In the rockfall prevention and control project, the reinforced concrete (RC) slab and sand (gravel soil) soil cushion layer are commonly used to form the protection structure, thereby resisting the ...rockfall impact. Considering that the oversized deformation of the cushion layer under impact load using the finite element simulation cannot converge, this article establishes a numerical calculation model using smoothed particle hydrodynamics–finite-element method coupling (SPH–FEM). First, the standard Lagrange finite-element mesh is established for the whole model using ABAQUS, and then the finite-element mesh of the soil cushion layer is converted to SPH particle at the initial moment of the calculation, and finally the calculation results are solved and outputted. The results indicate that, compared with the results of the outdoor rockfall impact test, the relative errors of the rockfall impact force and the displacement of the RC slab are within 10%, which proves the rationality of the coupling algorithm; moreover, in terms of the numerical simulation, the SPH–FEM coupling algorithm is more practical than the finite element for reproducing the mobility of the rockfall impacting the sand and soil particles. In addition, at an impact speed of less than 12 m·s
, the cushion layer is able to absorb more than 85% of the impact energy, which effectively ensures that the RC slab is in an elastic working state under small impact energy and does not undergo destructive damage under large impact energy; the peak impact force of the rockfall is approximately linear with the velocity, and the simulated value of the peak impact force is basically the same as that of the theoretical value of Hertz theory; the numerical simulation is good for reproducing the damage process of the RC slab in accordance with the actual situation. The SPH–FEM coupling algorithm is more justified than the FEM in simulating the large deformation problem, and it can provide a new calculation method for the design and calculation of the rockfall protection structure.
•The contact explosion size effect of reinforced concrete slab is revealed with experiments.•The impact echo device was used to test concrete damage under direct contact explosion.•Suggest choosing a ...scale ratio of more than 1/4 to reduce size effect under contact explosion.
The static size effect of concrete is well known; however, investigations on the size effect of reinforced concrete slabs under direct contact explosion remain scarce. It is of great importance to understand the size effect so that the scale model test results can be applied to real damage of full-scale structures subjected to explosion. This paper presents an experimental investigation consisting of eleven direct contact explosion tests carried out to investigate the size effect phenomenon in reinforced concrete slabs. The results indicate that the explosion size effect is clearly observed; that is, the specimens of smaller sizes had less bottom spalling damage even if the upper crater size was approximately the same proportion. Furthermore, the damaged area tended to decrease as the steel ratio increased. Non-destructive testing can detect the damage location and depth of reinforced concrete slabs after explosion by imaging. Finally, finite element model based on LS-DYNA is developed and validated by experimental results for the numerical investigation of the reinforced concrete slab under direct contact explosion.
Reinforced concrete containment is the last barrier of Nuclear Power Plant (NPP) to be used to protect against blast from incidental events or terrorist attacks. The configuration of reinforcement ...bar in containment dome of NPP is 60°, which is significantly different from the ordinary reinforced concrete (ORC) structures. In the present study, in order to precisely evaluate the blast resistance of RC slab with 60-degree angle of reinforcement (this type of RC slab is defined to be as a novel RC slab), a nonlinear finite element model is developed to predict the dynamic behaviors of the novel RC (NRC) slabs under blast loads. At first, the accuracy of the numerical simulations is verified with blast testing data reported by other researchers. Maximum deflections and blast resistances of NRC slabs subjected to blast loads are investigated numerically and compared with the ORC slabs. Intensive numerical simulations are then carried out to investigate the influences of thickness of slab, explosive charge and yield strength on maximum deflection and first principal stress of NRC slabs. Based on the numerical simulation data, empirical relations are suggested to predict blast resistance of ORC and NRC slabs based on the explosive scenarios, slab dimensions and reinforcement conditions.
•FE models of NRC slabs with 60-degree of reinforcement are established.•Maximum deflections and blast resistance of NRC slabs are investigated.•The best fitted curves of deflection δ and scale distance Z for NRC and NRC slabs are proposed.•Empirical relations are suggested to predict blast resistance of ORC and NRC slabs.
Reinforced concrete skew slabs are commonly used in bridges due to space constraints in motorways and in congested urban areas. Such slabs also often need to contain openings for architectural ...requirements or services, and this study seeks to determine the effect of these openings on the strength of the skew slabs. The finite element method was used to analyze 13 cases of slabs with skew angles of 45°. The first and second cases were used to validate the results with experimental work. Other cases studied the effect of the position and shape of openings on the strength of the skew slabs under both one-point and four-point loading conditions. The study also showed that the worst location for the opening was near the obtuse corners since this is where most of the load is transferred. With respect to the shape of openings, three different shapes with the same area were used: skew, circle, and square shapes. It was found that the effect of the opening shape depends on how many steel reinforcements are removed, as well as the appearance of negative cracking brought on as a result of the opening. Overall, the square shape introduces the smallest reduction in the skew slab strength compared with a slab with no opening. Accordingly, the study recommends that the strength of skew slabs can best be maintained if square openings are employed near the acute corners, alongside negative steel reinforcement to avoid cracking.
In this study, the expansion and deformation of alkali-silica reaction (ASR)-affected concrete structures under natural environment and multiaxial stress state are predicted. The performance of the ...ASR model proposed in previous research is quantitatively investigated in terms of relative humidity, multiaxial stress, and temperature dependencies based on experimental results. The simulation results indicate that the relative humidity-dependent expansion caused by the ASR can be simulated effectively by slightly modifying the relative humidity threshold in the model. In a simulation focusing on stress dependency, the insufficient consideration of the relationship between compressive stress and ASR gel absorption into pores in the model by previous research resulted in discrepancies between the simulation and experimental results. The performance of the model by previous research in simulating temperature dependency is improved by referring to the relationship between the expansion rate and temperature recorded from specimens exposed to the real environment. An exposure experiment of reinforced concrete (RC) slab on steel girders is simulated using the modified model. The results show that the modified model can reproduce the tendency of three-dimensional deformation of RC slab, while model improvement considering time-dependent and stress-dependent phenomena should be needed for long-term quantitative predictions.
Full-scale experiments involving actual geometries and charges are complicated and costly in terms of both preparation and measurements. Thus, scaled-down experiments are highly desirable. The ...present work aims to address the scaling of the dynamic response of one-way square reinforced concrete slabs subjected to close-in blast loadings. To achieve this objective, six slabs of two groups were tested under real blast loads. Three slabs with different scale-down factors were investigated using two scaled distances. Two major damage levels were observed, namely, spallation damage from a few cracks, and moderate spallation damage. The test results show that the macrostructure damage and fracture in the experiments are almost similar. However, the local damage in concrete slabs with larger-scale factors is slightly reduced compared with that of slabs with smaller-scale factors. Two empirical equations are proposed based on the results to correct the results when scaling up from the model to the prototype.
► Scaling the explosion resistance of a one-way square RC slab was investigated. ► Six slabs of two groups were tested under real blast loads. ► Two major damage levels were observed. ► The macrostructure damage and fracture in the experiments are almost similar. ► Two empirical equations are proposed to correct the scaling model.
•A beam-to-slab connection is developed for precast pre-stressed beam-to-column joint.•The seismic response of the proposed joint is investigated by experimental tests.•The performance of the ...proposed joint is compared to that of a conventional joint.•The proposed joint provides better energy dissipation and self-centering capacity.•The proposed joint preserves the slab from damage under large drift ratio.•The width of slab cracks is controlled below 0.4 mm and slab rebars remain elastic.
Conventional and pre-stressed precast reinforced concrete slabs are usually affected by severe damage induced by earthquakes. The repair of damaged slabs may compromise the resilience capacity of the structure. To overcome this drawback, this study introduces a new type of precast pre-stressed beam-to-column joint that prevents slab damage even under severe earthquakes. The connection between the slab and beam was made by using uplift-restricted slip-free rebar; contact surfaces between beam, column, and slab were smoothed to minimize interface friction. Deformation patterns of the proposed joint were analytically investigated and compared with those of a beam-to-column joint with conventional connection with the slab. Two 0.6-scale specimens were designed, the first with conventional beam–slab connection and the second with the proposed one, and tested under quasi-static conditions. Enhanced seismic behavior of the developed joint was demonstrated by results of seismic performance of these two specimens in terms of crack development, maximum bearing capacity, energy dissipation, and rebar strain. The proposed connection prevented damage in the slab up to a drift ratio equal to 1/18.
•Impact behaviour of FFRP-CFRC slabs were studied by experimentally.•The investigation of the effectiveness of different FFRP wrapping configurations.•Damage mechanisms of the FFRP-CFRC slabs have ...been described.•The theoretical method was used to predict the maximum impact force and deflection.
The impact behaviour of flax fibre reinforced polymer (FFRP) strengthened coconut fibre reinforced concrete (CFRC) slabs was investigated through experimental and theoretical studies. Plain concrete, CFRC and FFRP-CFRC slabs were built and tested under impact loadings. Impact results showed FFRP-CFRC specimens had better performance in aspects of energy absorption and keeping the integrity of the concrete, comparing with PC and CFRC specimens. Another impact test was carried out for finding the more effective wrapping configuration between three different wrapping designs of the FFRP strengthened CFRC slab, and their parameters, i.e. impact force history, strain history of FFRP, deflection history, energy absorption and damage pattern were discussed to evaluate the impact resistance. After the experimental study, theoretical analysis method was used to predict the maximum impact force as well as the maximum deflection, the results of which showed good agreement with the experimental results.
Deep learning has been widely employed in recent studies on bridge-damage detection to improve the performance of damage-detection methods. Unsupervised deep learning can be effectively utilized to ...increase the applicability of damage-detection approaches. Hence, the authors propose a convolutional-autoencoder (CAE)-based damage-detection approach, which is an unsupervised deep-learning network. However, the CAE-based damage-detection approach demonstrates only satisfactory accuracy for prestressed concrete bridges with a single-vehicle load. Therefore, this study was performed to verify whether the CAE-based damage-detection approach can be applied to bridges with multi-vehicle loads, which is a typical scenario. In this study, rigid-frame and reinforced-concrete-slab bridges were modeled and simulated to obtain the behavior data of bridges. A CAE-based damage-detection approach was tested on both bridges. For both bridges, the results demonstrated satisfactory damage-detection accuracy of over 90% and a false-negative rate of less than 1%. These results prove that the CAE-based approach can be successfully applied to various types of bridges with multi-vehicle loads.
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