OpenSees Example 9. Build & Analyze a Section Example

Introduction

For the case of the uniaxial section, moment-curvature and axial force-deformation curves are defined independently, and numerically.

For the case of the fiber sections (steel and RC), uniaxial materials are defined numerically (stress-strain relationship) and are combined into a fiber section where moment-curvature and axial force-deformation characteristics and their interaction are calculated computationally.

Input

Model Building

2D vs. 3D

While this distinction does not affect the section definition itself, it affects the degree-of-freedom associated with moment and curvature in the subsequent analysis.

There are two differences between the two models:

1. The space defined with the model command (# Define the model builder, ndm=#dimension, ndf=#dofs)

2D

model BasicBuilder -ndm 2 -ndf 3;

3D

model BasicBuilder -ndm 3 -ndf 6;

2. In the 3D model, torsional stiffness needs to be aggregated to the section

Uniaxial Section

Files Ex9a.build.UniaxialSection2D.tcl Ex9a.build.UniaxialSection3D.tcl LibUnits.tcl

Notes Flexure and axial behavior are uncoupled in this type of section

Lateral-Load Analysis

The following tasks are performed in the analysis

• define lateral-load parameters
• analyze

Static Static Pushover Files Ex8.genericFrame3D.analyze.Static.Push.tcl LibAnalysisStaticParameters.tcl Notes One-directional monotonic displacement-controlled static loading Static Reversed Cyclic Files Ex8.genericFrame3D.analyze.Static.Cycle.tcl LibAnalysisStaticParameters.tcl LibGeneratePeaks.tcl Notes One-directional displacement-controlled static loading Displacement cycles are imposed in positive and negative direction

Dynamic EQ Ground Motion Dynamic Uniform Sine-Wave Ground Motion Files Ex8.genericFrame3D.analyze.Dynamic.sine.multipleSupport.tcl LibAnalysisDynamicParameters.tcl Notes Sine-wave acceleration input Same acceleration input at all nodes restrained in specified direction Dynamic Uniform Earthquake Ground Motion (typical) Files Ex8.genericFrame3D.analyze.Dynamic.EQ.Uniform.tcl LibAnalysisDynamicParameters.tcl ReadSMDFile.tcl H-E12140.AT2 Notes Earthquake (from file) acceleration input Same acceleration input at all nodes restrained in specified direction Dynamic Multiple-Support Sine-Wave Ground Motion Files Ex8.genericFrame3D.analyze.Dynamic.sine.multipleSupport.tcl (this file may need to be corrected for displacement input) LibAnalysisDynamicParameters.tcl Notes Sine-wave displacement input Different displacements are specified at particular nodes in specified directions Dynamic Multiple-Support Earthquake Ground Motion Files Ex8.genericFrame3D.analyze.Dynamic.EQ.multipleSupport.tcl (this file needs to be corrected for displacement input) LibAnalysisDynamicParameters.tcl ReadSMDFileDisp.tcl H-E12140.DT2 (Displacement recording) Notes Earthquake (from file) displacement input Different displacements are specified at particular nodes in specified directions Dynamic Bidirectional Earthquake Ground Motion (typical) Files Ex8.genericFrame3D.analyze.Dynamic.EQ.bidirect.tcl LibAnalysisDynamicParameters.tcl ReadSMDFile.tcl (need to modify ReadSMDFile.tcl for displacement data) H-E12140.AT2 H-E01140.AT2 (acceleration recording in perpendicular direction) Notes Earthquake (from file) acceleration input Different ground motion in two directions Same acceleration input at all nodes restrained in specified direction

Run

The model and analysis combinations for this example are numerous. The following are an small subset, for demonstration purposes:

• To run W-Section Model, Static Pushover Analysis:

puts " -------------Elastic Model -------------"
puts " -------------Static Pushover Analysis -------------"
source Ex8.genericFrame3D.build.Wsec.tcl
source Ex8.genericFrame3D.analyze.Static.Push.tcl

• To run RC Model, Uniform Earthquake Excitation

puts " -------------Uniaxial Inelastic Section, Nonlinear Model -------------"
puts " -------------Uniform Earthquake Excitation -------------"
source Ex8.genericFrame3D.build.RCsec.tcl
source Ex8.genericFrame3D.analyze.Dynamic.EQ.Uniform.tcl

Notes

In this example, the following items are variables:

• Number of stories in Y direction
• Number of bays in X direction
• Number of bays in Z direction
• Elastic/Fiber Section
• Display: none/node numbering/deformed shape/mode shape (can choose which mode) (variable display scaling factor for both the deformed shape and the mode shape, this scaling factor is dependent on the user choice)

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