Inelastic behavior in steel special moment frames occurs through the development of plastic hinges at locations near the ends of the beam. The main objective of using a reduced beam connection is to force the formation of plastic hinges to be formed at the reduced beam section rather than at the ends of the beam which otherwise would lead to brittle failure of the beam-column connections. The beam has two reduced beam sections, each located at a certain distance from the face of the column, so that the plastic hinges are formed symmetrically at each of this section. When acted upon by lateral loads, the maximum moments occur at the ends of the beam. Therefore, the plastic hinges form at the reduced beam section. However, when a frame is subjected to a combination of gravity and lateral loads, the plastic hinge formation at one of the reduced beam section is not so clear and further analysis has to be done to study the effect. FEMA 350 indicates that the desired plastic hinge location is only valid for beams with gravity loads representing a small portion of the total flexural demand. If gravity demands significantly exceed 30% of the girder plastic capacity then further plastic analysis of the frame should be performed to determine the appropriate hinge locations. The scope of my thesis is mainly to study the combined effect of gravity and lateral loads on the formation of plastic hinges in steel moment frames with reduced beam section connections.

Reinforced concrete moment-resisting frames are structural systems that work to resist earthquake ground motions through ductile behavior. Their performance is essential to prevent building collapse and loss of life during a seismic event. Seismic building code provisions outline requirements for three categories of reinforced concrete moment-resisting frames: ordinary moment frames, intermediate moment frames, and special moment frames. Extensive research has been conducted on the performance of special moment-resisting frames for areas of high seismic activity such as California. More research is needed on the performance of intermediate moment frames for areas of moderate seismicity because the current code provisions are based on past observation and experience. Adapting dynamic analysis software and applications developed by the Pacific Earthquake Engineering Research (PEER) Group, a representative concrete intermediate moment frame was designed per code provisions and analyzed for specified ground motions in order to calculate the probability of collapse. A parametric study is used to explore the impact of changes in design characteristics and building code requirements on the seismic response and probability of collapse, namely the effect of additional height and the addition of a strong column-weak beam ratio requirement. The results show that the IMF seismic design provisions in ACI 318-08 provide acceptable seismic performance based on current assessment methodology as gravity design appeared to govern the system. Additional height did not negatively impact seismic performance, while the addition of a strong-column weak-beam ratio did not significantly improve results. It is the goal of this project to add insight into the design provisions for intermediate moment frames and to contribute to the technical base for future criteria.

Seismic design criteria have been heavily improved by the Federal Emergency Management Agency (FEMA) after the Northridge CA earthquake in 1994. Most of the damage observed was caused by brittle failure of moment frame connections. This failure was induced by the formation of the plastic hinge at undesirable locations in the beam and the column near the connection. Using welded flange plate (WFP) connections will force the formation of the plastic hinge away from the face of the column while preventing the brittle failure of the moment connection. FEMA-350 design criteria recommendations for WFP connections suggest that the plastic hinge will form away from the face of the column directly under the cover plate. The purpose of this research is to prove that the plastic hinge will form away from the face of the column, at a distance of approximately half the depth of the beam away from the cover plate. The further away the plastic hinge is from the face of the column the higher the connection demands. Therefore, underestimating the location of the plastic hinge could lead to under designed connections. The modeling and analysis of WFP connections was performed using finite element analysis software. A total of eight models with half beam half column configuration were considered in this study. Each selected section of beam and column was first designed, modeled and analyzed using WFP connections design recommendations from FEMA-350, with calculations modifications to account for the proposed plastic hinge location. Results were computed and comparisons were made in terms of plastic hinge location from the cover plates. Strength obtained for each model using finite element analysis software was also compared with hand calculations. This research also proves that increasing the thickness of the cover plates will generate an increase in the connection capacity and strength.

In this dissertation, the seismic behavior and design of AAC-infilled steel moment frames are investigated systematically. The fundamental vehicle for this investigation is the ATC-63 methodology, which is intended for the establishment of seismic design factors for structural systems. The ATC-63 methodology is briefly reviewed, including the concepts of archetypical structures, design rules and mathematical models simulating the behavior of those archetypes. A limited experimental investigation on the hysteretic behavior of an AAC-infilled steel moment frame is developed, conducted, and discussed. Using the experimental results of that investigation, the draft infill design provisions of the Masonry Standards Joint Committee (MSJC) are extended to AAC infills, and a mathematical model is developed and calibrated to simulate the behavior of AAC infills under reversed cyclic loads. Prior to application of ATC-63 methodology to AAC-infilled steel moment frames, the methodology is applied to an example steel moment frame to demonstrate the methodology and verify understanding of it. Then, archetypical infilled frames to be evaluated by the ATC-63 methodology are developed using a series of pushover analyses. Infill configurations whose total lateral strength in a particular story exceeds about 35% of the lateral strength of the bare frame in that story are observed to provoke story mechanisms in the frame. Based on this observation, archetypical infilled frames are selected conforming to two infill configurations: uniformly infilled frames, and open ground story frames. Each infill configuration includes archetypes whose ratio of infill strength to bare-frame strength at each story is less than 35%, and archetypes whose ratio is greater than 35%. The former archetype is typical of steel moment frames infilled with AAC; the latter archetype is typical of steel moment frames infilled with conventional (clay or concrete) masonry. The ATC-63 methodology, specialized for application to infilled frames, is applied to the archetypical infilled frames developed above. The performance of those archetypical infilled frames is evaluated, and seismic design factors are proposed for AAC-infilled steel moment frames. The extension of this work to other types of infilled frames is discussed. / text

Master of Science / Department of Architectural Engineering and Construction Science / Kimberly W. Kramer / In 2006, a research project was being carried out by architects at architecture/engineering firm Cannon Design involving an optimum bay size for a hospital. RISA computer modeling was used to explore a set of lateral force resisting system (LFRS) options for a building based on this optimum bay size and importance category. The structural material was first narrowed down to steel, and then moment frames and braced frames are examined. The LFRS was narrowed down to braced frames, discarding moment frames due to their inordinate story drift. Of the different types of braced frames, the study further narrowed the LFRS system to chevron braced frames. Then the precise arrangement of braces for a particular building size using this bay system was examined. The steel material cost of the final system was compared to a system that only included members sized for gravity loads to demonstrate the rough amount of cost that a lateral system can add to a building.

This thesis presents results of research aimed at developing an improved understanding of the behavior of column panel zones reinforced with doubler plates in seismic resistant steel moment frames. A primary goal of the research was to develop data to support the development of improved design guidelines for welding doubler plates to columns, with and without the presence of continuity plates. The research addressed several issues and questions related to welding and detailing of doubler plates. This included evaluation of the effects of welding the top and bottom of the doubler plate in addition to the vertical edges, the effects of extending the doubler plate beyond the panel zone, and the impact of welding a continuity plate to a doubler plate. These issues were investigated through detailed finite element models of a simplified representation of the panel zone region, subjected to monotonic loading. The results of the research suggest that, in general, there is little benefit in welding the top and bottom edges of a doubler plate if the vertical edges are welded, particularly in terms of overall panel zone strength and stiffness. However, the top and bottom welds provide some benefit in reducing stresses on the vertical welds. The results also suggest that extending the doubler plate above and below the panel zone has little benefit for heavy columns of shallow depth, such as the W14x398 considered in this analysis. However, extending the doubler plate did result in approximately a 10-percent increase in panel zone strength for deeper columns, such as the W40x264 considered in this analysis. Finally, the results showed that welding a continuity plate directly to a doubler plate had no adverse effects on the doubler plate in terms of increased forces or stresses. Interestingly, welding the continuity plate to the doubler plate simply changed the load path for transfer of load from the beam flange to the column web and doubler plate, but did not change the stresses in the doubler plate. Further research is needed to validate these findings for more accurate representations of the panel zone region of the column and for cyclic loading. / text

While moment frames are a popular lateral-force resisting system, their constant cross-section can lead to inefficiencies in energy absorption and stiffness. By tapering the flange width linearly toward the center of the beam length, the energy absorption efficiency can be increased, leading to a better elastic response from the beam and more elastic stiffness per pound of steel used. Lateral-torsional buckling is an important failure mode to be considered for tapered-flange moment frame shapes. No closed-form or finite element solutions have yet been developed for tapered-flange I-beams with a non-uniform, linear moment gradient and intermediate bracing conditions. In this study, finite element analysis is used to find the buckling stress of each W-shape in the AISC Steel Construction Manual with both a standard straight-flange and the proposed tapered-flange at several lengths and with three intermediate lateral bracing conditions (no bracing, mid-span bracing, and third-span bracing). Plots are generated for each shape at each bracing condition as the buckling stress versus length for both beams and columns. Overall, the results indicate that lateral-torsional buckling of tapered-flange I-beams is not a problem that would prohibit the wide-scale use of this configuration in moment frames. Also, the buckling capacity tapered-flange moment frame shapes can be reasonably estimated as 20% of the corresponding straight-flange moment frame shape.

No description available.

Steel moment frames are a popular seismic-force resisting system, but it is believed that they are susceptible to early fracture if there is a stress concentration in the plastic hinge region, also known as the protected zone. If a defect is present in this area, it may be repaired by grinding and/or welding, but little research has investigated how the repairs affect the performance of full-scale moment connections subjected to inelastic rotations. Thus, the goals of this research were to establish the performance of full-scale moment connections with repairs and defects, then develop a method for predicting fracture of the full-scale specimens using more economical cyclic bend tests. To do this, six full-scale reduced beam section (RBS) connections were tested having arrays of repairs or defects applied to the flanges. The repairs were 0.125 in. deep notches ground to a smooth taper and 0.25 in. deep notches ground to a smooth taper, welded, and ground smooth. The defects were sharp 0.25 in. and 0.375 in. notches. In addition, 54 bend tests were conducted on beam flange and bar stock coupons having the same repairs and defects, power actuated fasteners, puddle welds, and no artifacts. Finally, Coffin-Manson low-cycle fatigue relationships were calibrated using results from the cyclic bend tests with each artifact (repair, defect, or attachment method) and used in conjunction with estimates of full-scale plastic strain amplitudes to predict fracture of full-scale specimens. All four of the full-scale moment connections with repairs satisfied special moment frame qualification criteria (SMF). One full-scale specimen with sharp 0.25 in. notches satisfied SMF qualification criteria, but the flexural resistance dropped rapidly after the qualification cycle. On the other hand, the specimen with sharp 0.375 in. notches did not satisfy SMF qualification criteria due to ductile fractures propagating from the notches. The proposed method for predicting fracture of full-scale connections was validated using the six current and six previous full-scale RBS specimens. This method underpredicted fracture for eleven of the twelve specimens. The ratio of the actual to predicted cumulative story drift at fracture had a mean of 1.13 and a standard deviation of 0.19. / M.S. / Moment connections in steel structures resist earthquake loads by permanently deforming the material near the connection. This area is called the protected zone and is critical to the safety of the structure in an earthquake. Due to this importance, no defects are allowed near the connection, which can include gouges or notches. If a defect does occur, it must repaired by a grinding or welding. These are the required repair methods, but there have be no tests to determine how the repairs affect the strength and ductility of the connection. This research tested six full-scale moment connections with defects repaired by grinding and welding, as well as unrepaired defects. A correlation was also developed and validated between the full-scale tests and small-scale bend tests of steel bars with the same defects and repairs. This relationship is valuable because the small-scale tests are quicker and less expensive to conduct than the full-scale tests, meaning other defects or repairs could be easily tested in the future. All but one of the six full-scale specimens met the strength requirements and had adequate ductility. The one test specimen that failed had an unrepaired defect. The relationship between the full-scale and small-scale tests underpredicted fracture (a conservative estimate) for the five of the full-scale tests and overpredicted fracture (unconservative estimate) for one test.

A number of recent research studies have investigated the performance of panel zones in seismic-resistant steel Special Moment Resisting Frames (SMF). These recent studies investigated various options for attaching doubler plates to the column at beam-column joints in SMF for purpose of increasing the shear strength of the panel zone. This previous work was primarily focused on doubler plates that extend beyond the top and bottom of the attached beams, and considered cases both with and without continuity plates. As an extension to this previous research, this thesis explores the situation when a doubler plate is fitted between the continuity plates. The objective of this research was to evaluate various options for welding fitted doubler plates to the column and continuity plates through the use of finite element analysis, and to provide recommendations for design. The development and validation of the finite element model are described, along with the results of an extensive series of parametric studies on various panel zone configurations and attachment details for fitted doubler plates. Based on the results of these analyses, recommendations are provided for design of welds used for attaching fitted doubler plates in the panel zone of SMF systems. / text