Four aspects influencing the vibration characteristics of steel member supported floors were investigated. The four aspects are: 1) the number of tee-beams effective in resisting a heel-drop impact for steel joist and steel beam-concrete slab floors, 2) the effective moment of inertia of steel joist and joist-girder members, 3) the ability of joist seats to provide composite behavior between the supporting member and overlying slab, and 4) the effects of extending and restraining the bottom chords of joist members. A new equation was developed to predict the number of effective tee-beams. The proposed equation is recommended to replace the two current equations. The proposed equation is a regression equation based on the results of a finite element analysis of 240 floor systems and is considered to be more accurate than the current equations. Next, a study was undertaken to determine the relationship between the span-to depth ratio of a joist or joist-girder member and it's effective moment of inertia. Twenty five joists and joist-girders were modeled and analyzed using the finite element method and their effective stiffnesses calculated. The effective stiffness of each member was plotted against the respective span-to-depth ratio. A linear regression line was then fit to the data to mathematically represent the trend. Finally, a vibration test floor was constructed to investigate the joist seat behavior and extended bottom chords. Finite element models were developed and analyzed and frequency and stiffness tests were performed to evaluate the floor's behavior. Conclusions were then drawn and recommendations made concerning the joist seat behavior and the effects of extending joist bottom chords. / Master of Science

Thesis (M.S.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 133-138). Also available on the World Wide Web.

Thesis (M.S.)--University of North Texas, Dec., 2008. / Title from title page display. Includes bibliographical references.

This thesis presents elastic-plastic finite element analyses of seven long span composite open-web steel joists. These analyses account for the incomplete interaction between the concrete slab and the steel joist by modeling the nonlinear behavior of the steel shear connectors. Experimental tests on long span composite open-web steel joists were performed at Virginia Polytechnic Institute and State University. Measurements of joist deflections, member strains, and slip between the concrete slab and steel joist were recorded. The response of the finite element models agree reasonably well with the response of the test prototypes where the shear connector position was known. The finite element model can be generated on any general purpose finite element program that includes beam elements and nonlinear spring elements. The finite element model can give reasonable predictions of deflections and ultimate load capacity of a composite open-web steel joist. / Master of Science

Studies on the effective moment of inertia of girders that support concrete slabs using joist seats as the horizontal shear connections, and a cost efficiency analysis comparing composite and non-composite floor systems that meet vibrations design standards, were conducted. The first study was undertaken because over-prediction of girder effective moment of inertia was the suspected cause of several recent vibration problems in floors supported by widely spaced LH-series joists. Eight purpose-built floors of the type in question were subjected to experimental tests of girder effective moment of inertia and girder frequency. Frequencies were tested for two live loading cases. Three separate test configurations were made with each floor by changing the seat-to-girder connections between bolted, welded, and reinforced. In the study, 1) the accuracy of the current design practice is assessed, 2) a new relationship was proposed, and 3) suggestions for finite element modeling are made. In recent years, composite construction has been used to improve cost efficiency by reducing structural weight and in some cases by reducing story height. However, vibration problems are a design consideration in composite floors because lighter floors tend to be more lively. It is not clear if cost savings can be made with composite construction if vibrations are considered in the design. To compare the cost of composite and non-composite floors that satisfy AISC/CISC Design Guide criterion for walking excitation, four typical size bays were analyzed using commercial design software that finds the least expensive member configuration for a given bay size. All acceptable bay configurations of member sizes and spacing were evaluated for least non-composite and composite costs, then these results were compared. The findings show that composite construction can be more economical when initial dead load deflections do not control the design. / Master of Science

The objective of this research is to create a computationally efficient seismic analysis framework for cold-formed steel (CFS) framed-buildings supported by hysteretic nonlinear models for CFS members and screw-fastened connections. Design of CFS structures subjected to lateral seismic forces traditionally relies on the strength of subassemblies subjected to lateral loading of systems, such as strapped/sheathed shear walls and diaphragms, to provide adequate protection against collapse. Enabling performance-based seismic design of CFS buildings requires computationally efficient and accurate modeling tools that predict the nonlinear cyclic behavior of CFS buildings, the individual CFS components and connections. Such models should capture the energy dissipation and damage due to buckling and cross-sectional deformations in thin-walled CFS components subjected to cyclic loads such as those induced by earthquakes. Likewise, models for screw-fastened CFS connections should capture the energy dissipation and damage due to tilting, bearing, or screw shear when subjected to cyclic loading. In this dissertation, an analysis framework for CFS structures that captures the nonlinear cyclic behavior of critical components including axial members, flexural members, and screw fastened connections is presented. A modeling approach to simulate thin-walled behavior in CFS members is introduced where parameters were developed using results from an experimental program that investigated the cyclic behavior and energy dissipation in CFS axial members and flexural members. Energy dissipation and cyclic behavior of CFS members were characterized for members experiencing global, distortional and local buckling. Cyclic behavior and energy dissipation in thin steel plates and members was further investigated through finite element analysis in ABAQUS to provide a strategy for modeling steel columns cyclic behavior including local buckling. Model parameters were developed as generalized functions of the hysteretic energy dissipated and slenderness. The capabilities of the analysis framework are demonstrated through simulations of CFS wood sheathed shear wall cyclic responses validated with experimental results from full scale shear wall tests. / Ph. D.

The research was focused on the three major structural elements of a typical cold-formed steel building - shear wall, floor joist, and column. Part 1 of the thesis explored wider options in the steel sheet sheathing for shear walls. An experimental research was conducted on 0.030 in and 0.033 in. (2:1 and 4:1 aspect ratios) and 0.027 in. (2:1 aspect ratio) steel sheet shear walls and the results provided nominal shear strengths for the American Iron and Steel Institute Lateral Design Standard. Part 2 of this thesis optimized the web hole profile for a new generation C-joist, and the web crippling strength was analyzed by finite element analysis. The results indicated an average 43% increase of web crippling strength for the new C-joist compared to the normal C-joist without web hole. To improve the structural efficiency of a cold-formed steel column, a new generation sigma (NGS) shaped column section was developed in Part 3 of this thesis. The geometry of NGS was optimized by the elastic and inelastic analysis using finite strip and finite element analysis. The results showed an average increment in axial compression strength for a single NGS section over a C-section was 117% for a 2 ft. long section and 135% for an 8 ft. long section; and for a double NGS section over a C-section was 75% for a 2 ft. long section and 103% for an 8 ft. long section.