SEAOSC Committee Report: Non-Ductile Concrete Subcommittee of Existing Buildings Committee
Background: The Non-ductile Concrete Subcommittee (NDC) of the Existing Buildings Committee is continuing its working group analyses in which five ordinances/guidelines are being applied to typical reinforced concrete buildings. As stated in previous committee reports, the objective is to provide information so that the members of the subcommittee can make comparisons of the concrete evaluation and analysis procedures specified in the ordinances/guidelines. The ordinances/guidelines to be used include LA. City Division 95, FEMA 273 (ATC-33), ATC-40 (Prop. 122), OSHPD Section 1600, Division III-R, and FEMA 178 (ATC-22).
Analyses:
The analysis of the first building selected for analysis using Division 95 is essentially complete. The overall building was analyzed using a three-dimensional SAP2000 model for the iterative analysis of the building model, and a two-dimensional FEM/I model was used to determine the nonlinear force deformation characteristics of the shear wall/caisson subsystems. Most of the lateral deflection of the shear wall/caisson subsystems is attributed to the lengthening of the caisson. Accordingly, the caissons are an essential part of the model, and they should be included in the analysis model. The roof displacement was about five inches and the effective building period is about one second. Initially, reductions in stiffness for the columns were not included and they were overstressed in shear. However, when reductions were included for the columns (30% of gross section), they were found to be satisfactory in shear. The BIAX program will be used to obtain strain limits for the columns.
The progress on the application of FEMA 273 to the building selected for analysis using the Nonlinear Static Procedure (NSP) was discussed. An initial estimate of the target displacement that will be used for the pushover analysis was calculated to be about four inches, which is of the same order as the final displacements calculated using Division 95. A FEM/I model will be used for the shear wall/caisson subsystems in the NSP analysis. The nonlinear Static Procedure analyses are proceeding, as well as the analyses using Linear Static Procedure (LSP) and the Linear Dynamic Procedure (LDP).
The evaluation of the building using FEMA 178 has been completed, and 10 deficiencies were noted. One of the evaluation statements requires the reinforcing steel (in both directions) for concrete walls to be greater than 0.0025 times the gross area of the wall. The members think this requirement needs to be questioned and recommendations for revision need to be presented. The categorization of the building was questioned, and a Type 9 category should be considered.
Progress on the application of the other ordinances/guidelines will be discussed at future meetings of the subcommittee. It should be noted that a member of SEAONC has volunteered to participate in the OSHPD Section 1600, Division III-R analysis with us.
Next Meeting: A more detailed description of the NDC work plan and current progress is available in the minutes of the meetings of the Non-ductile Concrete Subcommittee. The next meeting was scheduled for May 20.
Martin Johnson To Receive
Damping Comments
Dr. Roger E. Scholl, former Chair of the SEAOC Supplemental Damping Committee recently passed away after a short battle with cancer. Martin Johnson has been named as the Ad Hoc Committee Chair.
Members interested in providing review and comment on draft provisions for designing buildings using energy dissipation devices should contact Mr. Johnson at 714-833-3303 or fax: 714-833-3391. He needs the following information: name, company, affiliation, phone number, fax number, and e-mail address. Particularly sought are industry representatives.
The report on the IBC in the Seismology Committee minutes article in the April NEWSletter should be corrected to indicate that the structural subcommittee will adopt the codified NEHRP provisions as they see fit.
Congratulations to SEAOSC member John A. Martin & Associates, which recently received the Superior Award of the SEAOC Excellence in Structural Engineering Awards for UCLA Royce Hall Seismic Renovation/Corrections in Los Angeles.
Other recipients included Forell/Elsesser Engineers, Inc. of San Francisco for Oakland City Hall Seismic Isolation Retrofit; Curry Price Court of San Diego for Fiber Reinforced Plastic Model Range Arch in San Diego; Skidmore, Owings & Merrill LLP of San Francisco for the U.S. Court of Appeals Seismic Retrofit in San Francisco; and OLMM Structural Design of San Francisco for S.F. New Main Library.
The competition publicly recognizes creative achievement and innovation and educates the public regarding the contribution structural engineers make to public safety, accordingt to Allen Goldstein, SEAOC Executive Director, Sacramento.