This grid will fold into a compact unit so it can be moved from spot to spot. The construction of a reinforced concrete shell involves many problems, the design and construction of forms, reinforcement selection and placing, concrete materials and placing, and curing and decentering. On the other hand, a shell may be so large, that is not possible to place all of the concrete at one operation, and construction joints become necessary. The optimum number of uses appears to be from 6 to 10, depending on the total length for the time of construction, and the curing time between uses. 0000001230 00000 n 0000002668 00000 n The contractor must have a well-planned organization with good supervision, to achieve acceptable results and costs. Fortunately this type of shell is structurally self-supporting so it is not necessary to leave shores in place until the next element is joined to the structure. The aesthetics and functional solution of the architectural problems often have a more important effect on the selection of the structure than have the costs. There are many factors that make this possible. This criterion is not always useful, because it is difficult to define the best building, especially if there are intangibles that cannot be evaluated in terms of money. There are several methods to establish the thickness of the shell as the concrete is placed. If soil conditions are marginal, the reduced weight on the footings may save some concrete. It is often possible to build enclosures under the forms that can be insulated and heated. The contractor should study the plans in order to solve the construction problems before they become difficult in the field. In general, for any concrete structure, the longer the forms remain in place, the better the results. There is considerably more work for the crew to place the concrete from the bottom up than from the top down, because gravity is a very convenient concrete mover. The mechanical ingenuity of the contractor is very important for proper design of this type of forming system. The selection of the type of placing equipment, whether by pumping, by bucket and mobile crane, by movable wood runways and carts, should be the decision of the contractor, based on factors such as the equipment available, the steepness of the slopes, the form and shape of the shell, and the distance above the ground. 0000002136 00000 n On the other hand, alternate materials are also expensive. Shells have a great economic potential for the construction of low-cost industrial or commercial buildings to cover large areas. The latter must design the structure so it is easy to build, and must show sufficient details so the contractor can construct it economically. The volume of concrete in the roof, is usually less than the concrete in the floor slab. The factor next in importance is the cost of formwork; the contractor must use his ingenuity to devise form systems that can be erected, moved forward and re-erected at minimum cost. The shell was virtually plastered. If large numbers of elements are to be built, as for an industrial building, then it will pay to design these form units so they can be raised and lowered by hydraulic or mechanical jacks and have wheels to move them around. This method is satisfactory, either for small or large shells, where there is a single structural element. If this is not done, an air pocket or rough texture will result. A large shell will require a single use form unit unless there are many repeated uses. It is difficult to put a price on intangibles, especially if they are not absolutely necessary. "F$H:R��!z��F�Qd?r9�\A&�G���rQ��h������E��]�a�4z�Bg�����E#H �*B=��0H�I��p�p�0MxJ$�D1��D, V���ĭ����KĻ�Y�dE�"E��I2���E�B�G��t�4MzN�����r!YK� ���?%_&�#���(��0J:EAi��Q�(�()ӔWT6U@���P+���!�~��m���D�e�Դ�!��h�Ӧh/��']B/����ҏӿ�?a0n�hF!��X���8����܌k�c&5S�����6�l��Ia�2c�K�M�A�!�E�#��ƒ�d�V��(�k��e���l ����}�}�C�q�9 After casting the concrete, the earth is excavated. H���yTSw�oɞ����c [���5la�QIBH�ADED���2�mtFOE�.�c��}���0��8�׎�8G�Ng�����9�w���߽��� �'����0 �֠�J��b� It must be specified and detailed by the engineer, and may be expensive. In many cases there is a grid of reinforcing bars that must be held in place. The weight and cost of steel structures. Shells have also been built without forms by using a close grid of reinforcing bars with the concrete placed by shotcrete. These factors are not always properly evaluated by owners and architects, and the engineer should point them out. The economy of long span shells depends on many factors. Small to medium size shells may be placed at one time and construction joints may not be a problem. It is important to provide adequate lapping of the bars, or if the reinforcing is heavily stressed, the bars may be welded. If they are precast on the construction site, then the transportation is easier, but it is necessary to have large cranes to move and to lift them into place. A crew can be kept continuously busy removing and reerecting panels and shores. The joint efforts of the contractor and engineer will create a structure bringing pride and a sense of accomplishment to all parties. Determination of the shell form, its supports and loads (limit states) 2. 0000001870 00000 n It top forms become necessary, the most convenient method is to use wire mesh or metal lath panels that can be removed as soon as the concrete has been placed, so that the surface can be finished with the rest of the roof. Other types of shells have similar quantities. There are certain industries, particularly food handling and processing, where such dust free surfaces are most desirable. 0000000991 00000 n The quantity of materials is almost independent of the span, so the cost of longer spans may be only a little higher than for short spans. 0000000536 00000 n The objective of concrete placing is the production of a smooth dense solid texture on the under surface of the shell with no pockets or honeycombing. Academia.edu is a platform for academics to share research papers. These joints should be planned and specified by the engineer, and indicated on the construction drawings, together with the details of the method of stress transfer such as the inclusion of keyways, special reinforcing, and possible thickening of members.

design of concrete shell structures

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design of concrete shell structures 2020