Thèses sur le sujet « Reduced Beam Section »

The P-delta effect is a second order effect experienced by any structure when subjected to lateral loads like earthquake or wind loads, and is originated by an additional destabilizing moment generated due to the gravity acting on the laterally deflected member further displacing it. For the purpose of this research, displacement is considered as the study parameter to analyze the second order P-Delta effects. The main objective of this study is to investigate effects of forces causing P-Delta effects on Single Story Single Bay Steel Moment Frames with Reduced Beam Section Connection (RBS). FEMA-350 and AISC Seismic Design Manual suggest that, if the specified conditions are satisfied, there is no need to provide additional panel zone reinforcements as continuity and doubler plates. This study makes an effort to observe the effects of panel zone strength in formation of plastic hinges and in shifting fracture zone away from the column face on frames with RBS connections under P-Delta effects and find whether further increasing the stiffness of panel zone will have beneficial outcome or not.

The earthquake of Northridge, CA in 1994 caused damages in steel moment frame buildings due to the brittle fractures in beam to column connections. This led to the modifications and improvements in the connection detailing used prior to the Northbridge earthquake. These improvements included use of better welding material and process, use of cover plates (such as Welded Flange Plate connections (WFP)), Reduced Beam Section (RBS) etc. RBS and WFP connections are the two most widely used connection configuration today. Both RBS and WFP connections allow the steel moment frame systems to extensively yield and deform plastically thus avoiding brittle fracturing occurring at the connections. Steel moment frames are comprised of beams and column, in which beams are rigidly connected with columns by welding or bolting. Members and joints resist flexural and shear forces and lateral stability is achieved through bending of the frame elements. WFP connection uses the cover plates of certain thickness and length. This addition of cover plate increases the depth of the beam at the face of the column and thus forces the plastic hinge to form away from face of the column at a certain distance. The RBS connection also protects the beam column connection by forcing the plastic hinge in a beam to form away from the face of the column at a certain distance within the reduced section. This research aims to compare the two types of steel moment connections, WFP and RBS connections, in terms of ductility, strength and stiffness. The connections were designed using the guidelines provided by Federal Emergency Management Agency FEMA-350 (2000) and AISC Seismic Design Manual. The modeling and analysis of the WFP and RBS connection was performed using finite element analysis software. A two story and two bay special moment resisting frame was considered for this study and the first story exterior beam column connection was designed using two different sections of beam and column. Total of four models were used in a half beam and half column configuration. Each selected section of beam and columns was first designed, modeled and analyzed using WFP criteria and then by RBS design guidelines. The span, height, boundary conditions and loads are kept typical for all four models. Results were computed and comparison is made in terms of ductility, strength and stiffness. Strength obtained for each model using finite element analysis software is also compared with hand calculations.

In 1994 there was an earthquake occurred in Northridge, California which caused damage in structures built with Steel Moment Frames (SMF) due to the brittle fractures in the beam and column connections. It has led to the major modifications and improvements in the connection detailing prior to the earthquake occurred in the Northbridge. These changes came up with better materials for welding and introduced the use of cover plate and Reduced Beam Section (RBS). RBS connections are the most widely used connection today and it allows the SMF systems to yield extensively and deform plastically by avoiding brittle fracturing at connections. The most important factors that affect the response along with the design of Steel Moment Frames (SMF) and Reduced Beam Section (RBS) connections are connection strength, stiffness, connection type, use of deep columns and phenomena associated with its instability, the strength of ductility of the column panel zone-beam instability.

Master of Science
Department of Architectural Engineering and Construction Science
Kimberly W. Kramer
Of seismic steel lateral force resisting systems in practice today, the Moment Frame has most diverse connection types. Special Moment frames resist lateral loads through energy dissipation of the inelastic deformation of the beam members. The 1994 Northridge earthquake proved that the standard for welded beam-column connections were not sufficient to prevent damage to the connection or failure of the connection. Through numerous studies, new methods and standards for Special Moment Frame connections are presented in the Seismic Design Manual 2nd Edition to promote energy dissipation away from the beam-column connection. A common type of SMF is the Reduce Beams Section (RBS). To encourage inelastic deformation away from the beam-column connection, the beam flange’s dimensions are reduced a distance away from the beam-column connection; making the member “weaker” at that specific location dictating where the plastic hinging will occur during a seismic event. The reduction is usually taken in a semi-circular pattern. Another type of SMF connection is the Kaiser Bolted Bracket® (KBB) which consists of brackets that stiffen the beam-column connection. KBB connections are similar to RBS connections as the stiffness is higher near the connection and lower away from the connection. Instead of reducing the beam’s sectional properties, KBB uses a bracket to stiffen the connection. The building used in this parametric study is a 4-story office building. This thesis reports the results of the parametric study by comparing two SMF connections: Reduced Beam Section and Kaiser Bolted Brackets. This parametric study includes results from three Seismic Design Categories; B, C, and D, and the use of two different foundation connections; fixed and pinned. The purpose of this parametric study is to compare member sizes, member forces, and story drift. The results of Seismic Design Category D are discussed in depth in this thesis, while the results of Seismic Design Category B and C are provided in the Appendices.

Moment resistant frames are mainly used in resisting lateral loads in buildings. During the 1994 Northridge Earthquake, some of these moment steel frame connections could not undergo inelastic deformation which led to many structural damages. New connection systems were proposed and tested which performed better than the pre-Northridge moment frame connections. Reduced beam section (RBS) connection is one of the most widely used connections after the Northridge Earthquake. Instead of increasing the steel at beam-column, the RBS connection rather removed steel from the flange of the beam. This connection thus gives the designer the option of deciding where the yield will occur in the frame. This research studies the three different parameters used in describing the location and configuration of the radius cut reduced beam section by employing finite element modeling. Variations in ductility, strength and elastic displacement were observed as these parameters were changed. Reducing the flange thus helped with ductility but affected the lateral load carrying capacity and stiffness of the frame.

It was not thought that there would be some major flaws in the design of widely used steel moment frames until the Northridge Earthquake hit the California on January 17, 1994. Until then, steel moment frames were practiced as the most ductile system and were used in buildings from few stories to skyscrapers. The heavy devastation from Northridge Earthquake was an alarm for all the people related to the design and construction of such structures and pushed everybody to act fast to find some possible solutions to such never-expected-problems. Following the earthquake, FEMA entered into a cooperative agreement with the SAC joint venture in order to get a transparent picture of the problems in the seismic performance of steel moment frames and to come up with suitable recommendations. The research was specifically done to address the following things: to inspect the earthquake-affected buildings in order to determine the damage incurred in the buildings, to find out ways to repair the damaged buildings and upgrade the performance of existing buildings, and to modify the design of new buildings in order to make them more reliable for seismic performance. Among the various new design suggestions, the Reduced Beam Section (RBS) connection has been one of the most efficient and reliable option for high ductility demands. The purpose of this research was to study the behavior of concrete slabs in the performance of steel moment frames with reduced beam sections based on ductility, strength and stiffness. The slab is an integral part of a building. It is always wiser to consider the slab in order to assess accurately the seismic behavior of a building under the earthquake loading. In this research, two sets of finite element models were analyzed. Each set had one bare steel moment frame and one concrete slab frame which acted as a composite section. The connections were designed using the AISC Seismic Design manual (AISC 2012). The finite element modeling was done using NISA DISPLAY-IV (NISA 2010). All the models, with and without the slab were analyzed under the same boundary conditions and loads. Both non-linear and linear analyses were performed. The results from non-linear analysis were used to compare the ductility and strength whereas linear analysis results were used to compare the stiffness between bare steel and composite frame models.

Lateral loads from Northridge Earthquake in 1994 caused brittle fractures at column-beam connections in rigid frame structures which hitherto were thought to have high ductility to resist such brittle fractures. These brittle fractures were caused by the moment frame connections’ inability to undergo inelastic deformation which eventually resulted in several structural damages. Reduced beam section (RBS) connection was among one of the solutions proposed by researchers following the Northridge Earthquake. In RBS connections, part of the beam flanges or web at a distance from the face of the column is selectively cut off to reduce its capacity in order to induce plastic hinge away from the beam-column interface. Reducing the beam section, weakens the beam and allows the groove welds and the panel zone to have a higher strength compared to the beam, thereby achieving stronger column-weaker beam design which have a better seismic performance. RBS must provide adequate combination of stiffness, strength and ductility in order to ensure acceptable seismic performance. The scope of this study is to compare strength, ductility and stiffness of reduced beam section under lateral loads only and combined gravity and lateral loads. Four finite element models were created with all conditions kept constant except loading conditions on the frames. Results from this study indicates that all models have almost the same stiffness with the models under combined gravity and lateral loads having higher ductility and ultimate strength.

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.

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.

碩士
國立臺灣科技大學
營建工程系
88
The excellent performance of the Reduced Beam Section used in steel beam-to-column connection has been well acknowledged in the recent years. However only the sections with good cutting shape can guarantee the development of wide plastic zone for dissipating large earthquake energy. This research employs Finite Element Method to analyze the behavior of Ductile Connections and Radius Cutting Connections with various beam length and cutting range. It is found that under earthquake load the Ductile Connection can develop a wide yield zone and maintain good flexural and buckling strength. While the yielding zone of the Radius Cutting Connection is relatively narrow as compared with the Ductile Connection. Beside, the large amount of cutout of radius cutting method will result in a significant reduction both in flexural and in buckling strength. A simplified numerical model is developed in this research to analyze the connection behavior, and the result is proven satisfactory.

碩士
國立成功大學
土木工程學系碩博士班
98
In this article, finite element program ABAOUS is used to simulate the situation of the connection of Reduced Beam Section under high temperature environment, and the structural behavior and destructive model of the connection of Reduced Beam Section under high temperature is observed. Meanwhile, the analytical result is compared with Full Scale specimen to investigate the influence of the cutting treatment of connection on the behavior of connection under high temperature environment. The assigning of temperature field uses Block Temperature Assigned Method and FDS-ABAQUS non-coupling analytical method, at this moment, the difference and applicability of two methods are also compared. Finally, the influence of normal steel and fire-resistant steel on the behavior of Reduced Beam Section connection under high temperature environment is investigated, that is, the level of enhancement of fire-resistant steel on the temperature resistant capability of cutting connection is studied. The result shows that the behavioral model of Reduced Beam Section connection under high temperature environment is similar to that of Full Scale one, that is, the destruction temperature and time has very small difference; meanwhile, Reduced Beam Section connection does not lead to fast destruction of the connection due to insufficient strength in the fire disaster caused by cutting treatment. The simulation results of Block Temperature Assigned Method and FDS-ABAQUS non-coupling analytical method are similar. Finally, from the analytical result, it can be seen that fire-resistant steel has certain degree of enhancement on the high temperature resistant capability of Reduced Beam Section connection.

碩士
國立交通大學
土木工程系
87
The wide spread brittle fractures occurred at the steel moment-resisting frame connections were observed after the 1994 Northridge earthquake. The observed damage prevented the welded beam-to-column connections from the intended inelastic behavior to resist earthquake ground shaking. Numerous researches were, then, undertaken to improve the behavior of such bolted web-welded flange connections. This research summarized the testing investigation results of the reduced beam section connections. An experimental research was conducted to investigate the ultimate flexural strength and ductility performance of reduced beam section (RBS) connections. A total of four full-scale specimens with radius-cut RBS were fabricated. The complete joint penetration groove weld between beam flange and column flange was constructed using high toughness weld metal. Electrode E7018 with high Charpy V notch value was used in the full penetration weld. Another feature was the removal of beam bottom flange backing bars. The specimens were tested under cyclic loads that were achieved by applying increments of stroke to the cantilever beam end by a hydraulic actuator. To prevent out of plane deformation of the beam, lateral bracing system was provided. Experimental results demonstrated that radius-cut RBS connections possessed sufficient flexural strength as well as excellent ductility. The plastic rotation of the beams could reach 3% and even higher than 4%. The design procedure and details for sizing the radius-cut RBS connection were suggested.

碩士
國立高雄應用科技大學
土木工程與防災科技研究所
105
The reduced beam section connection has been proved to be able to dissipate energy by the development of plastic hinge in the reduction area under cyclic loadings. The connection strength and stiffness would gradually decrease due to the local buckling behavior of the plates in the reduction area, which could effects the seismic performance of the building. To recover the performance of the connection, two methods by restrain the buckled plates have been proposed in the study. The FRP sheet is attached on the surface of the plate to enhance the out-of-plane stiffness and strength. The other method is to add steel channels on both sides of the buckled plate and infill the motor the restrain the out-of-plane deformation of the plate. The test results indicate that the anchoring strength of the sheet significantly affects the repair performance. Ductility is increased by adding bolts at the adhesive boundary. From the tests of the steel channels restrained plate, the strength and ductility are significantly increased comparing with that of the buckled plate without out-of-plane restraint.

碩士
國立臺灣大學
土木工程學研究所
87
Five welded beam-to-column moment connections consist of reduced beam sections are cyclically tested. Key parameters include the amount of radius cut and the strength of the beam-column panel zone. Test results indicate that the average strain hardening ratio of the reduced beam section is 1.20. The total plastic rotation capacity of each specimen exceeds 0.04 radian. For strong panel zone joints, most of the plastic rotation concentrates in the reduced beam section. For weak panel zone joints, test results confirm that the amount of beam strength reductions can be reduced thereby delaying the initiation of the inelastic local buckling at the reduced beam section. Test results illustrate that properly proportioned and constructed moment connections employing the reduced beam section and the weak panel can possess excellent inelastic deformation capacity. The paper concludes with recommendations for the design of the reduced beam section and the weak panel in order to achieve well balanced inelastic deformations.

Documentos apresentados no âmbito do reconhecimento de graus e diplomas estrangeiros
The recent earthquake have been shown steel moment frame (SMF) with weld connections are so brittle. According to researches, the more damage were due to cracking of the weld between the beam flange and the column face and induced concentrated stresses in this area. A useful approach to reduce the stress concentration at the panel zone is using of reduce beam section (RBS). Given the enormous impact of seismic behavior and ductility of the panel zone, RBS moves plastic hinge formation at appropriate distance from column face. In this study, a moment connection with different shape of reducing beam flange and web have been modeled using ABAQUS computer program and compared with each other during cyclic behavior. This paper is to present the results of numerical modeling on four subassemblies RBS moment connections. The beam flanges and web reduced by two method that were radial cutting and circular cutting. The circles of one of models were the same and one of them increase gradually. The main objectives are: (1) to comparison between all type of RBS connection on ductility; (2) to study the effect of all type of reduce beam connection on the concentration stress and strain in different zones (3) to study the effect of all type of reduce beam connection on the concentration equivalent plastic strain at integration point (PEEQ) in different zones ; (4) to obtain the influence of various type of reduce flange section on dissipated energy by the whole model; (5) to consider the buckling behavior of the exterior models; (6) to obtain connections secant stiffness and classification them. This study shown that RBS moment connection translate plastic hinge and concentrated of stress from connection to the reduce area. Also RBS connection with Variable radius Hole (RBS-VH) increase stiffness of panel zone, dissipated energy by whole model and ductility of connection. The result of this study show that all models have reached to 0.04 radians rotation, and the strength of connection at 0.04 radians rotation, is more than 80 percent of the beam plastic moment capacity, (0.8Mp). Consequently this connection satisfies the criteria of AISC Seismic Provisions (2005) for special moment frame systems. According to AISC Specifications for Structural Steel Buildings (2005), if KL/ EI > 20, the connection can be considered as fully restrained. Where L and EI are length and bending rigidity of the beam respectively. Values of secant stiffness and KL/EI are presented in the result for all models. As the result shown, all values of KL/EI for RBS connection are greater than 20, therefore according AISC Seismic Provisions, this connection can be classified as a fully restrained (FR) connection. As the result shown, cut the flange area using circles that increase gradually provide beam and connection behavior against buckling.