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Title: Slender reinforced concrete columns under load and movement.
Author: Schofield, D.
ISNI:       0000 0001 3556 5413
Awarding Body: University of Bradford
Current Institution: University of Bradford
Date of Award: 1983
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Slender reinforced concrete columns have become widely used as structural members in recent years. Current Codes of Practice for Structural Concrete lack sufficient guidance to designers for their safe and efficient design. This investigation studies the behaviour of very slender, pin-ended, reinforced concrete columns, under short-term and sustained loads, by experiment and theoretical analysis. A new approach is used in the method of applying load to the column. A concentric axial load and independant primary end moments are considered. This allows the determination of secon~ary moments due to axial force and secondary deflections to be easily determined compared with the conventional eccentric load methods adopted in the past. A non-linear, second-order computer analysis has been developed which is capable of accurately predicting the deflections of hinged columns throughout the loading range from zero load to buckling failure, for any combination of eccentric loads and primary moments for short or sustained periods. It has the potential to accept end restraint in order to model framed columns. An extensive experimental programme of tests has been performed on 48 column specimens with slenderness ratios between 29 and 59 under short term loads and 5 specimens under sustained loads for up to two years. A total of 68 short column specimens with an identical section to the slender columns and material specimens were also tested. The specimens had a mean wet-cured cube strength of 42 N/ The results of these tests and, 120 similar results of other authors, confirmed the validity of the proposed theoretical analysis and the assumptions used. The computer program which is presented could be made available to design offices for use on a basic micro-computer. The design methods recommended by three Codes of Practice, CPII0:1972, ACI318:1977 and CPl14:1957, have been compared with the experimental and theoretical results of this work. CPII0 and ACI318 are shown to give conservative designs, with an overall load factor of 3.0 and 2.4 respectively, for design loads compared with the 25 year load given by the proposed theory. CPl14 gives design loads with an equivalent load factor of 1.35. These codes provide conservative designs, but CPII0, unlike ACI318, does not recommend the use of a second-order analysis or highlight the potential dangers of long-term distress due to creep deflections in slender columns. An alternative method of design to the current codes for slender columns is presented in the form of load moment interaction curves for buckling rather than material failure. These show both primary and secondary moments, and buckling loads for any slenderness ratio. The criterion of material failure at an ultimate compressive strain of 0.35% (CPII0) or 0.30% (ACI318) is shown to be incorrect when column failure occurs by buckling rather than compression. The observed compressive strain at failure of columns with slenderness ratios between 29 and 59 in this work was typically 0.1%.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Structural engineering