Effect of Loading Protocol on the Steel Moment Connections in Iran

Premature rupture of steel structures in seismic Northridge connections led to investigate the connection performance against the forces of earthquake, many researchers are studied. The performance of these joints and connections against forces caused by various kinds of earthquakes, accurate determination of the used parameters and bearing capacity parameters of connections. The fact that no two earthquakes are similar adds emphasis to adopting a coordinated approach for testing different structural elements. These requirements results in developing standard loading histories called loading protocols. Today, the ever-increasing development of using steel in the construction industry in Iran has become clearly evident. Considering the fact that Iran is an earthquake-prone country, identifying the behavior of these structures against earthquake forces assumed importance. Seven, twelve and twenty-story steel moment frames were selected as research models, and after preparing a proper list of accelerograms recorded in the course of earthquakes occurred in Iran during 1978-2007 , the seismic demands applied to structural components were estimated. Regarding the catastrophic aftermath of earthquakes, having a reliable approach to assess the seismic demands proper to the region of interest seems inevitable. The scope of this study is to provide a list of far-field seismic records applicable to 2-D nonlinear time history analyses in Iran. To do that a set of 2000 seismic records from Iran's seismic records database has been investigated based-on their characteristics, amongst are focal distance, magnitude, rupture mechanism, frequency content, and soil profile, resulting in compilation of a list of 20 accelerograms for the purposes of the two dimensional and non-linear analyses in Iran. The proposed accelerograms portray as a true area’s seismic movement as possible. In continuation of study, the final coefficient of scale for the accelerograms for the steel moment frames is calculated with a point to point differentiation method in periodic intervals corresponding to each frame. For the coefficient of scale, an operation conducted in a way that for each accelerogram in the average spectrum, an appropriate response is determined. Time-history dynamic analysis has been carried out by using the list of proposed accelerogram records aiming at preparing the loading protocol of steel moment connections, and the rainflow cycle counting technique has been employed to determine damage parameters for research models. Considering the fact that strength and deformation capacities depends on cumulative damage in earthquake engineering, every component has a permanent memory of past damaging events and at any instance in time it will remember all the past excursions (or cycles) that have contributed to the deterioration in its state of health. A loading protocol is developed specifically for this purpose.For developing the loading protocol of moment-resisting connections, the time history is analyzed using the proposed set of accelerograms recorded, and by applying the method of rainflow cycle counting, damage parameters are determined for the research models. The number of damaging cycles, total deformation range, deformation range and peak of deformation range are the employed parameters, which will be evaluated and compared for all the layers of the research models. Afterwards, statistical estimations are performed on damage parameters and target values are established. Finally, a loading protocol is recommended for moment-resisting joints commonly used in Iran which has the capacity of being applied to the considered structural elements under one general state.