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Abnormal growth of airway smooth muscle cells is one of the key features in asthmatic airway remodeling, which is associated with asthma severity. The mechanisms underlying inappropriate airway smooth muscle cell growth in asthma remain largely unknown. Myocd has been reported to act as a key transcriptional coactivator in promoting airway-specific smooth muscle development in fetal lungs. Whether Myocd controls airway smooth muscle remodeling in asthma has not been investigated. Mice with lung mesenchyme-specific deletion of Myocd after lung development were generated, and a chronic asthma model was established by sensitizing and challenging the mice with ovalbumin for a prolonged period. Comparison of the asthmatic pathology between the Myocd knockout mice and the wild-type controls revealed that abrogation of Myocd mitigated airway smooth muscle cell hypertrophy and hyperplasia, accompanied by reduced peri-airway inflammation, decreased fibrillar collagen deposition on airway walls, and attenuation of abnormal mucin production in airway epithelial cells. Our study indicates that Myocd is a key transcriptional coactivator involved in asthma airway remodeling. Inhibition of Myocd in asthmatic airways may be an effective approach to breaking the vicious cycle of asthmatic progression, providing a novel strategy in treating severe and persistent asthma. © 2022 The Authors. The Journal of Pathology published by John WileySons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Metal–organic frameworks (MOFs) have received great attention in environmental remediation application. In particular, one-dimensional (1D) MOF materials have excellent catalytic degradation perfor...

In this paper, a new seismic damage assessment method considering multi-modal contribution is proposed to evaluate the seismic damage of single-layer steel latticed shells more accurately and efficiently. In the proposed method, the contribution of each modal damage to the structural overall seismic damage is calculated based on a specially constructed equivalent static system derived in this paper, in which the structural multi-modal damage effects can be considered. Then, the measure technics of the structural seismic damage degree is proposed in this paper according to the equivalent static displacements, and then the recommended damage index equation is derived. Considering different actual engineering requirements, the damage assessment procedures for design and appraisal are given in this paper, respectively. Since the damage assessment process is based on the static analysis results of equivalent model, the proposed method retains the conceptual simplicity and computational attractiveness. For detailed comparative evaluation, several numerical examples carried out on a Kiewitt-6 single-layer latticed shell and a practical engineering structure, named Shanghai International Convention Centre, are conducted in this paper. In numerical examples, the influence of the damage assessment direction on the assessment results, the trend characteristic of damage index curves and its comparison with structural response are all discussed in detail. For practicality, combined with the numerical analysis results, seismic damage grades of single-layer latticed shells and the recommended values of characteristic points are discussed and obtained. Furthermore, seismic damage assessment results generated by the proposed method and the other three methods are compared, which confirms the necessity of considering multi-modal contribution and the satisfying accuracy and applicability provided by the proposed method in single-layer steel latticed shell seismic damage assessment.

The node positions of single-layer latticed shells in service usually deviate from their design positions, and a few nodes of the shell may exist larger positional deviations than other nodes, which could result in a progressive collapse or overall buckling of the shell. To avoid the significant loss of structure failure, these nodes with large positional deviations should be considered in the structural inspection sampling. However, existing sampling methods in the structural inspection are designed for independent products that ignore the dependence in these nodes and are unsuitable for node positional deviation inspection of single-layer latticed shells. To solve this problem, the node positional deviation aggregation is defined and calculated based on the theory of spatial local autocorrelation, and an improved adaptive web sampling (IAWS) method is proposed in this paper, which consists of three parts: calculation of node connection matrix, adaptive web sampling, and supplementary sampling. Specially, the supplementary sampling is proposed to improve the overall sampling accuracy for adaptive web sampling, and the selection of supplementary samples is based on the relationship between the sample position and the total node deviation reckoning error derived in this paper. Besides, two performance indicators are adopted to evaluate the overall reckoning accuracy of sample methods, and two new performance indicators are proposed to assess the deviation aggregation area sampling accuracy. The numerical analysis results of two Kiewitt shells and a cylinder shell show that IAWS can provide a higher sampling accuracy than random sampling, systematic sampling, and adaptive web sampling.

The TGF-β signaling pathway plays a pivotal role in controlling organogenesis during fetal development. Although the role of TGF-β signaling in promoting lung alveolar epithelial growth has been determined, mesenchymal TGF-β signaling in regulating lung development has not been studied in vivo due to a lack of genetic tools for specifically manipulating gene expression in lung mesenchymal cells. Therefore, the integral roles of TGF-β signaling in regulating lung development and congenital lung diseases are not completely understood. Using a Tbx4 lung enhancer-driven Tet-On inducible Cre transgenic mouse system, we have developed a mouse model in which lung mesenchyme-specific deletion of TGF-β receptor 2 gene ( Tgfbr2) is achieved. Reduced airway branching accompanied by defective airway smooth muscle growth and later peripheral cystic lesions occurred when lung mesenchymal Tgfbr2 was deleted from embryonic day 13.5 to 15.5, resulting in postnatal death due to respiratory insufficiency. Although cell proliferation in both lung epithelium and mesenchyme was reduced, epithelial differentiation was not significantly affected. Tgfbr2 downstream Smad-independent ERK1/2 may mediate these mesenchymal effects of TGF-β signaling through the GSK3β-β-catenin-Wnt canonical pathway in fetal mouse lung. Our study suggests that Tgfbr2-mediated TGF-β signaling in prenatal lung mesenchyme is essential for lung development and maturation, and defective TGF-β signaling in lung mesenchyme may be related to abnormal airway branching morphogenesis and congenital airway cystic lesions.

The successful generation of endodermal, ectodermal, and most mesodermal lineages from pluripotent stem cells has resulted in basic discoveries and regenerative medicine clinical trials of cell-based therapies. In contrast, the derivation of tissue-specific mesenchyme via directed differentiation in vitro has markedly lagged, due in part to a limited understanding of the signaling pathways regulating in vivo mesenchymal development and a lack of specific markers or reporters able to purify such lineages. The derivation of lung-specific mesenchyme is a particularly important goal since this tissue plays important roles in lung development and respiratory disease pathogenesis. Here we generate a mouse induced pluripotent stem cell (iPSC) line carrying a lung-specific mesenchymal reporter/lineage tracer facilitating the tracking and purification of engineered lung-specific mesenchyme. We identify the key signaling pathways (RA and Shh) necessary to specify lung mesenchyme from lateral plate mesodermal precursors and find that mouse iPSC-derived lung mesenchyme (iLM) expresses the molecular and functional phenotypes of primary developing lung mesenchyme. Purified iLM can be recombined with separately engineered lung epithelial progenitors, self-organizing into 3-dimensional organoids featuring significantly augmented structural complexity and lineage purity, including interacting juxtaposed layers of epithelium and mesenchyme. Co-culture with iLM increases the yield of lung epithelial progenitors and impacts epithelial and mesenchymal differentiation programs, suggesting functional epithelial-mesenchymal crosstalk. Our iPSC-derived population thus expresses key features of developing lung mesenchyme, providing an inexhaustible source of cells for studying lung development, modeling diseases, and developing therapeutics.

Optimizing electrode materials performance and improving the energy density of supercapacitors is a hot research topic. The complex hollow sphere structure material, as a supercapacitor electrode m...

Objective To explore the prevalence of contraceptive use, unintended pregnancy, and induced abortions within 24 months postpartum in eastern, central, and western regions of China and in China overall. Study Design We conducted a retrospective cohort study and selected women who delivered a live birth between 12 and 24 months before the survey at 60 hospitals in eastern, central, and western regions of China. We used structured questionnaires for data collection and applied life-table analyses to estimate the prevalence of contraception, unintended pregnancy, and abortions. We used clustered log-rank tests to compare trends and rate differences at each time interval between/among regions. Results A total of 19,939 postpartum women were contacted, and 18,045 (90.5%) of them agreed to be interviewed. The 6-, 12-, and 24-month rates for modern contraceptive methods were 62.7% (95% confidence interval [CI] 58.9–66.4), 72.4% (95% CI 68.8–75.7), and 73.2% (95% CI 69.6–76.6), respectively. Condoms accounted for 79% of contraceptive initiators. The 6-, 12-, and 24-month rates were 1.4% (95% CI 1.2–1.7), 5.3% (95% CI 4.5-–6.1), and 13.1% (95% CI 11.3–14.8) for unintended pregnancy; and 1.1% (95% CI 0.8–1.3), 4.0% (95% CI 3.4–4.6), and 10.4% (95% CI 8.9–11.8) for induced abortion, respectively. By 24 months postpartum, 3-quarters of unintended pregnancies ended in abortion. The 24-month rates of modern contraceptive methods (75.2% vs73.4%, 71.1%), unintended pregnancy (15.3% vs 11.1%, 12.6%), and induced abortion (11.8% vs 9.9%, 9.4%) were higher in the western region relative to the eastern or central regions. Conclusion Postpartum contraception use was relatively high in China but dominated by less-effective methods, and these may contribute to higher risks of unintended pregnancy and induced abortion during the postpartum period. Use of long-acting reversible contraceptives and effective and reliable short-acting methods should thus be fostered in postpartum family planning services in China. Implications A national postpartum family planning program is needed in China. Service providers should work on counselling postpartum women and their partners with respect to long-acting reversible contraceptive methods, and to effectively and reliably use short-acting methods during the postpartum period.

Supercapacitors made by wood scraps are low cost, ecofriendly and accessible. However, there are some problems, such as a small specific surface area and low specific capacitance. How to obtain a high-performance supercapacitor by effectively increasing the specific surface area without affecting the conductivity is still a challenge. In this paper, carbon nanotubes (CNTs) were first synthesized on the inner wall of tracheids in wood carbon slices, which have complete structures and do not require any conductive additives and binder. Nanonickel particles as catalysts were uploaded on the inner wall of each tracheid for growing the CNTs, which can increase the specific surface area from 365.5 to 537.9 m2 g−1, while improving the electrochemical performance to 215.3 F g−1 or 76.5 F cm−3. The energy density of the all-solid-state supercapacitor is 39.8 Wh kg−1, and 96.2% of the capacitance could still be retained after 10,000 charging/discharging cycles. This capacitance value is approximately five times as high as that of activated wood carbon and is equal to or higher than that of supercapacitors based on wood carbon slices with pseudocapacitance materials. CNTs will greatly promote the application of wood scraps as valuable commodities.

In this paper, a novel type of electrode material for high-performance hybrid supercapacitors is designed. The electrode mainly uses nitrogen-doped atoms to anchor the nickel-cobalt layered double hydroxide on the inner wall of wood-derived carbon tracheids from Chinese fir wood scraps. The specific capacity of the composite single electrode is 14.26 mAh cm−2 at 10 mA cm−2. The hybrid supercapacitor with a composite electrode cathode and nitrogen-doped wood-derived monolithic carbon materials as the anode has a high specific capacitance of 4.74 F cm−2 at 5 mA cm−2, and the capacitance retention rate is 93.15% after 8000 charge-discharge cycles. The highest energy density and power density reach 1.48 mWh cm−2 and 22.40 mW cm−2, respectively. After doping with nitrogen, the combination with the nickel-cobalt layered double hydroxide is more uniform and stable, and the capacitance and cycling stability are significantly improved.

The non-destructive damage identification approaches for existing structures become more of a concern due to safety requirements. However, the application of damage identification method is still limited for complex spatial structures. In this paper, a practical residual force decomposition (RFD) method is proposed to identify damaged members in existing reticulated shell structures. A parameterized model is built by taking the stiffness reduction into consideration. In the proposed RFD method, the significant damage can be recognized corresponding to the changes of the observed eigenvector of the reticulated shells, and the eigenvector changes can be easily transferred to a set of multivariate linear equations to locate the members with significant stiffness reduction. The inputs of the equations are discussed including the additional constraints and the selection of effective modes. According to the different proportion of the numbers of members and joints, three situations of the solution are discussed. Especially when the solution is not unique, the importance coefficients of structural members are introduced as additional constraints through Ritz vector sensitivity analysis and application of the Modal Assurance Criterion. Two illustrative examples including a single-layer Kiewitt-6 reticulated shell and a structural model of international convention center are adopted to demonstrate the effectiveness of the approach. The results show that the proposed method can yield a suitable damage identification.

An improved factored modal combination method is developed for evaluating the in-plane seismic demands of latticed arches. In the method, an improved equivalent static earthquake load profile (ESELP) is proposed and expressed as a combination of several modal ESELPs. Two factors, an extended modal combination factor and a modal load modification factor, are proposed and used to establish the modal ESELPs, in which higher mode and geometrical nonlinear effects are taken into account. A set of improved ESELPs are established by combining the modal ESELPs of the selected modes that contribute significantly to the structural response. The structural demands are obtained from the envelope result of nonlinear pushover analyses using all the improved ESELPs. Three circular latticed arch models and two non-circular latticed arch models are built, and 30 seismic excitations are selected to investigate the applicability of the proposed method. The results show that, for latticed arches whose number of significant modes is less than or equal to three, the proposed method provides relatively high accuracy in the estimation of seismic demands. The mean errors of the seismic demands given by the proposed method are relatively low compared with those obtained from the factored modal combination method and the extended modal pushover analysis.

Wood carbon slices derived from wood scraps for constructing energy storage electrodes are very important, because they have excellent characteristics, such as structural stability, long cycle life, abundant resources and low prices. However, they have low capacitance as electrode materials for supercapacitors. In this paper, we design a new concept to obtain a porous wood carbon electrode with a large specific surface area. Firstly, CO2 is used to activate carbonized wood to open some closed pores and create some new pores. The activated wood is then soaked into KOH solution to further create new pores. Finally, the carbonized wood is modified with HNO3. After the above treatments, the number of nanopores with a diameter of approximately 2 nm is greatly increased within the wood carbon slices, and their specific surface area is increased to 703.5 m2 g−1. The single electrode material shows excellent performance with a high specific capacitance of 285.6 F g−1 and a high energy density of 38.0 mWh cm−3, which has more than twice the capacitance of the supercapacitor based on biomass carbon materials modified by diluted HNO3. Therefore, the application of wood scraps can meet the basic energy storage needs and realize the waste into treasure.

In the safety assessment of existing spatial structures, sampling measurements are widely used to investigate structural geometries. The information from sampling measurements is limited and leads to the positional uncertainty of unmeasured nodes. Uncertain nodal positions have a significant influence on the stability assessment of the spatial structures with high geometric-imperfection sensitivity. To deal with the uncertainty of nodal positions, a probabilistic framework based on the randomness of nodal positional deviations was proposed. In the framework, uncertain nodal positions are modeled by random field, whose relevant parameters were inferred with the data from sampling measurements; based on the random field model, a full-probability analysis is adopted to determine the load-bearing capacity and further perform the stability assessment. According to the analysis of the correlation between nodal positions, correlated and uncorrelated random fields were respectively introduced to model the correlated and uncorrelated nodal deviations. And the detailed modeling methods were discussed, including the inference of distribution types, parameters and correlations. Finally, an existing single-layer reticulated shell was used to validate the reliability of the proposed probabilistic framework.

Mechanism of the initial reactions of chlorine trifluoride oxide (ClF3O) and aluminum based composite fuel was investigated using density functional theory (DFT) at B3PW91/6–311++G (d,p) level and experimental methods. The composite fuel mainly contained isopropyl nitrate (IPN), hexogen (RDX), ammonium perchlorate (AP), n-decane, paraffin and aluminum powder. The results showed that ClF3O reacted exothermically with IPN, RDX, and hydrocarbons (n-decane and paraffin) via electrophilic substitution. The equatorial F atom was the reactive site of ClF3O. The reactive sites of IPN, RDX and hydrocarbon were different C H bonds according to the results of dual descriptor index. Reactivity of the composite fuel components was in the sequence of n-decane ≈ paraffin > RDX > IPN » AP according to the energy barriers. The value of released energy from the reaction of ClF3O with n-decane was greater than 400 kJ/mol, resulting in thermal decomposition of the composite fuel. The results from XPS indicated that the composite fuel was wrapped by hydrocarbons. ClF3O reacted with hydrocarbon first and then initialized the combustion of the composite fuel in the presence of oxygen. The emission spectrum of the composite fuel combustion was studied using an intensified CCD camera. Five characteristic radical intermediates (CH, C2, OH, NO and AlO) were determined.

Severe vertical ground motions (VGMs) may lead to detrimental seismic damages of large-span planar steel structures (LSPSSs), thus the inelastic seismic demand of LSPSSs under VGMs needs to be quantified so as to ensure the structural seismic reliabilities. In view that the uncertainties of VGMs greatly influence the seismic responses of LSPSSs, the VGMs-induced seismic demands of LSPSSs are investigated in a probabilistic way in this paper. Based on 680 strong VGM records, the vertical ductility demands (μ) of 2,100 equivalent single-degree-of-freedom (ESDF) models representing a series of LSPSSs are computed. It is revealed that the influences of VGM properties, including peak ground acceleration, epicentral distance, hypocenter depth, moment magnitude and local site condition, are tiny and irregular on the values of μ. Accordingly, the probabilistic seismic demand model for LSPSSs under VGMs is established regardless of the VGM properties in this paper. From the 1,428,000 computed values of μ, the VGMs-induced seismic demand of LSPSSs follows a positively skewed probabilistic distribution, and the distribution could be well fitted by the lognormal distribution model. The parameters of the lognormal distribution model for μ are simulated by two elementary functions subsequently, in which the effects of vertical strength reduction factor R, post-yield stiffness ratio α and elastic vibrating period T are accounted for. Using the lognormal model and the proposed functions, a group of probabilistic inelastic seismic demand spectra for LSPSSs under VGMs are generated. The established probabilistic spectra could provide the statistic properties of both the peak and the residual seismic demand of LSPSSs in association with pre-set values of T, R and α. Combining the proposed model with certain seismic hazard models that define the probabilistic characteristics of VGMs, the seismic reliability of LSPSSs could be quantified, and a proper structural seismic performance could be guaranteed.

Metal-organic frameworks (MOFs) derived carbon based nanocatalysts have been widely used in the environmental field due to high porosity, rich structural diversity/adjustability, and controllable chemical compositions. However, a suitable carrier is very necessary for solving the issues of aggregation and recovery of nanoparticles. Here, waste biomass of sawdust with low cost, abundant resource and special lumen structure, has been used as scalable carrier for Co-MOFs (ZIF-67). Due to the coordination of Co ions with abundant oxygen-containing functional groups of wood, ZIF-67 could be uniformly grown in situ on the surface of poplar sawdust with tracheid skeleton, and a magnetic catalyst possessing micro-nano porous structure has been successfully prepared by further carbonization (Co@N-PC). The catalytic ability of Co@N-PC was studied by activating potassium peroxomonosulfate (PMS) to remove methylene blue (MB). The results indicate the degradation efficiency on MB of Co@N-PC can reach 100% within 30 min which shows excellent catalytic performance. The boosted MB degradation ability mainly results from its unique micro-nano porous structure facilitating efficient material transfer and electron transfer during degradation process. At the same time, a possible catalytic mechanism was proposed. Moreover, Co@N-PC can be easy to separate and reuse from the solution by an external magnet, and performed decent stability. This work not only provides a simple and effective strategy to design large-scale and commercially viable biomass/MOF derived catalysts for water treatment, but also offers a decent alternative for high value utilization of waste biomass.

An updated parametric hysteretic model for steel tubular members, in which the member compressive buckling is considered, is proposed in this paper. The model can be used for simulating the complex inelastic force-displacement hysteresis behaviour of steel tubular members. Based on the general aspects of hysteretic behaviour and the traditional Marshall model, the modified Marshall model is developed to improve the simulation accuracy, whose control parameters are determined by batch parameter analysis results. For the applicability in multiple hysteresis loop process, the initial member curvature under compression-tension during hysteretic loop process is studied and the computation methods under compression and tension are given individually based on the finite element analysis results and theoretical derivation. On this foundation, the model control parameter correction and axial compression capacity redefined with large initial member curvature during hysteretic loop process are executed in the updated parametric hysteretic model proposed later in this paper. Finally, in addition to the comparison with the finite element results, the rationality and applicability of the proposed model are also verified by several experiments and the good agreement in loop curve trend and hysteretic energy consumption are found between the simulated and experimental results.

Summary Airway smooth muscle is best known for its role as an airway constrictor in diseases such as asthma. However, its function in lung development is debated. A prevalent model, supported by in vitro data, posits that airway smooth muscle promotes lung branching through peristalsis and pushing intraluminal fluid to branching tips. Here, we test this model in vivo by inactivating Myocardin, which prevented airway smooth muscle differentiation. We found that Myocardin mutants show normal branching, despite the absence of peristalsis. In contrast, tracheal cartilage, vasculature, and neural innervation patterns were all disrupted. Furthermore, airway diameter is reduced in the mutant, counter to the expectation that the absence of smooth muscle constriction would lead to a more relaxed and thereby wider airway. These findings together demonstrate that during development, while airway smooth muscle is dispensable for epithelial branching, it is integral for building the tracheal architecture and promoting airway growth.

Full-scale experimental study and numerical analysis on behaviors and failure mechanisms of full high strength steel extended endplate connections in fire have been carried out and presented in this paper. The experimental behaviors of the connections were compared with the provisions of Eurocode 3. The test results show that the failure modes of the connections in fire are bolt failure with yielding of the flange, as same as those at ambient temperature. The failures of the bolts in fire are ductile while they are brittle at ambient temperature. The rotation capacity of the connections in fire is proved sufficient. What is more, at elevated temperature 550 °C, the plastic moment resistances of Q690 and Q960 full high strength steel endplate connections are only 40% of those at ambient temperature, while their initial rotation stiffness are 66 and 63% respectively. But the rotation capacities of Q690 and Q960 high strength steel endplate connections are 1.38 and 1.74 times of those at ambient temperature. Moreover, it is found that the component method Eurocode 3 proposed based on connections made of mild steels can be used to calculate plastic resistances and to predict failure modes of high strength steel endplate connections in fire, but it is not suitable to predict their stiffness. The suggestions about rotation capacity of connections in Eurocode 3 are found too conservative for high strength steel endplate connections in fire.

BackgroundPulmonary cysts and spontaneous pneumothorax are presented in most patients with Birt-Hogg-Dubé (BHD) syndrome, which is caused by loss of function mutations in the folliculin (FLCN) gene. The pathogenic mechanisms underlying the cystic lung disease in BHD are poorly understood.MethodsMesenchymal Flcn was specifically deleted in mice or in cultured lung mesenchymal progenitor cells using a Cre/loxP approach. Dynamic changes in lung structure, cellular and molecular phenotypes and signalling were measured by histology, immunofluorescence staining and immunoblotting.ResultsDeletion of Flcn in mesoderm-derived mesenchymal cells results in significant reduction of postnatal alveolar growth and subsequent alveolar destruction, leading to cystic lesions. Cell proliferation and alveolar myofibroblast differentiation are inhibited in the Flcn knockout lungs, and expression of the extracellular matrix proteins Col3a1 and elastin are downregulated. Signalling pathways including mTORC1, AMP-activated protein kinase, ERK1/2 and Wnt-β-catenin are differentially affected at different developmental stages. All the above changes have statistical significance (pConclusionsMesenchymal Flcn is an essential regulator during alveolar development and maintenance, through multiple cellular and molecular mechanisms. The mesenchymal Flcn knockout mouse model provides the first in vivo disease model that may recapitulate the stages of cyst development in human BHD. These findings elucidate the developmental origins and mechanisms of lung disease in BHD.

In order to reveal more information and better understanding on the behavior and failure mechanisms of high strength steel (HSS) extended endplate connections at ambient temperature and after fire, an experimental and theoretical study has been conducted and presented in this paper. The provisions of Eurocode 3 are verified with the test results. Because strength of bolts decreases more rapidly than that of structural steels, failure modes of endplate connections may change after fire. Hence, a series of equations are proposed to predict failure modes of endplate connections after fire. Furthermore, FE simulations which can predicate the performance of HSS extended endplate connections with reasonable accuracy are adopted to study the behaviors of the connections after cooling down from various fire temperatures and to validate the accuracy of the proposed equations. Moreover, a parametric study is carried out to explore an optimization design method. It is found that the current provisions of EC3 can justifiably predict failure modes and plastic flexural resistances of HSS extended endplate connections both at ambient temperature and cooling down from 550 °C, but it is not the case for their initial rotational stiffness and rotation capacity. In order to avoid brittle failure mode of endplate connections after fire, appropriately increasing the diameter or grade of bolts in the design is suggested. What is more, the match of steel grade and thickness of column flange and endplate as well as beam should be considered in the optimization design of beam-column endplate connections.

The step-by-step modeling method considering nonlinear effects is an effective method for analyzing the mechanical behavior of steel structures during construction. However, two problems have limited the widespread application of the traditional step-by-step modeling method: the positioning of newly assembled members and the transformation of the stiffness matrix and the nodal load and displacement vectors between different stages of construction. In this article, a new concept of “two moments of a construction stage” (the initial and final moments of each construction stage) is proposed to improve the step-by-step modeling method. Based on this concept, an improved step-by-step modeling method, which considers the modified design configuration positioning principle for newly assembled members and provides a method for modifying the structural stiffness matrix at the initial moment of any construction stage, is proposed. A calculation program block based on the proposed method is compiled to analyze the mechanical behavior of a plane frame and a plane shallow arch during construction. The mechanical behavior of an engineering application, the connective corridor of Shanghai International Financial Centre, is also analyzed using the proposed method, and the calculated results are compared with the monitoring results. The numerical results show that the modified design configuration positioning principle is applicable for the positioning of newly assembled members and that the modification method for the structural stiffness matrix and the nodal load and displacement vectors at the initial moment of a construction stage efficiently solves the problem of their transformation between different stages of construction. The improved step-by-step modeling method proposed in this article is more valid and accurate than other methods for analyzing the mechanical behavior of steel structures during construction.

The global stability of a spatial structure is usually analysed via a nodal load-displacement curve (NLDC). However, the global mechanical properties of a structure can hardly be reflected comprehensively by specific NLDCs, and no criterion is available to select the representative node for getting the most reasonable NLDC. In this paper, a scalar parameter derived from the incremental equilibrium equation of nonlinear stability analysis, named Eigen-stiffness, is defined to characterize the global structural stiffness. The Structural Eigen-curve (SEC), based on Eigen-stiffness, is proposed to depict the equilibrium path. Two types of extreme points on SEC are defined to determine the critical state of the structure, including the structural limit state and the structural snap-back. Firstly, the stability of a hinge-supported planar arch is analysed to introduce the SEC concept. Then a K6 reticulated shell is designed to give further understanding. Subsequently, practical application of the SEC is illustrated in the stability analysis of a roof structure, namely, Shanghai International Conference Centre. In addition, a parametric study on a K6 reticulated shell is carried out, based on the Eigen-stiffness and the SEC, to investigate the effects of the rise to span ratio and the geometric imperfection amplitude on the structural stiffness and the structural load-carrying capacity. The results demonstrate that the ultimate load-carrying capacity obtained from the SEC is equal to that from NLDC. More importantly, unlike NLDC, the SEC — free from node selection — can efficiently capture the features of global structural behaviour and the evolution of structural stiffness.

The mechanism of the reactions of ClF3O and n-decane had two stages. The first stage was the initial reaction between ClF3O and n-decane. The initial reactions were investigated using a density functional theory (DFT) method. The results showed that the critical part of the mechanism of the initial reaction was the roaming of the HF intermediate. A H atom on n-decane was abstracted by a F atom on ClF3O to produce HF. The formed HF roamed around and then broke to give ClFO, fluorinated decane and a new HF molecule. The initial reactions were considered to be barrier-less reactions and extremely exothermic. The average released energy of the initial reactions was 412.9 kJ mol−1, which was great enough to cause thermal decomposition of n-decane. The second stage included the reaction between ClFO and n-decane and the thermal decomposition of n-decane. The secondary reactions involving ClFO were also studied using a DFT method. ClFO was less reactive than ClF3O. The average energy barrier of the reactions of ClFO and n-decane was 116.3 kJ mol−1 and the average released energy was 266.5 kJ mol−1. Thermal decomposition of n-decane was evidenced by the emission spectra of the characteristic radical intermediates CH and C2, which were observed using an intensified charge-coupled device (ICCD) system. The main gaseous products of the thermal decomposition of n-decane, as identified using gas chromatography, were hydrogen, ethylene and acetylene. The experimental results showed that the thermal decomposition of n-decane was an important secondary reaction following the initial reactions.

The vertical component of seismic ground motions (VGM) may induce severe responses in roof-type structures such as mega canopies, large floors, etc. This paper proposes a ductility-based approach for estimating the inelastic responses of roof-type steel structures under VGMs. Due to the pre-loaded gravity, a roof-type steel structure exhibits obvious asymmetric hysteresis properties in the vertical direction. Accordingly, this kind of structure could be idealized as “one-side yielding” systems which only yield in the lower side of vibration, wherein the gravity effect and the VGM effect positively super-positions with each other. Based on the idealized model, the vertical ductility demand spectra and the vertical residual displacement spectra for roof-type steel structures are computed using 53 recorded strong near-fault VGMs. Taking into account the vertical strength reduction factor and the vertical post-yielding stiffness ratio, a vertical ductility demand model in the μ-T format is proposed for roof-type steel structures under VGMs. Meanwhile, the vertical residual displacement model is derived from the vertical ductility demand model, since the vertical residual displacement could be computed as the peak vertical displacement subtracted by the recoverable elastic displacement. An application of these proposed models is given in the paper. The vertical seismic responses of a large-span steel floor under VGMs are predicted based on the proposed models, and the obtained results (including both the peak and the residual responses in the vertical direction) show good accuracy as compared with the results given by nonlinear response history analysis.

A test series was carried out and reported in a companion paper on the semi-rigid behaviour of aluminium alloy gusset (AAG) joints subjected to bending moment and axial force. This paper presented the results of an extensive numerical analysis program devoted to the investigation of the bending behaviour of AAG joints. The analysis was developed by means of finite element (FE) models implemented in the non-linear code ABAQUS. The procedure was accurately calibrated on the basis of the available experimental results. It is indicated that the FE models could be used effectively to describe the mechanical performance of AAG joints, including the failure modes, deformation process and bending moment-rotation curves. Furthermore, the shear connector, the thick plate and the advanced contact of bolts and bolt holes could improve the bending behaviour of AAG joints. According to the deformation process of AAG joints, a four-line model was proposed to simulate the bending moment-rotation relationship. To develop a further understanding, the effects of the member height, axial force, bolt pretension force, bolt gap and material nonlinearity on the bending behaviour of AAG joints were investigated.

Vertical seismic excitations (VSEs) could induce severe damage to building structures and infrastructural facilities, especially to those with large-spans or long cantilevers. Thus, there is a need in engineering practice for estimating the seismic response of structures under VSEs. In this paper, a tentative investigation on VSEs-induced inelastic response of steel structures is proposed. The structure is transformed into an equivalent single-degree-of-freedom (ESDF) system in an extended pushover process, in which the vertical component of response is included. Considering the influence of gravity, a novel ESDF model with asymmetric vibrating characteristic is established. In this ESDF model, the inelastic response only occurs at the “lower” side of vibration, whereas at the other side, the system keeps elastic. Based on the idealized ESDF model and 53 recorded strong VSEs, the vertical inelastic displacement ratio (IDR) is computed. The averaged IDRs are plotted against the elastic vibrating period T, and fitted by a piece-wise function to generate the IDR spectra, in which the effects of strength reduction factor R and of post-yield stiffness ratio α are accounted for by fitting coefficients. The overall process for estimating the VSE-induced inelastic responses of steel structures, using the extended pushover procedure and the proposed IDR spectra, is summarized. In the numerical example, seismic responses of a large-span space truss subjected to VSEs are computed by means of the nonlinear RHA method and the proposed IDR-based method, respectively, the results demonstrate that the IDR-based method could yield an anticipative estimation of structural responses under severe VSEs. For mid-span displacement, error of the IDR-based method is less than 13.6%; for quantity of yielded member, error is less than 14.2%.

Single-layer reticulated shells with aluminium alloy gusset (AAG) joints have a significant application prospect in spatial structures. To investigate their buckling behaviour, a single-layer reticulated shell with AAG joints subjected to a concentrated load at central joint was tested. The tested shell was a K6 shell with 5 rings, 8 m span and 0.5 m height. Its failure mode, buckling behaviour, internal force distribution of members, stress distribution of plates and joint stiffness were discussed. Finite element (FE) method implemented in the non-linear code ANSYS was adopted for the further investigation of single-layer reticulated shells with AAG joints. The FE procedure was accurately calibrated on the basis of the available experimental results. To develop a deep understanding, parameter studies considering the influence of joint bending behaviour on the buckling behaviour of single-layer reticulated shells were conducted.