Sustainable Design and Optimization of Office Buildings in Steel and Composite Construction

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1 Sustainable Design and Optimization of Office Buildings in Steel and Composite Construction Martin Mensinger Chair for Metal Structures, Technische Universität München, Li Huang Chair for Metal Structures, Technische Universität München, Heidrun Hogger Chair for Metal Structures, Technische Universität München, ABSTRACT: Within the AIF-project Zutech P881 - Sustainable office and administration buildings in steel and steel composite construction planning tools and methods for the design and evaluation of such buildings are developed by an interdisciplinary research team. This paper starts from the general idea of the whole project, and focus on the discussing of an assistant design tool that enables the rapid structural design model auto-generation, optimization and evaluation. As a result of this paper and an early result of the overall project, the design and optimization of a rectangular steel-concrete composite floor is presented. 1 INTRODUCTION Within the AIF-project Zutech P881 - Sustainable office and administration buildings in steel and steel composite construction planning tools and methods for the design and evaluation of such buildings are developed by an interdisciplinary research team (Mensinger et al., 2011). Because of the primal consequences of flexibility for the construction and the future marketability of such buildings the consideration of its benefits and evaluation is a particular focus of the project. It is argued that steel and steel composite structures have high resource efficiency, high recyclability without loss of quality and great flexibility of space usage. The aim of the overall project is to complement the existing knowledge for the design of office buildings in steel and steel composite construction and its evaluation and to create practical tools for sustainable design in the form of planning recommendations and parts catalogs (see Figure 1). To enable quantified evaluation for designs at early planning phase, an assistant architectural design tool is being developed (Huang et al., 2012). With this tool assessment of sustainability considering not only ecological and economic issues but also socio-cultural and sociotechnological criteria and architectural aspects can be made based on the preliminary structural design proposal generated from the early architectural design. The assistant tool comprises a structure auto-generator of steel composite office buildings and architectural design and review interface. It has two roles to play. One is to illustrate sustainable design aspects by the quantified evaluation systems, while the other is to generate optimized preliminary structural designs proposals with the consideration of sustainability. The topic of bringing engineering knowledge into design exploration by using a genetic algorithm approach (GA) (Goldberg 1989) to find optimized structures for early conceptual architectural design phases has raised scientific interest. Examples are Rafiq et al. (2003), Grierson & Khajehpour (2002) and Turrin et al. (2011). In our problem we are using a GA to optimize the auto-generated structural design proposal. The model generation procedure will be explained with an example showing the details of the approach from the volumetric architectural design to the functional structural design model then to the structural design proposal. The question of how to handle the flexibility of office buildings will also be mentioned. Flexibility of space usage can be handled as additional architectural requirements or structural constrains of the functional structural design model.

2 Figure 1: The system structure. 2 OFFICE BUILDINGS Rectangle is a common pattern of footprints of administration and office buildings. According to Eisele (2011), office buildings can be modularized into different office types, which are composed of bars of office floors that can be arranged due to usage requirements (see Figure 2). Those bars have simple rectangle footprints. In section 5 we discuss the design and optimization of a rectangular floor in detail, which is the starting point of our research. Figure 2: Office Buildings as a System of assembled Bars from Eisele (2011).

3 Different variations of composite structure systems can be applied to the same architectural design model (Figure 1, 3 show some examples). In section 5 we describe an example using primarysecondary composite beam and slab floor system (Figure 3 in the middle) in detail. Figure 3: Three different floor system from SZS (2006) 3 DESIGN RULES AND EVALUATION OF DESIGNS Design rules from Eurocode 4 (2004) are used for the dimensioning and the verification of building elements. A preliminary structural design is considered, where we only deal with composite beams, composite slabs and steel columns. We have been working on the vertical load transfer and bracings and connections are currently neglected in our approach which leads to an underestimation of the needed material quantities. We have set up a single fitness function to estimate the sustainability performance of the designed structure. Equation 5.1 sums up the Carbon Dioxide Equivalents (CDE). We have added a penalty term calculated based on violation of constrains. This is intended that solution populations of impossible structural systems may die out due to the worse fitness values in the artificial evolution process. We consider adding also a bonus term, which particularly rewards optimal fulfilment of requirements such a preferred long-span structure for flexible office spaces. Figure 4 shows the verification process of the primary-secondary beam system presented in this paper. A challenging problem of using a GA approach for optimizing a structure model is to design the genome appropriately to encode the model sufficiently with all of the composite system s characteristics, the structural variation possibilities and the structural restrictions are wellhandled and balanced. For example in Figure 5, 6 primary-secondary composite beam and slab system is employed. One characteristic of the system is to maintain the main structure composed of continuous multi-span beams in one direction as the primary beams while single span beams in the other direction are the secondary beams. Future solution generations can lead to systems which use either the longitudinal or the transverse direction for the primary beams and can use different span widths for both the secondary and the primary beam. Finally the above mentioned requirements of architects for more flexibility of the space usage need to avoid e.g. several columns in certain areas. There are different possible ways to encode the structural system in the chromosome reflecting the architectural design. One way is to define a parametric model, which uses a set of parameters to define the structure model. Another way is to employ a topology optimization mechanism, e.g. in Nimtawat (2009, 2010) a grid-based model is used together with topology optimization. We are currently studying how to combine these two approaches to develop a hybrid method, which can use a parametric model to reflect the general composite structure system and grid-based topology optimization to modify specified sub-area to suit the additional architectural requirements (structural requirements). So far we have implemented a simple parametric model for a composite floor with rectangular footprint (presented in section 5).

4 Start to calculate an individual s fitness Decode the string to get a structural design model with all dimensioned elements: slab: type, thickness, max span secondary beam (single span): profile, steel grade, length primary beam (multi-span): profile, steel grade, span lengths column: profile, steel grade Check secondary beams: Calculate penalty and CDE Check primary beams: Calculate penalty and CDE Check the slab: Calculate penalty and CDE Check Columns: Calculate penalty and CDE Sum up CDE s and penalties to get the fitness value Figure 4: Calculating the penalty and Carbon Dioxide Equivalents (CDE) 4 FROM ARCITECTURAL DESIGN TO STRUCTURAL DESIGN We want to communicate and share engineering knowledge such as the necessary slab construction heights and grids for beam and column layouts together with estimates of necessary material consumption and the ecological footprint to be expected for a given volumetric design to support the architectural decision making process in early design phases. Figure 5 shows the detailed workflow of our approach. The architect starts with a volumetric architectural model (VAM) shown in Figure 5a that is an initial architectural layout design specifying space usage, circulation and access using the assistant design tool. With this tool the architect can apply predefined architectural design rules to the VAM. In our example, the architect specifies an allowable locating area for one intermediate row of columns (see the dark area on the boundary of the corridor in Figure 5b) and also two locating lines for columns on each longitudinal boundary (see the dark area on the boundary of the whole floor in Figure 5b). From the VAM and the design rules a functional structural design model (FSDM) (see Figure 5c) will be created. It describes requirements, specifications and constrains for the structural system to be designed. The FSDM serves as an input to the automated structure generator using a GA (see step 3 on Figure 5). The structure generator firstly applies a composite structural system as a parametric model on the FSDM without specified beam layouts and dimensioning, while column positions and their variation possibility are specified (see Figure 5d), secondly uses a GA to search for an appropriate optimized structural design proposal (see Figure 5e) based on the applied system. In the example illustrated in Figure 5a primary-secondary beam and slab floor system is applied, and the detailed specification, e.g. number of columns, number of secondary beams, elements profiles, slab thickness, etc. are optimized using a GA. The resulting structural system model will be submitted to the architect as initial structural design proposal in response to the first FSDM reflecting his design order (see step 5 on Figure 5). The structural model will be shown in the assistant design tool in an abstract presentation

5 (like Figure 2 left) with a volume representing the necessary slab construction height and gridline systems for beams, columns and (later) façade members. This keeps the VAM free from congested spaces. Additional information from estimating structural performance regarding necessary material consumption and the carbon footprint serves as a basis for later architectural design decisions. 1 2 (a) Initial VAM is created with the architectural design tool. (b) allowable column location (dark area on the boundary of the corridor and the whole floor) is added to VAM (c) FSDM is automatically generated by the architectural design tool (d) A structural system is chosen and applied by the structure model generator, while column positions and variation possibility are specified (e) Structure s geometry and elements are generated, dimensioned and optimized using a GA (f) Allowable column location is justified by the architect with architectural design tool and additional restrictions (representing more Flexibility) is added (g) Updated FSDM is generated by the architectural design tool (h) The structural system is updated, column position and variation possibility is updated (i) New Structural design proposal is generated using a GA. Figure 5: From a Volumetric Architectural Model (VAM) to a Structural Design Proposal.

6 Width: The architect may modify the model and possibly introduce additional requirements and restrictions on the structural system, e.g. modify the allowable column location, or make justification to the previous designs (see Figure 5f) and send an the updated FSDM (see Figure 5g) to the generator. These architectural-structural design iterations can be continued until the architect finds a satisfied design, which is compliant with the clients needs. 5 COMPOSITE FLOOR IN RECTANGULAR SHAPE This section presents an example of optimizing composite floor with a rectangular footprint. It has a layout of one row of rooms on each side and one corridor in between as shown on Figure 6, and uses a composite primary-secondary beam and slab system with a single row of intermediate columns, where the primary beam can be placed either in the transversal direction or in the longitudinal direction. The possible location of middle columns varies in a defined range from the boundary wall (see Figure 6a). The chromosome representing the structural model is shown and explained in Figure 7, each of the genes represents a geometric or a design parameter. Some of the parameters are illustrated in Figure 6a, the width and the length of the floor, the span (equally distributed) in longitudinal direction, etc. Length: Cells Corridor Cells Span in longitudinal direction: (a) Primary Beam in transverse direction (b) Primary Beam in longitudinal direction Figure 6: Composite Floor in Rectangular Shape. In system (a) x indicates intermediate columns location from the boundary and N 2 indicates the number of secondary beams between each pair of primary beams. Same parameters can be used for system (b) as well. The fitness value is calculated as Equation (5.1), where J is fitness value, V c is total volume of concrete, m r is total mass of reinforcement, m p is total mass of profile sheeting, m s is total mass of steel sections and A s is total surface area of steel sections, while a 1 to a 5 are corresponding coefficients for calculating CDE. They are provided in FIZ, FTB (2010) and EPD-BFS (2011). The last term P indicates the penalty term due to violation of design con-

7 strains, e.g. deflection constrains and stress constrains. The bonus term mentioned before is not considered in this example column position: = + 2 columns in each row: 11 = +1,, slab type: 1:Cofrastra {0:Holorib, 1:Cofrastra} slab thickness: 120mm {120,140,160,180} secondary beam s profile: 6:IPE220 {All available profiles} secondary beam s steel grade: S355 {235,355,460} primary beam s profile: IPE550 13:IPE550 {All available profiles} primary beam s steel grade: S460 {235,355,460} direction for primary beam: 0:longitudinal {0:longitudinal, 1:transverse} secondary beams in each span: 6 column s profile: 21:HEA280 {All available profiles} column s steel grade: S460 {235,355,460} Figure 7: A Chromosome Represents an Optimized Structural Model. l s is chosen from a set of values that predefined according to the size of Façade panels. J = a 1 V c + a 2 m r + a 3 m p + a 4 m s + a 5 A s + P (5.1) 6 SUMMARY AND OUTLOOK In this paper we presented an approach for sustainable design and optimization of office buildings as the early result of the AIF-project Zutech P881 - Sustainable office and administration buildings in steel and steel composite construction. We developed a concept to automatically generate structural models for estimating sustainability performance for early volumetric architectural design iterations for office buildings to provide rapid response concerning structure and sustainability performance. In this concept we defined a method to introduce architectural flexibility requirements as structural restrictions into structure auto-generation. So far we have implemented a model auto-generator for a composite floor with rectangular foot print with a composite primary-secondary beam and slab system. In our further work we want to handle more complex and general architectural designs of office buildings. We want to develop a generalized method to parameterize different composite structure systems and to encode them into the chromosomes of the GA automatically. That means to define how the system s geometry is specified, how the elements are located and how the load transfer system is defined, calculated and the members are analytically designed and verified. This includes description of the constituents that are columns, beams, floors, connections etc., relations between them, design rules, verification rules, restrictions, definitions of use cases and parameters. Other sustainability related assessment may be integrated, for example measurement of the overall building surface area can be used for energy consumption analysis.

8 ACKNOWLEDGEMENTS The authors wish to thank the Forschungsvereinigung Stahlanwendung e.v. (FOSTA) and the AiF Arbeitsgemeinschaft industrieller Forschungsvereinigungen for supporting and financing the research. The research project "Nachhaltige Büro- und Verwaltungsgebäude in Stahl- und Stahlverbundbauweise is a collaboration of the following universities: Lehrstuhl für Stahl und Leichtmetallbau, RWTH Aachen, Fachgebiet Entwerfen- und Baugestaltung, TU Darmstadt, Institut für Stahl- und Holzbau, TU Dresden, Institut für Technik und Arbeit e.v., TU Kaiserslautern, Lehrstuhl für Unternehmensrechnung und Controlling, TU Kaiserslautern, Computational Modeling and Simulation Group, TU München with the lead from Lehrstuhl für Metallbau, TU München. The authors want to thank Professor Dipl.-Ing. Johann Eisele and Dipl.-Ing. Frank Lang from TU Darmstadt for their contributions from the architectural side, Professor. Dr. Manfred Breit, Professor. Dr.-Ing. André Borrmann and Fabian Ritter, M.Sc. for their contributions on developing the concept. REFERENCES British Standards Institution. (2004). Eurocode 4: design of composite steel and concrete structures. London, BSI. Eisele, J. (2011). Nachhaltige Gebäudetypologien im Hochbau. In: Nachhaltig Planen, Bauen und Betreiben - Chancen für den Stahl(leicht)bau, 2011, Berlin, Germany. Forschungsinstitut der Zementindustrie (FIZ), Forschungsgemeinschaft Transportbeton e.v. (FTB). (2010). Ökobilanzielle Profile für Bauteile aus Transportbeton. Goldberg, D. E. (1989). Genetic algorithms in search, optimization, and machine learning. Reading, Mass: Addison-Wesley Pub. Co. Grierson, D. E. and Khajehpour, S. (2002). Method for conceptual design applied to office buildings. J. Comput. Civ. Eng. 16(2), pp Huang, L., Breit, M. and Mensinger, M. (2012). Approach to handle architectural flexibility requirements for automated structural design proposals of steel concrete office buildings in early design phases, In: Proc. of the EG-ICE Workshop on Intelligent Computing in Civil Engineering, 2012, Munich, Germany. Mensinger, M., Baudach, T., Breit, M., Eisele, J., Feldmann, M., Franz, C., Hogger, H., Kokot, K., Lang, F., Lingnau, V., Pyschny, D., Stroetmann, R. and Zink, K.J. (2011). Nachhaltige Bürogebäude mit Stahl. In: STAHLBAU 80 (10), pp Nimtawat, A. and Nanakorn, P. (2009). Automated layout design of beam-slab floors using a genetic algorithm. Comput. Struct. 87(21-22), pp Nimtawat, A. and Nanakorn, P. (2010). A genetic algorithm for beam-slab layout design of rectilinear floors. Eng. Struct. 32(11), pp Rafiq, M. Y., Mathews, J. D. and Bullock, G. N. (2003). Conceptual building design - Evolutionary approach. J. Comput. Civ. Eng. 17(3), pp Turrin, M., von Buelow, P. and Stouffs, R. (2011). Design explorations of performance driven geometry in architectural design using parametric modeling and genetic algorithms. Adv. Eng. Inf. 25(4), pp SZS STAHLBAU ZENTRUM SCHWEIZ. (2006). Bauen in Stahl: Brandschutz im Stahlbau. rich: SZS Stahlbau Zentrum Schweiz. Umwelt-Produktdeklaration (EPD). (2011). Baustähle: Offene Walzprofile und Grobbleche. (EPD-BFS nach ISO 14025) der Hersteller ArcelorMittal, Dillinger Hütte, Ilsenburger Grobblech, Peiner Träger und Stahlwerk Thüringen.