An Introduction to the 2015 NEHRP Recommended Seismic Provisions for New Buildings and Other Structures

Transcription

1 An Introduction to the 2015 NEHRP Recommended Seismic Provisions for New Buildings and Other Structures David R Bonneville 1 and Andrew M Shuck 2 ABSTRACT The 2015 NEHRP Recommended Seismic Provisions for New Buildings and Other Structures (NEHRP Provisions) serves as the consensus resource document for US seismic codes and standards. The NEHRP Provisions are developed by the Building Seismic Safety Council (BSSC) through a five-year project sponsored by the Federal Emergency Management Agency (FEMA). The Provisions are developed for the BSSC by its Provisions Update Committee (PUC). The PUC is supported by a group of Issue Teams, which develop technical proposals in the form of either seismic provisions with commentary or resource papers. The proposals are in the form changes to ASCE 7-10 and Commentary (ASCE 7-10), which are adopted as the basis for the Provisions. This paper provides a summary the key topics included in the 2015 NEHRP Provisions. The authors served as Chair and Assistant to the Chair of the PUC in the 2015 cycle and present this work as part of FEMA and BSSC s commitment to ongoing outreach to the engineering community. 1 Senior Principal at Degenkolb Engineers in San Francisco, California and the Chair of the 2015 NEHRP Provisions Update Committee. 2 Associate III at Wiss, Janney, Elstner Associates in Emeryville, California and Assistant to the Chair of the 2015 NEHRP Provisions Update Committee.

2 AN INTRODUCTION TO THE 2015 NEHRP RECOMMENDED SEISMIC PROVISIONS FOR NEW BUILDINGS AND OTHER STRUCTURES David R Bonneville 1 and Andrew M Shuck 2 ABSTRACT The 2015 NEHRP Recommended Seismic Provisions for New Buildings and Other Structures (NEHRP Provisions) serves as the consensus resource document for US seismic codes and standards. The NEHRP Provisions are developed by the Building Seismic Safety Council (BSSC) through a five-year project sponsored by the Federal Emergency Management Agency (FEMA). The Provisions are developed for the BSSC by its Provisions Update Committee (PUC). The PUC is supported by a group of Issue Teams, which develop technical proposals in the form of either seismic provisions with commentary or resource papers. The proposals are in the form of changes to ASCE 7-10 and Commentary (ASCE 2010), which are adopted as the basis for the Provisions. This paper provides a summary the key topics included in the 2015 NEHRP Provisions. The authors served as Chair and Assistant to the Chair of the PUC in the 2015 cycle and present this work as part of FEMA and BSSC s commitment to ongoing outreach to the engineering community. Introduction The NEHRP Recommended Provisions for New Buildings and Other Structures (NEHRP Provisions, the Provisions) serve as a platform for advancing seismic analysis and design concepts that exist in the current edition of ASCE 7 Minimum Design Loads for Buildings and Other Structures (ASCE, 2010) based on recent research and experience, and for and introducing new seismic concepts prior to their introduction to ASCE 7. The Provisions are developed through a consensus process involving a Provisions Update Committee (PUC) consisting of a group of experts selected to cover the range of seismic concepts contained in the Provisions. The PUC selects relevant topics it considers most appropriate for development within the five-year update cycle. Topics are then assigned to Issue Teams, which include both PUC members and others with expertise in the issues being considered. The 2015 edition of the NEHRP Provisions is being developed by the Building Seismic Safety Council (BSSC) through a five-year contract sponsored by the Federal Emergency Management Agency (FEMA). As initiated in the 2009 edition, the NEHRP Provisions are presented in three parts. Part 1 includes consensus-approved modifications to ASCE/SEI Part 2 provides commentary, also consistent with ASCE/SEI 7-10, and Part 3 contains resource papers covering material 1 Senior Principal at Degenkolb Engineers in San Francisco, California and the Chair of the 2015 NEHRP Provisions Update Committee. 2 Associate III at Wiss, Janney, Elstner Associates in Emeryville, California and Assistant to the Chair of the 2015 NEHRP Provisions Update Committee.

3 intended to stimulate discussion from the engineering community on new seismic design concepts. BSSC policies and procedures require that material developed for the Provisions, whether by Issue Teams or by the PUC itself, go through balloting by the PUC then, following approval by the BSSC Board of Direction, though balloting by the 50 BSSC member organizations. Primary Topics Addressed by the PUC and Issue Teams Evaluation and Quantification of Seismic Performance Objectives This effort includes a consideration of the Intent of the Provisions, in terms of the seismic performance expectations inherent in the current design provisions, and consideration of modifications of the design provisions to achieve enhanced seismic performance in future codes. The Intent language in our current Provisions (Section 1.1) defines life safety in terms of collapse resistance for all occupied buildings and addresses in general terms the loss of function for essential facilities and repair costs for all risk categories. For ordinary (Risk Category II) buildings in areas where the ground motion is probabilistically defined, the targeted performance is a 10% (or lower) collapse probability in the very rare Risk Targeted Maximum Considered Earthquake Ground Motion (MCE R ). In areas close to major active faults, the MCE R ground motion is deterministically defined using a shaking intensity that is one standard deviation above the mean ground motion resulting from a characteristic earthquake on the fault, and in these locations a higher collapse risk is possible. Lower collapse probabilities are defined for facilities housing essential functions or containing hazardous materials (Risk Category IV) and for those housing large or less mobile populations (Risk III), in which approximately 2.5% and 5% collapse probabilities respectively are targeted in the MCE R ground motion. Unlike life safety (addressed through collapse prevention), loss of function and economic loss are not quantitatively defined in the Provisions and this is considered to be a key area of future development for new building performance. In this update cycle a clear consensus did not emerge as to how the Provisions could be modified within Part 1 to address these performance measures. However, Part 3 of the Provisions contains a resource paper that summarizes discussions related to functional loss in terms of a functional level earthquake ground motion that is reduced from the MCE R ground motion and discusses economic loss without explicitly defining it. Nonstructural damage affecting life safety and functional loss is also discussed. The Provisions developments related to functional and economic loss were supported substantially by two Applied Technology Council (ATC) projects. Input was provided from the National Institute of Standards and Technology (NIST) funded project, ACT-84 Tentative Framework for Development of Advanced Seismic Design Criteria for New Buildings 100 % Draft (ATC, 2012), Charles Kircher, Project Director. In addition, the Applied Technology Council (ATC) was awarded a FEMA contract to benchmark building code (structural and nonstructural) performance on various building types using established FEMA methodologies, including FEMA P-695 Quantification of Building Seismic Performance Factors (ATC, 2009), Charles Kircher - Project Technical Director, for collapse prevention and FEMA P-58 Seismic Performance Assessment of Buildings 100% Draft (ATC, 2012), Ronald Hamburger - Project Technical Director, for all other performance levels. That project, titled ATC

4 Development of Seismic Performance and Methodology Calibration, Ronald Hamburger - Project Technical Director, provided valuable input into the discussions. Response History Analysis The 2015 Provisions provide a complete revision to the Seismic Response History Analysis (RHA) requirements given in Chapter 16 of ASCE/SEI The PUC judged that the current requirements lack specificity in many areas, leading to inconsistencies in interpretation. In the new provisions, collapse performance goals discussed above under the Evaluation and Quantification of Seismic Performance Objectives section are implicitly demonstrated through a prescribed set of analysis rules and acceptance criteria. The procedure is intended to provide buildings with equivalent or better seismic performance compared to designs using the Chapter 12 procedures. It includes a code-level evaluation of the building using either the Equivalent Lateral Force Procedure or the Modal Response Spectrum Procedure for the purpose of assuring that the structure designed using the RHA provisions will be equivalent in terms of strength (though not necessarily displacement). The nonlinear analysis is then performed to demonstrate that the structure has predictable and stable response under MCE R level ground shaking and to determine forces for force-controlled components. Service-level evaluation (to address for example Risk Category IV buildings) is not required because ground motion for such analysis is not provided by Chapters 11 and 12. The level of ground motion is defined by target spectra that may be derived from either the MCE R spectrum, which conservatively envelopes the results of seismic hazard analysis for each period, or a Conditional Mean Spectrum, in which the spectrum is calculated based on a spectral acceleration at an appropriate period and the mean of spectral acceleration values at other periods. The procedure requires eleven ground motions (selected based on judgment) representing near-field (if appropriate) and far field sites. The procedure specifies the lower bound (0.2T) and upper bound (generally 2.0T) period range for ground motions to be scaled to so they are representative of the site specific MCE R spectrum. Modeling requirements are given with the intent of reasonably capturing the spatial and temporal distributions of inelasticity. Three-dimensional analysis is required for the final analysis and requirements are specified for realistically addressing gravity loading, P-delta effects and diaphragm modeling to cover the range of expected stiffness. Inherent torsion is addressed through the modeling requirements in a manner similar to that given in Chapter 12 and accidental torsion is not required to be explicitly modeled (a rigorously debated issue), though the commentary provides recommendations for addressing buildings likely to perform in a highly torsional manner. Acceptance criteria are expressed in terms of global response in which unacceptable performance is defined based on possible collapse, story drift, non-convergence, deformationcontrolled response and force-based demands for brittle components; and element-level response, considering both deformation and force-controlled actions.

5 Design review is required for all structures designed in accordance with the RHA procedure. The review is required to be performed by one or more individuals with experience in ground motion selection and scaling, analytical modeling and structural system behavior. Diaphragm Issues The diaphragm provisions in ASCE 7-10 (and previous editions) take an elastic design approach for diaphragm elements, basing the forces on a multiple of the floor force calculated using the Equivalent Lateral Force (ELF) procedure. This has historically resulted in generally acceptable seismic diaphragm performance for most building configurations and diaphragm material types. Recent study has shown that the actual force levels imposed on diaphragms during ground shaking can be significantly higher than those currently in the code, however. The effects of higher modes than the first mode were found to contribute significantly to diaphragm response, and these findings prompted an investigation into the entire process of diaphragm design. The 2015 Provisions contain new equations for force demands that reflect test and analysis results and that yield larger design forces. Since diaphragms designed with the current procedure are generally well-behaving, though, the capacity side of diaphragm design has also been addressed. Results of component testing show that the observed ductility capacity of diaphragm systems compensates for these proposed higher design forces. In short, demands were previously underestimated but were also assessed against unrealistically limited elastic capacities. The new procedure, despite its higher calculated demands, yields a similar final design because of the additional consideration of diaphragm ductility. For diaphragms constructed of most materials (wood sheathing, metal deck, etc.), these provisions only mean an improved understanding of seismic diaphragm behavior, but the new procedure is more critical for precast concrete diaphragms. Tests show that, compared to other systems, precast concrete diaphragms have limited ductility; more specifically, the long diaphragm spans that precast diaphragms lend themselves to cause the relatively low performance of the system. The new diaphragm design procedure in the 2015 NEHRP Provisions is an alternative for all materials besides precast concrete. The provisions require the revised design procedure for precast diaphragms to balance the discrepancy between higher design forces and low seismic ductility. Base Isolation and Energy Dissipation Devices The chapters of the Provisions regarding base isolation and energy dissipation (based on Chapters 17 and 18 of ASCE 7-10, respectively) were revised to improve the design process for structures using these technologies. The provisions were arranged into a more logical structure based on the most commonly used design techniques for base isolation and energy dissipation. Updated considerations for design value variability, quality control, and quality assurance have been incorporated that take advantage of the knowledge base that has been built up over many years of extensive testing programs for base isolators and dampers.

6 Base isolation procedures now check force and displacement demands at the MCE R ground motion level because of the severe consequences of exceeding the limits of an isolation system (pounding as a result of isolator displacements exceeding the isolation moat gap, e.g.). Energy dissipation system design requires use of Design Earthquake and MCE R forces to achieve similar performance levels to the revised Base Isolation provisions. In addition, the ELF procedure for base-isolated structures has been expanded and adopts the multi-point design spectrum developed by the ground motion mapping team. This allows the demands at the longer periods experienced by isolated structures to be calculated with more confidence, while using the relatively simple and common ELF procedure. The combination of the Provisions structure, quality control requirements, and design procedure simplifications should encourage wider use of these technologies, which have been around for long enough to have gained the confidence of the industry as a whole. Soil Structure Interaction The Soil Structure Interaction (SSI) provisions are intended to allow a more complete and accurate analysis of the combined system including structure, foundation and underlying soil/rock, compared to the traditional fixed base assumption assuming free-field ground motions. The 2015 Provisions provide a complete revision to the ASCE 7-10 Chapter 19 SSI requirements, and allow the designer to account for foundation deformations, inertial effects and kinematic effects. Foundation deformations are addressed through requirements for capturing the translational and rotational movement at the soil-structure interface, either with elastic spring elements in the linear methods or through nonlinear modeling in the case of response history analysis. Inertial effects are addressed through consideration of foundation damping, including radiation damping (damping associated with wave propagation away from the structure) and hysteretic soil damping. Kinematic effects, which were not addressed in previous editions of ASCE 7, include base slab averaging, accounting for the incoherence of ground motions on large area foundations, and embedment effects, accounting for ground motion reductions with depth. Most of the changes to this chapter are based on recommendations from a NIST sponsored project titled Soil-Structure Interaction for Building Structures (NIST, 2012). The provisions impose several limitations on ground motion modifications (reductions) due to SSI effects. First, modifications due to kinematic effects are not permitted in either the ELF or MRS procedures since it was judged that these effects have not been studied sufficiently to determine whether they are valid for an inelastic spectrum, on which the R-factor assumptions are based. Additionally there was concern that reductions due to period lengthening resulting from inelastic yielding may not be accounted for in these analyses, leading to a possible overestimate of the reduction in response parameters. Also for the ELF and MRS procedures the maximum total reduction (from foundation damping) is limited to a percentage of the base shear, reflecting the limited understanding of how SSI effects interact with the R-factor. The reduction varies with R-factor and is permitted only for R=3 of less; the maximum reduction is limited to 30 percent.

7 All types of SSI reductions are permitted with the RHA. The analysis is required to be based on a site-specific response spectrum because it is judged that the more detailed knowledge of the site associated with this approach (as opposed to the general response spectrum based on mapped acceleration parameters) is needed for proper consideration of SSI effects. The design response accelerations modified for kinematic effects are permitted to be reduced to 80 percent of the site specific values, but not less than 70 percent of the standard (non-site specific) Chapter 11 spectrum. The number is reduced to 60 percent for designs that are peer reviewed. Consideration of foundation damping effects is to be based on direct incorporation of dashpot elements at the soil-foundation interface. Strength Design of Foundations The 2015 NEHRP Provisions allow for building foundations and the supporting soils to be designed using the strength design philosophy, or Load and Resistance Factor Design (LRFD). Traditional geotechnical engineering practice provides foundation recommendations based on allowable bearing stresses. It is common practice for allowable soil stresses for gravity loads to be arbitrarily increased by one-third for load combinations that include seismic forces. This practice is overly conservative and not consistent with the design basis of the NEHRP Provisions or ASCE/SEI 7, however, since it is not based on nominal soil strength or the dynamic properties of site soils. The new Provisions utilize foundation design forces that are modified to incorporate an R-factor-dependent multiplier into the forces. For example, non-light-framed systems need to be designed for horizontal earthquake effects, E h, of E h = (0.3R)ρQ E Q E (1) Where ρ is the redundancy factor and Q E is the effect of horizontal seismic forces. This equation is intended to force nonlinear mechanisms to occur primarily in the supported structure above the foundation, as this is the portion of the structure that dictates the R-factor. Buildings with small R-factors will not see an increase in force and it is anticipated that foundation mechanisms like rocking or sliding may develop for these structures. LRFD capacity procedures and reduction factors are also provided in the new sections. The Provisions have guidance for strength determination, resistance mechanism combinations, and presumptive capacity that result in nominal strengths consistent with the LRFD philosophy. Reduction factors (φ factors) are 0.45 for vertical resistance, 0.5 for lateral bearing pressure, and 0.85 for sliding. Soil Site Factors and Liquefaction The Provisions contain updated values for the F a and F v coefficents that scale the mapped spectral values S s and S 1 to obtain acceleration response parameters for sites with soil classification other than Site Class B. These coefficients were originally developed in the 1990s based primarily on recorded motions from the 1989 Loma Prieta Earthquake. Studies at the Pacific Earthquake Engineering Research Center considered shaking data from more recent earthquakes and combined this information with models of site nonlinearity to derive new coefficients. In general, the values for F a and F v are now somewhere between 80% and 120% of

8 their previously tabulated values. In addition, the new factors show that Site Class D is not necessarily the worst case (and, therefore, default) soil for all levels of seismicity, so an additional table has been added to clarify which amplification factors to use by default for undetermined soil classifications. Previous editions of the Provisions only included requirements for geotechnical investigations at liquefiable sites and there were no requirements for structures and their foundations on such sites. In an effort to standardize and guide liquefaction design, the Provisions now require that buildings be assessed for the potential consequences of liquefaction and soil strength loss, including but not limited to: estimated total and differential settlement, lateral soil movement, lateral loads on foundations, reduction of foundation soil bearing capacity, reduction of axial and lateral soil reaction on piles, and floatation of buried structures. These criteria are analyzed on the basis of peak ground accelerations, earthquake magnitudes, and source characteristics associated with MCE G peak ground accelerations, where MCE G represents the Maximum Considered Earthquake geometric mean ground motion. Evaluating liquefaction for MCE G ground motions is intended to minimize risk of collapse for the rare MCE ground motion, rather than at the building design level, which assumes a certain level of reserve building structural capacity. Design Mapping Similar to previous editions of the NEHRP Provisions, the 2015 Provisions contain updated seismic hazard maps developed by USGS. In 2008 (i.e., for the 2009 Provisions) the design maps were changed significantly, including the use of risk-targeted ground motions, maximum direction ground motions, and near-source 84th percentile ground motions. Mapping changes made by the USGS during this cycle were of a lesser magnitude. The new maps reflect findings from the last five years, driven primarily by regional seismic hazard model projects like UCERF 2. Updated MCE R spectral values are generally similar to previous values, but some locations do see a significant rise in their mapped accelerations. This is caused by longer assumed rupture lengths for the characteristic event that drives the deterministic hazard level; increasing the deterministic capping accelerations means that the probabilistic earthquake now governs at these locations. The values will be available in the Provisions and on the USGS website. The team in charge of updating the hazard maps also made a change to the 2015 IBC in order to implement a critical design change ahead of the typical adoption schedule. The hazard maps for Guam and American Samoa had previously been based only on judgment of the regional seismicity and not on rigorous studies. Such studies, when completed recently, showed that the hazard levels were substantially different from the previous values. For example, S s for Guam was updated to 2.87g from 1.5g, while S s for Tutuila in American Samoa was updated to 0.42g from 1.0g. These changes to the 2015 IBC mean that designs in Guam and American Samoa will incorporate this improved information much faster than would have otherwise been the case. The Provisions contain a number of additional ground motion-related updates that were done in support of other PUC efforts. Most importantly, there is now an alternative USGS-

9 provided design spectrum with substantially more resolution (i.e., more points than the traditional two-point spectrum) available to engineers. This spectrum contains detailed information based on the specific site conditions and defines the hazard at periods much longer than the currently referenced one second acceleration, S 1. Base isolation design will benefit the most from these provisions, as those structures depend heavily on knowledge of long-period accelerations. Additional Topics Incorporation of FEMA P695 and P795 FEMA P695 Quantification of Building Seismic Performance Factors (ATC, 2009) is a methodology to quantify the seismic performance factors for code-defined structural systems and to verify the adequacy of proposed new systems. FEMA P795 Component Equivalency Method (ATC, 2011) is a component-based methodology for verifying equivalency of components, connections and sub-assemblies proposed for substitution into an established structural system. Since their publication, P695 and P795 have been generally accepted as the most appropriate approach to assigning seismic design coefficients to new systems and for qualifying new components. The Provisions provide recommendations for adoption of these methodologies or other analytical approaches for justifying seismic design coefficients for alternative systems and for establishment of equivalency of new components. Simplified Seismic Design Category B Procedure The Provisions contain a new chapter, Chapter 24, that is a simplified, alternate seismic design procedure for structures in Seismic Design Category (SDC) B. A structure in SDC B designed using Chapter 24 is similar to a design using Chapter 12, but the engineer has the convenience of an abbreviated document to work within. For example, Chapter 24 does not contain the special lateral force resisting systems, removes T L from the calculation for the base shear coefficient, and only contains Chapter 13 requirements for parapet and hazardous materials provisions. A number of further simplifications arose from the effort to develop Chapter 24 as a standalone document. These include site factors for a subcategory of Site Class F soils, elimination of E v (vertical earthquake effects) in SDC B design, and exempting SDC B structures from accidental torsion checks unless they have Type 1B horizontal irregularities. Seismic Anchorage to Concrete PUC studies have been made in response to general concerns related to the complexity and possibly the conservatism inherent in the application of ACI Building Code Requirements for Structural Concrete (ACI, 2011) Appendix D. A Part 3 Resource Paper supports the technical basis for the Appendix D provisions, and provides discussion related to the following issues: evaluation of overstrength values for design and evaluation of non-yielding anchorage; consideration of material ductility and post-yield strength; evaluation of interaction

10 of connection parts; evaluation of stretch length and use of reinforcement as a yielding element; evaluation of pre-load and creep; and evaluation of concrete failure behavior and limit states. Rigid Wall/Flexible Diaphragm Buildings Building code provisions have traditionally defined system ductility in terms of the vertical elements of the lateral force resisting system, with more than 80 lateral systems defined in the table of seismic design coefficients. Many large footprint, low-rise buildings have long walls or braced frames at the perimeter with flexible diaphragms spanning between that experience significant mass participation in the diaphragm vibration modes. The behavior of these buildings is not reflected by the current practice of calculating design forces prescribed only on the basis of the vertical lateral force resisting system. Using recent studies as a basis, a Resource Paper in the Provisions outlines a new design procedure for structures dominated by diaphragm behavior. Modifications to Section of ASCE 7 The Provisions contain updates to Section of ASCE 7, the Simplified Seismic Design Procedure. The procedure has been streamlined to remove the fifteen percent massrigidity check, making the process more straightforward. In addition, all diaphragms, regardless of their actual rigidity, are allowed to be proportioned as if they are flexible diaphragms. This change is a result of extensive analysis that showed that buildings within the scope of section that were designed based on a flexible diaphragm assumption performed well. Modal Response Spectrum Analysis Engineers have long used Modal Response Spectrum Analysis (MRSA) as a tool to model the dynamic behavior of structures under seismic loading. MRSA can provide a good approximation of more sophisticated tools if structural ductility is limited and it requires only a fraction of the computing power used for nonlinear analyses. In cases where there is a large amount of nonlinearity, systems designed with R=8, e.g., the procedure becomes less accurate. The 2015 NEHRP Provisions address a number of problems with the previous MRSA provisions, including: removing the 15% reduction in base shear relative to the equivalent lateral force procedure, modifying the requirements for mass participation, requiring 3D analysis models, and updating the commentary associated with modal response combination techniques. In addition, a number of items have been targeted for further study during the next Provisions update cycle, including limiting ductility in modes that will behave elastically and the appropriate structural response parameter to use for scaling the analysis results. Concluding Remarks The 2015 NEHRP Provisions is intended to serve as a nationally applicable resource document including Part 1 charging language based on and modifying ASCE/SEI 7-10, Part 2 detailed commentary also consistent with ASCE/SEI 7-10, and Part 3 introducing of new technologies. This paper provides an overview of the work that went into the Provisions update project and is intended to contribute to the FEMA goal of outreach to the engineering community. The material in the Provisions represents the state of the art for many topics within

11 earthquake engineering and was developed by committed volunteers with specialties ranging across the technical spectrum of the practice. The updates to these topics, which were adjudged at the beginning of the 2015 NEHRP Provisions cycle as needing particular attention, represent a net progression towards reducing the earthquake hazard facing the public. Acknowledgements The authors wish to acknowledge those who are volunteering their time on the 2015 Provisions update effort, particularly the Provision Update Committee and the Issue Team chairs and members. In addition it is recognized that the Provisions update effort would not be possible without funding and technical support from FEMA and the staff of BSSC. References 1. American Society of Civil Engineers (ASCE), 2005, Minimum Design Loads for Buildings and Other Structures, (ASCE/SEI 7-05), ASCE, Reston, Virginia. 2. American Society of Civil Engineers (ASCE), 2010, Minimum Design Loads for Buildings and Other Structures, (ASCE/SEI 7-10), ASCE, Reston, Virginia. 3. Building Seismic Safety Council (BSSC), 2009, NEHRP Recommended Seismic Provisions for New Buildings and Other Structures, (FEMA P-750), prepared for the Federal Emergency Management Agency, Washington, DC. 4. Applied Technology Council (ATC), 2009, Quantification of Building Seismic Performance Factors, (FEMA P-695), prepared for the Federal Emergency Management Agency, Washington, DC. 5. Applied Technology Council (ATC), 2011, Component Equivalency Method, (FEMA P-795), prepared for the Federal Emergency Management Agency, Washington, DC. 6. Applied Technology Council (ATC), 2012, ACT-58 Seismic Performance Assessment of Buildings 100 % Draft, Applied Technology Council, Redwood City, California. 7. Applied Technology Council (ATC), 2012, ACT-84 Tentative Framework for Development of Advanced Seismic Design Criteria for New Buildings 100 % Draft, Applied Technology Council, Redwood City, California. 8. National Institute of Standards and Technology (NIST), Soil-Structure Interaction For Building Structures, Report No. NIST GCR , National Institute of Standards and Technology, U.S. Department of Commerce, Washington D.C. Project Technical Committee: Stewart, JP (Chair), CB Crouse, T Hutchinson, B Lizundia, F Naeim, and F Ostadan Working Group on California Earthquake Probabilities, The Uniform California Earthquake Rupture Forecast, Version 2 (UCERF 2), USGS Open File Report , U.S. Geological Survey, Reston, Virginia. 10. American Concrete Institute (ACI) Committee 318, 2011, Building Code Requirements for Structural Concrete, ACI , and Commentary, American Concrete Institute, Farmington Hills, Michigan.