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15 form (Ragheb 1994; Parra 1996; Yang 2000; McKenna and stress site response analyses (Kwok et al. 2007; Stewart et Fenves 2001). Other programs that have been used include al. 2008). Another interesting benchmarking exercise, the ABAQUS, ADINA, PLAXIS, and FLAC. The UBC sand evaluation of site response at Turkey Flat (Real et al. 2006; model (Byrne et al. 1995; Beaty and Byrne 1998) has Kramer 2009), highlighted the challenges in computing gained acceptance in the geotechnical earthquake engi- the response at a well-constrained relatively stiff soil site. neering community and is available in FLAC and more Hashash et al. (2010) provide a recent review of many of the recently in PLAXIS. issues associated with 1-D nonlinear site response analysis. Pore Water Pressure Dissipation and Redistribution Models GUIDANCE DOCUMENTS FOR SITE RESPONSE ANALYSIS The layers in a soil column have finite, saturated hydraulic The FHWA guidance document for seismic design of highway conductivities. Even though loading is relatively rapid dur- facilities (FHWA-NHI-11-032: LRFD Seismic Analysis and ing ground shaking, pore water redistribution may occur at Design of Transportation Geotechnical Features and Struc- that time as a result of differences in hydraulic gradients and tural Foundations, 2011) is posted at hydraulic conductivities between layers, following the prin- engineering/engineering/geotech/pubs/nhi11032/nhi11032. ciples of Terzaghi's theory of consolidation. pdf. In the meantime, an older document (Kavazanjian et al. 1997a, b) that focuses on geotechnical analysis and design of Martin and Seed (1978) introduced an early model for highway facilities, including dynamic site characterization for pwp dissipation and redistribution. Input parameters include site response analysis, is still available for download. Several constrained rebound modulus and (saturated) hydraulic con- other guidance documents are used in transportation engineer- ductivity. The incorporation of such a model in nonlinear ing and other seismic design practices. These documents and codes, such as CyberQuake, DESRA-2C, D-MOD_2, D their websites are listed in Table 1. Many of these documents MOD2000, DEEPSOIL, ABAQUS, PLAXIS, FLAC, and were referred to by survey respondents (see chapter four). OpenSees, allows for calculation of simultaneous genera- tion, dissipation, and redistribution of pwp during and after Most of the DOTs documents follow, in some way, the shaking. A pwp dissipation model for composite soil depos- general guidelines for conducting a site response analysis its (alternating sand and clay layers), developed by Mataso- outlined in AASHTO documents. Some documents discuss vic and Vucetic (1995a), is incorporated in D-MOD_2 and the use of equivalent-linear analysis while others discuss the D-MOD2000. use of nonlinear site response analyses with and without pwp generation. However, with the exception of NRC RG 1.208: A PerformanceBased Approach to Define the Site-Specific CALIBRATION AND BENCHMARKING STUDIES Earthquake Ground Motion, these documents do not provide sufficient guidance on the mechanics and steps required for A number of individuals and groups have conducted eval- developing design ground motions, characterizing the site, uations of site response analysis procedures versus mea- or performing appropriate site response analysis. sured response from earthquake recordings and downhole vertical arrays. SOFTWARE USED IN PRACTICE Researchers have used a range of inverse analysis tech- niques to calibrate soil constitutive models in site response Table 2 lists and classifies currently available site response analysis procedures to discover soil behavior. These include analysis software. However, any listing of such programs is ad hoc, system identification (e.g., Zeghal and Elgamal 1993; likely to be incomplete and subject to interpretation. Glaser and Baise 2000; Assimaki and Steidl 2007), and evo- lutionary soil models (e.g., Tsai and Hashash 2007). Table 2 shows that geotechnical engineers have a variety of equivalent-linear and nonlinear software to choose from Kramer and Paulsen (2004) conducted an informal sur- for 1-D and multidimensional site response analyses. Some vey on the practical use of site response analysis models. of the software is widely used, for example SHAKE and They found that 1-D equivalent-linear site response analysis its numerous DOS- and Windows-based derivatives. Some is by far the most commonly used approach and that there is of the Windows-based equivalent-linear software operates a lack of guidance on use of nonlinear site response analysis, as pre-processors and post-processors for SHAKE91 (e.g., so it is not used often. ProShake and SHAKE2000), whereas others were written from scratch (e.g., EERA and equivalent-linear mode of A number of benchmarking exercises have also been DEEPSOIL). The Windows-based software generally offers conducted to evaluate site response analysis tools. A key convenient plotting of input data (soil profile and ground recent exercise is the PEER benchmarking exercise for total motions) and resulting output. More important, they guide

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16 TABLE 1 GUIDANCE DOCUMENTS FOR SEISMIC DESIGN Document Website (if available) 1 Caltrans Seismic Design Criteria 2 Washington State Department of Transportation, Geotechnical Design Manual (2011) 3 Illinois Department of Transportation 4 AASHTO Guide Specifications for LRFD Seismic Bridge Design (1st Edition) (2010a) Revision to AASHTO Guide Specifications for LRFD Seismic Bridge Design 5 NCHRP Report 611 6 ASCE 7-05, ASCE 7-10 (pending) ASCE 4, ASCE 43-05 7 NRC RG 1.208: A Performance-Based Approach to Define the Site-Specific Earthquake Ground Motion 01-208/01-208.pdf 8 U.S. Army Corps of Engineers EM110-2-6050: Response Spec- tra and Seismic Analysis for Concrete Hydraulic Structures 9 Oregon Department of Transportation, Geotechnical Design Manual FinalGDM12-1009/Volume1GeotechDesignManualFinal_Dec2009.pdf 10 South Carolina Department of Transportation, Seismic Design Specifications for Highway Bridges 11 South Carolina Department of Transportation, Geotechnical Manual 12 Georgia Department of Transportation, Bridge and Structures Policy Manual BridgeandStructure/GDOT_Bridge_and_Structures_Policy_Manual.pdf 13 Rhode Island LRFD Bridge Design Manual TABLE 2 SITE RESPONSE SOFTWARE USED IN ENGINEERING PRACTICE Dimensions OI Equivalent-Linear Nonlinear DOS SHAKE/SHAKE91 AMPLE, DESRA-2C, DESRAMOD, D-MOD_2, DESRAMUSC, LS-Dyna, 1-D SUMDES, TESS, SIREN, Graphical User Interface ShakeEdit, ProShake, SHAKE2000, EERA, CyberQuake, D-MOD2000, DEEPSOIL, DEEPSOIL, WinMOC FLAC, NERA, VERSAT 1-D DOS FLUSH, SASSI, QUAD4/QUAD4M, DYNAFLOW, DYSAC2, TARA-2, FLUSH TARA-3 2-D / 3-D Graphical User Interface QUAKE/W, SUPER SASSI, SASSI2000 FLAC, PLAXIS, PLAXIS 3D, ABAQUS, OpenSees, VERSAT 2-D Notes: 1. Only the latest versions of a particular software are listed in Table 2. Full software reference is provided in Appendix C. 2. Several of the listed software have options to use more than one constitutive model, including equivalent-linear, bi-linear, and nonlinear models (e.g., FLAC, PLAXIS, ABAQUS, and D-MOD2000). 3. Several of the listed software have a pore water pressure generation option (e.g., D-MOD2000, DEEPSOIL, CyberQuake, DESRA-2C, DESRAMUSC, OpenSees, PLAXIS, TESS, SUMDES, DYSAC2, and FLAC). the user through the key elements of the input and reduce ates Inc., respectively). QUAKE/W is similar to QUAD4M, the number of errors. The importance of a user interface to but it does not calculate the average acceleration of sliding enhancing the quality of analysis cannot be overemphasized. mass as QUAD4M does and it has a Windows GUI. Nonlin- FLUSH, SASSI, and QUAD4M are well established and ear software for 1-D analyses with GUI are gaining popu- widely used 2-D, DOS-based, equivalent-linear programs. larity (e.g., as D-MOD2000 and DEEPSOIL in the United (Windows-based graphical user interfaces are available for States practice; Cyberquake in European practice). Nonlin- QUAD4M and SASSI, but they are proprietary to the United ear 2-D site response software with GUI, such as FLAC and States Army Corps of Engineers and Stevenson & Associ- PLAXIS, is also gaining acceptance.