Date of Award

5-2016

Document Type

Thesis

Degree Name

Master of Science in Civil Engineering (MSCE)

Department

Civil Engineering

First Advisor

Dr. Aman Mwafy

Second Advisor

Dr. Amr Sweedan

Third Advisor

Prof. Sabah Alkass

Abstract

Concrete-filled steel tubes (CFST) have been introduced in high-rise buildings in order to expedite construction and increase the confinement of concrete by the steel tube, and hence increase the capacity of the column cross-section. More recently, expansive additives (EAs) that counteract the shrinkage of concrete have been used in CFST to improve the bond between the concrete and steel tube. Although changing the confinement level exerted by the steel tube on concrete will have an impact on the behavior of CFSTs, little information is available regarding the influence of EAs on the mechanical characteristics of expansive concrete-filled steel tubular (ECFST) columns. The objective of this study is thus twofold: (i) to experimentally assess the behavior of concentrically loaded ECFSTs with different parameters, and (ii) to investigate the correlation between the test results and those obtained from different analytical modeling techniques and previous prediction approaches. The experimental program of this study consists of testing 16 CFST/ECFST columns. Fourteen concrete mixes are prepared with four different concrete strength values (16, 40, 50 and 90 MPa), four EA dosages (0%, 6%, 12% and 24%), and two concrete mixing approaches. Steel tubes in two different diameters (89.6 and 153.6 mm), thicknesses (2 and 3 mm), and lengths (370 and 1500 mm) are fabricated. In order to arrive at an effective prestressing action during the hardening process of concrete, two end plates are tied to each ECFST specimen immediately after casting. Each of the tested specimens is effectively instrumented using four LVDTs and several strain gauges. The behavior of the tested column specimens and those collected from previous studies is also assessed using two numerical modeling techniques, namely the fiber-based modeling (FBM) and finite element method (FEM), as well as using several prediction approaches. The results indicate that increasing the concrete strength significantly improves the axial load capacity of CFST columns by up to 76%. Using EA with a concrete strength of 40 MPa results in the most pronounced improvements in the axial load capacity of columns, whilst the most promising EA dosage for the ECFST short columns is 6%.Good agreement is observed between the experimental results and those obtained fromboth FBM and FEM in terms of ultimate load capacity, and hence the adopted modeling techniques can be used in further parametric studies on CFSTs/ECFSTs. It is also recommended to employ specific confined concrete models with the predictive approaches of Euro code 4 and AISC to arrive at the best correlation with CFST test results. This study provides insights into the behavior of pre-stressing CFST columns and presents test results with diverse parameters that contribute to filling gaps in the existing research, verify computational models and provide support for the development of prediction approaches for ECFSTs.

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