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Seismic collapse performance of Los Angeles soft, weak, and open-front wall line woodframe structures retrofitted using different procedures

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Abstract

The Los Angeles Soft-Story Ordinance was enacted with the goal of reducing the collapse risk of woodframe buildings with soft, weak and open-front (SWOF) wall lines. Four alternative retrofit methods are permitted under the Ordinance including a “SWOF-wall-line-only” retrofit in accordance with the Department of Building and Safety requirements or a “full-story” retrofit based on Appendix A4 of the 2012 IEBC, ASCE 41-13 or FEMA P807. A comparative assessment of the increase in collapse safety provided by the four alternative retrofit methods is presented. Nonlinear static and dynamic collapse analyses are conducted on a set of archetypical structural models, which have been developed based on an extensive survey of Los Angeles SWOF buildings. The effect of several building characteristics (e.g. number of stories, wall layout in 1st story) on the relative enhancement in collapse safety of the retrofitted buildings is also investigated. The number of stories is shown to have the greatest effect on the relative collapse safety benefits derived from the alternative methods. The number of SWOF wall lines and the ductility of the upper stories also impacted the extent to which the retrofits enhanced collapse safety.

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Acknowledgements

The research presented in this paper is supported by the National Science Foundation CMMI Research Grant No. 1538747.

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Authors and Affiliations

  1. Department of Civil and Environmental Engineering, University of California, Los Angeles, USA

    Henry Burton, Zhengxiang Yi, Damian Gutierrez & Koyejo Ojuri

  2. School of Architecture, Civil and Environmental Engineering, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland

    Aryan Rezaei Rad

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  1. Henry Burton
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  3. Zhengxiang Yi
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  4. Damian Gutierrez
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Correspondence to Henry Burton.

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Appendices

Appendix 1: Floor plan dimensions of archetype buildings

figure a
figure b
figure c

Appendix 2: Details of retrofit elements

2.1 Retrofit frame sizes

See Tables 4 and 5.

Table 4 Basic ordinance and FEMA P807 retrofit frame sizes
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Table 5 IEBC A4 and ASCE 41-13
Full size table

2.2 FEMA P807 retrofit panel identification, lengths and nailing

For the FEMA P807 retrofits, the only WSPs are 5′-0″ long with 8d @ 4″ O.C. nailing located at P1 and P7 (see Fig. 4c) in the L3 archetypes, with the exception of L3-2S-50X30-HWS (no panels are included in the FEMA P807 retrofit of this archetype).

2.3 IEBC A4 retrofit panel identification, lengths and nailing

The IEBC retrofit panels are summarized in Table 6 where the panels are labelled X′-X″; NX. X′-X″ is the length of the panel and NX is the nailing. The 10d @ 2″ O.C. nailing pattern is denoted as “N1” and the 10d @ 4″ O.C. nailing pattern is denoted as “N2”.

Table 6 IEBC A4 retrofit panels
Full size table

See Table 6.

2.4 ASCE 41-13 retrofit panel identification, lengths and nailing

The ASCE 41-13 retrofit panel lengths are summarized in Table 7. Only the L3 archetypes have panels and the nailing pattern is always 10d @ 2″ O.C.

Table 7 ASCE 41-13 retrofit panels
Full size table

See Table 7.

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Burton, H., Rad, A.R., Yi, Z. et al. Seismic collapse performance of Los Angeles soft, weak, and open-front wall line woodframe structures retrofitted using different procedures. Bull Earthquake Eng 17, 2059–2091 (2019). https://doi.org/10.1007/s10518-018-00524-w

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