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Nonlinear Analysis And Performance Assessment for 3D

Structure

Version: 5.0.0

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.

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• 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.

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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.

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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.

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Deformation Capacities

• 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 1.0.

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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.

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Shear Wall Structures

• 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.

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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.

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Analysis Sequence

• 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.

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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.

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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.

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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.

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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 2009 - Build 9.27.1734.0).

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• 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

http://www.youtube.com/watch?v=pSrLZwPA8H4

32 min

PERFORM-3D - 02 Compound Components for FEMA

Steel Frames

http://www.youtube.com/watch?v=EUzbY1Va21g

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

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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