Standard bolt holes punched in steel elements are either 1/16 inch or 1/8 inch wider than the bolt diameter. Oversized bolt holes can have larger clearances in order to make fit-up easier. While the bolt hole clearance can affect the available strength of an eccentrically loaded bolt group, Tables 7-6 to 7-13 of the AISC … Continue reading Eccentrically Loaded Bolt Groups with Bolt Hole Clearance
Category: Nonlinear Analysis
The Sensitivity Is in the Details
Although the Hardening and Steel01 uniaxial materials can be calibrated to give the same response, the DDM response sensitivity with respect to the same parameter can be different due to how the material models are implemented. Consider the truss model from a previous post on minimal DDM examples. The stress-strain response shows the elastoplastic tangent … Continue reading The Sensitivity Is in the Details
Losing Displacement Control
The DisplacementControl static integrator is commonly employed in nonlinear static pushover analysis. Unlike LoadControl, a displacement-controlled analysis is able to get past limit points of the model response. Displacement control requires a reference load pattern, a linear time series, and a nodal DOF to control during the analysis. This post will address ways to win … Continue reading Losing Displacement Control
Do It Your Self-Weight
Most solid elements in OpenSees don't do body forces very well, if at all. Among elements that have body forces, the implementation and execution are inconsistent. With surface loads, the story is even more convoluted. However, OpenSees is pretty good at dynamics, so all solid elements handle mass density. Yes, the implementations are inconsistent because … Continue reading Do It Your Self-Weight
Arc Length Parameters
Beyond load control, which cannot get past peaks in load-displacement response, OpenSees has several "continuation" methods for nonlinear static analysis of structural models. Implementation of continuation methods is based on the incremental-iterative framework by Clarke and Hancock (1990) with displacement control, minimum unbalanced displacement norm (MUDN), and arc length among the most frequently used in … Continue reading Arc Length Parameters
Eccentrically Loaded Bolt Groups
Tables 7-6 through 7-13 of the AISC Steel Manual contain values for C, the effective number of bolts that resist shear in eccentrically loaded bolt groups. For example, in a bolt group with three vertical rows of 4 bolts spaced s=3 inch with srow=3 inch row spacing and a load at $latex \theta$=30 degrees from … Continue reading Eccentrically Loaded Bolt Groups
Geometric Transformation
OpenSees offers three types of transformations between the basic system and global system for frame (beam-column) elements: Linear - small displacement assumptions for compatibility and equilibrium PDelta - small displacement assumption for compatibility with the $latex P-\Delta$ term included in equilibrium Corotational - large displacement assumption for compatibility and equilibrium Use the geomTransf command to … Continue reading Geometric Transformation
Pseudo-Time Is Not the Load Factor
In a nonlinear static analysis, the time series associated with lateral loads is typically linear: ops.timeSeries('Linear',1) In this case, the load factor, $latex \lambda$, associated with the time series is equal to the pseudo-time in the domain, i.e., $latex \lambda(t)=t$. Then, when you use the '-time' option in the node and element recorders, you get … Continue reading Pseudo-Time Is Not the Load Factor
Non-Convergence Is Not Structural Collapse
Legend has it that some published research results based on nonlinear dynamic analysis--incremental dynamic analyses, seismic fragility curves, Monte Carlo simulations, etc.--considered a non-convergent OpenSees model to indicate structural collapse or failure. Let's think about this for a minute. Here is the displacement response in two orthogonal directions at the top of a nearly 50 … Continue reading Non-Convergence Is Not Structural Collapse
See the Convergence
Surely you have seen norms fly across the screen when running OpenSees with the print flag of the convergence test set to 1. The screen output slows down your analysis significantly, so you should only use print flag equal to 1 when you are trying to diagnose convergence issues. From a Jupyter Notebook. With OpenSees.exe, … Continue reading See the Convergence
Portwood Digital 