Experimental investigations into deformations resulting from stresses perpendicular to grain in Swedish whitewood and redwood in respect of the dimensioning of concrete formwork
Deformations resulting from stresses perpendicular to grain in concrete formwork involving wooden shoring members have given rise to a number of problems on building sites. No quantitative relations between stresses perpendicular to grain and deformations have as yet been forthcoming. This has consequently resulted in the faulty dimensioning of concrete formwork. In serious cases, excessively large deformations of the type mentioned have caused the collapse of the forms for concrete casting. In less serious cases, formwork deformations have brought about bulbous protuberances on the surface of the concrete, an unacceptable situation, taken into consideration the planned installation of pre-fabricated supplementary units. The purpose of the investigation was to compile quantitative relations between stresses and subsequent deformations perpendicular to grain. Full-scale deformation tests were carried out on Swedish whitewood and redwood. During some of the tests, loading deformations were registered, and deformations at dead load (creep) were noted during others. The outcome of the results was that a relationship was obtained which quantitatively describes the dependence of the deformation resulting from stresses perpendicular to grain upon the load length parallel to grain, the volume weight, the humidity quotient and the load time. To facilitate practical application, the relations have been adapted to applicable grades of structural timber and have been represented graphically.To this can be added the discussion given in the appendix concerning the intensities and periods of active pressure on concrete forms which give rise to deformations resulting from stresses perpendicular to grain in supporting timber structure of concrete formworks. An application of the results of this investigation provides us with the possibility of calculating and limiting deformations in supporting timber structure of concrete forms.