Effects of slenderness in reinforced concrete column design

Abstract

To accommodate over growing population, scarcity of land and amplified price of property in Bangladesh, vertical extension of buildings has now become essential and many high-rise buildings are now being constructed in major cities. In addition, the use of high strength materials with innovative design approach with the help of design software, it is now possible to design smaller cross section of structural members than those designed in earlier time. This reduction incross-section is very important for column design as slenderness might influence the adequacy of the column. The design load of a slender column might approach buckling load and sway of the frame might be large enough to increase the moments obtained from first order analysis. Consideration of these effects is essential as column is the most important member in a structure. An inadequately designed column without any attention to slenderness might result in catastrophic failure of the whole structure .. ., . ,- To build awareness about slender column, this study has been carried ouLfor beamcolumn and flat-plate concrete structures; where corner, edge and inner columns have been considered, The methods described in ACI Code-318 (1999) for designing slender column have been reviewed. Slender column design procedures of ETABS and PCACOL software have been validated against manual calculation as per the - provisions of ACI Code. A limited parametric study has also been performed to identify the influencing factors of slenderness that should be considered before any design process started. The findings of the study are noticeable. Considering slenderness in column design is extremely important. Designer should check the slenderness effect in column before starting column design. The ACI Code limits for neglecting sway effect has been checked and found acceptable. P-Delta analysis should be run for every high-rise concrete structure to incorporated possible sway effect. Flat-plate frame structure has more sway effect than beam-column frame structure. Corner and edge columns need more attention due to susceptibility to slenderness. Column with height greater than 15' is substantially vulnerable to sway effect. The steel ratio might increase abruptly when slenderness exceeds a certain limit. Hopefully this study will increase some awareness to structural designers regarding slender column design. The designers should be able to decide when slenderness effect need to be taken care of and he could properly take the advantage of automatic design feature of software and the design will be more effective and correct.