Pounding of San Francisco-Type Soft-Story Corner Buildings

Abstract

We investigated 1920s-era four-story wood-frame corner buildings common to San Francisco, many of which were damaged in the city's Marina District during the 1989 Loma Prieta earthquake. Such buildings can have relatively weak and flexible first stories and are referred to as soft-story buildings. We calibrated two building computer models to simulate actual earthquake response. We then performed computer analysis to assess collapse performance under 22 hypothetical pounding situations of both as-built and retrofitted soft-story buildings. For this building type, we found that a typical pounding situation increased the collapse rate by 14%, and for retrofitted versions, pounding slightly decreased the collapse rate. However, there were factors that appear to significantly increase the rate, especially in combination: negligible building separations and multiple adjacent buildings having low effective damping and large mass. Based on the results, we outline an approximate way to account for pounding within the context of current design procedures. An upper bound on the pounding effect was found to be equivalent to about a 30% increase in demand.

Influence of bi-directional seismic pounding on the inelastic demand distribution of three adjacent multi-storey R/C buildings

“…More recently, the influence of pounding to a multi-storey wood frame building located at the corner of a typical building block in San Francisco has been assessed within a probabilistic seismic performance-based framework (Maison et al 2012). The above conspectus of recent published work reveals that research efforts to assess the influence of seismic pounding have focused either on simplified "academic examples" of structures represented by two-dimensional (2D) or three-dimensional (3D) FE models or on real-life case-studies of under-designed buildings.…”

“…It is noted that in most real-life cases, pounding of adjacent buildings takes place in a rather complex manner for a number of additional reasons (Jeng & Tzeng 2000, Maison et al 2012) such as that: (i) buildings are not constructed in series but within blocks, hence, particularly the corner buildings are subject to bi-lateral pounding, and (ii) due to the lack of available space and the cost of land in modern cities, newer structures are typically higher and slender than older ones, a fact that is commonly associated with the significant contribution of their higher, primarily torsional, modes of vibration.…”

Commentary on FEMA P-807 for Retrofit of Wood-Frame Soft-Story Buildings

“…In this section, the required first-story lateral peak (ultimate) strength from P-807 is compared to that from codes such as that for new construction (ICC 2012a) according to the International Building Code (IBC). A four-story apartment building (Figure 5) previously studied was used as an example (Building-1 in Maison et al 2012).…”

“…The hysteretic model used here (Figure 8) cannot be readily duplicated by commercial programs, so for the validation process, the model parameters were adjusted to a hysteretic behavior that the commercial program could produce. the 1989 Loma Prieta earthquake (more description of the calibration process can be found in Maison et al 2012). This strength-0.13W model was considered to be a somewhat lower-bound weak building (not median since ≪50% of the Marina buildings were red-tagged).…”

Pounding of San Francisco–Type Soft-Story Midblock Buildings

“…There is a need for better understanding how pounding affects collapse risk so that remediation plans can be rationally evaluated before being put in place. Accordingly, the Structural Engineers Association of Northern California (SEAONC) has promoted efforts to gain insight about pounding for an important class of street corner buildings (Maison et al 2012a). This paper, prepared by the SEAONC Existing Buildings Committee, supplements the original report and presents a next step by examining midblock buildings (Maison et al 2012b contains the full report).…”