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CONTENTS
Volume 9, Number 6, June 2012
 

Abstract
This paper deals with the structural behaviour of tapered concrete-filled steel composite (TCFSC) columns under eccentric loading. Finite element software LUSAS is used to perform the nonlinear analyses to predict the structural behaviour of the columns. Results from the finite element modelling and existing experimental test are compared to verify the accuracy of the modelling. It is demonstrated that they correlate reasonably well with each other; therefore, the proposed finite element modelling is absolutely accurate to predict the structural behaviour of the columns. Nonlinear analyses are carried out to investigate the behaviour of the columns where the main parameters are: (1) tapered angle (from 0o to 2.75o); (2) steel wall thickness (from 3 mm to 4 mm); (3) load eccentricity (15 mm and 30 mm); (4) L/H ratio (from 10.67 to 17.33); (5) concrete compressive strength (from 30 MPa to 60 MPa); (6) steel yield stress (from 250 MPa to 495 MPa). Results are depicted in the form of load versus mid-height deflection plots. Effects of various tapered angles, steel wall thicknesses, and L/H ratios on the ultimate load capacity, ductility and stiffness of the columns are studied. Effects of different load eccentricities, concrete compressive strengths and steel yield stresses on the ultimate load capacity of the columns are also examined. It is concluded from the study that the parameters considerably influence the structural behaviour of the columns.

Key Words
tapered concrete-filled steel composite column; eccentric loading; finite element; nonlinear analysis; ultimate load capacity; ductility; stiffness; concrete compressive strength; steel yield stress.

Address
Alireza Bahrami, Wan Hamidon Wan Badaruzzaman and Siti Aminah Osman: Department of Civil and Structural Engineering, Universiti Kebangsaan Malaysia, Bangi, Selangor, Malaysia

Abstract
This article presents the effect of replacement fly ash (FA) with diatomite (DE) on the properties of geopolymer mortars. DE was used to partially replace FA at the levels of 0, 60, 80 and 100% by weight of binder. Sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) solutions were used as the liquid portion in the mixture in order to activate the geopolymerization. The NaOH concentrations of 15M, Na2SiO3/NaOH ratios of 1.5 by weight, and the alkaline liquid/binder (LB) ratios by weight of 0.40, 0.50, 0.60 and 0.70 were used. The curing at temperature of 75oC for 24 h was used to accelerate the geopolymerization. The flows of all fresh geopolymer mortars were tested. The compressive strengths and the stress-strain characteristics of the mortar at the age of 7 days, and the unit weights were also tested. The results revealed that the use of DE to replace part of FA as source material in making geopolymer mortars resulted in the increased in the workability, and strain capacity of mortar specimens and in the reductions in the unit weights and compressive strengths. The strain capacity of the mortar increased from 0.0028 to 0.0150 with the increase in the DE replacement levels from 0 to 100%. The mixes with 15M NaOH, Na2SiO3/NaOH of 1.5, LB ratio of 0.50, and using 75oC curing temperature showed 7 days compressive strengths 22.0-81.0 MPa which are in the range of normal to high strength mortars.

Key Words
geopolymer; diatomite; workability; compressive strength; strain capacity.

Address
Theerawat Sinsiri and Tanakorn Phoo-ngernkham: School of Civil Engineering, Institute of Engineering, Suranaree University of Technology, Nakhonratchasima 30000, Thailand;
Vanchai Sata and Prinya Chindaprasirt: Sustainable Infrastructure Research and Development Center, Dept. of Civil Engineering, Faculty of Engineering, Khon Kaen University, Khon Kaen 40002, Thailand

Abstract
The interaction of plan geometry and structural configuration, a determinative factor in the earthquake behavior of buildings, has become a serious issue in the building industry in Turkey due to the poor seismic performance of R/C buildings during the latest earthquake. Consequently, designing new buildings without structural irregularities against earthquake loads is proving to be more significant. This study focuses on the effects of plan geometries on earthquake performances of buildings. In that respect, structural irregularities in the plan are investigated in detail based on the Turkish Earthquake Code (TEC 2007). The study is based on five main parametric models and a total of 40 sub-models that are grouped according to their plan geometries with excessive projections such as L-shaped, H-shaped, T-shaped and U-shaped models. In addition to these, a square model without any projections is also generated. All models are designed to have the same storey gross area but with different number of storeys. Changes in the earthquake behavior of buildings were evaluated according to the number of storeys, the projection ratios and the symmetry conditions of each model. The analysis of each structural irregularity resulted in many findings, which were then assessed. The study demonstrates that the square model delivers the best earthquake performance owing to its regular plan geometry.

Key Words
earthquake; architectural form; projections; structural irregularities.

Address
Tugba Inan and Koray Korkmaz: Izmir Institute of Technology, Department of Architecture, Izmir, Turkey;
Ismail H. Cagatay: Cukurova University, Civil Engineering Department, Adana, Turkey

Abstract
This study evaluates the permeability of cement-based composites, which are a mix of polyolefin fibers and silica fume. Test results indicate that permeability increases as the water/cementitious ratio increases. Silica fume in cement-based composites produced hydrated calcium silicate and filled the pores. However, permeability decreased as the addition of silica fume increased. Specimens containing polyolefin fibers also provided higher permeability resistance. The polyolefin fiber length did not have a significant effect on permeability. The decrease in the permeability is mainly due to the addition of silica fume and lower water/cementitious ratio. Addition of fibers marginally decreases the permeability. Incorporating polyolefin fiber and silica fume in composites achieved more significant decreases in permeability. The correlated test results reveal the interrelationship between them.

Key Words
polyolefin fiber; silica fume; diffusion coefficient; ponding depth; corrosion rate.

Address
Hui-Mi Hsu and An Cheng: Dept. of Civil Engineering, National Ilan University, Ilan 26047, Taiwan
Wei-Ting Lin: Dept. of Civil Engineering, National Ilan University, Ilan 26047, Taiwan; Institute of Nuclear Energy Research, Atomic Energy Council, Executive Yuan, 1000 Wenhua Road, Longtan 32546, Taiwan

Abstract
This paper presents Neuro-Fuzzy (NF) based empirical modelling of torsional strength of RC beams for the first time in literature. The proposed model is based on fuzzy rules. The experimental database used for NF modelling is collected from the literature consisting of 76 RC beam tests. The input variables in the developed rule based on NF model are cross-sectional area of beams, dimensions of closed stirrups, spacing of stirrups, cross-sectional area of one-leg of closed stirrup, yield strength of stirrup and longitudinal reinforcement, steel ratio of stirrups, steel ratio of longitudinal reinforcement and concrete compressive strength. According to the selected variables, the formulated NFs were trained by using 60 of the 76 sample beams. Then, the method was tested with the other 16 sample beams. The accuracy rates were found to be about 96% for total set. The performance of accuracy of proposed NF model is furthermore compared with existing design codes by using the same database and found to be by far more accurate. The use of NF provided an alternative way for estimating the torsional strength of RC beams. The outcomes of this study are quite satisfactory which may serve NF approach to be widely used in further applications in the field of reinforced concrete structures.

Key Words
reinforced concrete beam; neuro-fuzzy; torsional strength; building code.

Address
A. Cevik: Department of Civil Engineering, University Of Gaziantep, Gaziantep, Turkey
M.H. Arslan: Department of Civil Engineering, Selcuk University, Konya, Turkey
R. Saracoglu: Department of Electronic and Computer Education, Selcuk University, Konya, Turkey


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