Residual Capacity Research Articles

Low-Temperature In Situ Lithiation Construction of a Lithiophilic Particle-Selective Interlayer for Solid-State Lithium Metal Batteries.

Unexpected interface resistance and lithium dendrite puncture hinder the application of garnet-type solid-state electrolytes in high-energy-density systems. Different from the previous high-temperature (>180 °C) molten lithium that promotes the alloying reaction between the coating layer and Li to enhance the interface contact, herein, we introduce liquid-metal-like SbCl3 to construct a three-dimensional Li+ directional-selection interlayer by in situ low-temperature lithiation (80 °C). An interlayer with a more negative interface energy composed of SbLi3 and LiCl exhibits a superior affinity with Li and LGLZO, which reduces the interface resistance and suppresses the growth of Li dendrites by an insulated electron. The introduction of the SbCl3 modification layer into Li/Li symmetric cells enables charge/discharge at a current density of 6.0 mA cm-2 and operation for more than 1000 h under 2.0 mA cm-2 at room temperature. The full cells with the LiFePO4 cathode exhibit a high residual capacity of 144.8 mAh g-1 at 0.5 C after 1000 cycles and excellent cycling stability with a retention ratio of 94.7% at 1 C after 600 cycles. The low-temperature lithiation method based on an energy-saving perspective should be applied to other types of solid-state electrolyte modification strategies.

Cranial Electrode Belt Position Improves Diagnostic Possibilities of Electrical Impedance Tomography during Laparoscopic Surgery with Capnoperitoneum.

Laparoscopic surgery with capnoperitoneum brings many advantages to patients, but also emphasizes the negative impact of anesthesia and mechanical ventilation on the lungs. Even though many studies use electrical impedance tomography (EIT) for lung monitoring during these surgeries, it is not clear what the best position of the electrode belt on the patient's thorax is, considering the cranial shift of the diaphragm. We monitored 16 patients undergoing a laparoscopic surgery with capnoperitoneum using EIT with two independent electrode belts at different tomographic levels: in the standard position of the 4th-6th intercostal space, as recommended by the manufacturer, and in a more cranial position at the level of the axilla. Functional residual capacity (FRC) was measured, and a recruitment maneuver was performed at the end of the procedure by raising the positive end-expiratory pressure (PEEP) by 5 cmH2O. The results based on the spectral analysis of the EIT signal show that the ventilation-related impedance changes are not detectable by the belt in the standard position. In general, the cranial belt position might be more suitable for the lung monitoring during the capnoperitoneum since the ventilation signal remains dominant in the obtained impedance waveform. FRC was significantly decreased by the capnoperitoneum and remained lower also after desufflation.

Properties of polyoxymethylene fibre-reinforced seawater sea sand concrete exposed to high temperatures

Using seawater and sea sand to prepare concrete can reduce the adverse effects from the resource shortage and environmental pollution caused by the exploitation of freshwater and river sand. In addition, polyoxymethylene (POM) fibres have excellent alkali resistance and durability, which may considerably improve the mechanical properties of seawater sea sand concrete (SWSSC). Fires are a common structural disaster. Thus, the post-fire mechanical properties of POM fibre-reinforced SWSSC (POM-SWSSC) were experimentally studied herein to evaluate the residual bearing capacity of the POM-SWSSC structure after a fire. After the heating and cooling procedures, the apparent morphology and mass loss of POM-SWSSC were recorded, and the compressive and tensile properties of the POM-SWSSC were investigated. The test results indicate that the colour of the SWSSC changed from cyan to yellow with an increase in exposure temperature. When the temperature exceeded 400 °C, the mechanical properties of the POM-SWSSC deteriorated sharply. Compared with compressive strength, high temperature had a more significant effect on the tensile strength of SWSSC. The addition of POM fibres could alleviate this issue. Compared with other fibre-reinforced concretes, POM-SWSSC had a higher cube compressive strength and splitting tensile strength after exposure to 400 °C. A prediction model was proposed to quantify the effect of different high temperatures on the mechanical properties of NF-SWSSC and POM-SWSSC.

Simplified approach for modeling standard PVB at large deformations and long-term loading

Recently, the numerical simulation of the residual load-bearing capacity of laminated glass (LG) is an often discussed but not sufficiently solved problem in structural glass design yet. According to CEN/TS 19100:2021 (2021a), and CEN/TS 19100:2021 (2021b), the design in the Post Fracture Limit State (PFLS) is possible experimentally and numerically. Experimental verification requires large-scale component tests, which are often costly and time-consuming. The resource-saving numerical approach is to be preferred. However, at the moment, there is no sound numerical model capable of representing the complex load-bearing mechanisms of broken laminated glass (LG) in civil engineering practice. These mechanisms are the finite-strain response of the interlayer, the contact between glass fragments or shards themselves, and the bond between glass and interlayer. Delamination governs the latter one mainly. This work focuses on the experimental, mechanical, and numerical characterization of the finite-strain behavior of polymeric laminated glass interlayers at long load durations by the example of standard single-layer Polyvinylbutyral (PVB). Based on that, it introduces an approach enabling the simplified numerical simulation of LSG interlayers. The considerations rely on experiments and thermodynamic considerations.

Pharyngeal oxygen delivery device sustains manikin lung oxygenation longer than high-flow nasal cannula

Purpose Hypoxemia during a failed airway scenario is life threatening. A dual-lumen pharyngeal oxygen delivery device (PODD) was developed to fit inside a traditional oropharyngeal airway for undisrupted supraglottic oxygenation and gas analysis during laryngoscopy and intubation. We hypothesized that the PODD would provide oxygen as effectively as high-flow nasal cannula (HFNC) while using lower oxygen flow rates. Methods We compared oxygen delivery of the PODD to HFNC in a preoxygenated, apneic manikin lung that approximated an adult functional residual capacity. Four arms were studied: HFNC at 20 and 60 liters per minute (LPM) oxygen, PODD at 10 LPM oxygen, and a control arm with no oxygen flow after initial preoxygenation. Five randomized 20-minute trials were performed for each arm (20 trials total). Descriptive statistics and analysis of variance were used with statistical significance of P < 0.05. Results Mean oxygen concentrations were statistically different and decreased from 97% as follows: 41 ± 0% for the control, 90 ± 1% for HFNC at 20 LPM, 88 ± 2% for HFNC at 60 LPM, and 97 ± 1% (no change) for the PODD at 10 LPM. Conclusion Oxygen delivery with the PODD maintained oxygen concentration longer than HFNC in this manikin model at lower flow rates than HFNC.

Experimental and analytical studies on residual flexural behaviour of reinforced alkali-activated slag-based concrete beams after exposure to fire

Understanding the flexural behaviour of reinforced alkali-activated slag-based concrete beams after exposure to a fire is imperative to ensure their safety use and develop adequate retrofitting measures. However, up to this point in time, no relevant investigations on this specific subject have been reported. This paper presents an experimental study comparing the flexural behaviour of alkali-activated slag-based concrete (AAC) and Portland cement concrete (PCC) beams exposed to the standard ISO 834 fire curve. The research considers concrete strength and heating duration as research parameters. The test results revealed that AAC beams displayed a lower temperature field and experienced less mid-span deflection increase compared to PCC beams during heating. Normal-strength AAC and PCC beams exhibited comparable losses in flexural capacity after being heated for 1 h or 1.5 h. However, PCC beam with a concrete strength over 80 MPa experienced more capacity loss due to severe spalling during heating. On the other hand, compared with PCC counterparts, AAC beams exhibited lower residual flexural stiffness and experienced greater stiffness loss, mainly due to the formation of more cracks induced by thermal shrinkage of AAC. The flexural capacity and stiffness loss of AAC beams increased with increasing concrete strength and heating duration after fire exposure. The residual flexural capacities of RC beams were predicted using a simplified analytical model that incorporates heat transfer analysis and the 500 ℃ isotherm method. The predictions demonstrated excellent agreement with the test results.

Subtypes of Patients with Mild to Moderate Airflow Limitation as Predictors of Chronic Obstructive Pulmonary Disease Exacerbation.

COPD is a heterogeneous disease, and its acute exacerbation is a major prognostic factor. We used cluster analysis to predict COPD exacerbation due to subtypes of mild-moderate airflow limitation. In all, 924 patients from the Korea COPD Subgroup Study cohort, with a forced expiratory volume (FEV1) ≥ 50% and documented age, body mass index (BMI), smoking status, smoking pack-years, COPD assessment test (CAT) score, predicted post-bronchodilator FEV1, were enrolled. Four groups, putative chronic bronchitis (n = 224), emphysema (n = 235), young smokers (n = 248), and near normal (n = 217), were identified. The chronic bronchitis group had the highest BMI, and the one with emphysema had the oldest age, lowest BMI, and highest smoking pack-years. The young smokers group had the youngest age and the highest proportion of current smokers. The near-normal group had the highest proportion of never-smokers and near-normal lung function. When compared with the near-normal group, the emphysema group had a higher risk of acute exacerbation (OR: 1.93, 95% CI: 1.29-2.88). However, multiple logistic regression showed that chronic bronchitis (OR: 2.887, 95% CI: 1.065-8.192), predicted functional residual capacity (OR: 1.023, 95% CI: 1.007-1.040), fibrinogen (OR: 1.004, 95% CI: 1.001-1.008), and gastroesophageal reflux disease were independent predictors of exacerbation (OR: 2.646, 95% CI: 1.142-6.181). The exacerbation-susceptible subtypes require more aggressive prevention strategies.

Hybrid strengthening and flexural behaviour of post-tensioned laminated glass beams

The strengthening of glass for structural applications is challenging. EBR (External Bonded Reinforcement) reinforcement is often preferred, although limitations result from stress concentrations especially in the case of post-tensioning. This study explores the use of CFRP (Carbon Fiber Reinforced Polymers) and/or Fe-SMA (Iron-based Shape Memory Alloys) as reinforcement in hybrid and alternative configurations. Five full size laminated glass beams were tested in flexure, combining NSM (Near-Surface Mounted) and EBR techniques and exploring the efficiency of different alternative strengthening layouts (i.e. reinforcement material versus application technique) to overcome the current shortfalls of glass strengthening for structural applications. Even for lower reinforcement ratios, hybrid strengthening systems performed better and increased load-carrying capacity while delaying crack-induced deboning failure, when compared to conventional EBR systems. Residual strength ratio increased from 87 % to 160.8 % and ductility from 407 % to 971 %. The hybrid system combining NSM-CFRP and EBR-SMA reinforcements showed the best performance, increasing the initial fracture stress of glass and maintaining sufficient residual strength capacity, while allowing the safe post-tensioning.

Study on Lifetime Performance Evaluation of a Precast Prestressed Concrete Frame in Chloride Environments.

This study established a comprehensive framework for evaluating the lifetime performance of precast prestressed concrete frames exposed to chloride environments. The proposed analytical framework enabled a scientifically grounded and rational assessment of both the service life and residual load-carrying capacity of precast prestressed concrete frames in chloride environments. It further served as the foundational basis for making informed decisions regarding the repair and maintenance of pertinent structures. Based on Fick's second law, this evaluation framework established the probability distribution of the corrosion initiation time and cracking time of reinforced concrete structures due to corrosion expansion in a chloride environment. Additionally, based on the fragility analysis model and results of a precast prestressed concrete frame in a chloride environment, a practical method for evaluating the time-varying seismic performance of the precast structure considering the influence of corrosion was proposed. Furthermore, by employing the path probability model and reliability theory, time-varying reliability models were proposed to predict the three limit states of the precast prestressed concrete frame. According to the analysis results of a four-story planar frame, it could be seen that the corrosion initiation time and normal service limit state were highly sensitive to the chloride ion diffusion coefficient of the composite layer in precast concrete structures. Compared to cast-in-place structures, the presence of a composite layer in precast concrete structures could lead to more severe degradation of the time-varying seismic performance of the precast prestressed concrete frame.

Propagation and arrest of collapse failures in a buried offshore pipeline crossing reverse fault areas

Offshore pipelines crossing fault rupture areas suffer the risk of local buckling, which can in turn initiate propagating buckles. This study presents the results of evaluating several series of local collapses, subsequent propagating buckles, temporary buckling arrests, and crossover simulations of a deformed (due to reverse fault displacements) offshore pipeline under external overpressure. A numerical model of a buried pipeline with a single (twin) integral arrestor(s) was developed using a nonlinear vector form intrinsic finite element method. The residual external pressure capacity of a deformed pipeline after reverse fault displacements was assessed. Single integral arrestors at different installation sites and twin integral arrestors of different lengths were tested. Effects of fault dip angles on the propagation and arrest of collapse failures were investigated. The longitudinal and bending deformations caused by reverse fault displacements result in a significant decrease in the external pressure resistance of offshore pipelines. Four weak areas appeared around the bending regions, the size relationship of their collapse pressures determined the sequence of multiple local collapses and directions of the subsequent propagating buckles. Integral arrestors are effective designs with significant arresting efficiency in such scenarios. The flexure curve of the pipeline changed significantly only when an arrestor was installed in the left- or right-bending region. A large fault dip angle leads to both higher first collapse pressures and crossover pressures due to smaller bending deformations. A flipping crossover occurs when a downstream reverse ovality develops, which rotates the collapse direction by 90°. The material efficiency of integral arrestors will decrease with the occurrence of flipping crossovers.

The effect of inhaled extrafine beclometasone dipropionate/formoterol fumarate/glycopyrronium bromide on distal and central airway indices, assessed using Functional Respiratory Imaging in COPD (DARWiIN)

BackgroundThis study, in patients with symptomatic chronic obstructive pulmonary disease (COPD), explored switching therapy from non-extrafine high-dose inhaled corticosteroid/long-acting β2-agonist (ICS/LABA; fluticasone propionate/salmeterol [FP/SLM]) to extrafine medium-dose beclometasone dipropionate/formoterol fumarate dihydrate/glycopyrronium (BDP/FF/G), both via dry-powder inhaler. Functional Respiratory Imaging, a quantitative computed tomography method with 3D reconstructions of pulmonary anatomy, was used to assess airway geometry and lung function.MethodsPatients receiving a stable ICS/LABA regimen for ≥ 8 weeks were switched to FP/SLM 500/50 µg, one inhalation twice-daily (high-dose ICS) for 6 weeks. After baseline assessments (Visit 2 [V2]), therapy was switched to BDP/FF/G 100/6/10 µg, two inhalations twice-daily (medium-dose ICS) for 6 weeks, followed by V3. The primary endpoints were percentage changes in specific image-based airway volume (siVaw) and resistance (siRaw) from baseline to predose at V3 (i.e., chronic effects), assessed at total lung capacity (TLC) in central and distal lung regions. Secondary endpoints included siVaw and siRaw changes from pre-dose to post-dose at V2, and from pre-dose to post-dose at V3 at TLC (i.e., acute effects), and chronic and acute changes in siVaw and siRaw at functional residual capacity (FRC). Pre-dose forced expiratory volume in 1 s (FEV1) and COPD Assessment Test (CAT) were also assessed.ResultsThere were no significant changes in pre-dose siVaw or siRaw at TLC from baseline to V3, although at FRC there was a significant decrease in mean siRaw in the distal airways (− 63.6%; p = 0.0261). In addition, in the distal airways there were significant acute effects at TLC on mean siVaw and siRaw (siVaw: 39.8% and 62.6%; siRaw: − 51.1% and − 57.2%, V2 and V3, respectively; all p < 0.001) and at FRC at V2 (siVaw: 77.9%; siRaw: − 67.0%; both p < 0.001). At V3, the mean change in pre-dose FEV1 was 62.2 mL (p = 0.0690), and in CAT total score was − 3.30 (p < 0.0001).ConclusionsIn patients with symptomatic COPD receiving high-dose ICS/LABA, adding a long-acting muscarinic antagonist while decreasing the ICS dose by switching to medium-dose extrafine BDP/FF/G was associated with improved airway indices, especially in the distal airways, together with improvements in respiratory health status.Trial registration ClinicalTrials.gov (NCT04876677), first posted 6th May 2021

An experimental and numerical study of ultra-high strength concrete filled circular tube column post-fire

Extensive experimental research was conducted on 10 ultra-high strength concrete filled tubular (UCFCT) columns to investigate their performance after exposure to the ISO-834 standard fire and external load. Two different diameters of steel tubes (219.1 mm and 273 mm) with concrete strength ranging from 161 MPa to 181 MPa were included in the study. The primary parameter examined was temperature, ranging from 94 °C to 618 °C. The study obtained data on the residual capacity, working mechanism, and ductility of the columns under compressive load after the fire. The compression experiments revealed that the load capacity of the UCFCT columns remained high. As the columns deformed beyond the inflection point, the load capacity increased gradually without decline. This indicates that the UCFCT columns exhibited notable ductility even after the fire and cooling process. The residual capacity of the columns was influenced by the highest temperature experienced during the experiment. The study also observed the splitting of the ultra-high strength concrete (UHSC) inside the specimens and described the failure mode. Local wall buckling did not occur prior to yielding, and the specimens demonstrated strain-hardening after reaching the plastic point. The mechanical properties of the steel and UHSC were investigated and incorporated into a numerical model that satisfactorily described the post-fire behavior of the composite columns compared to the test data. Based on this theoretical model, the influence of changing material strength (steel and concrete), fire duration time, specimen diameter, and steel ratio on the residual capacity ratio and residual rigidity ratio was discussed. It was generally observed that sectional dimensions and fire duration time had a significant impact on the residual capacity ratio. Finally, formulas suitable for calculating the residual strength of ultra-high strength concrete-filled circular tube columns after exposure to the ISO-834 standard fire were developed based on the results of the parametric analysis.

It's time to stop using nitrous oxide for pediatric mask induction.

Mask induction of anesthesia for pediatric patients has included the use of nitrous oxide since the inception of pediatric anesthesia. However, the use of nitrous oxide precludes adequate preoxygenation. Additionally, pediatric physiology (less Functional Residual Capacity, higher oxygen consumption), increased risk of laryngospasm and lack of intravenous access increase the risk of a severe airway complication in the event of airway occlusion. Nitrous oxide does not facilitate tranquil mask placement on an unwilling child and does not meaningfully speed mask induction. Exposure to nitrous oxide has potential occupational health concerns and nitrous oxide has significant environmental detriment. Utilizing other, evidence-based, techniques to facilitate tranquil mask placement will assure that patients have a pleasant induction experience and avoiding nitrous oxide will reduce the environmental impact, as well as improve the safety of, pediatric mask induction.

Performance of pre-cracked beams exposed to corrosion environment cast with ultra-high performance concrete

Ultra-high-performance concrete (UHPC) is a unique type of concrete that has a lot of advantages in the construction sector. There is no risk for reinforced UHPC elements in an aggressive environment or coastal region, unless cracking occurs due to extra-loading or inaccurate structural design. For that, there is a need for this study to be considered. The core concentration of this study is towards understanding the shear behavior of pre-cracked beams cast with UHPC as affected by durability. This program presents materials used to reach the main aim of the present study. 72 specimens were conducted to study UHPC physical and mechanical properties to be compared with traditional normal concrete (NC). Moreover, 10 RC beams were cast to investigate the shear behavior of RC-UHPC beams with dimensions of 100 mm, 150 mm, and 1300 mm. Five non-exposure beams and five exposure beams were corroded by an accelerated corrosion cell, and half the potential cell readings were recorded. Obtained results for specimens provide that; UHPC eliminates deflection with high modulus of elasticity, in chloride penetration test UHPC is 200 times less than NC, and the reduction in bond strength test after corrosion exposure is 66.24 % and 1.69 % for NC and UHPC specimens, respectively. For pre-carking UHPC beams at 80 % of experimental ultimate load; cracking resistance for un-corroded beams exceeds the corroded beams by 250 %. The residual flexural capacities for corroded beams pre-cracking up to 80 % of E.U.L. are 61.6 % and 119 % for NC and UHPC beams, respectively. UHPC is much better than NC in corrosive environments.

Yangqing Chenfei formula alleviates crystalline silica induced pulmonary inflammation and fibrosis by suppressing macrophage polarization.

To explore the underlying mechanisms of the effects of Yangqing Chenfei formula (, YCF) on inflammation and fibrosis in silicosis via inhibition of macrophage polarization. A silicotic rat model was established via a single intratracheal instillation of silica particles on the first day of week 0. Subsequently, YCF was administered intragastrically to silicotic rats during weeks 0-2 and 5-8 twice daily. The mouse-derived alveolar macrophage cell line was used to investigate the mechanisms of YCF in M1/M2 polarization. YCF treatment effectively inhibited lung pathological changes, including inflammatory cell infiltration and tissue damage, and increased the forced expiratory volume in the first 0.3 s, functional residual capacity, and maximal mid-expiratory flow in weeks 2 and 8. Furthermore, the treatment improved lung functions by upregulating tidal volume, pause increase, and expiratory flow at 50% tidal volume from weeks 5 to 8. Moreover, YCF could significantly suppressed the progression of inflammation and fibrosis, by reducing the levels of inflammatory cytokines, as well as collagen- I and III. YCF treatment also decreased the numbers of macrophages and M1/M2 macrophages and the level of transforming growth factor-β (TGF-β). Additionally, YCF5, the effective substance in YCF, decreased lipopolysaccharide and interferon-γ-induced M1 macrophage polarization in a concentration-dependent manner. The mechanism of anti-M1 polarization might be related to a decrease in extracellular signal-regulated kinase, c-JUN N-terminal kinase, P38, and P65 phosphorylation. Furthermore, YCF5 inhibited interleukin-4-induced M2 macrophages by decreasing the protein and mRNA expressions of arginase-1 and CD206 as well as the levels of profibrotic factors, such as TGF-β and connective tissue growth factor. The mechanisms underlying the anti-M2 polarization of YCF5 were primarily associated with the inhibition of the nuclear translocation of phosphorylated signal transducer and activator of transcription 6 (p-STAT6). YCF significantly inhibits inflammation and fibrosis in silicotic rats probably via the suppression of M1/M2 macrophage polarization mediated by the inhibition of mitogen-activated protein kinase and nuclear factor kappa B signaling pathways and Janus kinase/STAT6 pathways.

Methodology for determining progressing ultimate states based on the displacement method

Solving of calculation problems for building structures is currently based on the principle of minimum total energy of structures deformation. However, it is not possible to determine the remaining bearing capacity of the structure using this principle. In the study it is proposed to use the criterion of critical levels of deformation energy to solve this problem. As a result, the ultimate state conditions of a design are formulated on the basis of extreme values of generalized parameters of designing over the whole area of their admissible values, including the boundary. The task is solved as a problem of eigenvalues for the stiffness matrix of the system. The extreme values of design parameters that correspond to critical energy levels are found, which are used to find the maximum possible value of the energy of deformation for the considered structure. The residual bearing capacity is calculated by the value of residual potential energy, which, in turn, is equal to the difference between the maximum possible value of the deformation energy of the structure and the work of external forces. A gradual methodology for investigating the progressive ultimate limit state is proposed, which is based on the sequential exclusion of those elements where the onset of the ultimate limit state is expected firstly. An example of the practical use of the proposed methods is given on the example of calculating a simple but visual design - a statically indeterminate truss.

Postfire performance of pultruded wood-cored GFRP sandwich beams

Wood-cored sandwich components have been extensively used in constructions of buildings and bridges. However, the existing studies on the postfire behavior of these components are very limited. This study aims to quantitatively evaluate the postfire residual properties of the pultruded wood-cored GFRP sandwich (PWGS) beams. This paper mainly comprises three parts: (i) review of fire experiment of the PWGS beams; (ii) postfire bending experiments conducted on the PWGS beams with different fire scenarios and (iii) numerical study on thermal and postfire thermomechanical responses. It was found the failure modes mainly depended on the number of exposed sides and the fire damage degree. For the three-sided fire-exposed specimens (except for the one with a 25 mm-thick calcium silica board), the progressive tension rapture of the charred fibers was the dominant failure mode. The other specimens, however, exhibited the brittle in-plane shear failure of the web. Moreover, after cooling down from 250 °C to 20 °C, the GFRP and wood exhibited 68 % and 35 % of recoveries of elastic modulus respectively. A three-dimensional thermal model with kinetic thermophysical sub-models considering heat transfer, water evaporation and decomposition was developed. The developed thermal model accurately predicted the temperature responses and charring profiles. Furthermore, a thermomechanical model considering the material damage was developed to accurately predict the elastic modulus distribution, postfire residual bending capacity and failure modes. This study provides the basis for the retrofit and the reinforcement of the fire-damaged PWGS beams. In the future, study on the fire resistance of the PWGS components in fire will be required.

Experimental study on fatigue behavior of UHPC joint in negative moment region of π-shaped steel–concrete composite beams

To improve the crack resistance of concrete bridge decks in the negative moment region of π-shaped steel–concrete composite beam, a novel ultra-high performance concrete (UHPC) joint was first proposed. Based on an actual bridge, a 1:2 scale model was then designed as the specimen. A fatigue test was conducted to investigate the variation of its structural properties during fatigue loading, and a static test was performed to evaluate its residual bearing capacity. The test results show that the new UHPC joint has good crack resistance under fatigue loading and can meet the engineering requirements. The stiffness of the specimen significantly decreases after 3 million fatigue cycles. However, without significant fatigue damage on the surface of specimen, plenty of stiffness is reserved. It is found that there is no significant slip between the concrete deck and steel girder, and between the UHPC and normal concrete in the static test after fatigue, indicating that the studs inside the π-shaped steel–concrete composite beam are arranged reasonably and the interaction of the overall structure is reliable. Furthermore, the ultimate bearing capacity of the specimen decreased by only 9.4% from its design value after being subjected to 3 million fatigue cycles. It is revealed that the application of UHPC in the composite beam effectively improves its crack resistance, resulting in a smaller reduction in bearing capacity. This paper can provide theoretical foundation for the preparation and application of the π-shaped steel–concrete composite beams with UHPC joints.

Axial compression behaviour and design of square tubed steel reinforced-concrete stub columns after fire exposure

The tubed steel reinforced-concrete (TSRC) column is an innovative type of steel-concrete composite column, the steel tube of which mainly provides confinement to concrete core without sustaining axial load directly. This paper presents the axial compressive behaviour of square TSRC stub columns after ISO 834 standard fire exposure, experimentally and numerically. Eighteen square TSRC stub columns were heated and cooled and subsequently loaded to failure under axial compression. The influences of heating time, concrete compressive strength and steel tube area ratio on the load vs. displacement response, failure mode, residual capacity and stiffness of the tested columns were investigated. Finite element analysis (FEA) models were then developed and validated against test results. The working mechanism, e.g. confinement effect and axial force distribution within the composite section, was studied via parametric studies. Both the residual ultimate capacity and axial stiffness of square TSRC stub columns decrease significantly with the increase in heating time. The negative effect of fire exposure on residual stiffness is more significant than on the residual capacity. Finally, practical equations for determining the residual ultimate capacity and residual compressive stiffness of square TSRC stub column were proposed, which remain consistent with the ambient-temperature methods given in current design standard.

A novel damage evaluation method for exposed column bases (ECBs) affecting the seismic properties of low‐rise steel moment‐resisting frames (MRF)

AbstractExposed column base (ECB) connections are widely used in low‐ and mid‐rise steel moment‐resisting frames (MRFs). In this study, we investigated the impact of ECB damage on the overall seismic properties of low‐rise MRFs. A novel method was proposed to evaluate the post‐earthquake conditions of steel frame structures based on the coupling coefficient (CC). Using only the strain gauge data of the columns in the bottom storey, a method using a modified CC was adopted to classify the degree of damage by estimating the residual capacity of the MRF and predicting the future seismic response under specific intensity levels of hypothetical earthquakes, considering both the structural and non‐structural components. The limit values of CC were obtained by solving the deduced equations. Finite element analyses were conducted to validate the proposed method. The method was applied for calculating the test data of a four‐storey MRF tested at the E‐Defense shaking table facility. Four loading cases comprising six groups of monitored data in the X‐ and Y‐directions were used in this study. A comprehensive and systematic evaluation result was eventually obtained, and the accuracy of the method was validated.