Assessing seismic collapse safety of modern reinforced concrete moment frame buildings.

摘要

A primary goal of seismic design requirements of building codes is to protect the life safety of building inhabitants during extreme earthquakes, which requires that the likelihood of structural collapse be at an acceptably low level. However, building codes and standards are empirical in nature, which results in the collapse safety of new buildings not being well understood.; In this research, we develop the tools and methods to quantitatively assess the collapse risk of reinforced concrete (RC) special moment frame (SMF) buildings. This primarily includes treatment of ground motions, element model calibration, and treatment of structural modeling uncertainties.; We use the above tools and methods to assess the collapse risk of 30 RC SMF buildings designed according to ASCE7-02. The collapse probability conditioned on a 2% in 50 year ground motion ranges from 0.03 to 0.20, with an average of 0.11. The mean annual frequency of collapse (lambdacol ) ranges from 0.7x10-4 to 7.0x10-4, with an average of 3.1x10-4.; The minimum base shear requirement of ASCE7-02 is an important component of ensuring relatively consistent collapse risk for buildings of varying height. Removing this requirement from ASCE7-05 has made taller buildings significantly more vulnerable to collapse; this should be considered in future revisions of ASCE7.; In the course of developing the tools for this research, we found that a RC column with ductile detailing and low axial load, the median plastic rotation capacity is typically 0.05-0.08 radians, and sigmaLN = 0.45 to 0.54. Not accounting for proper spectral shape (epsilon) of ground motion typically leads to an underestimation of the median collapse capacity by a factor of 1.5 and overestimation of lambdacol by more than a factor of 20. Structural modeling uncertainty is critical and increases lambda col by nearly a factor of 10.; Lastly, this study finds that aspects of the structural design (height, framing layout, etc.) have less impact on the final performance prediction than the aspects of the collapse assessment methodology (structural modeling uncertainties, and spectral shape). This emphasizes the importance of developing a systematic codified assessment method that can be used to demonstrate the performance of a structural system.