Direct plastic analysis of steel structures by flexibility-based element with initial imperfection

[EN] Second-order direct analysis has been used in some regions for reliable analysis and design of steel structures. Currently, the stiffness-based element is widely used with accuracy improved by enforcing equilibrium along mid-span or “stations” along the member length in order to achieve equilibrium which is not guaranteed along an element. In this paper, a flexibility-based beam-column element considering member imperfection based on Hellinger-Reissner functional is developed and used for practical second-order direct analysis. This new element is a flexibility-based element with member initial bowing at the element level for direct analysis of three-dimensional frame analysis whereas previous flexibility-based elements assumed perfectly straight geometry for the element. The fiber plastic hinge approach is adopted to account for the distributed plasticity of a section. The new flexibility-based element performs excellently for modeling of members under high stress with material yielded as the conventional stiffness-based element has less accuracy when few elements are used in modeling a plastic member. This will significantly enhance accuracy and computational efficiency for direct plastic analysis which can then be more widely used in practical design. Several examples are employed to validate the accuracy and efficiency of the proposed element along this line of thought.The authors are grateful for financial support from the Research Grant Council of the Hong Kong SAR Government on the projects “Second-order Analysis of Shallow Dome Structures made of Tapering Members (PolyU 152047/17E)” and “Second-Order Analysis of Flexible Steel Cable Nets Supporting Debris (PolyU 152008/15E) ”; from the Innovation and Technology Fund of the Hong Kong SAR Government for the project “Development of an Energy Absorbing Device for Flexible RockFall Barriers (ITS/059/16FP) ”; and from the Hong Kong Branch of the Chinese National Engineering Research Centre for Steel Construction of The Innovation and Technology Fund of the Hong Kong SAR Government for the project “Advanced Numerical Analyses for Building Structures Using High Performance Steel Materials”.Liu, Y.; Shu, GP.; Chan, SL. (2018). Direct plastic analysis of steel structures by flexibility-based element with initial imperfection. En Proceedings of the 12th International Conference on Advances in Steel-Concrete Composite Structures. ASCCS 2018. Editorial Universitat Politècnica de València. 393-400. https://doi.org/10.4995/ASCCS2018.2018.7281OCS39340

Study on the multidrug resistance and transmission factors of Staphylococcus aureus at the ‘animal–environment–human’ interface in the broiler feeding cycle

Multidrug-resistant Staphylococcus aureus (S. aureus) poses an increasingly serious threat to agricultural safety and public health. Based on the concept of “One Health,” this study analyzed the multidrug resistance and transmission factors of S. aureus isolated from the “animal–environment–human” interface during one feeding cycle of commercial broilers in China by using antimicrobial susceptibility testing and whole genome sequencing (WGS) technologies. The results showed that in stage 1, the isolation rate of S. aureus was 1.32% (6/453), that of workers was 25.0% (4/16), and that of environmental samples was 0.69% (2/287), and the multidrug resistance rate was 83.33%. After one feeding cycle, the isolation rate of S. aureus (221/772, 28.63%) increased significantly (p < 0.01) during stage 2, and the multidrug resistance rate was as high as 97%. The resistance rates to eight drugs including erythromycin, clindamycin, enrofloxacin, ofloxacin, doxycycline, florfenicol, tylosin, and tilmicosin were elevated, but the differences were not significant (p > 0.05). ST398 (79.13%) was the dominant strain in both stages, which was prevalent in 11 types of samples from 3 sources and clustered in the same sub-branch of the single-nucleotide polymorphism (SNP) evolutionary tree. The loci difference between the strains ranged from 1 to 541, with SNPs of less than 10 between the human strains of stage 1 and the three sources in stage 2. The 42 representative strains carried mobile elements, mainly plasmid replicons (10 types), transposons (3 types), and 20 antibiotic resistance genes in 9 classes. A total of 10 ST398 strains exhibited the fosB gene for fosfomycin resistance, and 6 ST9 strains from stage 2 exhibited the mecA resistance gene. The SNP evolutionary analysis revealed that the fosB resistance gene might have been brought in by workers during stage 1. This study revealed the critical impact of environmental residual and worker-carried S. aureus, as well as the transmission of antibiotic resistance in stage 1. It highlighted the importance of the “One Health” approach and biosecurity measures and provided recommendations for the prevention of the spread of pathogens and resistance

Comparative study regarding the stability of a proximal ulnar stump with or without distal oblique bundle reconstruction during the Sauvé‒Kapandji procedure: a finite-element analysis

BackgroundThe most common postoperative complication of the Sauvé‒Kapandji (S-K) procedure is proximal ulnar stump instability. The distal oblique bundle (DOB) is a stable tissue used to stabilize the distal radioulnar joint. This study created finite-element models of the distal oblique bundle (DOB) to determine its effect on the proximal ulnar stump instability encountered during the Sauvé‒Kapandji procedure.PurposeWe hypothesized that a proximal ulnar stump with distal oblique bundle reconstruction would provide greater stability than a proximal ulnar stump without distal oblique bundle reconstruction.MethodsDetailed CT imaging data acquired from a pathological specimen of the wrist joint were imported into a finite-element analysis software package, and the regions of interest, including bone, cartilage, ligaments and tendons, were extracted to create a 3-dimensional model. The volar/dorsal and medial/lateral displacements of the proximal ulnar stump and the stress changes exhibited by the bone and distal oblique bundle tendon were measured with and without DOB reconstruction under 60° pronation, neutrality, and 60° supination.ResultsWhen utilizing DOB reconstruction, the displacement of the radius relative to the proximal ulna stump was approximately 17.89 mm in the neutral position. The bone stress values corresponding to the neutral position, 60° pronation and 60° pronation were 1.01, 18.32 and 14.69 MPa, respectively. The stress peaks of the DOB tendon structure corresponding to the neutral position, 60° pronation and 60° pronation were 0.07 MPa, 2.21 and 1.55 MPa, respectively. Without DOB reconstruction, the displacement of the radius relative to the proximal ulna stump was approximately 18.05 mm in the neutral position. Under 60° pronation and 60° supination, the displacement values were approximately 14.62 mm and 16.89 mm, respectively. The peak bone stress values corresponding to the neutral position, 60° pronation and 60° supination were 1.02, 18.29 MPa and 14.41 MPa, respectively. The stress peaks of the tendon structure corresponding to the neutral position, 60° pronation and 60° pronation were 0.03, 0.87 and 0.85 MPa, respectively.ConclusionDOB reconstruction is capable of improving the stability of the proximal ulnar stump during the Sauvé–Kapandji procedure

Incrementally Learning the Hierarchical Softmax Function for Neural Language Models

Neural network language models (NNLMs) have attracted a lot of attention recently. In this paper, we present a training method that can incrementally train the hierarchical softmax function for NNMLs. We split the cost function to model old and update corpora separately, and factorize the objective function for the hierarchical softmax. Then we provide a new stochastic gradient based method to update all the word vectors and parameters, by comparing the old tree generated based on the old corpus and the new tree generated based on the combined (old and update) corpus. Theoretical analysis shows that the mean square error of the parameter vectors can be bounded by a function of the number of changed words related to the parameter node. Experimental results show that incremental training can save a lot of time. The smaller the update corpus is, the faster the update training process is, where an up to 30 times speedup has been achieved. We also use both word similarity/relatedness tasks and dependency parsing task as our benchmarks to evaluate the correctness of the updated word vectors. </jats:p

Incrementally Learning the Hierarchical Softmax Function for Neural Language Models

Neural network language models (NNLMs) have attracted a lot of attention recently. In this paper, we present a training method that can incrementally train the hierarchical softmax function for NNMLs. We split the cost function to model old and update corpora separately, and factorize the objective function for the hierarchical softmax. Then we provide a new stochastic gradient based method to update all the word vectors and parameters, by comparing the old tree generated based on the old corpus and the new tree generated based on the combined (old and update) corpus. Theoretical analysis shows that the mean square error of the parameter vectors can be bounded by a function of the number of changed words related to the parameter node. Experimental results show that incremental training can save a lot of time. The smaller the update corpus is, the faster the update training process is, where an up to 30 times speedup has been achieved. We also use both word similarity/relatedness tasks and dependency parsing task as our benchmarks to evaluate the correctness of the updated word vectors. © Copyright 2017, Association for the Advancement of Artificial Intelligence (www.aaai.org). All rights reserved