[american society of civil engineers atc and sei conference on improving the seismic performance of...

Seismic retrofitting of three important buildings in Italy and Turkey

Agostino Marioni1

1Alga SpA, Via dei Missaglia 97/A2, 20142 Milano, Italy [email protected]

ABSTRACT Three important projects of application of the seismic isolation to existing

buildings are described in the paper. The first project is located in Naples and consisted in a reinforced concrete

structure of 125x170x20 meter, belonging to the Municipality of Naples. The construction started in year 1976 and was stopped in year 1979 when all the foundations and the reinforced concrete frame was completed. In year 1999 the Municipality decided to complete the building but in the meantime the Italian Seismic Standard was changed and the already built structure was no more adequate for the newly defined seismic action implying a PGA of 0,25g. Seismic isolation was found to be the best and more economical solution to provide the building with the necessary resistance, minimizing at the same time the necessary strengthening to the existing structure and foundation. The seismic isolation has been provided through the application of 636 High Damping Rubber Bearings with equivalent viscous damping of 10%. The use of HDRB allowed to shift the period of the structure from 0,7 to 1,75 s and reducing the acceleration from 0,42 to 0,14g. To cut the columns ALGA developed special steel clamps, applied over and under the location of the cuts by use of prestressed bars in order to generate a friction suitable to support the load transferred by the concrete column. After the application of the clamps the vertical load of the column was released by use of hydraulic jacks, the column cut, the isolator installed and the clamps removed.

The second application has been made to the airport structure of Antalya, Turkey. The job consisted in cutting the reinforced concrete columns and applying 358 LRB. During the cutting phase the vertical loads were transferred to an auxiliary steel structure applied below the beams by use of hydraulic jacks. The base isolation allowed to shift the period to 2,69 s, reducing the acceleration to 0,1g, being the design PGA 0,4g. Peculiar aspect was the fact that the retrofitting has been performed without interfering with the airport activity.

The last project described, currently in progress, is the Justice Palace of Avellino, near Naples. For this project the use of sliding pendulum isolators has been foreseen as this was the only possible solution allowing to shift the period to 3,5 s and therefore reduce the acceleration below 0,07 g. In this way was possible to retrofit the structure avoiding any additional reinforcement to the upper structure. To reduce the dimensions of the isolators and to reduce the eccentricity caused by the design displacement, sliding pendulum with 2 spherical surface has been foreseen. The total number of sliding pendulum isolators is 220.

892ATC & SEI 2009 Conference on Improving the Seismic Performance of Existing Buildings and Other Structures

Copyright ASCE 2009 Improving the Seismic Performance of Existing Buildings and Other Structures

Dow

nloa

ded

from

asc

elib

rary

.org

by

WA

LT

ER

SE

RIA

LS

PRO

CE

SS o

n 05

/08/

13. C

opyr

ight

ASC

E. F

or p

erso

nal u

se o

nly;

all

righ

ts r

eser

ved.

INTRODUCTION Even if examples of measures to protect buildings from the earthquake can be

dated back thousands of years – the oldest mention known to the author was made by Plinius the Eldest for the temple of Diana in Ephesus (Turkey), built in the third century B.C. – the full awareness of the seismic risk and the knowledge of the way to mitigate it has been reached only at the end of the last century.

Seismic codes in the most advanced Nations reached their actual features very recently: AASHTO Guide Specification for Seismic Isolation Design in year 2000 and EN 1998 in 2005.

Also for the antiseismic devices the evolution, started probably in 1972 in New Zealand, generated a lot of ideas, prototypes and applications and since a few years can be considered a mature technique. In fact many reliable devices have been developed that proved their efficiency even passing true earthquakes without damages to the structures.

The most updated Standard for the antiseismic devices is the EN 15129, that will complete the formal vote phase just one day after the due date of this paper and will be probably already published at the time of this conference.

More familiar in the USA is surely the already mentioned AASHTO. We know almost everything about earthquakes (in reality every earthquake

teaches us something more) and how to mitigate their risks but the major problem are all the buildings erected before the Standards were issued.

Seismic retrofitting means improving the resistance of a structure so that it will be in accordance with the seismic standards.

Seismic retrofitting can be achieved either by strengthening the structure or by base isolating it.

When applicable the seismic isolation is for sure the most efficient and cost effective technique. In particular the base isolation gives the great advantage to protect also the content of the structure (which is essential for instance for hospitals) and to be applied with a minimum impact on the activity performed inside the structure.

In the following paragraphs three important applications designed by the Author and performed by its company ALGA will be shown.

THE MULTIPURPOSE BUILDING OF SOCCAVO (NAPLES, ITALY)

This building consists in a large reinforced concrete structure with columns and

beams having overall measures in plan of 125 x 170 m and a height of 20 m. It belongs to the Municipality of Naples.

The construction started in year 1976 and was stopped in year 1979, due to lack of funds from the Municipality, when all the foundations and the reinforced concrete frame were completed. In Fig. 1 is shown the aspect of the building after the stop of the works, in Fig 2 its plan at ground level.



Dow

nloa

ded

from

asc

elib

rary

.org

by

WA

LT

ER

SE

RIA

LS

PRO

CE

SS o

n 05

/08/

13. C

opyr

ight

ASC

E. F

or p

erso

nal u

se o

nly;

all

righ

ts r

eser

ved.

Figure 1 - The multipurpose building of Soccavo, Naples, before the completion

Figure 2 – Plan of the building at ground level In year 1999 the Municipality decided to complete the building but in the

meantime the Italian Seismic Standard was changed and the already built structure was no more adequate for the newly defined seismic action implying a PGA of 0,25g. Seismic isolation was found to be the best and more economical solution to provide the building with the suitable resistance, minimizing at the same time the necessary strengthening to the existing structure and foundation. The seismic isolation has been provided through the application of 636 High Damping Rubber Bearings with equivalent viscous damping of 10%. The use of HDRB allowed to shift the period of the structure from 0,7 to 1,75 s and to reduce the acceleration from 0,42 to 0,14g as shown in figure 3. To cut the columns ALGA developed special steel clamps, applied over and under the location of the cuts by use of prestressed bars in order to generate a friction suitable to support the load transferred by the concrete column. After the application of the clamps the vertical load of the column



Dow

nloa

ded

from

asc

elib

rary

.org

by

WA

LT

ER

SE

RIA

LS

PRO

CE

SS o

n 05

/08/

13. C

opyr

ight

ASC

E. F

or p

erso

nal u

se o

nly;

all

righ

ts r

eser

ved.

was released by use of hydraulic jacks, the column cut, the isolator installed and the clamps removed. The clamps and the phase of cutting the concrete column by diamond wire saw are shown in figure 4.

Figure 3 – Response spectra before and after the seismic retrofitting

Figure 4 – details of the clamps and the diamond wire cutting equipment After the cutting the columns required some strengthening and this has been

obtained by casting a new slab connecting all the column over the isolators and applying external steel shapes to replace the rebar in the cut area as shown in fig. 5.

Figure 5 –The supplementary slab and local strengthening of the columns

0 0,1

0,2

0,3

0,4

0,5

0,6

0 0,5

1 1,5

2 2,5

3 periodo

(s)

accelerazione (g)

Tinc

0.14g

0.42g

Tisol



Dow

nloa

ded

from

asc

elib

rary

.org

by

WA

LT

ER

SE

RIA

LS

PRO

CE

SS o

n 05

/08/

13. C

opyr

ight

ASC

E. F

or p

erso

nal u

se o

nly;

all

righ

ts r

eser

ved.

In figures 6, 7 and 8 are shown the details of the isolators, the work in progress

with the supplementary slab partially cast and the completed building.

Figure 6 –Detail of a HDRB

Figure 7 – The work in progress

Figure 8 – The building after the completed retrofitting Some interesting data about the production speed:



Dow

nloa

ded

from

asc

elib

rary

.org

by

WA

LT

ER

SE

RIA

LS

PRO

CE

SS o

n 05

/08/

13. C

opyr

ight

ASC

E. F

or p

erso

nal u

se o

nly;

all

righ

ts r

eser

ved.

The job has been performed by 3 teams of 3 specialists each, coordinated by a project manager. Each team, fully equipped by a pair of clamps, one diamond wire saw, jacks, pumps and all accessories, could install 20 isolators per week. The full job, including mobilization and de-mobilization lasted 6 months.

The total cost of the seismic retrofitting has been as follows: • Supply of the High Damping Rubber Bearings complete of their steel plates

for connection to the structures, including cutting of the columns and installation: 2,0 M$

• Construction of a slab connecting the columns over the isolators level: 0,9 M$ • Construction of retaining walls: 0,75 M$ • Accessories (expansion joints, flexible joints etc.): 0,15 M$ • Engineering : 0,4 M$ • Total : 4,2 M$ This value, compared to the whole building value (33.000 sqm x 4000 $/sqm =

132 M$) represents around 3%: a really negligible figure compared to the obtained benefits. The obtained benefits also include the commercial value of the supplementary slab, 10.000 square meter that is largely exceeding the cost of the retrofitting

THE AIRPORT OF ANTALYA, TURKEY

The airport of Antalya (figure 9) is a quite busy one and the number of

passengers in the year 2004 when the retrofitting has been performed was over 13 millions. Although the structure was recently completed in year 1994, the owner decided to upgrade it in conformity with the most recent seismic codes.

Figure 9 – The airport of Antalya: 18,8 million passengers in 2008 The structure consists two main parts, like most of the modern airports: the

check-in, shopping and office area is a three floors reinforced concrete structure with the central part in correspondence of the main hall covered by a steel roof; the boarding, disembarking and luggage handling area is also a reinforced concrete structure with up to three floors. In total there are 358 reinforced concrete columns.



Dow

nloa

ded

from

asc

elib

rary

.org

by

WA

LT

ER

SE

RIA

LS

PRO

CE

SS o

n 05

/08/

13. C

opyr

ight

ASC

E. F

or p

erso

nal u

se o

nly;

all

righ

ts r

eser

ved.

Figure 10 – The structural mesh of the Antalya airport The design of the base isolation was made utilizing LRB applied to all the

reinforced concrete columns. The LRB were selected in order to provide a period shift up to 2,69 seconds together with an equivalent viscous damping of 28% in order to reduce the acceleration in the base isolated structure under 0,1g hence avoiding any strengthening in the reinforced concrete structure. The design displacement of the structure is ±150 mm. The steel roof covering the main hall and supported by two independent parts of the structure has been provided of slider consisting in free sliding pot bearings with a displacement capacity of ±300 mm

The installation of the isolators, by cutting the reinforced concrete columns, was relatively simple because the structure was light (only two floors over the isolators level) and the beams were able to support the weight of the upper part of the structure during the cutting and installation phase. Therefore it was sufficient to place temporary steel I-beams aside the concrete columns and to release the weight of the structure by hydraulic jacks as shown in figure 11.

Figure 11 – Cutting the columns with diamond saw



Dow

nloa

ded

from

asc

elib

rary

.org

by

WA

LT

ER

SE

RIA

LS

PRO

CE

SS o

n 05

/08/

13. C

opyr

ight

ASC

E. F

or p

erso

nal u

se o

nly;

all

righ

ts r

eser

ved.

Figure 12 – Detail of a LRB after installation One essential requirement given by the Owner was not to interfere with the main

activity of the airport and to give the minimum possible interference with the auxiliary activities like shops and offices. The retrofitting has been performed during 4 months in winter time, when the air traffic in Antalya is reduced to a minimum, operating in small areas in order to reduce as much as possible the impact with the Airport’s activity.

Most of the columns were provided with architectural panels in FRC as shown in figure 13. After the installation of the isolators the retrofitting is practically not visible, unless for the 2 supplementary cuts in the FRC panels.

Figure 13 – After the completion of the work the columns are covered with the original FRC panels that make the retrofitting not visible



Dow

nloa

ded

from

asc

elib

rary

.org

by

WA

LT

ER

SE

RIA

LS

PRO

CE

SS o

n 05

/08/

13. C

opyr

ight

ASC

E. F

or p

erso

nal u

se o

nly;

all

righ

ts r

eser

ved.

THE JUSTICE PALACE OF AVELLINO, SOUTH ITALY The last project described, currently in progress, is the Justice Palace of Avellino,

near Naples. It consists of a 6 stories reinforced concrete building located near the centre town of Avellino, built in the years ’60 and comprising 220 columns (See Fig. 14, 15 and 16). At the time of construction Avellino was defined as Seismic Area 2, requiring to take into account a seismic action equivalent to 7% of the weight considered as a static horizontal load

Figure 14 – The Justice Palace of Avellino, located near town centre

Figure 15 – Plan of the foundations of the building

THE JUSTICE PALACE OF AVELLINO



Dow

nloa

ded

from

asc

elib

rary

.org

by

WA

LT

ER

SE

RIA

LS

PRO

CE

SS o

n 05

/08/

13. C

opyr

ight

ASC

E. F

or p

erso

nal u

se o

nly;

all

righ

ts r

eser

ved.

Figure 16 – Vertical section of the building

. The actual seismic code requires to consider the Acceleration Spectrum as

shown in Fig. 17 with PGA 0,32g. The Justice administration required to study the seismic upgrading of the building requiring the following performance targets:

• Upgrading shall be as far as possible applied with minimum interference with the activity operated inside the building.

• Strengthening of the existing reinforced concrete columns and beams shall be minimized

Base isolation, by inserting the isolators in the columns at the basement level, was immediately considered as the best possible solution, however, to avoid any strengthening in the column and beams the acceleration of 0,07g, equivalent to that taken into account at the time of construction, shall be reached. From the acceleration spectrum in figure 17 it may be seen that, to reach such an acceleration, the period shall be shifted over 3 seconds, with an equivalent viscous damping of the order of 30%.



Dow

nloa

ded

from

asc

elib

rary

.org

by

WA

LT

ER

SE

RIA

LS

PRO

CE

SS o

n 05

/08/

13. C

opyr

ight

ASC

E. F

or p

erso

nal u

se o

nly;

all

righ

ts r

eser

ved.

Elastic response spectrum (Avellino-ITALY)

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

0 0,5 1 1,5 2 2,5 3 3,5 4

Period (sec)

Rel

ativ

e A

ccel

erat

ion

(ag/

g)

Figure 17 – Acceleration spectrum for the Avellino Justice Palace and performance target of the isolation system

It is very difficult to reach such performance with an elastic system consisting of

HDRB or LRB. In fact HDRB car reach an equivalent viscous damping of 16-20% only and therefore should be combined with other energy dissipation devices. Furthermore with the elastic systems it is very difficult to reach the target period of 3 seconds: this would imply a very low stiffness that would largely increase the thickness and therefore the cost of the devices. A combination of elastic isolators and sliders could solve the problem but the dimensions of the sliders would be unacceptable for the existing columns. The design displacement with an elastic system would be ±260 mm implying a dimension of the sliders with 3000 kN capacity of 850 mm, not compatible with the minimum size of the columns of 600 mm.

The problem has been solved utilizing sliding pendulum isolators with double sliding surfaces as detailed in figure 18 with the following main characteristics:

• Radius of the spherical sliding surfaces 2400 mm • Friction coefficient of the sliding surface 0,03

That allowed to reach the following performances • Natural period of the isolated structure 3,14 seconds • Equivalent viscous damping 30% • Design displacement 153 mm • Nominal displacement 1,2*153 = 184 mm

It may be noted that the displacement to be taken into account using sliding pendulum isolators (184 mm) is considerably lower than in case of elastic isolators

PERFORMANCE TARGET

EFFECTIVE PERFORMANCE



Dow

nloa

ded

from

asc

elib

rary

.org

by

WA

LT

ER

SE

RIA

LS

PRO

CE

SS o

n 05

/08/

13. C

opyr

ight

ASC

E. F

or p

erso

nal u

se o

nly;

all

righ

ts r

eser

ved.

due to the fact that for the sliding pendulum the rotation of the structure around the vertical axe is equal to zero.

Figure 18 – Scheme of the double surface sliding pendulum isolators for the Avellino Justice Palace

The relative dimensions of the different types of isolators, drawn at the same

scale, are shown in figure 19. The only possibility to fit the isolators on the existing columns with minimum dimensions 600 x 600 mm was given by the solution with two sliding surfaces that also represented the cheaper one.

Figure 19 – Relative sizes of LRB and sliding pendulum with one or two sliding surfaces providing equivalent performances

Sliding pendulum isolators have been developed by ALGA since 2006 and the

first important application has been the seismic isolation of the Golden Ear bridge in Vancouver, Canada but after that some very important application followed, like the C.A.S.E. project in L’Aquila, Italy, where 4500 sliding pendulum isolators have been supplied: the largest base isolation project of the world.

The most peculiar aspect of the sliding pendulum isolators developed by ALGA are the sliding materials, the result of a joint research program performed in Joint

700 mm 700 mm 550 mm



Dow

nloa

ded

from

asc

elib

rary

.org

by

WA

LT

ER

SE

RIA

LS

PRO

CE

SS o

n 05

/08/

13. C

opyr

ight

ASC

E. F

or p

erso

nal u

se o

nly;

all

righ

ts r

eser

ved.

Venture with Politecnico di Milano. The material used for the isolators of Avellino Justice Palace is called Hotslide and is characterized by a very high compression strength and a very high resistance to heath. The compressive strength of Hotslide is shown in the following figure 20 in function of the temperature.

Figure 20 – The innovative material Hotslide provides outstanding compressive strength and resistance to high temperature

Hotslide contributed to dramatically improve the performances of the sliding

pendulum isolator: at 100°C its resistance is still greater than that of PTFE at ambient temperature; for short time it can resist up to 300°C without deterioration.

The use of Hotslide also allowed to reduce the size of the isolators as it can bear a compressive stress under seismic vertical loads over 50 MPa without risk of overheating.

Also for the Justice Palace of Avellino one essential requirement of the Owner was not to interfere with its activity. The retrofitting will be executed by cutting the columns in the basement, where the archive is located. To cut the columns and install the isolators it will be sufficient to temporary relocate some areas of the archive.

CONCLUSIONS

When applicable the seismic isolation is for sure the most efficient and cost

effective technique. In particular the base isolation gives the great advantage to protect also the content of the structure and to be applied with a minimum impact on the activity performed inside the structure.

Every seismic retrofitting project may propose different problems to be solved but the above described examples show how the existing techniques can be adapted to the most various situations

-

0

50

100

150

200

250

20 30 40 50 60 70 80

TEMPERATURE (°C)

CH

AR

AC

TER

ISTI

C S

TRE

NG

TH (M

Pa)

PTFEHOTSLIDE



Dow

nloa

ded

from

asc

elib

rary

.org

by

WA

LT

ER

SE

RIA

LS

PRO

CE

SS o

n 05

/08/

13. C

opyr

ight

ASC

E. F

or p

erso

nal u

se o

nly;

all

righ

ts r

eser

ved.

[american society of civil engineers atc and sei conference on improving the seismic performance of...

Documents