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CONTENTS
Volume 38, Number 3, September 2026
 

Abstract
Steel fiber reinforced concrete (SFRC) is a material with increased tensile strength and residual capacity compared to traditional plain concrete. SFRC has seen wider adoption in multiple countries following its inclusion in building codes that specify minimum requirements for strength and residual capacity. Numerous models have been developed to relate the mechanical properties of SFRC to its mixture characteristics. Empirical equations have been predominantly utilized in these studies, whereas models leveraging Machine Learning techniques remain relatively underexplored. This paper introduces an artificial neural network (ANN) approach for estimating the mechanical properties of SFRC. To this end, a database comprising results from 3- and 4-point bending tests (3PBT, 4PBT), double punch tests (DPT), splitting tensile tests (STT) and shear tests (SHT) was assembled and used as input data for training both ANN and traditional models. The results show that artificial neural networks (ANNs) outperform traditional empirical models in predicting SFRC's mechanical properties, achieving correlation coefficients above 0.9 with minimal root mean square errors and mean average pondered errors for indirect-tensile strength under STT, and residual flexural-tensile strengths under 3PBT, 4PBT, and DPT. A GUI tool has been developed and is included with both models to support user applications.

Key Words
double punch; neural networks 3PBT; neural networks 4PBT; shear; splitting tensile; steel fiber reinforced concrete

Address
Julian Carrillo: 1) Department of Civil Engineering, Universidad Militar Nueva Granada, Colombia; 2) Colombian Earthquake Engineering Research Network, Colombia
Esteban Lasso: Department of Civil Engineering, Universidad Militar Nueva Granada, Colombia
Orlando Arroyo: 1) Department of Civil Engineering, Universidad Industrial de Santander, Colombia; 2) Colombian Earthquake Engineering Research Network, Colombia

Abstract
To investigate the dynamic response of fresh concrete under surface vibration, a mesoscopic model of fresh concrete subjected to surface vibration was established using the Discrete Element Method (DEM). The evolution characteristics of particle velocity fields, contact force chain networks, and internal energy absorption fields during the vibration process were systematically analyzed. The results indicate that the particle velocity field exhibits an axisymmetric distribution with the vertical centerline of the specimen as the symmetry axis. The velocity magnitude attenuated in a "fan-shaped" pattern from the bottom of the surface vibrator and transitioned to a "U-shaped" distribution, with the velocity magnitude decreasing from 10-1 m/s to 10-2 m/s, representing a significant attenuation range. The contact force chain network initially formed loop structures, subsequently evolved into "root-like" configurations, and ultimately underwent buckling to form buckled structures. The probability of normal contact force chains decreased with an increase in the normalized contact force (defined as contact force/average contact force), while the probability of tangential contact force chains increased initially and subsequently decreased with the normalized contact force. During vibration, the translational kinetic energy increased rapidly initially and then gradually stabilized, whereas the rotational kinetic energy increased initially, decreased subsequently, and finally stabilized. The average translational kinetic energy of particles in the entire specimen was 0.098 J, and the average rotational kinetic energy was approximately 0.0007 J, indicating that the rotational kinetic energy of particles was negligible compared to the translational kinetic energy. These findings provide valuable insights into the compaction mechanisms of fresh concrete under surface vibration and offer guidance for optimizing surface vibration in concrete construction.

Key Words
compactness; discrete element; energy; fresh concrete; mesoscopic dynamic response; surface vibration

Address
Linjiang Yu, Qiuyue Chen, Liping He: China Communications Fourth Navigation Engineering Bureau Co., LTD., Guangzhou 510290, China
Zhenghong Tian: Hohai University, College of Water Conservancy and Hydropower, Nanjing, 210024, China

Abstract
Shrinkage-induced cracking is a critical durability concern in reinforced concrete (RC) slabs, where reinforcement detailing and boundary restraint interact to control crack initiation, propagation, and serviceability performance. In this study, the Concrete Damage Plasticity (CDP) model implemented in Abaqus was employed to simulate shrinkage-induced cracking under varying reinforcement ratios (0.5%, 1.0%, 1.5%), boundary restraint conditions (full versus one-edge restraint), cover depths, and subgrade friction coefficients. The results revealed that reinforcement and restraint act in a coupled manner to dictate crack morphology: higher reinforcement ratios refined crack networks and delayed initiation, while full-edge restraint promoted early stress concentration and through-crack formation. Quantitative indicators derived from the scalar stiffness degradation field (SDEG>=0.85) confirmed a non-monotonic effect of reinforcement, as the crack-affected fraction decreased from 0.104 at 0.5% to 0.067 at 1.0%, before rising again to 0.124 at 1.5%. Orientation analysis further showed that dominant cracks rotated from centrally nucleated perpendicular bands under full restraint to oblique, parallel fissures under one-edge restraint. Despite these variations, the maximum crack span consistently reached 3000 mm, while slabs with reinforcement ratios not less than 1.0% maintained maximum crack opening displacement (COD) below 0.3 mm, consistent with ACI 224R serviceability recommendations. This study demonstrates the capability of the CDP framework to capture shrinkage cracking behavior and establishes quantitative metrics that bridge numerical results with code-based crack control criteria, providing practical guidance for reinforcement detailing and restraint management in slab design.

Key Words
boundary restraint; concrete damage plasticity (CDP); cover depth; finite element analysis; reinforcement ratio; shrinkage cracking

Address
China Construction Third Engineering Bureau International Co., Ltd. (Oversea Business Department), No. 30, Beixing Road, Beijing 102600, China

Abstract
In order to prevent the destruction of ancient timber structures in the repair stage, the numerical simulation method is used in this study to analyze the influence of restorative disturbance on the mechanical behavior of ancient timber structures. Based on ABAQUS finite element software, a three-dimensional model of a timber frame is established incorporating an orthotropic elastoplastic material model based on the Hill yield criterion, using the column-and-tie timber structure as the research object. By controlling the energy conservation and hourglass effect of the system, the numerical simulation results are ensured to be effective and reliable. At the same time, the dynamic response characteristics of the column-and-tie timber structure under changes in parameters such as impact mass and impact velocity are studied, and corresponding repair recommendations are provided. The results show that the dynamic responses of the timber frame vary significantly under different working conditions. When the impact mass and impact velocity increase, the impact force and impact point displacement will increase with them, resulting in plastic strain damage, in which mortise-tenon joints are more prone to damage. The closer the impact position is to the joints, the more obvious the structural dynamic response will be. The results of this study can provide a reference for the problems of damage caused by restorative disturbance in the repair stage of column-and-tie timber structures.

Key Words
column-and-tie timber structures; impact response; numerical simulation; plastic strain damage; restorative disturbance

Address
Yunxiang Hu, Jiachang Bai, Chunjin Lu, Yanan Cao: North Minzu University, No. 204, Wenchang North Street, Xixia District, Yinchuan 750001, Ningxia, China
Ping Zhao: Xi'an University of Architecture and Technology, No. 13, Yanta Road, Xi'an 710055, Shaanxi, China

Abstract
This study investigates the microstructure of fire-damaged ordinary Portland cement (OPC) and 10% zeolite concretes after exposure to 800 oC and subsequent re-curing. Specimens were heated and then naturally cooled before being re-cured in either water or moist air at 25 oC or 60 oC for 28, 56, or 90 days. Scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS) and X-ray diffraction (XRD) analyses revealed that rehydration products contributed to compressive strength and volume of permeable pore voids recovery in the OPC concrete. However, re-curing the zeolite concretes resulted in the formation of needle-shaped crystals, tentatively identified as thaumasite-ettringite solid solution. While extending the re-curing period initially led to thaumasite formation, its subsequent decomposition at room temperature was observed. The combined volume expansion of thaumasite and rehydration products reduced the volume of permeable pore voids after re-curing. Re-curing at a 60 oC water bath prevented the formation of these needle-shaped crystals due to their instability at elevated temperatures. Regardless of the concrete mixture, specimens re-cured at 60 oC exhibited lower compressive strength compared to those re-cured at 25 oC. However, the re-curing temperature did not significantly affect the volume of permeable pore voids.

Key Words
microstructure; re-curing; rehydration reactions; thaumasite-ettringite solid solution; zeolite

Address
Hamed Kharrazi, Mohammad Shekarchi: School of Civil Engineering, College of Engineering, University of Tehran, Tehran, Iran
Babak Ahmadi: Concrete Technology Department, Road, Housing, and Urban Development Research Center (BHRC), Tehran, Iran

Abstract
This study investigated reinforcing bar corrosion, which affects the durability and structural safety of deteriorated reinforced concrete structures owing to aging, and the reduction in tensile strength among the mechanical property changes caused by it. Reinforcing bar corrosion leads to cross-sectional, material strength, and bond strength losses, impacting the mechanical properties, failure modes, and seismic performance of all members. To understand this, the expected corrosion of reinforcing bar specimens was estimated based on the amount of charge passing through the proposed circuit over a certain period, according to Faraday's law. The developed quantification method could be used to experimentally predict the corrosion characteristics of the reinforcing bar. Based on the results of monotonic tensile tests on 210 accelerated corroded reinforcing bar specimens, an appropriate reduction formula for the mechanical property of tensile strength loss was proposed. The validity of this formula was verified through the application of a validated nonlinear finite element analysis to deteriorated solid reinforced concrete column specimens—such as those subjected to aging—and by comparing and analyzing the experimental results.

Key Words
Faraday's law; nonlinear finite element analysis; reduction formula; reinforcing bar corrosion; tensile strength

Address
Tae-Hoon Kim, Choon-Seok Bang, Yun-Suk Kang, Leehyeon Kim: Track & Civil Infrastructure Division, Korea Railroad Research Institute, 176, Cheoldobangmulgwan-ro, Uiwang-si, Gyeonggi-do, 16105, Republic of Korea
Chang-Ho Sun, Ick-Hyun Kim: Department of Civil and Environmental Engineering, University of Ulsan, 93, Daehak-ro, Nam-gu, Ulsan-si, 44610, Republic of Korea

Abstract
This paper presents analytical and numerical approaches for predicting the interaction diagrams of the axial load-bending moment (P-M) and the moment-curvature (M-Psi) behaviour of reinforced concrete columns (RCC) reinforced with fiber-reinforced polymers (FRP) bars. The proposed models are based on strain compatibility and internal force equilibrium and were validated against 95 full-scale FRP bar RCC (FRP-RCC) available in the literature. A comprehensive parametric study was conducted to examine the influence of concrete compressive strength (fc'), the type and longitudinal reinforcement ratio of FRP bars (rhof), and the column slenderness ratio (kl/r) on the P-M interaction and the M-Psi relationship of FRP-RCC. The enhancement in axial load carrying capacity of carbon fiber reinforced polymer (CFRP) RCC and glass fiber reinforced polymer (GFRP) RCC, resulting from an increased rhof, was observed to be more significant in normal strength concrete (NSC) columns compared to high strength concrete (HSC) columns. However, when the axial load eccentricity increased, the enhancement in axial resistance of NSC columns (NSCC) and HSC columns (HSCC) due to an increase in rhof became approximately similar. Furthermore, considering the moment-curvature (M-Psi) relationship, increasing both the concrete compressive strength and FRP reinforcement ratio enhanced the flexural capacity and bending stiffness of RCC. Additionally, it was concluded that increasing rhof substantially increased the bending stiffness of RCC, particularly under moderate eccentricity.

Key Words
FRP bar; high strength concrete columns; interaction diagram; moment-curvature relationship; normal strength concrete columns

Address
İsmet Vapur, İlker F. Kara: Department of Civil Engineering, Mersin University, Mersin, 33110, Türkiye
Ashraf F. Ashour: Faculty of Engineering and Digital Technologies, University of Bradford, Bradford, UK

Abstract
This study presents a BEM model within a Multiscale Approach to model the mechanical behaviour of concrete with partial and total replacement of natural coarse aggregates (NCA) by recycled coarse aggregates (RCA) from construction and demolition waste (CDW). The Representative Volume Element (RVE) concept is adopted to represent the heterogeneous microstructure of the material, and the fracture process in the interfacial transition zone (ITZ) is modelled using cohesive-contact finite elements superposed on the BEM interface elements. Additionally, we consider the plasticity of the mortar matrix, while the aggregates are modelled as elastic. Different parameters are adopted for natural and recycled coarse aggregates, as well as for the cohesive-contact finite elements at the ITZ around the recycled aggregates. Eight different replacement percentages are adopted for aggregates, and the numerical results are compared with experimental results for 0%, 49,68%, and 100% of replacement. We show that the proposed model is stable and can reproduce the experimental results up to the peak load.

Key Words
boundary element method; cohesive fracture; concrete; multiscale modelling; recycled coarse aggregate; RVE

Address
Civil Engineering Department, Federal University of Catalão (UFCAT), Av. Dr. Lamartine Pinto de Avelar, 1120, Vila Chaud - CEP 75704-020 Catalão - GO Brazil

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