Comparison of Form-finding Methods to Shape Concrete Shells for Curved Footbridges
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Shells are attractive and efficient structures that play a special role for engineers and architects. However, only few bridges supported by concrete shells have been designed and built after the Musmeci’s bridge in Potenza (Italy). Several numerical form-finding methods have been implemented in the last decades to optimize the shape of shells. In the present paper, a comparison of the Thrust Network Analysis (TNA) and Particle-Spring System (PS) is made by searching the optimal shape of a concrete shell supporting the curved cantilevered deck of a pedestrian bridge under the same boundary conditions. Finite Element Analysis was performed to compare the structural behaviour of the footbridges optimized by the two different form-finding techniques. The effectiveness of both form-finding methods in minimizing unfavourable tensile stresses in concrete shells, thus taking advantage of mechanical properties of concrete, is investigated. Furthermore, transverse deflections of the curved cantilevered deck were reduced introducing an external prestressing system applied to the upper flange of the ring box girder. Finally, the obtained results can help architecture and engineering practitioners to develop innovative bridge conceptual design.Keywords:
Bridge (graph theory)
Flange
This research document focuses on prestressed PCBT girders made composite with a cast-in-place concrete deck and continuous over several spans through the use of continuity diaphragms. The current design procedure in AASHTO states that a continuity diaphragm is considered to be fully effective if a compressive stress develops in the bottom of the diaphragm when the superimposed permanent load, settlement, creep, shrinkage, 50 percent live load, and temperature gradient are summed, or if the girders are stored at least 90 days when continuity is established. It is more economical to store girders for fewer days, so it is important to know the minimum number of days that girders must be stored to satisfy AASHTO requirements. In 2005, Charles Newhouse developed the positive moment diaphragm reinforcement detail that is currently being adopted by VDOT. This thesis concludes that Newhouse’s detail, four No. 6 bars bent 180° and extended into the diaphragm, is adequate for all girders except for the PCBT-77, PCBT-85, and the PCBT-93 when the girders are stored for a minimum of 90 days. It is recommended that two additional bent strands be extended into the continuity diaphragm for these three girder sizes. It was also concluded that about half of the cases result in a significant reduction in the minimum number of storage days if the designer is willing to perform a detailed analysis. The other half of the cases must be stored for 90 days because the total moment in the diaphragm will never become negative and satisfy the AASHTO requirement. In general, narrower girder spacing and higher concrete compressive strength results in shorter required storage duration. The PCA Method was used in this analysis with the updated AASHTO LRFD creep, shrinkage, and prestress loss models. A recommended quick check is to sum the thermal, composite dead load, and half of the live load restraint moments. The girder must be stored 90 days if that sum is positive, and a more detailed time-dependent analysis would result in a shorter than 90 day storage period if that sum is negative.
Diaphragm (acoustics)
Shrinkage
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Deck slabs in ladder decks span longitudinally between transverse cross-girders and the primary function of these cross-girders is to support the deck slab. The girders may, however, need to perform the secondary function of preventing the slab from buckling in compression. The concrete deck slab of a ladder deck can have a very large transverse span between main girders. This large unsupported width can lead to buckling of the slab in compression unless it is prevented from doing so by transverse girders. If the spacing of the cross-girders is large, it is still possible for second-order bending moments to develop in the slab under the effects of global compression. This paper sets out guidance on the limiting spacing of main girders and cross-girders to avoid consideration of second-order effects and also the means of determining second-order effects in slabs and cross-girders when this becomes necessary.
Slab
Limiting
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Flange
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Flange
Pure bending
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The behavior of I-shaped steel girders with flanges made from concrete-filled tubes is investigated experimentally, focusing on concrete-filled tubular flange girders (CFTFGs) in positive bending regions where the concrete-filled tube is the compression flange. The investigation included CFTFGs that are either composite or noncomposite with a concrete deck. For the composite CFTFGs, girders with rectangular tubes and either a flat web or a corrugated web are studied, and for the noncomposite CFTFGs, girders with round tubes and flat webs are studied. The objectives are: (1) to provide experimental data demonstrating the load carrying capability of CFTFGs and the advantages of CFTFGs over conventional I-girders; and (2) to verify the adequacy of analytical models by comparing experimental and analytical results. The experimental results demonstrate the improved lateral torsional buckling capacity of CFTFGs, and their capability to carry factored design loads under construction conditions and in the final constructed condition. The comparison between experimental and analytical results shows the adequacy of simple analytical models for CFTFGs.
Flange
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The goal of structural design is to select member sizes that are proportional to thestructural geometry in order to achieve the most cost-effective design. Steel girders weretypically made of webs, flanges and a number of internal stuffeners, the main objectiveof this research is to develop a finite element model to study the effect of the shapes andlocations of openings on the behavior of hollow flange steel plate girders. In this study,seven models were analyzed in two groups. The first group study the effect of webopenings shape openings on the behavior of hollow flange steel plate girders, while thesecond group study the effect of web openings location on the behavior of hollow flangesteel plate girders. The girders are analyzed until the final failure has occurred. Theresults obtained from finite element analysis showed that that the absence of openinghad an important effect on the ultimate load capacity. The ultimate capacity of hollowflange steel plate girder with four squares opening decreased about 5% compared tohollow flanges steel plate girder without openings.
Flange
Ultimate load
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Horizontally curved, steel I-girder bridges can present unique challenges for engineers and contractors because the curved geometry can result in a complicated torsional response. The most complicated stages for predicting behavior of the girders usually occur during erection and construction when the loads and support conditions are the most unpredictable. Although laboratory experiments can provide valuable insight into the behavior, the high cost of the specimens often precludes meaningful experiments, whereas field monitoring of bridges during construction provides invaluable opportunities to understand the behavior and gather data for validating computational models. A horizontally curved, steel I-girder bridge was instrumented to monitor the bridge during erection and concrete deck placement. Stresses were monitored as girders were lifted into position, followed by measurements of vertical deflections, rotations, and stresses during the concrete deck placement. The stresses during the erection process were relatively low owing to the proper use of lifting and placing methods; however, high stresses can be induced after girders are placed when the cross frames are ratcheted into position. As expected, higher stresses, compared with the steel erection process, were recorded during the concrete deck placement. Nonetheless, the monitored bridge did not have stability problems because the bridge utilized a relatively stocky flange width-to-depth ratio. For bridges more susceptible to stability challenges, such as tightly curved bridges, highly skewed bridges, narrow bridges, bridges with odd span arrangement, or some combination of these attributes, it is recommended that the designer consider the implication of slender girders and explicitly design for the possibility of construction-related stability challenges. In addition, resulting from the limited availability of field measurements of horizontally curved girders throughout the construction process, the data represent a valuable resource researchers can use to validate computational models for conducting parametric investigations. This paper outlines the methods used during the field monitoring and summarizes the results from the field measurements.
Bridge (graph theory)
Flange
Instrumentation
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Efficient replacement of bridge decks is becoming increasingly important in high traffic areas due to public intolerance to extended bridge closure. Rehabilitation of deteriorated decks causes public inconvenience, travel delay, and economic hardship. Maintaining traffic flow during bridge deck repair is often difficult and requires extensive planning and coordination. Demolition of bridge deck that is compositely connected with either structural steel I-girders or precast concrete I-girders is one of the major items in deck replacement. This is very time consuming because removing concrete around shear connectors takes time and care to avoid damage to the girders. The objective of this research is to implement two new connection systems that were developed in the National Cooperative Highway Research Program (NCHRP) project 12-41, one system for steel girder/concrete deck connection and the other for concrete girder/concrete deck connection. For steel girder/concrete deck connection, a new large 31.8 mm (1 1/4 in.) diameter shear stud is used to replace popular 19.1 mm (3.4 in.) and 22.2 mm (7/8 in.) shear studs. Using the 31.8 mm (1 1/4 in.) studs results in higher construction speed and enhancement of deck removal. For concrete girders, a new debonded shear key system is used to replace the conventional roughened interface system. Shear friction theory is adopted to develop a design procedure for this new connection. Extensive tests and field implementation showed that the new shear key system has comparable structural behavior with the conventional roughened interface system.
Precast concrete
Structural system
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The influence of square opening sizes on the shear behaviour of hollow tubular flange plate girders is investigated herein. Accordingly, a three-dimensional finite-element model using Abaqus has been employed. The results of the hollow tubular flange plate girders with web openings are compared with equivalent I-section plate girders with flat flanges with openings which have been examined extensively in the literature. The results indicated that employing the hollow tubular flange plate girders with web openings instead of the corresponding I-section plate girders is a high-performance solution for the drop in shear owing to the presence of these openings. Additionally, it is found that there is no need to check the local stresses existing around the openings at the serviceability limit state for hollow tubular flange plate girders with web openings because any local yielding will have a limited effect on deflection. It is furthermore found that the design strength of hollow tubular flange plate girders should consider the sum of the contributions of both the web and the hollow flanges.
Flange
Serviceability (structure)
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Most of Nagoya City's expressway is built above streets which are 30- 50m wide. The Y-shaped double-deck structure chosen uses box girders with sound absorption boards to reduce noise. The structure of the foundations is illustrated. The alterations necessary to traffic flow, underground services and footpaths are discussed. Details are given of the erection of girders. The process of lifting girders to a height of 28m using rolling-up jacks is illustrated. The construction of a single deck branch of the expressway is also described. This includes the girder structure, foundation structure and the construction of underground sludge tanks. The placing of girders using setting beams is described. For the covering abstract see IRRD 873033.
Box girder
Foundation (evidence)
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