Strengthening existing reinforced concrete (RC) slabs using externally bonded materials is increasingly popular due to its adaptability and versatility. Nevertheless, ductility reduction of the ...rehabilitated flexural members with these materials can lead to brittle shear failure. Therefore, a new approach for strengthening is necessary. This paper presents a methodology to induce ductile failure of flexural strengthened one-way RC slabs. Ultimate failure loads can be considered to develop the proposed design methodology. Different failure modes corresponding to ultimate failure loads for RC slabs are addressed. Flexural and shear failure regions of RC slabs can be established by considering the failure modes. The end span of the concrete slab is shown for a case study, and numerical examples are solved to prove the essentiality of this methodology.
Reinforced concrete (RC) slabs are the major components for building structures and underwater engineering plants. However, blast loading, especially from contact explosion, can cause significant ...damage to the target structures both in air and water. The objective of this paper is to compare the damage characteristics of RC slabs subjected to air and underwater contact explosions. Three methods, i.e. fully coupled Eulerian-Lagrangian (CEL) method, smoothed particle hydrodynamics (SPH) method, and coupled finite element method and smoothed particle hydrodynamics method (FEM-SPH), are first employed to simulate the damage features of an RC slab to air contact explosion. Damage profiles of the RC slab to air contact explosion using the three methods are compared with the experiment results in the literature, and the applicability and suitability of these methods are discussed. Subsequently, the most effective method (i.e., FEM-SPH) is used to describe the dynamic response of the RC slab subjected to underwater contact explosion. Shock wave propagation characteristics from air and underwater contact explosions are discussed. Damage features of the RC slab to air and underwater contact explosions are compared. Damage characteristics and plastic deformation of reinforcement steel bars are also investigated.
•Three methods are used to predict the damage process of RC slabs to contact blast.•FEM-SPH is the most effective method for contact explosion analysis.•Charge shape sensitivity on damage mechanism is examined.•Failure modes of RC slabs under contact blast in air and underwater are compared.•Damage characteristics of RC slabs subjected to contact explosion are discussed.
Under the action of underwater explosion load, the reinforced concrete structure is easily destroyed, and the structure has the risk of overall instability. Therefore, it is proposed to arrange a ...polymer protective layer at the outside of the structure to achieve the effect of reducing the degree of damage. In this paper, field explosion tests were carried out on normal reinforced concrete (RC) slabs and reinforced concrete slabs with polymer protective layers (PRC). The dynamic responses and failure modes of the two slabs under different explosion loads were studied, and the protective performance of polymer layer was compared and analyzed. Numerical models were established based on the CEL method, and the numerical simulation can well reproduce the damage results of the specimens. Based on numerical simulations, the effects of charge mass on the failure modes, surface damage, and residual displacement of the kinds of two slabs were deeply studied. And the influence of charge mass and thickness on the protective effect of polymer layer was discussed. The results show that the polymer protective layer can reduce the explosion energy, reduce the damage and deformation of the slab, and effectively improve the anti-explosion performance of the RC slab.
•Under different underwater blast loads, there are four main damage modes of RC slabs.•RC slab with polymer layer has better anti-explosion performance than normal RC slab.•Polymer layer can effectively improve the surface stress distribution of RC slab.•Protective performance of polymer layer is inversely proportional to the charge mass.•Increasing the thickness of polymer layer can significantly improve the energy absorption effect.
This study performed a nonlinear finite element analysis on an ultra-high performance fiber reinforced concrete (UHPFRC) one-way reinforced concrete slab with openings. This study contributes to a ...comprehensive understanding of the previously unstudied behavior of one-way UHPFRC slabs with slits of varying sizes and placements; additionally, a comprehensive comparison is made between the structural behavior of conventional concrete RC slabs and UHPFRC slabs. This study constructed and validated a finite element model (FEM) using the authors' experimental data. Ten models are included in this analysis: In this experimental investigation, the aperture widths and positions of the slabs are altered to determine their effect on the results. In the initial phase of this numerical investigation, a FEM was constructed, and its accuracy was validated against five experimental data, one of which is a closed-loop reference. ABAQUS was utilized for the analyses. Behavior under a total load, maximal load, and failure modes of the validated FEM using experimental data closely match those of the experiment. Due to the use of UHPFRC to reduce the impact of openings on load capacity, the finite element analysis results were very near to the test results, with an average error of 2.232%. Five specimens of UHPFRC were analyzed with finite elements using a validated analytical model and the results of load-displacement behaviors. The finite element method is ideal for investigating the nonlinear behavior of multi-perforated slabs due to its reliability and efficiency.
•The dynamic equilibrium relationship of the three forces is analyzed.•The distribution of acceleration for the longer and thicker slabs shows a sinusoidal trend.•The slab stiffness by varying slab ...length and thickness obviously affects the reaction force.•The slab stiffness by varying slab thickness and rebar ratio affects the deformation.•The semi-empirical formulas are proposed to predict the reaction force time history.
The purpose of present study is to investigate the effect of global stiffness on the force response of thin GFRP reinforced concrete slabs simply supported by steel beams under drop-weight impact. Considering the strain rate effect of GFRP bars and concrete materials, a numerical model of GFRP-RC slabs was established and verified. The dynamic equilibrium relationship of the impact force, reaction force and inertial force was analyzed and intuitively explained from the velocity and displacement. Meanwhile, the effects of the global stiffness by varying the slab length, slab thickness and reinforcement ratio on the acceleration distribution, characteristic value of impact force and reaction force, failure pattern, displacement distribution and energy dissipation were evaluated in more detail. Eventually, the semi-empirical formulas considering key parameters were proposed to predict the reaction force time history of simply-supported RC/FRP-RC slabs under drop hammer impact. The results show that the effect of the slab stiffness by varying the slab length and thickness on the reaction force is significant, while the influence of reinforcement ratio is not obvious. The effect of global stiffness of the slab on the plateau value of the reaction force is similar to that on the plateau value of the impact force. The effect of the slab stiffness by varying the slab thickness and reinforcement ratio on the displacement is obvious, while varying the slab length hardly affects the deformation. The fitting equation considering key parameters can predict the simplified reaction force time history of simply-supported RC/FRP-RC slabs under impact loading. However, more experimental validation and extensive parametric studies are needed to improve their accuracy and applicability.
In this study, high strength seawater coral aggregate concrete (SCAC) with a compressive strength of 80 MPa was prepared, and seawater coral aggregate reinforced concrete slab (SCARCS) was designed ...with epoxy-coated steel bars. Combining with the AE technology, monotonic flexural static tests were conducted on SCARCS specimens with three varying reinforcement ratios (i.e., 0.85%, 1.13%, and 1.41%). Results showed that the increasing the reinforcement ratio led to an increase in peak bearing capacity and a decrease in center deflections at the peak. The loading process can be divided into four stages based on the varying magnitudes of the b-value and Ib-value. The primary mode of failure was tensile microcracks at various stages, and the ratio of shear microcracks reached its maximum value in the final stage of loading. Besides, based on the signal intensity analysis, it can be observed that the scale and complexity of cracks propagation inside the SCARCS specimen increased as the reinforcement ratio rose. In addition, back propagation neural network (BPNN) classification model optimized by deep belief network (DBN) algorithm was proposed to predict the damage degree of SCARCS during loading, and the average prediction accuracy of the proposed model was shown to be over 89%. The classification outcomes demonstrated that with an increase in the reinforcement ratio of SCARCS, the proportion of AE signals in Cluster 3 increased, while the proportion of AE signals in Cluster 2 dropped. Notably, both the average frequency and energy presented an ascending trend. The findings of this study provided valuable insights for designing and assessing the safety of SCAC structures for essential island and reef engineering infrastructure.
•High strength seawater coral aggregate reinforced concrete slab (SCARCS) was designed with epoxy-coated steel bars.•Loading process of SCARCS can be divided into four stages based on the varying magnitudes of the b-value and Ib-value.•As the reinforcement ratio rose, the scale and complexity of crack propagation inside SCARCS increased.•Optimized back propagation neural network model was proposed to predict the damage degree of SCARCS.
•An easy-to-disassemble friction damper is proposed for use in coupling beams.•Coupon and subassembly tests verified the performance of the friction dampers.•Overhead RC slab exhibited severe damage ...but marginal mechanical contribution.
In coupled wall systems, coupling beams distributed along the structural height are intended to yield and dissipate seismic energy under moderate and severe earthquakes. The use of specifically designed dampers in coupling beams can greatly enhance the seismic performance of a structure. In the present study, a friction damper incorporating brake pad-to-mild steel friction interfaces is proposed for installation in a steel coupling beam at the mid-span. Cyclic loading tests were conducted on the friction coupons and subassemblages of steel coupling beams with mid-span friction dampers. An RC slab, which rested on the top flange of the steel coupling beam without shear connectors, was included in one of the subassemblage specimens. The test results show that the friction dampers exhibited stable and full hysteretic responses with up to 8% chord rotation of the coupling beams. The friction coefficients were gradually increased and the clamping forces of the dampers relaxed during the cyclic loading. The average friction coefficient was close to the nominal value with a small deviation. However, the unintended out-of-plane bending of the steel teeth of the friction dampers reduced the effective normal force on the friction interfaces and, thus, led to a lower-than-expected shear strength of the damper. Though not composited with the steel coupling beam, the RC slab sustained severe flexural cracks as wide as 6 mm at 4% chord rotation of the coupling beam and, thus, might influence the postquake recovery of a building. A simple numerical model was established to investigate the respective contribution of each part of the coupling beam. The results show that the post-sliding stiffness introduced by the RC slab was less than 1% of the initial stiffness of the coupling beam and decreased rapidly with increasing deformation amplitudes. The shear force in the slab exceeded 10% of the strength of the friction damper at 4% chord rotation and is deemed to be a potential source of overstrength for the design of a coupling beam and the surrounding elements.
•ALE-FEM-SPH can simulate blast-induced perforation and fragmentation of RC slab.•A scaled blast parameter is proposed for damage prediction of RC slab.•Empirical formulae are proposed for damage and ...fragmentation prediction under close-in explosion.
Reinforced concrete (RC) structure is prone to suffer localized damage when exposed to close-in explosions. Spalling damage might occur due to the reflected tensile stress wave exceeding the concrete dynamic tensile strength. When the blast wave is intensive enough, it can also cause significant crushing damage on the contact surface, potentially leading to perforation when the crushing depth aligns with the spalling depth. This perforation/spalling damage can generate a large number of secondary fragments with high ejecting velocities. Additionally, the blast wave might pass through the perforation hole and cause further acceleration of the secondary fragments. In the author’s previous study, an ALE-FEM-SPH numerical model was established and validated with the existing testing data for the prediction of spalling damage as well as fragment sizes and velocities. As a continuous work, this study conducts numerical simulations to predict the perforation damage and fragmentation under higher-intensity blast loading. The results including centre perforation hole, spalling area on back surface, fragment ejecting velocities, fragment landing distance and fragment characteristics distributions are reported and studied. The acceleration effect on the secondary fragments by the traversed blast wave that further carries the fragments flying is also investigated. The numerical results show that using the scaled distance Z might not reliably quantify the perforation/spalling damage under close-in cylindrical TNT explosion. Given the identical scaled distance, the scenarios with different combinations of charge weight and standoff distance can result in large variations up to 300% in the predictions of damaged area and 50% for the maximum fragment ejecting velocities, respectively. A scaled blast parameter Z* is suggested and the empirical formulae are proposed for better quantification of the damaged area of RC slab as well as the fragment velocity and kinetic energy under close-in cylindrical TNT explosions.
In this work, carbon fiber-reinforced high-performance concrete (CF-HPC) slabs with coarse aggregate content of 25 vol%/35 vol%/45 vol% and carbon fiber content of 0.6 vol%/0.8 vol%/1.0 vol% were ...cured by ohmic heating (OH) curing under realistic severely cold condition for practical on-site construction. Results indicated that the coarse aggregate content has a substantial influence on the electrical resistance and curing time of concrete slab. Higher and lower content of coarse aggregate will lead to insufficient ohmic heats and curing time. On the contrary, carbon fiber content only has a limited influence on OH curing feature, such as slight value difference of electrical resistance and curing temperature. Besides, the correlation between the curing temperature of concrete slab and the associated factors (OH curing power, ambient temperature) was quantitatively analyzed. It is found that the OH curing power had a strong correlation with the concrete temperature during the most time of curing period, while the snowfall weather enhanced the correlation between ambient temperature and concrete temperature. At last, a criterion of feasible resistance range based on the experimental results and theorical analysis was proposed to evaluate the feasibility of OH curing and assist the concrete mix design.
•Carbon fiber-reinforced concrete slab was cured in realistic severely cold weather by ohmic heating curing.•Effect of coarse aggregate and carbon fiber content on electrical properties was analyzed.•Correlation between concrete slab temperature, ohmic heating power and ambient temperature was quantitatively evaluated.•The feasible resistance range was proposed to assess the feasibility of ohmic heating curing.
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•The blast damage features of the RC slab with polyurethane sacrificial cladding (PU-RCS) were experimentally and numerically studied.•The influence of the polyurethane sacrificial ...cladding on the damage mode of the RC slab was compared and analyzed.•Effects of the explosive charge and the thickness of polyurethane sacrificial cladding on the damage mode of PU-RCS were studied.•A prediction formula for the mid-span displacement of PU-RCS was proposed.
Sacrificial cladding has been widely used in the blast mitigation and protection of engineering structures, and its protection performance and mechanism have also attracted the extensive research interest of scholars. In order to study the blast damage mitigation effect of polyurethane (PU) sacrificial cladding on reinforced concrete structures, close-range explosion tests of the reinforced concrete slabs with polyurethane sacrificial cladding (PU-RCS) were carried out. At the same time, the reinforced concrete slabs (RCS) without polyurethane sacrificial cladding were set as the control group, and the influence of sacrificial cladding on the damage mode of the reinforced concrete slab was compared and analyzed. In addition, the SPH-FEM coupling model corresponding to the field explosion test was developed and verified by comparison with the test results. On this basis, numerical simulation analysis was used to investigate the dynamic response process of PU-RCS. Furthermore, the effects of the explosive charge and the thickness of polyurethane sacrificial cladding on the damage features of PU-RCS. Based on a large number of numerical simulation analyses, the prediction formula for the mid-span displacement of PU-RCS was proposed. The results show that under close-range explosion, the polyurethane sacrificial cladding can effectively disperse the blast loads, change the damage mode of the reinforced concrete slab, and demonstrate good mitigation ability. The proposed prediction formula can well predict the mid-span displacement of PU-RCS.
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