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Performance of in-situ concrete stitches in precast concrete segmentalbridgesLeung, Chun-yu, Cliff., 梁鎮宇. January 2012 (has links)
Multi-span precast concrete segmental bridges are commonly constructed using the balanced cantilever method, which essentially involves sequentially extending precast segments outwards from each pier in a balanced manner. A gap of 100 to 200 mm wide is usually provided around the mid-span location between the last two approaching segments to facilitate erection. In-situ concrete is then cast to ‘stitch’ the segments together, thus making the bridge deck continuous. In the current practice, the in-situ concrete stitches are usually designed to be capable of sustaining considerable sagging moment but only minimal hogging moment. Failure of stitches may occur under exceptional circumstances that may potentially trigger a progressive collapse. However, relatively little research in this area has been carried out.
In view of this, the author is motivated to undertake an extensive study of the behaviour of in-situ concrete stitches and the effects of their performance on the robustness of typical segmental bridges. Experimental study is carried out to examine the behaviour of in-situ stitches under different combinations of internal forces. Series of stitch specimens of different configurations are tested. Subsequent parametric studies are conducted numerically to examine the effects of various parameters on the load-displacement characteristics of the stitches. Formulae for strength estimation are proposed based on the results.
A study of robustness involves analyzing the collapse behaviour of a structure in an extreme event and the analysis should be carried out up to and then well beyond the state of peak strength of structural members. A finite element programme for post-peak analysis is therefore developed for the present study. As the ability of a member section to sustain large inelastic deformation can ultimately affect the robustness of a structure, an investigation is conducted to examine the effects of steel content, yield strength and prestressing level on the ductility and deformability of prestressed concrete sections.
Using the programme developed, the formation of collapsing mechanisms of a multi-span segmental bridge deck in an extreme event is examined. A typical bridge deck is subject to prescribed accidental load on its span in order to analyze the sequence of failure. Substantial redistribution of internal forces along the deck is observed as failures initiate, thus causing subsequent failures of other deck sections even though they have been designed to resist the internal forces at the ultimate limit state. The results indicate that any span of a multispan bridge may become a temporary end-span in the event of collapse of an adjacent span and the strength of the sections must be designed accordingly to prevent progressive failure. As a span becomes a temporary end-span, the in-situ concrete stitches may experience substantial moment and shear, and their failure could potentially trigger progressive collapse of the entire bridge deck.
Towards the end of the thesis, important design considerations that can enhance the performance of in-situ concrete stitches and robustness of precast concrete segmental bridges are presented. / published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy
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Uni-axial behavior of normal-strength concrete filled steel tubular columns with external confinementLuo, Lie, 罗冽 January 2012 (has links)
This thesis proposes two forms of external confinement for concrete filled steel tubular (CFST) columns. The confinement efficiency is studied by examining the axial strength enhancement and ductility improvement of the CFST columns with external confinement.
Due to the heavy demand of confining steel to restore the column ductility in seismic regions, it is more efficient to confine these columns by hollow steel tube to form CFST column. Compared with transverse reinforcing steel, steel tube provides a stronger and more uniform confining pressure to the concrete core, and reduces the steel congestion problem for better concrete placing quality. The CFST columns are therefore characterised by higher strength, ductility and large energy absorption before failure.
However, a major shortcoming of CFST columns is the imperfect steelconcrete interface bonding occurred at the elastic stage as steel dilates more than concrete in compression. This adversely affects the confining effect and decreases the elastic modulus. To resolve the problem, it is proposed in this thesis to use external steel confinement in the forms of rings and ties to restrict the dilation of steel tube. For verification, a series of uni-axial compression test was performed on some CFST columns with external steel rings and ties. From the results, it was found that the external steel rings could improve both the axial strength and stiffness of the CFST columns significantly. However, the steel ties could not improve either the axial strength or elastic stiffness significantly. The confining efficiency was then investigated by comparing the strength of these confined-CFST columns with the reinforced concrete (RC) columns counterparts with the same concrete and steel volume. It is evident that the axial strength of CFST columns is much higher than the RC columns, which suggests that the application of CFST columns can utilise less construction materials and reduce the demolition waste.
A theoretical model is also proposed for predicting the axial strength of ring-confined CFST columns. Comparison between the predicted results and the test results obtained by the author and other researchers shows that the proposed model gives good estimation for both unconfined and confined CFST columns. / published_or_final_version / Civil Engineering / Master / Master of Philosophy
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Seismic performance of full-scale reinforced concrete columnsBae, Sungjin 28 August 2008 (has links)
Not available / text
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Anchorage of grouted vertical duct connections for precast bent capsBrenes, Francisco Javier 28 August 2008 (has links)
Not available / text
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Non-destructive evaluation of gravity load carrying capacity and lateral load damage of reinforced concrete slab-column connectionsArgudo, Jaime Fernando 28 August 2008 (has links)
Not available / text
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Shear strength of concrete joints under dynamic loadsLui, Lup-moon., 呂立滿. January 1977 (has links)
published_or_final_version / Civil Engineering / Master / Master of Philosophy
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Elastic versus plastic design for a reinforced concrete buildingFogg, Ka Chung, 1939- January 1968 (has links)
No description available.
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The practice and effects of hot weather concretingCreager, William Bronson, 1948- January 1972 (has links)
No description available.
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Precast concrete connections with embedded steel membersMarcakis, Kostas January 1979 (has links)
No description available.
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A study of an interior joint for large panel precast buildings /Noor, Iqbal January 1987 (has links)
No description available.
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