Analytical and Numerical Investigation of Overstrength Factors for Very Short Shear Links in EBFs

Shujun Hu,Jingang Xiong,Qiang Zhou,Zhibin Lin 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.11

Shear links are key components in the Eccentrically Braced Frames (EBFs) that act as a structural fuse by dissipating seismic energy during severe earthquakes. Specification AISC 341, which is frequently used in the seismic design of steel structures, prescribes a constant overstrength factor of 1.50 for shear links. However, a few existing experimental results indicated that the overstrength of very short shear links with length ratio lower than 1.0 are much greater than required. In this paper, five basic factors influencing the overstrength of very short shear links are summarized as follows: web-ultimate-to-yield-shear-strength ratio, lengthto- stiffener-spacing ratio, flange-to-web-area ratio, flange-to-web-strength ratio, length-to-depth ratio. A numerical investigation with a detailed Finite Element (FE) model, verified by a comparison with existing experimental results, is conducted to investigate the combined effects of these five basic factors on the overstrength of very short shear links. Then, a new numerical model for predicting the overstrength value is proposed based on the FE analysis results and existing available experimental data by using the numerical fitting method, and it shows good agreement.

Seismic Analysis and Evaluation of Y-shaped EBF with an Innovative SSL-SSBC

Shujun Hu,Sizhi Zeng,Jingang Xiong,Xuefei Wang,Qiang Zhou,Xiong Xinfu 한국강구조학회 2020 International Journal of Steel Structures Vol.20 No.3

During severe earthquakes, the ductility and energy dissipation capacity of shear links in Y-shaped eccentrically braced frames (EBFs) are crucial to achieve desirable seismic performance and structural safety. In this study, an innovative SSLSSBC combining the advantages of a shear slotted bolted connection (SSBC) and a very short shear link is developed to improve the seismic performance of Y-shaped EBFs. Finite element (FE) analysis methods are fi rst validated through comparison with existing experimental results for slotted bolted connection and very short shear links. Further, FE simulations of the SSBC, very short shear link with shear slotted bolted connection (SSL-SSBC), and Y-shaped EBF are conducted to determine their mechanical behavior systematically. The FE results demonstrate that a reasonable SSBC can eff ectively increase the ductility and energy dissipation capacity through friction slipping, allowing the SSBC to maintain elastic behavior throughout the entire range of seismic loading, while the very short shear link in the SSL-SSBC could undergo severe damage to dissipate seismic energy. As expected, the SSL-SSBC is capable of working as both a shear dissipation damper and a metallic ductile damper in the Y-shaped EBF. This study also clearly identifi es that no yielding or damage of the very short shear links occurs during small and medium earthquakes, and the deformation and damage of the very short shear link can be minimized during severe earthquakes, allowing the seismic resilience capacity of the Y-shaped EBF to be dramatically enhanced.

Seismic Response of Resilient Steel Frame with Self-Centering SMA Brace

Shujun Hu,Liqing Chang,Bo Zhang,Sizhi Zeng,Fenghua Tang,Qing Zhi 한국강구조학회 2023 International Journal of Steel Structures Vol.23 No.6

An innovative self-centering shape memory alloy (SMA) brace aiming at improving the seismic performance and self-centering capacity of steel frame structures is proposed in this paper. A series of cyclic loading tests with six self-centering SMA brace (SC-SMAB) specimens was carried out to investigate the effects of SMA area, bolt torque and initial SMA force on the hysteresis curves, energy dissipation and self-centering capacity. In addition, based on the experimental results, a numerical model of SC-SMAB with the improved Graesser and Bouc–Wen model was established and validated. Three different single-bay plan configurations of 9 storey steel frames including bare steel frame (BSF), steel frame with slip braces (SF-SB) and steel frame with SC-SMABs (SF-SCB) were analyzed to evaluate the seismic response. The test results show that the SC-SMAB with the bolt torque of 10 N M and initial SMA force of 5 kN has the maximum bearing force and self-centering capacity ratio. The established numerical model can accurately predict the seismic performance of the SC-SMAB. The inter-story drift ratio, roof displacement and roof acceleration of SF-SCB are lower than those of the BSF and SF-SB evidently, which decrease by 62.21%, 29.46% and 28.36% respectively from BSF. The hysteresis curve of SC-SMAB in the steel frame has nearly ideal flag-shape with high bearing force, good energy dissipation capacity, small residual deformation and outstanding re-centering capacity.

Research on Hadoop Identity Authentication Based on Improved Kerberos Protocol

Daming Hu, Deyun Chen,Yuanxu Zhang,Shujun Pei 보안공학연구지원센터 2015 International Journal of Security and Its Applicat Vol.9 No.11

This paper researches the authentication mechanism of Kerberos protocol under HDFS, and points out the problems that identity authentication mechanism of Kerberos protocol faced in HDFS cluster environment: time synchronization, KDC security, dictionary attacks and denial mechanism. Aiming at these security problems, firstly, this paper provides an overview of the authentication process of the current Kerberos protocol under HDFS cluster environment; secondly, it modifies Kerberos protocol by using public key encryption and data signature mechanism; lastly, it provides the authentication process of improved Kerberos protocol in HDFS environment. Comprehensive analysis shows that both safety and time efficiency of the improved Kerberos protocol are improved compared with the existing identity authentication mechanism. It provides a more reliable and efficient identity authentication solution for HDFS cluster.

Research on Reliability of Hadoop Distributed File System

Daming Hu,Deyun Chen,Shuhui Lou,Shujun Pei 보안공학연구지원센터 2015 International Journal of Multimedia and Ubiquitous Vol.10 No.11

A technique for capturing structural crack geometry in numerical simulation based on the invariant level set method

Tao Wang,Shangtao Hu,Menggang Yang,Shujun Fang 국제구조공학회 2023 Structural Engineering and Mechanics, An Int'l Jou Vol.87 No.3

Engineering structures usually suffer from cracks. The crack geometry has an influence on the structural mechanical properties and subsequent crack propagations. However, as an extensively utilized method in fracture analysis, the extended finite element method provided by Abaqus fails to output the specific location and dimensions of fractures. In this study, a technique to capture the crack geometry is proposed. The technique is based on the invariant level set method (I-LSM), which can avoid updating the level set function during crack development. The solution is achieved by an open-source plug-in programmed by Python. Three examples were performed to verify the effectiveness and robustness of the program. The result shows that the developed program can accurately output the crack geometry in both the 2D and 3D models. The open-source plug-in codes are included as supplementary material.

Lateral Load Behavior of Self-centering Frame with Y-Eccentrically Braced Substructure: An Experiment and Numerical Analysis

Jingang Xiong,Moqiang Xiong,Youquan Liu,Xiang Li,Shujun Hu 대한토목학회 2024 KSCE Journal of Civil Engineering Vol.28 No.2

A novel self-centering frame with Y-eccentrically braced structure (SC-YEBFs) has been proposed in this paper to solve the problem that the storey drift of structure may exceed the specified limit in standards when self-centering beam-column joints are applied in high-rise and larger spans buildings, and the SC-YEBFs not only has the self-centering performance of self-centering frame system, but also has the high lateral stiffness and energy dissipating capacity of Y-Eccentrically braced frame. To study the lateral load behavior and influencing factors of SC-YEBFs, cyclic loading tests of two scaled specimens of SC-YEBFs substructure (SCS) were conducted, and seven finite element models corrected by the experiment were established to perform parametric analysis. The experiment and finite element analysis results indicated that the shear link has greatly increased the lateral stiffness and energy dissipating capacity of the self-centering structure, at the same time, it has maintained a good self-centering performance and replace ability. With an increase in the cross-sectional area and initial prestress of post-tensioned steel strands, the lateral load capacity and self-centering performance can be improved. The self-centering performance can be effectively improved by reducing the friction coefficient at the rotation connections. SC-YEBFs further extending the application field of self-centering structural systems, and making it possible to be applied to high-rise and larger spans structures.