Title: Some results of experimental researches on bond in reinforced concrete members

Author(s): J. J. Pędziwiatr, L.J. Jankowski

Publication: KILW

Volume: 53

Issue: 1

Appears on pages(s): 37-55

Keywords: bond,reinforced concrete

DOI:

Date: 1/1/2007

Abstract:
Intensive studies and experimental researches on bond, which have been carried from early 70, have not lead to significant results. In engineering practices and national codes, still exist recommendations based on researches from early 70 or even older. The main source of that situation is fact that most experiments were conducted on RILEM recommended specimens with a very short embedded length and under axial tension. Such researches are relatively cheap and easy to carry but their results cannot be used in concrete structures analysis. Too short development length leads to unrealistic values of both slips and bond stresses caused by effect of strain concentration and a slip of free bar end. At the other hand, their length cannot allow to create internal cracks, which play very important role in forces transfer from a bar to surrounding concrete. Our own researches were carried mainly on eccentric tension members that have length, which allow arising of several cracks. A shape of cross-section and such arrangement of bars position that they were faced with a specimen edge, make possibility to direct measurement of steel and concrete strains. Elastooptical surfaces glued to different parts of specimens allow observing changes in strains distribution on large areas and discovering some phenomenon, which can hardly be seen using classical methods. Thanks to researches, it was possible to explain some problems of crack creation and development and of forces transfer from a bar to concrete. It was confirmed that internal cracks play an important role in states of deformation and cracking for members under axial and eccentric tension, which are reinforced with deformed bars. Researches allow reliable explanation sources of such phenomenon as a very large variation of crack width and spacing values. Also non uniform concrete strain distribution in perpendicular cross-section in axially tensioned member, can be explain. Researches confirmed theoretical model presented earlier very well and allow extending and improving it.