Thesis (Ph. D.)--State University of New York at Binghamton, Mechanical Engineering Dept., 2005. / Includes bibliographical references.

Note:

This thesis investigates the torsional performance of steel structures with and without rigid diaphragm constraints through numerical simulations and evaluates the appropriateness of relevant design provisions in current seismic design codes. In the first part of the work, six theme structures with different (1) in-plane stiffness of diaphragm, and (2) horizontal configurations of vertical braced frames were designed and their performance evaluated through both nonlinear static and dynamic analyses. Comparisons of the analytical results between the structures with and without rigid diaphragm constraints indicate that the in-plane rigidity of the diaphragms affects the efficiency of in-plane force transfer mechanisms, resulting in different global ductility and strength demands. Rigid diaphragm structures exhibit higher global strengths as well as higher torsional rotation capacity because of the infinite in-plane stiffness of the diaphragm. Semi-rigid diaphragm structures have higher ductility demands due to the finite in-plane diaphragm stiffness. The inclusion of bi-axial forces in the analyses reduces the structural strength and increases the ductility demands on the peripheral frames. The axial forces in the collectors and chords that make up the diaphragm depend on (1) the sequence of brace buckling and (2) vertical configuration of the braced frames. The results show higher axial forces in collectors in the roof diaphragms, and higher chord axial forces in the third floor diaphragms. The shear connections in the beams that make up both the collectors and chords are susceptible to failure due to the significant increment of axial forces in those members. The conventional beam analogy used in design can severely underestimate the axial forces in chords and collectors when the structures step into the inelastic stage. / Ph. D.

No description available.

Thesis (M.S.)--University of Wisconsin--Madison, 1967. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

The lateral force resisting system (LFRS) of a steel building consist of two parts, i.e., a vertical LFRS such as braced frames or shear walls, and a horizontal LFRS with diaphragms playing a crucial role. There are various types of floor and roof diaphragms in steel buildings, such as concrete-filled steel deck diaphragms for the floor system and bare steel deck diaphragms for the roof system of a typical steel braced frame building, and standing seam roof diaphragms for a typical metal building. Compared to vertical elements of a building's LFRS, our understanding of the horizontal elements, i.e., the diaphragms, is grossly lacking. The motivation for this work comes from the gaps identified in the research, including the lack of generally adopted acceptance criteria and modeling protocols for seismic performance-based design of bare steel deck and concrete-filled steel deck diaphragms through linear and nonlinear analysis, the need to better understand the complex behavior of concrete-filled steel deck diaphragms with irregular configurations such as reentrant corners and openings under lateral loading, the absence of appropriate Rs values for the alternative diaphragm seismic design approach in the current building code that considers diaphragm inelasticity, and the demand for understanding the in-plane behavior of a standing seam roof system and its use in lateral bracing of rafters in metal buildings. A series of computational and experimental studies were conducted to investigate the behavior of diaphragms in buildings systems, including: 1) development of acceptance criteria and modeling protocol for performance-based seismic design of bare and concrete-filled steel deck diaphragms using a database of existing cantilever diaphragm tests; 2) a computational study on the nonlinear behavior of diaphragms with irregular configurations under lateral loading using high-fidelity finite element models validated against experiment test results; 3) investigation of the seismic behavior and performance of steel buildings with buckling restrained braced frames that considers different diaphragm design approaches and diaphragm inelasticity using nonlinear three-dimensional (3D) computational models; and 4) an experimental study that investigated the in-plane behavior of full-scale standing seam roof assemblies and their use in lateral bracing of rafters in metal building systems. The results of these studies contribute to a better understanding of the behavior of diaphragms in steel buildings and lead to several recommendations for diaphragm design. Firstly, a series of m-factors (ductility measures) and nonlinear modeling parameters (multi-linear cyclic backbone curves) were determined for bare steel deck diaphragms and concrete-filled steel deck diaphragms. These new provisions are recommended for adoption in ASCE 41 / AISC 342, which allows the use of ductility in steel deck diaphragms for their design and retrofits. Secondly, results of the finite element analysis on concrete-filled steel deck diaphragms revealed a concentrated distribution of shear transfer through the shear connections on the collectors of the diaphragm near braced frames and a stress concentration in the composite slab near reentrant corners and openings. Thirdly, results of eigenvalue analyses with nonlinear 3D building models showed that the consideration of diaphragm flexibility led to an increase in first mode period between 13% and 48%. A comparison of results from pushover analyses and response history analyses indicated that even though the pushover analyses (based on a first mode load pattern) identified the BRBF as being weaker than the diaphragms and therefore dominating the inelastic pushover behavior, response history analyses demonstrated that the diaphragms can experience substantial inelasticity during a dynamic response. The response history results also suggest that there would be a significant difference in seismic behavior of buildings modeled as two-dimensional (2D) planar frames as compared to the 3D structures modeled herein. Furthermore, the observed final collapse mode involves an interaction between large BRBF story drifts combined with diaphragm deformations that are additive and exacerbate second order effects leading to collapse. The computed adjusted collapse margin ratios for all buildings satisfied the FEMA P695 criteria for acceptance. Therefore, it is concluded that the alternative diaphragm design procedure with the proposed Rs values (Rs = 2 for concrete-filled steel deck diaphragm and Rs = 2.5 for bare steel deck diaphragm) are reasonable for use in design of these types of structures. Lastly, the effects of different standing seam roof configurations (panel type, clip type, thermal insulation, and purlin spacing) on the in-plane stiffness and strength of the standing seam roof system were investigated through an experimental testing program, and a method was described to use these experimental results in the calculations of required bracing for metal building rafters. / Doctor of Philosophy / A diaphragm is a horizontal structural component (e.g. floors and roof) that transfers lateral forces induced by wind or earthquakes to the vertical portions (e.g. frames and walls) of the lateral force resisting system (LFRS) of the building. There are various types of floor and roof diaphragms in steel buildings, such as concrete-filled steel deck diaphragms for the floor system and bare steel deck diaphragms for the roof system of a typical steel braced frame building, and standing seam roof diaphragms for a typical metal building. Compared to vertical elements of a building's LFRS, our understanding of the horizontal elements, i.e., the diaphragms, is grossly lacking. To address the research gaps in understanding the behavior of diaphragms and utilizing them in building design, this work presents a series of computational and experimental studies. In the first study, past experimental test data were analyzed to develop acceptance criteria and modeling protocol for performance-based seismic design of steel deck diaphragms. In the second study, finite element analyses were conducted to understand the nonlinear behavior of concrete-filled steel deck diaphragms subjected to in-plane lateral loading. In the third study, nonlinear three-dimensional computational building models were developed to investigate the seismic behavior and performance of steel buildings with different diaphragm design approaches and diaphragm inelasticity. In the fourth study, experimental testing on full-scale standing seam roof assemblies was conducted to investigate their in-plane behavior and their use in lateral bracing of rafters in metal building systems. The results of these studies contribute to a better understanding of the behavior of diaphragms in steel buildings and lead to several recommendations for diaphragm design.

The magnitudes of seismic forces which develop in floor diaphragms were investigated in this report to enable the development of a desktop floor diaphragm force design method for use in a structural design office. The general distributions of the forces which develop within the floor diaphragm were also investigated. Two and three dimensional, non-linear numerical integration time history analyses were performed to determine the trends and estimates of inertial and self-strain compatibility transfer forces within floor diaphragms. Sensitivity studies were carried out to determine which simplifying analytical modelling assumptions could be made in the analytical models. It was found that foundation flexibility, shear deformations in walls and the type of plastic hinge model, all affected the magnitudes of forces within floor diaphragms. A range of buildings with different stiffness, strength, height, types of lateral force resisting systems and different locations of the building including different seismic zones and soil types were modelled with the time history analyses method. The results indicated that the magnitudes of inertial forces were primarily related to higher dynamic modes of the structure and the transfer forces were related to the lower modes of vibration of the structure. It was identified that the maximum magnitudes of inertial and transfer forces do not occur simultaneously. The results also indicated that larger inertial and transfer forces, than those predicted by the Equivalent Static Analysis method, developed in the lower levels of the buildings. From these results a static force floor diaphragm design method was developed. Comparisons were made between both the inertial and transfer floor diaphragm forces obtained from the proposed static method, to values from time history analyses. These comparisons indicated that the floor forces obtained by the proposed method were generally larger than the floor forces obtained by the time history results. Elastic and inelastic finite element analyses were used to estimate the in-plane distributions of floor diaphragm forces for floor diaphragms with different geometries and lateral force resisting elements. Comparisons were made between the total tension forces obtained from the finite element analyses and Strut and Tie Analysis methods; these comparisons indicated the relative levels of redistribution of internal forces which could induce cracking within the floor. The comparisons indicated that redistribution cracking in the floors could develop around corner columns, re-entrant corners and openings.

Thesis (M.S.)--State University of New York at Binghamton, Dept. of Mechanical Engineering, 2007. / Includes bibliographical references.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 133-138). Also available via the Internet.

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: Richard E. Klingner. Vita. Includes bibliographical references.