squat silos containing grain-like material subjected to shaking ...Stefano Silvestri [email protected] Salvador Ivorra Chorro [email protected] Colin Taylor [email protected]

S E R I E S

SEISMIC ENGINEERING RESEARCH INFRASTRUCTURES

FOR EUROPEAN SYNERGIES

COMMISSION OF THE EUROPEAN COMMUNITIES

FP7- INFRASTRUCTURES-2008-1

SP4-Capacities

“Analysis of the dynamic behavior of

squat silos containing grain-like material

subjected to shaking-table tests”

Dora Foti [email protected]

Tomaso Trombetti

[email protected]

Stefano Silvestri [email protected]

Salvador Ivorra Chorro

[email protected]

Colin Taylor [email protected] Matt Dietz [email protected]

Final Meeting – ISPRA 28-30 May 2013 D. Foti - “Analysis of the dynamic behavior of squat silos…”

mailto:[email protected]















SEISMIC ENGINEERING RESEARCH INFRASTRUCTURES FOR EUROPEAN SYNERGIES

PRESENTATION LAYOUT • The test set-up

• The scientific background • The shaking-table tests performed and the first results

• The comparison with theory expectations

OBJECTIVES


• To find out the pressure that the grain-like material produces on

the silo walls due to time constant acceleration (for the

experimental verifications of the analytical findings obtained in

Silvestri et al., BEE 2012);

• To evaluate the influence of the base input (earthquake vs.

sinusoidal)


SPECIMEN DATA


Session 1 Sessions 2 and 3


SPECIMEN GEOMETRY

SILO SPECIMEN

(scale 1:10)

INSERTION OF BALLOTTINI

PARAMETERS



INSTRUMENTATION

• mono-directional accelerometers located

at the shaking-table foundation, glued to

the silo walls and placed inside the

Ballottini glass;

• vertical and horizontal strain gauges

positioned on the exterior side of the

walls at four different heights;

• LVDT placed at the top of the structure;

• film and Flexi Force pressure sensors

placed on the interior side of the walls, in

order to measure pressures

INSTRUMENTATION VIEW



FROM REALITY TO IDEALIZATIONS


A

• Flexible

• Compressible

grain

• Earthquake input

B1

• Flexible

• Uncompressible

grain

• Earthquake input

B2

• Flexible

• Uncompressible

grain

• Sinusoidal input

C

• Infinitely stiff

• Uncompressible

grain

• Constant input

REAL CASE IDEAL MODEL

z

yx

z

yx

z

yx

TEST SPECIMEN

z

yx


THE SPECIMEN MODEL IS SITUATED IN A CENTRAL POSITION

WITH RESPECT TO THE REAL CASE AND THE IDEAL MODEL:

1. The silo walls are considered not infinitely stiff but with some

flexibility associated to the acceleration profile;

2. The grain particles of the ensiled material are considered

uncompressible;

3. The inputs used are:

▫ Sinusoidal at low frequency that is comparable with the

constant input used for the theory;

▫ Un-scaled Earthquake closer to the real silo conditions


PROBLEM FORMULATION



20-22 August 2012:

• Silo with smooth walls (grain-wall friction coefficient ) and

filled with Ballotini glass up to a height of 120 cm.

• Input – white noises (ampl. 0.05g, 0.1g, 0.2g, 0.3g), sinusoidal (low

frequency) and earthquake accelerograms along Y direction.

Objective:

Analyze the behavior of the silo specimen under the specific conditions presented

above with respect to the theory expectation

0.30GW

SESSION 1



29-31 January 2013: • Silo with roughened walls (grain-wall friction coefficient ) and filled with

Ballotini glass up to a height of 60 cm.

• Input – white noises, sinusoidal at 1Hz and 2Hz along Y and Z directions and

earthquake accelerograms (South Iceland records).

Objective:

Analyse the repeatability and the initial conditions of the silo and monitor the effect of a

lower slenderness ratio

0.45GW

SESSION 2



1-2 February 2013:

• Silo with roughened walls (grain-wall friction coefficient ) and filled

with Ballotini glass up to a height of 120 cm.

• Input – systematic sinusoidal input (ampl. 0.1g-0.6g) at 1Hz and 2Hz along Y

direction.

Objective:

Analyze the behavior of the silo specimen under the specific conditions presented

above with respect to the theory expectation and the results of the first session

with particular attention on the effect of the increased roughness and the changed

internal friction coefficient of the ensiled material.

0.45GW

SESSION 3




ACCELERATION RESULTS


Session 1 – test S9

0 5 10 15 20 25 30 35 40-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

Accelerometers y=0.6(LEFT)- test - S9 - a =0.339g

Time (s)

Ho

rizo

nta

l A

ccele

rati

on

(g

)

h=0

h=0.44

h=0.84

h=1.24

h=1.54

0 5 10 15 20 25 30 35 40-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

Accelerometers y=-0.6(RIGHT)- test - S9 - a =0.339g

Time (s)

Ho

rizo

nta

l A

ccele

rati

on

(g

)

h=0

h=0.44

h=0.84

h=1.24

h=1.54

-2 -1.5 -1 -0.5 0 0.5 1 1.5 20

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

max/min horizontal accelerations. Filtered t=0- test - E17 - a =0.415g

Acceleration (g)

h (

m)

max y=0.6(LEFT)

min y=0.6(LEFT)

max y=-0.6(RIGHT)

min y=-0.6(RIGHT)

-2 -1.5 -1 -0.5 0 0.5 1 1.5 20

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

max/min horizontal accelerations. Filtered t=0- test - S9 - a =0.339g

Acceleration (g)

h (

m)

max y=0.6(LEFT)

min y=0.6(LEFT)

max y=-0.6(RIGHT)

min y=-0.6(RIGHT)

EARTHQUAKE

INPUT

SINUSOIDAL

INPUT




Session 2– test S50

0 5 10 15 20 25-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

Accelerometers y=0.6(LEFT) test S50 a = 0.2747 g

Time (s)

Ho

rizo

nta

l A

ccele

rati

on

(g

)

h=0

h=0.44

0 5 10 15 20 25-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

Accelerometers y=-0.6(RIGHT) test S50 a = 0.2747 g

Time (s)

Ho

rizo

nta

l A

ccele

rati

on

(g

)

h=0

h=0.44

-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.50

0.1

0.2

0.3

0.4

0.5

0.6

max/min horizontal accelerations. Filtered t=0 test S50 a = 0.2747 g

Acceleration (g)

h (

m)

max y=0.6(LEFT)

min y=0.6(LEFT)

max y=-0.6(RIGHT)

min y=-0.6(RIGHT)





0 5 10 15 20 25 30 35 40-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

Accelerometers y=0.6(LEFT) test S4 a = 0.325 g

Time (s)

Ho

rizo

nta

l A

ccele

rati

on

(g

)

h=0

h=0.44

h=0.84

h=1.24

h=1.54

0 5 10 15 20 25 30 35 40-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

Accelerometers y=-0.6(RIGHT) test S4 a = 0.325 g

Time (s)

Ho

rizo

nta

l A

ccele

rati

on

(g

)

h=0

h=0.44

h=0.84

h=1.24

h=1.54

-2 -1.5 -1 -0.5 0 0.5 1 1.5 20

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

max/min horizontal accelerations. Filtered t=0 test S4 a = 0.325 g

Acceleration (g)

h (

m)

max y=0.6(LEFT)

min y=0.6(LEFT)

max y=-0.6(RIGHT)

min y=-0.6(RIGHT)


STRAIN RESULTS



Session 2– test S50

0 5 10 15 20 25 30 35 40-80

-60

-40

-20

0

20

40

60

80

100

Vertical strain-gauges, y=0.6(LEFT) filt. t=0- test - S9 - a =0.339g

Time (s)

Vert

ical m

icro

-str

ain

h=0.18m

h=0.32m

h=0.62m

h=0.92m

0 5 10 15 20 25 30 35 40-150

-100

-50

0

50

100

150

200

250

Vertical strain-gauges, y=-0.6 filt. t=0- test - S9 - a =0.339g

Time (s)

Vert

ical m

icro

-str

ain

h=0.18m

h=0.32m

h=0.62m

h=0.92m

0 5 10 15 20 25-30

-20

-10

0

10

20

30

Vertical strain-gauges, y=0.6(LEFT) filt. t=0 test S50 a = 0.2747 g

Time (s)

Vert

ical m

icro

-str

ain

h=0.18m

h=0.32m

h=0.62m

0 5 10 15 20 25-100

-80

-60

-40

-20

0

20

40

60

80

Vertical strain-gauges, y=-0.6 filt. t=0 test S50 a = 0.2747 g

Time (s)

Vert

ical m

icro

-str

ain

h=0.18m

h=0.32m

h=0.62m


STRAIN RESULTS



COMMENTS

For all the sessions the maximum vertical strain is reached at height 0.18 m

(the lowest one), on the contrary the lowest vertical strain is set for height of

0.92 m. This is concordant with the behavior of the silo under a sinusoidal

input. Moreover the behavior of the two parts of the silo seems to be not

identical; this may be due to a squeezing of Ballottini glass along the

junction between the two polycarbonate semicircles

0 5 10 15 20 25 30 35 40-250

-200

-150

-100

-50

0

50

100

150

200

250

Vertical strain-gauges, y=0.6(LEFT) filt. t=0 test S4 a = 0.325 g

Time (s)

Vert

ical m

icro

-str

ain

h=0.18m

h=0.32m

h=0.62m

h=0.92m

0 5 10 15 20 25 30 35 40-250

-200

-150

-100

-50

0

50

100

150

200

250

Vertical strain-gauges, y=-0.6 filt. t=0 test S4 a = 0.325 g

Time (s)

Vert

ical m

icro

-str

ain

h=0.18m

h=0.32m

h=0.62m

h=0.92m


STRAIN RESULTS


Squeezing of Ballottini glass

along the junction between

the two polycarbonate

semicircles


PHYSICAL BEHAVIOR FOR A CHANGE

IN THE PGA o by looking at the mean plot (black line - Figure 1a), there is a clear change in the

physical behaviour for a value of PGA around 0.35 g.

o the same also for the case of input in Y and Z direction (Figure 1 b)

o Figure 1 c shows that for the case of rough walls surface the change in the

physical behavior seems to appear around 0.25g.


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

100

200

300

400

500

600

PGA [g]

max

[]

1Hz sinusoid (Y) - HBallottini

= 1.2 m

1pos

1neg

9pos

9neg

mean

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

50

100

150

200

250

PGA [g]

max

[]

1Hz sinusoid (Y&Z) - HBallottini

= 0.6 m

3pos

3neg

15pos

15neg

mean

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

100

200

300

400

500

600

PGA [g]

max

[]

1Hz sinusoid (Y) - HBallottini

= 1.2 m

3pos

3neg

15pos

15neg

mean

Figure 1b Figure 1c Figure 1a


INTERPRETATION OF

EXPERIMENTAL RESULTS The interpretation of the experimental results basically concerns the comparison between:

• the experimental bending moment at the base of the silo, as reconstructed from the strain values of the vertical strain gauges placed at a height z = 0.14 m from the table;

• the predicted value of the base bending moment, as given by the analytical formulations proposed by the authors (Silvestri et al. 2012);

• the Eurocode 8 prescribed values

The methodologies applied to reconstruct the experimental bending moment at the base of the silo (at a height z = 0.14 m) directly integrates the base vertical stresses multiplied by the corresponding lever arm over the whole circumferential cross-section.



METHODOLOGY

2

exp i i i

i

M t t A r

i polycarbonate it E t


x

y

30°

15°

42,43

44

4

3

43

16

15

42

2

41

14

60

57,96


Form the reconstruction of the experimental base bending moment

it is possible to note that the wall-grain friction coefficient strongly

affects the experimental base bending moment. This does not match

with Eurocode 8 prescriptions which do not take into account the wall-

grain friction coefficient at all.

0 5 10 15 20 25 30 35 40-1.5

-1

-0.5

0

0.5

1

1.5x 10

4 M(t) as re-constructed from base strains - a =0.33g

t [s]

M [kgcm]

first session: smooth walls

third session: roughened walls


INTERPRETATION OF THE RESULTS:

ROUGHENED

WALLS

SMOOTH

WALLS

All same

conditions,

except for the

wall-grain friction

coefficient


For h = 120 cm of the ensiled material the reconstructed experimental

bending moment is much closer to the prediction given by the

analytical formulas provided by the authors (Silvestri et al. 2012) than

the Eurocode 8 provision.


INTERPRETATION OF THE RESULTS:

0 5 10 15 20 25 30 35 40-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1x 10

4

0.891

2.4

3

0.951

2.6

3.2

Mpos/Mneg =1.1

M(t) as re-constructed from base strains - S2- a =0.101g

t [s]

M [kgcm]

M experimental

mean M experimental

M ns prediction

M EC8 simplified

M EC8 accurate

0 5 10 15 20 25 30 35 40-4

-3

-2

-1

0

1

2

3

4x 10

4

0.68

1

1.8

2.3

0.68

1

1.9

2.3

Mpos/Mneg =1


t [s]

M [kgcm]

M experimental

mean M experimental

M ns prediction

M EC8 simplified

M EC8 accurate

0 5 10 15 20 25 30 35 40-6

-4

-2

0

2

4

6x 10

4

0.55

1

1.5

1.8

0.59

1

1.6

2

Mpos/Mneg =1.1


t [s]

M [kgcm]

M experimental

mean M experimental

M ns prediction

M EC8 simplified

M EC8 accurate

0 5 10 15 20 25-2

-1.5

-1

-0.5

0

0.5

1

1.5

2x 10

4

0.831

2.3

2.8

0.781

2.1

2.6

Mpos/Mneg =0.94


t [s]

M [kgcm]

M experimental

mean M experimental

M ns prediction

M EC8 simplified

M EC8 accurate


END


Documents

squat silos containing grain-like material subjected to shaking ...Stefano Silvestri [email protected] Salvador Ivorra Chorro [email protected] Colin Taylor [email protected]