Browsing by Author "Hao, Rui"
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Item Computational engine for finite element digital twins of structural dynamics via motion data(Elsevier BV, 2024-10-01) Zhang, Youqi; Hao, Rui; Niiranen, Jarkko; Yang, Yaohua; Brühwiler, Eugen; Su, Di; Nagayama, Tomonori; Department of Civil Engineering; Structures – Structural Engineering, Mechanics and Computation; University of Tokyo; Swiss Federal Institute of Technology LausanneTypical structural health monitoring systems employ limited numbers of sensors capable of measuring discrete local behaviours. However, practical challenges arise as these sensor arrays cannot cover all local areas of interest. To address this challenge, this article introduces a novel method for twinning structural dynamic behaviour by constructing a finite-element-model-based digital twin, enabling the observation of non-sensor positions crucial for downstream tasks. The approach utilises streaming monitoring data, e.g., displacement and acceleration, as external dynamic loads to reproduce the dynamic response of the entire physical structure. Subsequently, the dynamic behaviour of specific non-sensor locations can be extracted from the digital twin. The method is formulated as a local-global-local procedure. To validate the proposed approach, two virtual experiments were conducted on: 1) a simply supported Euler-Bernoulli beam subjected to static loads and 2) a high-fidelity finite element model of a composite bridge carrying dynamic traffic loads. The results demonstrate remarkable accuracy in reproducing both global and local behaviours, facilitating observations at non-sensor positions for downstream estimations.Item Critical distance-based fatigue life evaluation of blunt notch details in steel bridges(Elsevier Science Ltd., 2023-02) Hao, Rui; Lehto, Pauli; Lin, Weiwei; Department of Civil Engineering; Department of Mechanical Engineering; Structures – Structural Engineering, Mechanics and Computation; Marine and Arctic TechnologyOrthotropic steel deck (OSD) is applied on many bridges around the world, but its drawback of being prone to fatigue has been a concern due to the damages observed. Fatigue cracks initiated from the blunt notch details in rib-to-floor beam connections have a different fatigue behavior compared to welded connections and deserve to be investigated further. To study the effect of notch radius on the fatigue performance of blunt notch detail, 27 specimens with different geometries were manufactured and tested with fatigue loads. The fatigue lives of specimens and their crack initiation locations were investigated, and the prediction on the fatigue life of notched specimens based on the theory of critical distance (TCD) was also conducted. For notched specimens made of S355, the predicted fatigue life using the TCD method is in good agreement with the experimental results. Also, it is found that the point method has higher accuracy compared to the line method and the use of one calibration curve of notched specimens could provide enough accuracy compared to the case when two calibration curves of notched specimens are used. By modifying the mathematical description of the stress distribution near the notch root, a new formulation of the critical distance-fatigue life relationship is here proposed and validated with the experimental results.Item Evolution of surface roughness of notched steel details under fatigue loading(Elsevier Ltd, 2023-12) Hao, Rui; Lin, Weiwei; Department of Civil Engineering; Structures – Structural Engineering, Mechanics and ComputationA fatigue crack initiates on the surface of the steel members, which can be attributed to the extrusions and intrusions caused by cyclic loading. The surface roughness parameters, including the statistical surface roughness and maximum surface roughness parameters, can characterize the increase in extrusion and intrusion. Six notched specimens were loaded with cyclic loading, and the evolution of the surface roughness parameters was monitored during the test to explore the characteristics of the surface roughness during the fatigue loading procedure in the high-cycle fatigue regime and clarify the effects of the initial surface finish and load ratio on the surface roughness evolution. Based on the test results, it was found that the 3D average surface roughness Sa and 3D root-mean-square surface roughness Sq were preferable for detecting the onset of fatigue cracks compared with the 2D average surface roughness Ra and 2D root-mean-square surface roughness Rq. The 3D maximum valley depth, Sv, was an effective indicator of the fatigue crack initiation location, except for compression-dominant fatigue loading. The evolution patterns of the 3D average surface roughness, Sa, and 3D root-mean-square surface roughness Sq during fatigue loading can be classified into three phases: instant response, damage accumulation, and crack-induced response. In addition, surface polishing is recommended for evaluation using 2D surface roughness parameters. However, it is not mandatory for evaluations using 3D surface roughness parameters. The effects of typical load ratios (0.1, −1, and 10) on the evolution pattern of the 3D statistical surface roughness parameters, especially in the instant response phase, were also investigated.Item Fatigue damage evaluation of cutout details in steel bridges(Aalto University, 2023) Hao, Rui; Markou, Athanasios, Dr., Aalto University, Finland; Rakennustekniikan laitos; Department of Civil Engineering; Structural Engineering, Mechanics and Computation; Insinööritieteiden korkeakoulu; School of Engineering; Lin, Weiwei, Prof., Aalto University, Department of Civil Engineering, FinlandFatigue damage is one of the most common and dangerous damage types in steel bridges, and many bridges are facing the challenge of ageing and its subsequent hazard risks. For steel bridges, the fatigue-prone details can be generally classified into two categories, welded and unwelded details. For welded details, the mechanism of fatigue crack initiation can be attributed to the initial weld defect introduced by the welding process, while for the unwelded structural details, the primary reasons for the fatigue crack initiation are distinguishable compared to that of welded ones. Fatigue damages in typical orthotropic steel decks are mostly found at rib-to-deck joints, rib-to-floor beam connections, butt weld connections, etc. In rib-to-floor beam connections, though the fatigue cracks initiated at welded joints and cutouts are both extensively observed, the latter attracts less attention, and its fatigue evaluation method is still not yet clear. Therefore, in this dissertation, the fatigue damage evaluation of cutout is performed. The primary goal of the research is to evaluate the possibility of fatigue crack initiation, and this overarching goal is further divided into three sub-goals: to detect the fatigue crack initiation in its early stage, to find a reliable theoretical method that is consistent with the civil engineering practice for predicting their fatigue lives, and to numerically predict their fatigue lives. To achieve these subgoals, laboratory fatigue tests on notched specimens with notch radii that are used in real bridges were first conducted, and for some specimens, the surface roughness parameters were also measured during the fatigue test. The surface roughness evolutions during the fatigue load were obtained, and effective crack detection parameters were also found. The prediction of fatigue life using the theory of critical distance was conducted, and a new formulation of critical distance-fatigue life relationship was proposed and validated with experimental data. In the numerical modelling prediction for fatigue, a new SWT model-based algorithm for the fatigue crack initiation life prediction of notched details in the high-cycle fatigue regime was proposed by considering the cycle-by-cycle fatigue damage accumulation, and the damage model was implemented by employing the UDMGINI subroutine written with Fortran code. A good agreement between the predicted fatigue initiation life and experimental results was confirmed. This study yielded three main conclusions regarding the assessment of fatigue in cutout details within the high-cycle fatigue regime. Firstly, the statistical surface roughness parameters proved effective in detecting fatigue crack initiation. Secondly, a new logarithmic formulation of the critical distance-fatigue life relationship was proposed. Lastly, a new SWT model-based algorithm for the fatigue crack initiation life prediction of notched details in high-cycle fatigue regime was proposed. These three key findings can serve as a foundation for evaluating fatigue damage in cutout details and make significant contributions to bridge engineering.Item Fatigue Life Prediction of Notched Details Using SWT Model and LEFM-Based Approach(MDPI AG, 2023-03) Hao, Rui; Wen, Zongyi; Xin, Haohui; Lin, Weiwei; Department of Civil Engineering; Structures – Structural Engineering, Mechanics and Computation; Xi'an Jiaotong UniversityThe fatigue crack initiation life of unwelded steel components accounts for the majority of the total fatigue life, and the accurate prediction of it is of vital importance. In this study, a numerical model utilizing the extended finite element method (XFEM) and Smith–Watson–Topper (SWT) model is established to predict the fatigue crack initiation life of notched details extensively used in orthotropic steel deck bridges. Using the user subroutine UDMGINI in Abaqus, a new algorithm was proposed to calculate the damage parameter of SWT under high-cycle fatigue loads. The virtual crack-closure technique (VCCT) was introduced to monitor crack propagation. Nineteen tests were performed, and the results were used to validate the proposed algorithm and XFEM model. The simulation results show that the proposed XFEM model with UDMGINI and VCCT can reasonably predict the fatigue lives of the notched specimens within the regime of high-cycle fatigue with a load ratio of 0.1. The error for the prediction of fatigue initiation life ranges from −27.5% to 41.1%, and the prediction of total fatigue life has a good agreement with the experimental results with a scatter factor of around 2.Item Fatigue Tests and Analysis on Welded Joints of Weathering Steel(MDPI AG, 2022-10) Sheng, Rongrong; Liu, Yuqing; Yang, Ying; Hao, Rui; Chen, Airong; Department of Civil Engineering; Structures – Structural Engineering, Mechanics and Computation; Tongji University; Anshan Iron and Steel Group Co., Ltd.To investigate the fatigue performance of vertical web stiffener to deck plate welded joints in weathering steel box girders, six specimens of the weathering steel (WS) Q345qNH, four specimens of WS Q420qNH, and four specimens of the plain carbon steel (CS) Q345q for comparison were tested by a vibratory fatigue testing machine, considering different steel grades, yield strengths, stiffener plate thicknesses, and weld types. The fatigue strength was evaluated based on S-N curves and the crack propagation was analyzed by linear elastic fracture mechanics (LEFM). The results show that the fatigue crack of the welded joints was initiated from the end weld toe of the deck plate and subsequently propagated both along the thickness of the deck plate and in the direction perpendicular to the stiffener plate. The fatigue crack initiation and propagation life of WS Q345qNH specimens were longer than those of CS Q345q specimens. The fatigue crack propagation life of WS Q345qNH specimens was longer than that of WS Q420qNH specimens, while the initiation life bore little relationship to the yield strength. Increasing the stiffener plate thickness effectively delayed crack initiation and slowed down its propagation. Compared with fillet welds, full penetration welds extended the fatigue crack propagation life, while no significant improvement was implied for the initiation life. The WS and CS specimens could be classified as having the same fatigue strengths by nominal stress, hot spot stress, and effective notch stress approaches, which were FAT 50, FAT 100, and FAT 225, respectively. Meanwhile, their material constants for LEFM were relatively close to each other.Item High-fidelity time-series data synthesis based on finite element simulation and data space mapping(Academic Press, 2023-10-01) Zhang, Youqi; Li, Zhenkun; Hao, Rui; Lin, Weiwei; Li, Lingfang; Su, Di; Department of Civil Engineering; Structures – Structural Engineering, Mechanics and Computation; Hong Kong Polytechnic University; University of TokyoDynamic responses can provide rich information for supporting the entire life cycle of structures, and they can either be measured from actual structures or simulated using the finite element (FE) method. For the FE simulation, insufficient fidelity of simulation data can significantly affect the confidence of analysis results, while FE model updating methods can partially address this problem by reducing the simulation error. However, most FE model updating methods inevitably update the hyperparameters of FE models using sophisticated algorithms with high computational complexities. Thus, one question was raised: whether there is a mapping that can transfer the FE simulation data to the corresponding measurement data directly without performing FE model updating? To achieve this, we proposed a data synthesis method using FE simulation and deep learning space mapping, which can be used to synthesise high-fidelity dynamic responses excited by some unseen load patterns in the measurement. A Dilated Causal Convolutional Neural Network (DCCNN) was designed for realising space mapping. Vibration experiments were conducted on both an I-shaped steel beam and the corresponding FE model to establish datasets and test the proposed method. The quality of the synthetic data was analysed in both the time domain and the frequency domain. The accurate amplitudes, natural frequencies, and mode shapes of the synthetic data successfully demonstrate the effectiveness of the proposed high-fidelity data synthesis method.Item Mechanical behavior of steel-concrete composite beams with discontinuous concrete deck(2021-08-23) Koski, Samu; Hao, Rui; Insinööritieteiden korkeakoulu; Lin, WeiweiBridge accessories are known to have an effect on stiffness of a bridge. In recent studies also presence of expansion joints between precast accessory elements and the joint positioning have been found to have an effect on the deck stiffness. Additionally stress concentrations are observed in bridge deck at the joint location. This thesis analyses load test data of two steel-concrete composite beams with different joint patterns in the concrete parts and conducts numerical analyses on both cases, in order to determine the effect of the joint location on strength and stiffness of the structure under negative bending moment. Furthermore, attempt is made to investigate formation of stress concentration at the joint locations observed in preceding research. In Case 1 the beam has a joint in the concrete part at the midpoint of the beam. In Case 2, two joints are placed in the concrete part, exactly halfway between midpoint and the support point on each side of the beam. The load type is negative three-point bending with concrete parts of the beams under tension. Both cases were loaded until measured force imposed on the beam started to decrease as displacement of the midpoint was increased. Numerical analyses were conducted on both cases using ANSYS finite element analysis software. Both cases were modeled with 3D components of exact specimen geometries using simplified shear connection. Load test results showed higher ultimate load capacity for Case 2. Case 2 was found to undergo plastic deformation at higher load compared to Case 1. In numerical analyses the models were loaded by imposing incremental displacement in 0.25 mm steps up to 10 mm. In Case 1 numerical model replicated load-displacement behavior with 4.9 % error and strain development in steel profile with 11.4 % error, while in Case 2 the error rate of numerical analysis was 5.8 % for load-displacement. However, up to 45 % differences were found in strain values compared to load test results in Case 2. Load test results suggest that the location of joints in concrete part does have a significant effect in the mechanical behavior of the beam. In neither case stress concentrations in the steel part were found to occur in the numerical analysis. However, stress concentration was observed in the reinforcement in the numerical analysis. Thesis contains a review of problems encountered in numerical analysis and proposes improvements for further research.Item Short-term and long-term behavior of RC beams strengthened by galvanized steel mesh laminate(ELSEVIER SCI LTD, 2022-07-18) Hao, Rui; Lin, Weiwei; Al-Nuaimi, Nasser A.; Hawileh, Rami A.; Abdalla, Jamal A.; Elshafie, Mohammed Z.E.B.; Department of Civil Engineering; Structures – Structural Engineering, Mechanics and Computation; Qatar University; American University of SharjahSteel reinforced polymers (SRP) are useful in a wide range of applications, including strengthening of existing reinforced concrete (RC) structures, due to their numerous advantages like high strength, low maintenance, light weight and low cost. As such, galvanized steel mesh (GSM) has emerged as an option in the strengthening of RC structures. Although numerous studies were performed on GSM strengthened RC beams, the durability of such strengthening systems is yet to be fully understood. This paper presents an experimental and numerical study to investigate the strengthening effect of GSM on RC beams as well as the time-depended behavior of RC beams with and without strengthening. Reinforced concrete beams without strengthening were used as control beams. For the strengthened beams, both high cord density galvanized steel mesh (HSM) and medium cord density galvanized steel mesh (MSM) were used after which the beams were exposed to Qatar atmospheric environment for different periods of time following 28 days of water curing. Finite element analyses using ABAQUS software were conducted to predict the mechanical behavior of the RC beams with and without strengthening. The results showed an improvement ranging from 46% ∼ 57% in the ultimate load of GSM strengthened beams, with a higher initial cracking load ranging from 3% ∼ 35% when compared to the unstrengthened beams. On the other hand, the time-dependent effect of the concrete has limited influence on the initial cracking load of both systems (before and after strengthening) while the ultimate load increased gradually with time due to the strength development of concrete. The results obtained from this study are useful in improving the design, construction, and maintenance of RC beams strengthened with GSM laminates.Item Structural behavior of steel-concrete composite beams with expansion joints in the concrete slab(2022-01-24) Hosseini, Mahmoud; Hao, Rui; Insinööritieteiden korkeakoulu; Lin, WeiweiThis master thesis comprises the hypothesis regarding the structural effects of concrete parapets on the overall strength of bridge structures. In design practice, concrete parapets of a bridge structure are treated only as a superimposed dead load. However, recent studies have shown that an increase in the load-bearing capacity of bridge structures is observable when concrete parapets are treated as structural elements. In this study the effect of the concrete parapets was examined on steel-concrete composite beams with expansion joints in the concrete slab. In first step the structural behavior of steel-concrete composite beams is studied through an experimental test, where beams were subjected to both negative and positive bending moments simulating the concrete parapets and bridge deck in a continuous bridge. In second step, experimental specimens are simulated using finite element analysis software, Abaqus. The numerical models proved a good agreement with experiment test and provided the framework for development of parametric analysis. Based on experimental studies and parametric analysis, it was found that for steel-concrete composite beams subjected to sagging bending moment expansion joints lead to smaller flexural rigidity, local instability failures in steel flange and crushing of concrete near expansion joints cross-sections. In steel-concrete composite beams subjected to hogging bending moment less tensile stress was observed in the steel web close to the cross-sections of the expansion joints. However, no significant change in the neutral axis and load-bearing capacity was observed.
