Project

Stability of Structures

Goal: All Dear Colleagues – Collaborators and Their Laboratories are invited to attach to this project Their old, new and future works or messages about Stability of Structures, especially: buckling, wrinkling, crimpling, crumpling ... and their energy absorption as well as about dynamic stability, slope stability .. of axially and non-axially loaded structures like columns, tubes, pipes, beams, plates, boxes, tanks, silos, pales, poles, pillars, conical shells, thin-walled structures as well as nanostructures, foams, gels.. et cetera .. made of metals, wood, plywood, bamboo, bones, composite, laminate, glass, ceramic, gypsum, concrete, rock, brick .. et cetera ..

If any RSGate Member wants to be added to the project as the Collaborator (at least a co/authorship of one work about the stability and following of 50 Members of the Project would be required), He needs to be a follower of a member of the project ... , sorry ... , but in another way, the system of the project doesn't recognize Him, and He can't be added ...

Naturally, all Dear Colleagues–Collaborators are asked to add every Colleague, which works on the stability (at least the co/authorship of one work about the stability and following of 50 Members of the Project would be required) ... - and don't hesitate to invite them ...

Dear Colleagues–Collaborators, I would like to thank You very much for Your current engagement in our Project, but let me allow to remind You what does mean "Collaboration" in the case of our Project, i.e.:
1. every Colleague–Collaborator of our Project should attach at least 1 work about "Stability of Structures" or a message about it,
2. every Colleague–Collaborator of our Project should follow each other (at least 50 Members of the Project),
3. every Colleague–Collaborator of our Project should read and recommend, if only would be so possibility regarding a scientific level of researches, all works with each other,
4. every Colleague–Collaborator of our Project should comment works to each other if only would be a reason to do that - comments naturally may be critical but with respect to authors,
5. every Colleague–Collaborator of our Project should cite each other - if only would be so possibility regarding research works of each one, i.e. in every new work attached to our Project should be cited a big number, e.g. 100 (a minimum number: 50) works of Collaborators of our Project,
6. every Colleague–Collaborator of our Project should collaborate and write common (with the Collaborators as co-authors) papers, books, ... and other kinds of works, if only would be so possibility,
7. if any Colleague–Collaborator of our Project has a possibility to help to publish works about "Stability of Structures" (e.g. as a member of a scientific journal or publishing house editorial board) should give massage about it in the "goal of the project" or in "updates" in our Project,
8. if any Colleague–Collaborator knows about a conference with "Stability of Structures" as a panel or topic - He should inform us in the "goal of the project" or in "updates" in our Project ...

I hope that the above rules of our Project would help us to get success in our scientific work ... , every one of us would like that His work would be noted, read, recommended, commented, discussed, and cited ... , but somebody should do that ...

Simultaneously I would like to note that renunciation of the rules of the Project, can be taken by other Collaborators as a kind of dishonesty, especially when a Collaborator would like to obtain a lot of "Reads", "Recommendations" and "Citations", but self doesn't take any so activity .

Date: 31 August 2019

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Project log

Huseyin Karadag
added 6 research items
In this study, the utilization of steel slag in road base layer was evaluated by using finite element method. Plane strain finite element analyses were carried out by using Plaxis software to calculate rutting behaviour of steel slag material. Hardening soil model with small-strain stiffness (HSsmall) was used to examine deformation behaviour of layered pavement where as asphalt concrete modelled using linear elastic model. Deformation behaviour of steel slag was compared to crushed limestone. The first findings gave very promising results that were obtained for steel slag when compared to crushed limestone. After 10,110 triangular load cycles, maximum deformation at the surface of the asphalt for steel slag based road cross-section layer was obtained less than those obtained for crushed limestone based road cross-section.
This study evaluates the behavior of an 15 m deep anchored contiguous pile wall in stiff over consolidated fissured Ankara Clay. The wall consists of 650 mm diameter drilled shafts at 1000 mm spacing, with five rows of anchors. The geotechnical parameters of the soil had to be estimated by combining the results of very limited in-situ and laboratory tests with those obtained through empirical relationships. Plane strain finite element analyses were then performed to predict the wall behavior, focusing mainly on the deformations. The results of the numerical analyses were then compared with those obtained by in-situ measurements from three inclinometers and settlement benchmarks. The results indicate that, with the selection of appropriate constitutive model and soil parameters obtained through local correlations, plane strain finite element analyses are capable of predicting the behavior of anchored contiguous pile walls in a stiff over consolidated clay with sufficient accuracy.
Within the context of this study, the deformation behaviour of multi layered highway road embankment consist of asphalt concrete supported by the underlying base and subbase layer under repetitive wheel load were analysed using finite element methodology. Plane strain finite element analyses were carried out by using Plaxis software to calculate rutting behaviour of embankment. Asphalt concrete was modelled using linear elastic model whereas hardening soil model with small-strain stiffness (HSsmall) was used to examine deformation behaviour of base, subbase and subgrade layers due to its capability to model stress dependent stiffness, unloading-reloading behaviour and hysteric damping.
Pawan Kumar
added a research item
This paper analyzed static bending and deflection of the porous core functionally graded piezoelectric (PCFGP) sandwich plate resting on the Winkler/Pasternak/ Kerr foundations under thermomechanical and electromechanical loading with different conventional and unconventional boundary conditions. First-order shear deformation theory (FSDT) based displacement field and von Karman geometric nonlinear strain are used for problem formulation. The governing equations of the PCFGP sandwich plate are obtained using Hamilton’s principle. A higher-order finite element method has been employed with a modified iterative Newton-Raphson scheme for solving the governing equations. Convergence and comparison studies demonstrate that the validation of the current model has suitably correct. It has been observed that an increase in the porous exponent in the core part of the sandwich plate reduces the stiffness of the plate with an increase in stress, deflection, and electric potential. The maximum stress, deflection, and electric potential are obtained for porosity dispersion in the Uniform pore distribution (UD) type, while minimum in Unsymmetric pore distribution (USD) type dispersions. Hence, the different embedding porosity in the core part of the sandwich plate plays a significant role in reducing plate structural weight and offering good stability in plate structural bending stiffness.
Rizky Chandra Ariesta
added a research item
The stress concentration factor (SCF) can lead to the failure of ship construction. That problem can occur with hotspot stress expansion in the local area because of the acting load and structural details shapes. However, there is no method for the asses of structure design failure in the minor openings such as a dry hole and scallop dimension. Furthermore, the research aims for evaluating stress concentration performed using the diameter and width (d/W) ratio. The model of plates generates to identify stress phenomena on the isotropic ship plate. The numerical simulation was carried out using finite element analysis and proven by experimental method with the installation of the strain measurement on several working loads of 30% and 60% under yield strength. The plate used for analysis is an A36 steel plate commonly used in the shipbuilding industry. The plate model with the hole was identified, which shows the stress concentration that occurs increases after the d/W of the isotropic plate also increases, then the comparative stress plot. Moreover, based on the numerical and experimental analysis, the comparisons of stress concentration factors within different radius holes have been completed for assessment. Finally, result from numerical and experimental obtained error values below 3%.
Kuo Tian
added a research item
Purpose The purpose of this paper is to propose a numerical prediction method of buckling loads for shell structures under axial compression and thermal loads based on vibration correlation technique (VCT). Design/methodology/approach VCT is a non-destructive test method, and the numerical realization of its experimental process can become a promising buckling load prediction method, namely numerical VCT (NVCT). First, the derivation of the VCT formula for thin-walled structures under combined axial compression and thermal loads is presented. Then, on the basis of typical NVCT, an adaptive step-size NVCT (AS-NVCT) calculation scheme based on an adaptive increment control strategy is proposed. Finally, according to the independence of repeated frequency analysis, a concurrent computing framework of AS-NVCT is established to improve efficiency. Findings Four analytical examples and one optimization example for imperfect conical-cylindrical shells are carried out. The buckling prediction results for AS-NVCT agree well with the test results, and the efficiency is significantly higher than that of typical numerical buckling methods. Originality/value The derivation of the VCT formula for thin-walled shells provides a theoretical basis for NVCT. The adaptive incremental control strategy realizes the adaptive adjustment of the loading step size and the maximum applied load of NVCT with Python script, thus establishing AS-NVCT.
Ali A. Abdulhameed
added a research item
The term "peak ground acceleration" (PGA) is frequently used to describe ground motions accurately. Identifying the ground motion components within a defined zone is critical for structural engineering design. The purpose of this study is to develop novel models for predicting the PGA using Artificial Neural Networks-Gravitational Search Algorithm (PGAANN-GSA) and Response Surface Methodology in the case of the Iraqi database (PGARSM). This paper grants the prediction of PGA for the seismotectonic of Iraq, which is considered the earlier attempt in Iraqi region, and other related domains. The magnitude (Mw) of the earthquake, the average shear-wave velocity (Vs30), the focal depth (FD), and the distance between the station and the earthquake source were all used in this study (REpi). The proposed models are constructed using a database of 187 previous ground motion records from Iraq's tectonic zones, and this dataset is also utilized to evaluate the effect of each specified parameter on the PGA. The statistical results demonstrate that the proposed models exhibit a high degree of correlation, perfect mean values, a low coefficient of variance (CoV), fewer errors, and an acceptable performance index (PI) value compared to actual PGA values confirming their accuracy and consistency. However, the composite ANN-GSA model performs better than the RSM model. A correlation between the standardized plot and Pareto chart of the most influential parameters on PGA was identified, with the Mw and Vs30 having the most significant influence on PGA, followed by the FD and REpi having the slightest influence on PGA.
Param D G
added a research item
Buckling analysis of thick isotropic plates subjected to uniaxial and biaxial in-plane forces is presented using the 5th order shear deformation theory. The 5th order shear deformation theory considers both transverse shear deformation and transverse normal strain deformation effects. The assumed displacement field accounts for non-linear variation of in-plane displacements as well as transverse displacement through the plate thickness. The condition of zero transverse shear stresses on the upper and lower surface of plate is satisfied. Hence, the present formulation does not require any shear correction factor generally associated with the first order shear deformation theory (FSDT). Numerical results for buckling analysis include the effects of side to thickness ratio and plate aspect ratio for simply supported isotropic plates. The results of present theory are compared with classical plate theory (CPT), first order shear deformation theory (FSDT), higher order shear deformation theory (HSDT) and trigonometric shear deformation theory (TSDT).
Vahid Refaeinejad
added a research item
In Ultra-short pulsed laser heat problems, two dominant effects are considered, the non-Fourier heat conduction and the coupling effect between temperature and strain rate. In the present study, the thermoelastic vibrations of the Euler-Bernoulli microbeam resonator under pulsed laser heating have been investigated by considering the effect of the length parameter based on the modified couple stress theory. The equation of motion of the system is extracted using Hamilton’s principle and the equations of thermal and vibration coupling are solved by combining the two methods of finite sine Fourier transform and Laplace transform. The obtained results have been compared with the results of continuous classical theory. Also, increasing the length scale in the modified couple stress theory reduces the temperature and increases the frequency of heatwave oscillations distributed in the resonator.
Khondaker Sakil Ahmed
added a research item
The Padma Multipurpose Bridge (PMB) is a dream infrastructure to connect the southwest to northern and eastern regions of Bangladesh. Padma Bridge is expected to generate substantial impacts, in terms of transport, the national and regional economy, increase in production, employment, income, and ultimately, poverty reduction. However, it is considered one of the most challenging engineering projects in the world in terms of concept, design, management, and construction. In this study, a 3D Finite Element (FE) model of the actual PMB has been developed using a commercial computer package. Since the bridge is composed of seven repetitive (6x150m) 900mm modules made of composite steel warren truss, the FE model is idealized for a single module six-span continuous straight module. The superstructure of the bridge is separated from the substructure by the Friction Pendulum Bearing (FPB). Accounting loads from all possible sources, HL-93 vehicular live load is considered for the upper deck and Dedicated Freight Corridor (DFC) loadings are assumed for the railway where wagon loads are combined from different locomotives. To achieve accurate soil-structure interaction, p-y soil spring following API guideline was adopted to conform flexible support system. The bridge's performance has been evaluated for the 475-year, 975 years, and 2475-year return periods for Service Level, Design Basis, and the Maximum Credible Earthquake (MCE), respectively. It is observed that the bridge pier reached only 28% of its axial capacity and 36% of its flexural capacity for a seismic situation of 2475 yrs of return period. On the other hand, the pier has reached only 41% of its shear capacity and only 24% of the shear capacity of the applied reinforcements of the section.
Alexander Zolochevsky
added a research item
Introduction. Viruses are a large group of pathogens that have been identified to infect animals, plants, bacteria and even other viruses. The 2019 novel coronavirus SARS-CoV-2 remains a constant threat to the human population. Viruses are biological objects with nanometric dimensions (typically from a few tens to several hundreds of nanometers). They are considered as the biomolecular substances composed of genetic materials (RNA or DNA), protecting capsid proteins and sometimes also of envelopes. Objectives. The goal of the present review is to help predict the response and even destructuration of viruses taking into account the influence of different environmental factors, such as, mechanical loads, thermal changes, electromagnetic field, chemical changes and receptor binding on the host membrane. These environmental factors have significant impact on the virus. Materials and methods. The study of viruses and virus-like structures has been analyzed using models and methods of nonlinear mechanics. In this regard, quantum, molecular and continuum descriptions in virus mechanics have been considered. Application of single molecule manipulation techniques, such as, atomic force microcopy, optical tweezers and magnetic tweezers has been discussed for a determination of the mechanical properties of viruses. Particular attention has been given to continuum damage–healing mechanics of viruses, proteins and virus-like structures. Also, constitutive modeling of viruses at large strains is presented. Nonlinear elasticity, plastic deformation, creep behavior, environmentally induced swelling (or shrinkage) and piezoelectric response of viruses were taken into account. Integrating a constitutive framework into ABAQUS, ANSYS and in-house developed software has been discussed. Conclusion. Link between virus structure, environment, infectivity and virus mechanics may be useful to predict the response and destructuration of viruses taking into account the influence of different environmental factors. Computational analysis using such link may be helpful to give a clear understanding of how neutralizing antibodies and T cells interact with the 2019 novel coronavirus SARS-CoV-2.
Nicolò Vaiana
added a research item
International short course at California State University, Long Beach (US) Instructors: D Losanno and N Vaiana
Soheil Gohari
added a research item
A Levi-type analytical solution procedure is developed to characterize static and dynamic response of smart laminated simply-supported composite rectangular plates induced by inclined piezoelectric actuators under (1) constant electrical voltage and (2) time-dependent electrical voltage with excitation frequency. The key to development of this analytical solution procedure is to employ the higher order finite integral transform and discretized higher order partial differential unit step function equations. Unlike earlier studies, this research aims to investigate the effect of inclination angle of piezoelectric actuators on static and dynamic deformation response of laminated composite plates under both static and dynamic conditions. The developed analytical solution procedure is implemented computationally through Matlab-based computer code. Its accuracy is initially investigated through convergence study and results comparison with the published literature for a particular case when inclination angle is θ = 0°, which is only limited to the bending deformation response. Since there is no published benchmark data for twisting deformation response analysis caused by inclination angle of piezoelectric actuators (θ ≠ 0°), a set of robust and realistic numerical analysis using Abaqus finite element analysis (FEA) is conducted. Good agreement between the results is observed. Unlike applied electrical voltage, inclination angle of a piezoelectric actuator does not have a significant impact on twisting deformation response during static mode; whereas, both the excitation frequency and inclination angle can significantly influence the maximum amplitude of vibration.
Angela Shvets
added a research item
The strength of the coupling device under the action of operating loads with regard to the non-central interaction of two cars is defined. When longitudinal force is transmitted through the coupler, the points of its possible rotation can be either the upper ribs of the shank end surface or the upper ribs of the damping device body support surface. The tail part of the coupler is under conditions of eccentric compression (or tension) by the force, which is non-parallel to the longitudinal axis. Through any cross-section of the shank, transverse and longitudinal forces are transmitted, applied at a point far from the center of gravity of the section. Using the principle of addition of forces action, a dependence for the definition of the maximum normal stresses in the extreme fibers of the analyzed section of the shank of the coupler, the most distant from the main axis of inertia, has been obtained. The damage to the area of the coupler shank jumper and the bending of the shank in the horizontal and vertical planes, which occur during operation, are justified. Calculation methods make it possible to study the influence of eccentricities of longitudinal force application relative to the coupler axis and the difference of coupler axis levels in the analyzed sections on the magnitude of the compressive operating loads. Application of the obtained results will not only help to ensure the strength of the coupling devices, but will also ensure the freight cars' durability under conditions of increasing train weight and increasing train speed.
Seval Pinarbasi
added 5 research items
Thirty-six years after its publication, Turkish Building Code for Steel Structures was replaced with a more rational specification, Specification of Design and Construction of Steel Structures (SDCSS), which was prepared almost entirely based on the current American steel design specification (AISC 360-16). European steel design specification (EC3) is also widely used in Turkey for the design of steel structures constructed with the collaboration of Turkish and European companies. It is essential for a steel designer using both SDCSS and EC3 to comprehend the basic differences between these specifications. This study aims to compare the design guidelines defined in AISC 360-16 (so in SDCSS) and EC3 for rolled I-shaped steel members subjected to axial compression thoroughly. For various steel grades, member lengths, and 153 different European I/H sections, design buckling resistances and design compressive strengths are computed and compared. It is shown that there are at most 3% difference between the effective areas computed using both specifications. It is highly recommended that the change of cross section class be allowed while calculating design buckling resistances. For the studied sections and steel grades, the resistance-to-strength ratios are found to be as high as 1.24 but not smaller than 0.907.
Members with varying geometrical and/or material properties are commonly used in many engineering applications. Stepped columns with internal axial loads constitute a special case of such nonuniform columns. Crane columns in industrial buildings or structural columns supporting intermediate floors are important applications of stepped members in civil engineering. Since neither axial load nor stiffness is constant along the column height, the stability analysis of a stepped column is usually more complicated than that of a uniform column. Determination of exact buckling loads for stepped columns with different end conditions is not always practical. This paper shows that variational iteration method (VIM), a kind of analytical technique recently proposed for solution of nonlinear differential equations, can satisfactorily be used to obtain approximate solutions for buckling loads of stepped columns with internal axial loads. VIM solutions perfectly match with the exact solutions available in the literature for some special cases of two-segment stepped columns. For many other cases, that is, for various values of three design parameters, namely, (i) load ratio, (ii) stiffness ratio, and (iii) length ratio, approximate buckling loads for two-segment stepped columns are determined using VIM and presented in tabular form which can easily be used by design engineers.
Since compression members, such as columns in a multistory building, are mostly the key elements in a structure, even a small decrease in their load carrying capacity can lead to catastrophic failure of the structure. A compression member has to be designed to satisfy not only the strength and serviceability requirements, but also the stability requirements. In fact, the behavior of a slender column is mostly governed by the stability limit states. In an attempt to construct ever-stronger and ever-lighter structures, many engineers currently design slender high strength columns with variable cross sections and various end conditions. Even though buckling behavior of uniform columns with ideal boundary conditions have extensively been studied, there are limited studies in the literature on buckling analysis of nonuniform columns with elastic end restraints since such an analysis requires the solution of more complex differential equations for which it is usually impractical or sometimes even impossible to obtain exact solutions. This paper shows that variational iteration method (VIM) can successfully be used for this purpose. VIM results obtained for columns of constant cross sections, for which exact results are available in the literature, agree with the exact results perfectly, verifying the efficiency of VIM in the analysis of this special type of buckling problem. It is also shown that unlike exact solution procedures, variational iteration algorithms can easily be used even when the variation of column stiffness along its length and/or the end conditions are rather complex.
Pawan Kumar
added a research item
The current study is focused on the static and vibration analysis of a sigmoid smart functionally graded (SFG) plate resting on the two parameters elastic foundation exposed to electromechanical loading at different boundary conditions. The sigmoid law (S-Law) is used to evaluate the distribution of SFG properties along the thickness direction. The governing equation of the motion of the SFG plate is obtained using first-order shear deformation theory (FSDT) and Hamilton's principle. The derived governing equation is then solved employing the higher-order finite element method (HFEM) using 9-noded Lagrange quadrilateral elements with 54 degrees of freedom (DOFs) per element. Convergence and comparative tests were carried out for the effectiveness and accuracy of the present approach. Non-dimensional frequency increases negative electric loading (V) and reduces positive electric loading at a constant side to thickness ratio. The effect of the shear layer parameter on the stress and deflection of the SFG plate is more compared to the Winkler foundation. The obtained results are helpful for the accurate design of the SFG based structures under electromechanical loading.
Khondaker Sakil Ahmed
added a research item
The design of double shear bolted connections in structural steel is governed by four different failure modes; tear out, splitting, net-section, and bearing. Ten machine learning (ML) approaches was explored on a comprehensive database of 455 experimental results for identifying the failure modes of double shear bolted connections. Among them, Random Forest (RF), CatBoost, XGBoost, and Gradient Boosting (GB) attained 90-92% accuracy on the testing dataset for classifying the failure modes. The best-performing models revealed that the ratio of the edge distance-to-bolt diameter (e2/d0) is the most important feature with an influence of nearly 30% on the failure mode of the connections. Interestingly, the number of bolt rows in a connection also influences the failure mode, which was not captured by existing equations and design codes. Finally, a user interface capturing all proposed ML models was developed to identify the failure modes of double shear bolted connections.
SURAJ PRAKASH HARSHA
added a research item
In this study, dynamic response analysis of functionally graded gears (FGGs) has been performed using a 6-degree of freedom dynamic model. The pinion and gear are divided into homogeneous sub-domains of uniform thickness, conforming to the gear tooth profile. The material composition varies radially according to power-law gradation with metal at the innermost and ceramic at the outermost surface. Mesh stiffness and transmission error of FGGs have been evaluated using a finite-element-based numerical method employing contact analysis. Results show that for considered values of gradient index (GI), FGGs show a 10% to 50% reduction in mesh stiffness with a 30% to 60% reduction in weight compared to steel gears of exact specifications. Also, FGGs show a 4% to 12% reduction in dynamic factor and a 9% to 17% reduction in peak-to-peak displacement amplitude than steel gears over the selected values of GI.
Hartmut Pasternak
added a research item
The paper presents failure modes like excessive deformations of a conical hopper, vibrations of locally buckled column-supported silos and the bolt failure of a corrugated silo. Diskutiert werden Schadensfälle wie übermäßige Verformungen an Trichtern, das Schwingungsverhalten von örtlich ausgebeulten Silos auf Stützen und Schrauben- versagen in Wellblechsilos.
Hartmut Pasternak
added a research item
Scientific Journal of Civil Engineering In this paper, the advantages of the general method for verification of the lateral torsional buckling are demonstrated through the calculation of a real steel frame with variable cross-section in Germany. According to the Eurocode 3, the minimum load amplifier of the design loads and the minimum amplifier for the in plane design loads to reach the elastic critical load with regards to lateral or lateral torsional buckling are determined with the linear buckling analysis and the geometrically and materially nonlinear analysis using finite element method. The results show that shell models can create arbitrarily complex cross-sections and obtain more accurate results comparing to beam elements. Finally, the practical implementation of the reinforcement of steel frame is shown.
Mahesh KUMAR C L
added a research item
In General, the structure in high seismic areas may be susceptible to the severe damage. Along with gravity load structure has to withstand the lateral load which can develop high stresses. Now a day, shear wall in R.C. structure and steel bracings in steel structure are most popular system to resist lateral load due to earthquake, wind, blast etc. The bracing is one of the best lateral load resisting systems and it will be the viable solution for enhancing earthquake resistance. A Bracing is a system that is provided to minimize the lateral deflection of structure. The members of a braced frame are subjected to tension and compression, so that they are provided to take these forces similar to a truss. Braced frames are always designed of steel members. Use of the braced frames has become very popular in high rise structure and also in seismic design of them. So there is a need of precise and exact modeling and analysis using software ETABS to interpret relation between brace frame and without brace frame aspects. The present study assesses the seismic response of steel structure with concentric bracing system. Two structural configurations were utilized; vertical irregular model (VIRM), vertical irregular model with concentric bracing (VIRM_CB). A 15 storey steel moment resisting frame was analyzed for all zones of soil type-II (medium). The analyses were carried out to assess the structural performance under earthquake ground motions. These models are compared in different aspects such as storey drift, storey displacement and base shear. Index Terms-base shear ,concentric brace,storey drift, storey displacement.
Farshad Nobakht-Kolur
added a research item
Marine fouling is a major concern in marine aquaculture industry. It changes the flow field around the cage, reduces water exchange across the nets and affects the current/wave-induced forces acting on the structure. The current/wave forces induced to marine-fouled planar net panels were studied by previous researchers. The current paper reports the results of a series of small-scale physical model tests conducted to study the wave forces induced to marine-fouled 3D aquaculture net cages. Using load cells fixed on the mooring lines, the time series of the forces generated by irregular waves propagating through the clean and fouled fish cage models were recorded. The artificial fouling was representative of hydroids, an important fouling organism in the aquaculture industry. Time and frequency domain analysis were performed on the in-line (surge) and cross-line (sway) wave force data. The experimental results showed that the surge force amplitudes increased up to around 160% and by the fouling. The sway force showed up to around 50% decrease by the fouling. The probability distribution of the force response to irregular waves was not significantly affected by the fouling. The force transfer functions from the time and frequency analysis were in reasonable agreements. The fouling, interestingly, increased the linearity of the wave-force interactions and provided stronger associations between the input forcing and the output response.
Amer Alomarah
added a research item
A hybrid auxetic structure named a re‐entrant chiral auxetic structure (RCA) was recently developed based on topological features of both re‐entrant and chiral auxetic honeycombs. In this study, the in‐plane quasi‐static and dynamic performances of the (RCA) are compared. Experimental specimens for both the quasi‐static and dynamic tests were designed to have identical dimensions and fabricated from polyamide12 (PA12) using an additive manufacturing process, Multi Jet Fusion (MJF). Compressive tests were conducted at constant velocities of 0.066 mm/s on a Zwick Roell machine and of 5 m/s on an Instron VHS 8800 high speed machine for quasi‐static and dynamic compressions, respectively. Numerical models were developed using ABAQUS/Explicit and verified by experiments. Results evidenced that performances of the RCA were sensitive to the crushing velocity. Moreover, the base material (PA12) displayed poor ductility under impact loads, therefore, fracture of the structural members dominates the deformation of the structure when it was dynamically crushed. Energy absorption of specimens that were quasi‐statically crushed outperformed those under dynamic compression. Furthermore, discrepancy in Poison’s ratio curves was observed under quasi‐static and dynamic tests due to the change in the deformation modes. This article is protected by copyright. All rights reserved.
Hartmut Pasternak
added 3 research items
For the structural design of welded girders with numerical approach, residual stresses and initial deformations or geometric imperfections need to be considered. Nowadays, with the development of computer technology and finite element theory, the numerical welding simulation approaches have improved significantly. Howev-er, the three dimensional welding simulation requires a huge amount of computing resources, which limits its wide application. This paper presents a simplified numerical approach based on a modified, so-called local-global model approach. This approach was developed and calibrated with experimental investigation by means of the single- and double-sided welded girders. By comparing the results of numerical calculations and exper-imental results, it shows that the simplified welding simulation cannot only calculate the residual stress of welded girders with single- and double-sided welds relatively accurately, but also obtain acceptable results of the deformations caused by the welding process. Besides, the calculated residual stress distribution can be au-tomatically inputted into the numerical model for the subsequently further buckling analysis of the welded girders. The calculation results show that the buckling load obtained by numerical approach are in good agreement with the experimental results and the both welded girders have a relatively smaller different of bending capacity, despite clearly different residual stress distributions is exist.
The lateral-torsional buckling resistance of welded steel girders is affected by their residual stresses and geo-metric imperfections. Generally, both influences are mainly controlled by the manufacturing process, in partic-ular the welding of the girder. This paper presents experimental investigations on four laterally unbraced welded steel girders with thin-walled I-sections, whose flange-to-web junctions are welded from one or two sides to evaluate the fabrication influence. The investigations include lateral-torsional buckling tests under combined bending and torsion loading caused by three-point bending due to an eccentric vertical single force. The geometric imperfections of the welded test girders are determined by 3D laser scanning. The test results show that the influence of the geometric imperfections and the residual stresses on the lateral-torsional buck-ling resistance is limited for the tested girders.
In steel structures, welding is one of the favorable joining methods. To consider negative effects of the joining technique residual stresses and distortions can be found with different welding simulation tools. The usage of different tools will require know how of the process as well as the input of energy, geometry and the material. In addition, there is a large time amount necessary the build-up the working model with the required boundary conditions. To reduce modelling and welding time a welding tool was developed and will be used to analyses in a quite simple and easy-applicable manner residual stresses. It will show a better direct link between weld manufacturing and capacity calculations. The simplified approach will be compared with earlier fill scale simu-lation efforts in a case study. The application of such approach for considering welding effects in the compo-nent design of welded plate girders is however still quite unusual even in steel research. Especially multi-layer welds, which are found in joining thick plates, require multiple calculation steps and generate the need of sim-plifications. Therefore, the existing welding tool, which is able to calculate I-girders, is expanded to multi-layer welds. Finally, this approach will have developed and calibrated with experimental investigation by means of a multi-layer welded girders.
Farshad Nobakht-Kolur
added 2 research items
The Wave Spectrum Calculator is used to extract the wave spectrum from the input water surface elevations. This is used in the experimental and numerical simulations to fit the best wave spectrums on data. Moreover, it can be used to check and verify the input wave spectrum with theories. It can calculate the spectra parameters and wave energy magnitudes for time-domain and frequency-domain analysis methods.
The Zero-Up Crossing Method Calculator is used to extract the wave heights and periods from the input water surface elevations. This is used in the experimental and numerical simulations to extract the real wave heights and periods and comprise them with corresponding theory data. Moreover, it can be used to check and verify the variation of wave parameters produced by the wave-maker and the corresponding input parameters to check the accuracy of the wave-maker. It can calculate the input wave heights and periods in the time-series and mean values of them for the time-domain analysis method.
Fabio Rizzo
added 2 research items
Cable supported glass façades are sensitive to wind action because of their flexibility. Conventional laboratory testing to check a façade reliability under the wind action is generally carried out by uniformly air pressure tests. However, the typical wind action on a surface is known to be not uniform because it varies due to building aerodynamics and wind flow turbulence, and this aspect should be properly considered for testing protocols. This paper discusses the structural response of cable-supported glass façades, through time history Finite Element (FE) analyses, under different wind action combinations that varies based on the building aerodynamics (plan shapes and roof curvatures), the wind direction (0° and 90°), and the glass panel position (up and down). Such a finding is further enforced by the presence of flexible supports for the constituent glass modules. The presented results show a strong dependence of the structural response on the wind action configuration, and thus suggest the need of new testing protocols for similar systems. [ACCEPTED]
The interaction between a pedestrian bridge for a motorway crossing and air pressure waves induced by the truck passage is discussed with reference to a slender footbridge in Pregnana (Italy). The experimental campaign was necessary, as very significant vibrations induced by truck passage were observed during the construction process before building the reinforced concrete plate on the deck. Results obtained from monitoring of the air pressures and accelerations caused by the truck passage under the bridge along with truck speeds have shown a phenomenon known as a piston effect occurring during the passage. Based on the statistical analysis of these measured values, the spatial distribution of the wave on the bridge was elaborated. Numerical analyses of the bridge without the reinforced concrete plate on the deck suggest that the piston effect should be calculated to safely construct light bridges. [ACCEPTED]
Farshad Nobakht-Kolur
added 2 research items
Ever growing global demand for aquatic resources due to population growth, limitation in freshwater resources and uncertainty and restrictions associated with wild fish stocks and other aquatic resources have pushed the aquaculture industry offshore into deeper waters. Concurrent advances in the offshore technology provided a ground for the development of more innovative and challenging structures. Marine fouling is an important concern in offshore structures. Underwater surface of man-made structures is quickly covered by unwanted aquatic organisms. The presense of the fouling changes the flow regime around the structure, thus the wave/current induced forces. Despite the important contributions of previous studies, the biofouling effects on the wave induced force and hydraulic response of the fish cage have not received due attentions in the literature. The current thesis reports on an attempt for better understanding the marine fouling effects on regular and irregular wave-induced forces and on the hydraulic response of the gravity fish cages. A structured review of the literature related to the fluid structure interactions in marine fouled fish cages is presented. Results of experimental studies on small scaled fish cages with clean and artificial fouled nets under regular and irregular wave action are then reported in four separated chapters. Soft fouling, hydroid Ectopleura larynx, is simulated artificially with different lengths but constant thickness, roughness and material. Regular wave tests on hydraulic response of the cages show that, wave transmission, set-up and energy coefficients have decreased up to 6%, 9% and 20%, respectively by the fouling. Vertical asymmetry factor upstream the cage was unaffected by the fouling, however, the asymmetry factors downstream of the cage was meaningfully affected by the fouling. Results also show that fouling has not provided any significant horizontal nonlinearity in and around the cage. Regular wave tests on the cages show that, the surge, heave and pitch response amplitude operators (RAOs) increased up to 52%, 32% and 36%, respectively by the fouling but, sway and roll RAOs decreased up to 36% and 34%, respectively. Moreover, surge, heave and sway asymmetry increased, decreased and increased, respectively by the fouling and fouling length. Irregular wave tests on hydraulic response of the cages show that, wave transmission, set-up and zeroth-momentum coefficients decreased up to 7%, 7% and 13%, repectively by the fouling. Moreover, the aforementioned coefficients increased by the wave peak period at constant significant wave height and decreased by the significant wave height at constant peak period. Irregular wave tests on the cages show that, fouling growth significantly affects the wave induced force spectra. Significant surge and heave force amplitudes (F1/3) increased up to 160% and 88% by the fouling but, for sway force decreased up to 51%. The results also shows that, fouling growth causes shift and increase in the natural frequency of the structure and peak frequency of the force response spectra. It is observed that, coherency function increased by the fouling. In general, transfer functions for the surge and heave force response increased. This was the opposite with the sway response. It is also noticed that soft fouling increased the linearity of wave-force interactions.
The current paper reports the results of a series of small-scale physical model tests conducted to study the marine fouling effects on the wave attenuation/build-up around/inside a 3D floating gravity net cage. The artificial fouling modelled was representative of hydroids, an important fouling organism in the marine aquaculture industry. Regular wave groups with different heights, periods, and steepness were examined. The cage hydraulic response inside and around the cage models was analysed. Changes made by the cage presence to the height, energy flux, geometry and nonlinearity of the waves traversing the cage models were studied. Attenuation of the wave height and energy was observed downstream of the cage models, which grew smaller in the fouling presence and further by the fouling length. Build-ups of the wave height and energy occurred inside the cage models, which grew weaker in the fouling presence and with longer fouling. The fouling effects on the hydraulic response were more pronounced downstream as compared to those inside and upstream of the cage. The experimental data were used to derive nonlinear regression equations, indicative of the primary trends for the wave attenuation/build-up, around/inside the cage.
Ehsan Noroozinejad Farsangi
added a research item
Rainwater may penetrate through the cladding, enter the wall assembly, and cause damage to the façade components and interior finishes, which are moisture sensitive, most of the time. In the current paper, the performance assessment of a skylight with a full-scale mock-up has been evaluated. The mock-up was erected for an actual project to verify the acceptance criteria for the skylight's technical, functional, and architectural details. The test was conducted at the Aluminum Technology Auxiliary Ind. (ALUTEC) facility in the Industrial Zone, Doha, Qatar. The fabricated full-scale mock-up has a rectangular plane configuration of 6.625 m (length) by 3.315 m (width) that belongs to a skylight measuring 36 m by 18 m. The ASTM E283, ASTM E331, and ASTM E330 standards were followed during the experiment. Air infiltration/exfiltration, static water penetration, structural performance, post-structural static water penetration, and structural proof loading tests were performed in an airtight chamber. After recording the residual displacements, the test findings for all the make-up components, namely steel tubes, glass, and aluminum sandwich panels, were determined and found within acceptable limits.
Natalia V. Smetankina
added 2 research items
One of the most topical issues in aircraft building is checking the engines for bird strike resistance, i.e. their airworthiness following an in-flight bird strike. The most critical aircraft units are the turbojet engines. In this case, the turbofan blading is affected the first thing. Its deformation or failure can result in the failure of the entire engine. Numerical simulation of the process allows for a qualitative and quantitative assessment of the consequences of a bird strike on the blades. This enables to avoid full-scale experiments and design properly the units affected by such action. The paper deals with improving the accuracy of simulation modelling of the behaviour of the material of the fan rotor blades of a turbojet aircraft engine in the event of bird strike by using adapted finite-element computational models. Bird action is argumentatively replaced with a system of equivalent quasistatic loads. The most critical events of blade impact with medium and big-size birds were selected by analysing experimental data. The force impulses were compared to determine the strike locations and the sizes and masses of birds that are most dangerous from the viewpoint of disturbance of strength properties. Variant computational analyses deal with studying construction behaviour under static action of the joint load by centrifugal forces and loads that simulate bird action on the fan blading. The stress–strain state characteristics are used to assess the behaviour of the material and its strength properties. Simulation accuracy is confirmed by comparison with the results of bench tests.
Khondaker Sakil Ahmed
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Reinforced concrete (RC) structures containing flat slab system and core shear wall have become popular and have been used extensively all over the world for the last few decades. They provide substantial advantages over the traditional beam-column-slab structures in terms of architectural aesthetics, easier fixing of electrical, lift, and plumbing lines. Usually, the building system consists of an RC core shear wall and columns directly connected to the slabs. Though the design procedure is similar to the structural type consisting of moment frames, the existing force-based seismic design practice has some limitations in considering response modification factors, design overstrength, deflection amplification factors, ductility, etc. In this study, an 8-storey flat slab RC structure with core shear-wall and gravity columns is considered for non-linear dynamic analysis. The displacement-based design approach addressed six pairs of ground motions. The core wall was modelled as fiber hinge model where hysteretic responses of both concrete and steel fiber responses are investigated. The results are presented in terms of the storey response, base shear, and roof displacement of the structure. Column, wall, and fiber hinges responses highlight the states of individual components as well as the fibers. Finally, the stress and strain levels of concrete and steel fibers are examined to check the overall status of the structural system.
Pawan Kumar
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Purpose The static, buckling, and vibration response of the hybrid ceramic–metal plate, in which properties vary as a Power–law (P-) and Sigmoid law (S-) based distribution subjected to thermo-electro-mechanical loading, has been analyzed. Methods The governing equations of motion obtained using first-order shear deformation theory (FSDT) with von-Karman displacement field and the principle of virtual displacements for the hybrid ceramic–metal plate is solved by the nine-node interpolation function with seven degrees of freedom using the finite element method. Results It has been observed that the Dimensionless centerline deflection and the stresses of hybrid ceramic-metal plates increase when the temperature difference increases from ΔT=0K to ΔT=100K and with an increase in the volume fraction exponent (p). There is an increase in the dimensionless frequency and the critical buckling load factor as the boundary condition changes from SSSS to CCCC. Conclusions The obtained results are essential for the functionally graded thermoelectric piezoelectric-based smart structures under different operating conditions like thermoelectric and piezoelectric effects.
Alexander Zolochevsky
added a research item
A physical model for describing the diffusion creep in perovskite-type material given oxygen non-stoichiometry and tensile-compressive asymmetry is developed. Reference tests for determining the creep parameters in the constitutive equations are discussed. The proposed model is used for combined numerical-and-analytical simulation of diffusion creep in a hollow thick-walled perovskite cylinder under generalized plane strain conditions. The analytical solution for oxygen non-stoichiometry is used. Also, the closed-form general expressions for stresses in a hollow cylinder undergoing diffusion creep at a given oxygen chemical potential gradient are derived. The numerical integration is performed using the-Runge-Kutta-Merson method of the fourth order with automatic step control. The stress redistribution over time in the cylinder under the diffusion creep conditions is analyzed. The numerical results related to tensile-compressive asymmetry and oxygen surface exchange in a perovskite cylinder are discussed.
Ehsan Noroozinejad Farsangi
added a research item
Should you receive this invitation, we appreciate it if you can submit a one (1) page chapter proposal that explains how the proposal fits the scope and the goal of the book described broadly in the Title. Please direct any inquiries to Dr. Ehsan Noroozinejad and/or Prof. Mohammad Noori at: ehsan.noroozinejad@ubc.ca ; mnoori@calpoly.edu
Ehsan Noroozinejad Farsangi
added a research item
Dear Colleagues: We are pleased to announce that we have organized a Special Book Volume to be published by CRC Press/Taylor & Francis Publisher, USA, entitled: Automation in Construction toward Resilience: Robotics, Smart Materials & Intelligent Systems The book chapters should be within the following topics: Computer-Aided Design; Resilience; Dampers; Shape Memory Alloys; Structural Health Monitoring; Modular Constructions; Smart Sensors; Robots; Decision Support Systems; Automated Inspection; Management Information Systems; Intelligent Control Systems; Building Information Modelling; Internet of Things; Internet of Drones; Prefabricated Construction; Smart Construction; Artificial Intelligence; Construction Management; Smart Contract; Augmented Reality; Virtual Reality; Mixed Reality Methods; Fiber-Optic Sensors; 3D Printing; Sustainability; Sustainable Materials; Deep Learning; Transfer Learning; 3D Semantic Segmentation; Redundancy; Reliability Optimization; Surrogate Model; Features Extraction; Digital Twins; Unmanned Aerial, Ground, And Marine Vehicles; 5G Communication in Construction; Big Data and Cloud Computing Methods; Intelligent Maintenance
László Kiss
added a research item
https://jtambg.eu/papers/2021/JTAM2021_4_437-451.pdf The article is devoted to the static, planar buckling problem of pinned-fixed shallow circular arches subject to a concentrated force. The non- linear model is based on the single-layer Euler-Bernoulli theory. The related coupled differential equations of equilibrium are solved in closed-form. It is found such arches can undergo limit point buckling. The model is applica- ble not only to homogeneous but also for nonhomogeneous material distribu- tions. The analytical results are compared with the results for pinned-pinned and fixed-fixed members. There are certain geometries and material distribu- tions when the buckling load is almost the same for all these three support arrangements. Otherwise, as the included angle is increased, the difference between the critical loads also increases. The new findings are validated by means of literature and finite element results.
Kaddari Miloud
added a research item
This work investigates a new type of quasi-3D hyperbolic shear deformation theory is proposed in this study to discuss the statics and free vibration of functionally graded porous plates resting on elastic foundations. Material properties of porous FG plate are defined by rule of the mixture with an additional term of porosity in the through-thickness direction. By including indeterminate integral variables, the number of unknowns and governing equations of the present theory is reduced, and therefore, it is easy to use. The present approach to plate theory takes into account both transverse shear and normal deformations and satisfies the boundary conditions of zero tensile stress on the plate surfaces. The equations of motion are derived from the Hamilton principle. Analytical solutions are obtained for a simply supported plate. Contrary to any other theory, the number of unknown functions involved in the displacement field is only five, as compared to six or more in the case of other shear and normal deformation theories. A comparison with the corresponding results is made to verify the accuracy and efficiency of the present theory. The influences of the porosity parameter, power-law index, aspect ratio, thickness ratio and the foundation parameters on bending and vibration of porous FG plate.
Magdalini D. Titirla
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In this paper a comparison of the seismic performance of three symmetric in plan reinforced concrete (RC) buildings strengthened with viscous or friction dampers are presented. An overview of the optimal design of each type of dampers is described. Three buildings (a four-storey building, a nine-storey building, and a sixteen-storey building) were subjected to seven (real and artificial) seismic recorded accelerograms. Nonlinear dynamic time history analyses were carried out. The effects of each strengthening solution are presented in terms of the maximum horizontal displacement at the top of each building, the maximum inter-story drift and the maximum acceleration at the top of the building. The outcomes of this comparison show that viscous dampers (VDs) provide a significant reduction for mid-rise buildings, while friction dampers (FDs) increase the performance of all structures under seismic action. Further useful results were observed.
Hartmut Pasternak
added a research item
Enge Ringsteifen können die Tragfähigkeit der Kreiszylinderschale erheblich verbessern und deren Beulen wirksam verzögern. Die im Teil 1 vorgestellten Untersuchungen haben dies eindrucksvoll bestätigt. Auch numerische Verfahren können das Stabilitätsproblem von Schalen schnell und effektiv analysieren. Es gibt jedoch noch eine Herausforderung, die experimentellen Ergebnisse exakt nachzurechnen, weil die tatsächliche Geometrie im numerischen Modell schwer zu rekonstruieren ist. In diesem Beitrag wird das abstandsgewichtete Interpolationsverfahren basierend auf einer Mapping-Beziehung verwendet, um die mit 3D-Scan erhaltene Geometrie auf das numerische Modell abzubilden. Das Newton-Raphson-Verfahren mit begleitender Eigenwertanalyse wird eingesetzt, um die Traglast der ringversteiften Kreiszylinderschalen unter Axialdruck schnell zu erhalten. Darüber hinaus werden durch eine Vielzahl von Parameterstudien die Einflussfaktoren von Ringsteifen auf die Tragfähigkeit der Kreiszylinderschale analysiert. Schließlich wird ein Ingenieurmodell aus den Ergebnissen der Parameterstudie abgeleitet. Mit diesem vereinfachten Modell können Ingenieure nur mit einem Taschenrechner oder einer Tabelle arbeiten.
A.B.M Supian
added a research item
Pultruded glass fibre reinforced polymer (pGFRP) composites provide outstanding properties for composite polymer cross arms in power transmission line applications. This study has investigated the effects of various stacking sequences of fibres directions of pGFRP on flexural strength and creep behaviour. The use of static four-point bending flexural tests revealed that Stacking Sequence 2 (±45/0/90/0/90/0) had a significant flexural strength of 399.9 MPa while Stacking Sequence 1 (±45/90/0/±45) had a flexural strength of 242.5 MPa. Furthermore, the four-point bending creep experiments were performed at three distinct stress levels, notably 12%, 24%, and 37% of the ultimate flexural strength, to characterise the creep behaviour of distinct stacking sequences. Moreover, Findley’s power law equation for bending creep behaviour has revealed that the time- dependent reduction factor of Stacking Sequence 1 and Stacking Sequence 2 estimates a drop in flexural modulus of 23% and 10% respectively.
Private Profile
added a research item
Call for paper of special Issue "Hydraulic Engineering Modeling and Technology"-Sustainability (SCI, Q2, IF: 3.251), thanks. This Special Issue, entitled “Hydraulic Engineering Modeling and Technology”, focuses on the recent advances in modeling and analysis technology of hydraulic engineering, including the digital twin technology, physical and numerical modeling. The Special Issue welcomes research papers and review articles in both academia and industry from across the globe to discuss topics related to the design and operation of hydraulic engineering to promote global sustainable development. Potential topics include (but are not limited to) the following: 1-Innovative digital-twin technology in hydraulic engineering; 2-Technology of intelligent construction and health monitoring in hydraulic engineering; 3-Modeling and seismic analysis of towering hydraulic structures in high-intensity regions; 4-CFD modeling for complex flow fields in flow conveyance structures; 5-Novel technology in flow-induced vibration of gate structure considering the fluid–structure interaction effect; 6-Modeling and safety analysis of water pipeline in pumped-storage power station; 7-Safety-evaluation modeling for long-term service behavior of concrete structure in dams; 8-Modeling and structural analysis of coasts, ports and offshore engineering under extreme weather; 9-Safety-evaluation technology of hydraulic structures subjected to landslide surge and shock-wave loads under climate change scenarios; 10-Disaster mechanism and intelligent early warning model of a long-distance water conveyance project in a cold region; 11-Coupled dynamic modeling and stability evaluation of a wind–photovoltaic–hydropower hybrid system; 12-Engineering hydrological computation models under climate changing; 13-Hydrodynamic and water quality control technology for water transfer project; 14-Flood risk modeling by hydrological and hydraulic approaches; 15-Modeling and analysis of water-conveyance tunnel engineering https://www.mdpi.com/journal/sustainability/special_issues/Hydraulic_Engineering_Modeling_Technology
Panumas Saingam
added 2 research items
Seismically retrofitting reinforced concrete (RC) building with a combination of buckling-restrained braces (BRBs) and elastic steel frames offers a practical solution that provides additional lateral stiffness and energy dissipation capacity. However, the available methods to vertically distribute the BRB sizes based on equivalent linearization do not consider the additional stiffness due to the composite behavior between the RC frame and the elastic steel frame, which may lead to an overly conservative estimate of the BRB stiffness demands. This study proposes a retrofit design method incorporating the composite behavior. Numerical models considering the detailed composite behavior are developed and calibrated against quasi-static cyclic loading tests, and a simplified evaluation method is proposed. A four-story RC school building is used as a benchmark model, and the proposed retrofit design method is validated using nonlinear response history analysis. The analysis results suggest that taking the composite behavior into account by using the proposed retrofit design method more accurately estimates the lateral stiffness of the retrofitted structure and leads to a more economic retrofit.
Previous earthquakes have caused extensive damage to reinforced concrete (RC) structures with insufficient lateral force resistance or energy dissipation capacity. There is a need to retrofit vulnerable existing RC buildings, particularly those not originally designed for seismic effects or designed to an outdated seismic specification. This study investigates the use of friction dampers as displacement-dependent energy dissipation devices to retrofit RC moment frame structures. First, an experimental program was conducted to characterize the dynamic behavior of friction brace dampers with several different materials, finding that a sintered metal compound provided a stable friction coefficient of 0.4. A strength-based equivalent linearization design procedure was then developed based on the required friction slip force and considering the cracked state of the existing RC structure. A four-story RC school building was then designed using the proposed retrofit design method, validated using nonlinear response history analysis and compared to a previous retrofit scheme that employed buckling-restrained braces (BRBs) and a stiffness-based equivalent linearization design method. The analysis results suggest that the proposed retrofit design method and friction brace dampers are effective in reducing the maximum story drift.
Djamel Boutagouga
added 2 research items
A great deal of research has been conducted to improve the understanding of the behavior of new types of shear connectors. This article presents the study of I-shaped connectors behavior under monotonic load welded in four different orientations in order to get the position which gives the high shear strength and the best ductility. For this purpose, eight push-out test specimens with I-shaped shear connectors with different orientations and dimensions were tested in C20/25 and C30/37 concrete classes. The load-slip behavior and failure modes of the tested connectors are presented and discussed. Furthermore, a non-linear 3D finite element modelling of the push-out test is performed in order to further investigate the influencing parameters on the I-shaped connectors behavior. Hence, a parametric study is carried out by using the established 3D finite elements model to study the influence of concrete strength, connector’s steel grade, reinforcements, height and length of the connector. Both experimental and numerical results show that there is a privilege orientation for which the shear strength of an I-shaped shear connector is significantly higher than that of all other tested orientations.
Eighteen (18) circular short composite columns including 9 concrete-filled steel columns and 9 concrete-filled stainless steel columns, were experimentally studied in this paper. All composite columns have the same dimensions: D= 160 mm, H= 300 mm and t= 2 mm. The objective of this study is to shed light on the effect of the number and arrangement of lateral and longitudinal welds on the resistance and behavior of concrete-filled composite columns. Based on the results obtained, it was confirmed that weld joints have slight effect on the bearing capacity and instability modes of the studied composite columns. Lateral and longitudinal welds were very successful in conveying compression and bending efforts. The experimentally measured load-bearing capacities of the composite columns were compared to those predicted by Eurocode 4, AISC 360-16 and the equation proposed by Giakoumelis and Lam. All the results predicted by the AISC 360-16 code showed a good concordance with the experimental test results. However, the predictions calculated by the EC4 and the equation proposed by Giakoumelis and Lam were not conservative. This investigation shows that the use of lateral and longitudinal welds in composite columns applications would result in a reliable and economical design. This encourages designers to build their confidence in the use of this type of waste metal plates as structural components of locally produced materials.
Alexander Zolochevsky
added a research item
Viruses are a large group of pathogens that have been identified to infect animals, plants, bacteria and even other viruses. The 2019 novel coronavirus SARS-CoV-2 remains a constant threat to the human population. Viruses are biological objects with nanometric dimensions (typically from a few tens to several hundreds of nanometers). They are considered as the biomolecular substances composed of genetic materials (RNA or DNA), protecting capsid proteins and sometimes also of envelopes. The study of viruses and virus-like structures has been analyzed using models and methods of nonlinear mechanics. In this regard, quantum, molecular and continuum descriptions in virus mechanics have been considered. Application of single molecule manipulation techniques, such as, atomic force microcopy, optical tweezers and magnetic tweezers has been discussed for a determination of the mechanical properties of viruses. Particular attention has been given to continuum damage–healing mechanics of viruses, proteins and virus-like structures. Also, constitutive modeling of viruses at large strains is presented. Nonlinear elasticity, plastic deformation, creep behavior, environmentally induced swelling (or shrinkage) and piezoelectric response of viruses were taken into account. The environment is considered to be made up of those parts of the universal system with which the virus interacts. Integrating a constitutive framework into ABAQUS, ANSYS and in-house developed software has been discussed. Link between virus structure, environment, infectivity and virus mechanics may be useful to predict the response and destructuration of viruses taking into account the influence of different environmental factors. Computational analysis using such link may be helpful to give a clear understanding of how neutralizing antibodies and T cells interact with the 2019 novel coronavirus SARS-CoV-2.
Abdolrasoul Ranjbaran
added 2 research items
A phenomenon is defined as the change in the state of the system, which is defined by the key parameter, called the stiffness. The system stiffness is defined as a ratio of its extreme value. The ratio connecting the system stiffness to its upper bound is called the Persian curve. The method is called the change of state philosophy, which is digested in the Persian curves. The Persian curves are super functions of the state variable via the state functions and two control parameters. The state variable is a scaled identification parameter of the system. The state functions are two specific functions of the state variable. The control parameters are selected from the real-world data (certain data for key parameters of the system). The Persian curve has the basic properties of the probability, so is called the Persian probability function. In view of the Persian curve, it is concluded that all natural phenomena are certain. The lack of knowledge led the human to divide into certain and stochastic. The Persian curve is a happy ending to probability era.
A phenomenon is defined as the change in the state of the system, which is defined by the key parameter, called the stiffness. The system stiffness is defined as a ratio of its extreme value. The ratio connecting the system stiffness to its upper bound is called the Persian curve. The method is called the change of state philosophy, which is digested in the Persian curves. The Persian curves are super functions of the state variable via the state functions and two control parameters. The state variable is a scaled identification parameter of the system. The state functions are two specific functions of the state variable. The control parameters are selected from the real-world data (certain data for key parameters of the system). The Persian curve has the basic properties of the probability, so is called the Persian probability function. In view of the Persian curve, it is concluded that all natural phenomena are certain. The lack of knowledge led the human to divide into certain and stochastic. The Persian curve is a happy ending to probability era.
Alexander Zolochevsky
added 2 research items
Розроблено фізичну модель для опису дифузійної повзучості в перовскитоподібному матеріалі з урахуванням нестехіометрії кисню і різноопірності розтягуванню-стисненню. Обговорюються базові експерименти для визначення параметрів повзучості в визначальних рівняннях. Запропонована фізична модель використовувалася в чисельно-аналітичному методі розрахунку на дифузійну повзучість порожнистого товстостінного пероскитового циліндра, що функціонує в умовах узагальненої плоскої деформації. Залучається аналітичне рішення для кисневої нестехіометрії. Також отримані загальні вирази в замкнутій формі для напружень в порожнистому циліндрі при повзучості і градієнті хімічного потенціалу кисню. Чисельне інтегрування за часом здійснювалося методом Рунге-Кутта-Мерсона четвертого порядку з автоматичним вибором кроку. Аналізується перерозподіл напружень в часі в циліндрі в умовах дифузійної повзучості. Обговорюються чисельні результати, пов'язані з асиметрією розтягуванню-стисненню та поверхневим обміном кисню в пероскитовому циліндрі при повзучості.
In the present paper, the nonlinear problem of diffusion creep and stress evolution has been formulated for tubular perovskite-type membranes of a high-temperature catalytic membrane reactor. For this purpose, the impact of point defects (oxygen vacancies) and volume microstructural defects (voids) of perovskites on the creep deformation of a thick-walled hollow cylinder is analysed at high temperatures and under generalized plane strain in conditions of radial oxygen vacancies gradient. Transport of oxygen vacancies through the membrane thickness is described by Fick's second law. The constitutive equation of diffusion creep and damage evolution equation for voids have been specified for perovskites under complex stress state. The analytical-numerical method has been discussed for solving the initial-boundary value problems of the diffusion creep for thick-walled hollow cylinder, taking into account damage development in a form of oxygen vacancies and voids. An example of creep analysis of perovskite-type thick-walled hollow cylinder is considered under radial oxygen vacancies gradient and, additionally, under radial temperature gradient with the assessment of its long-term strength.
Ali Akhavan Attar
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Several studies had been performed on accumulative roll bonding (ARB) for AA1050; however, most of them were conducted at room temperature. Here, the ARB process was performed on AA1050 plates through nine cycles at elevated temperature. An innovation introduced a new parameter (\(\frac{UTS\times El.}{\varepsilon }\)) to compare the strength-elongation balance between the present study and previous works. Also, as another parameter, the toughness was compared. Comparing these parameters with previous works showed that the considered samples in the present study performed 14 to 63% better than the other samples, so they were more industrially favorable in terms of mechanical behavior and performance. ARB process at elevated temperature may slightly lead to grain growth compared to room/cryogenic temperature, but creates a better elongation, which ultimately leads to a better balance of the strength-elongation parameter. The results showed that the effect of inter-cycle heating was found significant on microstructural evolution and mechanical behavior. Upon five cycles of the process, the grain size was decreased from 35 to 1.8 μm. The yield strength and ultimate strength increased up to 305% and 94%, respectively. Microhardness test showed that warm ARB reduces inhomogeneity factor in the thickness after 3 cycles. Fractography by SEM showed that the sample failed through shear ductile rupture and that the dimples became smaller, more elongated, and shallower onto the failure surface as the number of ARB cycles increased. In short, the warm process is preferred to the cold process to achieve better mechanical performance and toughness.Graphic Abstract
Ali A. Abdulhameed
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The introduction of concrete damage plasticity material models has significantly improved the accuracy with which the concrete structural elements can be predicted in terms of their structural response. Research into this method's accuracy in analyzing complex concrete forms has been limited. A damage model combined with a plasticity model, based on continuum damage mechanics, is recommended for effectively predicting and simulating concrete behaviour. The damage parameters, such as compressive and tensile damages, can be defined to simulate concrete behavior in a damaged-plasticity model accurately. This research aims to propose an analytical model for assessing concrete compressive damage based on stiffness deterioration. The proposed method can determine the damage variables at the start of the loading process, and this variable continues to increase as the load progresses until complete failure. The results obtained using this method were assessed through previous studies, whereas three case studies for concrete specimens and reinforced concrete structural elements (columns and gable beams) were considered. Additionally, finite element models were also developed and verified. The results revealed good agreement in each case. Furthermore, the results show that the proposed method outperforms other methods in terms of damage prediction, particularly when damage is calculated using the stress ratio.
Several stress-strain models were used to predict the strengths of steel fiber reinforced concrete, which are distinctive of the material. However, insufficient research has been done on the influence of hybrid fiber combinations (comprising two or more distinct fibers) on the characteristics of concrete. For this reason, the researchers conducted an experimental program to determine the stress-strain relationship of 30 concrete samples reinforced with two distinct fibers (a hybrid of pol-yvinyl alcohol and steel fibers), with compressive strengths ranging from 40 to 120 MPa. A total of 80 % of the experimental results were used to develop a new empirical stress-strain model, which was accomplished through the application of the particle swarm optimization (PSO) technique. It was discovered in this investigation that the new stress-strain model predictions are consistent with the remaining 20% of the experimental stress-strain curves obtained. Case studies of hybrid-fiber-reinforced concrete constructions were investigated in order to better understand the behavior of such elements. The data revealed that the proposed model has the highest absolute relative error (ARE) frequencies (ARE10 % and the lowest absolute relative error (ARE > 15 %) frequencies (ARE > 15 %).
Safaa Qays
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Most reinforced concrete buildings were constructed with rectangular or square columns. To satisfy the structural requirements, the cross-section size of these types of columns is much large than the thickness of the partitions. As a result, a part of these columns is protruded out the walls, certainly. The emergence of the column edges, out of partitions, has many architectural or service disadvantages. To overcome the effects of these limitations, a high strength concrete can be used in columns’ construction to produce columns with small cross-sectional dimensions. But this solution may results in more slender columns. Thus the problem of instability may be faced. Actually, this problem is difficult to be avoided with traditional columns. In this study, the modern types of columns called Specially Shaped Reinforced Concrete (SSRC) columns are proposed to be used in the construction to overcome the limitations mentioned above. Consequently, this research is conducted to study the structural response of slender columns with special cross-sectional configuration subjected to compression. The study comprises three parts; analytical, experimental, and numerical studies. From the analytical study, the computer program is constructed to evaluate the strength of SSRC columns, the analytical results are compared with experimental results of sixteen column specimens tested up to failure. Finally, these specimens, in addition to twelve specimens for the parametric study were simulated using the nonlinear finite element program (Abaqus). The research includes three types of slender columns with special shaped: crucifom (+), T, and L-shaped columns, the results of these columns were compared with those of square-shaped columns. The cross-sectional area of all specimens was the same of 180 cm2. The variables studied in this study were: the cross-sectional shape, slenderness ratio, and the eccentricity of the load. The ultimate strength reached by numerical models analyzed by the proposed computer program or by Abaqus softwear was compared with the test results. The results showed good agreement between numerically predicted values and those recorded experimentally. Besides, the study showed that the use of SSRC led to improve the strength, especially with a high value of a slenderness ratio, as well the deformations were reduced as compared with equivalent square-shaped specimens. Also, the Increase of the column’s slenderness ratio led to a reduction in strength for all types of specimens. With the column’s slenderness ratio does not exceed 40, it was observed that the strength was slightly affected, e.g., the maximum loss in strength approximately 10%, while this effect becomes larger with slenderness ratio more than 40 reached to 35% when slenderness ratio equal to 80. At the end of the study, two design approaches were proposed to evaluate the strength of SSRC columns under concentric loading. Briefly, the results show a good structural response of SSRC as compared with square-shaped columns. However, further studies are needed to establish the behavior of these types of columns, particularly with varying the state of loading.
Pawan Kumar
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This paper has done static and vibration response analysis of the sigmoid functionally graded piezoelectric (S-FGP) tapered plate under thermo-electric load with different even/uneven type porosity. The governing equations of plate motion are derived using first-order shear deformation theory (FSDT) based displacement fields with Hamilton’s principle, and material property distribution is considered as per sigmoid law in the thickness direction of the FGP plate. The obtained governing equations are solved using the higher-order finite element method (FEM) with nine noded interpolation functions with 63 degrees of freedom (DOFs) per element. Convergence and the comparison study have been performed to exhibit the efficacy of the present study. It is observed that parameters like the non-dimensional center deflection, non-dimensional stress, and non-dimensional frequency are decreased as the material gradient index increases. The positive and negative types of electric loading have considerable effects on the pre/post type buckling configuration of the porous S-FGP tapered plate under thermal effect. The present analysis results can be used in the various smart structure application made of porous FGP materials.
Kuo Tian
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As a widely used non-destructive buckling experimental technique, the vibration correlation technique (VCT) is able to determine the buckling load without reaching the collapse point. Following the experimental procedure, the numerical implementation of VCT can be easily realized. That is to say, the numerical VCT (NVCT) can be used for predicting buckling load. In this paper, the derivation of NVCT formulas is firstly presented for cylindrical shells under axial compression load. Aiming at accelerating the repeated eigenvalue analysis in NVCT, the combined approximation (CA) method is combined with NVCT. Then, the computational procedure of CA-NVCT is provided. Aiming at the verification of the effectiveness of the CA-NVCT, three analysis examples are carried out including variable-stiffness composite cylindrical composite shell, isotropic cylindrical shell and composite cylindrical shell with various types of imperfections. Finally, an optimization design is carried out to improve the buckling load of a composite cylindrical shell against imperfections based on the CA-NVCT. In comparison to results obtained by buckling experiments and typical buckling numerical methods, the high prediction efficiency and accuracy of the CA-NVCT in buckling analysis and optimization are verified.
Ehsan Noroozinejad Farsangi
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In this study, the combination of magnetorheological dampers and tuned mass dampers (MR + TMD) as a hybrid control system is investigated on a 15-story shear building where MR damper is attached to the TMD to generate active control force of TMD. The seismic responses of the structure are reduced by employing MR + TMD on rooftop of the structure. The MR damper's control voltage is generated by combining IT2FLC and FOPID. The FOPID + IT2FLC, TMD, and control voltage parameters are optimized using the observer-teacher-learner-based optimization (OTLBO) algorithm to minimize the maximum displacement of the building rooftop under far-field and near-field earthquake excitations. To conduct additional research, the same method was used to mitigate structural responses for PID, FOPID, IT2FLC, and a combination of fuzzy logic type-1 (FLC) and FOPID (FOPID + FLC). All of these controllers' performances in mitigating seismic responses are compared to those of the uncontrolled system and to each other. The results indicate that FOPID + IT2FLC outperforms PID, FOPID, and FOPID + FLC controllers. Additionally, the building's rooftop displacement was reduced by an average of 35.06% using the FOPID + IT2FLC system for sixteen far-field and near-field earthquake records. Moreover, the hybrid MR + TMD system performs better than other conventional controllers.
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Space frame structures