|Title:||Web crippling behaviour in cold-formed steel profiled deckings under lateral concentrated loads|
|Subject:||Hong Kong Polytechnic University -- Dissertations.|
Plates, Iron and steel.
Decks (Architecture, Domestic) -- Design and construction.
Steel -- Creep.
|Department:||Department of Civil and Structural Engineering|
|Pages:||xvi, 202 leaves : ill. ; 30 cm.|
|Abstract:||In this thesis, both extensive experimental and numerical investigations into web crippling and section failure of profiled steel deckings are carried out and reported. Cold-formed steel profiled deckings named the profiled Deck R50 consist of a unit tough width of 200mm and height of 52mm are used in this study. For the web crippling tests, Decks R50 with different steel grades and thicknesses are tested under both internal and end loading conditions with practical range of load bearing widths. A total of 52 tests are carried out under each loading condition. From the extensive experimental investigation carried out, a mode of failure is identified among all tests, that is, the web crippling failure. For specimens tested under internal loading condition, local failure is observed at the web-trough corner directly under the point of load application. Moreover, apparent local plate buckling in the trough of the decking is observed well before the web crippling failure. While for specimens tested under end loading condition, local plate buckling in the trough of the decking is also observed well before the web crippling failure. Furthermore, local failure is observed at the web-trough corner at the inner edge of the load application length while excess web buckling is apparent near the web-flange corner at the outer edge of the load application length. After careful execution of web crippling tests, an advanced three-dimensional finite element models with material and geometry non-linearity are established to simulate the web crippling behaviour. Different variables such as the corner radius and spring stiffness which used to simulate the loading condition, as well as the lateral restraint for study of shear stud effect and initial geometrical imperfection are studied using the finite element models. While insignificant effect on the web crippling resistances and displacement characteristics are resulted from the variation of spring stiffness and initial geometrical imperfection, great discrepancy in the web crippling resistance is resulted due to the change of corner radius and lateral restraint. Larger corner radii use in the finite element models tend to induce a lower web crippling resistance, and vice versa. Whereas for the lateral restraint is used to study the provision of shear studs provided at different trough spacing in the deckings, the lateral restraints provided at the symmetrical axes at the trough along the longitudinal direction of the decking is for simulation of shear stud provided at every trough in the deckings, while for the case where lateral restraints released is to simulate when shear studs are provided only at every second trough. Numerical results have shown that the latter case results in a significant reduction in web crippling resistances. Comparison on both the web crippling resistances and the deformed shapes at failure between the numerical and the test results from tests is found to be highly satisfactorily. Moreover, an extensive parametric study is performed to generate design data for web crippling resistances of re-entrant deckings with different steel grades and thicknesses under a practical range of bearing lengths. It is shown that the proposed finite element models are effective to predict the web crippling resistances of cold-formed steel deckings. Furthermore, a simple and yet effective design charts are also proposed which employs directly the numerical results obtained from the parametric study. The second study is on section failure under co-existing moment, shear and web crippling forces. The section failure is examined experimentally using the one-point load tests. A total of 42 tests are carried out with Decks R50 of different steel grades and thicknesses. Different span lengths are also considered under four different load bearing widths. Among all tests performed, obvious combined bending and web crippling failure were observed. Moreover, local buckling at the tough is observed in all tests prior to ultimate load were reached. For numerical investigation into section failure, advanced three-dimensional finite element models with material and geometrical non-linearity are established. Comparison on both the section failure resistances and the deformed shapes at failure between the numerical and the test results is found to be highly satisfactory. After systematic data analyses on the section failure of profiled steel deckings, design charts with improved accuracy in load prediction are developed for deckings with different steel grades and clear spans under a practical range of bearing lengths. The use of these design charts will lead to a convenient and reliable approach for design of deckings. Furthermore, the coexisting moment, shear and web crippling forces is also considered which eliminates the need of two concurrent design equations.|
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