Experimental database, analysis and design of noncompact and slender concrete-filled steel tube (CFT) members

Concrete-filled steel tube beam-columns are categorized as compact, noncompact or slender depending on the governing tube slenderness ratio. AISC 360-10 specifies the provisions for designing noncompact and slender rectangular and circular CFT members under axial compression, flexure, and combined axial and flexural loading. This research presents the development and evaluation of these design provisions. Available experimental databases of CFT members are reviewed, and a new experimental database of tests conducted on noncompact and slender CFT members is compiled. Detailed 3D finite element method (FEM) models are developed for noncompact and slender CFT members, and benchmarked using experimental results. The AISC 360-10 design provisions for noncompact and slender CFT members are then evaluated by both the experimental test results and additional FEM analysis that address the gaps in the experimental database. The current AISC 360-10 P-M interaction equations are updated using the results from comprehensive parametric studies (conducted using the benchmarked FEM model). Effective stress-strain curves for the steel tube and concrete infill are also developed. The validation of these effective stress-strain curves are confirmed by implementing them in a benchmarked nonlinear fiber analysis based macro mode

Analysis and behavior of high-strength rectangular CFT columns

[EN] The current AISC Specification (AISC 360-16) specifies the material strength limits for concrete-filled steel tube (CFT) columns. According to AISC 360-16, the steel yield stress (Fy) for CFT columns should not exceed 525 MPa, and the concrete compressive strength (f’c) should not exceed 70 MPa. CFT columns are classified as high strength if either Fy or f’c exceeds these specified limits, and are classified as conventional strength if both Fy and f’c are less than or equal to the limits. Due to lack of adequate research and comprehensive design equations, AISC 360-16 does not endorse the use of high-strength materials for CFT columns. This paper makes a contribution towards addressing this gap using a two-step approach. The first step consists of compiling an experimental database of high-strength rectangular CFT column tests in the literature and evaluating the possibility of extending the current AISC 360-16 design equations to high-strength rectangular CFT columns. The second step consists of developing and benchmarking detailed 3D nonlinear finite element models for predicting the behavior of high-strength CFT columns from the database. The benchmarked models are being used to perform comprehensive parametric studies to address gaps in the database and propose design equations for high-strength rectangular CFT members, which will be part of a future paper.Lai, Z.; Varma, A. (2018). Analysis and behavior of high-strength rectangular CFT columns. En Proceedings of the 12th International Conference on Advances in Steel-Concrete Composite Structures. ASCCS 2018. Editorial Universitat Politècnica de València. 245-252. https://doi.org/10.4995/ASCCS2018.2018.6957OCS24525

A contrast-enhanced CT-based radiomic nomogram for the differential diagnosis of intravenous leiomyomatosis and uterine leiomyoma

ObjectiveUterine intravenous leiomyomatosis (IVL) is a rare and unique leiomyoma that is difficult to surgery due to its ability to extend into intra- and extra-uterine vasculature. And it is difficult to differentiate from uterine leiomyoma (LM) by conventional CT scanning, which results in a large number of missed diagnoses. This study aimed to evaluate the utility of a contrast-enhanced CT-based radiomic nomogram for preoperative differentiation of IVL and LM.Methods124 patients (37 IVL and 87 LM) were retrospectively enrolled in the study. Radiomic features were extracted from contrast-enhanced CT before surgery. Clinical, radiomic, and combined models were developed using LightGBM (Light Gradient Boosting Machine) algorithm to differentiate IVL and LM. The clinical and radiomic signatures were integrated into a nomogram. The diagnostic performance of the models was evaluated using the area under the curve (AUC) and decision curve analysis (DCA).ResultsClinical factors, such as symptoms, menopausal status, age, and selected imaging features, were found to have significant correlations with the differential diagnosis of IVL and LM. A total of 108 radiomic features were extracted from contrast-enhanced CT images and selected for analysis. 29 radiomics features were selected to establish the Rad-score. A clinical model was developed to discriminate IVL and LM (AUC=0.826). Radiomic models were used to effectively differentiate IVL and LM (AUC=0.980). This radiological nomogram combined the Rad-score with independent clinical factors showed better differentiation efficiency than the clinical model (AUC=0.985, p=0.046).ConclusionThis study provides evidence for the utility of a radiomic nomogram integrating clinical and radiomic signatures for differentiating IVL and LM with improved diagnostic accuracy. The nomogram may be useful in clinical decision-making and provide recommendations for clinical treatment

Lithospheric Architecture and Metallogenesis in Liaodong Peninsula, North China Craton: Insights from Zircon Hf-Nd Isotope Mapping

The Liaodong Peninsula is an important mineral province in northern China. Elucidating its lithospheric architecture and structural evolution is important for gold metallogenic research and exploration in the region. In this study, Hf-Nd isotope maps from magmatic rocks are constructed and compared to geological maps to correlate isotopic signatures with geological features. It is found that gold deposits of different age periods in Liaodong are located in areas with specific εHf(t) and εNd ranges (Triassic: from −8 to −4 and from −12 to −8, Jurassic: from −22 to −8 and from −14 to −8, Cretaceous: from −12 to −10 and from −22 to −20), respectively. This may reflect that when the Paleo-Pacific plate was subducted beneath the North China Craton, the magma was derived from the juvenile lower crust and the ancient lower crust, and formed the low-to-moderate hydrothermal Au-(Ag) and Pb-Zn deposits in the Triassic. In the Jurassic, continued subduction may have led to lithospheric thickening. Subsequently, the magma from the ancient lower crust upwelled and formed low-to-moderate hydrothermal Au deposits and porphyry Mo deposits. In the Cretaceous, crustal delamination may have taken place. The magma from the ancient lower crust upwelled and formed various low-to-moderate hydrothermal Au deposits

Hybrid SVM-CNN Classification Technique for Human–Vehicle Targets in an Automotive LFMCW Radar

Human–vehicle classification is an essential component to avoiding accidents in autonomous driving. The classification technique based on the automotive radar sensor has been paid more attention by related researchers, owing to its robustness to low-light conditions and severe weather. In the paper, we propose a hybrid support vector machine–convolutional neural network (SVM-CNN) approach to address the class-imbalance classification of vehicles and pedestrians with limited experimental radar data available. A two-stage scheme with the combination of feature-based SVM technique and deep learning-based CNN is employed. In the first stage, the modified SVM technique based on these distinct physical features is firstly used to recognize vehicles to effectively alleviate the imbalance ratio of vehicles to pedestrians in the data level. Then, the residual unclassified images will be used as inputs to the deep network for the subsequent classification, and we introduce a weighted false error function into deep network architectures to enhance the class-imbalance classification performance at the algorithm level. The proposed SVM-CNN approach takes full advantage of both the locations of underlying class in the entire Range-Doppler image and automatical local feature learning in the CNN with sliding filter bank to improve the classification performance. Experimental results demonstrate the superior performances of the proposed method with the F 1 score of 0.90 and area under the curve (AUC) of the receiver operating characteristic (ROC) of 0.99 over several state-of-the-art methods with limited experimental radar data available in a 77 GHz automotive radar

Insight of Salt Spray Corrosion on Mechanical Properties of TA1-Al5052 Self-Piercing Riveted Joint

Self-piercing riveted (SPR) joints in automobiles inevitably suffer from corrosion damage and performance reduction. In this work, the influence of salt spray corrosion on the mechanical properties of TA1-Al5052 alloy SPR joints was studied. The TA1-5052 SPR joints were prepared and salt spray tests were carried out for different durations. The static and fatigue strengths of the joints after salt spray corrosion were tested to analyze the effect of salt spray duration on the performance of the joints. The results show that the joints’ static strength and fatigue strength decrease with prolonged salt spray time. The salt spray duration affects the joint’s tensile failure mode. The tensile failure without corrosion and with a short salt spray time is the fracture failure of the lower aluminum sheet, and the tensile failure of the joints after a long time of salt spray corrosion is the failure of the rivets. The fatigue failure form of the SPR joint is the formation of fatigue cracks in the lower aluminum sheet, and salt spray time has little effect on the fatigue failure form. Salt spray corrosion can promote the initiation and propagation of fatigue cracks. The fatigue crack initiation area is located at the boundary between the lower aluminum sheet and the rivet leg. The initiation of cracks originates from the wear zones among the sheet metal, rivets, and salt spray particles

Developing a self-piercing riveting with flange pipe rivet joining aluminum sheets

This paper proposes a self-piercing riveting (SPR) method which uses a flange pipe rivet. This joining technology can solve the problems of oblique rivet and incorrect rivet position which are usually found in the SPR with a pipe rivet. The lap shear strength of the joint with a flange pipe rivet is higher than that of a joint with a conventional rivet. In this research, a flange pipe rivet was placed between two sheets with a force applied to the top sheet by a punch riveting machine. The flange pipe rivet moved downward along with the top sheet to induce appropriate bending and form a mechanical interlock in both sheets. Finite element (FE) analysis of the SPR with a flange pipe rivet was done by DEFORM software. The simulated joint cross-section shapes were observed, and the influence of the flange pipe rivet parameters on joint quality was analyzed. Simultaneously, some riveting experiments on joining aluminum sheets were conducted taking into consideration different rivet heights and chamfer angles. The results show that the joining surface is smooth and the simulated joint cross-section shapes are in good agreement with the experimental results. The joining property with a chamfer angle of 45° and a rivet height of 5 mm is found to be the best in joining the Al6063 aluminum alloy sheets with a thickness of 2.4 mm by using the SPR with a flange pipe rivet

Chinese High Rise Reinforced Concrete Building Retrofitted with CLT Panels

Cross laminated timber (CLT) panels have been gaining increasing attention in the construction field as a diaphragm in mid- to high-rise building projects. Moreover, in the last few years, due to their seismic performances, low environmental impact, ease of construction, etc., many research studies have been conducted about their use as infill walls in hybrid construction solutions. With more than a half of the megacities in the world located in seismic regions, there is an urgent need of new retrofitting methods that can improve the seismic behavior of the buildings, upgrading, at the same time, the architectural aspects while minimizing the environmental impact and costs associated with the common retrofit solutions. In this work, the seismic, energetic, and architectural rehabilitation of tall reinforced concrete (RC) buildings using CLT panels are investigated. An existing 110 m tall RC frame building located in Huizhou (China) was chosen as a case study. The first objective was to investigate the performances of the building through the non-linear static analysis (push-over analysis) used to define structural weaknesses with respect to earthquake actions. The architectural solution proposed for the building is the result of the combination between structural and architectonic needs: internal spaces and existing facades were re-designed in order to improve not only the seismic performances but also energy efficiency, quality of the air, natural lighting, etc. A full explanation of the FEM modeling of the cross laminated timber panels is reported in the following. Non-linear FEM models of connections and different wall configurations were validated through a comparison with available lab tests, and finally, a real application on the existing 3D building was discussed

An Improved Dual Second-Order Generalized Integrator Phased-Locked Loop Strategy for an Inverter of Flexible High-Voltage Direct Current Transmission Systems under Nonideal Grid Conditions

High-voltage flexible power systems, with their intrinsic characteristics, play an increasingly important role in electronic power systems. Synchronization between the inverter and the grid needs to be achieved by a phase-locked loop (PLL), the performance of which determines the quality of power transmission. This paper proposes a PLL adapted to extremely harsh grid conditions. Firstly, the traditional synchronous reference frame PLL and the dual second-order generalized integrator (DSOGI-PLL) are analyzed, and the errors in phase-locking and the shortcomings of these two methods in the presence of DC components in the grid are pointed out. Secondly, based on the harmonic grid voltage, a repetitive control internal model is introduced by DSOGI to realize the real-time tracking and regulation of the harmonic signals in order to suppress the harmonic voltage disturbance. In addition, a DC bias elimination and frequency adaptive method is proposed to solve the problems of DC bias and grid voltage frequency fluctuation in order to achieve adaptive tracking of the grid phase. Finally, the superiority of the proposed strategy is verified through simulations and experiments