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CONTENTS
Volume 84, Number 2, October25 2022
 


Abstract
Corrosion of steel reinforcement is considered as the main cause of concrete structures deterioration, especially those under humid environmental conditions. Hence, fiber reinforced polymer (FRP) bars are being increasingly used as a replacement for conventional steel owing to their non-corrodible characteristics. However, predicting the shear strength of beams reinforced with FRP bars still challenging due to the lack of robust shear theory. Thus, this paper aims to develop an explicit data driven based model to predict the shear strength of FRP reinforced beams using multi-objective evolutionary polynomial regression analysis (MOGA-EPR) as data driven models learn the behavior from the input data without the need to employee a theory that aid the derivation, and thus they have an enhanced accuracy. This study also evaluates the accuracy of predictive models of shear strength of FRP reinforced concrete beams employed by different design codes by calculating and comparing the values of the mean absolute error (MAE), root mean square error (RMSE), mean (u), standard deviation of the mean (o), coefficient of determination (R2), and percentage of prediction within error range of +-20% (a20-index). Experimental database has been developed and employed in the model learning, validation, and accuracy examination. The statistical analysis illustrated the robustness of the developed model with MAE, RMSE, u, o, R2, and a20-index of 14.6, 20.8, 1.05, 0.27, 0.85, and 0.61, respectively for training data and 10.4, 14.1, 0.98, 0.25, 0.94, and 0.60, respectively for validation data. Furthermore, the developed model achieved much better predictions than the standard predictive models as it scored lower MAE, RMSE, and o, and higher R2 and a20-index. The new model can be used in future with confidence in optimized designs as its accuracy is higher than standard predictive models.

Key Words
concrete beams, evolutionary polynomial regression analysis, FRP bars, shear strength, soft computing

Address
Saif Alzabeebee: Department of Roads and Transport Engineering, University of Al-Qadisiyah, Al-Qadisiyah, Iraq
Moahmmed K. Dhahir: Institute of Concrete Structures, Technical University Dresden, Dresden, Germany; Department of Civil Engineering, University of Al-Qadisiyah, Al-Qadisiyah, Iraq
Suraparb Keawsawasvong: Department of Civil Engineering, Thammasat School of Engineering, Thammasat University, Pathumthani, 12120, Thailand

Abstract
The use of electricity and communication between electronic devices is increasing daily, which makes the stability of electrical power supply vital. Since the 1990s, large earthquakes have occurred frequently causing considerable direct damage to electrical power facilities as well as secondary damage, such as difficulty in restoring functions due to the interruption of electric power supply. Therefore, it is very important to establish measures to protect electrical power facilities, such as transformers and switchboards, from earthquakes. In this study, a 154 kV transformer whose service life had expired was installed on the base fabricated by simulating the field conditions and conducting the shaking table tests. The dynamic characteristics and seismic behavior of the 154 kV transformer were analyzed through the resonance frequency search test and seismic simulation test that considers the front, rear, left, and right directions. Since the purpose of this study is to analyze the acceleration amplification in the bushing due to the acceleration amplification, the experimental results were analyzed focusing on the acceleration response and the converted acceleration amplification ratio rather than the failure due to the displacement response of the transformer. The seismic force amplification at the transformer bushing was evaluated by simulating the characteristics of electrical power facilities in South Korea, and compared with the IEC TS 61463 acceleration amplification factor. Finally, the amplification factor at zero period acceleration (ZPA) modified for each return period was summarized. The results of this study can be used as data to define the amplification factor at ZPA of the transformer bushing, simulating the characteristics of electrical power facilities in Korea.

Key Words
earthquakes, electricity, power supply, transformer, zero period acceleration

Address
Nakhyun Chun: Structural and Seismic Tech. Group, KEPCO Research Institute, Daejeon, 34056, Republic of Korea
Bubgyu Jeon, Sungwan Kim, Sungjin Chang: Seismic Research and Test Center, Pusan National University, Yangsan, 50612, Republic of Korea
Suwon Son: Department of Architectural and Civil Engineering, Kyungil University, Gyeongsan, 38428, Republic of Korea

Abstract
A strategic structure when exposed to direct hit of conventional bomb/projectile are severely damaged because of large amounts of energy released by the impact and penetration of bomb. When massive concrete slabs suffer a direct hit, the energy released during impact and penetration process are able to easily break up large mass of concrete. When over stressed under such impact of bombs, the concrete structure fails showing brittle behavioural nature. This paper is intended to study and suggest the protective measures for structures used for strategic application by adopting a means to dissipate the large quantum of energy released. To quantitatively evaluate the force, displacement and energy in such scenario, a fine numerical model of the proposed layered structure of different combinations was built in ANSYS programme in which tri-nitrotoluene (TNT) explosive was detonated at penetration depth calculated for GP1000 Lbs bomb. The distinct blast mitigation effect of the proposed structure was demonstrated by adopting various layers/barriers created as protective measures for the strategic structure. The calculated result shows that the blast effect on the structure is potentially reduced due to provision of buster slab with sand cushioning provided as protective measure to the main structure. This concept of layered protective measures may be adopted for safeguarding strategic structures such as Domes, Tunnels and Underground Structures.

Key Words
buster slab; missile attack; protective layer; strategic attack

Address
Bishwajeet Choubey: CCE R&D South, Defence (R&D) Organization, Akbar Road, Secunderabad, 500009, India
Sekhar C. Dutta, Md. Ahsaan Hussain: Department of Civil Engineering, IIT (ISM) Dhanbad, 826004, India

Abstract
This paper presents experimental modal analysis and static load testing results to validate the accuracy of dynamic parameters-based damage locating indices in RC structures. The study investigates the accuracy of different dynamic-based damage locating indices compared to observed crack patterns from static load tests and how different damage levels and scenarios impact them. The damage locating indices based on mode shape curvature and mode shape fourth derivate in their original forms were found to show anomalies along the beam length and at the supports. The modified forms of these indices show higher sensitivity in locating single and multi-cracks at different damage scenarios. The proposed stiffness reduction index shows good sensitivity in detecting single and multi-cracks. The proposed anomalies elimination procedure helps to remove the anomalies along the beam length. Also, the adoption of the proposed weighting method averaging procedure and normalization procedure help to draw the overall crack pattern based on the adopted set of modes.

Key Words
anomalies elimination procedures; damage locating; dynamic parameters; modal testing; weighting and normalization procedures

Address
Moatasem M. Fayyadh: Asset Lifecycle, Sydney Water, 2150 NSW, Australia
Hashim Abdul Razak: Department of Civil Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia

Abstract
The mechanical behavior of prestressed concrete haunched beams (PSHBs) was investigated in depth using a finite element modeling technique in this study. The efficiency of finite element modeling was investigated in the first stage by taking into account a previous study from the literature. The first stage's findings suggested that finite element modeling might be preferable for modeling PSHBs. In the second stage of the research, a comprehensive parametric study was carried out to determine the effect of each parameter on PSHB load capacity, including haunch angle, prestress level, compressive strength, tensile reinforcement ratio, and shear span to depth ratio. PSHBs and prestressed concrete rectangular beams (PSRBs) were also compared in terms of capacity. Stochastic analysis was used in the third stage to define the uncertainty in PSHB capacity by taking into account uncertainty in geometric and material parameters. Standard deviation, coefficient of variation, and the most appropriate probability density function (PDF) were proposed as a result of the analysis to define the randomness of capacity of PSHBs. In the study's final section, a new equation was proposed for using symbolic regression to predict the load capacity of PSHBs and PSRBs. The equation's statistical results show that it can be used to calculate the capacity of PSHBs and PSRBs.

Key Words
finite element modeling; load capacity; parametric analysis; prestressed concrete haunched beams; prestressed concrete prismatic beams; stochastic analysis

Address
İsmail Özoğul: Department of Civil Engineering, Graduate School of Natural and Applied Sciences, Gaziantep University, Türkiye
Mehmet E. Gülşan: Department of Civil Engineering, Faculty of Civil Engineering, Gaziantep University, Türkiye

Abstract
In order to improve the cracking resistance of reinforced concrete and give full play to the advantages of prefabricated assembly structure in construction, prestressed reinforced concrete composite beam (PRCC) is proposed. Through the bending static test of seven I-shaped beam specimens, the bending failure modes and bearing capacity of PRCC and reinforced concrete composite beam are compared and analyzed, and the effects of prestress size, prestressed reinforcement layout and prestress application sequence on the flexural behavior of PRCC beams are studied. The results show that the cracking load and ultimate load of PRCC beams significantly increased after prestressing, and prestressed tendons can effectively control the crack development. With the increase of prestressing degree, the deformation resistance and bending stiffness of PRCC beams are increased. The application sequence of prestress has little influence on the mechanical properties of PRCC beams. The crack width, stiffness and normal section bearing capacity of PRCC beam are analyzed, and the calculated results are in good agreement with the experimental results.

Key Words
bending bearing capacity; crack width calculation; reinforced concrete composite beam; unbonded prestress

Address
Manxin Hu, Yong Yang, Yicong Xue: School of Civil Engineering, Xi'an University of Architecture & Technology, Xi'an, Shaanxi, China
Yunlong Yu: School of Civil Engineering, Xi'an University of Architecture & Technology, Xi'an, Shaanxi, China; Key Lab of Structural Engineering and Earthquake Resistance, Ministry of Education, China

Abstract
The use of lateral reinforcement in confined concrete columns can improve bearing capacity and deformability. The lateral responses of lateral reinforcement significantly influence the effective confining pressure on core concrete. However, lateral strain-axial strain model of concrete columns confined by lateral reinforcement has not received enough attention. In this paper, based on experimental results of 85 concrete columns confined by lateral reinforcement under axial compression, the effect of unconfined concrete compressive strength, volumetric ratio, lateral reinforcement yield strength, and confinement type on lateral strain-axial strain curves was investigated. Through parameter analysis, it indicated that with the same level of axial strain, the lateral strain slightly increased with the increase in the unconfined concrete compressive strength, but decreased with the increase in volumetric ratio significantly. The lateral reinforcement yield strength had slight influence on lateral strain-axial strain curves. At the same level of lateral strain, the axial strain of specimen with spiral was larger than that of specimen with stirrup. Furthermore, a lateral strain-axial strain model for concrete columns confined by lateral reinforcement under axial compression was proposed by introducing the effects of unconfined concrete compressive strength, volumetric ratio, confinement type and effective confining pressure, which showed good agreement with the experimental results.

Key Words
axial strain, confined concrete, lateral reinforcement, lateral strain, passive confinement

Address
Chongchi Hou: School of Civil Engineering, Shenyang Jianzhu University, 25 Hunnan Middle Road, Shenyang, China
Wenzhong Zheng: School of Civil Engineering, Harbin Institute of Technology, 73 Huanghe Road, Harbin, China

Abstract
Using non-destructive Acoustic Emission (AE) and optical Digital Image Correlation (DIC) methods, the momentcurvature behavior of steel and GFRP bars reinforced concrete beams under flexure was explored in this study. In the tension zone, laboratory studies were carried out on steel-RC and GFRP-RC beams with varying percentages of longitudinal reinforcement ratios of 0.33 %, 0.52%, and 1.11%. The distinct mechanism of cracking initiation and fracture progression of failure in steel-RC and GFRP-RC beams were effectively correlated and picked up using AE waveform characteristics of the number of AE hits and their amplitudes, AE energy as well as average frequency and duration. AE XY event plots and longitudinal strain profiles using DIC gives an online and real-time visual display of progressive AE activity and strains respectively to efficaciously depict the crack evolution and their advancement in steel-RC and GFRP-RC beams. They display a close matching with the micro and macro-cracks visually observed in the actual beams at various stages of loading.

Key Words
acoustic emission, digital image, hits, moment-curvature, surface strains

Address
Gaurav Sharma: Civil Engineering Department, Amity University, Uttar Pradesh, 201310, India
Shruti Sharma: Civil Engineering Department, Thapar Institute of Engineering and Technology, Patiala, 147004, India
Sandeep K. Sharma: Mechanical Engineering Department, Thapar Institute of Engineering and Technology, Patiala, 147004, India

Abstract
In this paper, a particular type of all-steel HSS brace members with a locally reduced cross-sectional area was experimentally and numerically investigated. The brace member was strengthened against local buckling with inner and outer boxes in the reduced area. Four single-span braced frames were tested under cyclic lateral loadings. Specimens included a simple steel frame with a conventional box-shaped brace and three other all-steel reduced section buckling-restrained braces. After conducting the experimental program, numerical models of the proposed brace were developed and verified with experimental results. Then the length of the proposed fuse was increased and its effect on the cyclic behavior of the brace was investigated numerically. Eventually, the brace was detailed with a fuse-to-brace length of 30%, as well as the cross-sectional area of the fuse-to-brace of 30%, and the cyclic behavior of the system was studied numerically. The study showed that the proposed brace is stable up to a 2% drift ratio, and the plastic cumulative deformation requirement of AISC (2016) is easily achieved. The proposed brace has sufficient ductility and stability and is lighter, as well as easier to be fabricated, compared to the conventional mortar-filled BRB and all-steel BRB.

Key Words
concentric brace, cyclic curve, ductility, energy dissipation, HSS box, local buckling, reduced cross-section

Address
Elham Parsa, Mohammad Ghazi and Farhang Farahbod: Department of Civil Engineering, College of Engineering, West Tehran Branch, Islamic Azad University, Tehran, 14687-63785, Iran

Abstract
Lumped damage mechanics (LDM) is a recent nonlinear theory with several applications to civil engineering structures, such as reinforced concrete and steel buildings. LDM apply key concepts of classic fracture and damage mechanics on plastic hinges. Therefore, the lumped damage models are quite successful in reproduce actual structural behaviour using concepts well-known by engineers in practice, such as ultimate moment and first cracking moment of reinforced concrete elements. So far, lumped damage models are based in the strain energy equivalence hypothesis, which is one of the fictitious states where the intact material behaviour depends on a damage variable. However, there are other possibilities, such as the energy equivalence hypothesis. Such possibilities should be explored, in order to pursue unique advantages as well as extend the LDM framework. Therewith, a lumped damage model based on the energy equivalence hypothesis is proposed in this paper. The proposed model was idealised for reinforced concrete structures, where a damage variable accounts for concrete cracking and the plastic rotation represents reinforcement yielding. The obtained results show that the proposed model is quite accurate compared to experimental responses.

Key Words
energy equivalence hypothesis; lumped damage mechanics; precast tunnel segments; reinforced concrete

Address
Renério Pereira Neto, Daniel V.C. Teles, Camila S. Vieira: Laboratory of Mathematical Modelling in Civil Engineering, Post-Graduate Programme in Civil Engineering, Federal University of Sergipe, São Cristóvão, Sergipe, Brazil
David L.N.F. Amorim: Laboratory of Mathematical Modelling in Civil Engineering, Post-Graduate Programme in Civil Engineering, Federal University of Sergipe, São Cristóvão, Sergipe, Brazil; Post-Graduate Programme in Civil Engineering, Federal University of Alagoas, Maceió, Alagoas, Brazil


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