Contribution à l'étude générale des dalles: Fid-Bau Portal

Contribution à l'étude générale des dalles

Borderie, P. / Absi, E. / Bonvalet, C.

Abstract Cette contribution concerne divers procédés d'analyse des contraintes des dalles biaises. Ce sont: - des méthodes analytiques: calcul par la méthode des Différences Finies; calcul par la méthode des Équivalences; - des méthodes expérimentales: étude sur petits modèles élastiques; mesure sur ouvrages réels. Les différentes méthodes sont exposées et les résultats obtenus sur huit ouvrages biais sont comparés. Parmi ces ouvrages, le plus biais possède un angle aigu égal à environ 16o. Les concordances entre les résultats sont satisfaisantes, tant du point de vue moments fléchissants et de torsion, que du point de vue réactions d'appuis et flèches, et permettent d'assurer la validité des méthodes de calcul présentées.

Summary The work most currently used to cross a span of less than fifteen meters is the reinforced concrete slab. The determination of the forces straining skew slabs on the basis of the methods applicable to straight slabs led to results that were the more erroneous the smaller the skew angle. The difficulty seems to have been surmounted for the first time for singlebay slabs, simply supported, by jensen in 1941. Between 1950 and 1960 the determination of the principal moments was made by the use of tests on models. The present contribution concerns various procedures for the analysis of the stresses of skew slabs, with simple or multiple bays, which among others are available to planners of works of this type. These procedures are based on: - analytical methods: Calculation by the method of Finite Differences; Calculation by the method of Equivalences; - experimental methods: Study on small elastic models; Measurement on real works. The theoretical bases of the analytical methods are developed, after a review of the fundamental equations which we owe to Lagrange. A theoretical analysis of the influence of the value of Poisson's ratio is presented. A historical survey of the experimental methods applicable to the study of slabs is given, and the methods most currently used at the present time are described in the form of an application to a structure having a very slight acute angle. Finally, after having defined the dimensional characteristics of eight skew slabs, the sharpest of which has an angle of approximately 160, the theoritical and experimental results obtained from these structures are compared. The comparison of the values of the flexure and torsion moments, of the reactions of support and the sags, shows a satisfactory concordance between the two groups of results and brings out the value, from the points of view of precision and economy, of the programmes of calculation by computer developed for this type of work.