Non-linear finite-element modelling of reinforced concrete deep beams
A.H. Alwathaf, Sana'a University, Yemen
The characteristic behaviour and failure mechanism of a deep beam is investigated using non-linear finite-element analysis in this study. An accurate stress-strain relation is incorporated to describe the stress-strain behaviour of the concrete under compression for uniaxial and also for biaxial stress states. Material non-linearity in the compressive stress field is considered for the concrete in the orthogonal directions and the effect of microcracking confinement and softening on the stress-strain relationship under biaxial stresses are included, employing the equivalent uniaxial strain concept. A computer code FEARCB (finite-element analysis of reinforced concrete beams) is developed to analyse deep beams until failure. The applicability of the proposed finite-element model is investigated by demonstrating the non-linear structural response and failure mechanism of different deep beams and comparing with the available experimental work. Good agreement is achieved between the developed finite-element model and the experimental test results.
Concrete gravity-based structures used for offshore LNG storage and regasification in the Adriatic Sea
J. Naess, Aker Solutions AS, Norway S.I. Giske, Aker Solutions AS, Norway L. Bjerkeli, Skanska Norge AS, Norway
A concrete gravity-based structure, used as an offshore liquid natural gas (LNG) receiving and regasification terminal, has been built and installed in the Adriatic Sea. The design, construction and interfaces of the concrete structure posed many challenges which drew on expertise learnt elsewhere in the world of offshore marine concrete structures. The integration of the LNG tanks and the regasification topsides into a compact concrete structure tested the ability to produce a consistent and easily constructed solution. The resulting structure was simple, efficient, robust, durable and the first of its kind.
Unconventional cable-stayed bridges: structural behaviour and design criteria
A.M. Ruiz-Teran, University of East London, UK
Under-deck and combined cable-stayed bridges are two relatively new bridge types that have been developed over the last 30 years. Most of these bridges have been constructed in Germany, Japan, France and Spain, and have been designed by outstanding structural engineers such as Leonhardt, Schlaich, Manterola, Virlogeux and Cremer. The main advantages of these bridge types are: their great structural efficiency; the small amount of materials that they require (allowing economic and sustainable proposals); their great construction possibilities, allowing an increase in the span range of certain construction methods; and their strong aesthetic characteristics owing to the different layouts that can be defined with the stay cables. This paper revises the structural behaviour and design criteria of under-deck and combined cable-stayed bridges, and summarises the main research contributions of the PhD thesis submitted by the author Dr Ana M. Ruiz-Teran, to whom the fib Diploma 2009 for Research (Young Engineers Award) has been recently presented for this work.
Span-to-height ratio limits for prestressed concrete members
P.G. Debernardi, Politecnico di Torino, Italy M. Taliano, Politecnico di Torino, Italy
This paper reports the main results of a parametric analysis which was performed to define appropriate limits for the span-to-height ratio of prestressed concrete beams or slabs that are in compliance with the deflection control required by international standards (Eurocode 2, Model Code 1990) for concrete buildings structures. Two deflections were considered: the total deflection and the active deflection that occurs after construction, in both cases under the quasi-permanent load combination. The active deflection has to be considered when fragile elements such as partitions or glazing are present on the structure. Four structural systems were considered: simply supported fully or partially prestressed beams with an I-section and simply supported or fixed-end slabs with a rectangular cross-section. The load history first included the application of the prestress and the dead load and then the application of the remaining quasi-permanent load. Taking into account the effects of imposed deformations the structure was designed to obtain the geometrical properties strictly necessary for the ultimate limit state (ULS) and for stress limitation in service under quasi-permanent and characteristic load combinations. The results allow the influence of some of the variables that most affect the deflection to be evaluated, such as the span and the height of the beams, the concrete strength, the permanent load and the variable-to-permanent load ratio.
Belgrade's Delta City shopping mall - design and construction
S.B. Marinkovic, University of Belgrade, Serbia V.M. Kokovic, University of Belgrade, Serbia I.S. Ignjatovic, University of Belgrade, Serbia V.H. Alendar, DN Engineering Consultants, Belgrade Serbia
The structure of Delta City shopping mall in Belgrade consists of two separate structures: the structure of the mall and the structure of the multi-storey open garage. The overall dimensions of the irregular layout of the structure are 210 m x 120 m, with four main levels in the mall and five parking levels in the garage. Because of the different exposure conditions, the structure of the garage is separated from the mall's structure with an expansion joint at all of the levels, except the level of the foundation slab. The mall's framed structure is designed without any expansion joints, except for temporary joints during the construction stage. It consists mainly of reinforced concrete columns cast in place, at typical spans of 8.2 m x 8.2 m, precast reinforced concrete simple beams and precast prestressed hollow core slabs. The moment resistant reinforced concrete frames cast in place are designed mostly at the facade, to provide additional seismic resistance and to control lateral deflections. The main structure of the open multi-storey garage consists of reinforced concrete frames cast in place and precast hollow core slabs, and it is designed for exposure class XD3, with special attention paid to durability requirements. Owing to the mainly precast structure, especially the hollow core slabs as a floor solution, the complete concrete structure of approximately 80 000 m2 was constructed in less then 12 months.
Bond to concrete action of reinforcing bars with different deformation patterns
A. Semchenkov, Research and Development Institute for Concrete (NIIZhB), Moscow, Russia V. Meshkov, Research and Development Institute for Concrete (NIIZhB), Moscow, Russia A. Kvasnikov, Research and Development Institute for Concrete (NIIZhB), Moscow, Russia
At present in Russia hot-rolled reinforcing bars are mainly manufactured using two deformation (rib) patterns, either with ring-like ribs of constant height or with two-row crescent-shaped ribs of 'European' style. Steel of both grades A400C and A500C can be produced with one or other of these rib patterns. Often it is difficult to identify on site an actual grade of rebars. To improve the situation a new specific deformation pattern for A500C grade steel was developed. The rebar-to-concrete interaction for the three patterns mentioned above is evaluated by means of the analysis of failure of concrete keys formed between transverse ribs of a steel bar. For this purpose the authors employed some principles of analysis that previously had been used for key joints of concrete floor panels. The bond behaviour is subsequently classified as 'rigid' or 'soft', the latter being considered as more favourable. The structural advantages of commercial production in Russia of A500CP grade reinforcing steel using the newly developed deformation pattern are described.
