A study on the ultimate performances of elastomeric bearings in Korea

As part of the efforts to improve the performances and reliability of the elastomeric bearings produced in Korea, this paper evaluates experimentally the validity of the ultimate loads of the design allowable values of KS F 4420 purposed for the design of elastomeric bearings in Korea. To that goal, a series of tests including ultimate compression test, ultimate shear test and shear fatigue test were conducted on elastomeric bearings designed in compliance with KS F 4420. The results showed that failure occurred at loads 16 to 26 times larger than the allowable compressive stress and made it possible to conclude that the so-designed elastomeric bearings secured sufficient reliability regard to the vertical performance. In the case of the shear performance, the elastomeric bearings failed in a load range larger than the allowable design values but the performances were also seen to fluctuate sensitively according to the fabrication conditions of the bearings. Especially, the tests revealed that the shear performance degraded significantly or that early failure occurred when the internal rubber layer of the bearings were not fabricated using a single rubber layer. Since the elastomeric bearing can be used in the seismic design complementarily to seismic devices, even if it is not a seismic isolator, the bearing should secure high shear performance. The routine by which some companies are fabricating the internal rubber layer by stacking several rubber pads to form one layer is not only degrading the performance of the elastomeric bearing but may also provoke unexpected failure. This stresses the need for the establishment of specifications forbidding such customary practice.