Northridge Welded Steel Moment-Frame Damage Data and Its Use for Rapid Loss Estimation

Abstract

FEMA-351, Recommended Seismic Evaluation and Upgrade Criteria for Existing Welded Steel Moment-Frame Buildings, offers two methods for estimating seismic losses in pre-Northridge WSMFs: detailed and rapid. The rapid method uses empirical relationships between seismic demand parameters and either damage levels or repair costs. The relationships are based on actual damage data collected after the 1994 Northridge earthquake. This paper summarizes the Northridge data, explains the FEMA-351 rapid method loss functions, and comments on the nature of the damage data and its application to loss estimation. Use of the loss functions can be enhanced by understanding their inherent assumptions and uncertainties and by considering how the underlying data was collected and interpreted in the years following the 1994 earthquake.

Method for detecting moment connection fracture using high-frequency transients in recorded accelerations

“…Damage information on study buildings was obtained from case studies [48,49], damage surveys [50][51][52], and unpublished inspection reports. The number of connections inspected varied from building to building, but all buildings had some connections inspected, and in many buildings every connection was inspected.…”

A proposed method for the detection of steel moment connection fractures using high-frequency, transient accelerations

“…Due to its composition of primarily code-instrumented buildings, the dataset is heavily biased towards taller buildings, with the median building height being 12 stories. In contrast, the SAC database developed for loss estimation studies (Bonowitz and Maison, 2003) has a median building height of 4 stories, which is much more representative of the regional WSMF population. Unfortunately, there are no strong motion records available from low-rise WSMFs (less than 4 stories), and a limited number from mid-rise WSMFs (5-8 stories).…”

“…Unpublished reports by engineering consultants documenting the results of investigations performed to satisfy a mandatory inspection and repair ordinance in Los Angeles, described in FEMA 355-E (FEMA 200b), exist for a number of the buildings as well. In addition, damage surveys were performed after the Northridge earthquake by several investigators (SAC 1995b, FEMA 2000b, Bonowitz and Maison 2003. These surveys typically covered fairly large samples of buildings and were intended for use in studying broad trends rather than extracting information for specific buildings.…”

“…SAC 1995a; Naeim et al 1999) and verified using inspection reports and/or repair drawings by the consulting engineer. These buildings were grouped into the bins shown in Table 2 based on a damage ratio, which was defined as the number of damaged connections divided by the total number of inspected connections (Bonowitz and Maison 2003). Minor weld cracks only detectable with ultrasonic testing (FEMA designation W1) were not included, as these are considered by many researchers to be pre-existing conditions (see Paret 2000), and regardless, probably would not generate the sudden connection property changes necessary to cause acceleration transients.…”

“…A number of case studies (SAC 1995a;Cohen 1996;Naeim 1997;Naeim et al 1999), damage surveys (SAC 1995b;FEMA 2000b;Maison and Bonowitz 2003), and unpublished inspection reports provide detailed information. Inspection reports were required for compliance with mandatory inspection and repair ordinances.…”