Failure Modes Research Articles

Enhancing safety: Multi‐institutional FMEA and FTA on 177Lu$^{177}{\rm Lu}$‐based radio‐pharmaceutical therapy

AbstractPurposeThis study investigates potential failure modes and conducts failure mode and effects analysis (FMEA) and fault tree analysis (FTA) on the administration of DOTATATE (LUTATHERA) and PSMA‐617 (PLUVICTO). The quality management (QM) process in radiopharmaceutical therapies (RPTs) requires collaboration between nuclear medicine (NM) and radiation oncology (RO) departments. As part of a multi‐institutional study, we surveyed various departments to identify and analyze failure modes, leading to a proposed comprehensive QM program. RPT teams in RO or NM clinics can benefit from this study by continually improving their practice.MethodsWe reviewed the literature to investigate the administration of Pluvicto and Lutathera, focusing on prospective procedural failures and potential failure modes (PFMs) and their outcomes. We distributed an FMEA survey to multiple experienced centers in ‐based RPTs and calculated risk priority number (RPN) for various PFM. We conducted an FTA using this information to pinpoint the root causes of potential failures.ResultsThe findings from the literature review and survey responses on the prospective study have identified several critical areas at risk of failure. These areas include non‐optimized treatment delivery, inadequate patient monitoring, and lack of safety training, leading to radiation contamination from the dose excreted by the patients after treatment administration. A segmented FTA was created based on the FMEA results, focusing on radiation contamination with a high RPN value.ConclusionBy identifying the root causes of failures and proposing targeted improvements to the existing QM measures, this analysis enhances safety in treatment delivery of ‐based RPTs. Given the limited number of prospective risk analysis studies in RPTs, our research addresses the necessity for more such studies and recommends methods to apply this study to other RPTs.

Influence of Compressive Strength and Steel-Tube Thickness on Axial Compression Performance of Ultra-High-Performance Concrete-Filled Stainless-Steel Tube Columns Containing Coarse Aggregates

With the increasing use of concrete-filled steel tubular (CFST) structures, exposed steel tubes are highly susceptible to corrosion, posing potential safety hazards. This study innovatively proposes the use of stainless-steel tubes instead of traditional carbon-steel ones and introduces coarse aggregates into ultra-high-performance concrete (UHPC), forming a coarse aggregate-incorporated ultra-high-performance concrete-filled stainless-steel tube (CA-UFSST). The inclusion of coarse aggregates not only compensates for the shortcomings of UHPC but also enhances the overall mechanical performance of the composite structure. Twenty sets of specimens were designed to analyze the influence of four parameters, including the coarse aggregate content, compressive strength, stainless-steel-tube thickness, and stainless-steel type on the axial compression performance of UHPC. The experimental results indicate that the failure mode of UHPC is related to the confinement ratio. As the confinement ratio increases, the failure mode transitions from shear failure to bulging failure. The addition of coarse aggregates enhances the stiffness of the specimens. Furthermore, this paper discusses the applicability of six current codes in predicting the bearing capacity of CA-UFSST and finds that the European code exhibits the best prediction performance. However, as the confinement ratio increases, the prediction accuracy becomes notably insufficient. Therefore, it is necessary to establish a more accurate calculation model for the axial compression bearing capacity.

Finite Element Modelling of Circular Concrete-Filled Steel Tubular Columns Under Quasi-Static Axial Compression Loading

This paper presents a modified finite element analysis (FEA) model for predicting the axial compression strength of large-diameter concrete-filled steel tubular (CFST) stub columns, addressing the gap in research that has often focused on smaller diameters. The size effect, which significantly impacts the structural performance of large-diameter CFST columns, is a key focus of this study. The goal is to validate the accuracy and reliability of the modified FEA model by comparing its predictions with experimental data from the literature, specifically examining ultimate axial load capacity, failure modes, and deformed shapes. In addition to validating the model, this study includes a comprehensive parametric analysis that explores how critical geometric parameters such as the diameter-to-thickness (D/t) ratio and length-to-diameter (L/D) ratio affect the axial compressive behavior of CFST stub columns. By systematically varying these parameters, the research provides valuable insights into the load-bearing capacity, deformation characteristics, and failure mechanisms of CFST columns. Furthermore, the material properties of the steel tube—particularly its yield strength—and the compressive strength of the concrete core are investigated to optimize the design and safety performance of these columns. The results indicate that the FEA model shows excellent agreement with experimental results, accurately predicting the axial load-strain response. It was observed that as the diameter of the steel tube increases, the peak stress, peak strain, strength index, and ductility index tend to decrease, underscoring the size effect. Conversely, an increase in the yield strength and thickness of the steel tube enhances the ultimate strength of the CFST columns. These findings demonstrate the reliability of the modified FEA model in predicting the behavior of large-diameter CFST columns, offering a useful tool for optimizing designs and improving safety margins in structural applications.

Application of Resonance Method in Composite Fault Diagnosis of Bearings

Poisson white noise is a more accurate representation than ideal Gaussian white noise for simulating the noise background during early bearing failures. In the context of strong Poisson white noise interference, the failure mode of rolling bearings usually remains undetermined. This paper proposes a new method for diagnosing unknown bearing faults in bearings, diagnosis is proposed, which effectively identifies unknown faults across various components. The theoretical characteristics of Poisson white noise are initially analyzed and discussed. Then, to extract potential fault characteristic information, a false characteristic frequency of bearing is constructed in the response spectrum, and the response results at this false fault characteristic are obtained. Finally, coherent resonance (CR) is introduced, and false frequencies caused by false faults are eliminated by defining a quality factor. To verify the effectiveness of the method, the experimental and simulation results were compared with the decomposition results of the SVMD algorithm. The SNR of the experimental signals for outer and inner ring faults under variable speed conditions increased to 8.62[Formula: see text]dB and 11.74[Formula: see text]dB, respectively. Results indicate show that this method not only successfully identifies fault features, but also exhibits a strong noise reduction effect.

Extended Failure Mode and Effects Analysis for Development of Hot Desert Test Cycle Proposal

ABSTRACTA growing number of gigawatt‐scale photovoltaic (PV) power plants are being established in hot desert regions worldwide, which are favored for their vast available land, high solar irradiance, long sunshine hours, and relatively low maintenance needs. This study combines insights from global PV experts on degradation rates, failure mode and effects analysis (FMEA), and desert weather conditions to develop a hot desert test cycle (HDTC). The average degradation rate for PV modules installed in hot desert regions over the past 10 years is estimated to be around 1.63% per year. Eighteen failure modes were identified and analyzed using FMEA. According to the results, the main degradation mechanisms include UV light‐induced degradation (UVLID), thermomechanical failures in interconnects and fingers, light‐elevated temperature‐induced degradation (LeTID), and abrasion of the glass and antireflection coatings. A radar map comparison shows that desert environments experience UV exposure, ambient, and module temperatures that are more than twice as high as those in moderate climates. The HDTC protocol was developed based on FMEA results and desert‐specific weather conditions. It includes tests for desert UV exposure, temperature cycles, mechanical loads, and sand/brush abrasions. To ensure consistency across countries, there is a plan to establish an internationally recognized standard that complements existing IEC standards. As the industry grows, desert regions are expected to place greater emphasis on adopting desert‐specific testing standards for the qualification and evaluation of PV modules.

Experimental and analytical assessment of the bending behaviour of floating inflated membrane beams

The study aims to study the bending and failure behaviour of the inflated membrane beams under floating conditions to support their application in floating platforms. Bending tests are conducted to assess the structural stiffness and ultimate bearing capacity of the beam with various diameters and inflated pressures. With the elastic modulus determined through four-point bending tests, a new analytical formula based on Winkler elastic foundation theory is then developed to predict the deflection of the beams. The results revealed that the beams initially undergo total submersion, followed by end turn-up and anti-arching deformation in the loaded section. The bearing capacity of the beams increases with the increase in internal pressure and diameter. Localised wrinkling is a typical failure mode at low internal pressures, while at high pressures, the failure mode shifts to boundary failure, characterised by submerging in water. The experimental and analytical results show quite good agreement, confirming the accuracy of the current analysis. Overall, this paper contributes to understanding the bending and failure behaviour of inflated membrane beams under floating conditions and supports the offshore structure safety design.

Component‐section transverse‐pressure effect on internal damage and failure mode of post‐installed rebar

AbstractA post‐installed rebar (PIR) is commonly used to establish structural connections between new components and existing structures, such as structural member extensions or concrete layer overlays in the construction/strengthening/retrofitting of buildings or bridges. In joint connections, the anchored PIR system always bears a non‐negligible compression in the component section, which is derived from the loads and self‐weight and has a confinement effect on the anchorage zone. However, excessive pressure can result in the fracture of the adhesive component, thereby leading to brittle failure in the PIR system. Owing to the important role of the adhesive component in the PIR system, this study is focused on the internal damage to the PIR system, and the effect of transverse pressure on the failure modes is investigated. This study comprises an experimental investigation of the failures of a PIR system under transverse pressure and a description of the internal damages based on the test results. Finally, an elastic analysis was established to explain the internal cracking and investigate the stress distribution in the PIR system. The tests on 34 pull‐out specimens showed two typical failures for the PIR system under transverse pressure (adhesive–rebar [A–R] interface failure and adhesive fracture failure). The A–R interface failure resulted from the shearing failure in the adhesive component, while the adhesive fracture failure resulted from the propagation of longitudinal and transverse cracks. The elastic analysis indicated that cracking in the concrete and adhesive component was dominated by circumferential stress, and the rebar rib direction and adhesive component thickness had a significant influence on the stress distribution. Based on this, some suggestions for anchorage design were made.

Size and microstructural factors affecting the micro-hole expansion ratio and fracture toughness of dual phase steel sheets

The microscopic hole expansion ratio (μHER) of a ferritic-martensitic (∼10 %) dual phase steel was measured using a novel in-situ scanning electron microscope based miniature hole expansion setup. The effect of extrinsic parameters such as specimen thickness and machining conditions, and intrinsic parameters such as hardness differential (ΔH =Hα'-Hα) between the soft ferrite matrix and hard martensite islands on μHER values was studied. The miniature HER setup allowed site-specific measurement of microscopic strain localizations in the DP microstructure through high resolution digital image correlation under the triaxial state of stress. The results from these experiments were juxtaposed against another triaxial state of stress ahead of a crack tip, in a fracture toughness (JIc) test using the single edge notched tensile (SENT) geometry for the same thickness and microstructural conditions of DP steel. It was found that the tempered DP specimen with lower ΔH resulted in a ∼45 % higher μHER as compared to the as-received DP600, although both specimens exhibited similar JIc values. This apparent discrepancy between the trends in μHER and JIc values was explained in terms of the differences in failure modes, triaxiality and plastic zone evolution in the two conditions.

Finite Element Modeling and Artificial Neural Network Analyses on the Flexural Capacity of Concrete T-Beams Reinforced with Prestressed Carbon Fiber Reinforced Polymer Strands and Non-Prestressed Steel Rebars

The use of carbon fiber reinforced polymer (CFRP) strands as prestressed reinforcement in prestressed concrete (PC) structures offers an effective solution to the corrosion issues associated with prestressed steel strands. In this study, the flexural behavior of PC beams reinforced with prestressed CFRP strands and non-prestressed steel rebars was investigated using finite element modeling (FEM) and artificial neural network (ANN) methods. First, three-dimensional nonlinear FE models were developed. The FE results indicated that the predicted failure mode, load-deflection curve, and ultimate load agreed well with the previous test results. Variations in prestress level, concrete strength, and steel reinforcement ratio shifted the failure mode from concrete crushing to CFRP strand fracture. While the ultimate load generally increased with a higher prestressed level, an excessively high prestress level reduced the ultimate load due to premature fracture of CFRP strands. An increase in concrete strength and steel reinforcement ratio also contributed to a rise in the ultimate load. Subsequently, the verified FE models were utilized to create a database for training the back propagation ANN (BP-ANN) model. The ultimate moments of the experimental specimens were predicted using the trained model. The results showed the correlation coefficients for both the training and test datasets were approximately 0.99, and the maximum error between the predicted and test ultimate moments was around 8%, demonstrating that the BP-ANN method is an effective tool for accurately predicting the ultimate capacity of this type of PC beam.

Analysis of damage characteristics of reinforced concrete slabs under explosive impact and research on CFRP reinforcement

To study the damage characteristics and damage model of reinforced concrete slabs under explosive impact, the failure modes of reinforced concrete slabs under near-field and contact explosion were first studied through on-site experiments. A coupled model was established based on the Coupled Eulerian-Lagrangian (CEL) method using AUTODYN finite element software. The reliability of the model was verified by comparing the numerical simulation results with experimental results. Based on this, a fully coupled model of Carbon Fiber Reinforced Polymer (CFRP) reinforcement for reinforced concrete slabs under contact explosion was established, and the influence of different CFRP thicknesses and reinforcement methods on the blast resistance performance of reinforced concrete slabs was discussed. The research results indicate that under the action of near-field explosions, the front face of reinforced concrete slabs mainly experiences slight peeling damage, and the central area of the back face forms seismic collapse and peeling damage, with damage cracks diverging from the center to the surrounding areas; Under the action of contact explosion, the front face of the reinforced concrete slab produces blast pits, the back face forms a seismic collapse zone, and peeling damage occurs; The CFRP reinforcement layer can improve the blast resistance performance of reinforced concrete slabs; There is an optimal thickness when using CFRP to enhance the blast resistance of reinforced concrete slabs.

Short cross-laminated timber plates subjected to out-of-plane loads

The use of cross-laminated timber (CLT) panels has increased significantly, driven by the demand for more sustainable structural solutions. When used in short spans, the load capacity of CLT panels can be significantly enhanced; however, their behaviour and failure mechanisms differ from those of large spans. This study evaluates the mechanical behaviour of short-span CLT panels made from Pinus taeda L. under out-of-plane loads, through experimental analyses on full-scale panels. Fourteen industrially manufactured panels were tested in four-point bending tests, using adhesive weights of 250 and 220 g/m². The values of maximum bending moment, shear force, and their respective resistances were analysed based on the observed failure modes. The transverse modulus of elasticity was determined using strain gauges. It was found that short panels, with a span-to-depth ratio of 9 ≤ l/h ≤ 12, exhibited bending moment and shear force failures, with no significant differences between adhesive weights. Discrepancies in shear resistance and stiffness values compared to existing standards suggest the need for reduced-specimen testing for greater accuracy.

Human errors analysis for remotely controlled ships during collision avoidance

To address human errors in collision avoidance tasks of remotely controlled ships, this study aims to develop a comprehensive framework for human error analysis within the context of autonomous ships. Firstly, the Hierarchical Task Analysis method is utilized to identify crew collision avoidance tasks associated with the traditional ship, and these tasks are then dissected into different operational stages using the Information Decision Action in a Crew cognitive model. Secondly, a combination of the fault hypothesis method and expert opinions are used to identify potential human error that may occur during collision avoidance operations of remotely controlled ships. Thirdly, an integrated approach is proposed to build a quantitative risk assessment model, which combines Failure Mode and Effects Analysis, Evidential Reasoning, and Belief rules-based Bayesian Network. Then, axiomatic analysis is used to verify the robustness and applicability of the risk assessment model. Finally, based on the results of quantitative risk assessment, specific measures are proposed for enhancing the safety of collision avoidance process of remotely controlled ships. The findings show that uncoordinated interactions of human-computer systems during the decision-making stage are a pivotal factor in the collision avoidance process. Therefore, future design efforts for remote-control centre should prioritize improving the clarity of human-computer interaction interfaces.

Abstract Su403: Iterative Simulation to Optimize Mechanical CPR Device Application

Mechanical chest compression devices (MCDs) are commonly used for in-hospital and emergency department (ED) cardiac arrest resuscitation. Manufacturer guidelines and educational materials demonstrate that in the prehospital setting, MCDs can be deployed with an interruption in CPR of less than 15 seconds. No similar materials exist for the in-hospital environment, where observational studies have noted median CPR interruptions of up to 40 seconds for MCD deployment. With the integration of extracorporeal CPR (eCPR) into OHCA systems of care, the need to transfer patients with ongoing CPR to MCDs in the ED is growing. To develop a hospital-specific procedure for receiving a patient in cardiac arrest and deploying the MCD with minimal no-flow time. We used an iterative participatory design process to develop a procedure for receiving patients in cardiac arrest from Emergency Medical Services (EMS). Tasks included transferring a patient, replacing defibrillator pads, and deploying the hospital MCD with minimal no-flow time. Participants including ED physicians, nurses, and respiratory therapists performed a series of simulations using a high-fidelity manikin, resuscitation equipment, and an MCD. Simulations were followed by focused debriefings, participant-directed modification of the working procedure, and repeat simulation until participants expressed satisfaction with the procedure. Participant roles were shuffled after each round. The primary outcome was the duration of CPR interruption required to deploy the MCD; change in this time over successive iterations was assessed using a Wilcoxon signed-rank test. The final procedure described a sequence of steps and responsibilities that participants deemed efficient and reproducible. Through seven simulation-debriefing cycles, CPR interruption associated with MCD deployment decreased from 19 to 10 seconds (p = 0.033). The most common failure modes that participants corrected during modifications involved needed equipment that was out of reach, obstructed provider positioning, and poorly defined roles. On subsequent days, two additional groups of on-shift ED providers deployed the MCD in less than 15 seconds following the developed procedure. Using an iterative design process, we created an MCD deployment procedure that minimized CPR interruptions and was acceptable to hospital staff. This represents an effective, low-cost methodology to design a process for transfer of care during CPR and MCD deployment.

Validity of Laws for Predicting Lifespan of Welded Points Under Variable Loading

The article examines the validity of the laws for predicting the life of welded points under variable amplitude loading, using three steels (HE360D, XE360D and XES) supplied by ArcelorMittal to Renault for the manufacture of automobile chassis parts. The fatigue tests revealed two modes of failure: cracking of the sheets at medium stresses and shearing of the molten core at high forces. For lifespan prediction, three damage laws were studied: Miner's law, Mesmacque and Amrouche law, and a proposed model. Miner's law, despite its simplicity and wide distribution, shows notable limitations in the presence of variable loads, because it does not take into account the interactions between successive load levels. The law of Mesmacque and Amrouche uses a damage indicator linked to the FN curve of the material, allowing a cycle by cycle estimation of the residual lifespan. However, it remains non-conservative at low effort. The proposed model, based on Chaboche law, overcomes some of its theoretical drawbacks, notably the dependence on the calibration parameters of the SN curve. By fitting this curve within a specific calibration window, the model improves forecast accuracy by taking into account parameter variability. This proposed model provides more reliable lifespan predictions that better correlate with experimental results, especially for low effort levels where Miner's law fails. The validation approach is based on comparing the predictions of the damage laws with the experimental results, by evaluating the deviation from the first bisector of the graphs. The results show that Miner's law is unsuitable for effort levels, while the proposed model turns out to be the most precise and conservative. The law of Mesmacque and Amrouche falls between the two, presenting a certain justice but remaining overall non-conservative. In conclusion, the proposed model offers a better match with experimental data, making its predictions more reliable for industrial applications.

Fracture strength of direct occlusal veneers with different short fiber-reinforced composite cores and veneering materials: an in-vitro study

ObjectiveThe objective of this study is to evaluate the effectiveness of two different viscosities of short fiber-reinforced composite resin (SFRC) cores and two different viscosities of veneering composite resins on the fracture strength of direct occlusal veneers.Materials and methodsOne maxillary premolar was virtually prepared for an occlusal veneer and printed into resin dies. In total, (n = 48) resin dies were printed and assigned into three groups according to the type of core material of the occlusal veneer; mono-structured without a SFRC core, a high viscosity SFRC core, and a low viscosity SFRC core. Each group was re-divided into two subgroups (n = 8) according to the veneering composite resin; packable composite resin and injectable composite resin. Mono-structured and bi-structured direct occlusal veneers were fabricated on the resin dies using the mentioned core and veneering materials with the occlusal replica technique. Fracture strength was evaluated using a universal testing machine and the mode of failure was inspected. Statistical analysis to compare the core and veneering materials was performed using independent t test (P ≤ 0.05) and one-way ANOVA followed by tukey’s post hoc test (Pa ≤ 0.0166) when appropriate. Interactions between subgroups were tested using two-way ANOVA, and one-way ANOVA was used to compare all subgroups followed by tukey’s post hoc test (Pa ≤ 0.0033). Intergroup comparison between failure modes were performed using chi square test (Pa ≤ 0.0033).ResultsThe presence of a SFRC core significantly improved the fracture strength of the specimens. There was no significant difference between the fracture strength of high viscosity SFRC and low viscosity SFRC cores. Specimens veneered with injectable composite resin had significantly superior fracture strength compared to packable composite resin. Additionally, there was a weak correlation between fracture strength and mode of failure.ConclusionShort fiber reinforced composite resin significantly increases the fracture strength of direct occlusal veneers. Injectable composite resin has significantly higher fracture strength than packable composite resin as veneering materials of direct occlusal veneers.Clinical relevanceBi-structured direct occlusal veneers fabricated of injectable composite resin with low viscosity SFRC cores can withstand high masticatory forces in stress-bearing areas.

Modelling and experimentation of failure modes to obtain safe operating range for improved dielectric elastomer actuation performance

Abstract Dielectric elastomers (DEs) possess high energy density, lightweight, and low response time making them suitable material candidatures for electromechanical transducers (ET). Performance enhancement of ET necessitates escalated electrical load making prone to failure and subsequently hindering reliability and life cycle. Existing models towards failure mitigation focus on mechanical and electrical loads individually with constant relative permittivity, whereas DEs undergoes combined loading and stretch-electrostriction in real-time application. This study aims to identify safe design and operating parameters by addressing various modes of failures under combined loads and stretch-electrostriction. Under combined load, pre-strain emerges as a crucial parameter to reduce EMI, while extensive pre-strain leads to diminish thickness which in turn promotes electrical breakdown of elastomer. The optimized design for DEs exhibit substantial failure suppression at a pre-strain value of 1.7 ( λ pre ) under maximum electrical load of 37.66 MV / m ( E max ). The efficacy of optimized parameters for the failure suppression is verified through an in-house fabricated planar actuator. Operation within the identified range of parameters is observed to enhance the reliability and lifespan of DE-actuators, marking a noteworthy advancement in the field of soft robotics.

Numerical study of cellular beams under different types of loading

The integration of cellular metal beams in high-rise buildings allows for optimized space utilization for technical equipment, while also reducing floor height and, consequently, the overall weight of the superstructure. However, while these openings provide design flexibility, they can also decrease structural stability by causing deformations in the web posts, especially under concentrated loads. This study focuses on evaluating the strength and stability of open-section beams under various load conditions, using numerical simulations and three-point bending tests. Specific reinforcement solutions were developed to counter instability phenomena and enhance mechanical performance. The results indicate that the finite element model used in simulations provides accurate and consistent predictions with experimental data, validating its utility for in-depth analysis of displacements and failure modes. Notably, the addition of stiffeners proved effective in reducing displacements and enhancing beam stability. This work, still in its exploratory phase, aims to develop a theoretical formula to estimate the contribution of supports to elastic stiffness, paving the way for advances in the use of reinforced metal beams in high-rise construction.

Experimental analysis of the influence of concrete top slab thickness and longitudinal reinforcement on the shear strength of flat slab ribs

AbstractThis paper reports a study on reinforced concrete waffle flat slabs under center loading. The study variables were concrete top slab thickness (CTST) and flexural reinforcement ratio. Twelve square slabs 1800 mm wide, 1800 mm long, and 150 mm thick were produced. The specimens were tested to failure to assess their behavior throughout load application and their failure mode. None of the slabs had shear reinforcement in the ribs. The experimental findings showed that both CTST and flexural reinforcement ratio increased the stiffness and the ultimate strength of the slabs. The most significant gains were found in the slabs with higher thickness values and higher reinforcement ratios. The results of the database showed that all codes had underestimated the ultimate strength of the slabs, as they presented rather conservative values. The modified normative equations were able to reduce the coefficient of variation of the database by at least 50%.

Enhancing Quality Control in the Mix Design of High-Strength Concrete Using a Capacity-Based Approach

The mix design of concrete is an important aspect that affects its strength and durability. This paper aims to revisit the existing mix design method given in IS 10262:2019 through a capacity-based approach. The approach involves identifying the possible failure modes in concrete and eliminating the undesirable ones leading to significant reduction in dispersion. This is accomplished by utilizing coarse aggregates that meet a specific minimum strength requirement or threshold (e.g., ~ 77 MPa for M95 grade of concrete), which is determined through a priori estimating the cohesion and friction angle of the concrete. The methodology to estimate the cohesion and friction angle from a single unconfined compression test is proposed based on the Mohr–Coulomb theory and using the orientation of failure plane of fractured specimen as a supplemental information from the same experiment. This paper also offers a simple and approximate test procedure to estimate the aggregate's compressive strength (~ 106 MPa in this mix design) reasonably which is essential for the capacity-based mix design. An experimental programme is also carried out to design the concrete mix using the proposed capacity-based approach. The results indicate that M95 concrete is achieved with a low standard deviation and coefficient of variation (~ 3%), falling in class of excellent quality control as per ACI 214R-11. This quality control is crucial in seismic structural design as variations in concrete strength is likely to negate the underlying principle of strong column–weak beam philosophy resulting in the triggering of undesirable shear modes of failure.

Experimental and numerical study on the torsional behavior of rectangular hollow reinforced concrete columns strengthened By CFRP

This paper reported a series of hysteretic torsion experiment to investigate the torsional behavior of rectangular hollow reinforced concrete (RHRC) column strengthened by fiber reinforced polymer (FRP). Six RHRC column specimens with different number of longitudinal reinforcements, spacing of stirrup and strengthening method using FRP were designed. One was not strengthened, four were strengthened with CFRP, one was strengthened with CFRP and GFRP. The experimental results showed that the primary failure modes of specimens were the spalling of surface concrete with the detachment of FRP. In details, under the hysteretic torsional load, the interaction between adhesive and concrete caused the intersecting diagonal cracks in the internal concrete. Compared with the hysteretic curve of specimen without FRP strengthening, FRP strengthening can significantly improve the initial stiffness by 50 % and peak torsional strength by 70 %. For RHRC column without strengthening, the fullness was poor because of the weak torsional energy dissipation. The FRP strengthening can also enhance the torsional energy dissipation and seismic behavior of RHRC column. To predict the complex torsional behavior of RHRC column strengthened by FRP, a finite element (FE) model and a constitutive model were developed. The FE model considered potential cracks in concrete and FRP–concrete interface based on the application of the cohesive zone model (CZM), whereas the constitutive model accounted for interface damage and plasticity. The results of the performed simulations indicated that the proposed model can effectively represent the hysteretic mechanical behavior of columns under torsional load, which cannot be achieved using conventional FE methods.