Structures最新文献

The sound barrier installed on high-speed railway bridges withstands repeated train-induced wind load, which may lead to concrete damage at its anchorage end. This paper focuses on the assessment of concrete static damage at the sound barrier anchorage end under train-induced wind loads. The nonlinear finite element model of the sound barrier anchorage system is established to analyze the stress distribution, strain distribution and static damage of concrete structure at the anchorage end under 400 km/h train-induced wind loads in respect of different bolt preloads. The simulated results illustrate that both mortar and concrete near bolt holes suffer a certain degree of tensile and compressive damage. The maximum tensile and compressive damage factor values for mortar and concrete are 0.930, 0.643 and 0.892, 0.434 respectively. In addition, the effects of train-induced wind load on the internal force of the sound barrier anchorage take nearly no account, with a maximum of only 0.68 %. The results indicate that bolt preload is the most significant factor for concrete static damage, while the train-induced wind load appears negligible. An appropriate bolt preload can avoid the concrete static damage of the sound barrier anchorage end, and guarantee the structural stability of the sound barrier.

Low-aspect-ratio reinforced concrete (RC) shear walls have been commonly used in several nuclear facilities in containment and safety-related structures. Despite being a potential alternative to reduce rebar congestion and subsequently minimize complex construction activities typically associated with nuclear facilities, there has been limited experimental research on investigating the impact of using high-strength reinforcement (HSR) on the seismic performance of such walls, particularly in a multi-storey context. This lack of research is mainly due to considerable challenges imposed when testing such multi-storey nuclear RC shear walls in most laboratories. Therefore, the current study presents the experimental results of two two-storey low-aspect-ratio nuclear RC shear walls that were tested utilizing the seismic hybrid simulation testing technique. In this respect, walls W1-NSR and W2-HSR were designed using normal-strength reinforcement (NSR) and HSR, respectively, where the two test walls had comparable capacities to allow for direct comparisons. Both walls were subjected to various ground motion levels, spanning from operational to design and beyond-design earthquake scenarios. The experimental findings are then presented to include the force-displacement responses, the multi-storey effects, ductility capacities, lateral and rotational stiffnesses, rebar strains, and cracking patterns of the test walls. Subsequently, an economic assessment was carried out to quantify the total rebar weights and the corresponding construction costs of such walls. In addition, the expected seismic repair costs were determined based on a three-dimensional digital image correlation technique that provided information on the damage states of the test walls under different earthquake levels. The results show that although W1-NSR and W2-HSR attained similar force and moment capacities, W2-HSR achieved a relatively higher ductility capacity than W1-NSR. However, larger cracks were observed in W2-HSR compared to W1-NSR, which was attributed to the associated larger rebar spacing in the former relative to the latter. The economic assessment results demonstrate that using HSR minimized the rebar weights and construction costs, while both walls had similar seismic repair costs at their design and beyond-design earthquake levels. Both the seismic performance and economic assessment results presented in the current study are expected to aid future editions of relevant design standards in adopting HSR in nuclear construction practice.

Surface waviness is crucial for the quality of components produced via the wire and arc additive manufacturing (WAAM) process. This study presents a novel method for predicting surface waviness, employing an advanced model to optimize process parameter configurations using a combination of Rank-Gaussian particle swarm optimization (RGPSO) and an Artificial Neural Network (ANN). The novelty of this process is that the RGPSO not only optimizes the hyperparameters of the ANN model to enhance prediction performance, but also addresses surface waviness optimization. The RGPSO algorithm's optimization performance is evaluated using 23 benchmark functions, demonstrating competitiveness against nine comparative meta-heuristic algorithms. Experimental data on surface waviness from the literature are utilized to train, test and validate three different prediction models, including a standalone ANN model, a PSO optimized ANN (PSO-ANN) model, and an RGPSO optimized ANN (RGPSO-ANN) model. The results indicate that the developed RGPSO-ANN model achieves the highest accuracy in terms of the metrics $\mathrm{RMSE}$ (0.019), $R$ (0.996), $R^2\left(0.990\right),\mathrm{MAE}$ (0.013), $\mathrm{RMSLE}\left(0.013\right),$and $\mathrm{MAPE}$ (3.46 %). It performs better than the PSO-ANN model ($\mathrm{RMSE}$ 0.026, $R$ 0.975, $R^{2}0.982,$ $\mathrm{MAE}$ 0.019, $\mathrm{RMSLE}$0.019$,a$nd $\mathrm{MAPE}$ 5.73 %), and better than the ANN ($\mathrm{RMSE}$ 0.046, $R$0.991, $R^{2}0.944,$ $\mathrm{MAE}$ 0.034, $\mathrm{RMSLE}0.032$ and $\mathrm{MAPE}$ 9.31 %). The RGPSO, PSO and other optimization algorithms are then applied to minimize the surface waviness of a WAAM component. RGPSO achieved the optimal value (0.1631 mm), which corresponds to a 12.6 % reduction compared to the best value obtained using PSO.

This paper experimentally investigates the efficacy of two jacketing techniques in the rehabilitation of square and circular reinforced concrete (RC) columns that were exposed to highly elevated temperatures. Twenty-four RC columns were tested under an axial compression load, which was divided into three groups. The first group consisted of the control specimens without applying any strengthening approach. Group 2 consisted of the columns with the strengthening configuration of near-surface-mounted (NSM) rebars and carbon fiber-reinforced polymer (CFRP) layers. Regarding the third group, columns were strengthened using two layers of welded-wire mesh (WWM) and ultra-high-performance fiber concrete (UHPFC) jacketing. Four columns from each group were subjected to an elevated temperature of 600 °C for a duration of 3 h, while the remaining half were subjected to room temperature. The results showed that after three hours at a temperature of 600 °C, both strengthening schemes successfully restored and exceeded the initial load-carrying capability of all columns. Utilizing WWM with UHPFC jacketing as new strengthening technique proved to be the most efficient method for reinstating the load-carrying capability of circular columns (+321.8 %) and square columns (+140.6 %) that were subjected to high temperatures. Additionally, an analytical model was proposed to estimate the ultimate load capacity of RC columns after rehabilitation.

Accurate and efficient dynamic analysis is essential for the reliable operation and optimal design of the wire rope hoisters. However, traditional 3D finite element (FE) methods require a significant amount of time for long and geometrically complex steel wire ropes that makes it impossible to predict dynamic performances of wire rope winding hoisters. For this problem, an equivalent mechanical modeling method for different wire ropes is proposed in this work. Based on this method, an equivalent mechanical model (EMM) is established for a circular arc wire rope with a fan-shaped strand cross section and verified by experimental tests. It is also validated that this EMM has the capability of characterizing mechanical behaviors of tension, torsion and bending deformations of the wire rope at the same time. Base on the EMM, a full-size 3D FE model of the double-rope winding hoister is established for the first time to investigate its dynamic performances during the lifting processes under a long-distance, high-speed, heave-load condition. Apart from the coupling axial and lateral vibrations and dynamic tension fluctuations of the wire ropes, the multi-layer winding process of ropes and the interaction between the ropes and the drums and sheaves as well as the rope itself are captured by this FE model against the traditional theoretical method. The accuracy of the FE model is finally verified by an experimental test using a double rope winding hoister test prototype. The method proposed in this work can contribute to the early design and analysis of wire rope drive hoisters.

The current study investigates the flexural performance and design of hybrid cold-formed steel built-up I-section beams, which are increasingly popular in the construction industry. These beams combine the benefits of both an "I" section and a closed-box section in their cross-section profile. They are constructed from two identical plain channels placed back-to-back with space between them and top and bottom cover plates, fastened together by screws. A nonlinear finite element (FE) model was developed to consider initial geometric imperfections, material and geometric non-linearities. The model was validated against the test results of cold-formed steel (CFS) built-up beams from the companion paper and literature. Once validation was successful, a comprehensive parametric study using finite element modelling was conducted to generate data on hybrid cold-formed steel built-up I-section beams across a broader range of cross-sectional slenderness, hybrid ratio, aspect ratio of the cross section and thickness of the cover plates. The parametric results were used to analyse the influence of key parameters on the moment carrying capacity and buckling modes. The applicability of the current Direct Strength Method in the AISI S100–16 specifications was evaluated based on these results, revealing that it is unconservative. Additionally, modified design procedures and equations were suggested for hybrid CFS built-up I-section beams vulnerable to local buckling in major axis bending, which were then evaluated through reliability analysis.

Precast concrete pavement (PCP) technology represents a highly effective method for accelerating construction processes and minimising traffic disruptions. This paper provides a comprehensive overview of various PCP systems by introducing their configurations, applications, and advantages. Key design considerations are summarised, with a focus on the design of pavement slabs, base layers, and pavement joints. To further interpret joint performance, the load transfer characteristics of dowel bars are systematically analysed, including load transfer efficiency, mechanisms, and dowel group action. Both elastic and plastic models for analysing the behaviour of dowel bars embedded into concrete are explored in depth. To address critical issues such as stress concentration and steel corrosion in jointed concrete pavements, this paper recommends appropriate retrofitting approaches regarding materials and connection design. The application of finite element analysis (FEA) in modelling jointed concrete pavements is also investigated, with five typical modelling techniques introduced. Significant observations on pavement joint design are summarised in the conclusion. In the future, to align with the trend of carbon reduction and expand the application of PCP technology, the use of reusable pavement systems with demountable connections and integrated sensors is recommended. Such innovations will support the sustainable development of civil infrastructure.

In this study, a modified dynamic model which distinguishes between liquid oscillation and sloshing in vertical columns is derived for toroidal tuned liquid column dampers (TLCDs). In the modified model of toroidal TLCDs, the primary sloshing mode within vertical columns is modeled as mass–spring-dashpot systems, whereas the oscillatory behavior of the liquid is analyzed employing the conventional theory of TLCDs. The accuracy of the modified dynamic model in capturing bidirectional liquid responses is verified by computational fluid dynamics (CFD)-based simulations. A large number of CFD-based simulations are performed to establish a ready-to-use suggested formula for a newly introduced parameter (which is related to the geometric configuration of liquid containers and the initial liquid depth) in the modified model. Subsequently, considering the maximum allowable liquid displacement in vertical columns, an optimized design approach for toroidal TLCDs installed in symmetric and asymmetric structures is illustrated. On the basis of the proposed optimization design method, the bidirectional vibration control effects of toroidal TLCDs are comprehensively analyzed under El Centro, Loma Prieta, Northridge, and Chi–Chi seismic excitations in both the time and frequency domains. The results demonstrate the effectiveness of toroidal TLCDs for bidirectional seismic control of structures.

Underground structures with large openings (USLO), especially those that allow natural light and fresh air, have emerged as alternatives to mitigate the weaknesses of traditional underground frame-box structures. For the USLO, two ends of the upper-story beam are generally recognised as weakest regions during strong earthquakes; however, insufficient attention has been paid to improving their seismic safety. This study performed a detailed numerical comparison of the conventional USLO and beam-end horizontal haunch retrofitting USLO under different seismic intensities, and evaluated the effectiveness of the proposed retrofitting scheme. The finite element numerical modelling approach was validated against shaking table test results, where the numerical results were in good agreement with measured data. Based on the validated numerical methods, the two ends of the upper-story beam in the conventional USLO were strengthened with horizontal haunches. Both soil-structure systems were excited by equal earthquake loads. Various seismic responses were compared between the conventional and retrofitted USLO, including structural strain, tensile damage, and story drift. Numerical simulation results indicate that beam-end horizontal haunch retrofitting significantly reduces the tensile strain and maximum damage degree at the ends of the upper-story beam, as well as the upper-story drift, without changing the lower-story drift. Therefore, beam-end horizontal haunch retrofitting is a potentially effective measure for improving the seismic performance of the USLO.

To overcome the shortcomings of traditional concrete structures such as long construction cycle, high construction cost and poor durability, seven composite beams with a UHPC stay-in-place formwork (UCB) and one reinforced concrete (RC) beam were designed. An experimental study was conducted to investigate the flexural behavior of composite beams under the static load. The research parameters include formwork thickness, reinforcement rate, and formwork surface treatment. The results revealed that roughening the surface of UHPC formwork has a positive impact on enhancing the integrity of composite beams. The utilization of UHPC stay-in-place formwork can effectively improve the stiffness, cracking load, and peak load of members. Compared with that of the RC beam, the cracking load and peak load of composite beams increased by 63 % ∼ 103 % and 6 % ∼ 15 %, respectively, and the yielding stiffness increased by 23 % ∼ 41 %. Different from the RC beam, new cracks occurred on one side of the initial crack's end and continued to extend upwards rather than along the original crack. The existence of a significant quantity of tiny cracks in composite beams effectively slowed down the increase in the width of pre-existing cracks in the early stage of loading. Due to the multi-crack pattern exhibited by the UHPC formwork, the strain concentration of the steel bars was effectively mitigated. When subjected to the same load level, the strain of the longitudinal steel bars in composite beams was smaller than that of the RC beam. The formula for calculating the flexural bearing capacity of composite beams is established through theoretical analysis. In addition, the numerical model of the composite beam is established by the finite element method (FEM). The influence of the contact method of the UHPC-NC interface on the flexural performance of the composite beam is explored. The supplementary analysis of the parametric study of the reinforcement rate and the UHPC formwork thickness is carried out. When using ABAQUS for the numerical analysis of the composite beam, it is appropriate to adopt the cohesion model or the Tie model for the UHPC-NC interface, and it is not appropriate to use the Coulomb friction model.