A new energy absorber for earthquake resistant buildings
The research work which has been reported in this thesis is associated with the design of an energy absorbing device. The device as well as being capable to absorb high amount of energy, possess all the necessary properties of a structural member. Most energy absorbing devices have not the necessary conditions to be used as a structural members. Their problems have been demonstrated in chapter 1 and chapter 3 of the this thesis. In order to overcome these problems an alternative kind of energy absorbing device, has been proposed. The inversion of tubes has been proposed as the basic of the work. This is a wellknown energy-absorbing principle and has been widely used in industry and many mechanical engineering cases as the basic of design. However, the device has some disadvantages and these required improvement. The following steps have been taken to improve the energy absorbing characteristics: 1- Normally the energy absorbing capacity of the device is limited due to buckling. This problem has been improved by including an adhesive within the device. 2- The second problem in this energy-absorbing device is that its elastic stiffness is very low and this is unacceptable for a structural member. The elastic stiffness has been improved by forming a stiff shell at the top of the tube. 3- The device undergoes a significant change in length during the energy absorbing process and if it is not compensated in some way, the device will be useless in the subsequent cycles of vibration. A special mechanism has been installed in the device to solve this problem. This enables the deformation to be compensated after the absorption process. Two major applications for the device have been considered to be studied in the thesis: First because of its special response at high speed loading, it has been installed in a simply supported framework. The middle member of this framework has been replaced by the energy absorbing device and the behaviour of the framework has been analysed under an explosive load. In order to determine the advantages of the installation of this device in a framework, this framework has also been analysed without the inclusion of the device. The comparison of these results showed that when the framework is equipped with the absorber, a great reduction in the forces and strains of the members of the framework have been achieved. The framework has become 2.5 times stronger, when just one device was used in the frame. In the second application of the device, its behaviour has been studied as an absorber of a first soft story method. The first soft story is one of the ideas which has been presented for the isolation of buildings from earthquake effects, however, no proper absorber has been suggested to be used in this method. This device has an excellent performance in this regard, because of its shortening ability and its compact form along with its high energy absorbing capacity. Two energy absorbing devices were inserted in the braces of a single degree freedom structure and subjected to a high rate base acceleration. For a comparison, the behaviour of the frame, when it was not equipped with the devices, was also analysed. The results indicated that by the inclusion of the absorber, the acceleration has been decreased more than three times. The forces in the members were also three times less than the frame without the device. Finally, the behaviour of a multi story building has been examined when it was equipped with two energy absorbing device in the braces of the first floor. The results showed that a great reduction in the accelerations, velocities and also the forces and moments has been achieved, as was the case in the previous example. By using this absorber in the braces, the accelerations and velocities were four times less than the case which the frame did not include any absorber. In simple words, this energy absorber is similar to the dampers, which are used in the vehicles to reduce vibrations, but with this difference that the dampers in the car are active all the time while this damper is activated only when a high rate loading is applied.