| Author | Qureshi, Muhammad Irshad |
| Call Number | AIT Diss. no.ST-16-04 |
| Subject(s) | Precast concrete construction
|
| Note | A dissertation submitted in partial fulfillment of the requirements for the
degree of Doctor of Engineering in
Structural Engineering, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. ST-16-04 |
| Abstract | The conventional structural systems are designed to saturate the force demands by allowing yielding at predetermined locations in structural members. However, damage at these locations after a major seismic event leads to an expensive repair work. In recent years, an alternative precast post-tensioned rocking wall structural system is developed for high seismic regions. A rocking wall uses the gap opening and closing (geometric nonlinearity) at the wall-foundation joint to limit the seismic force demands while keeping the damage to a minimum level. For a widespread use of this structural system, there is a need for reliable numerical models that can predict all of the aspects of their dynamic behavior. Furthermore, suitable design procedures are required to ensure a reliable and well predicted performance under different levels of seismic hazard.
One of the conspicuous features of rocking wall seismic behavior is the presence of gap opening and closing phenomenon, characterized by an interaction of wall base and foundation top called as a contact. A short-duration, high-velocity contact in a dynamic domain called as an impact has been found to induce short-duration large-amplitude accelerations, both in horizontal and vertical directions called as horizontal acceleration spikes (HAS) and vertical acceleration spikes (VAS) respectively, in the system response. In the current study, numerical models are developed to predict the dynamic behavior of rocking wall structures including the acceleration spikes along with the identification of their effects on the dynamic performance of rocking walls. For this purpose, two important parameters of impact phenomenon i.e. contact stiffness and contact damping are studied in detail and guidelines are developed for modeling them. The finite element numerical models, based on the proposed guidelines about contact parameters, are found to predict the overall dynamic behavior of rocking walls along with the acceleration spikes quite efficiently. The acceleration spikes are found to be dependent on the lateral velocity at impact and the initial contact stiffness. So a velocity-dependent energy dissipation device along with a soft contact is found to be suitable for reducing these effects in low-rise rocking wall structures.
To study the effectiveness of design procedures in predicting the seismic demands of rocking wall structures, five case study rocking walls are selected, and designed using the displacement based design (DBD) procedure. Furthermore, two different capacity design procedures are used to predict the high seismic force demands due to higher mode effects. The DBD procedure is found to be reasonably effective in predicting the displacement and inter-story drift demands while the conventional capacity design procedures are found to be conservative for shear demands and non-conservative for moment demands. To further understand the seismic force demands, modal decomposition of dynamic responses is carried out by using nonlinear modal response history analysis procedure. The results showed that the gap opening at the base of the rocking wall changes the boundary condition at the base from fix to an almost pin. Therefore, a modified capacity design procedure is proposed in the current study based on the use of modified modal properties of the rocking walls and is found to be quite efficient in predicting the force demands in these structures. Furthermore, the modal decomposition results are used to effectively devise a dual gap opening mitigation technique to reduce the higher mode effects in rocking wall structures. A detailed discussion about the location, detailing and design strength of the extra gap opening is carried out by considering different performance parameters. |
| Year | 2016 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. ST-16-04 |
| Type | Dissertation |
| School | School of Engineering and Technology (SET) |
| Department | Department of Civil and Infrastucture Engineering (DCIE) |
| Academic Program/FoS | Structural Engineering (STE) /Former Name = Structural Engineering and Construction (ST) |
| Chairperson(s) | Pennung Warnitchai; |
| Examination Committee(s) | Anwar, Naveed ;Punchet Thammarak ;Amorn Pimanmas; |
| Scholarship Donor(s) | Higher Education Commission (HEC), Pakistan ;AIT Fellowship; |
| Degree | Thesis (Ph. D.) - Asian Institute of Technology, 2016 |