For RC columns exposed to blast loads, fibre reinforced polymer (FRP) is employed to examine its effectiveness in strengthening the concrete structure against blast load. It should be noted that no ...systematic studies could be found in the literature to derive pressure and impulse (P-I) diagram for FRP retrofitted RC columns. Therefore, the objective of this research is to develop finite element model to provide data for use in the development of P-I diagram that can be used to mitigate blast hazards and predict damage in RC columns retrofitted with FRP. In this study, various strengthening scheme performed against blast loads numerically by running computer simulations using the commercial software LS-DYNA. Validation of the models is performed based on the blast field test to investigate the accuracy of model simulations to present the behaviour of the models. The research compared the structural behaviour of an un-strengthened RC column with various column strengthened with different FRP wrap thickness, strength and arrangement. The results of the simulations showed that strengthening with FRP is an effective way to increase the blast resistance capacity of columns. This information would allow the designer to identify the critical location for placing blast barriers for protection purpose.
•Enhanced damage in reinforced concrete columns is due to 2D blast wave propagation.•The 2D wave propagation transitions into 1D wave propagation in walls.•A 500 g TNT contact explosion on square ...column resulted in damage index of 1.•67% increase in width reduced damage index to 0.71 when subjected to 500-g TNT.•140% in width reduced damage index from 1 to 0.48 when subjected to breach charge mass.
The response of reinforced concrete (RC) members subjected to contact explosion effects is more severe than the response to non-contact explosions due to local material failure. The shock-wave reflection within the RC member causes severe local material damage. The resulting loss of concrete cross-section reduces the axial load and bending capacity of the RC member. It is hypothesized that the concrete loss from the sides can be prevented by increasing the aspect ratio of the cross-section. In a low aspect ratio RC column, the reflection is from three faces whereas in RC slabs and high aspect ratio columns the shock-wave reflection from the back-face only is significant. This study experimentally investigates the response of rectangular RC columns with varying widths of the cross-section, subjected to contact explosion effects. A range of aspect ratios was investigated to preclude the side face damage for a given depth of rectangular RC column. High fidelity numerical models were developed to predict the blast-response and the residual axial capacity of the blast-damaged rectangular columns. The numerical models were validated, and the results show a good correlation with the experimental results. Using a rectangular RC column aspect ratio with a width that precludes the side face spall significantly improves the residual axial capacity of the blast-damaged columns. Furthermore, parametric analyses were performed to numerically investigate the influence of the width on the residual axial load carrying capacity of rectangular RC columns subjected to contact explosion effects of breach-charge mass required for the provided depth. An increase in the width of the column improved the damage resistance even though the rectangular column was breached around the point of detonation. Hence, increasing the width of the rectangular RC columns can be effectively used to mitigate contact explosion effects.
The seismic ductility spectra (SDS) method is a crucial tool to quickly evaluate the ductility demand of bridge columns with varied constitutive models. However, conventional SDS methods usually do ...not consider the characteristics of pulse-like excitations, which tend to cause severe structural damage. To address this challenge, near-fault pulse seismic ductility spectra (NFPSDS) based on Machine learning (ML) are developed in this study, where two ML models, i.e., the Random Forest (RF) and the artificial neural network (ANN), are utilized to map the relationship between seismic demand and a pulse-structure coupled index α1-p (the structural fundamental period (T1) relative to pulse period (Tp)). Then, the influence of column parameters (such as fundamental period and longitudinal reinforcement ratio) and pulse parameters (such as pulse period and peak pulse velocity) on NFPSDS is quantitatively investigated. Thus, by employing the NFPSDS method, the reasonable design range of longitudinal reinforcement ratio can be obtained under different pulse periods and pulse velocities. Overall, the NFPSDS method significantly benefits the practice for seismic design of structures in near-fault regions.
•The near-fault pulse seismic ductility spectra method considering the characteristic of pulse-like excitations is proposed.•The effect of some structural and pulse parameters on proposed spectra is quantitatively investigated.•The proposed spectra is applied to obtain the suitable design range of structural parameters with the change of pulse period.
The connection joint between a steel beam and a reinforced concrete (RC) column is crucial for strengthening and renovating the existing buildings; hence, designing simple, safe, and reliable ...connection joints is necessary. This study proposed a novel steel bearing–square RC column connection joint with adhesive bonding and self-locking and investigated seven half-scale connection joints with variable joint configurations under vertical loads. The typical failure modes, load–slip behavior, interfacial shear stress, and slip stiffness were analyzed through a parametric study of the taper angle of the square tube, the height of the steel bearing (i.e. contact area between the tube and the concrete), the structural adhesive, and the type of steel bearing surrounding the RC column. The results demonstrated that for a steel bearing–square RC column connection joint with adhesive bonding and self-locking, the typical failure process included at least two load fluctuations with multiple peaks. Moreover, the presence of adhesive bonding substantially improved the slip stiffness of the connection joint specimen relative to specimens with only self-locking. Additionally, the taper angle of the square tube influenced slip stiffness; however, the influence of the taper angle decreased with increasing contact area. Finally, regardless of the surrounding type and taper angle, the first peak load increased with the larger contact area, and the type of steel bearing surrounding the RC column had an obvious influence on slip stiffness. Furthermore, a finite element model was proposed to simulate the working performance of the proposed connection joint based on experimental data. The simulation showed that joint failure occurred mainly owing to the buckling of the vertical stiffeners and the outward deformation or tearing of the square rings, and the tilting of the joint due to local falling off of the structural adhesive must be prevented.
•New steel bearing–square RC column connection with adhesive bonding and self-locking.•Tests of seven steel beam–RC connection joints with variable joint configurations.•Failure, load–slip behavior, slip stiffness etc. of joints tested for vertical loads.•A finite element model proposed to analyze joint performance.
This study aims to examine the influence of eccentric axial loads on the lateral low-velocity impact behaviors of RC columns. Firstly, the numerical simulation approach is validated by accurately ...reproducing the impact force, as well as the deflection, axial load and failure mode of columns in pendulum impact and eccentrically loading tests. Secondly, the effects of the axial load ratios and eccentric distances on the dynamic behaviors of RC columns are analyzed as follows: (i) Increasing the axial load ratio and the eccentric distance at the impact direction can reduce the deflection of RC columns when the axial load ratio is relatively low; (ii) the instability failure could occur on columns with large enough axial load and impact energy; (iii) the eccentric distance of axial loads on the fixed-supported RC column can be neglected since the induced boundary rotation is constrained by fixed supports; (iv) for RC columns with pinned-fixed or pinned-pinned supports, the eccentric distance at the impact direction should be considered, while the eccentric distance at the vertical impact direction can be neglected. Furthermore, the dynamic coupled flexural and shear resistance function of eccentrically loaded RC columns are established and validated. A 2DOF model is presented to predict low-velocity impact behaviors of RC columns with varying axial load ratios and eccentric distances. The failure modes transition mechanism induced by the axial load is further revealed. Increasing axial loads can enhance columns’ flexural resistance and tendency of failure mode from flexural to shear/flexure-shear. The P-δ effect is amplified by larger axial loads and deflections, causing the instability failure of columns. Finally, a theoretical impact energy of the critical instability of eccentrically loaded RC columns is proposed to assist the structural impact-resistant design.
•Numerical simulation approach was established for RC columns under lateral impact.•Influence of eccentric axial loads for dynamic behaviors of RC columns is evaluated.•A 2DOF model is developed for lateral impacting eccentrically loaded RC columns.•The critical instability impact energy is proposed for RC columns.
•Experimental testing of corrosion damage low-strength concrete columns under compressive loading.•Influence of corrosion damage on inelastic buckling of stocky low-strength concrete columns.•Impact ...of corrosion on confined low-strength concrete behaviour under cyclic loading.•Influence of cross sectional shape on failure modes of corroded column under cyclic loading.
New codes have recently introduced seismic detailing for new structures. However, there are still older reinforced concrete (RC) structures without proper ductile detailing for earthquake resistance in seismic-prone areas. These structures are further impacted by the corrosion of their embedded reinforcing bars, which further reduces the strength and ductility under axial cyclic loading. This paper summarises the results of an experimental investigation performed on low-strength short RC columns, with different confinement configurations, subject to varying degrees of corrosion to investigate their structural responses to axial cyclic loading. The experiment was conducted on 30 short RC columns (square and circular) with three levels of confinement and steel reinforcement corrosion loss ranging from 0% to ∼ 30% subjected to cyclic compressive loading. The test results show that corrosion and inadequate confinements have a significant negative impact on the structural responses of corroded columns.
To study the effect of the axial compression ratio, torsion-bending ratio, and eccentricity on the mechanical performance of reinforced concrete (RC) columns under combined loadings, the numerical ...analysis is implemented based on ABAQUS and agrees well with the experimental results. The bearing capacity increased with the increase of the axial compression ratio, but the energy dissipation and ductility decreased. The bearing capacity and stiffness are degraded with the increase of the torsion-bending ratio. When the eccentricity increased from 0.125 to 0.25, the numerical results show the poor seismic performance. The results show that loading methods affected the mechanical performance, and the negative effect of the torque is noticeable. Moreover, the unified bearing capacity of RC columns under combined torsion is calculated by the modified existing Park & Ang failure criterion.
•Numerical analysis for investigating the bearing capacity is implemented.•The bearing capacity increases with the increase of the axial compression ratio.•The bearing capacity and stiffness degrade with the increase of the torsion-bending ratio.•The loading methods have an negative effect of the torque.
Fiber reinforced polymer (FRP) materials continue to demonstrate outstanding performance for strengthening and repairing reinforced concrete structures. However, one of the most significant problems ...that still has to be tackled is premature failure brought on by the FRP debonding. This research sought to determine how damaged RC columns could be strengthened with aramid (one type of FRP) composites and how that would affect their seismic responses. To further understand the individual effects of each strengthening material on seismic performance, hysteretic responses, such as strength, ductility, and energy dissipation, were examined and compared. Analytical modeling is validated based on the experimental results. Experimental results are validated with comparative study against other solid experimental results within the broader field. Effective bond length (EBL) is crucial for understanding the bonding between aramid fibers and concrete, however various models have different ways of calculating the value of EBL. Therefore, this research examined earlier experimental investigations of EBL and employing finite element (FE) methods established a novel relationship between the EBL and the aramid-to-concrete bond, based on experimental results.
•Experimental assessment with various specimens such as RC columns and RC columns with retrofitted aramid sheets.•Developing the FE model to investigate the response of the structural columns.•Considering the effect of the retrofit system on the RC columns.•Proposing the best-fit empirical model between the effective bond length (EBL) and the aramid-to-concrete bond.
Confinement of reinforced concrete (RC) columns through external bonding (EB) of fibre-reinforced polymer (FRP) composite becomes less effective in non-circular sections. The effectiveness of FRP ...confinement reduces with an increase in the size of the cross-section. Hence, it is essential to develop an effective FRP strengthening technique for large-sized square columns. Hybrid FRP strengthening combines the advantage of both near-surface mounting (NSM) and EB strengthening procedures for enhancing the overall performance of RC members under different load combinations. Sixteen square RC columns of various size ratios 1.0 and 1.5 were cast, strengthened and tested to understand the efficacy of the hybrid FRP technique. In addition to the tests, detailed nonlinear finite element (FE) models were developed and validated with the test results and data from the literature. Results show that the efficiency of EB and Hybrid FRP strengthening decreased with the increase in sectional ratio of square columns. Hybrid FRP strengthening improved strength and ductility for all size ratios compared to EB or NSM FRP strengthening alone. Using validated FE models, a parametric study was also conducted to understand the effect of EB and NSM reinforcement ratio and column size on the efficiency of Hybrid FRP strengthening.
•Four balanced failures defined for corroded RC columns in eccentric compression.•Six failure modes identified for corroded RC columns in eccentric compression.•Failure mode-based bearing capacity ...calculation method proposed for corroded RC columns under eccentric compression.
This paper proposed a failure mode-based calculation method for bearing capacities of corroded RC columns under eccentric compressive loads, which considered corrosion-induced mechanical property degradation of steel bars, cross-sectional reduction of steel bars and cross-sectional reduction of concrete. Through analyzing the stress and strain distributions over the normal cross-section, four balanced failures and six failure modes were identified for corroded RC columns under eccentric compressive loads. Balanced corrosion degrees were defined and methods to calculate them were proposed. Based on corrosion degree and balanced corrosion degrees, the failure mode of an eccentrically compressed corroded RC column could be predetermined in advance. Then, the methods to calculate the eccentric compressive bearing capacity under each failure mode were proposed. Subsequently, a dataset of eccentric compressive tests on 118 corroded and 27 non-corroded RC columns was established. The eccentric compressive bearing capacities calculated by the proposed failure mode-based method were found in good agreement with the test results, which demonstrated the validity of the proposed method. The failure mode-based calculation method will contribute to not only rapid and accurate performance evaluation of existing corroded RC columns, but also fast and efficient time-dependent reliability analysis for planned RC columns.
