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Structural Concrete, Vol. 3, no. 3, September 2002

Advances in precast concrete in mixed construction

K. S. Elliott, University of Nottingham

Mixed construction is now being used in the majority of new multi-storey buildings, once the traditional domain of cast-in-situ concrete and structural steelwork. Mixed precast construction means the combined use of precast concrete with steelwork, timber, cast-in-situ concrete and masonry. The combination is made for the benefit of the building process at large and does not necessarily have to be designed and constructed compositely. Mixed construction maximises the structural and architectural advantages in combining components made of different materials, but it requires the cooperation of the architect, structural designer, services engineer, manufacturer, supplier and contractor. It is possible that some client and architectural demands can only be satisfied using mixed construction. In 2002 the fib Commission 6 on Prefabrication will publish a state-of-the-art report on the use of precast concrete in mixed construction. This paper summarises the report.

Structural Concrete, Vol. 3, no. 3, December 2002

Influence of traffic loads on permanent deflections of prestressed concrete bridges

Z. Smerda Technical University Brno, VIAPONT Ltd, Brno, Czech Republic
J. Smerda VIAPONT Ltd, Brno, Czech Republic

The rising volume of traffic on concrete road bridges has caused designers to consider the problem of permanent deflections caused by repeated traffic loading. However, it should be stated that the correct method for calculating such deflections is currently unclear and consequently gives rise to unrealistic estimations. Moreover, a lack of knowledge regarding the full spectrum of traffic loads and the effects of repeated loads upon concrete deformation exacerbate the problem. This paper attempts to determine the permanent deflection of prestressed concrete bridges without cracks.

Structural Concrete, Vol. 3, no. 3, December 2002

Minimum cost design of concrete sandwich panels made of HPC faces and PAC core: the case of in-plane loading

Catherine G. Papanicolaou, University of Patras, Greece
Thanasis C. Triantafillou, University of Patras, Greece

This paper presents a minimum cost design procedure for precast structural sandwich panels made of HPC (high-performance concrete - i.e. high-strength and fibre-reinforced) faces and a pumice aggregate concrete (PAC) core, which might also include a layer of thermal insulating material. Attention has been focused on the selection of materials' strength and members' geometrical parameters, as well as on the material cost functions for both concrete types. The strength-based design case study resides with the format of Eurocode 2 and takes into consideration failure modes associated with in-plane loading, such as flexure, shear and local buckling of the compressed faces, with respect to the presence of the insulating layer. The solution of the optimisation problem is attained through the development of a computer program using available algorithm codes provided by Matlab®. The optimisation procedure results in the derivation of design recommendations, which encompass the objective of minimum cost for the elements under investigation.

Structural Concrete, Vol. 3, no. 3, September 2002

Assessment of fire-damaged concrete using crack density measurements

Neil R. Short, Aston University, Birmingham
John A. Purkiss, Aston University, Birmingham
Sarah E. Guise, Aston University, Birmingham

Petrographic techniques have been developed to determine the nature and density of cracks that have developed after subjecting concrete to steady-state and transient heating regimes. The steady-state investigations showed that there was a good correlation between measurements of crack density and measurements of residual compressive strength. Crack density measurements taken on samples after transient heating have shown that the depth to which the compressive strength of the concrete is likely to have been significantly affected can be identified. Thus, this technique should provide very useful information for the evaluation of fire-damaged concrete.

Structural Concrete, Vol. 3, no. 3, September 2002

Bond of prestressed strands to concrete: transfer rate and relationship between transmission length and tendon draw-in

Sérgio M. R. Lopes, University of Coimbra
Ricardo N. F. do Carmo, Polytechnic of Coimbra

This paper presents an experimental study on the bond of strands prestressed by pretensioning to concrete. Ten beams with different cover values were tested and the results are presented and analysed. In eight of the beams, transfer of the prestressing force was gradual, and sudden in the remaining two beams. A relationship between the transmission length and the bond draw-in at the end of the beam is proposed and compared with predictions found in the literature. The variation of the tendon force along the transmission length is also plotted on graphs and the results are compared with those proposed by Rôs. The comparison with Rôs' predictions shows that experimental values obtained in the current investigation deviate from the expected values by up to 10%.

Structural Concrete, Vol. 3, no. 2, June 2002

Full-scale static loading tests on concrete armour units with the incorporation of LD-slag

G. De Schutter, Ghent University, Belgium
K. Audenaert, Ghent University, Belgium
J. De Rouck, Ghent University, Belgium

LD-slag is an industrial by-product resulting from the transformation of hot metal into steel by oxygen refining. In order to avoid waste disposal, the incorporation of LD-slag in concrete armour units for breakwaters has been studied. Due to the higher density of LD-slag in comparison with traditional aggregates, a higher hydraulic stability of the armour units is obtained for a given unit size. Static loading tests showed that the mechanical behaviour of breakwater armour units made with the LD-concrete is comparable to the mechanical behaviour of units made with traditional concrete. However, durability problems might occur due to an insufficient volume stability of the LD-slag. To overcome this problem, treated slag has to be used.

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