The Impact of Bearing Conditions on the Behavior of Cold-Formed Steel Stud Assemblies

The objective of this study is to explore the structural response of cold-formed steel stud assemblies (i.e., stud and track) with partial bearing conditions. It is hypothesized that studs bearing under partial bearing conditions (i.e., not fully bearing on a concrete slab) may result in reduced axial capacities. Currently, the behavior of these systems on concrete slabs due to member instabilities is not well-understood, and cold-formed steel design specifications provide no guidance. This study provides an integral experimental and numerical investigation of the stability response of the studs under partial bearing conditions in order to quantify the reduction of their axial capacities. A variety of partial bearing conditions are considered in this study by parametrically varying edge (i.e., where the steel stud assembly is close to the concrete slab edge) and overhang (i.e., steel stud assembly is outside the edge) distances. The non-uniform bearing stress underneath the stud caused by concrete cracking, crushing, or a combination thereof is measured to relate with the reduction of the axial capacity of the stud. The results of this study will be used to develop design guidelines for stud wall assembly under non-uniform bearing conditions

Incorporating the shear and transverse extension effects in the global and distortional buckling modes

The traditional global (G), distortional (D), and local (L) mode classes of thin-walled members are conventionally defined according to the characteristics of deformation shape, and the shear and transverse extension strains are separated to form the Shear and Transverse extension mode class (ST), which are not considered in the G, D, and L classes. This paper proposes a new set of basic mode definitions based on the orthogonal completeness principle and the force characteristics, which are more compatible with the complexity of the stress-strain relationships. In contrast to the current generalized beam theory (GBT) and constrained finite strip method (cFSM), the proposed G, D, and L classes span the entire deformation space of the thin-walled member, and are strictly orthogonal to each other with respect to the stiffness of the member. The GD mode class is proposed at first as the deformation of thin-walled members subjected to cross-section mid-line direction uniformly distributed forces, through which the corresponding shear and transverse extension effects are introduced in the G and D modes. The D class is further defined based on an additional force characteristic. Finally, the G and L classes are derived based on orthogonal conditions. Buckling mode decomposition and identification according to the proposed mode classes are realized based on finite strip models of thin-wall members. The numerical example shows that the effects from shear and transverse extension deformations can be reasonably accommodated in the resulting global and distortional buckling modes of the proposed method.The support of this work by the National Program on Key Research and Development Project (No. 2019YFD1101003) and the State Scholarship Found (No. 202006055016) is gratefully acknowledged. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the above funding agencies

Numerical study on residual stresses in press-braked advanced high-strength cold-formed steel angles by finite element simulation

Cold-formed steel is widely used in structural framing for its beneficial high strength-to-weight ratio, recyclability, and for convenient transportation and construction. The rapid advancement of metallurgy during the past two decades has resulted in a new family of steel known as advanced high-strength steel (AHSS) that has a unique microstructure which enables un- precedented combinations of strength and ductility. The material properties and behavior of the AHSS structural members must be quantified to bring AHSS to the construction industry. The cold-forming process, such as press-braking, induces residual stresses which affect the strength and stability behavior of the structural members. Existing numerical studies quan- tified the residual stress of conventional cold-formed steel, but studies of residual stresses in high-strength cold-formed steel are limited. This paper develops computational models to simulate the press-brake process of cold-formed AHSS sections and investigates their residual stress distribution through the simulation. The results are validated with recently conducted experimental studies. Numerical modeling of the press-braking process on AHSS angles by the finite element method was conducted. The model incorporated the residual stresses induced by coiling and uncoiling before the press-braking opera- tion was performed. Lipped angles were studied where the angles were press-braked from a 1.8-mm thick dual-phase steel sheet with a nominal yield strength of 580 MPa and a nominal ultimate strength of 980 MPa. Two different inner corner radii, 1.98-mm and 3.57-mm (5/64-inch and 9/64-inch), were investigated. Stresses at the cross-section corners, legs, and lips on both inner and outer surfaces along the sheet coiling direction were extracted from the analysis results. The stress data from the simulation was validated with its counterparts from a series of experimental measurements using the sectioning method, which are presented in a companion paper.The authors would like to thank Prof. Benjamin Schafer at Department of Civil and Systems Engineering, Johns Hop- kins University for his suggestions on the technical issue re- solving of this numerical study

Numerical investigation of the impact of bearing condition on the axial behavior of variable-height cold-formed steel stud wall assemblies

This paper is devoted to identifying and numerically characterizing the strength of cold-formed steel (CFS) wall assemblies of various height with non-uniform bearing conditions. The results are for a means of evaluating existing design guidelines presented in the North American Specification of the American Iron and Steel Institute (AISI S100-16). In this standard, the bearing condition of the members is not included in equations for predicting axial strength. However, based on the recent experiments done by the authors, non-uniform stress distributions at the ends of CFS studs, caused by different bearing conditions, can reduce the axial capacity of the assemblies. The sources of nonuniformity considered were finite flexibility of the concrete slabs, uneven bearing surfaces provided by the slabs, distance of the wall assemblies to the slab edge, or overhang conditions caused by construction error. In the experiments done by the authors, the height of lipped-channels was fixed to 12 inches to enable comparison across specimens. However, in typical construction, wall assemblies installed on concrete slabs are generally full-height (8 ft or higher) and thus globally-dominant. In this paper, various heights are considered for the studs. They are determined based on the local, distortional, and global buckling half-wavelengths. The impact of bearing conditions on the strength is further elucidated via high-fidelity 3D finite element analyses (FEA). The results of FEAs clarify how the non-uniform stress distribution at the ends of the studs or partial bearing conditions can impact their strengths when they buckle locally, distortionally, and globally. The finite element models are calibrated with existing experimental results. Comparison to available experimental results and to the governing design codes are provided.The authors would like to gratefully thank American Iron and Steel Institute (AISI) for their financial support and Mark Gauthier, the Universit

VGOS: Voxel Grid Optimization for View Synthesis from Sparse Inputs

Neural Radiance Fields (NeRF) has shown great success in novel view synthesis due to its state-of-the-art quality and flexibility. However, NeRF requires dense input views (tens to hundreds) and a long training time (hours to days) for a single scene to generate high-fidelity images. Although using the voxel grids to represent the radiance field can significantly accelerate the optimization process, we observe that for sparse inputs, the voxel grids are more prone to overfitting to the training views and will have holes and floaters, which leads to artifacts. In this paper, we propose VGOS, an approach for fast (3-5 minutes) radiance field reconstruction from sparse inputs (3-10 views) to address these issues. To improve the performance of voxel-based radiance field in sparse input scenarios, we propose two methods: (a) We introduce an incremental voxel training strategy, which prevents overfitting by suppressing the optimization of peripheral voxels in the early stage of reconstruction. (b) We use several regularization techniques to smooth the voxels, which avoids degenerate solutions. Experiments demonstrate that VGOS achieves state-of-the-art performance for sparse inputs with super-fast convergence. Code will be available at https://github.com/SJoJoK/VGOS.Comment: IJCAI 2023 Accepted (Main Track

A Method for Stability Analysis of Periodic Delay Differential Equations with Multiple Time-Periodic Delays

Delay differential equations (DDEs) are widely utilized as the mathematical models in engineering fields. In this paper, a method is proposed to analyze the stability characteristics of periodic DDEs with multiple time-periodic delays. Stability charts are produced for two typical examples of time-periodic DDEs about milling chatter, including the variable-spindle speed milling system with one-time-periodic delay and variable pitch cutter milling system with multiple delays. The simulations show that the results gained by the proposed method are in close agreement with those existing in the past literature. This indicates the effectiveness of our method in terms of time-periodic DDEs with multiple time-periodic delays. Moreover, for milling processes, the proposed method further provides a generalized algorithm, which possesses a good capability to predict the stability lobes for milling operations with variable pitch cutter or variable-spindle speed

Appliance of plastic hinge method considering distortional buckling in pushover analysis of cold-formed rack structure

The objective of this paper is to develop a yielding surface of thin-walled cold-formed steel members subjected to distortional buckling, and then integrate the surface into pushover analysis of rack structures. Distortional buckling is one of the dominant buckling behaviors of rack members due to their intrinsic section profile. In this study, the Axial-Moment-Moment (PMM) interaction surface for a perforated omega column is established using the finite element method and compared with the theoretical one by EN 15512. It is found that the theoretical PMM domain might be conservative. Then, pushover analyses using these two PMM surfaces along with PMM from ASCE 7 are performed on a cold-formed steel rack. The pushover curve and failure mechanism of the models are analyzed with those from a detailed shell Finite Element model and a full-scale experiment. Finally, this approach of employing distortional PMM is comprehensively assessed from computational cost and reliability for its efficiency in engineering practice.We are grateful to Natural Science Foundation of Jiangsu Province for their financial support (No: BK20191268) to this paper