|Title:||Roles of shear connectors in composite columns under different loading histories|
Hong Kong Polytechnic University -- Dissertations
Department of Civil and Structural Engineering
|Pages:||ix, 135 leaves : ill. ; 30 cm|
|Abstract:||This dissertation described the roles of shear connectors in composite columns under different loading histories. The design philosophies of current design codes, BS 5400 and Eurocode 4, were reviewed and compared. It was found that the recommended interfacial bond stress between steel and concrete, as stated in both codes, were similar. However, the long term creeps effect of concrete, which might affect the redistribution of total loading, was only considered in the Eurocode 4. The parameters that affected the interfacial forces transmitted between the concrete and steel section and hence the necessity of shear connectors, were identified. They included (1) the thickness of concrete cover, (2) the amount of hoop reinforcement, (3) the size of the steel section, (4) the creep and shrinkage effect and (5) the loading history of the composite columns. For a similar steel section, it was shown that an increase in concrete cover or the amount of horizontal hoop reinforcement might enhance the force transfer between the steel and concrete section. On the other hand, increasing of size of the steel section (depth of section) or concrete shrinkage would impose a negative influence on the force transfer. The effect of loading history depended on the lock-in stresses of the components. Among all the factors identified, the effect of section size was considered to be the most important. The loading redistribution from concrete core to the steel section, as a result of long term creeps effect, was studied parametrically. From the study, it was found that the maximum value of load redistributed, hence the interfacial bond stress, was merely depended on the coefficient of creep and did not relate to other factors such as the cross-sectional area and strength of the material considered. The range of the loading redistributed in practical situations was checked and it was found that the provision of shear connectors under normal circumstances was considered not necessary. The parameters that affected the strength of shear connectors were also discussed. The recommended strength by the current codes, BS 5400 and Eurocode 4, were compared. It was seen that the codified values agreed with each other with a maximum difference of about 10%. Since the loading history played an important role to shear force transfer, the provision of shear connectors for the composite columns used in top down construction method was discussed. A design procedure was established to the composite columns where the steel core was pre-loaded before concrete casting. A working example simulating in Hong Kong practice for top down construction was presented to illustrate the construction sequences and the design considerations.|
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