Elastomeric rubber-steel insulators with lead core C.M.M. EL. ISO. LRB
This typology of rubber-steel isolator is equipped with a central core in pure lead inserted into the isolator which has the function of increasing the dissipative capacity of the device and providing a considerable initial rigidity (before the yielding of the core itself) which can be useful in order to limit the structure displacements under service forces (e.g. wind force).
The features of the isolator (constitutive bond and damping) are therefore provided both by the physical and dimensional features of rubber layers and by the dimensions of the central lead core, which are selected ad-hoc in order to ensure the best compliance with the design performance requirements.
C.M.M. has three types of certified compounds to tune the performances of EL.ISO isolators, which differ according to the value of Shore A hardness and of shear modulus G (such values directly influence the horizontal stiffness of the isolator):
The features of the isolator (constitutive bond and damping) are therefore provided both by the physical and dimensional features of rubber layers and by the dimensions of the central lead core, which are selected ad-hoc in order to ensure the best compliance with the design performance requirements.
C.M.M. has three types of certified compounds to tune the performances of EL.ISO isolators, which differ according to the value of Shore A hardness and of shear modulus G (such values directly influence the horizontal stiffness of the isolator):
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The damping capacity of the isolator during shear strain cycles is completely or partially provided by the specific composition of rubber compounds: for each compound the guaranteed minimum equivalent damping corresponding to a shear strain of 100% is b=25-45%.
Mechanical behaviour and mathematical modelling
Such behaviour can be modelled for the first load ramp by means of a bilinear force-displacement law: for a determined value of shear stress (depending on the dimension of the lead core) the core reaches the yield producing a sudden decreasing of stiffness of the whole isolator: however, by reversing the load, the lead can regain the initial elastic strength, ensuring that the cyclic behaviour is the typical behaviour of an element with high dissipative capacity.
Mechanical behaviour and mathematical modelling
Such behaviour can be modelled for the first load ramp by means of a bilinear force-displacement law: for a determined value of shear stress (depending on the dimension of the lead core) the core reaches the yield producing a sudden decreasing of stiffness of the whole isolator: however, by reversing the load, the lead can regain the initial elastic strength, ensuring that the cyclic behaviour is the typical behaviour of an element with high dissipative capacity.
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Fy: yield strength dy: deplacement to yield kpre: pre-yield stiffness (mainly due to the lead core) kpost: post-yield strength (mainly due to the rubber layers) |
Experimental cycles of C.M.M. isolator EL.ISO. LRB at 100% deformation
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