Journal Jan 2024

Numerical study of CFST, CFFT and CFDTS short columns using ABAQUS N. A. G. K. Manikanta Kopuri, Ranjeet Sah, S. Anitha Priyadharshani

Concrete filled steel tube (CFST) columns are commonly used in bridges and buildings because of their high strength, high energy absorption and better ductility in comparison to conventional columns. Corrosion of steel in the CFST columns is a serious issue in terms of maintenance and cost when used in marine environmental conditions. Concrete filled glass fiber reinforced polymer tube (CFFT) columns with high strength to weight ratio and high corrosion resistance can be used instead of steel tubes in marine environments. Also, the concrete filled double tube sections (CFDTS) columns with better axial compression performance, stiffness, ductility and durability can be used for marine conditions. Hence in the present study axial compression behavior of CFFT and CFDTS (outer GFRP tube and inner steel tube) columns of aspect ratio length (L)/diameter (D) = 2 are investigated and compared with CFST columns of same aspect ratio L/D = 2. Nonlinear finite element analysis of CFST, CFFT and CFDTS columns with dimensions 152.4 × 304.8 mm are carried out using ABAQUS. Thickness of outer tubes considered are 3, 4.5 and 6 mm for all three types, whereas thickness of inner tubes considered for CFDTS columns are 1.5, 2 and 2.5 mm. The axial load carrying capacity of columns increases with increase in thickness of outer GFRP tubes as well as inner steel tubes by 13 %. CFDTS columns have more load carrying capacity and ductility than CFST and CFFT columns with same aspect ratios, CFDTS columns are lighter than CFST columns and almost same weight as that of CFFT columns with same aspect ratios. Hence CFDTS columns are the best among the studied options for marine structural applications.

Compressive strength and drying shrinkage of concrete containing fine recycled concrete aggregates Aiman Abdullah Mohammed AL-Odaini, Jamaludin Bin Non, Munaf Mohamed Salem Hasson

The experimental research examines the production of laboratory concrete by replacing natural fine aggregates with recycled fine aggregates. The main aim of this work is to determine the compressive strength and drying shrinkage of ordinary Portland cement (OPC) concrete using fine recycled concrete aggregates (FRCA) and natural coarse aggregates (NA) with various water cement ratios (0.70, 0.63 and 0.57). For this purpose, three (3) series of concrete specimens are cast and analysed. For each series, five (5) replacement levels (0, 25, 50, 75 and 100 %) are adopted. All concrete specimens have been cured until the day of testing, except for the drying shrinkage specimens which have been cured for 7 days. All mixtures are designed with natural and recycled fine aggregates. However, natural coarse aggregates have been used in all cases. FRCA is obtained from crushed concrete using a jaw crusher. The effects of FRCA content on the compressive strength and drying shrinkage of concrete are determined and compared with the control concrete. It can be stated that the evolution of compressive strength is similar to that of the control concrete. However, the results of drying shrinkage after a period of 28 days revealed that the replacement percentage is a significant factor in recycled aggregates present within the mixture. The drying shrinkage in the recycled concrete with substitution levels lower than 50 % is similar to the control concrete. However, when 100 % fine natural aggregates are replaced with fine recycled concrete aggregates, there is a 30-50 % increase in drying shrinkage as compared to what is experienced by the control concrete.

Justification of strong column weak beam theory by evaluation of ductility of column and beam sections using first principles Jayanta Nath Chowdhury, Santanu Bhanja

Ductility plays an important role in aseismic design of structures. Reinforced concrete sections can be made ductile in flexural mode of failure as other failure modes are brittle in nature. Ductility of beams are higher than those of columns which are subjected to axial forces along with flexure. The aim of the present work is to demonstrate the influence of axial forces on curvature ductility, and plastic rotation of reinforced concrete (RC) sections. In the present study curvature ductility values of a column section with reinforcement distributed on two sides have been evaluated and compared with the curvature ductility values of a similar section acting in flexure only, i.e., beam. Other parameters like reinforcement content and their distribution in the sections, effective covers, grades of steel and concrete have been considered similar for both the sections. Using the fundamental principles of limit state method curvature ductility and plastic rotations of beam and column sections have been evaluated. Results indicate that the curvature ductility and plastic rotations of columns are lower than the corresponding values for beams. Thus to ensure ductile failure, beams should fail first and not columns. This justifies the strong column-weak beam theory. Columns with higher levels of axial forces exhibit significantly less curvature ductility and plastic rotations than columns with lower levels of axial forces.

Material development and construction of lightweight geopolymer concrete canoe Tejas Joshi, Urmil Dave, Shivang Kadiya, Divyesh Ghelani, Arihant Jain

This study focuses on the development of a sustainable lightweight geopolymer concrete (LGPC) canoe, with the goal of reducing the environmental impact of concrete construction. Eco-friendly materials, including fly ash, ground granulated blast furnace slag (GGBFS), and alcofine, were utilized in the mixture design of LGPC. To achieve a lightweight GPC mix, lightweight expanded clay aggregate (LECA), glass microspheres, and treated styrofoam residue were incorporated. A combination of sodium hydroxide and sodium silicate served as the alkaline liquids for binding. The hull design and stability analysis of the canoe were conducted using Maxsurf software. In laboratory testing, the LGPC exhibited a density of 1050 kg/ m3 and a compressive strength of 15.4 MPa. Subsequently, the construction of the canoe was carried out using the developed LGPC, with a comprehensive description of the step-by-step construction process provided. The final test involved placing the canoe in a water body, where it successfully floated. This innovative approach to creating a lightweight, eco-friendly LGPC canoe demonstrates the potential for sustainable concrete construction practices and their applicability in real-world settings.

Development and performance assessment of quaternary blended concrete reinforced with multi walled carbon nano tubes Praseeda Dandu, K. Srinivasa Rao

In the present study, quaternary blended concrete developed by replacing cement partially with the industrial waste such as vetrified tiles powder, silica fume and fly ash was reinforced with multi walled carbon nano tubes (MWCNT) at dosage rate of 0.01, 0.02, 0.03, 0.05 and 0.1 % by weight of cementitious material. The quaternary blended concrete with and without reinforcement were subjected to the compressive, flexural and split tensile strength tests. The obtained results for both types of mixes were compared and inferences were drawn. The observed compressive strength values for the mix reinforced with MWCNT was found to increase by 12, 16, 21 and 32 % up to the MWCNT dosage of 0.05 % at 28 days of curing age in comparison to the unreinforced quaternary blended concrete. The compressive strength at 0.1 % dosage of MWCNT decreased at all curing ages. When compared with the mixes reinforced with MWCNT, it was observed that there is an increase of about 32 % in compressive strength at 28 days. It was also inferred that the mixes with MWCNTs up to the dosage rate of 0.05 %, the strength increased from 6.10 to 7.25 MPa for 7 days curing age and from 6.83 to 8.95 MPa for 28 days of curing period. There was an observed increase up to 31 % for the reinforced mix in relative to the quaternary blended concrete pertaining to the flexural strength and an increase of 40 % in case split tensile strength up to 0.05 % dosage 28 days of curing period. It is concluded that the blended concrete mix reinforced with a dosage rate of 0.05 % with MWCNTs serves to be optimum reinforced quaternary blended concrete which can be utilized for the construction activities owing to the improved flexural and tensile strengths developed.

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