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

Written on 19 August 2011.

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

Written on 19 August 2011.

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

Written on 19 August 2011.

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

Written on 19 August 2011.

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.

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

Written on 19 August 2011.

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

Written on 19 August 2011.

New trends in prestressed concrete bridges

M. Virlogeux, Consulting Engineer and Designer

This paper aims to give an overview of the recent evolution in the design and construction of prestressed concrete bridges worldwide. Several major trends are evidenced. Certainly those which have the larger influence for the industry due to their wide applications are the development of external prestressing, now systematically used in some countries for medium span bridges; the emergence of high performance concrete which extends the possibilities at the same time as improving the durability of concrete structures; and the more and more frequent association of steel and concrete to constitute composite bridges of different types and composite elements in bridges, allowing for many innovative structures. Considering more specific applications, a section is devoted to cable-stayed bridges which received very interesting development during the last ten years; and another section evokes the more and more extensive use of heavy prefabrication in large projects, with elements up to several thousand metric tons. The paper concludes with a word on bridge architecture, showing that good structural designs can produce elegant prestressed concrete bridges.