Residual Capacity Research Articles

Effect of Obesity on Lung Function in the Pediatric and Adult Populations with Asthma: A Review.

Obesity and asthma are major global health concerns, particularly in industrialized nations. Obesity has been shown to have detrimental effects on the respiratory system and lung function owing to metabolic issues and immunological consequences. Research has indicated that obese patients with asthma (atopic or T2-high and non-atopic or T2-low) have diminished lung function in terms of functional residual capacity (FRC), residual volume (RV), expiratory reserve volume (ERV), the FEV1/FVC ratio, and FEF 25-75% due to mechanical fat loading on the diaphragm and central adiposity when compared to non-obese asthmatic patients. Therefore, it is plausible that changes in lung function are the result of a combination of mechanical (fat loading on the diaphragm, central adiposity, bronchial hyper-reactivity, and an increase in cholinergic tone), environmental (diet and exercise), and inflammatory factors (local and systemic), which can lead to the obesity-related asthma phenotype characterized by severe asthma symptoms, poor response to corticosteroid treatment, loss of lung function, and poor quality of life from an early age.

The impact of antenatal and postnatal indoor air pollution or tobacco smoke exposure on lung function at 3 years in an African birth cohort.

Indoor air pollution (IAP) and tobacco smoke exposure (ETS) are global health concerns contributing to the burden of childhood respiratory disease. Studies assessing the effects of IAP and ETS in preschool children are limited. We assessed the impact of antenatal and postnatal IAP and ETS exposure on lung function in a South African birth cohort, the Drakenstein Child Health Study. Antenatally enrolled mother-child pairs were followed from birth. Lung function measurements (oscillometry, multiple breath washout and tidal breathing) were performed at 6 weeks and 3 years. Quantitative antenatal and postnatal IAP (particulate matter [PM10 ], volatile organic compounds [VOC]) and ETS exposures were measured. Linear regression models explored the effects of antenatal and postnatal exposures on lung function at 3 years. Five hundred eighty-four children had successful lung function testing, mean (SD) age of 37.3 (0.7) months. Exposure to antenatal PM10 was associated with a decreased lung clearance index (p < 0.01) and postnatally an increase in the difference between resistance at end expiration (ReE) and inspiration (p = 0.05) and decrease in tidal volume (p = 0.06). Exposure to antenatal VOC was associated with an increase in functional residual capacity (p = 0.04) and a decrease in time of expiration over total breath time (tE /tTOT ) (p = 0.03) and postnatally an increase in respiratory rate (p = 0.05). High ETS exposure postnatally was associated with an increase in ReE (p = 0.03). Antenatal and postnatal IAP and ETS exposures were associated with impairment in lung function at 3 years. Strengthened efforts to reduce IAP and ETS exposure are needed.

Non-Invasive Ventilation Reduces Postoperative Respiratory Failure in Patients Undergoing Bariatric Surgery: A Retrospective Analysis.

Background and Objectives: Postoperative non-invasive ventilation (NIV) has been proposed as an attractive strategy to reduce morbidity in obese subjects undergoing general anaesthesia. The increased body mass index (BMI) correlates with loss of perioperative functional residual capacity, expiratory reserve volume, and total lung capacity. The aim of the current study is to evaluate the efficacy of NIV in a post-anaesthesia care unit (PACU) in reducing post-extubation acute respiratory failure (ARF) after biliointestinal bypass (BIBP) in obese patients. Materials and Methods: A retrospective analysis was conducted from January 2019 to December 2020 to compare acute respiratory failure within the first 72 postoperative hours and oximetry values of obese patients who underwent BIBP after postoperative NIV adoption or conventional Venturi mask. Results: In total, 50 patients who received NIV postoperative protocol and 57 patients who received conventional Venturi mask ventilation were included in the study. After 120 min in PACU pH, pCO2, pO2, and SpO2 were better in the NIV group vs. control group (p < 0.001). Seventy-two hours postoperatively, one patient (2%) in the NIV group vs. seven patients (12.2%) in the control group developed acute respiratory failure. Therefore, conventional Venturi mask ventilation resulted in being significantly associated (p < 0.05) with postoperative ARF with an RR of 0.51 (IC 0.27-0.96). Conclusions: After bariatric surgery, short-term NIV during PACU observation promotes a more rapid recovery of postoperative lung function and oxygenation in obese patients, reducing the necessity for critical care in the days following surgery. Therefore, as day-case surgery becomes more advocated even for morbid obesity, it might be considered a necessary procedure.

Study on the static and fatigue performance of MCL-shaped shear connectors

Seven specimens were prefabricated and conducted in the static and fatigue tests to investigate the static mechanical properties and fatigue performance of the MCL (modified clothoid) shape composite dowels. The failure mode, ultimate carrying capacity, shear stiffness, relative slippage, stiffness degradation and residual load-bearing capacity were studied. Additionally, a theoretical model for calculating the residual load-bearing capacity was proposed. Results showed that the failure mode of the specimens under static and fatigue loads is the concrete shear failure. The failure process included the following stages: the bonding failure, yielding of penetrated bar and concrete shear failure. During fatigue test, the static stiffness of the MCL-shaped composite dowel increased initially, then decreased linearly, and dropped abruptly in the final stage. The results obtained from the theoretical model agreed well with the experimental findings.

Low-frequency oscillometry indices to assess ventilation inhomogeneity in CF patients.

The utility of the forced oscillations technique (FOT) in cystic fibrosis (CF) remains uncertain. The aim of this study was to explore the ability of lower-frequency FOT indices, alone and after adjustment for the lung volume, to assess the extent of ventilation inhomogeneity in CF patients with varying disease severity. Forty-five children, adolescents, and adults with CF (age 6.9-27 years) underwent spirometry, FOT, and nitrogen multiple-breath washout (N2-MBW) measurements. The respiratory resistance and reactance at 5 Hz (Rrs5 and Xrs5, respectively) were recorded, and a novel FOT index, the specific respiratory conductance (sGrs), was computed as the reciprocal of Rrs5 divided by the functional residual capacity. The sGrs correlated well with the lung clearance index (LCI) (Spearman's r: -.797), whereas the correlation of Rrs5 and Xrs5 with the LCI, albeit significant, was weaker (r: .643 and -.631, respectively). The sGrs emerged as the most robust predictor of LCI regardless of the severity of lung disease, as reflected by patients' age and lung function measurements. Most importantly, the relationship between sGrs and LCI remained unaffected by lung hyperinflation, as opposed to that of the LCI with the spirometric and standard FOT indices. In CF patients, the FOT indices at 5 Hz and the novel, volume-adjusted parameter sGrs, reflect the extent of lung involvement and the underlying ventilation inhomogeneity in a way comparable to N2-MBW. Future research should explore the role of lower-frequency FOT in assessing the severity and monitoring the progression of CF lung disease.

A two-level strategy to assess the bearing capacity of corroded structures via long-gauge fiber-optic sensors

Corrosion of steel in concrete is the most common deterioration mechanism for structures located in aggressive environments. This research proposes a two-level strategy to assess the residual bearing capacity of corroded structures by detecting and quantifying corrosion via a new kind of long-gauge fiber Bragg grating (FBG) sensors. Compared with the traditional point strain gauges, this new sensor has been developed for both local and global structural monitoring by measuring the averaged strain within a long gauge length. According to the mechanical relationship between the moving load and the long-gauge strain influence line (IL), an IL aera-based difference index is established to identify the presence of the damage and the corrosion is quantified in terms of reduction of sectional area of reinforcement (Level 1); and then an elaborate finite element (FE) model is built to perform failure analysis to assess the residual bearing capacity by modifying the material constitutive model according to the corrosion condition (Level 2). A laboratory experiment is conducted to verify the effectiveness and accuracy of the proposed method.

Residual load-bearing capacity of corroded reinforced concrete columns with an annular cross-section

Reinforced concrete (RC) columns with an annular cross-section are commonly utilized as supporting structural members in ocean engineering structures, and their structural performance deterioration is mainly caused by the corrosion of rebar in aggressive marine environment. This paper proposes an effective method to investigate the effects of rebar corrosion on the structural performance of the annular RC columns under various loading conditions. Firstly, the material degradation and residual structural strength models are proposed based on the analysis of the corrosion-induced deterioration of RC structures. Then, the general method for determining the load-bearing capacity is developed using the equivalent steel ring assumption. To improve computational efficiency and practical applicability, an effective method for assessing the residual load-bearing capacity is proposed by simplifying the calculations of rebar load-bearing capacity coefficients using the regression fitting approach. Finally, the effectiveness of the proposed simplified method is demonstrated with the relevant experimental data available. The results show the capacity deterioration rate is strongly related to the corrosion level and loading condition with the most severe degradation typically at the corrosion level of 5–10%, and the smaller and larger eccentric columns drop the capacities by about 28% and 41% at 10% corrosion level, respectively.

Practice of continuous positive airway pressure application in Neonatal Intensive Care Unit. Cross sectional study

BackgroundContinuous positive airway pressure (CPAP) is a simple, inexpensive, and gentle mode of respiratory support for neonates.This is beneficial for spontaneously breathing neonates by maintaining functional residual capacity in the alveoli to prevent atelectasis and improve oxygen exchange. The aim of this study was to assess the practice of continuous positive airway pressure application in neonatal intensive care. MethodsA hospital based prospective observational descriptive study was conducted on 60 neonates from March 15, 2022 to July 30, 2022 at NICU Unit at XXX Comprehensive Specialized Hospital, July 2022, North-west Ethiopia.Descriptive statistical analysis with SPSS version 25 was used. ResultsThe overall practice of CPAP use were (73.4%), with assessment of parameters such as initial nursing care before initiation of CPAP (82.2%), Setting up of CPAP (94.1%), preparing the Baby for CPAP (65.3%), Connecting the nasal prong system to the neonate (50%), Methods of Securing CPAP device (96.7%), Performing safety check for Troubleshooting in CPAP (78.3%) and Monitor of CPAP and On-going assessments (46.6%). ConclusionThe practice of CPAP application was good at Initial nursing care before initiation of CPAP, Setting up of CPAP, and Methods of Securing CPAP device. However, there was poor practice in connecting the nasal prong system to the neonate, preparing the Baby for CPAP, performing safety checks for troubleshooting in CPAP, Monitoring of CPAP and On-going assessments.

Simultaneous quantification of hyperpolarized xenon-129 ventilation and gas exchange with multi-breath xenon-polarization transfer contrast (XTC) MRI.

To demonstrate the feasibility of a multi-breath xenon-polarization transfer contrast (XTC) MR imaging approach for simultaneously evaluating regional ventilation and gas exchange parameters. Imaging was performed in five healthy volunteers and six chronic obstructive pulmonary disease (COPD) patients. The multi-breath XTC protocol consisted of three repeated schemes of six wash-in breaths of a xenon mixture and four normoxic wash-out breaths, with and without selective saturation of either the tissue membrane or red blood cell (RBC) resonances. Acquisitions were performed at end-exhalation while subjects maintained tidal breathing throughout the session. The no-saturation, membrane-saturation, and RBC-saturation images were fit to a per-breath gas replacement model for extracting voxelwise tidal volume (TV), functional residual capacity (FRC), and fractional ventilation (FV), as well as tissue- and RBC-gas exchange (fMem and fRBC , respectively). The sensitivity of the derived model was also evaluated via simulations. With the exception of FRC, whole-lung averages for all metrics were decreased in the COPD subjects compared to the healthy cohort, significantly so for FV, fRBC , and fMem . Heterogeneity was higher overall in the COPD subjects, particularly for fRBC , fMem , and fRBC:Mem . The anterior-to-posterior gradient associated with the gravity-dependence of lung function in supine imaging was also evident for FV, fRBC , and fMem values in the healthy subjects, but noticeably absent in the COPD cohort. Multi-breath XTC imaging generated high-resolution, co-registered maps of ventilation and gas exchange parameters acquired during tidal breathing and with low per-breath xenon doses. Clear differences between healthy and COPD subjects were apparent and consistent with spirometry.

Experimental study on the anti-blast performance of polyurea reinforced concrete arch structures

In order to study the anti-blast performance of the concrete arch structure strengthened by polyurea, the bottom (inner side) of the concrete arch structure is reinforced by coating polyurea with different thicknesses, which conducts anti-blast tests on the composite arch structure under the blast load of TNT in the air. The test recorded the dynamic response data of arch structure under the action of blast load, including reflected pressure at the vault, strain of the bars and deformation of arches. In order to further evaluate the damage of the arch under blast load, quasi-static loading tests were carried out on the residual bearing capacity of the damaged arch structures. Through the analysis of the damage to the arch structure after blast load, this paper clarifies the reinforcement mechanism of polyurea on concrete arch structure. Compared with the reinforced concrete(RC)arch structure, the damage and deformation of the composite arch can be controlled by coating polyurea, thus further improving the structural integrity of the composite arch after blast load. The experimental results show that anti-blast capacity and ductility characteristics of the arch strengthened by polyurea have improved than those of RC arch structure, and the overall mechanical properties of the composite arch structure have strenthened with the increase of the polyurea reinforced thickness. By adopting the rational design of polyurea reinforcement layer and concrete arch structure, a protective structure with better anti-blast performance can be manufactured.

Residual load capacity of HVFA reinforced concrete after elevated temperature heating: Experimental and analytical study

High volume fly ash (HVFA) is used as structural concrete's main constituent in the current concrete construction practice. The residual load capacity of HVFA reinforced concrete after elevated temperature heating is needed for retrofitting compression members after fire exposure. In this experimental study, an effort has been made to estimate the axial load capacity of concrete containing HVFA after 28 and 90 days of curing after elevated temperature heating at 200 °C, 400 °C and 600 °C. The 35% and 50% amount of cement was partially replaced by fly ash. The weight loss and crack pattern in reinforced HVFA concrete were also studied. It has been observed that after heating at elevated temperature, the compression behavior of fly ash concrete is better than that of plain concrete. The analytical models are proposed to estimate the residual load capacity of HVFA concrete columns after exposure to elevated temperature. The model predictions are reasonably good. These models can be used to assess the load carrying capacity of columns in concrete buildings containing HVFA after elevated temperature exposure for deciding strengthening schemes.

Feasibility of Tiotropium Bromide Treatment in Patients with Asthma-COPD Overlap Syndrome and its Effect on Lung Function

Objective: To explore the feasibility of tiotropium bromide therapy and its effect on the lung function of patients with asthma-COPD overlap syndrome (ACOS). Method: The 58 subjects selected in this study were all ACOS patients admitted to our hospital (Hohhot First Hospital) from October 2020 to October 2022. They were grouped according to the random number table method and divided into a control group (29 cases) and an observation group (29 cases). The control group received routine treatment plus salmeterol-fluticasone powder inhalation treatment, and the observation group received tiotropium bromide treatment. The relevant indicators of the two groups were compared. Results: The total clinical effective rate of the observation group was significantly higher than that of the control group. Besides, the forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1) levels, and ACT scores of the two groups increased after treatment, with the observation group having better results than the control group. The residual volume-total lung capacity ratio (RV/TLC), acute exacerbation frequency, and CAT scores all decreased, with the observation group showing smaller values than the control group. The difference between the results of both groups were significant (P &lt; 0.05) Conclusion: Tiotropium bromide has a significant clinical effect in the treatment of ACOS patients and can effectively improve the lung function of patients.

Impact performance of fire-damaged hybrid steel-BFRP reinforcement concrete beams: Influence of area ratio and arrangement of BFRP bars

Hybrid steel-BFRP reinforced concrete (HRC) beams have demonstrated their ability to meet the rigorous demands for both strength and serviceability. However, the mechanical properties of HRC beams under fire accompanied by impact loadings are not yet clear. In order to delve into the impact resistance of HRC beams under high temperatures, a three-dimensional numerical model was crafted to account for both the effects of strain rate and temperature degradation. The study aimed to examine how the impact resistance of HRC beams is influenced by varying area ratios and arrangements of BFRP bars. The model's reliability was ascertained through a comparison between its simulation outcomes and the results of physical tests. The results show that HRC beams exhibit a significant reduction in stiffness, impact and internal force under fire conditions (39 %, 38 % and 72 % for a fire duration of 45 min, respectively). Furthermore, the damage is concentrated in the mid-span. The impact performance of HRC beams at room and high temperatures is between those of pure steel-RC beams and pure-BFRP beams. The variations under the same fire conditions in the displacement and internal force of beams with different BFRP bars area ratios reach 70 %, while with different arrangements of BFRP bars do not differ much (within 20 %). The dynamic to static stiffness ratio and ultimate load ratio is reduced following the growth of BFRP bars area ratio (max. gap up to 56 % and 25 %) and fire time (max. gap up to 15 % and 20 %). Therefore, specimen design prioritizes the bar arrangement with better corrosion resistance. Additionally, the residual bearing capacity of HRC beams is only 10–40 % of the original under 45 min fire duration. The association of residual load capacity and displacement with fire time shifted from linear to nonlinear with rising temperature.

Comparison of axial behavior of RC columns using alkali-activated slag-based concrete and OPC concrete during and after fire

As no study on fire behavior of RC columns using alkali-activated concrete has been reported so far, this paper presents an experimental program comparatively investigating the thermal response and structural behavior of reinforced columns using alkali-activated slag-based concrete (AAC) and Portland cement-based concrete (PCC) during and after subjecting to the standard fire curve, with concrete strength and fire duration as test parameters. The experimental and analytical studies showed that compared with PCC columns, AAC columns had slightly lower temperature field but faster increase of axial deformation during fire. AAC and PCC columns using normal-strength concrete had equivalent residual axial capacity after exposure to fire. However, AAC columns using high-strength concrete retained greater load-bearing capacity than their PCC counterparts due to the spalling of high-strength PCC columns. AAC columns had lower axial stiffness than PCC columns at ambient temperature due to lower elastic modulus of AAC, but they had similar axial stiffness after exposure to fire of 2 h since PCC underwent more degradation of elastic modulus under high temperature. Furthermore, as concrete strength and fire duration increased, the axial contraction under heating and axial capacity loss after heating of AAC columns increased. A numerical method based on finite difference was used to predict the temperature field and corresponding residual axial capacity of RC columns after the fire.

Experimental investigation on residual capacity of square steel-reinforced concrete-filled steel tubular columns after fire

PurposeSteel-reinforced concrete-filled steel tubular (SRCFST) columns have been increasingly popular in engineering practice for the columns' excellent seismic and fire performance. Significant design progress guidance has been made through continuous numerical and experimental research in recent years. This paper tested and analysed the residual loading capacity of SRCFST columns under axial loading after experiencing non-uniform ISO-834 standard fire.Design/methodology/approachThe experimental research covered the main parameter of heating conditions, 1-side and 2-side fire, through two specimens. Two specimens were heated and loaded simultaneously in the furnace for 240 min. After cooling, the columns were moved to the hydraulic loading system and loaded to failure to determine the columns' residual capacity.FindingsThe experimental results indicated that the non-uniform heating area plays an essential role in the overall performance of SRCFST columns, the increasing heating area of columns results in lower residual loading capacity and stiffness. The SRCFST columns still had a high loading capacity after heating and loading in the fire.Originality/valueThe comparison of experimental data against design results showed that the design method generated a 16% safety margin for S2H4 and a 39% safety margin for S1H4.

Effect of Fire Flame (High Temperature) on the Behaviour of Axially loaded Reinforced SCC Short Columns

Experimental research was carried out to investigate the effect of fire flame (high temperature) on specimens of short columns manufactured using SCC (Self compacted concrete). To simulate the real practical fire disasters, the specimens were exposed to high temperature flame, using furnace manufactured for this purpose. The column specimens were cooled in two ways. In the first the specimens were left in the air and suddenly cooled using water, after that the specimens were loaded to study the effect of degree of temperature, steel reinforcement ratio and cooling rate, on the load carrying capacity of the reinforced concrete column specimens. The results will be compared with behaviour of columns without burning (control specimens). The results showed that, the ultimate load capacity of columns exposed to fire decreases with increasing the fire flame temperature. At burning temperature 300 Co , 500 Co and 700 Co , the average residual ultimate load capacity for gradually cooled specimens were 91%, 81% and 71% respectively. By increasing the ratio of longitudinal reinforcement 44% , the maximum improvement in the ultimate load capacity was 24% and 17% for the gradually and sudden cooling respectively at Co 500 . For the same longitudinal reinforcement ratio and fire burning temperature, the ultimate capacity for the sudden cooling specimens was less than that of gradually cooled specimens by about 10%.

The Influence of Breathing Exercises on Regional Ventilation in Healthy and Patients with Chronic Obstructive Pulmonary Disease

We hypothesized that the respiratory exercises have uniform effects on ventilation in healthy subjects but the effects varied in patients with chronic obstructive pulmonary disease (COPD). In this study, a total of 30 healthy volunteers and 9 patients with COPD were included. Data were recorded continuously during (1) diaphragmatic breathing; (2) pursed lip breathing with full inhalation; (3) pursed lip combining diaphragmatic breathing. The sequence of the three breathing exercises was randomized using machine generated random permutation. Spatial and temporal ventilation distributions were evaluated with electrical impedance tomography. Results showed that, tidal volume was significantly larger during various breathing exercises compared to quiet tidal breathing, in both healthy and COPD (p < 0.01). However, for other EIT-based parameters, statistical significances were only observed in healthy volunteers, not in patients. Diaphragmatic breathing alone might not be able to decrease functional residual capacity in COPD and the effect varied largely from patient to patient (6:3, decrease vs. increase). Ventilation distribution moved toward ventral regions in healthy during breathing exercises (p < 0.0001). Although this trend was observed in the COPD, the differences were not significant. Ventilation became more homogeneous when diaphragmatic breathing technique was implemented (p < 0.0001). Again, the improvements were not significant in COPD. Regional ventilation delay was relatively high in COPD and comparable in various breathing periods. In conclusions, the impact of pursed lip and diaphragmatic breathing varied in different patients with COPD. Breathing exercise may need to be individualized to maximize the training efficacy with help of EIT.

Residual trapping of CO2, N2, and a CO2-N2 mixture in Indiana limestone using robust NMR coreflooding: Implications for CO2 geological storage

Carbon capture and sequestration (CCS) in geological formations is a prominent solution for reducing anthropogenic carbon emissions and mitigating climate change. The capillary trapping of CO2 is a primary trapping mechanism governed by the pressure difference between the wetting and nonwetting phases in a porous rock, making the latter a key input parameter for dynamic simulation models. During the CCS operational process, however, the CO2 is prone to contamination by impurities from various sources such as surfaces (e.g., pipelines and tanks) and the subsurface (e.g., existing natural gas). Such contamination can strongly influence the overall CO2 wettability, storage capacity, and containment security. Hence, the present study uses the nuclear magnetic resonance (NMR) core flooding technique to investigate and compare the residual saturations of pure CO2, pure N2, and a 50:50 CO2/N2 mixture in an Indiana limestone. The longitudinal and transverse relaxation times (T1 and T2) are measured to examine the displacement process of the pore network, and the trapping mechanism is evaluated at the pore scale as a determinant of the field-scale flow behavior. The NMR T1-T2 and 2D maps are used to observe the fluid configurations in the pore network, and the T1/T2 ratios are used to evaluate the microscopic wettability of the limestone grains by the pore-space fluids following each drainage/imbibition process step. The results indicate substantial residual gas trapping in the rock for the CO2-brine, N2-brine, and CO2/N2-brine systems, corresponding to gas saturations of 25%, 27%, and 26%, respectively. In the CO2-brine system, the intermolecular interplay between the CO2-enriched brine and limestone grains results in a higher T1/T2 ratio and significantly reduces the hydrophilicity of the limestone. Furthermore, the NMR T2 distribution reveals the occurrence of preferential water displacement into the large pores (r > 1 µm) and from the intermediate pores (0.03 µm < r < 1 µm), whereas water remains immobile in the smaller pores (r < 0.03 µm). The insignificant difference in residual trapping saturation between pure CO2 and the CO2-N2 mixture indicates the potential to allow for impurities in the CO2 phase in CCS without reducing the residual trapping capacity. Thus, the present work provides comprehensive information on the impact of gas injection on residual gas trapping in subsurface geological formations at the pore scale, thereby aiding in the development of CCS and other potential applications in enhanced oil recovery (EOR).

Setting the optimal positive end-expiratory pressure: a narrative review.

The primary goals of positive end-expiratory pressure (PEEP) are to restore functional residual capacity through recruitment and prevention of alveolar collapse. Through these mechanisms, PEEP improves arterial oxygenation and may reduce the risk of ventilator-induced lung injury (VILI). Because of the many potential negative effects associated with the use of PEEP, much research has concentrated on determining the optimal PEEP setting. Arterial oxygenation targets and pressure-volume loops have been utilized to set the optimal PEEP for decades. Several other techniques have been suggested, including the use of PEEP tables, compliance, driving pressure (DP), stress index (SI), transpulmonary pressures, imaging, and electrical impedance tomography. Each of these techniques has its own benefits and limitations and there is currently not one technique that is recommended above all others.

Test and damage assessment of shallow buried RC tunnel under explosion

As a major element of the transportation network, tunnels are unavoidably threatened by accidental loads such as vehicle bombs and tank truck explosions. The goal of this research is to explore the dynamic characteristics and damage assessment of tunnel structures under contact blast loads. First, three scaled-down reinforced concrete tunnel models were made, and the explosion test and static loading test were carried out successively to evaluate the axial residual bearing capacity, axial displacement and failure mechanism of the tunnel. Secondly, the finite element model is built by utilizing LS-DYNA, and the reliability of the finite element method is confirmed by comparing the data of the explosion test with the static loading test. At the same time, the calculation method for damage coefficient and the classification criteria for damage grade based on axial residual bearing capacity are presented. Then, based on the finite element method, the propagation process of the explosion shock wave in the tunnel and the damage mechanism of the tunnel are investigated. Finally, seven explosion scenarios are developed, the damage degree of these seven tunnels under the blast load is quantitatively analyzed, and further anti-blast design ideas are put forth. The study in this article may give an intended reference for the damage assessment, anti-explosion design and strengthening work of reinforced concrete tunnels.