This paper presents a comprehensive numerical and theoretical investigation into the flexural capacities of composite joints with reinforced concrete (RC) slab. The improved 3D (three-dimensional) ...numerical models were established by MSC. Marc (2012) and calibrated by the experimental observations presented in the companion paper (Mou et al., 2019a 1). Supplementary parametric studies were then undertaken to examine the effect of concrete slab, size effect (H), axial-force ratio (n), slab thickness (hs), concrete compressive strength (fc’), and the width-to-thickness ratio of column (D/t) on the flexural capacities of the composite joints. Employing the yield line mechanism theory, a calculation method incorporating the effect of the RC slab for the composite joint was proposed. The proposed formulae were featured with a favorable accuracy and suggested to be applied for the design of composite joints in the steel structural systems.
•Parametric analysis is performed to clarify the flexural performance of bare or composite joints.•Five parameters were varied to examine their influence.•The calculation formulae to evaluate the bending moment of composite joints are proposed.
•Drop-weight impact tests were performed on steel or GFRP bars RC slabs.•Effects of bar type, reinforcement ratio and arrangement were investigated.•Effects of concrete strength and slab thickness ...were also investigated.•Singly RC slab with higher tensile bars than doubly RC slab perform better.•The results obtained from experiment and numerical simulation are in good agreement.
Reinforced concrete slabs are common structural elements that could be exposed to impact loading. Although use of reinforced concrete slabs and utilization of Fiber Reinforced Polymer (FRP) as alternative to traditional steel reinforcement slabs are growing, but the influence of various parameters on their response under impact loads is not properly evaluated. This study investigated the effect of rebar’s material, amount and arrangement of reinforcements, concrete strength and slab thickness on dynamic behavior of reinforced concrete slabs using both laboratory experiments and numerical simulations. Performance of fifteen 1000 × 1000 mm concrete slabs, including two 75 mm thick plain slabs, five 75 mm thick steel reinforced concrete slabs, six 75 mm thick reinforced concrete slabs with Glass Fiber Reinforced Polymer (GFRP) bars and two 100 mm thick steel reinforced concrete slabs under drop weight impact loads was experimentally investigated. Failure mode, crack development, displacement-time, strain-time, and acceleration-time responses were studied and compared between various slabs. Finite element analyses and simulation of specimens were conducted using LS-DYNA explicit software. The results obtained from experiments and numerical models are in good agreement, and they indicate that increasing the reinforcement ratio or the slab thickness enhance the behavior of RC slabs under impact loads. By adjusting the amount and arrangement of GFRP, better performance in GFRP slabs than steel reinforced slabs can be achieved, which considering the corrosion resistance of this material, can make it an appropriate selection of reinforcement material.
•Spalling damage is the main damage mode of RC slabs under close-in blast.•Higher charge weight leads to more fragments and propels them to a farther distance.•The proportion of small fragments ...increases as the charge weight increases.•Fragments velocity can be up to 100 m/s under 6kg TNT at 0.4m standoff distance.
Most of the injuries resulting from an explosion are not caused by the shock waves, but rather by the high-speed flying sharp fragments due to concrete spalling and crushing. The commonly used reinforced concrete (RC) components in building and infrastructure construction suffer this typical damage when subjected to close-in blast loads. The numerous ejecting concrete fragments generated from the crushing and spalling damage would threaten the occupants and equipment inside the building structures. Therefore, it is of great significance to study the local damage and fragments of RC members under close-in explosions. In this paper, five RC slabs in size of 1 × 2 × 0.12 m were tested under blast loads generated by 2kg, 4kg and 6kg TNT charges detonated with 0.4 m standoff distance. Significant local damage such as spalling and crushing of the RC slabs were observed, and a lot of ejecting fragments with different sizes and splattering distances were collected. The fragment mass, fragment size and splash distributions were analyzed in detail with respect to the mass of the TNT charge. It is found that higher charge weight will lead to more fragments and also propel them to a farther distance. The proportion of small fragments increases as the charge weight increases. High-speed camera was used to monitor the projection of fragments and found that the maximum ejecting velocity of fragments from RC slab under close-in blast loads is up to 100 m/s when the mass of TNT charge is 6 kg. The concrete fragment with such high ejecting velocity could be very dangerous to the occupants and equipment.
•Damaged RC slabs strengthened with UHPC layer were modeled and verified by experiments.•Two different load patterns: negative bending moment and positive bending moment.•Existed cracks in RC slab ...was modeled by geometry discontinuous before strengthening.•Two different interface modeling concepts: adhesion and friction (AASHTO) and friction only (ACI).
Ultra-high performance concrete (UHPC) has been developed as an innovative cementitious based material. It can be used for repairing and strengthening existing reinforced concrete (RC) structures because of its excellent mechanical performance, such as high tensile and compressive strengths, long-term durability, and low permeability. However, when using UHPC to strengthen existing RC structures for flexure members, there is limited information on simulating existed cracks in RC structures and considering interface modeling between RC substrate and UHPC overlay. This research developed a finite element (FE) model to investigate flexural behaviors of UHPC-RC composite slab with introducing existed cracks in RC substrate by geometry discontinuous, approximately matched with experimental results previously published by the authors. Meanwhile, based on recent research on the bond strength of UHPC to concrete, a UHPC-RC interfacial model was included in the FE model. The FE model was validated with experimental laboratory results previously published by the authors, and a good agreement was obtained between numerical and experimental results. Finally, a parameter study was conducted to investigate the strengthening effects and optimizing strengthening parameters by using the developed FE model. Results showed that the effect of existing cracks on the ultimate flexure capacity of UHPC-RC cannot be neglected, and the interface model has a precise accuracy in FE modeling.
•Reinforced concrete slabs have been subjected to blast loading.•Influence of increase in the explosive charge and the standoff distance have been studied.•Outcome enable better understanding of the ...performance of field structures against blast loading.•Blast pressure and damage increased with the explosive charge but reduced with standoff distance.•Finite element simulations have reproduced the spalling, scabbing and the formation of crater.
The civilian buildings and the military structures have been unexpectedly exposed to the risk of terrorist attacks, particularly in the form of vehicle bombing and other portable detonation devices and explosives. For example, the recent incident happened in Sri Lanka wherein more than 250 people were killed and about 500 people had been injured. The high mobility of these potential threats is also a major challenge to the structural safety of any building. The chances of a full-fledged war with any country albeit low cannot be neglected. During such attacks, the bunkers and protective shelters in the field areas are highly vulnerable to the blast by high explosive rounds of Mortar, Rocket Launchers and Artillery shells with proximity fuzes which generate a rapid release of energy in the form of shock waves. The release of high energy and the developed shock waves are associated with significant structural and collateral damage. Considering the vulnerability when the structures are subjected to such intense loadings, an experimental and numerical study has been carried out to investigate the damage resistance of reinforced concrete (RC) slabs against blast loading. The target slabs (1000 mm × 1000 mm × 100 mm) have been subjected to blast developed by three different weights of explosive equivalent to the quantity of explosive commonly used by terrorists and military in mortars, high explosive shells of rocket launcher and artillery shells with proximity fuzes. The explosive has been detonated from two different standoff distances corresponding to the scaled distance 0.079–0.527 m/kg1/3. The different failure modes and levels of blast-induced damage enabled better understanding of the performance of RC slabs when subjected to a similar impact/shock by mortars and rocket launchers. The one-way bending of the slab becomes more dominant with an increase in the explosive charge. On the other hand, the localized failure of the slab transformed into a globalized deformation with the increase in the standoff distance. The finite element simulations performed in ABAQUS/Explicit reproduced the damage, formation of the crater and spalling/scabbing of concrete. The blast pressure increased with an increase in the amount of TNT while reduced with the increase in the standoff distance.
“Mechanical Research of Reinforced Concrete Materials” describes the mechanical properties of reinforced concrete materials. The topics include theoretical, experimental and numerical studies, to ...evaluate the general deformation response, damage evolution and failure patterns of ordinary and high-performance reinforced concrete materials under various loading conditions (e.g., quasi-static, dynamic, fatigue, and impact).
•Locally resonant metamaterials-based RC metaslabs for broadband flexural vibration control.•Hybrid vibration control behavior integrating local resonance bandgap and vibration isolation.•Numerical ...models for designing local resonance bandgap and vibration isolation.•Full-scale experiments for validating the proposed technique and analytical models.•Up to 99.94 % reduction in initial four modal responses of the fabricated RC metaslab.
In this study, a novel method is introduced, integrating the principles of the local resonance bandgap (LRBG) with vibration isolation techniques to achieve broadband flexural vibration control in plate structures. This methodology employs locally resonant metamaterial units incorporated into a reinforced concrete (RC) slab, making it suitable for real-world engineering applications. Concurrently, the construction specifics associated with this methodology are elucidated. The mechanisms behind LRBG and vibration isolation within the metaslab were examined using numerical analyses. From these analyses, the frequency range conducive for broadband flexural vibration control was estimated, factoring in both material properties and geometric dimensions. Experimental results on a full-scale RC metaslab, measuring 4,200 × 3,000 × 210 mm, validate that the fabricated metaslab introduces a broadband vibration control region attributed to both the LRBG and vibration isolation phenomena. These findings closely align with the numerical estimations. All bending modal responses inherent in the unmodified RC slab were encompassed within this broadband frequency range. Furthermore, the maximal and initial four modal responses of the RC metaslab were attenuated by up to 81.19 %, 99.57 %, 99.94 %, 99.71 %, and 99.79 %, respectively.
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Spalling is a typical damage mode of reinforced concrete (RC) structures subjected to blast and impact loads. Concrete debris from spalling damage could be ejected with high velocities therefore ...impose significant threats to surrounding structures and people. Current numerical methods such as finite element method (FEM) based on continuum damage mechanics have inherent limitations in predicting fragmentation due to element distortion caused by large deformation and heavy discontinuity, which lead to simulation overflow, while the discrete element methods and particle methods that predefine the weaker sections and particle sizes result in inaccurate fragment size and shape prediction. In this study, an Arbitrary Lagrangian Eulerian-FEM-smoothed particle hydrodynamics (ALE-FEM-SPH) coupling method is employed to predict the spalling damage of a RC slab subjected to blast load. In this method, the RC slab is modelled using Lagrangian meshes, while the air and the explosive charge are modelled using ALE meshes. In the simulation the Lagrangian elements that experienced large deformation (e.g., spalling damage) are transformed into SPH particles to avoid erosion of the elements. A modified post-process fragment recognition program is proposed to obtain the fragment characteristics (e.g., fragment size distribution and velocity). The numerical results are compared with test results by other researchers, and a good agreement is achieved in terms of the spalling area of the slab, the fragment velocity and fragment size distribution, validating the accuracy of the ALE-FEM-SPH coupling method for predicting the blast fragments of concrete structures.
•ALE-FEM-SPH method to predict blast fragmentation is established.•Crack band theory can better predict fragment velocity.•3D binary graph fragment identification program is proposed for brittle material.•Fragment characteristics can be used for further risk analysis.
► The experiments are conducted using four slabs under close-in blast loading. ► Numerical simulation studies of the concrete damage are also conducted. ► The damage criteria are established for ...different levels based on experiments. ► The failure mode of RC slab changed from overall flexure to localized punching failure.
Terrorist attacks using improvised explosive devices on reinforced concrete buildings generate a rapid release of energy in the form of shock waves. Therefore, analyzing the damage mode and damage mechanism of structures for different blast loadings is important. The current study investigates the behavior of one-way square reinforced concrete (RC) slabs subjected to a blast load through experiments and numerical simulations. The experiments are conducted using four 1000mm×1000mm×40mm slabs under close-in blast loading. The blast loads are generated by the detonations of 0.2–0.55kg trinitrotoluene explosive located at a 0.4m standoff above the slabs. Different damage levels and modes are observed. Numerical simulation studies of the concrete damage under various blast loadings are also conducted. A three-dimensional solid model, including explosive, air, and RC slab with separated concrete and reinforcing bars, is created to simulate the experiments. The sophisticated concrete and reinforcing bar material models, considering the strain rate effects and the appropriate coupling at the air–solid interface, are applied to simulate the dynamic response of RC slab. The erosion technique is adopted to simulate the damage process. Comparison of the numerical results with experimental data shows a favorable agreement. Based on the experimental and numerical results, the damage criteria are established for different levels of damage. With the increase of the explosive charge, the failure mode of RC slab is shown to gradually change from overall flexure to localized punching failure.
