the

difference

between the damage of the different parts of the structure. As discussed in chapter

5 the structure is

split up in three parts through dilatations. The part of the walkway adjacent to the

land shows large

horizontal displacements in the axial direction and damage at the pile caps. The

part of the walkwayadjacent to the platform shows large vertical deformations and damage at so-called

imposed hinges.

The mooring platform however has very little damage and no significant

deformations. For this

reason the platform will not be reviewed. Further should be noticed that no part of

the structure

displaced in the horizontal in the transversal direction, despite heavy accelerations

in this direction.

The damages of the walkway will be discussed in the remainder of this chapter.

First all the

damages will be summed up in a list of damages. Second the plausible origin of the

different parts is

discussed and compared to each other.

Figure 6.1: Side view of both parts of the walkway


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Figure 6.2: Front view of the walkway, photo taken from the platform

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6.1 The list of damages

The walkway is damaged with seven different sorts of damages. Most of the

damages are related to each other or a direct result of one another. I include

extraordinary displacements under the name damages; it has a large effect on the

serviceability limit state of the walkway. All the damages will be illustrated withphotos and shortly discussed. Below is the list of damages.

1. Uneven extraordinary vertical displacement2. Bursting of the floor and beams3. Yielding of floor reinforcement4. Extraordinary axial horizontal displacement5. Bursting of pile caps6. Tear out of piles7. Fracture of the pile cap reinforcement

1. Uneven extraordinary vertical displacement

The platform adjacent part of the walkway shows large and uneven vertical

displacement. Near the platform the walkway has risen and at the other side, the

walkway has come down. As a result of the displacement two plastic hinges have

been formed. The formation of the hinges is associated with heavy damage to the

floor and the beams. The piles dont seem to resist the movement and displace

accordingly. Because of this, the pile caps are intact in this area.

Figure 6.3: Extraordinary vertical displacement

2. Crushing of the floor and beams

In the plastic hinges a large angular rotation took place. The rotation is approximately 25. The

rotation is far too large for the concrete, hence large cracks appeared over the full

width of the hinge and large chunks of concrete burst of the deck. At some parts the

whole reinforcement cover came off, see Figure 6.4. In the beams the concrete burst

due to crushing. Also here large cracks and spall off of the concrete can be seen,

see Figure 6.3. The continuity of the structure at the hinge is only and fully

preserved by the reinforcement.

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3. Yielding of floor reinforcement

Together with the bursting of the concrete, the floor reinforcement deformed. The

deformation made the rotation possible. In order to deform the steel yielded. The

deformations are plastic and irreversible. Probably the beam reinforcement

yielded as well.

Figure 6.4: Exposure of the reinforcement, due to complete spall off of concrete

4. Extraordinary axial horizontal displacement

The first three damage topics all occurred solely in the platform adjacent walkway.

At the walkway part adjacent to the land other damages occurred. To begin with, in

this part mainly extraordinary horizontal displacements occurred, the vertical

displacement is of lesser magnitude, see Figure 6.1. For the most part the horizontal

displacement is accompanied by a large rotation of the piles. The rotation is similar

to the vertical displacement of the other part of the walkway. Only here the hinges

are formed between the piles caps and the piles.

5. Crushing of connection blocks

An indirect result of the rotation between piles and the pile caps is the cracking and bursting of

concrete. Because of the imposed force by the pile, the internal stress in the concrete becametoo

large. At some places the whole cover of the reinforcement came off. Logically spall

off mainly occurs at the corners of the pile caps, see Figure 6.5.

Figure 6.5: Spall off of the connection block concrete cover

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6. Tear out of piles

However not all piles displaced along with the superstructure, some piles are

totally tore out of the connection blocks, see Figure 6.6. This happened with three

piles. All three piles have the same property, all are the inner pile of a lateral

diagonal pile pare, see Figure 5.3.

In Figure 5.3 you can see, that the inner diagonal pile is not in line with the beam

above. The pile has a free end connected only with the concrete of the elongated

pile cap. This weaker type of

connection is probably the cause that the piles tore out.

7. Fracture of the block reinforcement

Together with the tearing of the piles, the reinforcement of the connection block

deformed heavily

and broke. In this stat the reinforcement does not perform it task in any way. In

Figure 6.6 and Figure

6.7 examples are shown.

Figure 6.6: Tear out of a diagonal inner pile

Figure 6.7: Tear out of another diagonal inner pile


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6.2 Description of three possible origins of the damage to the pier

From the preceding paragraph we can conclude that all damages to the structure are a direct or

indirect result of the large horizontal and vertical displacement. In order to find the

origin of the pier

damage, we should find the origin of the structural displacements. Out of theliterature of piers and

pile supported wharfs, three cases are known to cause large deformations in case of

earthquake

load: deformation due to an inertia force at the deck itself; deformation due to an

horizontal force

from an anchoring construction and deformation due to liquefaction. All three cases

will be

discussed, with emphasis on the probability, that the mechanism in question is the

actual cause.

Deformation due to inertia force at the deck

The most obvious origin of permanent deformation and damage is an inertia force

at the deck. Every

object with foundation and mass gets deformed under earthquake load; the

question of importance

is whether the deformation is elastic of plastic. Figure 6.8 gives a graphical

representation of this

type of deformation to a similar type of structure, namely a pile-supported wharf.

The image

corresponds with the extraordinary axial horizontal displacements (damage type 5)

of the land

adjacent part of the walkway. The piles follow the large horizontal displacement of

the deck and

plastic hinges are formed at the fixation point in the soil. At the pile cap connection

with the

superstructure a hinge is formed as well, accompanied with severe damage.

It is possible that also at the platform adjacent part this type of mechanism is the

cause of the damage. But this type of deformation does not explain the large

vertical displacement of thewalkway. Deformation due to inertia force at the deck will be considered in the

analyses for both

walkway parts.

Figure 6.8: Side view of the deformation of a pile supported wharf due to inertia force on the deck (PIANCwg34)


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Deformation due to horizontal force from the anchoring construction

Due the horizontal force of an anchoring construction, pile supported constructions

can be damaged.

The mooring platform and the land part of the pier can be classified as anchoring

construction of the

walkway. But these construction parts did not cause the deformation for two

reasons. Firstly the

mooring platform and the land part of the pier did not have great deformations.

Secondly thewalkway and the anchoring constructions are not structurally connected. The

deformation should

have been passed on by structure to structure contact. This could explain little

deformation of the

walkway, but given the minor weight of the platform and the land pier-part, this

cannot be the cause

of the large deformations.

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Deformation as a indirect result of liquefaction

Liquefaction has the result that the fixing point of the foundation will be lower in the

soil. The free

length of the piles becomes larger and the piles are possibly not enough stiffanymore to prevent

buckling. When the whole soil liquefies unto the end of the pile, the pile support

even can be

modeled as a hinge or a role. In this case the foundation of the structure is clearly

the weakest part.

The structure or a part of it may displace as a whole, leaving the superstructure

intact. In fact this is

what we see at platform adjacent part of the walkway. Three parts have displaced

as a whole.

Between the parts hinges are formed. The parts itself, regarding the superstructure,

stayed intact.

It is possible that at the land adjacent part of the walkway liquefaction occurred.

However it cannot

be the only source of the deformation and damage at this part. At this part three

piles were torn out

of the connection blocks. The tearing out requires great force, and the result of

liquefaction is mainly

force introduced by displacement.

Figure 6.9: side view of the deformation of a pile supported wharf due to liquefaction (PIANC wg34)

To conclude over the whole walkway probably two mechanisms caused large

deformations and

damage; an inertia force at the deck and liquefaction of the soil. For the land

adjacent part of the

walkway the emphasis is on the inertia force and for the platform adjacent part

the emphasis is on

liquefaction.


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muelle lo rojas guidoppoo

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