No description available.

An efficient beam-column approach, using an improved step-by-step numerical method, is developed in the current research for studying the ultimate strength problems of stiffened panels with two load cases: 1) under longitudinal compression, and 2) under transverse compression. Chapter 2 presents an improved step-by-step numerical integration procedure based on (Chen and Liu, 1987) to calculate the ultimate strength of a beam-column under axial compression, end moments, lateral loads, and combined loads. A special procedure for three-span beam-columns is also developed with a special attention to usability for stiffened panels. A software package, ULTBEAM, is developed as an implementation of this method. The comparison of ULTBEAM with the commercial finite element package ABAQUS shows very good agreement. The improved beam-column method is first applied for the ultimate strength analysis of stiffened panel under longitudinal compression. The fine mesh elasto-plastic finite element ultimate strength analyses are carried out with 107 three-bay stiffened panels, covering a wide range of panel length, plate thickness, and stiffener sizes and proportions. The FE results show that the three-bay simply supported model is sufficiently general to apply to any panel with three or more bays. The FE results are then used to obtain a simple formula that corrects the beam-column result and gives good agreement for panel ultimate strength for all of the 107 panels. The formula is extremely simple, involving only one parameter: the product λΠorth2. Chapter 4 compares the predictions of the new beam-column formula and the orthotropic-based methods with the FE solutions for all 107 panels. It shows that the orthotropic plate theory cannot model the "crossover" panels adequately, whereas the beam-column method can predict the ultimate strength well for all of the 107 panels, including the "crossover" panels. The beam-column method is then applied for the ultimate strength analysis of stiffened panel under transverse compression, with or without pressure. The method is based on a further extension of the nonlinear beam-column theory presented in Chapter 2, and application of it to a continuous plate strip model to calculate the ultimate strength of subpanels. This method is evaluated by comparing the results with those obtained using ABAQUS, for several typical ship panels under various pressures. / Ph. D.

Ductile plastic hinge zones in beams of reinforced concrete frames are known to incur extensive damage and elongate. This ‘beam elongation’ can inflict serious damage to adjacent floor diaphragms, raising concerns of life safety. In light of this, the slotted reinforced concrete beam was investigated as a promising non-tearing floor substitute for conventional design. It consists of a conventional reinforced concrete beam, modified with a narrow vertical slot adjacent to the column face, running approximately three-quarters of the beam depth. Seismic rotations occur about the remaining concrete “top-hinge”, such that deformations are concentrated in the bottom bars of the beam, away from the floor slab, and beam elongation is minimised. The inclusion of the slot raised several design issues which needed to be addressed. These were the shear transfer across the top-hinge, buckling of bottom longitudinal reinforcement, low cycle fatigue, bond anchorage of reinforcement in interior joints, interior joint design, detailing with floor units and beam torsion resulting from eccentric floor gravity loads. These issues were conceptually investigated in this project. It was found that most issues could be resolved by providing additional reinforcement and/or specifying alternative detailing. As part of the experimental investigation, quasi-static cyclic tests were performed on in-plane beam-column joint subassemblies. Specimens tested included exterior and interior joint subassemblies with slotted-beams and a conventional exterior joint as a benchmark. This was followed by a test on a slotted-beam interior joint subassembly with precast floor units and imposed gravity load. Experimental tests revealed significant reductions in damage to both the beam and floor when compared to conventional beams. Issues of bar buckling, bond-slip and altered joint behaviour were also highlighted, but were resolved in the final test. A simple analytical procedure to predict the moment-rotation response of slotted-beams was developed and verified with experimental results. This was used to perform sensitivity studies to determine appropriate limits for the concrete top-hinge depth, top-to-bottom reinforcement ratio and depth of diagonal shear reinforcement. For the numerical investigation, a multi-spring model was developed to represent the flexural response of slotted-beams. This was verified with experimental tests and implemented into a five-storey, three-bay frame for earthquake time history analyses. To provide a benchmark, a conventional frame was also setup using the plastic hinge element developed by Peng (2009). Time history analyses showed that the slotted-beam frame response was very similar to the response of a conventional frame. Due to greater hysteretic damping, there was a slight reduction in the average interstorey drift and lateral displacement envelopes. The slotted-beam frame also exhibited 40% smaller residual drifts than the conventional frame. The research carried out in this thesis showed slotted reinforced concrete beams to be an effective non-tearing floor solution, which could provide a simple and practical substitute for conventional reinforced concrete design.

The recent earthquakes in Christchurch have made it clear that issues exist with current RC frame design in New Zealand. In particular, beam elongation in RC frame buildings was widespread and resulted in numerous buildings being rendered irreparable. Design solutions to overcome this problem are clearly needed, and the slotted beam is one such solution. This system has a distinct advantage over other damage avoidance design systems in that it can be constructed using current industry techniques and conventional reinforcing steel. As the name suggests, the slotted beam incorporates a vertical slot along part of the beam depth at the beam-column interface. Geometric beam elongation is accommodated via opening and closing of these slots during seismically induced rotations, while the top concrete hinge is heavily reinforced to prevent material inelastic elongation. Past research on slotted beams has shown that the bond demand on the bottom longitudinal reinforcement is increased compared with equivalent monolithic systems. Satisfying this increased bond demand through conventional means may yield impractical and economically less viable column dimensions. The same research also indicated that the joint shear mechanism was different to that observed within monolithic joints and that additional horizontal reinforcement was required as a result. Through a combination of theoretical investigation, forensic analysis, and database study, this research addresses the above issues and develops design guidelines. The use of supplementary vertical joint stirrups was investigated as a means of improving bond performance without the need for non-standard reinforcing steel or other hardware. These design guidelines were then validated experimentally with the testing of two 80% scale beam-column sub-assemblies. The revised provisions for bond within the bottom longitudinal reinforcement were found to be adequate while the top longitudinal reinforcement remained nominally elastic throughout both tests. An alternate mechanism was found to govern joint shear behaviour, removing the need for additional horizontal joint reinforcement. Current NZS3101:2006 joint shear reinforcement provisions were found to be more than adequate given the typically larger column depths required rendering the strut mechanism more effective. The test results were then used to further refine design recommendations for practicing engineers. Finally, conclusions and future research requirements were outlined.

Este trabalho apresenta uma análise numérica e experimental sobre o comportamento estrutural de ligações parafusadas viga-pilar com chapa de topo estendida. Discute-se, em particular, o comportamento da chapa de topo e dos parafusos na determinação da capacidade resistente dessas ligações. A análise de resultados numéricos é utilizada como base para as discussões neste trabalho e a modelagem numérica, realizada em elementos finitos com o software ANSYS, incluiu modelos tridimensionais de ligações com chapa de topo estendida e de ligações duplo “T". Com os resultados numéricos e experimentais, os mecanismos de transferência dos esforços entre viga e pilar e os mecanismos de plastificação da chapa de topo e dos parafusos são observados, avaliando-se as linhas de plastificação na chapa de topo em confronto com a metodologia proposta pelo Eurocode 3 na determinação dos perfis “T" equivalentes. Para esses fatores, observou-se que os modos de falha indicados pelo Eurocode 3 não representam satisfatoriamente o comportamento das ligações analisadas. A modelagem numérica, por sua vez, mostrou-se generalista e representativa como ferramenta para análises paramétricas e como complemento de análises experimentais / This work presents a numerical and experimental analysis on the structural behavior of bolted beam-column extended end plate connections. The behavior of the end plate and bolts used in the calculations of the end plate strength is specially discussed. Numerical results are used as basis to the discussions presented in this work and the modeling methodology, with FE models built with the ANSYS code, included 3D models of extended end plate and T-stub connections. The beam-to-column load transfer mechanisms and the yielding mechanisms at end plates and bolts are observed using numerical and experimental results. The yielding lines at the end plate are evaluated against the methodology proposed by Eurocode 3 for the calculations on the equivalent T-stub. Regarding the aforementioned factors, it is shown that the collapse modes indicated by Eurocode 3 do not represent satisfactorily the behavior of the analyzed connections. The numerical modeling was found to be general in application and reliable as a tool for parametric analyses and as a complement to experiments

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High performance cementitious composites have been increasingly used for a range of structural applications in many countries. More recently, a notable interest has been focused on structural performance under seismic loading. However, a critical lack of coherent information and experimental/numerical data available in the literature has to be recognized along with the absence of specific and well-accepted code-guidelines for use of FRC in seismic applications. More specifically, when dealing with seismic resistant frame systems, few researchers have investigated in the past the seismic response of beam-column joints reinforced with steel fibres. These preliminary experimental tests have shown that adding steel fibres in joints is an effective method for improving joint behaviour and energy absorption capacity as well as enhancing the damage tolerance of joints and reducing the number of stirrups in seismic joints. However, due to the limited number of experimental tests as well as of the wide dispersion in the type and mechanical properties of the fibres adopted in these independent researches, the actual contributions of concrete, steel fibres and stirrups to the overall joint shear capacity has not yet been clearly identified and understood. This research aims to investigate the seismic behaviour and failure modes of beam-column joint subassemblies reinforced with steel fibres with the intent to provide preliminary suggestions for a simple but rational analytical procedure to evaluate the joint shear strength when either fibres and/or stirrups are adopted. As part of a more comprehensive on-going research campaign on the seismic behaviour of FRC members and systems, six 2-D exterior beam-column joint subassemblies were tested under simulated seismic loading (quasi-static cyclic loading regime) at the Civil Engineering Laboratory of the University of Canterbury. In order to assess the contribution of steel fibres to the joint (panel zone) shear strength, both under-designed systems (with no transverse reinforcement in the joint, following older practice before the pre-1970s) and well designed systems (following the NZ concrete design standard NZS 3101:1995) were adopted as benchmark specimens. The performance of steel fibre reinforced beam-column joints were compared with that of conventional joints. Results showed that using steel fibre reinforced concrete (SFRC) within beam-column joints can significantly enhance the shear resistance capacity of joints. However, using steel fibre reinforcement alone can not prevent buckling of the reinforcing bars when joints are under high intensity seismic loading. Furthermore, the test results also showed that using steel fibre reinforcement is an effective method to reduce the lateral reinforcement in the beam plastic hinge region. As part of the analytical investigation, a simplified procedure to evaluate the joint shear contribution provided by different amounts of fibres with or without the presence of stirrups has been also introduced. Influence of the axial load on the joint nominal shear capacity has been accounted for by adopting principle stresses. Tentative strength degradation curves (principle tensile stress vs. shear deformation) have also been calibrated on the experimental data which confirmed that a tentative relationship between the joint shear contributions provided by concrete, stirrups and steel fibres was a viable tool for designing SFRC joint. Furthermore, joint shear resistance coefficient contributed by steel fibres has been compared with previous experimental test available in literature to obtain an appropriate value for SFRC joint design guidelines. M_N performance based domain visualization has also been used to evaluate the hierarchy of strength and sequence of events of beam-column joint subassemblies.

In the past few years, some experimental investigations have been conducted to verify seismic behaviour of fiber reinforced polymer reinforced concrete (FRP-RC) beam-column joints. Those researches were mainly focused on exterior beam-column joints without lateral beams. However, lateral beams, commonly exist in buildings, can significantly improve seismic performance of the joints. Moreover, the way the longitudinal beam bars are anchored in the joint, either using headed-end or bent bars, was not adequately addressed. This study aims to fill these gaps and investigate the shear capacity of FRP-RC exterior beam-column joints confined with lateral beams, and the effect of beam reinforcement anchorage on their seismic behaviour. Six full-scale exterior beam-column joints were constructed and tested to failure under reversal cyclic loading. Test results showed that the presence of lateral beams significantly increased the shear capacity of the joints. Moreover, replacing bent bars with headed-end bars resulted in more ductile behaviour of the joints.

In the past few years, some experimental investigations have been conducted to verify seismic behaviour of fiber reinforced polymer reinforced concrete (FRP-RC) beam-column joints. Those researches were mainly focused on exterior beam-column joints without lateral beams. However, lateral beams, commonly exist in buildings, can significantly improve seismic performance of the joints. Moreover, the way the longitudinal beam bars are anchored in the joint, either using headed-end or bent bars, was not adequately addressed. This study aims to fill these gaps and investigate the shear capacity of FRP-RC exterior beam-column joints confined with lateral beams, and the effect of beam reinforcement anchorage on their seismic behaviour. Six full-scale exterior beam-column joints were constructed and tested to failure under reversal cyclic loading. Test results showed that the presence of lateral beams significantly increased the shear capacity of the joints. Moreover, replacing bent bars with headed-end bars resulted in more ductile behaviour of the joints.

Steel moment frames are often used in structures to provide lateral strength and stiffness to the structure. These frames are subject to failure modes including buckling in the out of plane direction in a lateral-torsional buckling mode. This failure mode is influenced by interactions of the members through their connections. While the flexural behaviour has been studied in depth and for some time, the effect of torsional warping interaction between members has not been studied extensively. This work presents an analysis of the effect of including the effects of warping interaction or neglecting them, as is done in the current design practice. The issues of inelastic behaviour are considered, as well as the case of torsionally sensitive members. A joint element model is created to treat the warping displacements and their continuity through the joint. The study finds that the current practice of neglecting the warping displacement continuity appears to be a conservative assumption. It is recommended that the present practice of neglecting the effects of warping in analysis of frames continues. / Structural Engineering