Double curved precast load bearing concrete elements

Abstract

The construction of free form building stagnated, due to the high construction cost of it. Double curved surfaces are only applied at projects with a high profile and projects above average budget during years. The problem with double curved surfaces is mainly the formwork. The present days used techniques to construct these formworks are statically. For example: wooden, steel or milled EPS formwork could only be used for one shaped elements. The lack of repetition and so the reusability of the formwork, which means that for a free form surface for every element a unique formwork is needed, makes the construction very expensive. A feasible way for mass production of unique shaped double curved elements could be achieved by a flexible formwork: a formwork that can be adjusted in every desired shape. It consists of a flexible layer that can be deformed into the desired curved surface by adjusting for example pistons, actuators or pins. Recently K. Huyghe and A. Schoofs have executed a series of experiments with a flexible formwork, build earlier by D. Rietbergen and Dr. Ir. K. Vollers. The purpose of this master thesis was to solve more aspects of the flexible formwork, and to make it a feasibly system. The main focus was the behavior of the flexible layer, at some places the flexible layer did not though the actuators. Predicting the behavior of the deformed flexible layer makes an accurate production possible. To be able to determine the behavior of the flexible layer some models are proposed. With these models the reaction forces at the supports could be determined, compression forces means that the flexible layer though the supports. The first model that is proposed, is for a single curved element. For the double curved mould surface two models are proposed, a plate model and a strip model. With tests at the Stevin Laboratory these models are verified, and some other aspects are tested, for example the flexible border of the formwork. Tests indicate that a plate is not suitable for the flexible layer, it buckles due to the plate stresses. The strip mould consists of two layers of strips, perpendicular to each other. The top layer of the strips is the mould surface. Tests showed that it is possible to produce double curved elements with the strip mould. Conclusions and recommendations. The models that are proposed in this thesis describe the behavior of the flexible layer well. A plate does not fulfil the function of a flexible layer. Tests have shown that it is possible to produce double curved elements with the strip mould as flexible layer. To cover the strips an additional layer is needed. In these tests polyether is used, as well for the borders. The protection of the polyether with sealant made the concrete element very rough. Another material has to be found as elastic layer, or to protect the polyether.