Nonlinear Analysis And Performance Assessment for 3D Structure

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1 Exclusive Distributor in the Middle East for CSI Software licensing, technical support and training solutions For Sales: For Technical Support: For Licensing: Nonlinear Analysis And Performance Assessment for 3D Structure Version: HOME PERFORM-3D Overview Displacement Based Design Traditionally, earthquake-resistant design has been strength-based, using linear elastic analysis. Since inelastic behavior is usually allowed for strong earthquakes, this is not entirely rational. Strength-based design considers inelastic behavior only implicitly. Displacement-based (or deformation-based) design considers inelastic behavior explicitly, using nonlinear inelastic analysis. Displacement-based design recognizes that in a strong earthquake, inelastic deformation (or ductility) can be more important than strength. PERFORM-3D allows you to use displacement-based design. Capacity Design The response of a structure to earthquake ground motion, whether elastic or inelastic, is highly uncertain. 1

2 Capacity design is a rational way to improve the response of a structure in a strong earthquake, by deliberately controlling its behavior. Capacity design controls the inelastic behavior of a structure, by allowing inelastic behavior only in locations chosen by the designer. In these locations the structural components are designed to be ductile. The rest of the structure remains essentially elastic, and can be less ductile. Controlling the behavior in this way improves reliability, reduces the amount of damage, and can reduce construction costs. PERFORM-3D allows you to apply capacity design principles. What PERFORM-3D is NOT PERFORM-3D has powerful capabilities for inelastic analysis, but it is not intended for general purpose nonlinear analysis. If you have no idea how your structure will behave when it becomes inelastic in a strong earthquake, PERFORM-3D can probably help you to identify the weak points, and hence can guide you in improving the design. However, PERFORM-3D is not intended for design by analysis, where the engineer expects the analysis to determine exactly how a structure will behave. PERFORM-3D is a powerful tool for implementing displacement-based design and capacity design. It will help you to produce better designs, but it will not do the engineering for you. PERFORM-3D FEATURES: Features-PERFORM-3D Modeling Elements PERFORM-3D includes the following element types: o Frame element for beams, columns and braces. o Wall element for shear walls. o Slab element for floors. o Bar elements (with only axial stiffness) of various types. o Buckling restrained brace. o Gap elements. o Seismic isolators of rubber and friction pendulum type. o Fluid damper, with nonlinear relationship between force and deformation rate. 2

3 o Connection panel zone, to model shear deformation in beam-to-column connections. o Infill panel, with only shear strength and stiffness. o Deformation gages of various types. These elements have no stiffness. They are used for calculating deformations, and hence deformation demand/capacity ratios. Components In PERFORM-3D, most elements are made up of a number of components. For example, a beam element might consist of several components. Component Properties All inelastic components have essentially the same force-deformation relationship. This is a basic tri-linear relationship, with optional strength loss. 3

4 Hysteresis Loops The hysteresis loop for an inelastic component can be varied to account for stiffness degradation. The loop can be plotted to check that it has the expected shape. 4

5 Deformation Capacities Fz LLC Deformation capacities can be specified for inelastic components, for calculating deformation demand/capacity ratios. Deformation capacities can be specified for up to 5 performance levels. Demand/Capacity Ratios PERFORM-3D includes a large number of components, both inelastic and elastic. During an analysis, D/C ratios are calculated as follows: o Deformation D/C ratios are calculated for inelastic components. o Hence, components that are allowed to become inelastic can be checked to make sure they have sufficient ductility. o Strength D/C ratios are calculated for elastic components. o Hence, components that are required to remain essentially elastic can be checked to make sure they have sufficient strength. Limit States The number of components with D/C ratios can be very large. To simplify decision making, components that have similar D/C measures can be grouped into Limit States. An example D/C measure is the concrete tension strain in a shear wall. Each limit state has a usage ratio, which is the maximum D/C ratio for any component in the limit state. For a structure to satisfy the performance requirements, the usage ratios for all limit states should not exceed

6 Frame Structures Simple frame structures consist of beam and column elements. Beam and column elements can be made up of a variety of components, and may be elastic or inelastic. P-delta effects can be considered or ignored. 6

7 Shear Wall Structures Fz LLC Shear walls are modeled using plane wall elements. Complex shear cores are made up of plane elements. Wall elements can have inelastic behavior in bending and/or shear. Coupling beams are usually modeled using beam elements, with inelastic behavior in either bending or shear. Complex Structures Large and complex structures can be analyzed. 7

8 Import from SAP2000 and ETABS Models can be imported to PERFORM-3D from SAP2000 or ETABS. These are partial models, consisting mainly of nodes, elements and loads. Component properties are not included, because these properties are different in PERFORM-3D than in SAP2000 and ETABS. Features-PERFORM-3D Analysis Analysis Types PERFORM-3D can run the following analysis types: o Mode shapes, periods, and effective mass factors. o Gravity load. o Static push-over. o Response history for earthquake ground motion. o Response history for dynamic forces. o Response spectrum analysis (with limitations). The nonlinear analysis strategies are very reliable, even when inelastic components have negative stiffness, and when P-delta effects cause the structure to become unstable. 8

9 Analysis Sequence Fz LLC The most common analysis sequence is: o Apply gravity loads. o Run one or more static push-over analyses, with constant gravity load. o Run one or more earthquake response history analyses, with constant gravity load. This is a standard sequence. A general sequence can also be applied, for example cyclic push-over as follows: o Apply gravity loads. o Add push-over loads to a specified drift in the positive direction. o Add push-over loads to a specified drift in the negative direction. o Etc., progressively increasing the specified drift in each direction. Analysis Series An analysis series is a series of analyses, with a standard or general analysis sequence. For each analysis series, the following structure properties can be changed: o The mass distribution and magnitude. This can affect static push-over analysis as well as dynamic response history analysis. o The amount and type of damping for dynamic response history analysis. o The strengths and stiffnesses of the structural components (within certain limits). This allows you to change the structural properties without setting up a new analysis model. Features-PERFORM-3D Behavior Check Tools for Understanding Behavior PERFORM-3D includes a number of tools for processing the analysis results. One set of tools allows you to study the behavior of a structure, and to check that the analysis look reasonable. These tools are as follows: o Deflected shapes. These can be animated, for both static push-over and dynamic response history analysis. o Time histories of many response quantities, including node displacements, velocities and accelerations; element and component forces and deformations; and forces on structure sections that cut through all or parts of the structure. o Hysteresis loops for inelastic components. 9

10 o Moment and shear diagrams for beams, columns, and shear walls. These can be animated. o Energy balance, showing strain energy, kinetic energy, inelastic work, and damping energy. This includes a comparison of external and internal work, which provides a good indication of the numerical accuracy of the analysis. These tools are not directly useful for making design decisions. For this, see the next section, Performance Assessment. 10

11 Features-PERFORM-3D Performance Assessment Tools for Assessing Performance The results of an analysis are useful only if they are presented in a way that supports decision making for design. PERFORM-3D includes powerful tools that assess the performance of a structure, and hence support design. These tools are as follows: o Target displacement calculation for push-over analysis. A number of methods can be used, including those in ASCE 41 and FEMA 440. o Usage ratio plots for single load cases. As the drift increases in a push-over analysis, or time increases in a response history analysis, the usage ratios for the limit states progressively increase. A usage ratio plot shows how the usage ratios vary for user-selected groups of limit states. o Usage ratio envelopes for load combinations. It is common practice to run response history analyses for several earthquakes (often 7 or more), and to assess performance based the mean values of the usage ratios. The tool implements this procedure. o Deflected shapes with color coding based on D/C ratio. These can be used to identify hot spots where the components are most heavily deformed. 11

12 User Processing of Analysis Results The PERFORM-3D analysis results are saved in a number of results files, each file containing results of a specific type (for example, node displacements). If the performance assessment tools in PERFORM-3D do not meet your needs, you can access the results files, and process the results in any way that you choose. You must, of course, write computer code to do the processing. You can use almost any programming language. 12

13 PERFORM-3D System Requirements Processor: Minimum: Intel Pentium 4 or AMD Athlon 64 Recommended: Intel Core 2 Duo, AMD Athlon 64 X2, or better A CPU that has SSE2 support is required The SAPFire Analytical Engine includes a multi-threaded solver that can take advantage of multi-core CPUs Operating System: Microsoft Windows XP with Service Pack 2 or later, Microsoft Windows Vista, or Microsoft Windows 7, 32- and 64-bit versions With a 64 bit operating system, the SAPFire Analytical Engine can utilize more than 4 GB of RAM, making it possible to more efficiently solve larger problems Memory: Minimum: 2 GB for XP O/S, 4 GB for Vista/Windows 7 O/S Recommended: 4 GB for 32-bit O/S, 8 GB or more for 64-bit O/S The problem size that can be solved & the solution speed increases considerably with more RAM Vista/Windows 7 requires more RAM than XP for the operating system itself Disk Space: 6 GB to install the program. Recommended: 500GB or larger Hard Disk Drive (7200 rpm SATA) Additional space required for running and storing model files and analysis results, dependent upon the size of the models Video Card: Minimum: Supporting 1024 by 768 resolution and 16 bits colors for standard (GDI+) graphics mode Recommended: Discrete video card with NVIDIA GPU or equivalent and dedicated graphics RAM (512 Mb or larger) for DirectX graphics mode. The card must be DirectX 9.0c compatible (DirectX SDK Aug Build ). 13

14 DirectX graphics mode fully utilizes the hardware acceleration provided by a GPU and dedicated graphics RAM. For better graphics quality in terms of anti-aliasing and line thickness, the device raster drawing capabilities should support legacy depth bias. PERFORM 3D Watch and Learn Title Length Click to Play PERFORM-3D - 01 Starting a Model 32 min PERFORM-3D - 02 Compound Components for FEMA Steel Frames 13 min Disclaimer: In an effort to highlight certain key capabilities, artistic license may have been taken during the making of these videos. Some input may have been skipped for the sake of brevity, resulting in movies that do not portray all of the steps necessary to create a complete analysis or design. Users should consult the associated program documentation to make sure that they understand all input and modeling assumptions. Note: If you would like to download the Watch and Learn videos for offline viewing, please click here. NEWS- PERFORM-3D V5 Enhancements PERFORM-3D V5 Enhancements A 64-bit version of the analysis engine is now utilized when Peform-3D is installed on a 64 bit computer. The 32-bit analysis engine is still used on 32-bit computers. The 64-bit engine allows larger problems to be solved, and tends to run faster than the 32-bit engine. A large-capacity eigenvalue routine has been added. In earlier versions, the eigenvalue routine could not accommodate structures with very large numbers of 14

15 mass points. The new eigenvalue routine (the same as in SAP2000) allows a larger number of mass points than was previously possible. Warnings are now provided when an unstable or ill-conditioned stiffness matrix is detected. When an analysis model is set up for a complex structure, a common problem is that the model may be poorly conditioned numerically, or may be unstable. For an explanation of the causes of poor conditioning and instability, see the book Modeling for Structural Analysis: Behavior and Basics, by Powell, Chapter 3, especially Section 3.5, available from CSi. Formal documentation is now provided describing the format of the binary results files. For each analysis, Perform-3D writes the analysis results in a number (often a large number) of short binary files. Many users access these binary files directly, to add post-processing operations that are not included in the graphical user interface. The number of modes shapes printed in the text file M000.txt can now be specified. In earlier versions, all mode shapes were printed in this file, and for a large structure the file could be very large. Usually the number now specified will be zero, so that detailed mode shapes are not printed, and the M000.txt file will be quite short. The analysis logs for each Analysis Series are now written to separate files, making them more manageable. In earlier versions, a log of each analysis in the series is also included in ECHO.txt, showing details of the analysis, the computation time for each analysis step, and an energy balance. For a large structure, this made the ECHO.txt file very long 15