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Required Number of Records for ASCE/SEI 7 Ground Motion Scaling Procedure


Printable USGS Open File Report 2011 - 1083, 34 p. (2.0 Mb)

Juan Carlos Reyes, Universidad de los Andes, Bogota, Colombia, jureyes@uniandes.edu.co

Erol Kalkan, U.S. Geological Survey, Menlo Park, ekalkan@usgs.gov

Plain English Summary

The procedures and criteria in 2006 IBC (International Council of Building Officials, 2006) and 2007 CBC (International Council of Building Officials, 2007) for the selection and scaling ground-motions for use in nonlinear response history analysis (RHA) of structures are based on ASCE/SEI 7 provisions (ASCE, 2005, 2010). According to ASCE/SEI 7, earthquake records should be selected from events of magnitudes, fault distance, and source mechanisms that comply with the maximum considered earthquake, and then scaled so that the average value of the 5-percent-damped response spectra for the set of scaled records is not less than the design response spectrum over the period range from to 0.2Tn to 1.5Tn (where Tn is the fundamental vibration period of the structure). If at least seven ground-motions are analyzed, the design values of engineering demand parameters (EDPs) are taken as the average of the EDPs determined from the analyses. If fewer than seven ground-motions are analyzed, the design values of EDPs are taken as the maximum values of the EDPs. ASCE/SEI 7 requires a minimum of three ground-motions. These limits on the number of records in the ASCE/SEI 7 procedure are based on engineering experience, rather than on a comprehensive evaluation. This study statistically examines the required number of records for the ASCE/SEI 7 procedure, such that the scaled records provide accurate, efficient, and consistent estimates of “true” structural responses. Based on elastic-perfectly-plastic and bilinear single-degree-of-freedom systems, the ASCE/SEI 7 scaling procedure is applied to 480 sets of ground-motions. The number of records in these sets varies from three to ten. The records in each set were selected either (i) randomly, (ii) considering their spectral shapes, or (iii) considering their spectral shapes and design spectral-acceleration value, A(Tn). As compared to benchmark (that is, “true”) responses from unscaled records using a larger catalog of ground-motions, it is demonstrated that the ASCE/SEI 7 scaling procedure is overly conservative if fewer than seven ground-motions are employed. Utilizing seven or more randomly selected records provides a more accurate estimate of the EDPs accompanied by reduced record-to-record variability of the responses. Consistency in accuracy and efficiency is achieved only if records are selected on the basis of their spectral shape and A(Tn).

Resumen Espanol

Actualmente, la selección y escalamiento de registros sísmicos para ser utilizados en un análisis dinámico no-lineal de estructuras está basado en las provisiones del ASCE/SEI 7. Debido a que el número de registros requerido en el estándar ASCE está basado más en experiencia ingenieril que en una evaluación rigurosa, este estudio evalúa estadísticamente el número de registros requerido por el ASCE/SEI 7 de tal manera que al escalar los registros se obtenga una estimación precisa, eficiente y consistente de la “verdadera” respuesta estructural. Basado en sistemas elasto- plásticos y bilineales de un grado de libertad, el procedimiento de escalamiento de ASCE/SEI 7 es aplicado a 480 sets de movimientos sísmicos variando el número de registros por set de tres a diez. Se demuestra que los resultados obtenidos con el procedimiento de la ASCE/SEI 7 son demasiado conservadores cuando se emplean menos de siete registros. Utilizando siete o más registros seleccionados de manera aleatoria se obtiene una estimación más precisa de los EDPs y menor variabilidad en las respuestas. Cuando la selección de registros sísmicos se basa en su forma espectral y en la pseudo-aceleración de diseño, aumenta la precisión y eficiencia del procedimiento.

Related Publications

Reyes J.C. and Kalkan E..Reyes J.C. and Kalkan E. “How Many Records Should be Used in ASCE/SEI-7 Ground Motion Scaling Procedure", Earthquake Spectra, 2012, 28(3): 1205-1222.

 

Comparison of benchmark and ASCE/SEI 7 deformation values for bilinear systems. The benchmark EDPs correspond to the mean of 30 deformation values. The deformation values for each set scaled by the ASCE/SEI 7 procedure are obtained as the maximum deformation values of 3, 4, 5 and 6 records in each of seven sets. For almost all cases, ASCE/SEI-7 yields conservative result when less than seven ground motions are used.