GTSTRUDL Users Group
23rd Annual Meeting and Training Seminar
Marriott Hotel
Delray Beach - Florida, U.S.A.
June 22-25, 2011
Structural Engineering
Department
Mechanical Engineering
Department
THE MODAL PROPERTIES OF THE ‘PALAZZO
LOMBARDIA’ BUILDING, THE NEW SEAT FOR THE
REGIONE LOMBARDIA IN MILAN: A COMPARISON
BETWEEN NUMERICAL ANALYSIS AND EXPERIMENTAL
RESULTS
Elena Mola, PhD – ECSD Srl, Engineering Consulting and Structural Design, Milano
Prof. Alfredo Cigada – Dept. Of Mech. Eng., Politecnico di Milano
Prof. Franco Mola – Dept. Of Struct. Eng., Politecnico di Milano
Gianfranco Stella, SE – CAD Data Consult Srl, Milano
Prof. Marcello Vanali – Dept. Of Mech. Eng., Politecnico di Milano
PALAZZO LOMBARDIA: THE ARCHITECTURAL DESIGN
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
2
PALAZZO LOMBARDIA: FACTS AND FIGURES
Credits
-
-
OWNER: Regione Lombardia
CONSTRUCTION SUPERVISION: Infrastrutture
Lombarde SpA
ARCHITECTURAL DESIGN: Pei Cobb Freed & Partners
Architects with Caputo Partnership and Sistema
Duemila
STRUCTURAL DESIGN: Prof. Ing. Franco Mola
CONTRACTORS:
‘Consorzio Torre’: Impregilo, Cile, C. M. B.,
Consorzio, Cooperative Costruzioni,
Costruzioni Giuseppe Montagna, Pessina
Costruzioni, Sirti, Techint Infrastrutture
CONSTRUCTION STARTED: October 2006
CONSTRUCTION ENDED: November 2009
Figures
total surface of the construction area:
230.338sq
total surface of the Complex: 30.000sq
global built surfaces: 190.000sq
public spaces: 4.500sq
parking spaces: 35.150sq
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
3
PALAZZO LOMBARDIA: STRUCTURAL DESIGN HIGHLIGHTS
a.
The complex is made of five lower buildings
(about 40m high, called Cores 2, 3, 4, 5 and 6),
surrounding the high-rise Tower (Core 1), which,
at 161.20m, is currently the tallest building in Italy
b.
The curvilinear, intersecting shapes of the
buildings define an inner covered public ‘plaza’,
having an area of about 4200m2, covered by a
steel truss system supporting transparent Texlon
ETFE (ethylene-co-tetrafluoroethylene) cushions
c.
The structural system is entirely made of
reinforced concrete load bearing elements,
except for the Auditorium area in Core 4 and the
‘Velarium’ on top of Core 1, a three-storey high
belvedere area to be used for official public
purposes and rented for private events. For the
two parts structural steel was employed.
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
4
PALAZZO LOMBARDIA:
STRUCTURAL DESIGN HIGHLIGHTS OF CORE 1
1.
The load bearing elements of Core 1 are entirely made of reinforced concrete: the
lateral load bearing capacity is fully provided by a central stairways core, whereas the
vertical structural elements are circular columns with varying cross sections, with
diameters ranging between 120cm and 65cm.
2.
The slabs of Core 1 starting from the ground floor are 35cm thick, fully bi-directional
reinforced concrete structural systems (‘bubbledecks’): the reduction of the weight is
obtained by inserting high density polyethylene (PEHD) spheres with a diameter of
270mm in the slab
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The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
5
PALAZZO LOMBARDIA: STRUCTURAL DESIGN HIGHLIGHTS OF CORE 1
3.
The structural system achieved by means of steel encasing for the vertical elements and light
weight ‘bubbledeck’ slabs exhibits the behaviour of a continuous plate on point supports (the
columns) and continuous support (the walls of the core).The encasing elements were thus
holed so that slab rebar and concrete could pass through, thus making the column-to-slab
joints completely effective in bearing lateral load induced moments.
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
6
PALAZZO LOMBARDIA: STRUCTURAL DESIGN HIGHLIGHTS OF CORE 1
3.
The foundations of Core 1 is made of a slab with a thickness ranging between 2 and 4m.
Under the slab, the ground was injected with compacting grout columns, having a diameter of
1.5m, spacing between 3 and 4m, and depth between 14 and 22 m. Self compacting concrete
was used to cast the lower layer of the slab, then normal concrete was used for the remaining
depth. The two layers were interconnected by means of vertical steel bars purposely
distributed in the slab and joined by means of steel couplers.
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
7
PALAZZO LOMBARDIA: STRUCTURAL DESIGN HIGHLIGHTS OF CORE 1
3.
The inner stairway core is a C55 reinforced concrete hollow core element with mean
rebar content of 200 kg/m3
4.
The most severe lateral load condition for its pre-dimensioning is wind loading, which
induces a base shear 3.3 times higher than those induced by earthquake loading
5.
The inner core takes up 65% of the total vertical loads and self-weight
6.
The construction method used for the stairway core is the industrialized moving
formwork
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
8
PALAZZO LOMBARDIA: NUMERICAL ANALYSES
o Finite Element Model Features
• A finite element model of Core 1 was implemented, using
GT STRUDL®, a commercial software for structural analysis
• In order to derive the modal features of the structure, a
linear dynamic modal analysis was then carried out, in order to
provide accurate numerical predictions of the modal response
of the building, which would be compared to a series of dynamic
excitation tests that were to be run on the ‘as-built’ structure as
a pre-requisite for its final validation.
•
52757 6-degrees-of-freedom joints
•
A total of 316542 degrees of freedom
•
53910 shell elements
•
9088 linear element (beams and columns)
•
77171 load types,
•
27 basic loading conditions and 5 loading combinations
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
9
PALAZZO LOMBARDIA: NUMERICAL ANALYSES
• The so-called ‘bubble slabs’ (i.e. cast-in-situ
RC slabs lightened by means of poliethylene
spheres) were modelled by means of shell
elements with an equivalent thickness to provide
the correct flexural stiffness.
o Modeling assumptions (1)
0.20
0.30
0.33
0.35
0.35
0.40
0.44
0.45
0.65
1.83
1.90
Z the ‘Palazzo Lombardia’ Building:
The Dynamic Behavior of
Comparison betweenY Numerical
Model and Experimental Results
X
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
10
PALAZZO LOMBARDIA: NUMERICAL ANALYSES
•In order to investigate the sensitivity of the
modal properties to the effective stiffness
distribution in slabs, two different meshing
options were implemented.
•Called NO RIGID JOINTS ,the first mesh
would not take into account the stiffening
effect of the columns’ effective cross
sections on the joints of the slabs mesh;
• The second meshing option , called
TOTAL RIGID JOINTS , would take into
account the presence of the columns’ cross
sections by means of an additional infinitely
rigid constraint imposed to the joints of the
mesh where each columns was present and
in its immediate vicinity. This option has
been abandoned.
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
o Modeling assumptions (2)
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
11
• The tirdh meshing option , called
RIGID JOINTS , would take into
account the same effect assuming
a different thickness of element
rounding the joint on the axis of
column.
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
12
PALAZZO LOMBARDIA: NUMERICAL ANALYSES
o Modeling assumptions (3)
• Modal dynamic analyses were
carried out assuming linear elastic
behaviour of materials
• A mean value of the compressive
strength was derived from the
compressive strenght tests carried
put on cubes during the
construction on the different
structural elements
• For the different structural
elements, by applying the Model
Code
90
formulation,
the
corresponding elastic modulus was
computed
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
13
PALAZZO LOMBARDIA: NUMERICAL ANALYSES
o Modeling assumptions (4)
•The results proved that the
sensitivity of the first modal
frequencies and eigenvector
to this parameter was much
lower than that to the
refinement of the mesh
•for the foundation
properties, a subgrade
coefficient value of 2.0x10-3
N/mm3 was assumed; this
was the design value used in
the pre-dimensioning
analyses run separately on
the foundations alone
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
14
PALAZZO LOMBARDIA: NUMERICAL ANALYSES
o Modeling assumptions (4)
• Modal frequencies and modal
shapes also depend on the actual
mass distribution
•Since the experimental dynamic
excitation tests would be run at the
end of construction, but before the
whole static permanent loading
would be in place, it was necessary
to make a computation of the actual
masses present on the structure at
the moment of testing.
•For the final simulations it was
assumed that a fraction of 20% of
the permanent loading would be
present.
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
15
PALAZZO LOMBARDIA: NUMERICAL ANALYSES
o Modeling assumptions (3)
• Modal frequencies and modal shapes also depend on the actual mass distribution
•Since the experimental dynamic excitation tests would be run at the end of construction,
but before the whole static permanent loading would be in place, it was necessary to
make a computation of the actual masses present on the structure at the moment of
testing.
•For the final simulations it was assumed that a fraction of 20% of the permanent loading
would be present.
•Finally, as for the foundation properties, a subgrade coefficient value of 2.0x10-3 N/mm3
was assumed; this was the design value used in the pre-dimensioning analyses run
separately on the foundations alone
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
16
THE DYNAMIC EXCITATION TESTS
Introduction
Pre-test: Ambient Vibrations
Operational Modal Analysis to get a first experimental estimate of the natural frequencies and mode
shapes
Forced Vibrations tests
Stepped sine excitation with varying resolution frequency, changed accordingly to the resonance
positions known from OMA.
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
17
THE DYNAMIC EXCITATION TESTS: INTRODUCTION
Mechanical Engineering Department Politecnico di Milano
Dynamic tests at real scale are a valuable tool to
refine and update numerical models
Static numerical models need a further refinement
to account for dynamic features
Mass and stiffness distributions are given at a
certain uncertainty level. Damping coefficients
are hard to be estimated and affected by strong
non-linear behaviors
A check on both static and dynamic behavior
can help narrowing these uncertainties
A further goal of dynamic excitation testing,
which is growing in importance, is trying to
lay down the basis for a proper monitoring,
as intended for Palazzo Lombardia
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
18
THE DYNAMIC EXCITATION TESTS: FEATURES

The main problems in testing a skyscraper are:
 a proper forecast of the mode shapes, to fix
sensors in the right positions
 the certainty to have a proper input to excite the
structure

The global response is dominated by the behaviour of
Core 1, which can be approximated with a cantilever
beam

the numerical model provided an initial approximation
of the expected vibration modes and frequencies

To confirm the FEM results a PRE-SET of the structure
subject to ambient vibrations was carried out
(Operational Modal Analysis)
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
19
OPERATIONAL MODAL ANALYSIS
Low noise Seismic Piezo accelerometers
On the 38th floor

This is a typical case of Operational Modal Analysis
(OMA), as the input is roughly known.

Unknown input: wind and traffic
even if the signal to noise ratio is less
favourable in this kind of tests, acquisition
through the whole week has allowed an
output quality improvement thanks to
continuous averaging, especially selecting
the periods with higher vibration levels
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
20
3
AMBIENT VIBRATIONS: PSD 24 HRS
Weak axis: all the 3
y-sensors measure
the same
0.33 Hz
1
Strong axis: all the 3
x-sensors measure
the same
2
PSD
-7
CRANE
10
Compatibility with
torsion: 3y has
the highest peak
0.42 Hz
Ampiezza [(m/s 2)2 / Hz]
0.65 Hz
02 X
02 Y
01 X
01 Y
03 X
03Y
higher amplitudes as the
distance from the main
core increases
Uncertain area,
small excitation,
further investigation
-8
10
Any contribution at higher
frequencies is not so easy
detectable, having peaks
close to the transducers
noise floor.
-9
10
0.2
0.4
0.6
0.8
1
1.2
Frequenza [Hz]
1.4
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
1.6
1.8
2
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
21
THE IDENTIFIED MODES (VECTORS HAVE REAL LENGTHS)
0.42 Hz mode
0.33 Hz mode
3
1
3
1
2
2
CRANE
CRANE
3
1
0.65 Hz mode
2
CRANE
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
22
COMPARISON WITH THE NUMERICAL MODEL
Natural
frequency
NUMERICAL
NO RIGID
NODE
Natural frequency
EXPERIMENTAL
(Ambient excitation)
[Hz]
[Hz]
0.33
0.37
0.55
1.11
1.21
0.33
0.42
0.65
1.28
1.36
Ratio
EXP /
NUM
1.01
1.13
1.17
1.15
1.12
It seems reasonable!!
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
COMPARISON WITH THE NUMERICAL MODEL
Natural
frequency
NUMERICAL
RIGID NODE
Natural frequency
EXPERIMENTAL
(Ambient excitation)
[Hz]
[Hz]
0.34
0.42
0.58
1.16
1.28
0.33
0.42
0.65
1.28
1.36
Ratio
EXP /
NUM
0.96
1.00
1.12
1.11
1.06
It seems reasonable!!
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
24
COMPARISON WITH THE NUMERICAL MODEL
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
25
FORCED VIBRATION TESTS

Based on the numerical model results and on the first operational analysis

The sensors were located on three different floor levels, the 21st, the 32nd and the top
floor, the 38th, considered enough to point out the first vibration mode shapes.

Each floor has been instrumented with 2-axis accelerometers in the horizontal plane,
capable to identify flexural modes (strong and weak axis) and torsion modes.
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
26
SIDE VIEW: SENSORS POSITIONS
38
32
21
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
27
TOP VIEW: FLEXURAL-STRONG AXIS
5
1
2
Flexural-strong axis
3
4
6
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
28
TOP VIEW: FLEXURAL-WEAK AXIS
5
2
1
Flexural-weak axis
3
4
6
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
29
TOP VIEW: TORSION
5
1
2
3
4
6
Torsion
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
30
THE DYNAMIC TESTS: ENVIRONMENTAL EXCITATION


During the tests, a rather windy day
has been analyzed separately from
the rest, allowing for a spectrum
detection with a best signal to noise
ratio.
It is observed, for the first flexural
mode, an increase of the
acceleration peaks at different
heights, as expected, and coherent
with a cantilever first mode.
Further confirmation of the
predicted mode shapes and
frequencies
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
31
FORCED VIBRATIONS
THE MAIN TROUBLE:
THE INERTIAL EXCITER
Problems in producing a meaningful force at low
frequencies
High energies at low frequencies:
-Long strokes (2 m)
-Big masses (1000 kg)
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
32
FORCED VIBRATIONS
THE MAIN TROUBLE:
THE INERTIAL EXCITER
• The usual test is a stepped sine
• We need to transmit high force levels
at low frequencies
• Assumed a sine wave the force is:
F  ma  mx 2
F = transmitted force
a = peak acceleration
x = peak displacement
2 = circular frequency
 is very low (natural frequencies below 1 Hz) →
we need long strokes and high mass to gain
back the very low  (also squared)
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
33
WE HAVE DECIDED TO USE A LINEAR MOTOR
PROVIDED BY SIEMENS (A SHORT MAGLEV)
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
34
INPUT: EXCITATION- INERTIAL EXCITER
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
35
OUTPUT ACCELERATION - TIME
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
36
THE DYNAMIC TESTS: IMPOSED INPUT EXCITATION

Measurements have been analyzed through a synchronous approach, reducing spectral leakage
and allowing for a correct estimation of the natural frequency positions.

A substantial confirmation of the ambient vibration tests is evident, even if this time data are
evaluated with respect to the given input;

Also meaningful phase information are added, testifying the presence of real resonances, with
a much better signal to noise ratio
Amplitude [(m/s2)/N]
2
x 10
Frequency response functions
-6
1.5
P381X
1
P381Y
0.5
0
0.2
P382X
0.4
0.6
0.8
1
Frequency [Hz]
1.2
1.4
P38
1.6 2Y
P383X
P383Y
200
Phase [°]
P384X
100
P384Y
0
-100
-200
0.2
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
0.4
0.6
0.8
1
Frequency [Hz]
1.2
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
1.4
1.6
37
EXPERIMENTAL AND NUMERICAL RESULTS: COMPARISON
AND DISCUSSION



The model that took into account the stiffening effects of the columns on the slab elements
better predicted the modal frequencies, but both of them matched the measured values
extremely well.
The ‘rigid-joints’ model, as expected, improves the predicted frequencies, particularly in the
weak direction (i.e. the second vibration mode).
In both cases, though, the ratio of numerical vs experimental frequencies is included in a
range of less than 10% on the first five modes (down to less than 5% on the first two
modes), which is extremely good, and particularly impressive for a model with this
complexity and such a high number of degrees of freedom.
NO SLAB-TO-COLUMN JOINT CONSTRAINT
CONSTRAINED SLAB-TO-COLUMN JOINTS
With foundation mass
Weight = 109533 T
With foundation mass
Weight = 109533 T
Freq. cyc/sec Ratio
Ratio
Gap
Freq. cyc/sec Ratio
Ratio
Gap
MODE Meas. Num. meas/num num/meas %
MODE Meas. Num. meas/num num/meas %
1
0.32 0.32
0.97
1.01
-0.93
1
0.32 0.34
0.95
1.05
-5.1
2
0.40 0.37
1.04
0.92
7.60
2
0.40 0.40
0.99
1.01
-1.0
3
0.63 0.55
1.13
0.87
13.22
3
0.63 0.57
1.11
0.90
10.0
4
1.25 1.09
1.13
0.87
12.83
4
1.25 1.12
1.11
0.90
10.2
5
1.35 1.19
1.11
0.89
11.42
5
1.35 1.24
1.08
0.92
7.5
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
38
EXPERIMENTAL AND NUMERICAL RESULTS: COMPARISON AND
DISCUSSION

o
As for the modal shapes, the eigen vectors exhibit full compatibility with the measured
accelerations at the floors, both in direction, proportion and sign, which confirms a modal
response dominated by the cantilever flexural mode along the strong axis (Mode 1, with
almost 50% normalized participation factor), followed by a cantilever flexural mode along
the weak axis (Mode 2, 42% normalized participation factor) and showing torsional effects
only in higher modes (for example Mode 4, involving both X and Y directions with the same
normalized participation factor, much lower than the first two).
Mode 1 – Freq. 0.32 Hz
o
Mode 2 – Freq. 0.40 Hz
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
o
Mode 4 – Freq. 1.09 Hz
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
39
EXPERIMENTAL AND NUMERICAL RESULTS: COMPARISON AND
DISCUSSION




The reason why the comparison between experimentally and numerically derived modal frequencies yielded very
good results are mostly but not only related to the structural configuration.
The basic conceptual design configuration of the structure is based on the optimization of the stiffness ratio of the
core vs that of the columns and on the reduction of differential lateral and vertical displacements of columns and
core.
The dynamic behavior of the structure is thus characterized by the first two modal shapes being almost totally
uncoupled inflections along the two main stiffness axes, with no major torsional effects affecting the modal
response and significant torsional effects being present only in higher modes.
Also, the very strict quality control procedure carried out both on the materials and on the construction methods
guaranteed that the mechanical properties assumed in the design and modeling phase would be the same in the
‘as built’ structure, meaning that the estimate of the structural stiffness made by the software, based on material
properties, would be very accurate
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
40
DEVELOP OF PROJECT






An interesting develop of investigation and refining of model is related to the value assumed for the elastic
behavior of fondation soil assumed for the modal analysis.
NNR-TD2.2 : NO RIGID JOINT - LESS RIGID SOIL
NRI-TD2.2 : RIGID JOINT - LESS RIGID SOIL
NRI-TD5.0: RIGID JOINT - MORE RIGID SOIL
NRI-TD2.2 versus NNR-TD2.2 : better accuracy of 2^ frequency – affectect by slab-column stiffness
NRI-TD5.0 versus NRI-TD2.2 : better accuracy of all frequency
12.7
% OF ACCURACY
(frequencies)
14.0
12.0
10.6
10.0
10.0
8.0
9.6
9.9
9.1
6.0
11.2
10.0
11.610.9
7.7
8.3
6.8
4.0
2.8
2.0
2.6
0.0
SHAPES
1
2
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
3
4
NNR-TD2.2
NRI-TD5.0
5
NRI-TD2.2
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
41
CONCLUSIONS




The set of dynamic excitation tests carried out on ‘Palazzo Lombardia’ proved to
be an effective and reliable tool to validate the finite element modeling
assumptions and the basic conceptual choices enforced in the design phase.
The structural system exhibited a good response to dynamic excitation, governed
by mostly uncoupled flexural deflection vibration modes, associated to low
frequencies, making it less sensitive to potential earthquake excitations.
The global numerical analysis model implemented in GT STRUDL proved to be
well tuned, as for the basic parameters and assumptions and able to derive the
modal properties of the structure with good accuracy. The experimental tests
were also an additional method to enforce a final quality control on the materials
and the construction method: they highlighted a good correspondence between
the ‘as-designed’ structure and the ‘as-built’ one.
The numerical analysis model, thus experimentally validated, can now be used as
the basis for the planned continuous monitoring activity on the Tower.
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
42
ACKNOWLEDGEMENTS
‘Palazzo Lombardia’:
 Owner: Regione Lombardia
 Architectural Design: Pei Cobb Freed & Partners
Architects (USA) with Caputo Partnership (ITA) and
Sistema Duemila (ITA) - Architectural Project Supervisor:
Arch. Henry N. Cobb
 Structural Design: Prof. Ing. Franco Mola - ECSD Srl –
Engineering Consulting & Structural Design, Milano (ITA)
 Construction Supervisor: Infrastrutture Lombarde Spa
 General Contractor: Consorzio Torre Spa
 Leading Contractor: Impregilo Spa - President and
General Manager: Ing. Gaetano Salonia
 Site Technical Manager: Ing. Vinicio Scerri
 Construction Site General Manager and Safety
Supervisor: Ing. Guglielmo Fariello
-
CONSTRUCTION STARTED: October 2006
-
CONSTRUCTION ENDED : November 2009
The Dynamic Behavior of the ‘Palazzo Lombardia’ Building:
Comparison between Numerical Model and Experimental Results
Ing. Gianfranco Stella
Ing. Chiara Pozzuoli
43