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CONTENTS
Volume 30, Number 3, February10 2019
 

Abstract
In this research, the behavior of tube-in-tube BRBs (TiTBRBs) has been investigated. In a typical TiTBRB, the yielding core tube is located inside the outer restraining one to dissipate energy through extensive plastic deformation, while the outer restraining tube remains essentially elastic. With the aid of FE analyses, the monotonic and cyclic behavior of the proposed TiTBRBs have been studied as individual brace elements. Subsequently, a detailed finite element model of a representative single span-single story frame equipped with such a TiTBRB has been constructed and both monotonic and cyclic behavior of the proposed TiTBRBs have been explored under the application of the AISC loading protocol at the braced frame level. With the aid of backbone curves derived from the FE analyses, a simplified frame model has been developed and verified through comparison with the results of the detailed FE model. It has been shown that, the simplified model is capable of predicting closely the cyclic behavior of the TiTBRB frame and hence can be used for design purposes. Considering type of connection detail used in a frame, the TiTBRB member which behave satisfactorily at the brace element level under cyclic loading conditions, may suffer global buckling due to the flexural demand exerted from the frame to the brace member at its ends. The proposed TiTBRB suit tubular members of offshore structures and the application of such TiTBRB in a typical offshore platform has been introduced and studied in a single frame level using detailed FE model.

Key Words
tube-in-tube buckling restrained brace; buckling restrained braced frame; offshore platforms; cyclic loading; FE analysis

Address
(1) Shahrokh Maalek, Moharram Dolatshahi Pirooz, Seyed Taghi Omid Naeeini:
School of Civil Engineering, College of Engineering, University of Tehran, Iran;
(2) Hamid Heidary-Torkamani:
School of Civil Engineering, College of Engineering, University of Tehran, Tehran, Iran.

Abstract
One of the most important design criteria in underground structure is to design lightweight protective layers to resist significant blast loads. Sandwich blast resistant panels are commonly used to protect underground structures. The front face of the sandwich panel is designed to resist the blast load and the core is designed to mitigate the blast energy from reaching the back panel. The design is to allow the sandwich panel to be repaired efficiently. Hence, the underground structure can be used under repeated blast loads. In this study, a novel sandwich panel, named RC panel - Helical springs- RC panel (RHR) sandwich panel, which consists of normal strength reinforced concrete (RC) panels at the front and the back and steel compression helical springs in the middle, is proposed. In this study, a detailed 3D nonlinear numerical analysis is proposed using the nonlinear finite element software, AUTODYN. The accuracy of the blast load and RHR Sandwich panel modelling are validated using available experimental results. The results show that the proposed finite element model can be used efficiently and effectively to simulate the nonlinear dynamic behaviour of the newly proposed RHR sandwich panels under different ranges of free air blast loads. Detailed parameter study is then conducted using the validated finite element model. The results show that the newly proposed RHR sandwich panel can be used as a reliable and effective lightweight protective layer for underground structures.

Key Words
lightweight sandwich panel; RHR; helical springs; free air blast loads; RHT

Address
(1) Mohamed Rashad, T.Y. Yang:
Department of Civil Engineering, University of British Columbia, Vancouver, Canada;
(2) Mostafa M.A. Wahab:
Department of Civil Engineering, Military Technical Collage, Cairo, Egypt;
(3) T.Y. Yang:
International Joint Research Laboratory of Earthquake Engineering, Tongji University, Shanghai, China.

Abstract
In the present study, a numerical and experimental investigation has been carried out on the seismic behavior of RC columns of a bridge which damaged under corrosive environments and retrofitted by various techniques including combined application of CFRP sheets and steel profiles. A novel hybrid retrofitting procedure, including the application of inner steel profiles and outer peripheral CFRP sheets, has been proposed for strengthening purpose. Seven large-scale RC columns of a Girder Bridge have been tested in the laboratory under the influence of simultaneous application of constant axial load and the lateral cyclic displacements. Having verified the finite element modeling, using ABAQUS software, the effects of important parameters such as the corrosion percentage of steel rebars and the number of CFRP layers have been evaluated. Based on the results, retrofitting of RC columns of the bridge with the proposed technique was effective in improving some measures of structural performance such as lateral strength degradation and higher energy absorption capability. However, the displacement ductility was not considerably improved whereas the elastic stiffness of the specimens has been increased.

Key Words
seismic retrofitting; RC columns; corrosion; CFRP sheets; steel reinforcement; finite element analysis

Address
Department of Civil Engineering, Sahand University of Technology, Tabriz, Iran.


Abstract
This paper investigates the effects of the tensile catenary action on dynamic increase factor (DIF) in the nonlinear static analysis for progressive collapse of steel-frame buildings. Numerical analyses were performed to verify the accuracy of the empirical and analytical expressions proposed in the literature in cases where the catenary action is activated. For this purpose, nonlinear static and dynamic analyses of a series of steel moment frame buildings with a different number of spans and stories were carried out following the alternate path method. Different column removal scenarios were considered as separate load cases. The dynamic increase factor that approximately compensates for the dynamic effects in the nonlinear static analysis was selected so to match results from the nonlinear dynamic analysis. The study results showed that the many expressions in literature may not work in cases where the catenary stage is fully developed.

Key Words
progressive collapse; nonlinear pushdown analysis; dynamic increase factor

Address
Department of Engineering, University of Campania "Luigi Vanvitelli", via Roma 29, 81031, Aversa (CE), Italy.


Abstract
In this paper, numerical and experimental assessments have been conducted in order to investigate the capability of using CFRP for the seismic capacity improvement and relocation of plastic hinge in reinforced concrete connections. Two scaled down exterior reinforced concrete beam to column connections have been used. These two connections from a strengthened moment frame have been tested under uniformly distributed load before and after optimization. The results of experimental tests have been used to verify the accuracy of numerical modeling using computational ABAQUS software. Application of FRP plate on the web of the beam in connections to improve its capacity is of interest in this paper. Several parametric studies were carried out for CFRP reinforced samples, with different lengths and thicknesses in order to relocate the plastic hinge away from the face of the column.

Key Words
CFRP plate; plastic hinge relocation; finite element; rehabilitation; strengthening

Address
(1) Zhenyan Luo:
School of Resources and Safety Engineering, Central South University, Changsha, 410083, China;
(2) Hamid Sinaei, Zainah Ibrahim, Mahdi Shariati, Zamin Jumaat:
Department of Civil Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia;
(3) Mahdi Shariati:
Faculty of Civil Engineering, University of Tabriz, Tabriz, Iran;
(4) Karzan Wakil:
Research Center, Sulaimani Polytechnic University, Sulaimani 46001, Kurdistan Region, Iraq;
(5) Binh Thai Pham:
Institute of Research and Development, Duy Tan University, Da Nang 550000, Vietnam;
(6) Edy Tonnizam Mohamad:
of Tropical Geoengineering (GEOTROPIK), Faculty of Civil Engineering, Universiti Teknologi Malaysia, Johor Bahru, Malaysia;
(7) Majid Khorami:
Universidad UTE, Facultad de Arquitectura y Urbanismo, Calle Rumipamba s/n y Bourgeois, Quito, Ecuador.

Abstract
In this paper, analysis of critical fluid velocity and heat transfer in the nanocomposite pipes conveying nanofluid is presented. The pipe is reinforced by carbon nanotubes (CNTs) and the fluid is mixed by AL2O3 nanoparticles. The material properties of the nanocomposite pipe and nanofluid are considered temperature-dependent and the structure is subjected to magnetic field. The forces of fluid viscosity and turbulent pressure are obtained using momentum equations of fluid. Based on energy balance, the convection of inner and outer fluids, conduction of pipe and heat generation are considered. For mathematical modeling of the nanocomposite pipes, the first order shear deformation theory (FSDT) and energy method are used. Utilizing the Lagrange method, the coupled pipe-nanofluid motion equations are derived. Applying a semi-analytical method, the motion equations are solved for obtaining the critical fluid velocity and critical Reynolds and Nusselt numbers. The effects of CNTs volume percent, AL2O3 nanoparticles volume percent, length to radius ratio of the pipe and shell surface roughness were shown on the critical fluid velocity, critical Reynolds and Nusselt numbers. The results are validated with other published work which shows the accuracy of obtained results of this work. Numerical results indicate that for heat generation of Q = 10 MW/m3, adding 6% AL2O3 nanoparticles to the fluid increases 20% the critical fluid velocity and 15% the Nusselt number which can be useful for heat exchangers.

Key Words
critical fluid velocity; nanocomposite pipes; nanofluid; heat generation; temperature-dependent

Address
Department of Mechanical Engineering, Kashan Branch, Islamic Azad University, Kashan, Iran.


Abstract
The optimum cost of a reinforced concrete plane and space frames have been found by using the Genetic Algorithm (GA) method. The design procedure is subjected to many constraints controlling the designed sections (beams and columns) based on the standard specifications of the American Concrete Institute ACI Code 2011. The design variables have contained the dimensions of designed sections, reinforced steel and topology through the section. It is obtained from a predetermined database containing all the single reinforced design sections for beam and columns subjected to axial load, uniaxial or biaxial moments. The designed optimum beam sections by using GAs have been unified through MATLAB to satisfy axial, flexural, shear and torsion requirements based on the designed code. The frames\' functional cost has contained the cost of concrete and reinforcement of steel in addition to the cost of the frames\' formwork. The results have found that limiting the dimensions of the frame\'s beams with the frame\'s columns have increased the optimum cost of the structure by 2%, declining the re-analysis of the optimum designed structures through GA.

Key Words
optimum design; genetic algorithm; space frame; reinforced concrete

Address
(1) Chulin Chen:
School of Architechure and Art, Central South University, Changsha 410075, China;
(2) Salim Taib Yousif:
Department of civil engineering, Isra University, Amman, Jordan;
(3) Rabi\' Muyad Najem:
Department of civil engineering, Mosul University, Mosul, Iraq;
(4) Ali Abavisani:
DLSIIS, Universidad Politecnica de Madrid, Madrid, Spain;
(5) Ali Abavisani:
Centre for Biomedical Technology, Universidad Politecnica de Madrid, Madrid, Spain;
(6) Binh Thai Pham:
Institute of Research and Development, Duy Tan University, Da Nang 550000, Vietnam;
(7) Karzan Wakil:
Research Center, Sulaimani Polytechnic University, Sulaimani 46001, Kurdistan Region, Iraq;
(8) Edy Tonnizam Mohamad:
Centre of Tropical Geoengineering (GEOTROPIK), Faculty of Civil Engineering, Universiti Teknologi Malaysia, Johor Bahru, Malaysia;
(9) Majid Khorami:
Universidad UTE, Facultad de Arquitectura y Urbanismo, Calle Rumipamba s/n y Bourgeois, Quito, Ecuador.

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