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CONTENTS
Volume 88, Number 1, October10 2023
 

Abstract
In this study, forced vibration behavior of a piezo magneto electric sandwich Timoshenko beam is investigated. It is assumed a sandwich beam with porous core and graphene platelet reinforced composite (GPLRC) in facesheets subjected to magneto-electro-elastic and temperature-dependent material properties. The magneto electro platelets are under linear function along with the thickness that includes a cosine function and magnetic and electric constant potentials. The governing equations of motion are derived using modified strain gradient theory for microstructures. The effects of material length scale parameters, temperature change, different distributions of porous, various patterns of graphene platelets, and the core to face sheets thickness ratio on the natural frequency and excited frequency of a sandwich Timoshenko beam are scrutinized. Various size-dependent methods effects such as MSGT, MCST, and CT on the natural frequency is considered. Moreover, the final results affirm that the increase in porosity coefficient and volume fractions lead to an increase in the amount of natural frequency; while vice versa for the increment in the aspect ratio. From forced vibration analysis, it is understood that by increasing the values of volume fraction and the length thickness of GPL, the maximum deflection of a sandwich beam decreases. Also, it is concluded that increasing the temperature, the thickness of GPL, and the initial force leads to a decrease in the maximum deflection of GPL. It is also shown that resonance phenomenon occurs when the natural and excitation frequencies become equal to each other. Outcomes also reveal that the third natural frequency owns the minimum value of both deflection and frequency ratio and the first natural frequency has the maximum.

Key Words
forced vibration; graphene platelets reinforced composite; piezo magnetic-electric; porous core; temperature dependent material properties; Timoshenko sandwich beam

Address
Mohammad Safari, Mehdi Mohammadimehr and Hossein Ashrafi: Department of Solid Mechanics, Faculty of Mechanical Engineering, University of Kashan, Ghotb Ravandi Blvd., Kashan, Iran

Abstract
Seismic risk assessment studies are one of the most crucial instruments for mitigating casualties and economic losses. This work utilizes fragility curves to evaluate the seismic risk of single-story precast buildings, which are generally favored in Marmara's organized industrial zones. First, the precast building stock in the region has been categorized into nine sub-classes. Then, seven locations in the Marmara region with a high concentration of industrial activities are considered. Probabilistic seismic hazard assessments were conducted for both the soil-dependent and soil-independent scenarios. Subsequently, damage analysis was performed based on the structural capacity and mean fragility curves. Considering four different consequence models, 630 sub-class-specific loss curves for buildings were obtained. In the current study, it has been determined that the consequence model has a significant impact on the loss curves, hence, average loss curves were computed for each case investigated. In light of the acquired results, it was found that the loss ratio values obtained at different locations within the same region show significant variation. In addition, it was observed that the structural damage states change from serviceable to repairable or repairable to unrepairable. Within the scope of the study, 126 average loss functions were presented that could be easily used by non-experts in earthquake engineering, regardless of structural analysis. These functions, which offer loss ratios for varying hazard levels, are valuable outputs that allow preliminary risk assessment in the region and yield sensible outcomes for insurance activities.

Key Words
consequence models; fragility curves; hazard analysis; precast buildings; loss functions

Address
Ali Yesilyurt: Department of Earthquake Engineering, Disaster Management Institute, Istanbul Technical University, 34469, Istanbul, Turkey
Oguzhan Cetindemir: Department of Civil Engineering, Gebze Technical University, 41400, Kocaeli, Turkey
Seyhan O. Akcan: Department of Civil Engineering, Bogazici University, 34342, Istanbul, Turkey
Abdullah C. Zulfikar: Department of Civil Engineering, Gebze Technical University, 41400, Kocaeli, Turkey

Abstract
This paper presents a finite element (FE) simulation of eccentrically loaded lightweight aggregate concrete-encased steel (LACES) columns with H-shaped steel sections, analytical equations are also established to estimate the columns' axial and bending moment interaction capacities. The validity of the proposed models is checked by comparing the results with experimental data. Good agreements between the test and proposed models' results are found with acceptable agreements. Moreover, design parameters, including the lightweight aggregate concrete (LWAC) strength, eccentricity, column slenderness ratio, and confinement, are studied using the FE analysis, and their efficiency factors are discussed. The results show that the ultimate axial capacity of the LACES composite columns subjected to eccentric loading is negatively affected by the increase in the columns' height, but it is positively affected by the increase of the confinement. Increasing the eccentricity and columns' height reduced the columns' stiffness. In addition, the ultimate capacity of the LACES column is significantly influenced by the LWAC strength and eccentricity, where the ultimate capacity of the LACES column is significantly increased by increasing LWAC strength, and it is remarkably decreased by increasing the eccentricity. When the eccentricity changed from zero to 70 mm, the ultimate axial capacity and stiffness decreased by 67.97% and 63.56%, respectively.

Key Words
concrete encased steel (CES) composite column; eccentric behavior; FE analysis; interaction diagram (ID); lightweight aggregate concrete (LWAC); steel reinforced concrete (SRC)

Address
Mostafa M.A. Mostafa: Civil Engineering Department, Faculty of Engineering, Al-Azhar University, Qena 83513, Egypt

Abstract
This paper handles the results of an extensive parametric study on the rotational stiffness of the flexible base connection using ABAQUS program. The results of the parametric study show the relation between the applied moment and the relative rotation for 96 different base connections. The configurations of the studied connections considered different numbers, diameters, and spacing of the anchor bolts along with different thicknesses of the base plate to investigate the effect of these parameters on the rotational stiffness behavior. The results of the previous parametric research used through the whale optimization algorithm (WOA) to detect different equation formulation of the moment-rotation (M-or) equation to detect optimum equation simulates the general nonlinear rotational behavior of the flexible base connection considering all variables used in the parametric study. WOA is a relatively new promising algorithm, which is used in different types of optimization problems. For more verification, the classical genetic algorithm (GA) is used to make a comparison with WOA results. The results show that WOA is capable of getting an optimum equation of the M-or relation, which can be used to simulate the actual rotational stiffness of the flexible base connections. The rotational stiffness at H/150 can be calculated using WOA (1) method and be used as a design aid for engineering design.

Key Words
flexible base connection; flexural stiffness; genetic algorithm; rotational stiffness; whale optimization algorithm

Address
Mahmoud T. Nawar: Engineering Management Department, College of Engineering, Prince Sultan University, 11586 Riyadh, Saudi Arabia; Department of Structural Engineering, Zagazig University, Zagazig, Egypt
Ehab B. Matar, Hassan M. Maaly, Ahmed G. Alaaser: Department of Structural Engineering, Zagazig University, Zagazig, Egypt
Osman Hamdy: Department of Civil Engineering, Zagazig Higher Institute of Engineering & Technology, Zagazig, Egypt

Abstract
With the gradual implementation of long-span suspension bridges into high-speed railway operations, the main beam's bending stiffness contribution to the live load response permanently grows. Since another critical control parameter of railway suspension bridges is the beam-end rotation angle, it should not be ignored by treating the main beam deflection as the only deformation response. To this end, the current study refines the existing method of the main cable shape and simply supported beam bending moment analogy. The bending stiffness of the main beam is considered, and the main beam

Key Words
analytical method; beam-end rotation angle; gravity stiffness; live load; main beam deflection; suspension bridge

Address
Wen-ming Zhang, Jia-qi Chang, Xing-hang Shen, Xiao-fan Lu: The Key Laboratory of Concrete and Prestressed Concrete Structures of the Ministry of Education, Southeast University, Nanjing 211189, China
Tian-cheng Liu: CCCC Highway Bridges National Engineering Research Centre CO., Ltd., Beijing 100088, China

Abstract
The reinforced concrete (RC) structures might need strengthening or upgradation due to adverse environmental conditions, design defects, modification requirements, and to prolong the expected lifespan. The RC beams have been efficiently strengthened using the near surface mounted (NSM) approach over the externally bonded reinforcing (EBR) system. In this study, the performance of RC beam elements strengthened with NSM-steel rebars was investigated using an experimental program and nonlinear finite element modeling (FEM). Nine medium-sized, rectangular cross-section RC beams total in number made up for the experimental evaluation. The beams strengthened with varying percentages of NSM reinforcement, and the number of grooves was assessed in four-point bending experiments up to failure. Based on the experimental evaluation, the load-displacement response, crack features, and failure modes of the strengthened beams were recorded and considered. According to the experimental findings, NSM steel greatly improved the flexural strength (up to about 84%) and stiffness of RC beams. The flexural response of the tested beams was simulated using a 3D non-linear finite element (FE) model. The findings of the experiments and the numerical analysis showed good agreement. The effect of the NSM groove and reinforcement on the structural response was then assessed parametrically.

Key Words
crack characteristics; finite element modeling; flexural strengthening; NSM-steel

Address
Md. Akter Hosen, Khalid Ahmed Al Kaaf: Department of Civil and Environmental Engineering, College of Engineering, Dhofar University, PO Box 2509, PC 211, Salalah, Oman
A.B.M. Saiful Islam: Department of Civil & Construction Engineering, Imam Abdulrahman Bin Faisal University, 31451, Dammam, Saudi Arabia
Mohd Zamin Jumaat: Department of Civil Engineering, Faculty of Engineering, University of Malaya, 50603, Kuala Lumpur, Malaysia
Zaheer Abbas Kazmi: Department of Civil & Construction Engineering, Imam Abdulrahman Bin Faisal University, 31451, Dammam, Saudi Arabia

Abstract
An accurate and highly efficient inverse element labelled iPCB is developed based on the inverse finite element method (iFEM) for real-time shape estimation of plane-curved structures (such as arch bridges) utilizing onboard strain data. This inverse problem, named shape sensing, is vital for the design of smart structures and structural health monitoring (SHM) procedures. The iPCB formulation is defined based on a least-squares variational principle that employs curved Timoshenko beam theory as its baseline. The accurate strain‒displacement relationship considering tension-bending coupling is used to establish theoretical and measured section strains. The displacement fields of the isoparametric element iPCB are interpolated utilizing nonuniform rational B-spline (NURBS) basis functions, enabling exact geometric modelling even with a very coarse mesh density. The present formulation is completely free from membrane and shear locking. Numerical validation examples for different curved structures subjected to different loading conditions have been performed and have demonstrated the excellent prediction capability of iPCBs. The present formulation has also been shown to be practical and robust since relatively accurate predictions can be obtained even omitting the shear deformation contributions and considering polluted strain measures. The current element offers a promising tool for real-time shape estimation of plane-curved structures.

Key Words
inverse finite element method; plane-curved structures; shape sensing; strain sensors; Timoshenko beam

Address
Runzhou You, Liang Ren, Tinghua Yi and Hongnan Li: School of Civil Engineering, Dalian University of Technology, No.2 Linggong Road, Ganjingzi District, Dalian, Liaoning, PR China

Abstract
In this study, circular thin-walled reinforced high strength concrete-filled steel tube (RHSCFST) stub columns with various tube thicknesses (i.e., 1.8, 2.5 and 3.0mm) and reinforcement ratios (i.e., 0, 1.6%, 2.4% and 3.2%) were fabricated to explore the influence of these factors on the axial compressive behavior of RHSCFST. The obtained test results show that the failure mode of RHSCFST transforms from outward buckling and tearing failure to drum failure with the increasing tube thickness. With the tube thickness and reinforcement ratio increased, the ultimate load-carrying capacity, compressive stiffness and ductility of columns increased, while the lateral strain in the stirrup decreased. Comparisons were also made between test results and the existing codes such as AIJ (2008), BS5400 (2005), ACI (2019) and EC4 (2010). It has been found that the existing codes provide conservative predictions for the ultimate load-carrying capacity of RHSCFST. Therefore, an accurate model for the prediction of the ultimate load-carrying capacity of circular thin-walled RHSCFST considering the steel reinforcement is developed, based on the obtained experimental results. It has been found that the model proposed in this study provides more accurate predictions of the ultimate load-carrying capacity than that from existing design codes.

Key Words
axial compression; circular thin-walled stub column; concrete-filled steel tube; ductility; high strength concrete; ultimate loading-carrying capacity

Address
Meng Chen, Yuxin Cao and Ye Yao: School of Resources and Civil Engineering, Northeastern University, Shenyang, 110819, China

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