The ANSI/AISC 360-10 Appendix-6 provisions provide limited guidance on the bracing requirements for beam-columns. In cases involving point (nodal) or shear panel (relative) lateral bracing only, these provisions simply sum the corresponding strength and stiffness requirements for column and beam bracing. Based on prior research evidence, it is expected that this approach is accurate to conservative when the requirements can be logically added. However, in many practical beam-column bracing situations, the requirements cannot be logically added. This is because of the importance of the brace and transverse load position through the cross-section depth, as well as the fact that both torsional and lateral restraint can be important attributes of the general bracing problem. These attributes of the bracing problem can cause the current beam-column bracing requirement predictions to be unconservative. In addition, limited guidance is available in the broader literature at the current time regarding the appropriate consideration of combined lateral and torsional bracing of I-section beams and beam-columns. Nevertheless, this situation is quite common, particularly for beam-columns, since it is rare that separate and independent lateral bracing systems would be provided for both flanges. More complete guidance is needed for the proper consideration of combined bracing of I-section beams and beam-columns in structural design. This research focuses on a reasonably comprehensive evaluation of the bracing strength and stiffness requirements for doubly-symmetric I-section beams and beam-columns using refined Finite Element Analysis (FEA) test simulation. The research builds on recent simulation studies of the basic bracing behavior of beams subjected to uniform bending. Various cases of beam members subjected to moment gradient are considered first. This is followed by a wide range of studies of beam-column members subjected to constant axial load and uniform bending as well as axial load combined with moment gradient loading. A range of unbraced lengths are considered resulting in different levels of plasticity at the member strength limit states. In addition, various bracing configurations are addressed including point (nodal) lateral, shear panel (relative) lateral, point torsional, combined point lateral and point torsional, and combined shear panel lateral and point torsional bracing.

AN ABSTRACT OF THE THESIS OF TARUN KUMAR DONGA, for the Master of Science degree in Civil Engineering, Presented on August 29th 2017, at Southern Illinois University Carbondale. TITLE: EFFECT OF TEMPERATURE INCREASE ON BUCKLING OF AXIALLY RESTRAINED BEAM-COLUMNS WITH DOUBLE CURVATURE MAJOR PROFESSOR: Dr. Aslam Kassimali, Ph.D. The main objective of this research was to study the buckling and post-buckling response of axially restrained beam-columns under thermal loading. Also the effects of slenderness ratios on pre-buckling and post-buckling behavior which is neglected in (AISC 2010 specification) for Structural Steel Buildings, was examined. The results of this study indicate that: a) The deflection and end moment amplification factors are significantly smaller for the restrained beam-columns under temperature increase than the corresponding unrestrained beam-columns under mechanical axial loads. - b) The deflection amplification and moment amplification factors tend to increase with increasing ratio of end moments. c) Thermal amplification factors, even in the pre buckling range, were found to be smaller than the AISC (2010) specification values, the difference was more significant for longer beam columns as compared to shorter ones.

A database of composite column tests was augmented and utilized to evaluate the proposed AISC 2005 provisions. The database consists of column and beam-column steel-concrete columns (or encased, SRC), circular concrete filled tubes (CCFT), and rectangular concrete filled tube (RCFT). Information on material and geometric properties on each specimen was summarized. The database includes 119 SRC columns, 136 SRC beam-columns, 312 circular CFT columns, 198 circular CFT beam-columns, 222 rectangular CFT columns and 194 rectangular CFT beam-columns. The database has a total of 1181 specimens, an addition of 451 specimens over those in the original database (Aho 1996). The data on each specimen was analyzed and compared with current design provision for composite columns (AISC 1999 and Eurocode 4), and reassessed by the upcoming 2005 AISC specification. The data indicates that the Eurocode gives good predictions for columns and the AISC 2005 method performs very well for beam-columns. For rectangular CFT columns, all three methods predict the ultimate capacity very well. The main improvement for the AISC 2005 method is its ability to handle specimens which have high yield stress and/or high strength concrete.

Master of Science / Department of Civil Engineering / Asad Esmaeily / Performance-based building design is a necessity in geographic locations where buildings are susceptible to large earthquakes and high winds. This design method requires an analysis of the performance of the structural system with loadings and deflections caused by earthquakes and wind. Current design codes include the load intensity in analysis procedures, but do not consider the effect of load pattern in the performance analysis of reinforced concrete columns. Because a thorough analysis must take into consideration load pattern and load intensity, computer software is ideal to analyze these systems. A computer program was originally developed by Esmaeily (USC_RC), and was revised later to be renamed (KSU_RC) in order to make the analysis of concrete column performance accurate, yet simple for design purposes. This analytical tool used analytical methods and material models, verified against experimental data, to accurately predict the performance of reinforced concrete columns under various loading conditions, including any pattern in lateral direction and independently variable axial load. However, the program was limited to circular, rectangular, hollow circular and rectangular sections and uniaxial lateral curvature and displacement. The next generation of the program, KSU RC 2.0, was developed to overcome the aforesaid limitations.

No description available.

The work described herein emphasizes a new fiber-based approach to modeling the response of structural frames subjected to realistic fire conditions. The proposed approach involves the development and validation of two finite elements that can be used collectively to simulate the thermal and mechanical response of structural frames at elevated temperatures. To model the thermal response, a special-purpose fiber heat transfer element is introduced. The first of its kind, the fiber heat transfer element uses a combination of finite element and finite difference methods to provide an accurate and highly efficient solution to the three-dimensional thermal problem. To simulate the mechanical response, a flexibility-based fiber beam-column element is used. The element presented here extends the formulation of Taucer et al. (1991) to include thermal effects, geometric nonlinearities, and residual stresses. Both fiber elements are implemented in ABAQUS (2007) using the user-defined element (UEL) subroutine. The element formulations are verified by analyses of benchmark experimental tests and comparisons with traditional finite elements. Results indicate that both elements offer superior accuracy and computational efficiency when compared to traditional methods of analysis. Analyses of structures subjected to non-uniform heating emphasize the advantages of the fiber-based approach. To demonstrate a realistic application of the proposed approach, the work concludes with an investigation of the response of unprotected steel beams subjected to localized fires. Because realistic fires are considered, the treatment of strain reversal upon cooling is also addressed. The analyses are used to demonstrate that the standard fire test is generally unconservative at predicting the time at failure of a structure subjected to realistic fire conditions, since failure depends more on the evolution of temperatures within the steel beams than the duration of fire exposure. The analyses also show that critical temperatures from the standard fire test are conservative and thus offer a better means for predicting failure in steel structures within the scope of the standard fire test. / Ph. D.

El empleo de estructuras mixtas de acero-hormigón ha experimentado un aumento creciente en las últimas décadas, dado qu permiten un mejor aprovechamiento de las características de los materiales empleados, en comparación con estructuras de hormigón armado y acero trabajando de forma independiente. Este trabajo de investigación se centra en el estudio y análisis de pilares mixtos de tipo perfil tubular de acero, CFT (Concrete Filled Tube), rectangular o cuadrado, rellenos de hormigón de alta resistencia. Este tipo de pilares cuenta con ventajas respecto a otros pilares mixtos como el hecho de que el perfil de acero sirve de enconfrado para el núcleo de hormigón y a su vez, cuenta con suficiente capacidad resistente como para soportar las cargas exixtentes en fase de construcción. Todo ello permite un importante ahorro, tanto económico, como en las plazos de ejecución. Otras ventajas de estos pilares es que el perfil tubular confina el núcleo de hormigón y este a su vez evita que se produzca el pandeo local del tubo de acero, permitiendo así su plastificación y máximo aprovechamiento. Estas ventajas, proporcionan a los soportes ductibilidad característica muy importante frente a la acción sísima, de ahí que el uso de este tipo de pilares se haya extendido en países como Japón, Estados Unidos y China. Es importante, también, destacar el aumento de resistencia al fuego del sistema en comparación con un perfil de acero hueco. A partir del análisis del estado actual del conocimiento se ha planteado una campaña experiemental que cubre los aspectos no estudiados hasta el momento, y que constituyen los casos más habituales en la práctica real: soportes esbeltos o semiesbeltos sometidos a carga axial y diagrama de momentos no constante. En total se han efectuado 78 ensayos sobre pilares mixtos. Los resultados experimentales se comparan con las previsiones de las normativas de referencia más importantes para el cálculo de pilares mixtos: EC4, AISC 2010, BS5-400:2005, AS5100-6, DBJ13-51, etc, comprobando su validez para el tipo de pilar estudiado. Finalmente se ha planteado un modelo de cálculo simplificado basado en el método de amplificación de momentos y se ha ajustado el factor de rigidez a flexión de los pilares, así como un factor de conversión a diagrama de momentos constantes. / Hernández Figueirido, D. (2012). Estudio experimental del pandeo de perfiles tubulares rectangulares de acero, rellenos de hormigón de alta resistencia, bajo carga axial y diagrama de momentos variables [Tesis doctoral]. Editorial Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/14724