SARH K.
Ph.D. thesis,
University of Paris VI
Advisor: Professor GIBERT René-Jean
357 Pages
in french
 

In nuclear power plants, large size overhead cranes, such as reactor building crane and turbine building crane are used for transporting heavy loads on the operating floor, and call for safety and reliability
even during strong earthquake. The possibility of sliding at the interface between the traveling crane and the supporting railway significantly reduces the vibration energy transmitted.

This study deals with a large program verification of seismic behavior of the nuclear overhead cranes in consequence of their classification in the category of materials, which are important for nuclear safety.

Seismic analysis of these overhead cranes is reconsidered, in particular to reduce the important margins due to the non-consideration of the slip at the braked rollers.

Shaking tests, which were performed on a scaled model, putted on a shaking table, show some friction phenomenon like the participation of eigenmodes which frequencies are higher than the cut-off frequency of the excitation. Only the influence of horizontal seismic excitations is examined.

A finite-element model of the scaled model with Coulomb damping at the supports is developed using the mechanical code ASTER. This numerical model gives good results compared to experimental ones, and it shows the same friction phenomenon.

This numerical model is then used to develop a new simplified method of seismic calculation based on the elastic response spectrum. This simplified method, called sliding spectrum method, is based on the new theory of the sliding eigenmodes. Effects of vertical motion are not taken into an account. This method does not overestimate the response in comparison with the linear method in which no sliding is considered at the supports. It gives a practical means for seismic calculation design of sliding structures, which is less time consuming than the Time history calculations (Monte-Carlo simulations).

PAPAIN M.H.
SARH K.
GUIHOT P.
Service Ensembles de Production
Département Acoustique et Mécanique Vibratoire
58 pages
96NB00017
in french
 

A study about the "Behavior of Multi-Degrees-Of-Freedom sliding structures under random
excitations" has been carried out. One of the purposes is to validate and improve if
necessary the so called "Sliding Response Spectrum Method".

The emphasis in this report is on the practical application of this method in the case of a
simplified model of overhead crane and on its efficiency. First, the dynamical equations of a
sliding structure are recalled. Then the model of the overhead crane is detailed and the
simplified method is applied. The results are compared to those obtained from a time history
analysis with the mechanical code Aster. The accuracy of the method is also discussed.

The first comparisons were made about the simplified overhead crane with an horizontal
excitation choosen such that the structure is always sliding, and without vertical excitation.
Differences of five percent were noticed. To be more explicit about the origin of these small
discrepancies, a complementary study about a two degree of freedom sliding system is
made, always in the case of almost permanent sliding.

The obtained results provide a better understanding of the behavior of this simplified
method and of its limits. As a matter of fact, the imparted excitation on the sliding structure
depends on the sign of the sliding velocity and therefore not only on the initial excitation but
also on the dynamic behavior of the sliding structure. At the present time, the dependency
is not taken into account in the simplified method, which can lead to significant errors. For
the two degree of freedom sliding system, the actual behavior can be underestimated by
about twenty percent. The dependency could be taken into account by an improvement of
the modal combination rule. However, that remains to prove and to develop.

We can nevertheless consider that this simplified method could be used for the overhead
crane aseismic design, as these structures have a prevailing first symmetrical mode, as the
studied model. Some complementary studies must be realized in order to really get a sound
method usable for industrial purposes. The case of an unsymmetrical loading (trolley throw
off the center) and also the effects of the vertical strong motion must still be taken into
account.

GUIHOT P.
PAPIN M.H.
SARH K.
Service Ensembles de Production
Département Acoustique et Mécanique Vibratoire
10 pages
96NB00076
in english
 

In nuclear power plants, large-size overhead cranes, such as reactor building crane and
turbine building crane are used for transporting heavy loads on the operation floor, and call
for safety and reliability even during strong earthquake. The possibility of sliding at the
interface between the traveling crane and the supporting railway significantly reduces the
vibration energy transmitted.

We propose in this paper an experimental and numerical study performed on a simplified
scale model. A simplified modal method is developed in order to take into account this
possibility in the seismic analysis and design of sliding structures.

SARH K.
DUVAL C.
Service Ensembles de Production
Département Acoustique et Mécanique Vibratoire
56 pages
94NB00046
in french
 

This paper describes seismic tests on a traveling crane mockup. The tests are unidirectional
and the excitations of the type modulated sine, white noise and filtered white noise.

These tests are the first to be performed on the Acoustics and Mechanical Vibration
Department shaking table and evidence the technical possibilities of this equipment.

The tests show the contribution to the response made by dynamic modes where the
frequency is beyond the excitation frequency band. This phenomenon is due to the
non-linear aspects of the problem of the behavior of multi-modal structures on sliding
contact bearings.
 

SARH K.
DUVAL C.
Service Ensembles de Production
Département Acoustique et Mécanique Vibratoire
46 pages
93NB00120
in french
 

Calculation of the seismic response of structures on sliding supports involves the dual
problem of "non-linear" and "random" dynamic behavior.

After a review of the non-linearities common in dynamics, slipping is compared with a
hysteresis phenomenon. Simple examples are then used to present the Fokker-Planck
equation and the equivalent linearization method. Finally, the methods for modification of the
excitation spectrum intended for the engineering calculations are recalled.