Evaluation of the modal pushover analysis procedure using inelastic modal decomposition | |
| Author | Acharya, Sandesh Raj |
| Call Number | AIT Thesis no.ST-04-08 |
| Subject(s) | Modal analysis Structural dynamics |
| Note | A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Series Statement | Thesis ; no. ST-04-08 |
| Abstract | Current civil engineering practice prefers to use nonlinear static (Pushover) method for design and evaluation of structures subjected to seismic loads. Pushover analysis is obviously capable of providing good estimates of inelastic deformation demand of low-rise structures where the response is controlled by single fundamental mode. But response of high-rise structures is controlled by multi-vibration modes. Currently, modal pushover analysis (MPA) is under study to take into account the effect of higher mode. Results observed from various studies show that MP A procedure is not equally accurate for all conditions. Being an approximate method, however, it should obviously be evaluated more comprehensively before practical application on building evaluation design. A 40-story wall building is considered for the study. The building is modeled as a vertical cantilever beam (wall) with equal masses lumped at each story level. Formations of plastic hinges are allowed at base four stories. Modal decomposition of inelastic response of this building is carried out. Furthermore, modal properties for each mode are observed. Modal response from modal pushover and inelastic modal decomposition method are compared separately. Modal pushover analysis is developed under several assumptions. Reliability of such assumptions is studied. MP A is evaluated using inelastic modal decomposition method. This method provides facility to evaluate MP A for each mode. Hence, it can provide improved understanding of the inherent assumptions of modal pushover analysis. Modal pushover analysis seems very accurate for ground motions that have peak modal response at different time instant. For such ground motions, assumption of uncoupling of modes that provides to use separate pushover for desired modes becomes acceptable. Use of SRSS combination rule seems to be acceptable with some exceptions. Moment at the base, where the plastic hinges are allowed, is over estimated for such strong ground motion due to SRSS combination rule. Results from modal pushover analysis may be misleading for the ground motions that have peak modal response at same time instant. Modal responses are strongly coupled for such ground motions. Hence, assumption of uncoupling of modes becomes false. For such ground motion, the demands are unacceptably overestimated or underestimated. Modal properties of higher modes may significantly change due to yielding of first mode for these strongly coupled ground motion. Effect of such coupling becomes more important when higher mode response becomes predominant. |
| Year | 2004 |
| Corresponding Series Added Entry | Asian Institute of Technology. Thesis ; no. ST-04-08 |
| Type | Thesis |
| School | School of Engineering and Technology |
| 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) | Worsak Kanok-Nukulchai ;Barry, William Joseph ; |
| Scholarship Donor(s) | Government of Japan; |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 2004 |