There are two main challenges in the construction industry: carbon emissions and densification in cities. Timber high-rise might prove as a suitable solution to both these challenges. However, there is a lack of implementation of timber high-rise. This research argues that a lack of thorough analysis of timber design alternatives in the conceptual design phase results in the exclusion of further evaluation of timber building designs. This research aims to analyze timber building design alternatives more thoroughly by the development of a tool, based on the Multidisciplinary Design Optimization (MDO) method. In Grasshopper, a parametric model is created with which timber building designs are generated, validated, and optimized. Two main optimization objectives and two constraints are considered in the tool: Firstly, the structural constraint: Each building must be designed according to the constraints as determined in the Eurocode. Secondly, the architectural constraint: Each building must satisfy the architectural design requirements for acoustics, building height, and daylight entrance. Thirdly. the environmental objective: minimize the shadow costs, which are determined according to the MPG methodology. The MPG methodology uses Life Cycle Analysis data to assess the embodied energy impact of structural materials. This embodied energy impact is expressed in shadow costs. Lastly, the economical objective: minimize the construction costs. Based on the mentioned constraints, the tool aims to indicate the design situations in which timber high-rise can be competitive to an assessed concrete design alternative, considering the combination of properties for shadow costs and construction costs. By research and development of the Multidisciplinary Design Optimization tool and analyzing two case studies, a conclusion can be made. Two concrete buildings, which are based on a current Arcadis project, are used as case studies. Both concrete buildings represent a design situation. The main difference between these design situations is the building dimensions. Building A3 represents timber building designs that are created for a design situation with a floor area of 28.8 x 28.8 m and a height of 60 meters. Building B3 represents timber building designs that are created for a design situation with a floor area of 21.6 x 43.2 m and a height of 50 meters. For both case studies, an optimization will obtain timber building designs with an optimal combination of properties for shadow costs and construction costs. This resulted in the following results. For the design situation based on the concrete building "The Rectangle", the Pareto optimal timber building designs, referred to as Building B3, were found to be competitive with "The Rectangle". For the other analyzed design situation, the Pareto optimal timber building designs referred to as Building A3, were not found to be competitive with the concrete building "The Square". Considering the boundary conditions and scope of this research, it can be concluded that a design situation with a rectangular floor plan is favorable over a design situation with a square floor plan and a design situation with a building height of 50 meter is favorable over a design situation with a building height of 60 meter. Also, based on analysis of the case studies the following conclusions were made. Firstly, when the effect of carbon sequestration is excluded in the calculation of shadow costs, the use of timber and concrete in the structural system was found to generate comparable results considering their shadow costs. The inclusion of the effect of carbon sequestration during the lifetime of a timber building results in a reduction of shadow costs of approximately 40% compared to a similar concrete building. Secondly, considering the boundary conditions and scope of this research the ULS is found to be normative for a slenderness up to 2.35. When the slenderness is greater than 2.35, the along-wind acceleration was found to become normative. Next, for all Pareto optimal building designs, the ULS check was found to be normative over the SLS check. Lastly, the mass of the Pareto optimal timber building designs was found to be approximately 8 times smaller than their respective concrete design alternatives, resulting in a foundation with less construction costs and shadow costs.

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.