Slender Reinforced Concrete Columns Under Load And Movement PDF Download

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 secondary 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/sq.mm. 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, CP110:1972, ACI318:1977 and CP114:1957, have been compared with the experimental and theoretical results of this work. CP110 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.