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Title: Long slender reinforced concrete columns.
Author: Dracos, A.
ISNI:       0000 0001 3432 057X
Awarding Body: University of Bradford
Current Institution: University of Bradford
Date of Award: 1982
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The behaviour of very slender eccentrically loaded reinforced concrete columns is investigated, both analytically and experimentally, under short-term and sustained loading. Short-term loading investigations involved the testing of thirty-six columns having slenderness ratios between 28.85 and 57.69. The first twenty-four columns were cast with a concrete having a mean 28 day cube strength of 46 •. 82 N/mm2 and subjected to loading at eccentricities of 10mm and l5mm. The remaining twelve columns were cast with a concrete having a mean 28 day cube strength of 34.69 N/mm 2 and loaded at an eccentricity of l5mm. The behaviour of four columns cast with the stronger of the two concretes was monitored under sustained loading for a period of about eighteen months. These columns had slenderness ratios of 38.46 and 48.08 and loads were applied at eccentricities of 10mm and l5mm. An analytical procedure based on the classical equations of mechanics (equilibrium compatibility and properties of the constituents) has been developed to predict the behaviour of slender columns under an eccentric load. Comparisons between the observed and analytical behaviour of forty columns, indicate that the proposed analysis estimates closely the load capacity and load deformation behaviour of very slender reinforced concrete columns. The validity of the proposed method has also been demonstrated in extensive comparisons between predicted and experimental observations obtained from tests performed by other investigators on very slender columns. The design of very slender columns in accordance with CPllO is based on the assUmption that failure would occur when the maximum concrete compressive strain reaches an ultimate value of 0.0035. In tests this assumption has proven to be wrong as instability occurs at very low concrete strains, normally no more than 0.001. Thus the code mentiqned is incorrect in using a theory based on material failure· for very slender columns. The results of analytical studies into the behaviour of slender columns under sustained loading indicate that the present provisions in CPllO do not account fully for creep effects. As a consequence the recommendations of CPllO lead to unconservative designs. The recommendations of ACI318 on the other hand, agree in general with the analytical results.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Structural engineering