The primary goal of the research is to improve understanding of the behaviour of bridges influenced by shear in the prestressing cable ducts. This question arises during the evaluation of existing structures, whose durability is also often investigated.
A series of tests on prestressed concrete girders of the viaduct "Sopra Canteen" whose deck will be replaced in 2003 and 2004 will study the behaviour and resistance to shear thin ducts crossed by cable prestressing. Based on these data, the interaction between the disturbance in the flow constraints caused by the presence of cables and cracking produced by the deformation of the reinforcements, may be examined and lead to a better understanding of the phenomena. The result will be a more complete model, taking into account different factors.
It is planned to try a series of 5 beams with a length of 13 m and a weight of about 14 t.
Accredited laboratory tests.
Mechanical model of the behaviour of bridges influenced by shear in the prestressing cable ducts.
The validity of this model is demonstrated by a series of laboratory tests on real beams, extracted from the viaduct "Sopra Canteen" from the A2 whose deck will be replaced in 2003 and 2004.
Final report attached.
Behaviour of post-tensioned girders extracted from an existing bridge:
The girders failed in shear by crushing of the web along the post-tensioning tendons. The test results are used to understand the various loadcarrying mechanisms developed in the girder and to investigate the suitability of the approaches proposed by design codes and the stress field method to estimate the shear strength of such members. All versions of SIA 162, which do not consider this effect, provide unsafe results. On the other hand, SIA 262 and the stress field method give sufficiently accurate and conservative results.
Consequently, for the dimensioning of post-tensioned girders with thin webs, the approach
followed by the current SIA 262 can be followed, leading to sufficiently accurate and
conservative designs. For the checking of existing structures on the other hand, an
incremental approach seems more appropriate in cases where an insufficient strength is
found with the SIA 262 formulae. In such situations, it becomes necessary to develop
various stress fields, progressively improving their accuracy to estimate the shear strength
of the member.