Rationalising the Structural Material Choice Process for High Rise Buildings in the Netherlands

Abstract

The goal of this thesis is to create a decision-making framework for the structural material choice for high rise buildings (between 70 m and 250 m) in the Netherlands. The main research question is: How is the structural material for a high rise building in the Netherlands chosen and how can this process become structured? Currently of the buildings in the Netherlands above 120 m, 86% have only reinforced concrete as structural material. This raises the question if the preference in the Netherlands for concrete comes from a clear decision-making process or if it originates elsewhere? In theory this decision-making process follows an organized cycle called the Basic design cycle. In practice preferences based on experience gained from former projects play a role, which results in deviation from the theoretical decision-making process. By gaining insight in the differences between theory and practice in the decision-making process, this thesis tries to identify the main differences arising in the structural material choice process. Four differences between theory and practice – regarding the structural material choice process of high rise buildings in the Netherlands – have been identified. By conducting interviews, these differences between theory and practice have been further researched and confirmed. (1) Disproportionately less steel is used for the main load-bearing structure of high rise buildings in the Netherlands. (2) Reasoning behind design decisions is often not made clear. (3) Building methods of contractors influence the structural material choice. (4) Arguments and expectation don’t match reality. For example, figures based on the construction time of the buildings in the Netherlands above 120 m show that prefab concrete buildings don’t always have a shorter construction time than cast in-situ concrete. In this thesis Difference 2 and 3 are combined and addressed together by creating an advisory excel-tool. The goal of this excel-tool is to give the structural engineer – early in the design process of a high rise project – insight in the influence of the structural typology on: cost (direct and indirect costs) and sustainability (environmental cost). Early in the design process very little details are available about the design of the high rise building and a lot of things can still change. Because of that, the input of the tool is kept simple: the height of the high rise building. As output a top ten of structural combinations is given. The structural combinations are a combinations of (1) stability system, (2) structural material and (3) floor type. This top ten is determined by calculating the (direct and indirect) costs and the environmental cost (sustainability) of twenty-six different structural combinations at all heights within the height range of that stability system. Eventually the top ten shows which out of the twenty-six structural combinations have the lowest (direct and indirect) costs and the lowest environmental cost (sustainability). This way a structural engineer can explore early in the design process what the influence of his or her design choices are on the final result and take the top ten structural combinations into consideration.