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HomeMy WebLinkAbout03/20/2007, C2 - APPROVE AMENDMENT NO. 1 TO CONTRACT WITH URS FOR SEISMIC ANALYSIS OF SALINAS DAM council ul4Kl.�a,zco� agcnbA Report CZ CITY OF SAN LU I S OBISPO FROM: John Moss, Utilities DirectoF_^ Prepared By: Gary Henderson, Water Division Manager 4WH SUBJECT: APPROVE AMENDMENT NO. 1 TO CONTRACT WITH URS FOR SEISMIC ANALYSIS OF SALINAS DAM CAO RECOMMENDATION 1. Approve Amendment No. 1 to the contract with URS Corporation (URS) for Phase IIB seismic analysis of the Salinas Dam in the amount of $41,407-and authorize the Mayor to execute the contract. 2. Appropriate $41,407 from Water Fund working capital to the Salinas Dam Seismic Account (90626) for these services. DISCUSSION The City Council approved a contract with URS Corporation on January 17, 2006 to prepare a comprehensive structural analysis of the Salinas Dam. The U.S. Army Corps of Engineers currently own the dam, related facilities and property surrounding the reservoir and are interested in transferring ownership to a local agency. Once ownership transfer occurs, the dam will need to meet the State Division of Safety of Dam (DSOD) standards and the analysis is being undertaken to insure that the dam will meet all State standards prior to the transfer. The scope of work for the project was divided into three phases. Following each phase of work, meetings with DSOD are held to insure that the State staff concur with the analysis and direction being taken. The Phase I analysis involved development of the computer model and assumptions to be used in the more detailed non-linear analysis in Phase H. Phase II was completed in December of 2006 and indicates that there are some local areas within the structure that still exceed allowable stresses under the significant seismic loading conditions. Based on these results, URS and DSOD staff agree that an additional Phase II computer analysis (Phase IIB) with some modifications to the computer model are appropriate. This additional analysis was not included in the original scope of work. This additional work scope is identified in Exhibit A of Attachment 1 of this staff report. This additional work scope is identified as Phase IIB and will modify several assumptions relative to redistribution of the seismic loading on the dam structure. o • Salinas Dam Seismic Analysis Page 2 FISCAL IMPACT The additional compensation associated with this amendment to the contract with URS is $41,407. There is adequate funding currently available in Water Fund working capital for this project. ALTERNATIVES 1. Do Not Approve the Contract Amendment: The Council could decide not to proceed with the additional analysis. This would effectively stop all work associated with this analysis to identify the structural integrity of the dam and would not validate compliance with the State's standards. This would leave the structural integrity of the dam in a questionable position and may cause the DSOD to require significant and costly modifications to the dam structure prior to ownership transfer. This alternative is not recommended. ATTACHMENTS 1. Contract Amendment No. 1 with URS for Salinas Dam Non-Linear Dynamic Analysis Note: Original staff report for contract with URS available in Council reading file AMENDMENT NO. I TO AGREEMENT THIS AMENDMENT NO. 1 TO AGREEMENT is made and entered in the City of San Luis Obispo on this day of ,by and between the CITY OF SAN LUIS OBISPO,a municipal corporation,hereinafter referred to as City„and URS CORPORATION,hereinafter referred to as Contractor. WITNESSETH: WHEREAS, on February 9, 2006 the City entered into an Agreement with Contractor for a detailed . structural analysis of the existing Salinas Dam to evaluate the structure relative to State Division of Safety of Dams regulations;and WHEREAS, the City desires to amend the scope of services for more extensive structural analysis which was not included in the original work scope for the Contractor. NOW THEREFORE, in consideration of their mutual promises, obligations and covenants hereinafter contained,the parties hereto agree as follows: 1. The scope of services and related compensation is hereby amended as set forth in Exhibit A attached hereto. 2. All other terms and conditions of the Agreement remain in full force and effect. IN WITNESS WHEREOF, the parties hereto have caused this instrument to be executed the day and year first written above. APPROVED AS TO FORM: CITY OF SAN LUIS OBISPO By: City Attorney Mayor CONTRACTOR By: C 2 .3 Exhibit A PHASE-.IIB SUPPLEMENTAL NONLINEAR EARTHQUAKE ANALYSES OF SALINAS DAM QUEST STRUCTURES COST ESTIMATE TASK DESCRIPTION Labor($) 1. Model Development $7,668 Develop a new nonlinear model with 4 vertical contraction joints,2 horizontal liftlines, and the peripheral joints. Designated as Model-6, this new model will permit cracking and opening of one additional liftline in the upper portion of the dam for the purpose of relieving high tensile stresses in this region. 2. Nonlinear Static Analysis OF Model-6 $3,067 Run Model-6 for static loads including the gravity,water,and temperature loads. Process static stresses to assess dam performance under operating loads from which an estimation of probable tensile strength of the liftlines could be made. 3. Nonlinear Dynamic Analysis of Model-6 with Spectrum-matched Seismic Input $10,735 Run one nonlinear dynamic analysis for Model-6 using spectrum-matched input for comparison with the results of Model-5 which included only one liftline and showed high tensile cantilever stresses in the upper portion of the dam. 4. Nonlinear Analysis of Modell-6 with 10% Damping If the results from Task-3 indicate that tensile stresses are still high,Model-6 will be analyzed with a $7,668 higher damping of 10 percent of critical to account for the energy loss due to cracking and joint opening. Note that the nonlinear joint elements used in the model do not account for this energy loss. 5. Meeting with DSOD At this point we propose to meet with DSOD to discuss the results and obtain their $4,601 concurrence with the use of 10% damping and assumed tensile strengths of the parent concrete and liftlines before proceeding with completion of the analyses using natural earthquake records. 6. Test runs for scaling of Natural Earthquake Records _ Response Spectra_ of the selected-natural records significantly exceed the target $7,668 tesponse spectra near the peak of spectra.The effects of such high ground motions on the dam response need to be determined so that an appropriate scaling scheme can be adopted. For this purpose 2 to 3 analyses will be performed with limited data processing to provide input for scaling of the natural records. TOTAL FEE $41,407 c,� -y