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CONTENTS
Volume 35, Number 4, May25 2020
 

Abstract
In this paper, the influence of adding multi-walled carbon nanotube (MWCNT) on the pull behavior of steel and GFRP bars in ultra-high-performance concrete (UHPC) was examined experimentally and numerically. For numerical analysis, 3D nonlinear finite element modeling (FEM) with the help of ABAQUS software was used. Mechanical properties of the specimens, including Young\'s modulus, tensile strength and compressive strength, were extracted from the experimental results of the tests performed on standard cube specimens and for different values of weight percent of MWCNTs. In order to consider more realistic assumptions, the bond between concrete and bar was simulated using adhesive surfaces and Cohesive Zone Model (CZM), whose parameters were obtained by calibrating the results of the finite element model with the experimental results of pullout tests. The accuracy of the results of the finite element model was proved with conducting the pullout experimental test which showed high accuracy of the proposed model. Then, the effect of different parameters such as the material of bar, the diameter of the bar, as well as the weight percent of MWCNT on the bond behavior of bar and UHPC were studied. The results suggest that modifying UHPC with MWCNT improves bond strength between concrete and bar. In MWCNT per 0.01 and 0.3 wt% of MWCNT, the maximum pullout strength of steel bar with a diameter of 16mm increased by 52.5% and 58.7% compared to the control specimen (UHPC without nanoparticle). Also, this increase in GFRP bars with a diameter of 16mm was 34.3% and 45%.

Key Words
ultra-high-performance concrete; MWCNT; bonding behavior; pullout test; GFRP bars

Address
Bita Hosseinian Ahangarnazhad: Department of Civil Engineering, University of Tabriz, Tabriz, Iran
Masoud Pourbaba: Department of Civil Engineering, Maragheh Branch, Islamic Azad University, Maragheh, Iran
Amir Afkar: Research Center of Technology and Engineering, Standard Research Institute, Karaj, Iran

Abstract
Presented are experimental results from 24 full-scale push test specimens to study the behaviour of composite beams with trapezoidal profiled sheeting laid transverse to the beam axis. The tests use a single-sided horizontal push test setup and are divided into two series. First series contained shear loading only and the second had normal load besides shear load. Four parameters are studied: the effect of wire mesh position and number of its layers, placing a reinforcing bar at the bottom flange of the deck, normal load and its position, and shear stud layout. The results indicate that positioning mesh on top of the deck flange or 30 mm from top of the concrete slab does not affect the stud\' s s strength and ductility. Thus, existing industry practice of locating the mesh at a nominal cover from top of the concrete slab and Eurocode 4 requirement of placing mesh 30 mm below the stud\' s head are both acceptable. Double mesh layer resulted in 17% increase in stud strength for push tests with single stud per rib. Placing a T16 bar at the bottom of the deck rib did not affect shear stud behaviour. The normal load resulted in 40% and 23% increase in stud strength for single and double studs per rib. Use of studs only in the middle three ribs out of five increased the strength by 23% compared to the layout with studs in first four ribs. Eurocode 4 and Johnson and Yuan equations predicted well the stud strength for single stud/rib tests without normal load, with estimations within 10% of the characteristic experimental load. These equations highly under-estimated the stud capacity, by about 40-50%, for tests with normal load. AISC 360-16 generally over-estimated the stud capacity, except for single stud/rib push tests with normal load. Nellinger equations precisely predicted the stud resistance for push tests with normal load, with ratio of experimental over predicted load as 0.99 and coefficient of variation of about 8%. But, Nellinger method over-estimated the stud capacity by about 20% in push tests with single studs without normal load.

Key Words
push test; shear stud layout; wire mesh; composite secondary beams; metal decking

Address
Jawed Qureshi: School of Architecture, Computing and Engineering (ACE), University of East London,
4-6 University Way, Beckton, London, E16 2RD, UK
Dennis Lam: School of Engineering, University of Bradford, Bradford, BD7 1DP, UK


Abstract
Double skin composite walls are alternatives to concrete walls to resist gravity load in structures. The composite action between steel faceplates and concrete core largely depends on the internal mechanical connectors. This paper investigates the structural behavior of novel composite wall system with T section and under combined compressive force and bending moment. The truss connectors are used to bond the steel faceplates to concrete core. Four short specimens were designed and tested under eccentric compression. The influences of the thickness of steel faceplates, the truss spacing, and the thickness of web wall were discussed based on the test results. The N-M interaction curves by AISC 360, Eurocode 4, and CECS 159 were compared with the test data. It was found that AISC 360 provided the most reasonable predictions.

Key Words
composite wall; eccentric compressive loading; experimental behavior; T-shaped section; truss connector

Address
Ying Qin: Key Laboratory of Concrete and Prestressed Concrete Structures of Ministry of Education, Southeast University, Nanjing, China;
School of Civil Engineering, Southeast University, Nanjing, China
Xin Chen, Wang Xi, Xingyu Zhu and Yuanze Chen: School of Civil Engineering, Southeast University, Nanjing, China


Abstract
Steel-concrete composite slabs with profiled steel sheeting are widely used in the execution of floors in steel and composite buildings. The rapid construction process, the elimination of conventional replaceable shuttering and the reduction of temporary support are, in general, considered the main advantages of this structural system. In slabs with the spans currently used, the longitudinal shear resistance commonly provided by the embossments along the steel sheet tends to be the governing design mode. This paper presents an innovative reinforcing system that increases the longitudinal shear capacity of composite slabs. The system is constituted by a set of transversal reinforcing bars crossing longitudinal stiffeners executed along the upper flanges of the steel sheet profiles. This type of reinforcement takes advantage of the high bending resistance of the composite slabs and increases the slab\' s s ductility. Two experimental programmes were carried out: a small-scale test programme – to study the resistance provided by the reinforcing system in detail – and a full-scale test programme to test simply supported and continuous composite slabs – to assess the efficacy of the proposed reinforcing system on the global behaviour of the slabs. Based on the results of the small-scale tests, an equation to predict the resistance provided by the proposed reinforcing system was established. The present study concludes that the resistance and the ductility of composite slabs using the reinforcing system proposed here are significantly increased.

Key Words
composite slab; longitudinal shear; reinforcing system; transversal bars; experimental tests

Address
Rui Simões and Miguel Pereira: ISISE – Institute for Sustainability and Innovation in Structural Engineering; Department of Civil Engineering, University of Coimbra, Rua Luís Reis Santos – Polo II, 3030-788 Coimbra, Portugal

Abstract
This research presents the design and numerical assessment of composite steel-concrete frame structures with welded dissipative fuses. The assessment has been carried out based on linear response spectrum, nonlinear static pushover and time history procedures. The analytical expressions which define the envelope of the nonlinear response of the dissipative fuses are first presented and calibrated against experimental results available in literature. The assessment is then carried out according to a design methodology proposed herein. Outcomes of the numerical assessment indicate that the use of welded dissipative fuses successfully limited damage within the replaceable parts. Furthermore, although structures with dissipative fuses present lower strength and, generally, lower displacement capacity, their displacement ductility and global dissipative performance are generally higher than conventional structures, especially when the structure with dissipative fuses presents a dissipative configuration adjusted to the bending moment distribution diagram calculated for the applied seismic action.

Key Words
welded dissipative fuses; repairability; numerical model; seismic design; earthquake resistant frames

Address
Luís Calado, Jorge M. Proençaand João Sio: Department of Civil Engineering, Instituto Superior Técnico, U Lisboa, and CERIS, Av. Rovisco Pais, 1049-001 Lisboa, Portugal

Abstract
The present paper explores nonlinear dynamical properties of piezo-magnetic beams based on a nonlocal refined higher-order beam formulation and piezoelectric phase effect. The piezoelectric phase increment may lead to improved vibrational behaviors for the smart beams subjected to magnetic fields and external harmonic excitation. Nonlinear governing equations of a nonlocal intelligent beam have been achieved based upon the refined beam model and a numerical provided has been introduced to calculate nonlinear vibrational curves. The present study indicates that variation in the volume fraction of piezoelectric ingredient has a substantial impact on vibrational behaviors of intelligent nanobeam under electrical and magnetic fields. Also, it can be seen that nonlinear free/forced vibrational behaviors of intelligent nanobeam have dependency on the magnitudes of induced electrical voltages, magnetic potential, stiffening elastic substrate and shear deformation.

Key Words
refined beam; dynamic behavior; forced vibration; free vibration; piezoelectric reinforcement; nonlocal theory

Address
Raad M. Fenjan, Ridha A. Ahmed and Nadhim M. Faleh: Al-Mustansiriah University, Engineering Collage P.O. Box 46049, Bab-Muadum, Baghdad 10001, Iraq

Abstract
This paper aims to present an analytical methodology to investigate influences of nanoscale and surface energy on buckling stability behavior of perforated nanobeam structural element, for the first time. The surface energy effect is exploited to consider the free energy on the surface of nanobeam by using Gurtin-Murdoch surface elasticity theory. Thin and thick beams are considered by using both classical beam of Euler and first order shear deformation of Timoshenko theories, respectively. Equivalent geometrical constant of regularly squared perforated beam are presented in simplified form. Problem formulation of nanostructure beam including surface energies is derived in detail. Explicit analytical solution for nanoscale beams are developed for both beam theories to evaluate the surface stress effects and size-dependent nanoscale on the critical buckling loads. The closed form solution is confirmed and proven by comparing the obtained results with previous works. Parametric studies are achieved to demonstrate impacts of beam filling ratio, the number of hole rows, surface material characteristics, beam slenderness ratio, boundary conditions as well as loading conditions on the non-classical buckling of perforated nanobeams in incidence of surface effects. It is found that, the surface residual stress has more significant effect on the critical buckling loads with the corresponding effect of the surface elasticity. The proposed model can be used as benchmarks in designing, analysis and manufacturing of perforated nanobeams.

Key Words
surface energy effects; perforated nanobeams; thin and thick beams; non-classical; buckling; analytical solution

Address
Khalid H. Almitani: Department of Mechanical Engineering, Faculty of Engineering, King Abdulaziz University, P.O. Box 80204, Jeddah, Saudi Arabia
Alaa A. Abdelrahman: Department of Mechanical Design & Production, Faculty of Engineering, Zagazig University, P.O. Box 44519, Zagazig, Egypt
Mohamed A. Eltaher: Department of Mechanical Engineering, Faculty of Engineering, King Abdulaziz University, P.O. Box 80204, Jeddah, Saudi Arabia;
Department of Mechanical Design & Production, Faculty of Engineering, Zagazig University, P.O. Box 44519, Zagazig, Egypt


Abstract
Based on third-order shear deformation shell theory, the present paper investigates post-buckling properties of eccentrically stiffened metal foam curved shells/panels having initial geometric imperfectness. Metal foam is considered as porous material with uniform and non-uniform models. The single-curve porous shell is subjected to in-plane compressive loads leading to post-critical stability in nonlinear regime. Via an analytical trend and employing Airy stress function, the nonlinear governing equations have been solved for calculating the post-buckling loads of stiffened geometrically imperfect metal foam curved shell. New findings display the emphasis of porosity distributions, geometrical imperfectness, foundation factors, stiffeners and geometrical parameters on post-buckling properties of porous curved shells/panels.

Key Words
post-buckling; shell theory; porous material; curved shell; third-order theory

Address
Seyed Sajad Mirjavadi, Masoud Forsat and A.M.S. Hamouda: Department of Mechanical and Industrial Engineering, Qatar University, P.O. Box 2713, Doha, Qatar
Mohammad Reza Barati: Fidar project Qaem Company, Darvazeh Dolat, Tehran, Iran

Abstract
Consideration of the panel zone (PZ) deformations in the analysis of steel moment frames (SMFs) has a substantial effect on structural response. One way to include the PZ effect on the structural response is Krawinkler\'s PZ model, which is one of the best and conventional models. However, modeling of Krawinkler\'s PZ model has its complexity, and finding an alternative procedure for PZ modeling is of interest. In this study, an efficient model is proposed to simplify Krawinkler\'s PZ model into an Adjusted Rigid-End Zone (AREZ). In this way, the rigid-end-zone dimensions of the beam and column elements are defined through an appropriate rigid-end-zone factor. The dimensions of this region depend on the PZ stiffness, beam(s) and columns\' specifications, and connection joint configuration. Thus, to obtain a relationship for the AREZ model, which yields the dimensions of the rigid-end zone, the story drift of an SMF with Krawinkler\'s PZ model is equalized with the story drift of the same structure with the AREZ model. Then, the degree of accuracy of the resulting relationship is examined in several connections of generic SMFs. Also, in order to demonstrate the applicability of the proposed model in SMFs, several SMFs ranging from 3- to 30-story representing low- to high-rise buildings are examined through linear static and dynamic time history analysis. Furthermore, non-linear dynamic analyses of three SMFs conducted to validate the degree of accuracy of the proposed model in the non-linear analysis of SMFs. Analytical results show that there is considerable conformity between inter-story drift ratio (IDR) results of the SMFs with Krawinkler\'s PZ model and those of the centerline SMFs with AREZ.

Key Words
rigid-end zone; panel zone deformation; steel moment frames

Address
Hamed Saffari and Esmaeil Morshedi: Department of Civil Engineering, Faculty of Engineering, Shahid Bahonar University of Kerman, 22 Bahman Blvd,
P.O. Box 76175-133, Kerman, Iran


Abstract
The tension-only braced frames (TOBFs) are widely used as a lateral force resisting system (LFRS) in low-rise steel buildings due to their simplicity and economic advantage. However, the system has poor seismic energy dissipation capacity and pinched hysteresis behavior caused by early buckling of slender bracing members. The main concern in utilizing the TOBF system is the determination of appropriate performance factors for seismic design. A formalized approach to quantify the seismic performance factor (SPF) based on determining an acceptable margin of safety against collapse is introduced by FEMA P695. The methodology is applied in this paper to assess the SPFs of the TOBF systems. For this purpose, a trial value of the R factor was first employed to design and model a set of TOBF archetype structures. Afterwards, the level of safety against collapse provided by the assumed R factor was investigated by using the non-linear analysis procedure of FEMA P695 comprising incremental dynamic analysis (IDA) under a set of prescribed ground motions. It was found that the R factor of 3.0 is appropriate for safe design of TOBFs. Also, the system overstrength factor was estimated as 2.0 by performing non-linear static analyses.

Key Words
tension-only bracing; response modification factor; incremental dynamic analysis; seismic design; overstrength factor

Address
Mahdi Shariati: Institute of Research and Development, Duy Tan University, Da Nang 550000, Vietnam
Majid Lagzian and Shervin Maleki: Department of Civil Engineering, Sharif University of Technology, Tehran, Iran
Ali Shariati and Nguyen Thoi Trung: Division of Computational Mathematics and Engineering, Institute for Computational Science, Ton Duc Thang University,
Ho Chi Minh City 758307, Vietnam;
Faculty of Civil Engineering, Ton Duc Thang University, Ho Chi Minh City 758307, Vietnam



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