Master of Science / Department of Architectural Engineering / Kimberly W. Kramer / In structural steel connection design, simple shear connections are one of the most common connection types utilized. The industry, especially from the side of the engineer, tends to lean toward using Double Clip Angle Connections as the default standard for simple shear connections. A double clip angle connection is a connection consisting of two angles transferring the shear forces from one member to the next either through bolts or welds. The design of Double Clip Angle Connections is efficient and the connections themselves are easy to fabricate. However, benefits to utilizing other types of shear connections exist. Many of these benefits are seen in the fabrication shop or during erection and construction. This is especially true of single shear plate or shear tab connections when applied to open structure design. Shear tab connections consist of a single plate that transfers the shear forces from one member to the next with bolts or with welds. The design of shear tab connections can be a more involved process than the design of double clip angles. Sometimes the shear plate or shear tab has to be longer than is typical. This is called an extended shear plate connection. These extended shear plates can bring other variables into the design that typically don’t occur with Double Clip Angle Connections such as bending of the plate or the need for multiple bolt columns. However, with proper planning and detailing, the benefits and savings experienced in the fabrication or construction phase may outweigh what can be seen as a more laborious design task. The purpose of this report is to identify the possible benefits achieved in using each of these connections, highlight the differences in the design approach for each, and use a study model to compare the outcome of using one connection over another in the design of a typical open structure. Double clip angles are typically the most efficient approach when speed of design and simplicity of fabrication are the desired outcomes. However, shear plate or shear tab connections have the potential to provide safer erection alternatives and materials savings if used in appropriate ways and with the right applications.

The post-buckled performance of cross-braced single angles was experimentally determined. The results of this study will be used by the Bonneville Power Administration for the analysis of member performance in transmission towers.

The buildings that are designed according to the building codes generally perform well at severe performance objectives (like life safety) under high earthquake hazard levels. However, the building performance at low performance objectives (like immediate occupancy) under low earthquake hazards is uncertain. The motivation of this research is to modify the design and detailing rules to make the traditional systems perform better at multi-level hazards. This research introduces two new structural steel systems: hybrid Buckling Restrained Braced Frames (BRBF) and hybrid steel Moment Frames (MF). The "hybrid" term for the BRBF system comes from the use of different steel material including carbon steel (A36), high-performance steel (HPS) and low yield point (LYP) steel. The hybridity of the moment frames is related to the sequence in the plastification of the system which is provided by using weaker and stronger girder sections. Alternative moment frame connections incorporating the use of LYP steel plates are also investigated. The hybrid BRBF approach was evaluated on seventeen regular (standard) frames with different story heights, seismic design categories and building plans. By varying the steel areas and materials in the BRB cores, three hybrid BRBFs were developed for each regular (standard) frame and their behavior was compared against each other through pushover and incremental dynamic analyses. The benefits of the hybridity were presented using different damage measures such as story accelerations, interstory drifts, and residual displacements. Collapse performance evaluation was also provided. The performance of hybrid moment frames was investigated on a design space including forty-two moment frame archetypes. Two different hybrid combinations were implemented in the designs with different column sections and different strong column-weak beam (SC/WB) ratios. The efficiency of the hybrid moment frame in which only the girder sizes were changed to control the plastification was compared with regular moment frame designs with higher SC/WB ratios. As side studies, the effect of shallow and deep column sections and SC/WB ratios on the moment frame behavior were also investigated.   In order to provide adequate ductility in the reduced capacity bays with special detailing, alternative hybrid moment frame connections adapting the use of low strength steel were also studied. / PhD

Experiments were conducted on ASTM A572 50 and A992 steel over a range of intermediate strain rates in order to determine material strength properties of structural members subjected to dynamic loadings. The yield and ultimate tensile stress (UTS) of the steels were determined at increasing strain rates using a hydraulic apparatus and compared to static values obtained from ASTM E8 standardized tensile experiments. Results revealed that A572-50 steel exhibited an increase in yield stress of up to 35% and UTS of up to 20% as strain rate increased from 0.002 to 2.0 s-1. A992 steel demonstrated a similar increase in yield stress of up to 45% and UTS of up to 20%. Ratios of dynamic-to-static strengths were used to develop dynamic increase factor curves spanning the range of strain rates studied. These curves provide designers with material property values required for accurate and economical design of protective structures.

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The use of concrete-filled tubular composite members and composite beams has been implemented in many structural systems due to their robust structural performance, constructability, and inherent synergy when the steel and concrete components are properly designed and detailed together. While extensive research has been conducted on concrete-filled steel structural members, relatively little has been done regarding similar composite connections. Understanding how composite connections behave in structures and how they should be modeled during the design process is crucial to predict the actual structural behavior of these types of elements when subjected to different loading conditions. The goal of this research is to numerically evaluate CFTs or SRCs members and their connections subjected to axial, shear, and flexural load. Predicting composite connection behavior is exceptionally challenging due to the coupled behavior of the steel and concrete, the residual stresses in the steel, local buckling of the connection, and the sensitivity of the stress-strain response to the steel-concrete contact and confinement performance. To address these issues, a thorough literature search has been carried out and a state-of-the-art report on experimental and numerical models for composite connections is presented. The selected tests represent a range of geometries, materials, and governing failure modes. Initially, a generic connection modeling process was developed and calibrated against a classical test, then three more connections were modeled. To further the understanding of composite behavior, shear studs in steel-concrete composite beams were modeled next, taking as reference a recent experimental program that resulted in an unusual failure. Results indicate that the model can reproduce the most important behavioral aspects observed in the tests, tracking well the strength and stiffness of the samples up to ultimate. The load-deformation curves of the experimental specimens and the analytical models show very good agreement in their transitions and indicate that the behavior of the composite joints is controlled mainly by both the strength of the concrete and the confining effect of the steel tube in the joint. A data appendix containing 135 tests is described and the main characteristics of these tests are summarized in the text. / Doctor of Philosophy / Every day the population increase is more evident, and the main cities of the world are densifying. This implies the accelerated construction of all types of structures, especially tall residential buildings. For the design of these structures, architects design increasingly slender structures, which must be resilient under all types of forces. The foregoing is exerting pressure on structural engineers to design structures that have the capacity to be built in the shortest possible time without losing their functionality and safety. This is where steel and concrete composite construction plays an important role. The main advantage of composite construction is the synergy of both materials. Concrete is inexpensive and provides high stiffness, mass, and fire resistance. Structural steel has high strength, ductility, lightweight, and ease of construction. Composite construction has been used for a long time in tall buildings, and experimental and numerical research has been carried out, especially on the beam and column elements. However, comparatively little research has been done on composite connection behavior and design. This dissertation proposes a numerical evaluation of the composite connections in beams and columns under different types of loads in order to establish modeling parameters that facilitate the analysis and structural design of these elements. The important numerical models are validated with experimental investigations. The results show that the numerical models are capable of simulating the structural behavior of the tests, especially the damage mechanisms and the modeling of local behavior. This study contributes to the development of simulations of composite connections, determining modeling parameters, such as the contact resistance between steel and concrete and the distribution of shear studs in composite beams, among others.

Multi-pass fusion welding by a filler wire (welding electrode) is normally carried out to join thick steel sections used in most engineering applications. Welded joints in an installation, is the area of critical importance, since they are likely to contain a higher density of defects than the parent metal and their physical properties can differ significantly from the parent metal. Fusion arc welding process relies on intense local heating at a joint where a certain amount of the parent metal is melted and fused with additional metal from the filler wire. The intense local heating causes severe transient thermal gradients in the welded component and the resulting uneven cooling that follows produces a variably distributed residual stress field. In multi-pass welds, multiple thermal cycles resulted in a variably distribution of residual stress field across the weld and through the thickness. These complex thermal stresses generated in welds are undesirable but inevitable during fusion welding. Presence of such tensile residual stresses can be detrimental to the service integrity of a welded structure. In addition to a complex distribution of residual stress state, multi-pass welds also forms dendritic grain structure, which are repeatedly heated, resulting in segregation of alloying elements. Dendritic grain structure is weaker and segregation of alloying elements would result in formation of corrosion microcells as well as reduction in overall corrosion prevention due to depletion of alloying elements.

It is vital that Turkey keep abreast of developments in the world and build up its technology to become a developed country. Steel construction is one of these areas. In this context, the main purpose of this study was to define, analyze and evaluate the general characteristics of structural steel and steel construction with the purpose of throwing new light on its advantages and disadvantages. Within this framework, a literature survey was conducted on structural steel components and structures / and on steel construction in Turkey. Additionally, a case study was carried out on a steel office building in Ankara. In this, the T&uuml / rkiye Esnaf ve Sanatkar Kredi Kefalet Kooperatifleri Merkez Birligi (TESKOMB) Building was investigated in terms of the design and production criteria for steel structures and to determine problems faced during these processes. As a result of this study, the existing condition of the construction sector and the means to improve use of structural steel in Turkey were discussed more realistically.

Les aciers de construction au carbone manganèse (C-Mn) sont largement utilisés pour diverses applications mécaniques, et en particulier pour les tuyauteries de circuit secondaire des centrales nucléaires de type Réacteurs à Eau sous Pression (REP). La robustesse des composants des circuits sous pression des REP vis-à-vis de la fissuration doit être démontrée, tant au niveau de la conception que de l’exploitation. Les aciers au C-Mn sont sensibles au vieillissement sous déformation qui entraîne une chute importante de ductilité et de ténacité entre 150 et 350°C,températures de service des tuyauteries du circuit secondaire. Ce phénomène est dû à une interaction entre les atomes de solutés et les dislocations, et peut se traduire entre autres par une sensibilité négative de la contrainte à la vitesse de déformation, et des localisations de la déformation plastique (Lüders, Portevin – Le Chatelier). L’origine physique du vieillissement sous déformation a été beaucoup étudiée, surtout dans les métaux purs, en relation avec le phénomène Portevin-Le Chatelier (PLC), mais son influence sur les propriétés mécaniques et notamment la rupture reste très controversée. L’objectif de la thèse est de modéliser le comportement et la rupture d’un acier au C-Mn dans un large domaine de température compris entre 20 et 350°C, en tenant compte des phénomènes de vieillissement sous déformation, et en particulier des localisations de déformation. Le comportement et la rupture de l’acier au C-Mn étudié ont été caractérisés expérimentalement dans le domaine 20-350°C à l’aide d’essais de traction sur éprouvettes lisses, sur éprouvettes axisymétriques entaillées, et d’essais de déchirure sur éprouvettes CT. Le modèle d’Estrin Kubin McCormick, prenant en compte le vieillissement sous déformation, a été identifié dans cette même gamme de température et la plupart des effets du vieillissement sous déformation ont pu être simulés numériquement : sensibilité négative de la contrainte d’écoulement à la vitesse de déformation, bandes de Lüders, effet PLC, modification des propriétés mécaniques de traction… Le modèle ainsi identifié a été appliqué à l’étude de la rupture d’éprouvettes lisses, entaillées et CT. La baisse de l’allongement réparti est bien décrite en traction sur éprouvettes lisses. Pour prévoir la rupture des éprouvettes entaillées, l’approche locale de la rupture a été appliquée (modèle de Rice et Tracey). Cette étude a donc permis de disposer d’un modèle prenant en compte le vieillissement sous déformation de 20°C à 350°C et décrivant les localisations de déformation plastique de type Lüdersou PLC, pour différentes géométries d’éprouvettes. Ce modèle a été utilisé pour simuler la rupture des aciers au C-Mn, suscitant ainsi une vision nouvelle pour comprendre la baisse de ductilité associée au vieillissement dynamique. / Pas de résumé en anglais disponible.

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