This paper presents a critical comparison of the existing code provisions for the shear strength of concrete beams. The comparison is based on the computerized filtering-out of the inevitable statistical bias from the available multivariate database on shear strength, on an examination of the predicted size effects on shear strength and their underlying hypotheses and on the results of recent high-fidelity numerical simulations of shear failure. In addition to examining the existing models, the present comparison also provides several key considerations for testing the scientific soundness of any model of shear failure in concrete beams, which is necessary for future revisions to the design code provisions.

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.

The correlations among selected parameters of concrete were investigated for concrete mixes of the strength classes C20/25, C25/30, C30/37, C40/50 and C50/60. The focus was laid on correlations between basic mechanical parameters such as compressive strength, tensile strength and modulus of elasticity as well as parameters related to concrete fracture, represented here by specific fracture energy. Laboratory tests examining the fracture behaviour and mechanical properties were carried out in order to determine the fundamental concrete parameters. In particular, standard compression tests on test cubes and three-point bending tests on beams with central edge notch were performed. Additional material parameters were identified using the inverse analysis technique. Finally, correlation factors between different parameters of concrete were identified using the rank-order correlation method.