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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.

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

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.

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

FE analyses and tests of lap splices in frame corners

Karin Lundgren, Chalmers University of Technology, Goteborg, Sweden

Until recently, splicing of the reinforcement in frame corners had not been allowed by the Swedish Road Administration. Since this has led to reinforcement layouts that were hard to realise on site, the effect of splices placed in corner regions were examined. Four frame corners with differing detailing were tested. Furthermore, detailed three-dimensional non-linear finite element analyses of corners were conducted. The splitting stresses resulting from the anchorage were taken into account by the use of a new model of the bond mechanism. A parameter study of the importance of the loading conditions was made with two-dimensional models. The tests and analyses show that splicing the reinforcement in the middle of the corner has advantages over placing splices outside the bend of the reinforcement. They also indicate, in agreement with the previous analyses and tests, that provided the splice length is as long as required by the codes, there are no disadvantages in splicing the reinforcement within the corner of a frame.

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

Friction between concrete and slipform panel during slipforming

Kjell T. Fosså, Norwegian University of Science and Technology, Trondheim, Norway
Magne Maage, Selmer Skanska AS, Oslo, Norway

Tests are carried out in a vertical slipform rig in order to identify the main parameters affecting the lifting stress (friction) during lifting of the slipform panel. The results show that there is an almost linear correlation between the net lifting stress and the effective pressure. This means that the net lifting stress can be calculated based on the effective pressure by using the friction law. The lifting stress is affected by both the particle shape of the aggregates, roughness of the slipform panel and the workability in the early phase. The results also show that lower air content and a finer pore system (finer particle size distribution and higher particle concentration) in the concrete will result in a higher maximum lifting stress (friction). Also a lower lifting height or lower frequency will increase the lifting stress. It is assumed that higher lifting stress will increase the risk for surface damages during lifting of the slipform.

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