FEMA P 1051Earthquakes2015NEHRPProvisionsDesignExamples 2016
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FEMA P-1051, Earthquakes 2015 NEHRP Provisions Design Examples
| Published By | Publication Date | Number of Pages |
| FEMA | 2016 | 995 |
None
PDF Catalog
| PDF Pages | PDF Title |
|---|---|
| 3 | Recommended Seismic Provisions: Design Examples H1 FEMA P-1051/ July 2016 |
| 9 | 2.Fundamentals |
| 25 | 1.1 EVOLUTION OF EARTHQUAKE ENGINEERING |
| 29 | 1.2 HISTORY AND ROLE OF THE NEHRP PROVISIONS |
| 31 | 1.3 THE NEHRP DESIGN EXAMPLES |
| 34 | 1.4 REFERENCES |
| 35 | Contents |
| 36 | 2.1 EARTHQUAKE PHENOMENA |
| 38 | 2.2 STRUCTURAL RESPONSE TO GROUND SHAKING 2.2.1 Response Spectra |
| 44 | 2.2.2 Inelastic Response |
| 47 | 2.2.3 Building Materials |
| 48 | 2.2.4 Building Systems |
| 49 | 2.2.5 Supplementary Elements Added to Improve Structural Performance 2.3 ENGINEERING PHILOSOPHY |
| 51 | 2.4 STRUCTURAL ANALYSIS |
| 52 | 2.5 NONSTRUCTURAL ELEMENTS OF BUILDINGS |
| 53 | 2.6 QUALITY ASSURANCE |
| 57 | 3.1 BASIS OF EARTHQUAKE GROUND MOTION MAPS 3.1.1 MCE Ground Motion Intensity Maps in ASCE 7-05 and Earlier Editions |
| 58 | 3.1.2 MCER Ground Motions Introduced in the 2009 Provisions and ASCE 7-10 |
| 60 | 3.1.3 PGA Maps Introduced in the 2009 Provisions and ASCE 7-10 |
| 61 | 3.1.4 Long-Period Transition Period (TL) Maps Introduced in ASCE 7-05 3.1.5 Vertical Ground Motions Introduced in the 2009 Provisions 3.1.6 Updated MCER Ground Motion and PGA Maps in the 2015 Provisions and ASCE 7-16 |
| 62 | 3.1.7 Summary 3.2 DETERMINATION OF GROUND MOTION VALUES AND SPECTRA 3.2.1 ASCE 7-10 MCER Ground Motion Values |
| 63 | 3.2.2 2015 Provisions and ASCE 7-16 MCER Ground Motion Values |
| 64 | 3.2.3 2015 Provisions and ASCE 7-16 Horizontal Response Spectra |
| 65 | 3.2.4 ASCE 7-16 Vertical Response Spectra |
| 66 | 3.2.5 ASCE 7-10 Peak Ground Accelerations |
| 67 | 3.2.6 2015 Provisions and ASCE 7-16 Peak Ground Accelerations 3.3 SITE-SPECIFIC GROUND MOTION SPECTRA |
| 68 | 3.3.1 Site-Specific MCER and Design Ground Motion Requirements |
| 69 | 3.3.2 Site-Specific Seismic Hazard Characterization 3.3.3 Example Site-Specific MCER and Design Ground Motion Spectra |
| 83 | 3.4 SELECTION AND SCALING OF GROUND MOTION RECORDS 3.4.1 Nonlinear Response History Selection and Scaling |
| 92 | 3.4.2 Linear Response History Selection and Scaling |
| 94 | 3.4.3 With Seismic Isolation and Damping Systems Selection and Scaling |
| 100 | 3.5 REFERENCES |
| 107 | 4.1 NEW PROVISIONS FOR LINEAR DYNAMIC ANALYSIS IN FEMA P-1050 AND ASCE 7-16 4.1.1 Changes in the ASCE 7-16 Standard |
| 108 | 4.1.2 Differences between ASCE 7-16 and the 2015 NEHRP Provisions. |
| 109 | 4.2 THEORETICAL BACKGROUND 4.2.1 Analysis Procedures 4.2.1.1 Linear Response History Analysis by Direct Integration of the Equations of Motion. |
| 115 | 4.2.2 Modeling Systems for 3-D Response |
| 117 | 4.2.3 Selection and Modification of Ground Motions |
| 120 | 4.2.4 Runtimes and Storage Requirements 4.3 EXAMPLE APPLICATION FOR 12-STORY SPECIAL STEEL MOMENT FRAME STRUCTURE |
| 121 | 4.3.1 Description of Building and Lateral Load Resisting System |
| 125 | 4.3.2 Analysis and Modeling Approach |
| 128 | 4.3.3 Seismic Weight and Masses |
| 130 | 4.3.4 Preliminary Design using the ELF Procedure |
| 134 | 4.3.5 Modal Properties |
| 140 | 4.3.6 Analysis Results |
| 188 | 5.1 OVERVIEW OF EXAMPLE AND GENERAL REQUIREMENTS 5.1.1 Summary of the Chapter 16 Design Approach |
| 189 | 5.1.2 Description of Example Building and Site |
| 191 | 5.1.3 Linear Analysis for Initial Proportioning 5.1.4 Project-Specific Design Criteria |
| 202 | 5.2 GROUND MOTIONS 5.3 STRUCTURAL MODELING |
| 203 | 5.3.1 Overview of Modeling |
| 207 | 5.3.2 Gravity Load 5.3.3 P-Delta Effects |
| 208 | 5.3.4 Torsion 5.3.5 Damping 5.3.6 Foundation Modeling and Soil-Structure Interaction 5.4 ACCEPTANCE CRITERIA |
| 209 | 5.4.1 Global Acceptance Criteria |
| 211 | 5.4.2 Element-Level Acceptance Criteria |
| 231 | 5.5 SUMMARY AND CLOSING |
| 232 | 5.6 REFERENCES |
| 237 | 6.1 STEP-BY-STEP DETERMINATION OF TRADITIONAL DIAPHRAGM DESIGN FORCE |
| 238 | 6.2 STEP-BY-STEP DETERMINATION OF ALTERNATIVE DIAPHRAGM DESIGN FORCE Step 1: Determine wpx (ASCE 7-16 Section 12.10.3.2) Step 2: Determine Rs, Diaphragm Design Force Reduction Factor (ASCE 7-16 Table 12.10.3.5-1) |
| 239 | Step 3: Determine Cpx, Diaphragm Design Acceleration (Force) Coefficient at Level x (ASCE 7-16 Section 12.10.3.2) |
| 241 | Step 4: Determine Fpx, Diaphragm Design Force at Level x (Section 12.10.3.2) 6.3 DETAILED STEP-BY-STEP CALCULATION OF DIAPHRAGM DESIGN FORCES FOR EXAMPLE BUILDINGS |
| 242 | Example – One Story Wood Assembly Hall |
| 245 | Example – Three-Story Multi-Family Residential |
| 253 | 6.4 COMPARISON OF DESIGN FORCE LEVELS 4-Story Perimeter Wall Precast Concrete Parking Structure (SDC C, Knoxville) |
| 255 | 4-Story Interior Wall Precast Concrete Parking Structure (SDC D, Seattle) |
| 256 | 8-Story Precast Concrete Moment Frame Office Building |
| 257 | 8-Story Precast Concrete Shear Wall Office Building |
| 259 | Steel-Framed Assembly Structure in Southern California |
| 261 | Steel-Framed Office Structure in Seattle, WA |
| 262 | Cast-in-Place Concrete Framed Parking Structure in Southern California |
| 263 | Cast-in-Place Concrete Framed Residential Structure in Northern California |
| 264 | Cast-in-Place Concrete Framed Residential Structure in Seattle, WA |
| 265 | Cast-in-Place Concrete Framed Residential Structure in Hawaii |
| 266 | Steel Framed Office Structure in Southern California 6.5 SEISMIC DESIGN OF PRECAST CONCRETE DIAPHRAGMS |
| 267 | Step 1: Determine Diaphragm Seismic Demand Level |
| 268 | Step 2: Determine Diaphragm Design Option and Corresponding Connector or Joint Reinforcement Deformability Requirement Step 3: Comply with Qualification Procedure Step 4: Amplify Required Shear Strength |
| 269 | 6.6 PRECAST CONCRETE DIAPHRAGM CONNECTOR AND JOINT REINFORCEMENT QUALIFICATION PROCEDURE |
| 271 | 6.7 ACKNOWLEDGEMENT |
| 275 | 7.1 SHALLOW FOUNDATIONS FOR A SEVEN-STORY OFFICE BUILDING, LOS ANGELES, CALIFORNIA 7.1.1 Basic Information |
| 279 | 7.1.2 Design for Moment-Resisting Frame System |
| 287 | 7.1.3 Design for Concentrically Braced Frame System |
| 294 | 7.2 DEEP FOUNDATIONS FOR A 12-STORY BUILDING, SEISMIC DESIGN CATEGORY D 7.2.1 Basic Information |
| 303 | 7.2.2 Pile Analysis, Design and Detailing |
| 318 | 7.2.3 Kinematic Interaction |
| 319 | 7.2.4 Design of Pile Caps 7.2.5 Foundation Tie Design and Detailing |
| 320 | 7.3 FOUNDATIONS ON LIQUEFIABLE SOIL |
| 338 | 8.1 SOIL-STRUCTURE INTERACTION OVERVIEW |
| 340 | 8.2 GEOTECHNICAL ENGINEERING NEEDS |
| 341 | 8.3 FLEXIBLE BASE EXAMPLE |
| 344 | 8.3.1 Fixed Base Building Design |
| 345 | 8.3.2 Flexible Base Design |
| 346 | 8.3.3 Soil and Foundation Yielding |
| 347 | 8.4 FOUNDATION DAMPING EXAMPLE |
| 348 | 8.4.1 Radiation Damping |
| 350 | 8.4.2 Soil Damping 8.4.3 Foundation Damping 8.4.4 Linear procedure |
| 354 | 8.4.5 Nonlinear procedures 8.5 KINEMATIC INTERACTION |
| 355 | 8.5.1 Base-slab averaging |
| 356 | 8.5.2 Embedment 8.5.3 Nonlinear Example |
| 363 | 9.1 INDUSTRIAL HIGH-CLEARANCE BUILDING, ASTORIA, OREGON 9.1.1 Building Description |
| 367 | 9.1.2 Design Parameters |
| 368 | 9.1.3 Structural Design Criteria |
| 370 | 9.1.4 Analysis |
| 376 | 9.1.5 Proportioning and Details |
| 398 | 9.2 SEVEN-STORY OFFICE BUILDING, LOS ANGELES, CALIFORNIA 9.2.1 Building Description |
| 401 | 9.2.2 Basic Requirements |
| 402 | 9.2.3 Structural Design Criteria |
| 404 | 9.2.4 Analysis and Design of Alternative A: SMF |
| 420 | 9.2.5 Analysis and Design of Alternative B: SCBF |
| 434 | 10.1 INTRODUCTION |
| 438 | 10.2 SEISMIC DESIGN REQUIREMENTS 10.2.1 Seismic Response Parameters |
| 439 | 10.2.2 Seismic Design Category 10.2.3 Structural Systems 10.2.4 Structural Configuration |
| 440 | 10.2.5 Load Combinations |
| 441 | 10.2.6 Material Properties 10.3 DETERMINATION OF SEISMIC FORCES 10.3.1 Modeling Criteria |
| 442 | 10.3.2 Building Mass |
| 444 | 10.3.3 Analysis Procedures 10.3.4 Development of Equivalent Lateral Forces |
| 450 | 10.3.5 Direction of Loading 10.3.6 Modal Analysis Procedure |
| 452 | 10.4 DRIFT AND P-DELTA EFFECTS 10.4.1 Torsion Irregularity Check for the Berkeley Building |
| 454 | 10.4.2 Drift Check for the Berkeley Building |
| 458 | 10.4.3 P-delta Check for the Berkeley Building |
| 460 | 10.4.4 Torsion Irregularity Check for the Honolulu Building 10.4.5 Drift Check for the Honolulu Building |
| 462 | 10.4.6 P-Delta Check for the Honolulu Building |
| 463 | 10.5 STRUCTURAL DESIGN OF THE BERKELEY BUILDING |
| 464 | 10.5.1 Analysis of Frame-Only Structure for 25 Percent of Lateral Load |
| 466 | 10.5.2 Design of Moment Frame Members for the Berkeley Building |
| 490 | 10.5.3 Design of Frame 3 Structural Wall |
| 496 | 10.6 STRUCTURAL DESIGN OF THE HONOLULU BUILDING 10.6.1 Compare Seismic Versus Wind Loading |
| 499 | 10.6.2 Design and Detailing of Members of Frame 1 |
| 514 | 11.1 HORIZONTAL DIAPHRAGMS 11.1.1 Untopped Precast Concrete Units for Five-Story Masonry Buildings Assigned to Seismic Design Categories B and C |
| 532 | 11.1.2 Topped Precast Concrete Units for Five-Story Masonry Building Assigned to Seismic Design Category D |
| 542 | 11.2 THREE-STORY OFFICE BUILDING WITH INTERMEDIATE PRECAST CONCRETE SHEAR WALLS 11.2.1 Building Description |
| 543 | 11.2.2 Design Requirements |
| 545 | 11.2.3 Load Combinations 11.2.4 Seismic Force Analysis |
| 548 | 11.2.5 Proportioning and Detailing |
| 560 | 11.3 ONE-STORY PRECAST SHEAR WALL BUILDING 11.3.1 Building Description |
| 562 | 11.3.2 Design Requirements |
| 564 | Load Combinations 11.3.3 Seismic Force Analysis |
| 567 | 11.3.5 Proportioning and Detailing |
| 579 | 11.4 SPECIAL MOMENT FRAMES CONSTRUCTED USING PRECAST CONCRETE 11.4.1 Ductile Connections |
| 580 | 11.4.2 Strong Connections |
| 587 | 12.1 BUILDING DESCRIPTION |
| 590 | 12.2 PARTIALLY RESTRAINED COMPOSITE CONNECTIONS 12.2.1 Connection Details |
| 593 | 12.2.2 Connection Moment-Rotation Curves |
| 596 | 12.2.3 Connection Design |
| 601 | 12.3 LOADS AND LOAD COMBINATIONS 12.3.1 Gravity Loads and Seismic Weight |
| 602 | 12.3.2 Seismic Loads |
| 603 | 12.3.3 Wind Loads 12.3.4 Notional Loads |
| 604 | 12.3.5 Load Combinations |
| 605 | 12.4 DESIGN OF C-PRMF SYSTEM 12.4.1 Preliminary Design 12.4.2 Application of Loading |
| 606 | 12.4.3 Beam and Column Moment of Inertia |
| 607 | 12.4.4 Connection Behavior Modeling |
| 608 | 12.4.5 Building Drift and P-delta Checks |
| 610 | 12.4.6 Beam Design 12.4.7 Column Design |
| 611 | 12.4.8 Connection Design |
| 612 | 12.4.9 Column Splices 12.4.10 Column Base Design |
| 615 | 13.1 WAREHOUSE WITH MASONRY WALLS AND WOOD ROOF, AREA OF HIGH SEISMICITY 13.1.1 Building Description |
| 616 | 13.1.2 Design Requirements |
| 618 | 13.1.3 Load Combinations |
| 620 | 13.1.4 Seismic Forces |
| 621 | 13.1.5 Side Walls |
| 640 | 13.1.6 End Walls |
| 659 | 13.1.7 In-Plane Deflection – End Walls |
| 660 | 13.1.8 Bond Beam – Side Walls (and End Walls) |
| 661 | 13.2 FIVE-STORY MASONRY RESIDENTIAL BUILDINGS IN LOCATIONS OF VARYING SEISMICITY 13.2.1 Building Description |
| 664 | 13.2.2 Design Requirements |
| 666 | Load Combinations |
| 667 | 13.2.4 Seismic Design for Low Seismicity SDC B Building |
| 686 | 13.2.5 Seismic Design for Moderate Seismicity SDC C Building |
| 697 | 13.2.6 Low Seismicity SDC D Building Seismic Design |
| 705 | 13.2.7 Seismic Design for High Seismicity SDC D Building |
| 717 | 13.2.8 Summary of Wall D Design for All Four Locations |
| 723 | 14.1 THREE-STORY WOOD APARTMENT BUILDING 14.1.1 Building Description |
| 726 | 14.1.2 Basic Requirements |
| 729 | 14.1.3 Seismic Force Analysis |
| 731 | 14.1.4 Basic Proportioning |
| 752 | 14.2 WAREHOUSE WITH MASONRY WALLS AND WOOD ROOF 14.2.1 Building Description |
| 754 | 14.2.2 Basic Requirements |
| 755 | 14.2.3 Seismic Force Analysis |
| 757 | 14.2.4 Basic Proportioning of Diaphragm Elements (Traditional Method, Sec. 12.10.1 and 12.101.2) |
| 766 | 14.2.5 Basic Proportioning of Diaphragm Elements (Alternative Method, Sec. 12.10.3) |
| 767 | 14.2.6 Masonry Wall Anchorage to Roof Diaphragm |
| 781 | 15.1 BACKGROUND 15.1.1 Concept of Seismic Isolation 15.1.2 Types of Isolation Systems |
| 782 | 15.1.3 Design Process Summary |
| 783 | 15.2 PROJECT INFORMATION 15.2.1 Building Description |
| 788 | 15.2.2 Building Weights |
| 789 | 15.2.3 Seismic Design Parameters Performance criteria. The performance criteria are determined according to Standard §1.5.1: Design spectral accelerations. Chapters 11 and 21 of the Standard are used to determine the design spectral accelerations. The Standard incorporates changes to the ground motions (new USGS spectral accelerations and site coefficients) and new site-specific analysis requirements. Section 11.4.7 requires that a ground hazard analysis be performed in accordance with Section 22.2 on sites with an S1 greater than or equal to 0.6. For the purpose of this example, a generic site has been selected with details a |
| 790 | 15.2.4 Structural Design Criteria Design basis. Earthquake load effects (Standard Chapters 12 and 17). Superstructure design load combinations (Standard §2.3.2, using RI = 1). |
| 791 | 15.3 PRELIMINARY DESIGN OF ISOLATION SYSTEM 15.3.1 Elastomeric Isolation System |
| 792 | Force-displacement behavior. The hysteretic force-displacement behavior of LR bearings can be idealized as bilinear as illustrated in Figure 15.3-1. The two key parameters that characterize behavior are the characteristic strength Qd, which is primarily dependent on the mechanical properties of lead, and the post-elastic stiffness kd , which is primarily dependent on the mechanical properties of rubber. The value of the yield displacement Y is in the range 0.25 to 1.0 inch and, although it may affect the Nominal properties and bounding. The two important properties to determine are the effective yield stress of lead σYL and the shear modulus of rubber G. These properties are dependent on a variety of parameters and are manufacturer specific. |
| 793 | Preliminary design procedure. This procedure is based on examples in Constantinou et al. (2011) and involves assessing the bearing stability, which is a critical check for preliminary sizing of elastomeric bearings. Other adequacy checks are necessary but can be done later in design or by the bearing manufacturer. |
| 795 | Uplift assessment. At this point in design it is also worthwhile to assess the potential for uplift at bearings. Using preliminary estimates of axial loads along with the minimum vertical load combination, Equation 15.2-3, the uplift demand is about -350 kip (in tension). Tension in elastomeric bearings should be avoided, nevertheless, Constantinou et al. (2007) states that high quality manufacturers can sustain tensile pressure of about 3G before cavitation occurs (where G is the shear modulus of the el |
| 796 | 15.3.2 Sliding Isolation System |
| 797 | Force-displacement behavior. Sliding bearings are available in a number of different configurations, with a number of different sliding interfaces. The key dimensions of a double concave sliding bearing are illustrated in Figure 15.3-2, where R is the radius of curvature of the concave plates, μ is the coefficient of friction, d is the nominal displacement capacity and h is height to the pivot point. Although double concave bearings may be designed for a range of frictional and geometrical properties (Fe |
| 798 | Nominal properties and bounding. It is recommended to make contact with bearing manufacturers in order to help select a range of trial design friction coefficients and available radii of curvature and diameters (i.e. displacement capacity) of concave plates. |
| 799 | Preliminary design procedure. The selection of the double concave sliding bearing dimensions, as depicted in Figure 15.3-2, are explained in the preceding sections and are taken as: |
| 800 | 15.4 ISOLATION SYSTEM PROPERTIES 15.4.1 Overview |
| 801 | 15.4.2 Nominal Properties and Testing λ-Factors Interpreting Test Data from Lead-Rubber Bearings. For this example, dynamic testing per §17.8.2.2, Item 3 is conducted at a vertical load equal to D + 0.5L on two virgin (unscragged) bearings tested at a normal temperature of 20°C. This test consists of three fully-reversed cycles at a displacement amplitude of DM conducted dynamically at the effective period TM determined from the upper-bound properties. Therefore the speed of loading effects and heating effects are directly accounted for by the testing |
| 805 | Sliding bearings. Representative high-speed dynamic force-displacement behavior for a sliding bearing is illustrated in Figure 15.4-2. The test sequence is not too dissimilar from first half of the §17.8.2.2, Item 2b testing. It is noted that this data is for a triple concave sliding bearing, which is why there is a slope (apparent yield displacement) upon reversal of the direction of displacement. For the double concave sliding bearing described in this example the behavior would be more likened to the |
| 806 | 15.4.3 Aging and Environmental λ-Factors Elastomeric bearings. The aging and environmental factors for the shear modulus of rubber G are: Sliding bearings. The aging and environmental factors for the friction coefficient μ for an unlubricated PTFE-stainless steel sliding interface are: |
| 807 | 15.4.4 Specification λ-Factors 15.4.5 Upper- and Lower-Bound Force-Deflection Behavior LR bearings force-displacement behavior. The maximum and minimum λ factors for the shear modulus of rubber and effective yield stress of lead are calculated based on Equations 17.2-1 and 17.2-2, as follows: |
| 808 | Sliding bearings force-displacement behavior. The upper- and lower- bound force-displacement behavior of the sliding isolation system, based on the preliminary design, is illustrated in Figure 15.4-4. |
| 809 | 15.5 EQUIVALENT LATERAL FORCE PROCEDURE 15.5.1 Procedure |
| 810 | 15.5.2 Structural Analysis Modeling assumptions. To expedite calculation of loads on bearings and other elements of the seismic-force-resisting system, a three-dimensional mathematical model of the building is developed and analyzed using the computer program ETABS (CSI, 2013). Bearing dimensions and properties. The preliminary sizing of the bearing, per Section 15.3.1, used quick but conservative calculations. Using the more refined calculations that are set out in the following sections, it was decided to further optimize the sizing of the bearings to reduce structural shear. The final dimensions of all the 35 LR bearings and their properties (as determined in Section 15.4) are as follows: |
| 811 | Maximum displacement and effective period. The maximum displacement DM and effective period at the maximum displacement TM is calculated using the ELF procedure in Section 15.5.1, which is consistent with §17.5.3.1 and §17.5.3.2 of the Standard . The calculations for the upper- and lower-bound properties are documented in Table 15.5-2. |
| 812 | Lateral seismic forces and vertical distribution. The lateral shear force required for the design of the isolation system, foundation and other structural elements below the isolation system is given by Vb in Equation 17.5-5. The overturning loads (i.e. axial loads) from the superstructure, which are used for the design of the isolation system, foundation, and elements below the isolation system is given by the unreduced lateral force Vst in Equation 17.5-7. Subject to the limits of §17.5.4.3, the base s |
| 814 | Bearing vertical loads. The vertical/axial load on the bearings was calculated using the ETABS model for both the upper- and lower-bound properties. In this case the upper-bound properties gave the critical earthquake demands and are reported in Table 15.5-6 and 15.5-7. This table documents the loadings from dead and reduced live loadings, as well as the envelope of the maximum and minimum demands from horizontal earthquake and torsion actions. The X and Y directions referred to in the tables are illustr |
| 816 | Total maximum displacement. The maximum design displacement DM calculated previously represents the peak earthquake displacement at the center of mass of the building without the additional displacements that can occur at other locations due to actual or accidental mass eccentricity. The additional displacements due to torsion can be calculated from the ETABS model with the application of the torsional moment. However, the resultant total maximum displacement DTM may not be taken less than that calculat |
| 817 | Bearing stability and shear strain assessment. A more refined calculation of the minimum required individual rubber layer thickness for stability (per Equation 15.3-3), with compatible combinations of maximum axial loads and total maximum displacements, for each bearing location are documented in Table 15.5-9. The critical bearing location is Gridlines B4 and D4 which require a rubber thickness less than 0.28 inches which is at the lower limit for what can be satisfactorily constructed by manufactures. T |
| 818 | Story drifts. The Standard permits more liberal drift limits where the design of the superstructure is based on a nonlinear response history analysis (NLRHA). The ELF procedure and response spectrum drift limits are 0.015hsx for the reduced MCER level forces, which are increased to 0.020hsx for a NLRHA (where hsx is the story height at level x). Usually a stiff system (e.g., braced frame) is selected for the superstructure to limit damage to nonstructural components sensitive to drift and therefore the |
| 819 | 15.5.3 Limitation Checks |
| 820 | 15.6 DYNAMIC ANALYSES 15.6.1 Background 15.6.2 Structural Analysis and Modeling |
| 822 | 15.6.3 Ground Motion Records Selection and scaling of ground motions. The Standard requires that ground motions be scaled to match maximum spectral response in the horizontal plane. In concept, at a given period of interest, the maximum spectral response of scaled records should, on average, be the same as that defined by the MCER spectrum. The ground motion acceleration histories selection and scaling are illustrated in Chapter 3 of these NEHRP Design Examples. |
| 823 | Orientation of ground motion components for analysis. Only for sites within 3 miles of an active fault does the Standard specify how the two scaled components of each record should be applied to a three-dimensional model (i.e., how the two components of each record should be oriented with respect to the axes of the model). For other sites, the Standards commentary states that individual pairs of horizontal ground motion components need not be applied in multiple orientations. Guidance on the orientation 15.6.4 Vertical Response Spectrum Analysis Vertical Earthquake Spectrum. In the ELF procedure the vertical earthquake effects are accounted for by simply adding or subtracting 0.2SMSD or 0.2 |
| 824 | Analysis and Bearing Axial Loads. A vertical earthquake analysis requires careful modeling considerations. These are outlined in the Standard commentary §C17.6.2, such as including all structural elements in the model and adding more degrees of freedom (i.e. nodes along a beam or slab) so that the mass is realistically distributed across the building footprint. Consideration of the soil-structure interaction is also necessary and will require input from a geotechnical engineer. The modal analysis must als |
| 825 | 15.6.5 Nonlinear Response History Analysis Introduction. The two independent ETABS models, which represent upper- or lower-bound bearing properties, are analyzed for the set of seven pairs of horizontal ground motion records applied to the model in the one orientation only (i.e. are not rotated). The post-processing in this section takes the absolute maximum (i.e. maximum whether in the positive or negative directions) response for each ground motion. The average of these absolute maxima responses over the seven ground motions is then used for des |
| 826 | Torsion. The Standard §17.6.2.1 requires that the effect of torsion above the isolation interface, considering the most disadvantageous position of eccentric mass, be considered. There are two components of eccentric mass, the inherent eccentricity between the center of mass and center of rigidity and the accidental eccentricity. This accidental eccentricity approach is used to indirectly account for various effects, including: plan distributions of mass that differ from those assumed in design, variation Peak isolation system displacement and base shear. The isolation system displaces simultaneously in the X- and Y-directions at each increment in time with the resultant displacement being the vectorial (SRSS) combination of these two components. Simply taking the maximum X or Y displacement over the whole ground motion record and calculating their SRSS combination may be overly conservative. For example, Figure 15.6-4 shows the displacement history of the isolation system in the X and Y directions for gr |
| 828 | Story forces. Table 15.6-5 summarizes average (of seven ground motions) absolute maximum (maximum whether in the positive or negative direction) story shear force results at each level in the X and Y directions from the NLRHA and compares these values with story shear forces calculated by ELF formulas for unreduced design earthquake loads. The upper-bound isolation system properties gave the greater shear forces. Figure 15.6-5 shows story shears calculated by ELF formulas and by the NLRHA. |
| 829 | Bearing vertical loads. The combination of vertical/axial loads on the bearings to be used for design consist of static dead and live loads, torsion (from the ELF procedure per Table 15.5-6), vertical earthquake loads per the response spectrum analysis and given in Table 15.6-3, as well as the vertical effects of horizontal earthquake loads from the NLRHA per this section. The earthquake horizontal/overturning forces are calculated to be smaller in the NLRHA compared to the ELF procedure. These force need to be increased by the ratio of the NLRHA base shear to the minimum limit given by §17.6.4. This gives a scale factor of 1.2, per Section 15.6.5.3, on the earthquake overturning load. The scaled and factored minimum axial loads on the bearings, which were critical for upper bound properties, are given in Table 15.6-6. |
| 831 | 15.7 DESIGN AND TESTING REQUIREMENTS 15.7.1 Design Requirements Bearing design loads. |
| 832 | Bearing design displacements. Bearing force-displacement behavior and bounds. 15.7.2 Prototype Bearing Testing Criteria |
| 833 | 15.7.3 Production Testing |
| 838 | 16.1 BACKGROUND 16.1.1 Energy Dissipation Devices 16.1.2 Intent of Seismic Provisions |
| 840 | 16.2 PROJECT INFORMATION 16.2.1 Building Description |
| 842 | 16.2.2 General Parameters |
| 843 | Gravity loads. Seismic weight calculation. The seismic weight calculation assumes a 14 inch overhang of the slab around the perimeter of the building. The total seismic weight of building is 94 kips + 1,537 kips + 6 |
| 844 | 16.2.3 Structural Design Criteria Structural component load effects. The effect of seismic load is defined by Standard §12.4.2 as: Load combinations. Load combinations from ASCE 7-10 are as follows: Response history analysis combinations. The NLRHA can generate a large amount of data considering there are seven ground motions, each with two components that may be applied in multiple orientations, multiplied by maximum and minimum dampers properties, and with various load combination cases. This number of analyses may also be magnified by considering different cases of accidental eccentricity. |
| 845 | 16.3 DESIGN CONSIDERATIONS 16.3.1 Advantages of Using Dampers in New Construction 16.3.2 Early Design Decisions Performance goals. Typical practice is to use the FVD devices in new construction to reduce damage. Therefore the office building will be designed to achieve a higher performance level than the minimum requirements of the Standard. This will be achieved by sizing the seismic force resisting system (SFRS) such that all the structural members remain “essentially” elastic at the MCER level, with virtually all earthquake energy dissipated by the FVDs. Added damping. Added damping of 20 percent of critical in the fundamental mode of vibration is targeted for the initial sizing of the dampers. The optimal amount of added damping depends on the structure and excitation. Generalized damping levels from previous projects are as follows (Taylor 1999): |
| 846 | Placement and configuration of dampers. The design of the SFRS and/or damping system may be affected by requirements in the Standard which refer to the number and location of dampers. These include: |
| 847 | Analysis procedure selection. A nonlinear response history analysis (NLRHA) will be used to calculate the maximum displacement, velocities and forces at the MCER level which are used for the design of the damping system and to calculate frame moments, shears and axial forces at the design earthquake level for the design of the SFRS. Viscous damper velocity exponent. The force output of a linear and nonlinear fluid viscous damper is specified as follows: Fabrication and detailing. Further practical design considerations which are all interrelated include: |
| 848 | 16.3.3 Preliminary Sizing of Damping Devices Linear viscous dampers. The preliminary design is based on a practical method presented in Christopoulos and Filiatrault, 2006. The procedure calculates the linear viscous damping coefficients required of dampers at each story in order to achieve a certain damping ratio in a particular mode. This provides a rough initial estimate of order-of-magnitude of damping coefficients, which can later be refined by using nonlinear response history analysis to optimize the parameters of interest. |
| 852 | Nonlinear viscous dampers. Due to the advantages of using nonlinear FVD over linear FVD, as discussed in Section 16.3.2.5, it is decided to progress design with a nonlinear FVD with an exponent/alpha value of 0.4. |
| 854 | 16.4 STRUCTURAL ANALYSIS 16.4.1 Introduction 16.4.2 Ground Motions Histories |
| 856 | 16.4.3 Maximum and Minimum Damping Device Properties Overview. The nominal properties of damping devices can vary over their design life due to aging and environmental effects, can vary during seismic excitation due to speed of motion, first cycle and heating effects, and can vary between individual devices due to manufacturing tolerances. |
| 857 | Nominal properties and λ-factors. The nominal properties are typically determined based on advice from the manufacturer, which can be confirmed later by prototype and/or production testing. For the nonlinear FVD, the parameters of interest are the damping coefficient, CNL, and the nonlinear exponent α. Instead of optimizing for different values of CNL and α it may be more cost effective, and with less uncertainty, to directly adopt a device which the manufacturer has already produced and tested. It so hap |
| 859 | 16.4.4 Nonlinear Response History Analysis Modeling. A three-dimensional mathematical model of the building is created in ETABS (CSI 2013) to assess the effectiveness of the added damping system and to determine design actions. Structural elements part of the damping systems load path and the SFRS are included in the analysis model so that the deformations that occur in these members are accounted for. For example the in-plane stiffness of the diaphragm and stiffness of elements connected to the dampers (i.e. braces) is explicitly modeled. Failu |
| 860 | Analysis results. A NLRHA is conducted using the software ETABS with two models: one using the maximum damper properties and one using the minimum damper properties. The analysis is conducted at both the MCER and design earthquake hazard levels. The maximum value of story drift, damper force and damper displacement/stroke is calculated for each ground motion. The average of the maximum values from the seven ground motions is permitted to be used for design (Standard §18.3.3) and these values are summariz |
| 864 | Accidental mass eccentricity. The Standard has incorporated new provisions which permit the use of amplification factors to account for accidental mass eccentricity. The rationale behind this is to avoid doing (unnecessarily) large amounts of analysis to calculate the worst case of accidental eccentricity. |
| 865 | 16.5 DESIGN OF LATERAL AND DAMPING STRUCTURAL SYSTEMS 16.5.1 Seismic Force Resisting System Configuration and detailing. Structures that have damping system must have an independent SFRS in each lateral direction which provides a complete lateral load path and conforms with a type listed in Table 12.2-1 of the Standard. Steel special moment resisting frames (SMRF) are located on the perimeter of the example building to meet this requirement. The SMRF is designed and detailed as if the damping system was disconnected and this process is illustrated in Chapter 9 of these design examples. This is t |
| 866 | Minimum base shear. The minimum base shear Vmin used for design depends on the number of FVD at each floor level and if any horizontal or vertical irregularities exist. Vmin is calculated using the design earthquake which is two-thirds of the MCER. |
| 867 | Strength design of SFRS. There are three design checks to ensure that the SFRS is of adequate strength. Foremost the factored nominal capacity of the SMRF shall satisfy: |
| 871 | Permissible drift. The story drifts are only checked using the MCER ground motions using a model which includes the damping system. The maximum permitted drift by the Standard §18.4.1 is the smaller of: 16.5.2 Damping System Damping devices. The damping devices shall be sized to elastically resist the forces, displacements and velocities from the MCER ground motions. Furthermore since the redundancy criteria of §18.2.4.6 are not satisfied for stories 3-7, the devices at these stories must be capable of sustaining the force and displacement associated with a velocity equal to 1.3 times the maximum calculated velocity. For ease of construction and to control damper and detailing costs, all dampers will be designed for this pena |
| 872 | Framing, braces and connections. Other elements classified as part of the damping system include the braces in-line with the dampers, their connections, the framing (beams and columns) which encompass the damping devices and the collectors and diaphragm which bridge between the gridline where the dampers are located to the gridline where the SFRS’s are. The sizing of these elements must be such that they remain elastic for the unreduced linear-elastic MCER demands. The capacity of element is defined in th |
| 880 | 17.1 NONBUILDING STRUCTURES VERSUS NONSTRUCTURAL COMPONENTS |
| 881 | 17.1.1 Nonbuilding Structure |
| 882 | 17.1.2 Nonstructural Component 17.2 PIPE RACK, SEISMIC DESIGN CATEGORY D 17.2.1 Description |
| 883 | 17.2.2 Provisions Parameters |
| 884 | 17.2.3 Design in the Transverse Direction |
| 886 | 17.2.4 Design in the Longitudinal Direction |
| 888 | 17.3 STEEL STORAGE RACK, SEISMIC DESIGN CATEGORY C 17.3.1 Description |
| 889 | 17.3.2 Provisions Parameters |
| 890 | 17.3.3 Design of the System |
| 892 | 17.4 ELECTRIC GENERATING POWER PLANT, SEISMIC DESIGN CATEGORY D 17.4.1 Description |
| 894 | 17.4.2 Provisions Parameters |
| 895 | 17.4.3 Design in the North-South Direction |
| 896 | 17.4.4 Design in the East-West Direction |
| 897 | 17.5 PIER/WHARF DESIGN, SEISMIC DESIGN CATEGORY D 17.5.1 Description |
| 898 | 17.5.2 Provisions Parameters |
| 899 | 17.5.3 Design of the System |
| 900 | 17.6 TANKS AND VESSELS, SEISMIC DESIGN CATEGORY D |
| 901 | 17.6.1 Flat-Bottom Water Storage Tank |
| 904 | 17.6.2 Flat-Bottom Gasoline Tank |
| 908 | 17.7 VERTICAL VESSEL, SEISMIC DESIGN CATEGORY D 17.7.1 Description |
| 909 | 17.7.2 Provisions Parameters |
| 910 | 17.7.3 Design of the System |
| 918 | 18.1 DEVELOPMENT AND BACKGROUND OF THE REQUIREMENTS FOR NONSTRUCTURAL COMPONENTS 18.1.1 Approach to Nonstructural Components |
| 919 | 18.1.2 Force Equations |
| 921 | 18.1.3 Load Combinations and Acceptance Criteria |
| 922 | 18.1.4 Component Amplification Factor |
| 923 | 18.1.5 Seismic Coefficient at Grade 18.1.6 Relative Location of the Component in the Structure 18.1.7 Component Response Modification Factor |
| 924 | 18.1.8 Component Importance Factor 18.1.9 Accommodation of Seismic Relative Displacements |
| 925 | 18.1.10 Component Anchorage Factors and Acceptance Criteria |
| 926 | 18.1.11 Construction Documents 18.1.12 Exempt Items |
| 927 | 18.1.13 Pre-Manufactured Modular Mechanical and Electrical Systems 18.2 ARCHITECTURAL CONCRETE WALL PANEL 18.2.1 Example Description |
| 930 | 18.2.2 Design Requirements 18.2.3 Spandrel Panel |
| 937 | 18.2.4 Column Cover |
| 939 | 18.2.5 Additional Design Considerations |
| 940 | 18.3 SEISMIC ANALYSIS OF EGRESS STAIRS 18.3.1 Example Description |
| 942 | 18.3.2 Design Requirements |
| 944 | 18.3.3 Force and Displacement Demands |
| 947 | 18.4 HVAC FAN UNIT SUPPORT 18.4.1 Example Description |
| 948 | 18.4.2 Design Requirements 18.4.3 Direct Attachment to Structure |
| 950 | 18.4.4 Support on Vibration Isolation Springs |
| 955 | 18.4.5 Additional Considerations for Support on Vibration Isolators |
| 956 | 18.5 PIPING SYSTEM SEISMIC DESIGN |
| 957 | 18.5.1 Example Description |
| 962 | 18.5.2 Design Requirements. |
| 964 | 18.5.3 Piping System Design |
| 967 | 18.5.4 Pipe Supports and Bracing |
| 972 | 18.5.5 Design for Displacements |
| 974 | 18.6 ELEVATED VESSEL SEISMIC DESIGN 18.6.1 Example Description |
| 978 | 18.6.2 Design Requirements |
| 980 | 18.6.3 Load Combinations 18.6.4 Forces in Vessel Supports |
| 982 | 18.6.5 Vessel Support and Attachment |
| 985 | 18.6.6 Supporting Frame |
| 989 | 18.6.7 Design Considerations for the Vertical Load-Carrying System |
