Timothy M. Whalen

Database-assisted design for wind: basic concepts and software development

Standard provisions for wind loads on buildings have traditionally been based on summary tables and/or plots suitable for slide-rule calculations. The accuracy in the definition of wind loads inherent in such tables and plots is far lower than that inherent in current methods for stress computation. Advances in computational power now make it possible to reduce this discrepancy and achieve structural designs for wind that are significantly safer and more economical than current designs. This is true both for routine, low-rise structures and for flexible structures experiencing significant dynamic effects. In this paper, we present the concept of database-assisted design (DAD) along with a discussion of the application software Wind Load Design Environment, a user-friendly tool for designers and code writers that employs the DAD approach. The DAD approach entails the use of large databases of aerodynamic pressures, the optional use of databases of directional extreme wind speeds, and the use of structural information needed for the description of linear or nonlinear structural behavior. We present progress achieved to date, describe current efforts and future needs, and discuss the implications of DAD for reliability-based design and performance-based standards development.

The method of self-determined probability weighted moments revisited

Haktanir originally introduced the method of self-determined probability weighted moments as an extension of the traditional method of probability weighted moments for parameter estimation. While this method possesses many advantages, his algorithms introduced certain mathematical manipulations for numerical convenience or based upon special knowledge of the behavior of a data sample. Also, some of these algorithms relied upon inputs from numerical tables that are not widely accessible. To improve the usefulness of this method, new algorithms have been developed that directly implement the relevant equations and do not rely upon external results. In this paper, we show that these features extend the applicability of self-determined probability weighted moments without loss of accuracy in the parameter estimates. Examples from flood peak analysis and extreme wind speed estimation are presented.

Fatigue Strength and Evaluation of Double-Mast Arm Cantilevered Sign Structures

Double-mast arm cantilevered sign structures are widely used in Indiana and in many other states. Because of the large sign area and relatively high flexibility, wind loading on these sign structures occasionally produces significant stress cycles. Cracking caused by fatigue damage may occur at several critical spots on the sign structures. An analytical investigation of the fatigue lives of the critical details in double-mast arm sign structures is discussed in this paper. An analytical procedure is introduced, and wind load selection and simulation are explained. Finite element models based on a prototype double-mast arm sign structure are described, and dynamic analyses and fatigue life results are presented. It was found that the post-to-base plate socket weld connection was the most critical detail and that variations in the fatigue life occurred because of differences in the wind environment at various sites.

Fatigue Strength and Evaluation of Sign Structures. Volume I: Analysis and Evaluation

This report is a two-volume final report presenting the findings of the research work that was undertaken to evaluate the fatigue behavior of sign structures and, based on that evaluation, to recommend an inspection plan that can be effectively used to detect and minimize possible deterioration due to wind induced loadings of sign structures. The study included a number of signs that are commonly used in Indiana: single-mastarm and double-mastarm cantilever sign structures, box-truss sign structures, tri-chord sign structures, and monotube sign structures. Sign structures with typical dimensions and details were selected as prototypes for each of the various types of sign structures in the study and were subjected to various wind loading environments. The predicted fatigue behavior of the sign structures was used to identify the types of signs and the structural details that were most susceptible to fatigue damage. This information was used to develop an inspection guideline that provides information on where to look during an inspection for fatigue damage. An inspection plan was formulated by using a crack propagation analysis to evaluate crack growth under the most critical wind loading environment. Based on these analyses, an inspection period of four years was recommended for single and double mastarm cantilever sign structures (Class A) and an eight year inspection cycle was recommended for box-truss, tri-chord, and monotube sign structures.

Design and Application of a Nonlinear Energy Sink to Mitigate Vibrations of an Air Spring Supported Slab

In this paper we consider the application of a nonlinear energy sink (NES), a passive isolation device, to damp out energy from the low frequency modes of an air-spring supported slab to be installed at Purdue University’s Birck Nanotechnology Center. Analytical expressions to obtain energy sink design parameters, given some primary system specifications, have been derived. These expressions are then used to design the NES for the Birck air-spring supported slab. The designed NES is then analyzed via finite elements to study its efficacy in absorbing low frequency vibration from the slab. The study reveals that NES can serve as a good aid in dissipating vibrational energy induced by small disturbances in the slab.Copyright

Fatigue Strength and Evaluation of Sign Structures. Volume 2: Sign Structure Inspection Manual

This report is a two-volume final report presenting the findings of the research work that was undertaken to evaluate the fatigue behavior of sign structures and, based on that evaluation, to recommend an inspection plan that can be effectively used to detect and minimize possible deterioration due to wind induced loadings of sign structures. The study included a number of signs that are commonly used in Indiana: single-mastarm and double-mastarm cantilever sign structures, box-truss sign structures, tri-chord sign structures, and monotube sign structures. Sign structures with typical dimensions and details were selected as prototypes for each of the various types of sign structures in the study and were subjected to various wind loading environments. The predicted fatigue behavior of the sign structures was used to identify the types of signs and the structural details that were most susceptible to fatigue damage. This information was used to develop an inspection guideline that provides information on where to look during an inspection for fatigue damage. An inspection plan was formulated by using a crack propagation analysis to evaluate crack growth under the most critical wind loading environment. Based on these analyses, an inspection period of four years was recommended for single and double mastarm cantilever sign structures (Class A) and an eight year inspection cycle was recommended for box-truss, tri-chord, and monotube sign structures.