Study of Fuses Used in Steel Repairable Buildings with Seesaw Motion

Preventing the collapse of buildings during major earthquakes by using the capacity of plastic deformations of their structural members is regarded as the main philosophy behind most of the present seismic design codes. However, regarding large, especially near-source earthquakes, the amount of these plastic deformations may be so large that the building may lose its performance, and its demolishing may become inevitable. As a result, some adverse consequences are imposed to the stricken community. First, it is necessary to evacuate and shelter thousands, even hundreds of thousands of people who have lost their living or working spaces. Second, demolishing the severely damaged (but not collapsed) buildings is a very difficult and time consuming task since the considered ductility in design may not result in losing their integrity easily, and the common demolishing techniques may not be used for those buildings. Third, the debris removal of the demolished buildings, whose weight may be over millions of tons in case of large cities is very time consuming and costly. Finally, plenty of time and cost as well as a large number of skilled work forces are needed to construct the new buildings to replace the demolished ones.
Based on the above-mentioned issues, it is recommended to design and construct the buildings in such a way that they can be easily and quickly repaired with little cost, even after major earthquakes. Buildings that are created in this way can be called repairable or resilient buildings. Employing a structural system with seesaw motion is considered as one of the ways for creating earthquake-resilient buildings. In seesaw buildings, all circumferential columns at the lowest story are equipped with energy dissipating devices or structural fuses, all internal columns at that story are omitted, and a central mega hinge support with a grid of orthogonal strong girders are used to keep the integrity of the upper stories and transfer their gravity loads to the mega hinge support and the circumferential columns at the lowest story. In this research, the specifications of a kind of yielding-plates structural fuse, namely the initial stiffness and the yielding displacement, have been investigated and its application in a set of buildings with seesaw structural systems has been studied subjected to near-source earthquakes by performing a series of nonlinear time history analyses (NLTHA) using the scaled accelerograms of a set of selected earthquakes. Results of the conducted NLTHA indicate that the IO seismic performance level is mostly achieved in seesaw buildings by using the appropriate values for the aforementioned behavioral parameters of the structural fuses, while the conventional buildings with the same geometry mostly fail subjected to the same applied earthquakes. The maximum absolute acceleration of the buildings’ roofs and their base shear are significantly reduced by using the seesaw system; however, the roofs maximum displacements in some seesaw buildings are increased comparing to the conventional buildings, but they are still in the range of seismic design code limitations.