Zürich Stadtspital Triemli Personalhäuser – Resource assessment of structural elements

The Triemli Personalhäuser are three equal 15-story buildings located on the Zürich Triemli Stadtspital campus and erected between 1964 and 1969. Cast-in-place reinforced concrete (RC) slabs and walls form the building cores and their surrounding corridors. The rooms are arranged around these cores. The load-bearing intermediate walls, made of prefabricated masonry, support thin precast slabs used as permanent forms. A RC layer is cast over these precast slabs and connects the room slabs with the cast-in-place slabs of the corridors and cores. The self-supporting facade consists of precast RC panels. The City of Zürich plans the deconstruction of these three buildings, thus making available a large amount of RC elements composing the structure and the facades of these buildings. Little-known and rarely implemented, the reuse of concrete elements from obsolete buildings in new projects is a sustainable approach that promotes a circular economy. When reusing, the components of obsolete buildings are carefully dismantled without being crushed. They are then cleaned, possibly repaired or trimmed, and reused without many transformations in a new project, maintaining their shapes, technologies, and mechanical properties. In addition to maintaining the embodied energy and history of the reused components, reuse allows the construction industry to reduce demolition waste, greenhouse gas emissions, and material consumption. This report is a preliminary resource assessment and aims at inventorying and assessing all structural elements of the Triemli Personalhäuser, focusing on their potential value for reuse. Both precast and cast-in-place RC elements are included. They are part of the load-bearing structure or are self-supporting such as the precast facade elements. The proposed methodology allows identifying all properties needed to evaluate the potential for reuse of an element: geometry, material properties, current condition, aesthetics, accessibility, resistance, future durability and environmental impacts. After reviewing available reports and drawings on the buildings, onsite visits are carried out to complete the information and visually inspect the structural elements. During the inspection, the elements are assessed with regards to their suitability for reuse and their condition is classified into a five-grade scale. The investigations are completed with destructive and non-destructive testing of the material properties. Together, Buildings A, B and C are made up of approximately 7 000 m3 of materials constituting their load-bearing system, with approximately 2 500 m3 of precast concrete, 3 400 m3 of cast-in-place concrete and 1 100 m3 of masonry. Of this total, approximately 4% of the volume is dropped from the analysis due to the bad condition of the elements, namely the balcony slabs, the roof slab, and the external stairs. The other elements are in a good or acceptable condition and ae inventoried and analysed in detail. The inventoried elements are divided into 5 categories: (1) facade elements; (2) slab elements; (3) wall elements; (4) column elements; and (5) staircases. Each of these categories are subdivided into a certain number of element types for which a complete factsheet is prepared, including pictures, drawings and useful information on their condition. The volume and weight of each element types are given, as well as their share of the total material volume. The embodied global warming potential (in kgCO2eq) for fabrication and demolition of the elements is also calculated. The results of the investigation on material properties confirm sufficient compressive strength for all elements. The carbonation depths measured on the cores are lower than the cover thickness of the reinforcement. Thus, the concrete is not carbonated in the reinforcement areas and the risk of corrosion is kept low, insuring a good durability of the elements. This document should serve as a base for designing and planning future reuse applications for the concrete elements extracted when deconstructing the Triemli Personalhäuser. The information presented here will help the planners to prioritize the reuse strategy on the elements in the best conditions, with the largest volume share and thus with the largest embodied global warming potential.

Reuse in Architecture & Structural Design

Jan Friedrich Georg Brütting

Introduction The construction industry has an extensive impact on the global environment and will be facing three big challenges in the next decades: reducing its resource consumption, decreasing its energy use, and limiting its waste production. This is even more crucial, considering global population growth and increasing urbanization. Consequently, a shift of paradigm from a linear economy of make-use-dispose, towards a circular economy that advocates closed loops within the service life of materials and components is required. Recycling currently is the common strategy to make use of obsolete materials; however, it involves energy for reprocessing (e.g. melting steel scrap). Instead, direct reuse of components close to their original form has the potential to reduce environmental impacts further because sourcing additional raw material is avoided and only few energy is spent for transformation [1]. In the case of buildings and infrastructures, load-bearing systems contribute the most to the embodied environmental impacts. This is because of their big mass and energy intensive construction process. These observations suggest that reusing structural elements has large potential to reduce the environmental footprint of building structures. Reused components may consequently have a longer service life than the systems to which they initially belonged and disassembled buildings become a mine for new constructions. This idea is of course not a today’s invention, but has found application already far in the past as well as in recent building projects. Before industrialization, most building materials were sourced locally and reuse of building materials and components was the rule because it was more cost and time efficient than new production [1]. The scarcity of building materials had to be considered in design and construction. A classic example is the reuse of bricks throughout the Roman and Greek eras or in post-war times. Remarkable are also the stone columns of the Great Mosque of Cordoba, Spain, which were reused from nearby Roman and Visigoth ruins to support Moorish double arches (Fig. 1a). More recently, the steel structure of the BedZED project in London (Fig. 1b) was constructed from 90 % locally reclaimed elements [2]. Many other contemporary case studies in which bricks, timber, or steel elements have been reused are reported in [1] and [2]. An outstanding structure is the London Olympic Stadium (Fig. 1c), whose roof truss incorporates 2000 tons of steel pipeline tubes reused from a nearby development project [3]. At smaller scale, a strained grid-shell pavilion made of reclaimed skis has been built by the researchers at EPFL’s Structural Xploration Lab (Fig 1d). Recently this environmental-aware architectural and structural design is evolving. In addition, governments have understood the potential of circular economy and circular design. For instance, the European Commission has issued an EU action plan for the circular economy in order to reduce waste and landfill. Research While historic and contemporary projects, especially in Europe, highlight the environmental, time or cost benefits of building with reclaimed (structural) elements, many technological challenges remain. Buildings have to be carefully disassembled, which is often only possible for steel or wooden structures that are joined with reversible connections, or when elements can be cut and member ends are reshaped to fit new settings. Further, the quality and structural capacity of reclaimed elements has to be ensured. Under these assumptions, this research focuses on the standpoint of composing building structures from a stock of reclaimed elements. This entails reversing the conventional design process. The constrained availability of elements dictates the layout (topology and geometry) of the designed structure due to the a-priori set geometric and mechanical properties. The design shifts towards a “form follows availability” paradigm [1]. Structural optimization methods, which traditionally seek best performing structural systems under given boundary conditions, can be extended to integrate and facilitate element reuse in structural design. This research uses the combination of combinatorial optimization and form-finding methods to design reticulated structures from a given stock of reclaimed elements [4], where: 1) available elements are grouped by material, structural capacity and dimensions, 2) an optimal assignment of a subset of stock elements into a structural system is performed, and 3) the structure geometry is optimized. Generally, the assignment step 2) minimizes the structural weight to optimally utilize the available element capacities, whereas the geometry optimization step 3) is carried out to match truss geometry and available element lengths. This method is applied to optimize truss systems subject to differently composed stocks. In each case, varying cross section sizes or element lengths result in a different outcome of the designs. Figure 2 (a) shows a typical roof truss design, which is loaded at the top chord and is used as the initial topology for the introduced optimization method. The obtained layout for the case of using Stock A is reported in Fig. 1b. This stock consist of elements with 3.00m length which are n = 4 times available for each of the six cross-section groups. The use of the stock is indicated by the superimposed magenta colored bars on top of the grey ones. Due to limitations of the stock to 3.00 m elements only, the truss layout contains two arrays of three almost equilateral triangles. For the truss made from Stock B, which is composed of equivalent cross section groups but with variable element lengths, the found geometry is shallower and vaulted. In both cases, the geometry optimization allows to use most of the stock members with their full length. The exploration of these case studies concludes that the availability of elements has a significant influence on the final structural design as well as its structural performance. For example, if an insufficient amount of elements with small cross-sections is available, the structure will be oversized (i.e. the capacity of available members is not utilized) and environmental savings are diminished. Conclusion The proposed optimization and form finding method renders a first step towards facilitating the design with reused elements where the outcome is not as predictable as in the well-established conventional structural design process. Future research will extend this method towards different structural typologies such as bending and frame systems. Further, the question of customized connection details enabling the joining of stock elements has to be addressed.

2018

Assessment of the Environmental Impacts of Bridge Designs Involving UHPFRC

Numa Joy Bertola, Eugen Brühwiler, Célia Marine Küpfer

Ultra-High-Performance Fibre-Reinforced Cementitious Composite (UHPFRC) has been developed to design lightweight structures and enhance existing designs. As the environmental footprint of the construction industry must be significantly reduced, the potential to lower environmental impacts of structures using UHPFRC needs to be explored. While the greenhouse gas emissions of a volume of UHPFRC are higher than that of the same volume of concrete, UHPFRC enables the reduction in the amount of material required in structural designs and improves the durability of structures. The environmental impacts of structural designs must thus be compared on the cradle-to-grave use cycle of the design at a project scale. In this study, a methodology is proposed to evaluate the ecological burdens of several bridge designs involving various structural elements in UHPFRC. The method proposes an analysis over three time horizons: first, the construction phase, then including the scheduled maintenance, and finally, adding the elimination. A case study of a short-span bridge in Switzerland is used to assess three alternatives of bridge designs: a conventional reinforced-concrete structure, a composite timber–UHPFRC bridge, and a full-UHPFRC solution. The results show that timber–UHPFRC structures can significantly reduce the environmental impacts of bridge designs, showing promising results in terms of sustainable development. The use of the methodology supports bridge owners in assessing the environmental impacts of structural designs

2021

Addressing the need to monitor concrete fatigue with Non Destructive Testing: results of Infrastar European project

Antoine Bassil, Imane Bayane, Eugen Brühwiler, Xiao Wang

Fatigue is one of the most prevalent issues, which directly influences the service life expectancy of concrete structures. Fatigue has been investigated for years for steel structures. However, recent findings suggest that concrete structures may also be significantly subjected to fatigue phenomena that could lead to premature failure of certain structural elements. To date, fatigue of reinforced concrete has been given little focus. Knowledge on the influence factors and durability/capacity effects on this material should be improved. Current technological means to measure fatigue in civil structures like bridges and wind turbines (both onshore and offshore) are outdated, imprecise and inappropriate. Meanwhile, this topic has got much more attention as time-variant loading on concrete structures plays an increasing role, e.g. in bridges with increasing traffic and heavier trucks, and for wind turbines for renewable energy production, e.g. for offshore wind turbine support structures affected by wind and waves. The European Innovative Training Networks (ITN) Marie Skłodowska-Curie Actions project INFRASTAR (Innovation and Networking for Fatigue and Reliability Analysis of Structures - Training for Assessment of Risk) provides research training for 12 PhD students. The project aims to improve knowledge for optimizing the design of new structures as well as for more realistic verification of structural safety and more accurate prediction of the remaining fatigue lifetime of existing concrete structures. First, the INFRASTAR research framework is detailed. Then it will be exemplified through the presentation of the major results of the four PhD students involved in the work package dealing with auscultation and monitoring. This includes the development and improvement of Fiber Optics (FO) and Coda Wave Interferometry (CWI) for crack sizing and imagery, new sensor technologies and integration, information management, monitoring strategy for fatigue damage investigation and lifetime prediction.

2018

Reuse in Architecture & Structural Design

Jan Friedrich Georg Brütting

2018

Addressing the need to monitor concrete fatigue with Non Destructive Testing: results of Infrastar European project

Antoine Bassil, Imane Bayane, Eugen Brühwiler, Xiao Wang

2018