Dubai Municipality awarded to Porr Besix JV the Project for the Main Tunnel component of the Deep Storm Water System. The tunnel will collect both rainwater and groundwater from approximately 500 sq. km and transfer the captured flow to the sea. The Design Builder JV selected COWI as Designer of the entire Project and IC Consultant as Design Checker for the Tunnels. The Project includes approximately 10.3 km of 10-meter-inside diameter tunnel in rock, three construction shafts and one drop shaft. The main tunnel will convey stormwater and groundwater flows from the EXPO 2020 area near the intersection of Sheikh Mohammed Bin Zayed Road and Jebal Ali Lehbab Road to the sea close to the EGA facility. The tunnel will follow beneath the road easement along Jebal Ali Lehbab Road and along Sheikh Zayed Road and continue to the pumping station. The tunnel traversed through the Barzaman and Fars formation with an overburden of 33 m with maximum water pressure of 4.4 bar and was excavated by EPB TBMs. This project is characterized by its dimensions with an internal diameter of 10 m and 350 mm of segment thickness, and by the use of steel fibre reinforced concrete in the precast segmental lining. The use of fibres aims to reduce the CO2 footprint obtaining an optimized design from the environmental point of view. These facts are associated to a complex design of precast segments, in order to ensure their structural competence and their integrity according to the durability requirements, under large thrust forces (temporary loads) and permanent load. Hence, considering such complexities, the structural design has been carried out producing a 3D structural model by means of a sophisticated FEM structural software. Results of the model allow to identify areas of the segment where spalling and bursting stresses are generated along circumferential joints and maximum value of those stresses in the temporary load cases. Moreover, a structural design verification of the segment has been undertaken considering the contribution of steel fibres class 4c, as it is set up in the FIB model code, aiming to ensure that the precast segments are structurally competent and fulfil the durability requirements of the Project. The article details the design approach and the independent checker design verification approach. The experience gained during construction is also reported, describing challenging aspects of the Tunnel execution and an analysis of the lining damages.

Statischer Entwurf einer mit Stahlfasern verstärkten Tübbingauskleidung
Die Stadtverwaltung von Dubai vergab an die Arbeitsgemeinschaft Porr Besix das Projekt DS233/2 Deep Storm Water System - Main Tunnel. Der Tunnel wird sowohl Regen- als auch Grundwasser ableiten und fast 40 % des gesamten Stadtgebiets von Dubai entwässern. Das Projekt zeichnet sich durch seine Dimensionen mit einem Innendurchmesser von 10 m und einer Tübbingdicke von 350 mm sowie durch den Einsatz von stahlfaserverstärktem Beton in der vorgefertigten Tübbingauskleidung aus. Die Verwendung von Fasern zielt darauf ab, den CO2-Fußabdruck zu reduzieren, um ein aus ökologischer Sicht optimales Design zu erhalten. Um die statische Funktion und Integrität gemäß den Dauerhaftigkeitsanforderungen aufgrund der großen Vortriebspressenkräfte (temporäre Lasten) und unter permanenter Belastung zu gewährleisten, wurde ein 3D-Strukturmodell mithilfe einer FE-Software erstellt. Die Ergebnisse des Modells ermöglichen es, die Bereiche des Segments zu identifizieren, in denen Abplatzungen und Spaltzugspannungen entlang der Umfangsfugen entstehen, sowie den maximalen Wert dieser Spannungen in den temporären Lastfällen. Darüber hinaus wurde ein statischer Nachweis des Segments unter Berücksichtigung des Beitrags von Stahlfasern der Klasse 4c durchgeführt, wie es im FIB-Modellcode festgelegt ist, um sicherzustellen, dass die vorgefertigten Segmente die Anforderungen des Projekts an die statische Tragfähigkeit und Dauerhaftigkeit erfüllen. Der Artikel beschreibt detailliert den Entwurfsansatz und den Ansatz der unabhängigen Prüfung des Entwurfs.

State-of-the-art material laws in numerical models make it possible to integrate the structural design and the ultimate limit state analysis into the numerical model (“Implicit design”). The material laws limit the stresses to values, which the material can bear. Partial factors of safety on the load and resistance sides can also be taken into account. Using the example of a time-independent, 3D mathematical model for an underground railway station with tunnel junctions, which is being constructed by mining in soft soil, this paper investigates to what extent the material laws and the mathematical model fulfill the requirements laid down in the Eurocode for ultimate limit state analysis and how near these results are to the real situation.
Some simplifications and weaknesses of the mathematical model are explained, their effect on the results investigated and evaluated in relation to the uncertainties in the characteristics available for materials. Suggestions are made as to how the effects of defects in the model in an unsafe direction can be avoided. Further aspects, which can affect the reliability of calculations, are also pointed out.

Hochwertige Stoffgesetze in Berechnungsmodellen erlauben es, die Bemessung und den Tragsicherheitsnachweis in das numerische Modell zu integrieren (“Implizite Bemessung”): Die Stoffgesetze begrenzen die Spannungen auf Werte, die das Material ertragen kann. Auch Teilsicherheitsbeiwerte auf Last- und Widerstandsseite können erfasst werden. Am Beispiel des zeitabhängigen, räumlichen Rechenmodells für eine U-Bahnstation mit Tunnelverschneidungen, die in bergmännischer Bauweise im Lockergestein hergestellt wird, wird untersucht, wie weit die Stoffgesetze und das Rechenmodell die in den Eurocodes festgelegten Anforderungen zum Nachweis der Tragsicherheit erfüllen und wie realitätsnah die Berechnungsergebnisse sind.
Es werden einige Vereinfachungen und Schwächen des Rechenmodells beleuchtet, ihre Auswirkungen auf das Ergebnis untersucht und in Relation zu den Unsicherheiten bei den zur Verfügung stehenden Materialkennwerten bewertet. Vorschläge werden unterbreitet, wie Auswirkungen von Modellfehlern auf der unsicheren Seite vermieden werden können. Auf weitere Aspekte, die die Zuverlässigkeit von Berechnungen beeinträchtigen können, wird ebenfalls hingewiesen.

This paper reviews the differences between the alternative types of structural hollow section products (cold-formed versus hot-finished) as they affect structural design in Europe, using the relevant product and design standards, with an emphasis on Rectangular Hollow Sections (RHS). Manufacturers of cold-formed structural hollow sections (CFSHS) are more numerous, so that their products are more widely available. Hot-finished structural hollow section (HFSHS) products are typically between 24 % and 54 % more expensive in Germany than their cold-formed counterparts, the lower differences being for large tonnages - a strong inducement in favour of CFSHS. The price difference may also vary within the European Union. The geometric and product properties which are distinctly unique to CFSHS are presented and shown to offer no restrictions in their use when in compliance with the appropriate clauses in the European standards. These are the influence of corner radii, welding in the corner area, material choice to avoid brittle fracture and suitability for welding CFSHS. A comparison of the structural performance of CFSHS and HFSHS shows equally efficient structural designs for both products. The points covered are the design of compression members - unfilled and concrete-filled, joint resistance - which typically governs selection of member sizes, as well as fatigue design, fire design and the resistance of braced steel frames to severe seismic loading. CFSHS are shown to be adequate under all these situations.

As a source of sustainable, renewable, and clean energy, deep geothermal systems increasingly gain importance for the energy transition. In Germany, the North Alpine Foreland Basin is the success story for hydrothermal systems. Besides successful projects in the Munich area, recent attempts to establish successfully operating geothermal wells southwards, e.g., in Geretsried, failed due to a lack of permeability of the rock mass. Subsequent research in Geretsried found that all existing discontinuities are low to non-productive. The current project ZoKrateS, rethinking the Geretsried reservoir being a petrothermal play, bypasses these limitations by stimulating the existing fractures, and trying to keep them conductive by embedding proppants that prevent full closure. Four detached sections of the well GEN-1ST-A1 were subject to individual stages of stimulation. These four sections have been stimulated by placing proppants at injection pressures below the in-situ least principal stress at no microseismic activity. After injection the communication between well and formation appeared to be increased. Although data processing is still ongoing, linear correlations between cumulative injected volume and quasi-static pressure may be interpreted as channel flow within highly disturbed rock masses at intersections of faults. The high elasticity of these sections enables even low pressure to cause discontinuity opening below the least principal stress.
Geothermie als nachhaltige, erneuerbare und saubere Energie bekommt eine zunehmende Bedeutung als Baustein der Energiewende. In Deutschland ist das Nordalpine Vorlandbecken die Erfolgsgeschichte der hydrothermalen geothermischen Systeme. Im Raum München wurden einige erfolgreiche geothermische Projekte umgesetzt. Allerdings waren Projekte südlich Münchens wie das Projekt Geretsried aufgrund geringer Felspermeabilität nicht erfolgreich. Ein Forschungsprojekt in Geretsried konnte nachweisen, dass existierende Trennflächen gering bis gar nicht durchlässig waren. Das aktuelle Forschungsprojekt ZoKrateS hat das Reservoir Geretsried als petrothermales System verstanden und die existenten Trennflächen stimuliert, um die Trennflächen konduktiv durch den Eintrag von Stützmitteln zu erhalten. Vier abgetrennte Zonen der Bohrung GEN-1ST-A1 wurden einzeln stimuliert. In diese Zonen wurden erfolgreich Stützmittel bei Injektionsdrücken unterhalb der kleinsten Hauptnormalspannung ohne mikroseismische Aktivität eingebracht. Nach der Stimulation bestand eine erhöhte Kommunikation zwischen Formation und Bohrung. Es konnte eine lineare Korrelation zwischen injiziertem Volumen und quasi-statischem Druck beobachtet werden, dies kann als röhrenartiger Fluidfluss in stark zerklüftetem Fels an Störungsverschnitten interpretiert werden. Die hohe Elastizität dieser Bereiche erlaubt bei geringen Drücken eine Öffnung der Trennflächen.

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Bauwerksdiagnostische Untersuchungen sind die Voraussetzung für eine verlässliche Bewertung von bestehenden Tragwerken. Häufig fehlen konkrete und realistische Informationen über den tatsächlichen Bauwerkszustand und damit die Eingangsgrößen für die rechnerische Nachweisführung. Anders als bei Neubauten müssen diese Annahmen nicht geschätzt und durch zusätzliche Sicherheitselemente abgedeckt werden, sondern können zuverlässig mit ihrer tatsächlichen Eigenschaft sowie Streuung am Bestandstragwerk erfasst werden. Die Bauwerksdiagnostik bietet eine Vielzahl an Möglichkeiten, den Bestand und Zustand der Materialien sowie Konstruktionen realitätsgetreu zu erkunden. Die digitale Revolution des Bauwesens bedingt neue Konzepte, mit denen es gelingt, unsere bestehenden Tragwerke wesentlich effizienter und v. a. länger nutzen zu können. Der digitale Bauwerkszwilling ermöglicht die Zusammenführung und Verknüpfung von Daten unterschiedlichster Struktur und Herkunft. Damit müssen zwangsweise auch bauwerksdiagnostische Daten konsequent digitalisiert, in solche digitalen Zwillinge integriert und in Kombination mit den weiteren Bestands- und Zustandsdaten für den Nutzer aufbereitet werden. Dieser methodische Ansatz des Structural Information Modeling bildet die Grundlage für eine realistischere und zuverlässigere Bewertung bestehender Bauwerke.

Bauwerksdiagnostische Untersuchungen sind die Voraussetzung für eine verlässliche Bewertung von bestehenden Tragwerken. Häufig fehlen konkrete und realistische Informationen über den tatsächlichen Bauwerkszustand und damit die Eingangsgrößen für die rechnerische Nachweisführung. Anders als bei Neubauten müssen diese Annahmen nicht geschätzt und durch zusätzliche Sicherheitselemente abgedeckt werden, sondern können zuverlässig mit ihrer tatsächlichen Eigenschaft sowie Streuung am Bestandstragwerk erfasst werden. Die Bauwerksdiagnostik bietet eine Vielzahl an Möglichkeiten, den Bestand und Zustand der Materialien sowie Konstruktionen realitätsgetreu zu erkunden. Die digitale Revolution des Bauwesens bedingt neue Konzepte, mit denen es gelingt, unsere bestehenden Tragwerke wesentlich effizienter und v. a. länger nutzen zu können. Der digitale Bauwerkszwilling ermöglicht die Zusammenführung und Verknüpfung von Daten unterschiedlichster Struktur und Herkunft. Damit müssen zwangsweise auch bauwerksdiagnostische Daten konsequent digitalisiert, in solche digitalen Zwillinge integriert und in Kombination mit den weiteren Bestands- und Zustandsdaten für den Nutzer aufbereitet werden. Dieser methodische Ansatz des Structural Information Modeling bildet die Grundlage für eine realistischere und zuverlässigere Bewertung bestehender Bauwerke.

Structural Information Modeling - the digital transformation of building diagnostics
Building diagnostics are the prerequisite for a reliable evaluation of existing structures. Often, there is a lack of specific and realistic information about the actual condition of the structure and thus the input variables for the numerical verification. In contrast to new buildings, these assumptions do not have to be estimated and covered by additional safety elements but can be reliably measured with their actual properties as well as their scatter on the existing structure. Building diagnostics offers a multitude of possibilities to realistically assess the existing structure and the condition of materials as well as structures. The digital revolution in the construction industry implies new concepts that will make it possible to use our existing structures much more efficiently and, above all, for a longer period of time. The digital twin enables the merging and linking of gigantic data of the most diverse structure and origin. This means that structural diagnostic data must also be consistently digitized, integrated into digital twins and, in combination with the other inventory and condition data, prepared for the user in an intuitive manner. This methodical approach of Structural Information Modeling forms the basis for a more realistic and reliable assessment of existing structures.

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This two-part article gives an overview of the developments of the structural member verification in prEN 1993-1-1:2020 “Eurocode 3: Design of steel structures - part 1-1: General rules and rules for buildings”, one of the second generation of Eurocodes. These developments were undertaken by Working Group 1 (WG1) of Subcommittee CEN/TC250/SC3 and by Project Team 1 (SC3.PT1) responsible for drafting the new version of EN 1993-1-1. In the past, WG1 collected many topics needing improvement, and the systematic review conducted every five years also yielded topics needing further development. Based on this, the current version of EN 1993-1-1 has been developed into a new draft version prEN 1993-1-1:2020 enhancing “ease of use”. The technical content of this new draft was laid down at the end of 2019. Many improvements to design rules have been established with respect to structural analysis, resistance of cross-sections and stability of members. This two-part article focuses on member stability design rules and deals with the basis for the calibration of partial factors, the introduction of more economic design rules for semi-compact sections, methods for structural analysis in relation to the appropriate member stability design rules, new design rules for lateral torsional buckling plus other developments and innovations. This first part of the article primarily serves to explain the general background to the European Commission Mandate M/515 that led to the further evolution of the Eurocodes and to illustrate the developments in prEN1993-1-1:2020 that pertain to new material grades, partial factors, cross-sectional classification and structural analysis. These form the necessary background to the changes to member buckling design rules, which are treated more specifically in the second part.

This two-part article gives an overview of the developments of the structural member verification in prEN 1993-1-1:2020 “Eurocode 3: Design of steel structures - part 1-1: General rules and rules for buildings”, one of the second generation of Eurocodes. These developments were undertaken by Working Group 1 (WG1) of Subcommittee CEN/TC250/SC3 and by Project Team 1 (SC3.PT1) responsible for drafting the new version of EN 1993-1-1. In the past, WG1 collected many topics needing improvement, and the systematic review conducted every five years also yielded topics needing further development. Based on this, the current version of EN 1993-1-1 has been developed into a new draft version prEN 1993-1-1:2020 enhancing “ease of use”. The technical content of this new draft was laid down at the end of 2019. Many improvements to design rules have been established with respect to structural analysis, resistance of cross-sections and stability of members. This two-part article focuses on member stability design rules and deals with the basis for the calibration of partial factors, the introduction of more economic design rules for semi-compact sections, methods for structural analysis in relation to the appropriate member stability design rules, new design rules for lateral torsional buckling plus other developments and innovations. This second part of the article is dedicated to illustrating the most relevant changes to member buckling design rules.

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A framework with a robust design of the driving classes is fundamental for the tunnel design. During tunnel advance, the detailed design of the lining is depending on the documented geology and the observed system behaviour. To reduce costs, the excavation profile is optimized with the aim of reducing overbreaks and shotcrete masses. This achieved profile accuracy is beneficial for the load-bearing capacity of the rock and the shotcrete lining. For temporary and permanent tunnel shotcrete linings, the excavation profile accuracy influences the stress distribution, the crack pattern and the expected deformations. In the course of this study, the effect of the excavation geometry on the load-bearing capacity of the primary lining of drill and blast tunnels was examined. For this purpose, shotcrete linings, reinforced by steel meshes and fibre-reinforced linings, were compared in optimized and non-optimized scanned excavation cross-sections. In each case, an ultimate load and failure analysis was carried out to assess shells in the hardened state by means of numerical modelling (ATENA). The aim is to determine the load-bearing capacity of the shell structure in order to obtain a conclusion regarding its structural robustness. The interaction between the rock/soil soil and the structure as well as a time-dependent material behaviour were not considered. It could be shown how an irregular overbreak or an inconsistent shell thickness has a negative effect on the load-bearing capacity of the structure.

In Memoriam of Prof. Dr. Bernt Johansson
Representative steel design standards have limited the use of high-strength steels to tubular joints, partly because of concerns about their unique material characteristics. However, the mechanical background behind the limitations is unclear, and its validity needs to be re-evaluated. In this study, a set of CHS (circular hollow section) X-joints fabricated from cold-formed tubes was tested under static axial compression. Then, as supplemental work, extensive test-validated numerical analyses were carried out to investigate further the behaviour of high-strength steel CHS X-joints. In both the testing and the analyses, where three steel grades covering ordinary to very high-strength steels were considered, the high-strength steel joints showed satisfactory structural performance comparable with that of ordinary steel joints in terms of strength and ductility.

An experimental programme was proposed and carried out to assess the effectiveness of the mineral-based composite (MBC) technique for the flexural strengthening of negative moment regions in continuous reinforced concrete slabs. In addition to the testing of the two reference specimens, the experimental programme included the testing of nine continuous RC slab specimens with different strengthening techniques, namely, using ordinary steel bars and MBC material. This experimental programme was conducted to study the failure modes, the load-deflection behaviour and the failure loads.
Furthermore, we present and describe a comparative study between the two strengthening techniques, namely, steel reinforcing bars with MBC or steel bars with epoxy mortar. Based on the experimental results presented, both strengthening techniques for continuous slabs are evidently efficient. In this study the measured results for the average crack spacing were compared with the limits stipulated in CEB-FIP code 1990 and the failure load calculations were extended with an analytical approach based on the ultimate theory for the failure load calculation. In conclusion, the results obtained from the analytical model are in agreement with the experimental results.

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The paper presents the experimental tests carried out in the Boundary-Layer Wind Tunnel (BLWT) for the design of large roofs of the new Olympic stadium (Karaiskaki) in Pyraeus (Greece), Manfredonia (Italy) and "Delle Alpi" of Turin (Italy). In addition, a report about some results of the T.D. dynamic response analyses performed on the Karaiskaki structure and on the Olympic stadium in Rome will be given. The peculiar shape of these large structures and their particular location (two of them are in the immediate sea vicinity) let arise the question about the actual distribution of the wind loads, i.e. on the pattern of pressure coefficients (cp) over the entire roof. For every wind direction investigated, the following quantities have been evaluated: mean values of the aerodynamic coefficients cp, standard deviation of cp, maximum and minimum values of cp. Finally, the recorded data have been used for the numerical simulation of the dynamic response of the structure in Time Domain, whose aim is the definition of the design loads of the steel lattice struc-tures. A numerical model of the "Delle Alpi" stadium is also in preparation, allowing re-sults of dynamic response analyses, which are still in progress.

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