Reinforced Concrete Research Articles

Peridynamics simulations of the damage of reinforced concrete structures under radial blasting

Concrete is prone to damage under explosive loads, which can cause a large number of casualties and property losses. The concrete fragmentation process during explosion is transient and dynamic, and the experimental measurement of such events is difficult and risky to conduct, and the intermediate explosion process is difficult to observe in the experimental tests. Therefore, the numerical simulation is an ideal method to model and simulate the explosion process of concrete. Different from the traditional finite element method, Peridynamics (PD) method uses the spatial integral equation to replace the traditional local differential equation to solve the fragmentation problem with massive and complex discontinuous patterns. In this study, a peridynamics (PD) model is developed to simulate the failure process of reinforced concrete (RC) structures under radial blasting. Concrete PD models with different cavity sizes and reinforcement conditions were established and calibrated with the experimental data. We find that the crack growth and damage pattern obtained in the peridynamics simulation is consistent with the experiment test results, which verifies the feasibility of peridynamics method as a modeling tool for modeling concrete damage under explosive load and for evaluating anti-explosion performance of RC concrete structures.

Experimental Investigations of Seismic Performance of Girder–Integral Abutment–Reinforced-Concrete Pile–Soil Systems

Integral abutment bridges (IABs) have been widely applied in bridge engineering because of their excellent seismic performance, long service life, and low maintenance cost. The superstructure and substructure of an IAB are integrally connected to reduce the possibility of collapse or girders falling during an earthquake. The soil behind the abutment can provide a damping effect to reduce the deformation of the structure under a seismic load. Girders have not been considered in some of the existing published experimental tests on integral abutment–reinforced-concrete (RC) pile (IAP)–soil systems, which may not accurately represent real conditions. A pseudo-static low-cycle test on a girder–integral abutment–RC pile (GIAP)–soil system was conducted for an IAB in China. The experiment’s results for the GIAP specimen were compared with those of the IAP specimen, including the failure mode, hysteretic curve, energy dissipation capacity, skeleton curve, stiffness degradation, and displacement ductility. The test results indicate that the failure modes of both specimens were different. For the IAP specimen, the pile cracked at a displacement of +2 mm, while the abutment did not crack during the test. For the GIAP specimen, the pile cracked at a displacement of −8 mm, and the abutment cracked at a displacement of 50 mm. The failure mode of the specimen changed from severe damage to the pile top under a small displacement to damage to both the abutment and pile top under a large displacement. Compared with the IAP specimen, the initial stiffness under positive horizontal displacement (39.2%), residual force accumulation (22.6%), residual deformation (12.6%), range of the elastoplastic stage in the skeleton curve, and stiffness degradation of the GIAP specimen were smaller; however, the initial stiffness under negative horizontal displacement (112.6%), displacement ductility coefficient (67.2%), average equivalent viscous damping ratio (30.8%), yield load (20.4%), ultimate load (7.8%), and range of the elastic stage in the skeleton curve of the GIAP specimen were larger. In summary, the seismic performance of the GIAP–soil system was better than that of the IAP–soil system. Therefore, to accurately reflect the seismic performance of GIAP–soil systems in IABs, it is suggested to consider the influence of the girder.

Polypropylene Fiber as a Factor of Reduction of the Total Shrinkage Strain of Expanded Clay Concrete

Statement of the problem. The article presents the development features of the total shrinkage strain of expanded clay concrete, expanded clay fiber-reinforced concrete, expanded clay steel-reinforced concrete, and expanded clay fiber-steel-reinforced concrete. According to the analytical review, the shrinkage strain decrease as a result of the fibers adding was noted by the researchers without analyzing the reason for the phenomenon. Therefore the purpose of the study is to establish the reason for the decrease of the shrinkage strain of expanded clay concrete with the addition of polypropylene fibers. Results. It has been confirmed that the polypropylene fiber addition reduces the total shrinkage strain of expanded clay concrete by 29—34 % on the 120th day with the volume content of fibers of 0.36 %. Empirical dependences of deformations compatibility for expanded clay fiber-reinforced concrete and expanded clay fiber-steel-reinforced concrete are set forth. Conclusions. It has been experimentally established that fiber is a significant factor on the first days of the concrete mixture hardening, when the elastic modulus of the fiber is greater than or equal to the elastic modulus of the cement stone. Fibers act as a bond and affect the redistribution of shrinkage stresses within the composite, thus reducing the values of the total shrinkage strain.

Study on the deformation of hybrid BFRP-steel reinforced concrete beams considering crack development

Hybrid fiber-reinforced polymer (FRP)-steel reinforced concrete (RC) beams exhibit various flexural failure modes depending on different equal-stiffness reinforcement ratios, the post-yield stiffness ratio, and the bond-slip behavior. This study first develops a model for the tensile behavior of hybrid Basalt FRP (BFRP) -steel reinforced concrete chords, considering the modified Bertero-Popov-Eligehausen (mBPE) bond-slip model. The rationality of the tensile stiffening model was validated through comparisons with existing experimental tests on the axial tension of chords. Subsequently, a beam deformation correction calculation method considering ‘rigid-rotation’ was proposed. The corrected theoretical calculation of the beam’s peak load shows an error of 5.0% compared to the experimental value, while modified ultimate deformation exhibits an error of 4.7%. As the bond weakens, the theory proposed in this paper is more suitable for predicting the deformation capacity of hybrid reinforced beams. ACI 440.1R-15 underestimate deformations by approximately 77.8%, limiting the normative evaluation of deformation calculations for hybrid reinforced concrete beams considering bond slip. Finally, the influence of bond-slip parameters ( τm, sm and [Formula: see text]) and reinforcement configurations (equal stiffness reinforcement ratio, steel/BFRP reinforcement ratio, and post-yield stiffness ratio) on beam deformation and crack width was investigated. The results indicate that the peak bond strength is a key parameter affecting crack width and deformation of the beam. The exponential rise segment parameter α and the slip sm corresponding to peak bond strength mainly influence the load level corresponding to cracking.

Optimized Machine Learning Algorithms for Predicting the Punching Shear Resistance of Flat Slabs with Transverse Reinforcement

In the calculation of reinforced concrete (RC) flat slabs with transverse reinforcement, punching shear resistance is one of the most critical factors. It is true that design provisions may be implemented, but they often result in significant biases and deviations from expectations. This study aims to present an optimized machine learning (ML) algorithm for estimating the punching shear resistance. Four machine learning (ML) algorithms (SVR, DT, RF, and XGBoost) with Bayesian optimization (BO) are presented in this paper to provide accurate predictions for flat slabs. The adoptability and optimization of the models are achieved through the analysis of a database of 337 test specimens with nine design parameters. Machine learning (ML) techniques are used to estimate punching shear resistance, which is compared with design provisions and equations relating to critical shear crack theory (CSCT). According to this study, Bayesian optimization is still capable of improving the performance of conventional machine learning algorithms, while the XGBoost-based model offers advanced capabilities. Predictions based on BO-XGBoost are in good agreement with actual values (MAE, RMSE, and R2 are 0.09 MN, 0.14 MN, and 0.92, respectively) in test set. Following a detailed explanation using Shapley additive explanation (SHAP), a high-performance ML approach is used to investigate the predictive results. With the proposed optimized algorithms, it is possible to determine the punching shear resistance of flat slabs with transverse reinforcement during the preliminary stages of the construction.

Use of bore-epoxy anchorage system with CFRP laminates for shear strengthening of RC beams: An experimental and analytical investigation

Shear strengthening of reinforced concrete (RC) beams with externally bonded reinforcement (EBR) using carbon fiber reinforced polymer (CFRP) plates and sheets have become a widely accepted practice. To avoid the associated premature debonding failure, this study presents an experimental and analytical investigation on the use of bore-epoxy as an anchorage system for CFRP plates and sheets bonded on both sides of shear deficient RC beams of rectangular cross-sections. Nine (9) RC beams were prepared and strengthened with CFRP plates and sheets as EBR with bore-epoxy anchorage system considering different bore diameters and tested under four point bending. The results indicate that RC beams strengthened with bore-epoxy anchorage system have high shear strength as compared with the unstrengthened control beam and those strenghtended with the conventional EBR approach (without boring). The increase in the shear strength over the control beam was found to be up to 67 % and 121 % for cases of CFRP plates and sheets, respectively. Moreover, the increase of shear strength in comparison with the conventional EBR method ranged from 9.33 % to 20.36 % for CFRP plates and from 12.97 % to 36.10 % for CFRP sheets. Consistently, the contribution of bore-epoxy on the shear strength increased with the increase of bore diameter. Consequently, the existing formulas in the ACI440.2 R for predicting the shear strength of FRP strengthened RC beams were modified to incorporate the improvement made by the proposed bore-epoxy approach. The revised models predicted the experimental shear strength of RC beams, strengthened with bore-epoxy, with a good level of accuracy with average mean absolute percentage error (MAPE) = 6.07 %, 14.71 %, normalized mean square error (NMSE) = 0.097, 0.16, and coefficient of determination R2 = 0.912, 0.974 for plates and sheets, respectively.

Numerical analysis of fixed-end hollow rectangular beam under uniformly distributed load

The purpose of using opening in the reinforced concrete (RC) rectangular beam is the reduction of self-weight, cost, displacement, and strain. Therefore, this research performs linear elastic finite element analysis by using ETABS for fixed-ended RC hollow and solid rectangular beams under uniformly distributed loadings with variable beam lengths, compressive strengths, and opening sizes.The solid and hollow beams are considered to be a 2-nodded line element for the numerical analysis. The maximum range of validation result in case of hollow beam is found to be (3.9 to 7.9) %, which may indicate good accuracy of numerical analysis. The 50 × 50 mm opening size is suitable for 300 × 300 mm RC rectangular beam because of showing the positive normalized deflection of (0–1.45) % and lower strain rates (i.e. 0.13 % and 0.17 %) to compare the solid beam. This research may help professional engineers to use suitable opening size for design and construction works. Although, there is a scope to enhance this research in future by performing nonlinear analysis.

Machine learning – based approach for predicting pushover curves of low-rise reinforced concrete frame buildings

Reinforced Concrete (RC) frame buildings are prevalent worldwide due to their seismic performance and the broad availability of materials. Pushover analysis is regarded as one way to assess the seismic performance of these buildings, which is simple to interpret. The only downside of this method is that it requires developing nonlinear models, which can be time-consuming and computationally expensive. Recently, Machine Learning (ML) has emerged as an alternative to approximate the pushover response of RC frame buildings. However, there are still improvements in several areas, such as including relevant and easily obtainable parameters in structural design (e.g. reinforcement ratios), considering a wide range of building configurations, and comparing different ML techniques. This paper presents the development of two models based on Random Forest (RF) and Artificial Neural Network (ANN) to predict the pushover response of low-rise RC frame buildings, supported by a user-friendly graphical interface. First, a dataset of over 138000 Pushover analyses was performed on flexure-controlled RC frames ranging from two to five stories using OpenSeesPy, subsequently used to develop predictive ML models. These models are designed to offer a trilinear approximation of a building's Pushover curve, and they require input information that is available from the customary building design. The pushover predictions obtained with RF and ANN take 0.12 % and 3.05 % of the computing time compared to the OpensSeesPy nonlinear model. The proposed models demonstrate a high level of accuracy, with a coefficient of determination (R²) of over 0.88 and 0.81 in testing datasets for RF and ANN models, underscoring their potential to significantly streamline the seismic performance assessment process by providing quick Pushover curve estimations.

Lateral deflections of slender RC columns under eccentric compression loading with different end conditions

AbstractIn the literature, several methods have focused mostly on determining the lateral deflection of columns with pinned end conditions. This paper presents a powerful method that allows the calculation of lateral deflection for columns of different end conditions, with particular attention to reinforced concrete (RC) columns. By utilizing the moment–curvature relations, a numerical procedure to compute slopes and deflections of pin‐ended columns is proposed, in which the slopes and deflections are corrected via an efficient and fast technique. Accordingly, slopes and deflections of columns with different end conditions are determined via procedures that rely on a simple searching technique. The second‐order analysis is individually included in the calculations; therefore, the complexity arising from the direct impact of the axial load on the lateral deflection is averted. Therefore, the method has the potential for inclusion in many numerical models for different structural members. The equations derived via the developed method have identical responses to the expressions obtained via the exact methods. A series of numerical examples are presented to illustrate the applicability of the proposed method to RC columns with different loadings and end conditions. Finally, the proposed method is evaluated, and its accuracy is demonstrated via parametric verification. As the axial load increased, the lateral displacement increased somewhat. The greater the eccentricity is, the greater the lateral displacement. As the eccentricity increased, the failure mode of the RC column changed from compression failure to bending failure.

Structural response of precast reinforced concrete structure with emulative moment connections under internal column loss scenarios

Depending on the design, the connections of precast concrete (PC) structures can be susceptible to severe damage under large deformation. Consequently, PC structures may behave differently from cast-in-situ reinforced concrete (RC) structures under column loss scenarios. This study focuses on a class of PC structures that utilize splice sleeves (SSs) to assemble the precast components with integrated beam-column connections (IBCCs). This PC design can alleviate rebar congestion issues and minimize the need for post-cast concrete in the connection regions during assembly. The IBCCs are typically designed to mimic the behavior of corresponding RC connections under service loading conditions. However, the extent of structural emulation under column loss scenarios is not immediately clear. In this paper, the collapse behavior of PC structures with IBCCs under an internal column removal scenario is thoroughly assessed using experimental investigations and numerical analyses. Three PC subassemblages and one RC subassemblage are tested experimentally to provide experimental data for the calibration and validation of finite element (FE) models. The collapse behavior of full-span PC and RC subassemblages are next compared numerically under the internal column loss scenario, with an accompanying investigation on the influence of horizontal SSs. It is found that the PC subassemblages exhibit emulative collapse behavior as the RC subassemblage under internal column loss scenarios, provided that the horizontal SSs are located beyond the beam plastic region under the internal column loss scenario. To achieve the latter, a minimum distance of 0.15 L (L is clear beam span before column removal) is recommended for the positioning of horizontal SSs under the internal column loss scenario. Finally, it is shown that the fracture load and corresponding displacement can be enhanced with the incorporation of high ductility rebars.

Basic Study on the Proposal of New Measures to Improve the Ductility of RC Bridge Pier and Their Effectiveness

To enhance the seismic performance of reinforced concrete (RC) elements, it is essential to consider both strength and ductility post-yielding. This study proposed a novel method to improve the ductility of RC piers by using preformed inward-bending longitudinal reinforcements at the plastic hinges. Two full-scale model tests of standard and ductility-enhanced (DE) RC piers and numerical simulations were conducted. The lateral reversed cyclic loading experiments were conducted to assess the effectiveness of this new approach. The performance was evaluated regarding failure mode, plastic hinge distribution, hysteretic properties, normalized stiffness degradation, normalized energy dissipation capacity, bearing capacity, and ductility. Non-linear finite element method (FEM) analyses were also carried out to investigate the usefulness of the proposed method by DIANA, and simulation was validated against the experiment results by hysteretic curves, skeleton curves, failure mode crack pattern, ductility coefficient, and bearing capacity. The results indicated that the proposed method enhanced bearing capacity, resistance to stiffness degradation, energy dissipation capacity, and ductility. Additionally, it was observed that the preformed positions and curvature of the main steel bars influenced the plastic hinge location and the buckling of longitudinal reinforcements. FEM analysis revealed that it might be reasonable to deduce the other factors that influenced the ductility of the specimens by using the same material parameters and models.

Flexural performance of BFRP grid–ECC in strengthening damaged RC beams

An innovative strengthening method combining basalt fiber reinforced polymer (BFRP) grid and engineered cementitious composites (ECC) is proposed to address the shortcomings in the durability of bonded connections with FRP materials and concrete materials. In this method, the BFRP grid wraps around the original damaged reinforced concrete (RC) structure, and the outer layer is cast with ECC, which mainly acts as a binder to enhance the bonding effect. In order to verify the effectiveness of the proposed method, 10 specimens were prepared and their flexural characteristics and load carrying capacity were investigated. Some factors that may affect the effectiveness of strengthening, such as the degree of initial damage (expressed in terms of different initial damage loads), the thickness of the BFRP grid, and the method of reinforcement, were considered in the experiments. The experimental results show that the proposed strengthening method can significantly improve the bending capacity of the damaged RC beams (7%~43%) without significantly enlarging the cross-section and self-weight. In addition, during the loading tests, localized peeling between the BFRP grid–ECC layer and the RC beams occurs at the time of damage, meanwhile the BFRP grid breaks. This suggests that it is feasible to enhance the bond between BFRP grid and RC by using ECC layer instead of other materials as the bonding agents. The proposed strengthening method has a promising application in strengthening old/residual bridges. In addition, a simple formula for predicting the flexural load capacity of the strengthened beams is derived. The ratio of the proposed formula to test value is between 0.853 and 1.304. The flexural load capacity predicted by the proposed formula is in better agreement with the experimental results.

Seismic performance on PSPC beam - concrete encased CFST column frame with a built-in reduced beam section

The concrete-filled steel tubular (CFST) column is widely used to connect with a steel beam owing to the quick dry connection and acceptable seismic performance. Therefore, a partially steel-reinforced precast concrete (PSPC) beam with an embedded H-beam was developed to combine the merits of both the prefabrication in the precast concrete beam and the quick assembly in the steel beam. In this study, the developed beam was proposed to connect the concrete encased CFST column with a reduced beam section. A half-scaled frame substructure specimen with two floors and two bays was designed and tested under the cyclic loading to investigate the seismic performance. A series of seismic properties were analyzed, including the failure phenomena, hysteretic performance, stiffness degradation, and energy dissipation capacity. The dog-bone configuration was found to benefit the beam hinge failure mechanism and an acceptable deformation capacity (the ductility coefficient up to 2.77). The function of the H-beam contributed to stable energy absorption (the equivalent damping coefficient from 0.33 to 0.37). Finally, the proposed frame was compared with a reinforced concrete frame and a steel-reinforced concrete frame through numerical analysis. The partial steel-reinforced configuration had a positive influence on the bearing capacity, hysteretic performance, and safety storage. In addition, it could improve the cost-effectiveness with little decrease in the bearing capacity.

Experimental and numerical simulation of seismic behavior of reinforced concrete frames infilled with refractory straw blocks

Recent earthquakes have highlighted the vulnerability of infilled reinforced concrete structures due to the insufficient consideration of infill masonry walls' contribution to strength and stiffness. This study presents a novel refractory straw block (RSB) designed to address these challenges and improve the seismic performance of reinforced concrete (RC) frames. Unlike traditional infills, RSB is characterized by low-elastic-modulus, low-density, and high-ductility. Quasi-static tests were performed on three types of frames: unfilled, infilled hollow grouted bricks (HGB), and infilled RSBs. Failure model, stiffness, and load-displacement response of three specimens were investigated and analyzed. The results indicate that RSBs as infill material does not alter the failure mode and constitutive relationship of bare frame, while HGBs leads to shear failure. The peak load for the specimen IF-HGB was 69.3 kN at 1.1 % drift, compared to 38.8 kN at 2.4 % drift for the specimen IF-RSB, and 36.4 kN at 2.0 % drift for the specimen BF. The strengths of specimens IF-HGB and IF-RSB were 1.90 and 1.07 times that of specimen BF, respectively. The stiffness of specimen IF-HGB was 3.7 times that of the other specimens, but its allowable displacement was only 61 % of theirs. Dynamic time-history analyses were also performed on structures with no longitudinal infill (BF), with RSBs (SBF), and with fired bricks (FBF). At the design level of rare events (magnitude 8, PGA 400 gal), severe damage occurred, but collapse was limited. When the PGA increased further, the collapse probability of model FBF rose rapidly, whereas the collapse probabilities of models SBF and BF remained low and similar. Accounting for the confining effect of walls, model FBF showed a higher probability of severe damage than models SBF and BF, particularly under minor earthquakes. The maximum inter-storey drift ratio of the model SBF and FBF were respectively 1.2 times and 1.7 times that of the model BF, which shows that straw blocks as infill can greatly avoid the effect of infill on the seismic behavior of the structure. The study also emphasized the often-overlooked confining effect of masonry on columns, which can lead to unrealistic damage assessments and seismic shear force distributions.

Dynamic behaviour of ultra-high performance concrete beams with rectangular openings subjected to impact loads

To facilitate residents’ needs, contemporary building structures often incorporate prefabricated transverse openings in reinforced concrete (RC) beams to accommodate pipeline installations. However, these openings can potentially impact the load-bearing capacity of the beams, particularly as structures increasingly need to consider dynamic loading effects. The use of ultra-high performance concrete (UHPC) has proven effective in enhancing the dynamic resistance of RC beams with openings. This study employs numerical simulations in ANSYS/LS-DYNA to investigate the dynamic response of UHPC beams with rectangular openings exposed to low-velocity impact. The calibrated Continuous Surface Cap (CSC) model is primarily validated through quasi-static four-point loading tests on UHPC beams with openings. Following this validation, numerical simulations of drop hammer impact are carried out to comprehensively analyse the behaviour of UHPC beams with openings. Furthermore, parametric investigations are performed to evaluate the impact response of UHPC beams with large or small openings, considering various design factors such as opening size, opening position, stirrup quantity and UHPC strength level.

Equivalent thickness method of CFRP in chloride ion diffusion equation for CFRP–strengthened RC members and its load capacity assessment method

Carbon fiber reinforced polymer (CFRP)–strengthened reinforced concrete (RC) structures exhibit resistance to chloride ion penetration. However, accurately quantifying this resistance and predicting the load capacity of CFRP–strengthened RC beams subjected to chloride ion erosion requires further investigation. This paper introduces two equivalent thickness methods for non-fully bonded CFRP within the chloride ion diffusion equation: first method assumes CFRP having a fixed equivalent thickness, while the second method allows for CFRP having a linearly decreasing equivalent thickness depending on the depth within the concrete. A model is established between the reduction factor of load capacity in CFRP–strengthened RC beams and the concentration of diffusing chloride ions. Based on experimental results from our research group regarding chloride ion erosion in CFRP–strengthened RC members, both the equivalent thickness method and the load capacity model for CFRP were evaluated. The findings indicate that the chloride ion concentration predicted by the second equivalent thickness method outperforms the first, with an error of 13.1%. Furthermore, this method accurately predicts the chloride ion concentration after 60 days of exposure, exhibiting an error of 7.0%. Additionally, employing the proposed load capacity model, derived from the second equivalent thickness method, the calculated load capacity of CFRP–strengthened RC members subjected to chloride ion erosion shows only a 5.2% deviation from experimental results. This study concludes that the equivalent thickness of non-fully bonded CFRP decreases linearly with depth in concrete and establishes a direct correlation between load capacity and chloride ion concentration, thereby offering more targeted characterization methods.

The rebar corrosion length evaluation technique based on nonlinear ultrasonic guided wave energy flow

In offshore reinforced concrete (RC) structures, phenomena of rebar corrosion are widespread, seriously threatening the durability of the structures. However, the issue of entire rebar corrosion process detection, especially for the evaluation of local corrosion states and the scope, is also challengeable. The paper aims at utilizing the nonlinear ultrasonic guided wave (UGW) energy flow to identify reinforcement corrosion level and length during the entire corrosion process in RC structures and establishing a corresponding corrosion evaluation algorithm. Therefore, a corroded rebar with the surrounding concrete cover is simplified into a cylindrical layered structural model. Meanwhile, piezoelectric transducers are used for the actuation and reception of UGWs, and a granular material contact (GMC) model is applied to illustrate the mechanism for generating surface-contact-induced nonlinear components in scattering waves. Then, the propagation behavior of the nonlinear UGWs is analyzed by regarding the corrosion layer as a secondary sound source changing the wave energy flow. A corrosion evaluation algorithm based on the GMC model is established and validated by both experiment and finite element (FE) analysis. The results show that for a harmonic UGW excitation signal, the periodic relationship between the second-order nonlinear coefficient of received signal and the corrosion length is found in which the period is associated with the difference (kd) of 2 times of fundamental frequency wave number (2 kω) and double frequency wave number (k2ω). Particularly, as kd trends to zero, a degraded linear relationship is found for establishing the corrosion length evaluation algorithm with the relatively high evaluation precision and convenient evaluation technique.

Exploring the viability of copper slag geopolymer concrete in structural applications: A study on strength variability and seismic risk assessment

This study explores the use of copper slag (CS) as a sustainable alternative to natural sand (NS) in geopolymer concrete (GPC) for structural applications. Despite the potential of CS to promote environmental sustainability by repurposing industrial waste, its adoption in the construction industry remains limited. To address this gap, the study focuses on two main aspects: (i) modelling the uncertainty in the strength properties of CS-based GPC, and (ii) assessing the performance of CS-based GPC in seismic-resistant reinforced concrete (RC) framed buildings. The results show that the compressive strength of CS-based GPC is best represented by the Gumbel max and Gamma distributions, while the splitting tensile strength is well-modelled by Gamma and lognormal distributions. The flexural strength follows Gumbel max and Weibull distributions. These findings provide valuable data for probabilistic structural analysis and reliability-based design. Additionally, the seismic performance of RC frames made with GPC containing CS was found to be comparable to that of control frames with NS, confirming the viability of CS-based GPC in seismic-resistant structures. This research demonstrates that CS can be effectively utilized in GPC without compromising structural safety, contributing to more sustainable concrete construction practices.

Effect of Vertical Location of Post-Opening on Seismic Behaviour of RC Shear Wall: Experimental and Numerical Analysis

The seismic performance of reinforced concrete (RC) shear walls with post-openings is critical in civil engineering. This study investigates the influence of post-opening positions on the seismic behaviour of RC shear walls through both experimental and numerical approaches. Four shear wall specimens with varying positions of post-openings were subjected to pseudo-static tests. Additionally, Finite Element Method (FEM) simulations were employed to further analyse the structural responses of shear walls with post-openings. The results show that the vertical position of post-openings significantly affects the failure mode, peak bearing capacity, and overall seismic performance. Peak bearing capacity reductions were observed, with central and bottom openings diminishing capacity by up to 17.5% and 15.1%, respectively, while top openings had a minimal impact. Openings also influenced pre-crack initiation, yielding behaviour, and stiffness degradation, with central openings causing the most significant effects. The ductility and energy dissipation capacities of the shear walls were also affected by opening positions. Bottom post-openings led to a maximum ductility reduction of 18.4%, while top openings increased ductility by up to 24.6%. Energy dissipation capacity decreased with lower post-opening locations, with central and bottom openings reducing capacity by 78.9% and 63.0%, respectively. These findings emphasize the importance of considering opening location in the seismic design of RC shear walls to optimize structural performance.

Fragmentation behavior and velocity formula for secondary fragments from RC slabs during contact explosions

The failure process of reinforced concrete (RC) slabs under contact explosion is dominated by localized damages, accompanied by numerous flying fragments. These concrete fragments pose a significant threat to personnel and equipment, as well as causing dynamic deformation and failure of the retrofitting materials used to restrain the fragments. The behavior of concrete fragmentation during explosions has been seldom studied experimentally, and few fragment velocity formulas exist that incorporate multiple factors. In this paper, the fragmentation process is recorded using two high-speed cameras, revealing that concrete fragmentation during explosions exhibits notable zoning characteristics, with the maximum velocity observed at the center of the fragment cloud’s front. To predict this maximum velocity, a model is derived from dimensional analysis. Utilizing this model, velocity prediction formulas are proposed and validated by 29 contact explosion tests. The formulas consider the explosive-rebar position, slab thickness, explosive mass and explosive shape, and are further improved by considering the concrete cover. The results indicate that, when the slab is not breached, the deceleration of rebar on fragments is weak. However, once the slab is breached, this deceleration becomes increasingly significant as the defined scaled thickness (TS) decreases. In the limiting case, the fragment velocity when the charge is located above the rebar is 0.636 times that of when the charge avoids the rebar. Fragments when the charge avoids the rebar, should be regarded as the most unfavorable case in secondary fragment hazards assessment and structural design.