Introduction

The examples in this manual are listed in order of simplicity.

NOTE: gravity analysis is always included as part of the model building

Models

The following types of models are represented in these examples:

Elastic Elements

OpenSees Elastic Beam Column Element The elastic, uncoupled, axial and flexural stiffnesses are defined at the element level user specifies: E,I,A

Inelastic Elements

Uniaxial Section

The inelastic, uncoupled, axial and flexural stiffnesses are defined at the section level The OpenSees Uniaxial Section Command is used User specifies: Axial stiffness A Section Moment-Curvature characteristics via the OpenSees UniaxialMaterial Command

Fiber Section

The section is broken down into fibers where uniaxial materials are defined independently. The program calculates the coupled flexural and axial stiffnesses/strength by integrating strains across the section The OpenSees Fiber Section Command is used User specifies Stress-Strain characteristics via the OpenSees UniaxialMaterial Command for all number of materials Section geometry via series of Patches and Layers in the fiber section Two Section Geometries are presented *RC Rectangular Section *Standard AISC W section

Lateral Loads

The following types of lateral loads are represented in these examples:

Static Pushover

Control node is located at the highest floor Lateral-load distribution is proportional the the mass distribution along the height of the building Static analysis Two types

Monotonic Pushover

Reversed Cyclic Pushover

One-directional displacement-controlled static lateral loading Displacement cycles are imposed in positive and negative direction

Time-Dependent Dynamic Loads

Uniform Sine-Wave

Multiple-Support Sine-Wave

Sine-wave displacement input Different displacements are specified at particular nodes in specified directions

Uniform Earthquake

Earthquake (from file) acceleration input Same acceleration input at all nodes restrained in specified direction

Multiple-Support Earthquake

Earthquake (from file) displacement input Different displacements are specified at particular nodes in specified direction

Bidirectional Earthquake

Different inputs are specified for two directions Same acceleration input at all nodes restrained in specified direction

Simulation Process

Each example script does the following:

Build the model

1. model dimensions and degrees-of-freedom
2. nodal coordinates
3. nodal constraints -- boundary conditions
4. nodal masses
5. elements and element connectivity
6. recorders for output

Define & apply gravity load

1. nodal or element load
2. static-analysis parameters (tolerances & load increments)
3. analyze
4. hold gravity loads constant
5. reset time to zero

Define and apply lateral load

1. load pattern (nodal loads for static analysis, support ground motion for earthquake)
2. lateral-analysis parameters (tolerances & displacement/time increments)
   • Static Lateral-Load Analysis
     • define the displacement increments and displacement path
   • Dynamic Lateral-Load Analysis
     • define the input motion and all associated parameters, such as scaling and input type
     • define analysis duration and time increment
     • define damping
3. analyze

Introductory Examples

The objective of Example 1a and Example 1b is to give an overview of input-file format in OpenSees using simple scripts.
These scripts do not take advantage of the Tcl scripting capabilities shown in the later examples. However, they do provide starting a place where the input file is similar to that of more familiar Finite-Element Analysis software. Subsequent examples should be used as the basis for user input files.

OpenSees Example 1a. 2D Elastic Cantilever Column

• overview of basic OpenSees input structure
• coordinates, boundary conditions, element connectivity, nodal masses, nodal loads, etc.
• two-node, one element