bursi o.s., ceravolo r., di sarno l., erdik m., … et al...assessment of the seismic vulnerability...

Bursi O.S., Ceravolo R., Di Sarno L., Erdik M., Paolacci F., Sartori M., Pegon P.

SERIES Concluding Workshop - Joint with US-NEES “Earthquake

Engineering Research Infrastructures”

JRC-Ispra, May 28-30, 2013

In memory of Prof. Roy Severn

http://images.google.it/imgres?imgurl=http://www.merasa.org/img/fp7&imgrefurl=http://www.merasa.org/publications.html&h=295&w=409&sz=25&hl=it&start=1&tbnid=h0SqzU67P5ddpM:&tbnh=90&tbnw=125&prev=/images?q=FP7+logo&gbv=2&hl=it&sa=G

OUTLINE

Description of the TA research project RETRO

PsD test design

Test rig configuration

Numerical Models of the bridge

Selection of input signals

Integration scheme for PsD test

Test sequence

Preliminary numerical and experimental investigation

on the seismic response of the non-isolated bridge

Design of deck seismic isolation

Design method for FP bearings

Modeling and numerical results

Conclusions

Assessment of the seismic vulnerability of an old r.c

viaduct with frame piers and study of the effectiveness

of different isolation systems through pseudodynamic

test on a large scale model

TA Research projet: RETRO

• University Roma Tre (coordinator: Fabrizio Paolacci)

• University of Patras

• University of Naples and Sannio

• Politecnico di Torino

• Univertsity of Bogazici

• ALGA Spa Milan

Participants

F. Paolacci, R. Giannini, A. Mohamad, S. Alessadri, N. Makris, L. Di

Sarno, G. Della Corte, R. Derisi, R. Ceravolo, Luca Zanotti Fragonara, M.

Erdik, C. Yenidogan, A. Marioni, M. Sartori

Case Study

The case study is an old r.c.

viaduct (Rio Torto) placed along

the Firenze-Bologna Highway

between Roncobilaccio and Pian

del Voglio, and was built at the end

of the 50’s

It is characterized by:

• Thirteen-span (33 m) bays deck

with two independent roadways

sustained by 12 couples of piers

• Frame piers with height variable

between 14 and 50 m

• Ductile plain steel bars

Rio-Torto Viaduct

Gerber Saddles

Case Study Gerber Saddles

PsD test design: Test rig configuration

• Pier 9

– Height 10.3 m

– Hollow columns 64 cm

– Top beam 3.16 x 0.64 m

– Two middle beams

• Pier 11

– Height 5.8 m

– Solid columns 48 cm

– Top beam 3.0 x 0.48 m

– One middle beams

Non isolated case

SCALE 1:2.5


Non isolated case

18 Actuators will be used for the test!!!


Non isolated case: scale reduction

This is a well known problem that can be easily solved using dimensional analysis.

A scale factor 1:2.5 has been assumed in order to reduce lengths (Geometry and

displacements) at a level compatible with the requirements of the experimental

setup, especially in terms of maximum capacity of the actuators (Forces). Thus

the only reduction factors to be selected are those of length and forces. The other

can be evaluated by a dimensional analysis.


Non isolated case: scale reduction

The correct flexural strength of columns and transverse beams is realized with a

rigorous respect of the geometrical scaling of the prototypes, including the

reinforcement diameters and their position.

In particular for the columns of both #pier 9 and #11 plain steel rebars with

diameter of 8 and 10 mm has been used for respecting the similitude

requirements, given that the original diameters are 24 and 20 mm. Therefore only

a little approximation has been adopted for the 24 mm diameter.

About Shear strength of pier #9 and #11, because the high strength of columns

the problem is related only to transverse beams. In this case, because the full scale

diameter of the stirrups is 8 mm with maximum spacing of 20 mm, we decided

to adopt a scaled diameter of 3 mm with a spacing of 8 mm. Consequently,

whereas a correct scaling of the confinement effect is obtained, the shear strength

is a little bit underestimated, even if it is considered acceptable.

More delicate is the scaling effect on concrete–steel bond conditions.

Forturantely, because the experimental evidence has proved that in this case the

anchorage effect of hooks prevails, the simple geometrical scaling can be

accepted

The main advantage of this solution is

that it allows keeping the same system

for vertical load application on the

piers in both the isolated and non

isolated configurations while avoiding

any interaction between the vertical

loading system and the isolators.

The vertical load will be applied to the

isolators through a different vertical

loading system that allows to impose

the same vertical load (e.g., same

pressure) as that applied to the piers


FP BASE ISOLATION SYSTEM

Isolated case with FP

bearings

Substructuring

techniques

The main advantage of this solution is

that it allows keeping the same system

for vertical load application on the

piers in both the isolated and non

isolated configurations while avoiding

any interaction between the vertical

loading system and the isolators.

The vertical load will be applied to the

isolators through a different vertical

loading system that allows to impose

the same vertical load (e.g., same

pressure) as that applied to the piers


FP BASE ISOLATION SYSTEM

Isolated case with FP

bearings


Isolated case: scale reduction

The full scale model of Friction Pendulum isolators designed according to a

displacement-based design should have a Radius R=3000 mm and a friction

coefficient equal to 4%. The ultimate axial force if about 7500 kN, whereas the

seismic axial force is about 2800 kN.

Scale

facto

r 1:

2.5

Radius: R=3000 /2.5 = 1200 mm

Friction coefficient: =4%

kNNs 112

mm

kN.

R

Ns 9330

sN

Fu

ll S

cale

Radius: R=3000 mm

Friction coefficient: =4%

MOCK-UPS


10

.3 m

5.8

m

2.6

8 m

2

.84

m

3.1

0 m

2.4

0 m

2

.40

m

MOCK-UPS


PsD test design: Numerical Models

NON LINEAR

MODELING

1) Non-linear flexural

behaviour of the element

using a fiber discretization

of the sections

2) Non-linear shear

behaviour of transverse

beams using a global

model, calibrated by using

experimental results and

analytical models [Priestly,

Vecchio and Collins]

3) Strain-penetration effect

of the reinforcing bars at

the columns-foundation

joints using the Zhao and

Shitaran model

REFINED MODEL (OpenSEES)


Model Reduction

1) Guyan Method has been

used to reduce the single

piers into 4-3DOFs

superelement supposing

only a trasnversal

behaviour of all piers.

2) The vertical behaviour of

columns has been taken

into account using vertical

elastic springs.

3) The non-liner behaviour

of piers has been

modeled using a Bouc-

Wen softening hysteretic

spring

SIMPLIFIED MODEL (OpenSEES): Non Isolated

Guyan method

4-3 DOFs model P-DOF

Pier #9

Pier #11


The reduced 3DOFs model allows to handy

accomodate the isolation elements that are

simply placed between springs and link

element

SIMPLIFIED MODEL (OpenSEES): Isolated Case

Reduced DOFs model

PsD test design: Selection of Input

Two limit states are considered for the seismic performance assessment of the “as built” Rio-Torto bridge:

Damage Limit state (DLS) Ultimate Limit State (ULS)

Given the geographical position of the bridge and the recent

earthquake swarms occurred in the region it was assumed to use the seismic records of the 2012 Emilia (Italy) earthquakes.

The Mirandola records (MRN station) were utilized because of their seismological characteristics, i.e. PGAs and duration of the accelerograms.

The record of May 29th East-West was used for the DLS and the North-South component was used to assess the seismic performance at the ULS


Seismogenetic zone

0 0.5 1 1.5 2 2.5 3 3.5 40

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

T (sec)

Sa

(g

)

Life Safety

Near Collapse

Damage limit

1st period

Ground shaking Response Spectra

-200 -150 -100 -50 0 50 100 150 200 250

-250

-200

-150

-100

-50

0

50

100

911912913

914915

916

917

918

919

920

921

km

km

41.5

41.75

42

42.25

42.5

42.75

43

43.25

43.5

43.75

44

44.25

44.5

44.75

45

45.25

8.5 8.759 9.259.5 9.7510 10.2510.510.7511 11.2511.511.7512 12.2512.512.7513 13.2513.513.7514 14.2514.5

0 0.1 0.2 0.3 0.4 0.5 0.60

0.05

0.1

0.15

0.2

0.25

X: 0.1225

Y: 0.2924

PGA (g)

Pro

ba

bili

ty o

f o

ccu

rence

SLV

SLC

Seismic Hazard


ULS DLS

Record of the 29th May 2012 (N-S Component)

Record of the 29th May 2012 (W-E Component)

ULS

DLS

PsD test design: Integration scheme

At ELSA they have been using the so-called Continuous PsD scheme for

many years. This scheme allows to load the experimental structure

continuously (elapse time 2ms) by performing in the same loop the time

integration of the PsD model of the structure and the digital control of the

actuators loading the structure.

By avoiding the hold period associated with standard PsD implementation,

the continuous method avoids load relaxation problems, optimizes the ratio

signal/noise associated with the experimental errors, works with a constant

time dilation and thus globally improves the quality of the results.

The test of the viaduct is substructured, in the sense that a part of the

structure is in the laboratory (experimental structure), and the other part is

modeled numerically. The substructured test will be performed using an

inter-field version (Pegon 2008, Bonelli & al. 2008) of the time partitioned

scheme proposed by (Gravouil & Combescure, 2001).

This scheme works with different time steps for the two substructures. The

PsD scheme is in fact slightly modified using additional constrain steps,

which allows introducing integration substepping with respect to the time

integration of the numerical structure for which potentially complex and

non-linear models should be operated, requiring more computational time

than the 2ms needed by the PsD scheme.

PsD test design: Integration scheme

PsD test design: INSTRUMENTATION

2 typologies of sensors wil be used for the acquisition of kinematic quantities

Traditional instrumentation Innovative instrumentation (photogrammetry)

PsD test design: Test Program

Two configurations will be considered during the experimental tests: Slight damaged viaduct with FP isolators (config.1) Non-isolated viaduct (config.2)

The first configuration aims at verify the protection of the piers from developing any damage during the seismic action. The third configuration aims at inducing in the piers the damage suffered by the viaduct during a moderate earthquake. The tests will be performed in the following sequence:

Identification of the dynamic characteristics of the bridge 1 test on config.2 to induce DLS condition 2 tests on config. 1 for ULS condition 1 test on config. 2 for ULS condition


“As built” configuration

A preliminary investigation aiming at studying the seismic

response of the piers has been carried out both numerically

and experimentally.

In particular

Modal analysis

Experimental and numerical investigation on the cyclic

behaviour of the piers

Numerical simulation of the non-linear seismic response

of the entire viaduct in «as-built» configuration

This represents a useful tool to compare the response of

the viaduct during PsD test with the simulated response


MODAL ANALYSIS OF THE VIADUCT

2nd Mode 5th Mode

x

y

x

y


NON-LINEAR CYCLIC BEHAVIOUR OF THE PIERS

A preliminary investigation aimed at studying the cyclic behaviour of

the piers has been carried out experimentally at University Roma Tre

One of the piers have been tested in

the Laboratory of Univ. Roma Tre on

a 1:4 scale specimen and several

phenomena, typical of old frame r.c.

structures, have been observed:

• Shear cracking in the transverse

beam

• Cracks opening at the column base

and bottom

• Some slight Buckling phenomena

of the reinforcing bars


SEISMIC NON-LINEAR RESPONSE OF THE AS BUILT VIADUCT:

ULS CONDITIONS

The results of numerical simulation of the entire viaduct subjected to the

Emilia earthquake of 29th May 2011 (NS component) are shown.

Bas

e sh

ear

(kN

) B

ase

shea

r (k

N)

Bas

e sh

ear

(kN

)

Bas

e sh

ear

(kN

) B

ase

shea

r (k

N)

Bas

e sh

ear

(kN

)

Bas

e sh

ear

(kN

) B

ase

shea

r (k

N)

Bas

e sh

ear

(kN

)

Bas

e sh

ear

(kN

) B

ase

shea

r (k

N)

Bas

e sh

ear

(kN

)

Displacement(cm) Displacement(cm) Displacement(cm) Displacement(cm)



P.1 P.2 P.3 P.4

P.5 P.6 P.7 P.8

P.9 P.10 P.11 P.12 FOR

CE-

DEF

LEC

TIO

N C

YCLE

S



ULS CONDITIONS



Mo

men

t (k

Nm

) M

om

ent

(kN

m)

Mo

men

t (k

Nm

)

Mo

men

t (k

Nm

) M

om

ent

(kN

m)

Mo

men

t (k

Nm

)

Mo

met

(kN

m)

Mo

men

t (k

Nm

) M

om

ent

(kN

m)

Mo

men

t (k

Nm

) M

om

ent

(kN

m)

Mo

men

t (k

Nm

)

Curvature (1/cm) Curvature (1/cm) Curvature (1/cm) Curvature 1/cm)

Curvature (1/cm) Curvature (1/cm) Curvature (1/cm) Curvature (1/cm)

Curvature (1/cm) Curvature (1/cm) Curvature (1/cm) Curvature (1/cm)

P.1 P.2 P.3 P.4

P.5 P.6 P.7 P.8

P.9 P.10 P.11 P.12

MO

MEN

T-C

UR

VAT

UR

E C

YCLE

S



ULS CONDITIONS



Sh

ear

(kN

) Sh

ear

(kN

) Sh

ear

(kN

)

Sh

ear

(kN

) Sh

ear

(kN

) Sh

ear

(kN

)

Sh

ear

(kN

) Sh

ear

(kN

) Sh

ear

(kN

)

Sh

ear

(kN

) Sh

ear

(kN

) Sh

ear

(kN

)

Deformation Deformation Deformation Deformation



P.1 P.2 P.3 P.4

P.5 P.6 P.7 P.8

P.9 P.10 P.11 P.12 SHEA

R F

OR

CE-

DEF

OR

MAT

ION

CYC

LES


SEISMIC NON-LINEAR RESPONSE OF THE AS BUILT VIADUCT :

ULS CONDITIONS

The following main results are expected during PsD test

A maximum of 17 cm and 15 cm of lateral displacement are expected

for pier #9 and #11 respectively

The analysis of the cyclic response shows the high plastic deformations

to which pier #9 and # 11are subjected.

A pronounced pinching effect is also present in the cyclic response of

pier #11. This is due to the effect of shear and bond slip

The expected level of crack width at the column base due to the bar

slippage is of the order of 1.5 – 2 mm, as confirmed by the numerical

model

The slippage is not enough to avoid flexural damage in the columns as

shown by Moment-Curvature cycles (max ductility =3)

The level of shear damage in the transverse beam is also high (drift

1% ) as confirmed by the hysteretic behavior shown

Design of deck isolation systems using FP bearings

The second configuration of the viaduct during PsD tests will be the isolated one

using FP bearings with single sliding surface.

To maximize the effectiveness of the deck isolation system, the Gerber saddles

have been eliminated through a transverse pre-stressing system.

The design of the isolation system is based the assessment of the lateral-load

response of each pier previously presented

The method proposed to design FP bearing is based on the static lateral

response of the bridge neglecting the distributed mass of the piers, as

confirmed by non-linear analysis on the entire viaduct. The results from

pushover analyses provide the initial pier stiffness and the yielding strength


The FP isolation system has been designed according to a displacement-based

design method which is presented in detail in Della Corte et al. (2011). The method

is based on the direct displacement based procedure proposed by Priestley et al.

(2007).

According to the design method, assuming a dynamic friction coefficient equal

to 0.04 and a maximum sliding displacement equal to 0.10 m, the required

radius of curvature of the FP device is equal to 3 m.

A design deck displacement shape has been assumend in order to have a

maximum drift of 0.05% corresponding to initial yelding in the piers

The strength capacity of each pier must also be checked against the peak forces

transmitted by devices at the breakaway of the motion.

8%


SEISMIC NON-LINEAR RESPONSE OF THE ISOLATED VIADUCT :

DLS CONDITION


SEISMIC NON-LINEAR RESPONSE OF THE ISOLATED VIADUCT :

ULS CONDITION

CONCLUSIONS

A COMPLEX EXPERIMENTAL ACTIVITY IN GOING TO BE EXECUTED FOR THE SEISMIC ASSESSMENT OF AN OLD R.C. VIADUCT BY USING A PSD TEST CAMPAIGN

THE TECHNIQUE OF NON-LINEAR SUBSTRUCTURING WILL BE USED INCLUDING A HUGE NUMBER OF DOFs.

A LARGE SCALE TEST WILL BE EXECUTED ON TWO PIERS OF THE VIADUCT, WHICH ARE IN SCALE 1:2.5

A REFINED NON-LINEAR MODEL HAS BEEN PRELIMINARY USED TO CALIBRATE A REDUCED NON-LINEAR MODEL TO BE USED DURING THE PSD TEST

TRADITIONAL AND INNOVATIVE INSTRUMENTAIONS WILL BE USED DURING THE TESTS

TWO CONFIGURATIONS WILL BE TESTED. NON-ISOLATED AND ISOLATED A FP SYSTEM HAS BEEN DESIGN ACCORDING TO A NOVEL

DISPLACEMENT DESIGN METHOD A PRELIMINARY NUMERCIAL ANALYSIS HAS BEEN CARRIED OUT ON AS-

BUILT AND ISOLATED CONFIGURATION WITH FP BEARINGS, SHOWING A LARGE DAMGE CONDITION IN THE FIRTS CASE AND THE HIGH EFFECTIVENESS IN THE SECOND ONE.

bursi o.s., ceravolo r., di sarno l., erdik m., … et al...assessment of the seismic vulnerability...

Documents