Performance Evaluation of Rocking Wall Moment Frame Using Incremental Dynamic Analysis (IDA)

Conventional seismic lateral force resisting systems dissipate seismic energy through distributed damage to primary structural elements and residual drifts, which can result in significant socio-economic losses due to repair costs and business downtime after an earthquake event. Although these systems have low primary cost in the construction process, the recent recommendation of seismic design guidelines, which was minimizing the horrible seismic consequences of an earthquake led to the wide range of analytical and experimental research on the new generation of seismic structure system called low-damaged system. One of these low-damaged systems is Rocking wall.
Like a traditional structural wall, a base-rocking system acts as a vertical cantilever to transfer lateral building loads to the foundation through shear and bending moments in the wall. The system is not capable of transmitting tension to the foundation; however, it is not rigidly tied to it as a traditional wall. Base bending moments are resisted by the restoring moment available due to the gravity loads acting on the wall, and once that effect is exceeded, a gap opens at the base of the wall. Because no elements yield during this process, the nonlinear behavior of the structure is not associated with permanent deformations. Reports of retrofitting projects indicate that there are significant economic costs in the foundation of the shear walls due to the large reaction forces at the base of the wall. Therefore, it is expected to economize the cost of construction by extending the details of the design of the rocking systems.
On the other word, rocking walls can rock on the foundation during the earthquake by releasing the rotational constraint at the base, and they reduce residual drift by returning the attached structure to the original position.
In this research, the behavior of the Reinforce Concrete frame with rocking wall is investigated using nonlinear Incremental Dynamical Analysis in two 2D models with 5-storey and 10-storey.
Far field record set of the FEMA-p695 were used for IDA analysis and the structure response was compared with the corresponding frame response with conventional shear wall. There are 11 samples in total, four samples were designed for the 5-story model and seven samples for the 10-storey model, and 56 non-linear time histories analysis was performed on the each sample. Seven pairs of far field records, which are horizontal components were selected in proportion of record selection criteria of FEMA-p695. One of each pair of the records with larger peak ground acceleration was selected and they were scaled first to the gravity acceleration and second to the weight coefficient of intensity. Analysis and design of models are performed using SAP2000-v14 software.
Rocking walls are modeled such as pre-stress reinforce concrete wall with unbounded post-tensioned cables. Rocking movement is modeled using gap element and hinge constraint at the bottom of the wall. Rigid beams are used to connect the frame to the wall.
The results show that the rocking wall in both 5 and 10 storey models has a significant reduction in residual drift, and by equipping them with post-tensioned cables and dampers in 10-story model, can insure of the behavior of non-structural components during the earthquake. The connection of the frame to the wall was also investigated in different models, and hinge connection of the frame to the wall was evaluated well for the proper behavior of the rocking system.
Although the design and construction of such systems is still not common in the worldwide due to the high uncertainties, further study and research in this field can lead to applied design and evolution in the current constructions.
The purpose of this study is first to become more familiar with rocking walls and then to survey the behavior and performance of these walls in combination with concrete moment frame. However, simplification has been done in the software for simulation of this system, which will definitely affect the results. The general view obtained by these results will be effective in the study process on these systems.