Experimental Study on the Ultimate Shear Performance of Elastomeric Bearings of Doublefold Elastomeric Layer ()
Abstract
The elastomeric bearings shall not fail nor degrade the durability of the bridge due to the loss of its properties during its service life. Since the elastomeric bearings can be used in the seismic design complementarily to seismic devices, even if it is not a seismic isolator, they particularly should secure high shear performance. For elastomeric bearings to behave monolithically, the internal rubber which is located between the steel plates should be single rubber layer. In this study, a series of elastomeric bearings were fabricated and ultimate shear performance was investigated. Some specimens are of single elastomeric layer, the other are of doublefold elastomeric layer. Shear fatigue tests and ultimate shear tests were carried out. Tests results show that the elastomeric bearings whose internal rubber layer is formed by agglomeration of several rubber pads is likely to experience significant loss of its shear performance or early failure.
1. Introduction
The Elastomeric bearings are a laminated structure combining rubber and stiffening plate layers. They transfer the loads of the superstructure to the substructure and also absorb the movements of the superstructure caused by loading, creep, thermal change and drying shrinkage. In Korea, the Korean Industrial Standard KS F 4420 (KS) specifies requirements for the design, performance evaluation and fabrication of the elastomeric bearings [1]. For elastomeric bearings to behave monolithically, the internal rubber which is located between the steel plates should be the single rubber layer. In Korea, elastomeric bearings of doublefold elastomeric layer are common practice, because the current KS doesn’t restrict the use of doublefold elastomeric layer. Besides, since the performance of the elastomeric bearings designed in compliance with KS are not passing through the certification system of an authorized agency but rely on the in-house performance evaluation of the manufacturer, the lack of data enabling to verify objectively the performances is worrisome.
In this paper eastomeric bearings are fabricated in compliance with KS and their ultimate shear performances were investigated. Some specimens are of single elastomeric layer, the other are of doublefold elastomeric layer. The significant degradation of the shear performances of the elastomeric bearings fabricated by means of the common practice in Korea is revealed and directions enabling to improve these performances are suggested.
2. Fabrication of Specimens
A series of elastomeric bearings were designed and fabricated in compliance with KS. KS presents 6 types of elastomeric bearings. The adopted elastomeric bearings is of type B with outer steel plate of KS exhibiting a shear modulus of 0.9. It is a monolithic structure obtained by vulcanization of the rubber pad and external steel plates. Specimens were classified into S5 and S10. Specimen S5 has the doublefold elastomeric layer. Specimen S10 adopted the single elastomeric layer. The shapes and dimensions of the fabricated elastomeric bearings are presented in Figures 1 to 2 and in Table 1.
3. Shear Performance Test
3.1. Test Machine
Figure 3 shows a test machine. It can apply simultaneously vertical and horizontal loads. The capacity of the vertical actuator of the bearing testing device is a maximum load of 3500 kN and a stroke of 350 mm. The capacity of the horizontal actuator is a maximum load of 500 kN and a stroke of 700 mm.