Load measurement bearings
Monitoring bearings permit to read that load acting on the bearings when installed on the structure. They are equipped with an electrical connection capable of measuring the internal pressure acting on the surfaces in contact and transmit the data on a controller. The reading process is extremely simple and precise and provides a remarkably accurate and interesting data for evaluations and inspections after the launch of the major elements of a structure. It is possible to record vertical and horizontal loads, rotations, displacements in all directions. Also see the section Monitoring systems.
By the injection of special fluids inside the bearing basement these special bearings permit both an accurate reading of the vertical reactions, both the compensation of foundation settlements when predictable by increasing the height of the bearing itself. Depending on different needs the injection can be reversible or irreversible, to be carried out in one or in more stages.
Increasingly, due to special static schemes or by the action of seismic forces of considerable magnitude, are necessary anti-lifting bearings, that are able to absorb tensile forces in addition to the vertical compression. The tensile forces are transferred through the use of “C” shaped steel profiles that connect the upper to the lower plates thereby preventing the opening of the bearing.
Freyssinet Products Company Italia has considerable experience in this type of devices, having designed and built about three-quarters of the bearings of Taiwan High Speed Railway. In fact, because of the enormous value of the seismic action considered in the design and due to the loads acting in the transverse direction, the bearings are subjected to very high tensile stresses.
Used mainly in railways, where it is necessary to electrically insulate the superstructure from the substructure, these particular devices take advantage of the dielectric support (ie, the insulating properties) of PTFE. PTFE is placed between the horizontal surfaces in contact.
Through the use of special inserts of non-conducting materials other than PTFE, also the cylindrical contact surfaces along which the horizontal forces are transferred are insulated, thus allowing the bearing to be completely isolated.
The considerable experience accumulated over many works of high-speed rail projects in Italy and abroad make Freyssinet Products Company Italia a leader in this type of application.
Bearings, if properly designed, can be used to prevent the spread of the vibration even from outdoors to the structures (eg the protection of high-tech factories and equipment from vibrations caused by traffic) and from the structure to its surroundings (eg protection from vibration induced by high-speed railway lines of the external environment. One of the largest existing application in this field was made by isolating about 5 km of high-speed rail line in Taiwan.