This article aims to investigate the contact characteristics of mortise and tenon (M&T) joints in the traditional timber structures. In particular, the normal embedded compressive contact between ...contact surfaces of M&T joint was investigated. Based on basic contact theory and contact characteristics between mortise and tenon, a normal elasto-plastic contact model, which can reflect the real normal contact behavior of M&T joints in traditional wooden structures, was proposed. Coulomb friction contact was utilized to describe the tangential slipping characteristics of the contact surfaces. Micro-morphology scanning tests of wood samples with different roughness were carried out to determine the parameters involved in the normal contact model. The normal contact model subroutine of M&T joint was compiled by FORTRAN language, implemented into ABAQUS through user-defined interface (UINTER). Then the proposed model was verified by shear tests of wood contact surfaces considering different normal pressures. Finally, a finite element model (FEM) of straight tenon joint subjected to cyclic reversed loading, based on the proposed normal elasto-plastic contact model, was developed, and a FEM considering normal “hard contact” between the contact surfaces, was also performed. The simulation results were validated by the experimental results. Results showed that the user-defined normal elasto-plastic contact FEM was more in line with the actual force state and mechanical behavior of M&T joints, which can more accurately predict the failure modes and simulate the hysteretic behavior of M&T joints, compared to the FEM considering normal “hard contact” of the contact surfaces.
Wood infill walls have significant effect on the seismic performance of Chinese traditional timber structure. Based on cyclic tests of wood infill walls, a 1:6 scaled traditional timber structure, ...one direction with wood infill walls and the other direction without ones, were fabricated and subjected to artificial and recorded earthquake waves through shaking table tests. The dynamic characteristics, dynamic responses and energy dissipation in the two directions were comparatively discussed to quantify the contribution of wood infill walls. The test results indicated that the natural frequencies of the model with wood infill walls was much greater than that without ones, increased more than 25%, while the increase of damping ratio was relatively insignificant before experiencing earthquakes. And the acceleration responses of the structure incorporating wood infill walls were moderately increased due to the additional lateral stiffness provided by wood infill walls, while the displacement responses dramatically decreased, especially under strong earthquakes. In addition, the wood infill walls effectively decreased the proportion of plastic strain energy in total energy, which can contribute to reduce structural damage.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
This article presents a study on the mechanical properties and constitutive model of Dahurian larch wood under parallel-to-grain (ParG) and perpendicular-to-grain (PerG) cyclic loading. A total of ...twenty-four dog-bone specimens were designed and prepared. Failure modes, stress–strain curves, elastic moduli under monotonic loading, and unloading/reloading moduli under cyclic loading were analyzed. Results indicated that the tensile and compressive envelope curves of wood under cyclic loading are similar to the monotonic stress–strain curves. The unloading and reverse reloading stiffness of wood are significantly degraded in both material directions. Furthermore, a constitutive model that is capable of considering the degradation of cyclic compression unloading stiffness and the change in reverse compression (tension) stiffness after tension (compression) unloading was proposed. A comprehensive comparison with test results was conducted, and they are in good agreement. Thus, the correctness of the proposed constitutive model is verified.
This study investigates the enhanced effect of timber infill walls on the seismic behavior of traditional Chinese timber frames. Two 1/2 scaled traditional Chinese timber infill walls (TIWs), two 1/2 ...scaled timber frames with timber infill walls (TFTIWs) and one 1/2 scaled timber frame (TF) were fabricated and tested under low-cyclic reversed loading. The failure modes, strength, stiffness, and energy consumption capacity of the TIWs and the TFTIWs were obtained, and the effects of the TIWs on the seismic performance of the TFTIWs were investigated. The results showed that the TIWs can increase the stiffness and ultimate bearing capacity of the TF, up to 60% and 80%, respectively. The strength degradation coefficient of the TFTIWs was slightly higher than that of the TF when the inter-story drift ratio exceeded 0.02 rad, and the TIWs helped to mitigate the strength degradation of the TFTIWs. It was also found that the TFTIWs had a higher cumulative energy dissipation when compared with the TF (up to a 60% increase), indicating the TIWs had reasonably good energy dissipation capacity. When the TIWs generated a solid contribution to the carrying capacity and energy dissipation of the TF, the lateral drift thresholds were 1/100 and 1/43 of the column height, respectively. Furthermore, the TIWs and TFTIWs presented a good ductility, and the TIW could effectively reduce the pull-out amount of the tenon from the mortise of the TF; however, the TIWs had little influence on the stiffness degradation level or improvement of the ductility of the TF.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
This study aimed to create a predictive model based on machine learning to identify the risk for tracheobronchial tuberculosis (TBTB) occurring alongside
pneumonia in pediatric patients.
Clinical ...data from 212 pediatric patients were examined in this retrospective analysis. This cohort included 42 individuals diagnosed with TBTB and
pneumonia (combined group) and 170 patients diagnosed with lobar pneumonia alone (pneumonia group). Three predictive models, namely XGBoost, decision tree, and logistic regression, were constructed, and their performances were assessed using the receiver's operating characteristic (ROC) curve, precision-recall curve (PR), and decision curve analysis (DCA). The dataset was divided into a 7:3 ratio to test the first and second groups, utilizing them to validate the XGBoost model and to construct the nomogram model.
The XGBoost highlighted eight significant signatures, while the decision tree and logistic regression models identified six and five signatures, respectively. The ROC analysis revealed an area under the curve (AUC) of 0.996 for XGBoost, significantly outperforming the other models (
< 0.05). Similarly, the PR curve demonstrated the superior predictive capability of XGBoost. DCA further confirmed that XGBoost offered the highest AIC (43.226), the highest average net benefit (0.764), and the best model fit. Validation efforts confirmed the robustness of the findings, with the validation groups 1 and 2 showing ROC and PR curves with AUC of 0.997, indicating a high net benefit. The nomogram model was shown to possess significant clinical value.
Compared to machine learning approaches, the XGBoost model demonstrated superior predictive efficacy in identifying pediatric patients at risk of concurrent TBTB and
pneumonia. The model's identification of critical signatures provides valuable insights into the pathogenesis of these conditions.
Fires are always known for seriously deteriorating concrete in structures, especially for those with certain carbonation due to long-time service. In this paper, 75 prism specimens were prepared and ...divided into four groups (three carbonated groups and one uncarbonated group). Specimens were tested under different temperatures (20, 300, 400, 500, 600, and 700°C), exposure times (3, 4, and 6 hours), and cooling methods (water and natural cooling). Surface characteristics, weight loss rate, and residual mechanical properties (strength, initial elastic modulus, peak, and ultimate compressive strains) of carbonated concrete specimens after elevated temperatures were investigated and compared with that of the uncarbonated ones. Results show that the weight loss rates of the carbonated concrete specimens are slightly lower than that of the uncarbonated ones and that the cracks are increased with raising of temperatures. Surface colors of carbonated concrete are significantly changed, but they are not sensitive to cooling methods. Surface cracks can be evidently observed on carbonated specimens when temperature reaches 400°C. Residual compressive strength and initial elastic modulus of carbonated concrete after natural cooling are generally larger than those cooled by water. The peak and ultimate compressive strains of both carbonated and uncarbonated concrete specimens increase after heating, but the values of the latter are greater than that of the former. Finally, the constitutive equation to predict the compressive behaviors of carbonated concrete after high temperatures was established and validated by tests.
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FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
At present, super-resolution reconstruction technology is widely used in remote sensing as an effective means to improve the resolution. The super-resolution reconstruction technique reconstructs a ...series of low-resolution images into one high-resolution image by using complementary information provided by images pixel displacements. In this paper, the satellite video comes from Durango Mexico is used as experimental data. The Vandewalle motion estimation method and Interpolation reconstruction method are used to reconstruct the satellite video images, and the quality evaluation combines subjective evaluation with objective evaluation to appraise the results comprehensively and effectively. Experimental results show that static feature edges reconstructed by Interpolation reconstruction method are even more smooth and clear, and the detail information is more abundant, which can effectively improve the resolution of satellite video images.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Concrete behavior usually degrades due to freeze-thaw cycles, fire, or both. Existing studies on the degradation behavior of concrete due to exposure to high temperatures were primarily focused on ...unfrozen concrete. In this paper, the degradation behavior of damaged concrete, after different freeze-thaw cycles (25, 35, 45, and 55 cycles), exposure temperatures (20°C, 300°C, 400°C, and 500°C), and cooling methods (water-cooled and air-cooled), was tested with seventy-five prism specimens. The degradation behavior of the damaged concrete, such as surface characteristics, weight loss, compressive strength, peak strains, and elastic modulus, was studied and analyzed. Results show that (i) the surface color of the concrete does not change significantly throughout the test. As the number of freeze-thaw cycles and temperatures increase, the weight loss of the concrete specimens increases gradually. (ii) After freeze-thaw cycles, the relative strengths and elastic modulus of the concrete specimens significantly degrade compared with those of the unfrozen ones at same temperatures. (c) At elevated number of freeze-thaw cycles and exposure temperatures, the peak strain of the concrete increases gradually. (d) Cooling methods have different effects on the degradation of concrete under different number of freeze-thaw cycles. Finally, a uniaxial compression constitutive model for concrete after freeze-thaw cycles and then exposure to high temperatures was established and a good agreement was observed with test results.
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FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
Wood has been extensively used in Chinese ancient buildings, and it is important to clearly understand the mechanical properties of wood after exposure to elevated temperatures. In this paper, three ...kinds of tests with 102 clear wood specimens fabricated with Chinese Dahurian larch for each kind of test were conducted. The residual compressive strength, tensile strength, and shear strength parallel to grain of specimens after exposure to different temperatures (100°C, 150°C, 200°C, and 250°C) with various exposure times (15 min, 30 min, and 45 min) and different cooling methods (natural cooling and water cooling) were obtained. Results indicate that exposure to elevated temperatures causes great degradation of compressive strength, tensile strength, and shear strength parallel to grain. When the exposure temperatures exceed 200°C, the relative compressive strength, tensile strength, and shear strength parallel to grain decrease greatly with the increase of exposure time. The residual compressive strength, tensile strength, and shear strength of specimens after water cooling are lower than that after natural cooling. Exposure temperatures also have a great impact on the weight loss and color change of wood. Based on the test data, degradation models for the residual compressive strength, tensile strength, and shear strength of wood were developed. Furthermore, the damage constitutive model of compressive (CDMC) and tensile (CDMT) parallel to grain was established and validated reasonably by tests.
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FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
•The bending moment, initial stiffness and energy dissipation capacity of joint with gap gradually decrease as increasing the damage degree.•The existence of gap can reduce the ductility of joint and ...aggravate the degree of stiffness degradation of M-T joint at the same rotation.•The empirical degradation formulas related to key cyclic performance parameters are established.•A degraded hysteretic model is proposed to predict hysteretic behavior of a joint with gap.
Gaps are very common in the mortise-tenon (M-T) joints of traditional timber structures, and they significantly reduce the rotational performance of joints. To evaluate the effect of gaps on the rotational behavior of straight M-T joints, we fabricated four 1/3.2-scaled Chinese traditional straight M-T joint specimens using Pinus sylvestris logs, one without a gap and three with different gaps, and subjected them to cyclic loading tests strictly in accordance with the international test standard ISO-16670. The failure modes, strength, initial rotational stiffness, ductility, deformation, and energy dissipation capacity of the joints were investigated. The results indicated that the apparent slippage, the tenon pulled out, and the plastic deformation for the mortise edge were exhibited in the specimens with gaps. The bending moment, initial rotational stiffness, and energy dissipation capacity of the joints with gaps gradually decreased as the damaged degree increased. The ultimate rotation of joints with gaps reached 0.2 rad, indicating a good deformation capacity. Furthermore, the gap can aggravate the degree of stiffness degradation of the M-T joint at the same rotation. Based on the experimental results, the empirical degradation formulas related to key cyclic performance parameters, considering the gap effects, were established. Based on the degradation relationships of the key hysteretic parameters of the joint with gaps, a hysteretic model for a joint with a gap was proposed and validated. Good agreement between the model predictions and experimental results was observed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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