Load transfer from high-strength concrete columns through lower strength concrete slabs
Kayani, M. Khaliq-ur-Rashid
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https://hdl.handle.net/2142/23462
Description
Title
Load transfer from high-strength concrete columns through lower strength concrete slabs
Author(s)
Kayani, M. Khaliq-ur-Rashid
Issue Date
1992
Doctoral Committee Chair(s)
Gamble, William L.
Department of Study
Civil and Environmental Engineering
Discipline
Civil and Environmental Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Civil
Engineering, Materials Science
Language
eng
Abstract
Six specimens were tested to investigate the effects on high strength concrete columns due to the presence of ordinary strength floor concrete layer in between. The specimens consisted of four sandwiched type of columns and two edge columns. The four columns, 55 in. long, had a 7 in. layer of floor concrete. These column specimens were designed to study the influence of longitudinal as well as lateral steel on the strength characteristics and behavior of the floor concrete. Two edge columns specimens consisted of two column sections separated by a 7 in. floor slab extending beyond the column faces in three directions. The data from these tests combined with the previously reported similar studies was analyzed to find the appropriate parameters for the estimation of the apparent strength of the floor concrete to be used in the calculation of load carrying capacity of columns. The analysis reveals that Sec. 10.13 of the ACI code is not based on the appropriate parameters. The allowable ratio of 1.4 between the two concrete strengths within which there is no requirement to reduce the column capacity is not considered appropriate. Similarly, the calculation of the apparent floor concrete strength in case of interior columns as per Sec. 10.13.3 was also found to be too unconservative.
Mechanics of materials approach used for the analysis of the composite materials was applied for theoretical analysis of the problem. This approach with the use of the available test data lead to an expression for the calculation of the apparent floor concrete strength applicable to all kinds of columns in structures. A similar but simpler and more conservative expression was also devised purely on data analysis. These empirical relationships can be expressed as$$f\sbsp{cp}{\prime} = 2.0\ \lambda\sb{G}\ {f\sbsp{cc}{\prime}\ f\sbsp{cf}{\prime}\over f\sbsp{cc}{\prime} + f\sbsp{cf}{\prime}}$$The concrete strengths in the above equation are replaced by their square roots in the expression deduced from the mechanics of materials approach.
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