|Title:||Behaviour and modelling of steel-concrete composite shell roofs|
|Subject:||Hong Kong Polytechnic University -- Dissertations.|
Roofing, Iron and steel.
|Department:||Department of Civil and Structural Engineering|
|Pages:||xv, 420 leaves : ill. (some col.) ; 30 cm.|
|Abstract:||This thesis presents a study into the behaviour and modelling of Comshell roofs, with particular attention to stability problems that arise during the construction stage. Comshell roofs are formed by casting concrete on a thin stiffened steel base shell which serves as both the permanent formwork and the tensile steel reinforcement. The thin steel shell, constructed by bolting together open-topped modular units consisting of a base plate with surrounding edge plates, is a steel shell with thin stiffeners in both directions. This new system retains all the benefits of thin concrete shells, but eliminates the need for temporary formwork and minimises the required falsework. Therefore, the new system offers an attractive alternative to other structural systems for large-span roofs. A key design issue of a Comshell roof is the stability of the bolted steel base shell when subjected to wet concrete loading during construction. For the economic construction of Comshell roofs, a two-stage concrete casting approach is preferred. In Stage I of this process, concrete is cast to the level of the top of the edge plates on selected rows of the modular units to form stiff steel-concrete composite arches as the base shell is assembled. By the time that the assembly of the steel base shell is completed, it is already stiffened by the composite arches and can carry the wet concrete of Stage II casting without additional shoring even when rather thin steel sheets are used to fabricate the modular units. In such a two-stage construction process, the stability of the selected steel base arches in Stage I and the stability of the steel base shell segments between composite arches in Stage II under wet concrete loading need to be ensured. The main aim of the work presented in this thesis was to gain the first insight into these stability problems and to establish reliable numerical models. The results of several series of tests are presented in detail in the thesis. Tests conducted on bolted connections using a cantilever set-up are first presented, followed by flexural tests on flat panels composed of bolted modular units. Buckling tests on three steel base shells and a steel base shell stiffened by a steel-concrete composite arch are next described. Tests were also carried out on a composite arch and a model Comshell roof. These tests provided not only valuable insight into the various possible failure modes of Comshell roofs during both the construction and the service stages for the first time but also important test data for the development of reliable numerical models for these tests and for real Comshell roofs. An innovative pulley-based loading system developed during the present project to apply a large number of point loads simultaneously to closely simulate a uniformly distributed load is also presented. A large amount of numerical modelling work using the general purpose finite element program ABAQUS was undertaken. This numerical modelling effort was concerned with the prediction of the behaviour of steel panels, steel base arches and steel base shells. The development and verification of a relatively simple yet reasonably accurate model for the bolted connections was the focus throughout the numerical modelling work. The development of such a connection model and its verification and assessment through comparisons with test results are discussed in detail in the thesis. The thesis also presents a feasibility study of the Comshell roof system through a parametric study in which the verified numerical model was deployed to analyse steel base shells and arches of realistic dimensions in a two-stage construction process. This parametric study not only demonstrated the capability of the numerical modelling procedure developed in this project but also confirmed the feasibility of constructing Comshell roofs using very thin steel sheets that allow the use of press forming of modular units in practical applications.|
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