Sheathing Braced Design of Wall Studs

This report was prepared as part of the American Iron and Steel Institute sponsored project: Sheathing Braced Design of Wall Studs. The project also received supplementary support and funding from the Steel Stud Manufacturers Association. Additional project information and documentation is available at www.ce.jhu.edu/bschafer/sheathedwalls. Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the author and do not necessarily reflect the views of the American Iron and Steel Institute, nor the Steel Stud Manufacturers Association

Prototype selection for parameter estimation in complex models

Parameter estimation in astrophysics often requires the use of complex physical models. In this paper we study the problem of estimating the parameters that describe star formation history (SFH) in galaxies. Here, high-dimensional spectral data from galaxies are appropriately modeled as linear combinations of physical components, called simple stellar populations (SSPs), plus some nonlinear distortions. Theoretical data for each SSP is produced for a fixed parameter vector via computer modeling. Though the parameters that define each SSP are continuous, optimizing the signal model over a large set of SSPs on a fine parameter grid is computationally infeasible and inefficient. The goal of this study is to estimate the set of parameters that describes the SFH of each galaxy. These target parameters, such as the average ages and chemical compositions of the galaxy's stellar populations, are derived from the SSP parameters and the component weights in the signal model. Here, we introduce a principled approach of choosing a small basis of SSP prototypes for SFH parameter estimation. The basic idea is to quantize the vector space and effective support of the model components. In addition to greater computational efficiency, we achieve better estimates of the SFH target parameters. In simulations, our proposed quantization method obtains a substantial improvement in estimating the target parameters over the common method of employing a parameter grid. Sparse coding techniques are not appropriate for this problem without proper constraints, while constrained sparse coding methods perform poorly for parameter estimation because their objective is signal reconstruction, not estimation of the target parameters.Comment: Published in at http://dx.doi.org/10.1214/11-AOAS500 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

Electrostatic Field Classifier for Deficient Data

This paper investigates the suitability of recently developed models based on the physical field phenomena for classification problems with incomplete datasets. An original approach to exploiting incomplete training data with missing features and labels, involving extensive use of electrostatic charge analogy, has been proposed. Classification of incomplete patterns has been investigated using a local dimensionality reduction technique, which aims at exploiting all available information rather than trying to estimate the missing values. The performance of all proposed methods has been tested on a number of benchmark datasets for a wide range of missing data scenarios and compared to the performance of some standard techniques. Several modifications of the original electrostatic field classifier aiming at improving speed and robustness in higher dimensional spaces are also discussed

Impact of Corner Radius on Cold-formed Steel Member Strength

The objectives of this paper are to expl ore (a) how corners of cold-formed steel members are included or ignored in current design methods, and (b) the effectiveness of recent proposals for modifying the strength prediction for local buckling to account for corners. The imp act of round corners is examined on the behavior and strength of isolated elements and on full members using material and geometric nonlinear collapse analysis with shell finite elements in ABAQUS. Comparisons between the available methods and the nonlinear finite element analysis are completed to explore the regimes in which the methods are accurate, as well as when they are deficient. The current appr oach in the main Specification of AISI-S100-07, which applies no reductions regardless of corner size, is demonstrated to be uncons ervative. Initial recommendations for the design of sections with large corner radi us by effective width and direct strength methods are provided

Buckling Analysis of Cold-formed Steel Members with General Boundary Conditions Using CUFSM Conventional and Constrained Finite Strip Methods

The objective of this paper is to provide the theoretical background and illustrative examples for elastic buckling analysis of cold-formed steel members with general boundary conditions as implemented in the forthcoming update to CUFSM. CUFSM is an open source finite strip elastic stability analysis program freely distributed by the senior author. Although the finite strip method presents a general methodology, the conventional implementation (e.g. CUFSM v 3.13 or earlier) employs only simply-supported boundary conditions. In this paper, utilizing specially selected longitudinal shape functions, the conventional finite strip method is extended to general boundary conditions, including the conventional case: simply-simply supported, as well as: clamped-clamped, clamped-simply supported, clamped-free, and clamped-guided. The solution remains semi-analytical as the elastic and geometric stiffness matrices are derived in a general form with only specific integrals depending on the boundary conditions. An example of the stability solution is provided. The selection of longitudinal terms to be included in the analysis is discussed in terms of balancing accuracy with computational e fficiency. Also herein, the constrained finite strip method is extended to general boundary conditions. Both modal decomposition and identification can be carried out based on the new bases developed for the constrained finite st rip method, and illustrative examples are provided. This extension of CUFSM is intended to aid the implementation of the direct strength method to the cas e of general boundary conditions

Measured Geometric Imperfections for Cee, Zee, and Built-Up Cold-Formed Steel Members

Geometric imperfections play an important role in the performance and behavior of cold-formed steel members. The objective of this paper is to present recent results from measurements of cold-formed steel members conducted by a laser scanner. The measurements provide complete and precise three-dimensional point clouds of the specimens and can be processed to determine dimensional variations as well as variations within the plates. Processing of the data can range from simple: e.g., mean lip length, to complex: e.g., modal decomposition magnitudes of the measured imperfections. Three different shapes of cold-formed steel members are selected for study: Cee, Zee, and built-up sections comprised of back-to-back Cee’s. Realized dimensions of the studied cold-formed steel members are statistically explored providing mean and standard deviation and correlation data amongst the dimensions (flange width, lip length, flange-to-lip angle, etc.) can be readily performed. In addition, global (bow, camber, and twist) imperfections and cross-section Type I and Type II plate imperfections are determined from the scanned specimens. Modal imperfections decomposed into local, distortional, and global can also readily be calculated. The paper aims to demonstrate the worth of performing the three-dimensional geometric imperfection scanning and to provide useful data for simulations of cold-formed steel members. In the future it is anticipated that a systematic study of member imperfections could be used to provide definitive characterizations to help enable geometric imperfection selection in new analysis-based design approaches

Comparison of AISI Specification Methods for Members with Single Intermediate Longitudinal Stiffeners

In the current AISI specification, there are two different methods for calculating the effective widths of longitudinally stiffened elements. The first method “B4.1” applies solely to the element with only one intermediate stiffener, whereas the second method “B5.1” works only for those elements with more than one intermediate stiffener. Both methods are accurate in finding the design moments if used appropriately. Although two methods are developed to handle different cases, for some sections with one intermediate stiffener, the second method also works accurately, giving the same result as the first method does for calculating design moments. For some other sections with one intermediate stiffener, the multiple stiffener method when applied to the case of a single stiffened becomes different. These different sections can be distinguished with sets of parameters discussed herein. By comparing the design moments obtained with the same sets of parameters, one can predict when the two methods would have the largest difference and no difference in calculating the design moments and effective widths

Observations and models for needle-tissue interactions

The asymmetry of a bevel-tip needle results in the needle naturally bending when it is inserted into soft tissue. In this study we present a mechanics-based model that calculates the deflection of the needle embedded in an elastic medium. Microscopic observations for several needle- gel interactions were used to characterize the interactions at the bevel tip and along the needle shaft. The model design was guided by microscopic observations of several needle- gel interactions. The energy-based model formulation incor- porates tissue-specific parameters such as rupture toughness, nonlinear material elasticity, and interaction stiffness, and needle geometric and material properties. Simulation results follow similar trends (deflection and radius of curvature) to those observed in macroscopic experimental studies of a robot- driven needle interacting with different kinds of gels. These results contribute to a mechanics-based model of robotic needle steering, extending previous work on kinematic models