This Broadening Participation Research Initiation Grants in Engineering (BRIGE) grant provides funding for the characterization of the translational and rotational strong ground motions in the vicinity of the fault and for the investigation of their effects on the dynamic response of building structures. The primary objectives of this research are to (1) investigate the characteristics of the dynamic ground deformation field in the near-fault region, (2) explore the effects of tectonic regime and soil conditions on the amplitude and frequency characteristics of near-fault ground motions, (3) derive damping coefficients for the analysis and design of buildings equipped with base isolation and passive energy dissipation devices subjected to near-fault seismic excitations, and (4) investigate the nonlinear response of symmetric and asymmetric buildings to near-fault translational and torsional ground motions.
If successful, the results of this research will improve the parameterization of the translational and rotational ground motions in the vicinity of the earthquake source and contribute to the evaluation of their effects on the dynamic response of buildings in the context of performance-based earthquake engineering. This research will also assess the effectiveness of damping coefficients and accidental eccentricity levels proposed in design codes for buildings. It is anticipated that the proposed research will advance the knowledge in the fields of earthquake engineering and engineering seismology, and will enhance the safety of communities in areas of high seismicity. An education and outreach plan will follow closely the development of the research activities. This plan includes the involvement of minorities and underrepresented groups at the university level and through K-12 outreach activities with the objective of broadening their participation in math, science and engineering.
Sites located in the immediate vicinity of active tectonic faults have large potential to experience ground motions characterized by intense pulses of relatively long duration in the event of an earthquake. Forward rupture directivity and permanent translation (fling) are the two most common effects that give rise to such strong motion pulses. Long-period structures are particularly susceptible to seismic excitations of this kind. Code provisions have historically been developed based on ground motions recorded not sufficiently close to the causative fault. Thus, the effect of the impulsive character of the near-fault seismic excitations on the elastic and inelastic response of civil engineering structures has recently become a significant concern for reliable aseismic structural design. The primary research objectives of this award were to: (1) investigate the effects of soil conditions and tectonic regime on near-fault strong motion pulses; (2) derive damping coefficients for the single-degree-of-freedom system subjected to near-fault seismic excitations; (3) investigate the torsional response of symmetric buildings to near-fault obliquely incident SH-waves; and (4) investigate the dynamic response of asymmetric-plan buildings to near-fault translational and torsional ground motions. The following significant results were drawn from the conducted research: 1. Damping coefficients proposed in design codes and previous studies, based primarily on far-field ground motion records, tend to not be conservative for near-fault seismic excitations. A new approach was recommended for the derivation of damping coefficients appropriate for engineering analysis and design in the immediate vicinity of the fault. This includes the normalization of the period axis with respect to the period of the ground velocity pulses recorded in the near-fault region. 2. The effects of soil conditions and tectonic regime on the pulse period of near-fault ground motions were investigated. The results showed that for earthquakes of smaller magnitude, the pulse period is longer at soil sites than at rock sites. As earthquake magnitude increases, the pulse period values at rock and soil sites converge. Regression analyses for interplate and intraplate records were also performed to assess the effect of tectonic regime on the pulse period of near-fault ground motions. 3. The torsional response of buildings subjected to near-fault pulse-type motions was computed for buildings with different configuration parameters. A parametric study revealed that the controlling factors of the model’s response are the shear wave velocity, the angle of incidence, and specific ground motion parameters. Further, physical constraints were exerted on the angle of incidence by relating it to the shear wave velocity and wave apparent horizontal velocity. 4. Broadband synthetic time histories and response spectra consistent with the seismological and geodetic characteristics of the 2010 Haiti earthquake were generated. The lack of strong motion instruments in the vicinity of the specific earthquake had hindered the estimation of the amplitude, duration and frequency characteristics of the ground shaking in the near-fault region. The results of this study will contribute to the development of seismic building codes and safer building practices in Haiti, and will facilitate the rigorous interpretation of the observed structural and geotechnical damage. The implementation of the project’s research and broadening participation plan provided training, development and mentoring opportunities to several students at the undergraduate and graduate levels, including students from underrepresented groups. Five graduate and three undergraduate students worked on various aspects of the project. The research conducted by the graduate students was an integral part of their Ph.D. Dissertation and M.S. Theses. The undergraduate students also played an important role in achieving the research and outreach objectives of the project. The PI worked closely with all students providing them training in the areas of earthquake engineering and engineering seismology, contributing to the development of their writing and presentation skills, and mentoring them in terms of their success in the academic field or profession they have been entering. This award made possible for all students to get involved in high-quality research and motivated them to focus on and excel in their studies. This award also facilitated a productive collaboration with a High School in the DC metropolitan area. A large number of ethnic minority students were reached through a visitation program to the High School (11 visits) and through a visitation program of High School students to CUA (3 visits). That interaction included in-class lectures, demonstrations, projects, computer assignments, etc. One high school student also worked under the PI’s supervision during the summer of 2011. The outreach activities of this project also included participation in a summer camp organized by the School of Engineering at CUA and participation in an acoustics demonstrations event organized by the Department of Mechanical Engineering at CUA. This award also facilitated the offering of relevant graduate courses at CUA. Graduate students from the Departments of Civil and Mechanical engineering and non-degree students (i.e., professional engineers in the DC metropolitan area) attended these courses.
