Appendix IIDeveloping additional evaluation criteria for smaller<strong>and</strong> larger earthquakesAs discussed above, the SPUR performance objective contemplates asingle hazard level. For more robust evaluation results, for comparisonwith existing st<strong>and</strong>ard procedures for safety evaluation, <strong>and</strong> for thefacilitation of more nuanced policy distinctions, it might be useful <strong>to</strong>develop additional evaluation criteria related <strong>to</strong> either larger or smallerhazards.For example, use of a larger hazard (such as the full code levelhazard without the adjustment fac<strong>to</strong>r) might help distinguish relativelybrittle structural systems (such as non-ductile concrete) fromrelatively ductile systems (such as wood frame). Many systems willperform adequately at the primary hazard level recommended above,with critical deficiencies only manifesting in stronger shaking. This iswhy some codes <strong>and</strong> st<strong>and</strong>ards, including the seismic rehabilitationst<strong>and</strong>ard known as ASCE 41, 41 set performance objectives attwo levels. Similarly, liquefiable soil might be a much higher risk<strong>to</strong> shelter-in-place performance in the code’s MCE event than atthe fac<strong>to</strong>red hazard level. Therefore, we recommend the use of asecondary higher hazard (or other supplemental criteria) for certainstructure types, such as mid- <strong>to</strong> high-rise non-ductile concrete.Similarly, use of a smaller hazard could help distinguish “worst of theworst” buildings from other buildings whose shelter-in-place capacityis only marginally inadequate. This distinction could be useful inmaking loss estimates <strong>and</strong> in guiding policy decisions by the city <strong>and</strong>mitigation decisions by the building owner. Therefore, we recommendthe use of a secondary lower hazard (or other supplemental criteria)if needed for purposes of policy development. ASCE 31 is currentlyin an update cycle, <strong>and</strong> the new version is expected <strong>to</strong> include newevaluation criteria that address this issue; supplemental shelter-inplaceevaluation criteria could be based on the revised ASCE 31provisions as they become available.Categories of potential deficiencies that could impactshelter-in-place capacitySince shelter-in-place performance can be affected by more thanjust structural performance, we recommend that shelter-in-placeevaluation criteria consider five broad categories of potentialdeficiencies, generally consistent with the scope of ASCE 31:A. Geotechnical or geologicB. StructuralC. NonstructuralD. ContentsE. Utilities infrastructureThe shelter-in-place criteria described below are a subset <strong>and</strong>, insome cases, an extension of ASCE 31 provisions. In general, therecommended criteria are derived by considering shelter-in-placecapacity equivalent <strong>to</strong> conditions that would be expected <strong>to</strong> receivean ATC-20/DBI green tag within hours of the design event. Thatis, a building can be said <strong>to</strong> have shelter-in-place capacity if it hasno deficiencies that contemplate either an ATC-20 “red-taggable”damage pattern or a loss of habitability unacceptable <strong>to</strong> DBI,accounting for the fact that certain habitability requirements areexpected <strong>to</strong> be waived at different stages of the recovery period.The following subsections describe a process for modifying orextending relevant ASCE 31 provisions for each deficiency category:A. Critical geotechnical or geologic deficienciesGeotechnical or geologic deficiencies are those related <strong>to</strong> performanceof the soil or ground supporting the structure. ASCE 31 contemplatesthree potential geotechnical or geological deficiencies: liquefaction,slope failure <strong>and</strong> surface fault rupture. We recommend waiving thesurface fault rupture issue, since no fault traces have been identifiedin San Francisco’s developed areas.For liquefaction <strong>and</strong> slope stability, <strong>to</strong> avoid the cost of geotechnicalinvestigation, we recommend allowing the use of a DBI-approvedmap based either on investigation reports approved for previousprojects or on research such as that reflected by the “Liquefaction<strong>and</strong> L<strong>and</strong>slide Zones” map in Figure 13. To be clear, Figure 13 ispresented here not as final criteria but as an example of the resourcesfrom which the city might derive San Francisco–specific criteria. Itmight be tempered, for example, with a map of areas similar <strong>to</strong> thosethat experienced significant lateral spread or settlement in the LomaPrieta earthquake.Whether location in a liquefiable area should au<strong>to</strong>matically make abuilding shelter-in-place-deficient remains an open question <strong>to</strong> beresolved by additional research <strong>and</strong> by consideration of the city’sselected resilience objective.B. Structural deficienciesStructural deficiencies are those related <strong>to</strong> the walls, frames <strong>and</strong> otherstructural members meant <strong>to</strong> resist earthquake forces. Shelter-inplacecapacity requires that a building remain structurally stable <strong>to</strong>the degree that it would receive an ATC-20 green tag following thedesign event. The relevant ASCE 31 provisions are therefore thosethat are most closely related <strong>to</strong> ATC-20’s structural criteria, whichconsider partial or <strong>to</strong>tal collapse, significant out-of-plumbness orobvious severe damage <strong>to</strong> structural elements. Therefore, we41 Seismic Rehabilitation of Existing Buildings [ASCE/SEI 41-06] (AmericanSociety of Civil Engineers, 2006).38 SPUR Report > January 2012
<strong>Safe</strong> <strong>Enough</strong> <strong>to</strong> <strong>Stay</strong>Figure 13: Liquefaction <strong>and</strong> L<strong>and</strong>slide Zones in San FranciscoZones of required investigation for liquefaction <strong>and</strong> earthquake-induced l<strong>and</strong>slides in San FranciscoSource: “Seismic Hazard Zones, City <strong>and</strong> County ofSan Francisco,” (California Department of Conservation,Division of Mines <strong>and</strong> Geology, November 17, 2000)http://gmw.consrv.ca.gov/shmp/download/pdf/ozn_sf.pdfLiquefactionAreas where his<strong>to</strong>ric occurence indicate a potential forpermanent ground displacements.1 mile<strong>Earthquake</strong>-Induced L<strong>and</strong>slidesAreas where previous occurrence of l<strong>and</strong>slide movementindicate a potential for permanent ground displacements.SPUR Report > January 2012 39
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