CROSS Safety Report
Inadequate design and quality assurance on a mandatory seismic retrofit project
A tenant's structural engineer discovers widespread design and related quality problems on a mandatory seismic retrofit project.
Lack of several fundamental quality activities in design, construction, and code compliance are apparent.
Key Learning Outcomes
For structural design engineers:
In retrofit of existing buildings designs and contract documents require knowledge of existing construction
During construction periodic field visits and sign off that the construction generally conforms with the requirements of the contract document is typically mandatory, and where not mandatory is highly desirable
In retrofit of existing buildings where design documents do not represent existing construction, consult the designer of record before proceeding
For building authorities:
Careful plan checking and site visits to verify conformance of construction with the design documents can avert problems like the one experienced in this case
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This case involves design problems and inadequate quality assurance on a mandatory seismic retrofit for ‘soft story’1 deficiencies in a city2 in Northern California. Despite the problems identified, both the design and the completed construction were approved by the city. The problems were found only when a tenant requested that the reporter make a review of the work for unrelated purposes. The retrofit plans do not match the building. Critical shear wall locations are shown on the retrofit plans with orientations and lengths that do not match actual conditions. An existing bay window is shown straight. An existing lightwell is omitted. Existing basement/foundation walls are shown as concrete but are, in fact, unreinforced brick.
Plans include details only for full-height shear walls when the actual walls are much shorter due to basement/foundation wall height. Retrofit shear walls have incorrect orientation, height, tie-down locations, anchor types, and anchor capacities. The contractor appears to have improvised changes to suit the actual conditions without consulting with the design engineer or filing required revision sketches. The project went through city plan review and inspection processes flagging none of these errors, and the city generated a certificate of final completion.
The building that is the subject of this report was under a mandatory city retrofit program, which is specific in its evaluation and retrofit requirements. Unfortunately, numerous quality shortcomings in design, construction, and field observation resulted in a retrofit that failed to provide the desired performance improvements.
Expert Panel Comments
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The report offers incomplete detail on how the quality problems on this project occurred because the reporter was not the retrofit designer and learned of the problems only after construction was completed. An appropriately Licensed Design Professional (LDP) must evaluate the existing conditions and design a retrofit to meet the ordinance requirements. Typically the LDP must observe the retrofit construction at intervals appropriate for the work (there are some exceptions to this) and ‘sign off’ at project completion that the work substantially complies with the LDP's design documents. Such requirements were part of the ordinance of this project's jurisdiction.
The LPD's plans reportedly do not match the existing building. The reporter notes that the contractor improvised to suit field conditions rather than consulting the LDP about how to deal with discrepancies between the drawings and field conditions. While not absolving the LDP and contractor of their responsibilities, the city’s department of building inspection had responsibility to review the LDP's drawings and inspect the work before issuing a certificate of final completion. The plan review might not have caught the discrepancies between the plans and the existing conditions, but a final inspection should have. Severe inadequacies in the LDP's retrofit plans were exacerbated and perpetuated by the contractor's improvisation, which was further perpetuated by inadequate field observation by the LDP and inspection by the city.
1. Soft story’ is a technical term defined in US codes and standards related to seismic evaluation and design. Generally, it refers to a structural irregularity, often related to architectural features, in which one or more lower stories of a building are substantially less stiff in seismic resistance than stories above. Soft-story (and similar ‘weak-story’) effects make buildings seismically vulnerable and have resulted in failures or collapse of buildings in earthquakes. While the term is generic with respect to structural systems and materials, past earthquakes in California caused multiple failures of wood residential buildings where the first story was ‘soft’ or ‘weak’ due to open spaces for car parking or large openings in perimeter wall lines for garage doors and storefronts. Recognizing this several jurisdictions in California have implemented mandatory retrofit programs for soft-story vulnerability. Understandably but contrary to the engineering standards, these jurisdictions use ‘soft story’ as a shorthand term to mean wood residential buildings of a certain size and age, typically built before 1980, and having at least three residential units. This report reflects that shorthand usage. See City of San Francisco Mandatory Soft Story Program and Los Angeles Department of Building Safety Soft-Story Retrofit Program.
2. For confidentiality, the city is not identified herein.
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