Simulated Response of Degrading Hysteretic Joints With Slack Behavior

Type of Document Dissertation
Author Heine, Christian P
Author's Email Address cheine@vt.edu
URN etd-08092001-100756
Title Simulated Response of Degrading Hysteretic Joints With Slack Behavior
Degree PhD
Department Wood Science and Forest Products
Advisory Committee
Advisor Name Title
J.D. Dolan Committee Chair
F. Woeste Committee Member
J.R. Loferski Committee Member
M.P. Singh Committee Member
R.H. Plaut Committee Member
Keywords

* brittle failure
* hysteresis model
* slack systems
* genetic algorithm
* multiple bolts
* dynamic

Date of Defense 2001-06-22
Availability unrestricted
Abstract

A novel, general, numerical model is described that is capable of predicting the load-displacement relationship up to and at failure of multiple-bolt joints in timber of various configurations. The model is not tied to a single input function and bolt holes are permitted to be drilled oversize resulting in a slack system.

The model consists of five parts. A new mathematical hysteresis model describes the stiffness of the individual bolt at each time step increment and accounts for non-linear and slack behavior; a mechanically-based structural stiffness model explains the interaction of one bolt with another bolt within a joint; an analytically-based failure model computes the stresses at each time step and initiates failure if crack length equals fastener spacing; a stochastic routine accounts for material property variation; and a heuristic optimization routine estimates the parameters needed.

The core model is a modified array of differential equations whose solution describes accurate hysteresis shapes for slack systems. Hysteresis parameter identification is carried out by a genetic algorithm routine that searches for the best-fit parameters following evolutionary principles (survival of the fittest). The structural model is a linear spring model. Failure is predicted based on a newly developed 'Displaced-Volume-Method' in conjunction with beam on elastic foundation theory, elastic theory, and a modified Tsai-Wu Failure criterion.

The devised computer model enhances the understanding of the mechanics of multiple-bolt joints in timber, and yields valid predictions of joint response of two-member multiple-bolt joints. This research represents a significant step towards the simulation of structural wood components.

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