Rubber Bearings Essay

CHAPTER I

THE PROBLEM AND ITS BACKGROUND

Introduction

Recent earthquakes, particularly the magnitude 6.2 Earthquake in Davao on February 16, 2013, the 5.7 Earthquake in Southern Mindanao on June 1, 2013 and the deadliest earthquake in the Philippines for the past 23 years, the magnitude 7.2 Earthquake in Bohol on October 15, 2013, have caused significant loss of life and severe damage to property. Many aseismic construction designs and technologies have been developed over the years in attempts to mitigate the effects of earthquakes on buildings and their vulnerable contents. Reducing the effects of severe ground motions on the buildings and their contents is always one of the most popular topics in the area of civil and structural Engineering

The construction methodology is the same with elastomeric bearings; however, the damping is increased by adding carbon block and other fillers. In addition, it has an adequate resistance to service loads. The damping characteristic is in between hysteric and viscous. The energy dissipation is linear and quadratic for hysteric and viscous, respectively. The energy absorption capability help reduced the earthquake energy transmitted to the superstructure.

Lead Rubber Bearings Lead Rubber Bearing (LRB) are elastomeric bearings that contain one or more lead plugs inserted into their preformed holes. The lead provides significant stiffness under service loads and low lateral loads as compare to the elastomeric bearings.

During high lateral loads, the load yields and the lateral stiffness of the LRB is significantly reduced. This increases the duration of the period of the structure and thereby serves as the purpose of base isolation system. The bearing is cycled into a hysteric damping as it absorbs the energy. LRB has a range of damping from 15% to 30% which is a function of displacement. Figure 4 show the alternating sheet of steel shims and rubbers circumscribing a lead

This significant reduction in base shear provides the engineer with the ability to eliminate the ductility demand and hence damage to the structural system.

2.The ability of a relatively stiff building to move as a rigid body above the isolators with little or no amplification of forces above the isolators. A fixed base building will amplify the ground accelerations by a factor of 2.5 to 4 at the roof depending on the structural system. When comparing the forces at the roof, a base isolated building will provide a factor of 8 to 12 reduction in the forces compared to the fixed base building. An example of this was the two 6 storey reinforced concrete buildings in the 1995 Kobe, Japan earthquake discussed above. Components of a building that are sensitive to floor accelerations in an earthquake include the mechanical and electrical equipment, the contents, the manufacturing processes, elevators, sprinkler systems and ceiling and lights. The order of magnitude reduction in floor accelerations provided by base isolation greatly enhances the safety of all of these components of a