Abstract
There are many examples of steel structures subjected to severe environmental conditions with bolted connections
directly exposed to extreme climatic agents such as freeze-thaw cycles or low temperatures. Some examples are: steel bridges,
mining transfer towers, wind towers... These service conditions neither are included in Eurocode 3 or EN1090-2, nor there are
references in other international standards. In this experimental research, 46 specimens of non-slip joints with HV M20 bolts and
four different types of contact surfaces have been studied. Half of the specimens were subjected to fourteen twelve-hours freezethaw cycles, with periodic immersion in water and temperature oscillation. Subsequently, half of the connections were subjected
to a slip test under monotonic load at temperature of -20 ± 0.5 °C and the other half at room temperature. The results were
compared with others equal joints not subjected to freeze-thaw cycles and kept at room temperature for the same time. This
finally resulted in 4 sets of joints by combining the freeze-thaw degradation or not with the low-temperature conditions or not in
the slip testing. Therefore, a total of 16 different conditions were studied by also considering 4 different contact surfaces between
the joined plates in each set. The results obtained show influence of environmental conditions on the slip resistant capacity of
these joints.
Address
A. Fuente-Garcia, M.A. Serrano-López, C. Lopez-Colina and F. Lopez-Gayarre: EPS Engineering, Dep. Construction, University of Oviedo, Campus de Viesques, 33203 Gijon, Spain
Abstract
This paper investigates dynamic characteristics of a graphene nanoplatelets reinforced composite (GNPRC)
sandwich doubly curved shell based on the first-order shear deformation theory (FSDT) and Hamilton's principle. The sandwich
doubly curved shell is fabricated from a core made of honeycomb materials sandwiched by composite GNPs reinforced facesheets. Effective materials properties of composite face-sheets are assumed to vary based on Halpin-Tsai micromechanical
models and rule of mixture. Furthermore, the material properties of honeycomb core are estimated using Gibson's formula. The
fundamental frequencies of the shell are computed with changes of main geometrical and material properties such as amount
and distribution type of graphene nanoplatelets, side length ratio, thickness to length ratio of and side length ratio of honeycomb.
The Navier's technique is presented to obtain responses. Accuracy and trueness of the present model and analytical solution is
confirmed through comparison of the results with available results in literature. It is concluded that an increase in thickness to
length ratio yields a softer core with lower natural frequencies. Furthermore, increase in height to length ratio leads to significant
decrease in natural frequencies.
Abstract
This paper has focused on presenting vibration analysis of trapezoidal sandwich plates with 3D-graphene foam
reinforced polymer matrix composites (GrF-PMC) core and FG wavy CNT-reinforced face sheets. The porous graphene foam
possessing 3D scaffold structures has been introduced into polymers for enhancing the overall stiffness of the composite
structure. Also, 3D graphene foams can distribute uniformly or non-uniformly in the plate thickness direction. The effective
Young's modulus, mass density and Poisson's ratio are predicted by the rule of mixture. In this study, the classical theory
concerning the mechanical efficiency of a matrix embedding finite length fibers has been modified by introducing the tube-totube random contact, which explicitly accounts for the progressive reduction of the tubes' effective aspect ratio as the filler
content increases. The First-order shear deformation theory of plate is utilized to establish governing partial differential
equations and boundary conditions for trapezoidal plate. The governing equations together with related boundary conditions are
discretized using a mapping-generalized differential quadrature (GDQ) method in spatial domain. Then natural frequencies of
the trapezoidal sandwich plates are obtained using GDQ method. Validity of the current study is evaluated by comparing its
numerical results with those available in the literature. It is explicated that 3D-GrF skeleton type and weight fraction, carbon
nanotubes (CNTs) waviness and CNT aspect ratio can significantly affect the vibrational behavior of the sandwich structure. The
plate's normalized natural frequency decreased and the straight carbon nanotube (w=0) reached the highest frequency by
increasing the values of the waviness index (w).
Key Words
3D graphene foam; Generalized Differential Quadrature (GDQ) method; laminated trapezoidal plates;
vibrational analysis; wavy CNT-reinforcement
Address
Yingqun Zhang, Qian Zhao, Qi Han:School of Architecture and Engineering, Weifang Engineering Vocational College, Weifang, ShanDong 262500, China
N. Bohlooli:School of Civil Engineering, Urmia University, Urmia, Iran
Abstract
In this paper, geometrically nonlinear free vibration analysis of Mindlin viscoelastic plates with various geometrical
and material properties is studied based on the Von-Karman assumptions. A novel solution is proposed in which the nonlinear
frequencies of time-dependent plates are predicted according to the nonlinear frequencies of plates not dependent on time. This
method greatly reduces the cost of calculations. The viscoelastic properties obey the Boltzmann integral law with constant bulk
modulus. The SHPC meshfree method is employed for spatial discretization. The Laplace transformation is used to convert
equations from the time domain to the Laplace domain and vice versa. Solving the nonlinear complex eigenvalue problem in the
Laplace-Carson domain numerically, the nonlinear frequencies, the nonlinear viscous damping frequencies, and the nonlinear
damping ratios are verified and calculated for rectangular, skew, trapezoidal and circular plates with different boundary
conditions and different material properties.
Key Words
Mindlin viscoelastic plate; nonlinear complex eigenvalue problem; nonlinear damping ratio; nonlinear
frequency; nonlinear viscous damping frequency
Address
Nasrin Jafari and Mojtaba Azhari:Department of Civil Engineering, Isfahan University of Technology, Isfahan 84156-83111, Iran
Abstract
The mechanical properties of polymeric composites are degraded under elevated temperatures due to the effect of temperature on the mechanical behavior of the resin and resin fiber interfaces. In this study, the effect of temperature on the impact response of the carbon fiber reinforced plastics (CFRP) was investigated at low-velocity impact (LVI) using a drop weight impact tester machine. All the composite plates were fabricated using a vacuum infusion process with a stacking sequence of [45/0_2/-45/90_2]s, and a thickness of 2.9 mm. A group of the specimens was exposed to an environment with a temperature cycling at the range of -30 °C to 65 °C. In addition, three other groups of the specimens were aged at ambient (28 °C), -30 °C, and 65 °C for ten days. Then all the conditioned specimens were subjected to LVI at three energy levels of 10, 15, and 20 J. To assess the behavior of the damaged composite plates, the force-time, force-displacement, and energy-time diagrams were analyzed at all temperatures. Finally, radiography, optical microscopy, and scanning electron microscopy (SEM) were used to evaluate the effect of the temperature and damages at various impact levels. Based on the results, different energy levels have a similar effect on the LVI behavior of the samples at various temperatures. Delamination, matrix cracking, and fiber failure were the main damage modes. Compared to the samples tested at room temperature, the reduction of temperature to -30 °C enhanced the maximum impact force and flexural stiffness while decreasing the absorbed energy and the failure surface area. The temperature increasing to 65 °C increased the maximum impact force and flexural stiffness while decreasing the absorbed energy and the failure surface area. Applying 200 thermal cycles at the range of -30 °C to 65 °C led to the formation of fine cracks in the matrix while decreasing the absorbed energy. The maximum contact force is recorded under cyclic temperature as 5.95, 6.51 and 7.14 kN, under impact energy of 10, 15 and 20 J, respectively. As well as, the minimum contact force belongs to the room temperature condition and is reported as 3.93, 4.94 and 5.71 kN, under impact energy of 10, 15 and 20 J, respectively.
Key Words
CFRP; delamination; Low-velocity impact (LVI); radiography; thermal cycling
Address
Fathollah Taheri-Behrooz and Mahdi Torabi: School of Mechanical Engineering, Iran University of Science and Technology, Tehran, 16846-13114, Iran
Abstract
This paper proposes a comprehensive investigation on lateral stiffness of corner-supported steel modular frame
using splice connection. A full-scale modular frame with two stacked steel modules under lateral load is tested. Ductile pattern in
the transfer of lateral load is found in the final failure mode. Two types of lateral stiffness, including tangent stiffness and secant
stiffness, are defined from the load-displacement due to the observed nonlinearity. The difference between these two types of
stiffness is found around 20%. The comparisons between the experimental lateral stiffness and the predictions of classical
methods are also conducted. The D-value method using hypothesis of independent case is a conservative option for predicting
lateral stiffness, which is more recommended than method of contraflexural bending moment. Analyses on two classical shortrod models, including fix-rod model and pin-rod model, are further conducted. Results indicate that fix-rod model is more
recommended than pin-rod model to simplify splice connection for simulation on lateral stiffness of modular frame in elastic
design stage.
Key Words
d-value method; lateral stiffness; modular frame; parametric study; short-rod model
Address
Yi-Fan Lyu"Department of Civil and Environmental Engineering, National University of Singapore, Singapore 119077
Guo-Qiang Li:College of Civil Engineering, Tongji University, Shanghai, China, 200001
Ke Cao:1)School of management science and real estate, Chongqing University, Chongqing, China, 400044 2)6Research Center for Construction Economics and Management, Chongqing University, Chongqing, China, 400044
Si-Yuan Zhai:College of Civil Engineering, Chongqing University, Chongqing, China, 400044
De-Yang Kong:Department of Civil and Environmental Engineering, National University of Singapore, Singapore 119077
Xuan-Yi Xue:College of Civil Engineering, Chongqing University, Chongqing, China, 400044
Heng Li:Department of Building and Real Estate, The Hong Kong Polytechnic University, Hong Kong
Abstract
This research studies the primary resonance and nonlinear vibratory responses of multilayer functionally graded
shallow (MFGS) shells under external excitations. The shells considered with functionally graded porous (FGP) core and resting
on two types of nonlinear viscoelastic foundations (NVEF) governed by either a linear model with two parameters of Winkler
and Pasternak foundations or a nonlinear model of hardening/softening cubic stiffness augmented by a Kelvin–Voigt viscoelastic
model. The shells considered have three layers, sandwiched by functionally graded (FG), FGP, and FG materials. To investigate
the influence of various porosity distributions, two types of FGP middle layer cores are considered. With the first-order shear
deformation theory (FSDT), Hooke's law, and von-Karman equation, the stress-strain relations for the MFGS shells with FGP
core are developed. The governing equations of the shells are consequently derived. For the sake of higher accuracy and
reliability, the P-T method is implemented in numerically analyzing the vibration, and the method of multiple scales (MMS) as
one of the perturbation methods is used to investigate the primary resonance. The results of the present research are verified with
the results available in the literature. The analytical results are compared with the P-T method. The influences of material,
geometry, and nonlinear viscoelastic foundation parameters on the responses of the shells are illustrated.
Key Words
FG porous core; method of multiple scales; multilayer FG shallow shells; nonlinear viscoelastic foundation;
P-T method; primary resonance
Address
Kamran Foroutan and Liming Dai: 1)Sino-Canada Research Centre of Nonlinear Dynamics and Noise Control of Xiamen University of Technology and the University of Regina,
Xiamen University of Technology, China
2)Industrial Systems Engineering, University of Regina, Regina, SK, S4S 0A2, Canada
Abstract
Shape memory alloys (SMAs) have emerged as a novel functional material that is being increasingly applied in
diverse fields including medical, aeronautical and structural engineering to be used in the active, passive and semi-active
structural control devices. This paper is mainly aimed at evaluating the ductility and response modification factor of the steel
plate shear wall (SPSW) frames with and without the Ni-Ti shape memory alloys. To this end, different configurations were
utilized, in which the walls were used in the first, third, middle, and all stories. The models were numerically analyzed using
OpenSees Software. The obtained results indicate that improving the shape memory properties of alloys can greatly enhance the
ductility and response modification factor. Furthermore, the model whose first and third stories are equipped with the SMA shear
wall was found to be 290% more ductile, with a greater response modification factor compared to the unequipped frame.
