Shiling Pei

An approach to quantify the influence of ground motion uncertainty on elastoplastic system acceleration in incremental dynamic analysis

Inclusion of ground motion–induced uncertainty in structural response evaluation is an essential component for performance-based earthquake engineering. In current practice, ground motion uncertainty is often represented in performance-based earthquake engineering analysis empirically through the use of one or more ground motion suites. How to quantitatively characterize ground motion–induced structural response uncertainty propagation at different seismic hazard levels has not been thoroughly studied to date. In this study, a procedure to quantify the influence of ground motion uncertainty on elastoplastic single-degree-of-freedom acceleration responses in an incremental dynamic analysis is proposed. By modeling the shape of the incremental dynamic analysis curves, the formula to calculate uncertainty in maximum acceleration responses of linear systems and elastoplastic single-degree-of-freedom systems is constructed. This closed-form calculation provided a quantitative way to establish statistical equivalency for different ground motion suites with regard to acceleration response in these simple systems. This equivalence was validated through a numerical experiment, in which an equivalent ground motion suite for an existing ground motion suite was constructed and shown to yield statistically similar acceleration responses to that of the existing ground motion suite at all intensity levels.

Dual Objective Design Philosophy for Tornado Engineering

Tornadoes like all natural hazards posses a full range of intensities with the majority having winds below 130 mph. In this paper, a dual objective-based tornado engineering design philosophy is explained that has the simultaneous objectives of (1) reducing monetary losses due to damage; and (2) reducing loss of human life. While these objectives may seem an obvious goal for any design code related to natural hazards they have not yet been adequately addressed within the context of tornado hazard by engineers and scientists. Consider that at the center of a tornado swath for a large Enhanced Fujita (EF) 5 tornado there are slabs swept clean of the residential building that once stood there, corresponding to a degree of damage (DOD) of level 10. Moving out perpendicular to the direction of the tornado path the DOD reduces at some gradient to a DOD of 1, which is the threshold of visible damage. To date, it has been widely agreed upon that there is little that can be done against intense tornadoes in woodframe buildings except seeking shelter. There are two considerations or design objectives for the approach outlined in this paper: damage (D) and life safety (L). Damage can be controlled at lower levels of the Enhanced Fujita scale wind speeds, i.e. EF0 and EF1, through the use of engineered connectors, design ensuring continuous vertical uplift load paths, and horizontal load distribution and load path. This is handled typically at the component design level, i.e. connectors, single load paths. For wind speeds corresponding to EF2 and EF3 level, both component and systemlevel loading must be considered to enable better performance. System level performance is related to load sharing amongst wall lines and distribution of the lateral load path as a whole throughout the building as it is racked by wind and amplified further by windborne debris catching on the structure. In tornadoes with wind speeds corresponding to EF4 and EF5-level damage, the major issue becomes system effects and focuses on other alternatives to provide life safety to the building occupants. These alternatives are above or below ground safe rooms and neighborhood safe shelters.

Variability in Wood-Frame Building Damage using Broad-Band Synthetic Ground Motions: A Comparative Numerical Study with Recorded Motions

Earthquake damage to light-frame wood buildings is a major concern for North America because of the volume of this construction type. In order to estimate wood building damage using synthetic ground motions, we need to verify the ability of synthetically generated ground motions to simulate realistic damage for this structure type. Through a calibrated damage potential indicator, four different synthetic ground motion models are compared with the historically recorded ground motions at corresponding sites. We conclude that damage for sites farther from the fault (>20 km) is under-predicted on average and damage at closer sites is sometimes over-predicted.