The Local Web Buckling Strength of Stiffened Coped Steel I-Beams

Michael C. H. Yam,Angus C. C. Lam,Feng Wei,K F Chung 한국강구조학회 2007 International Journal of Steel Structures Vol.7 No.2

In steel construction the flange of a steel I-beam is usualy coped to allow clearance at the connection. The presence of acope in a beam wil reduce the strength of the beam in the coped region. Local web buckling at the coped region may occurwhen the cope length is long and/or the cope depth is large, provided that lateral-torsional buckling of the beam is prevented.coped I-beams although no experimental evidence was provided to support the recomendation. In order to verify suchrecomendation, an experimental and numerical investigation of coped I-beams with stiffeners at the coped region wasconducted and reported in this paper. The study showed that current recommendations did not consider the web distortionproperly, i.e. local web buckling could not be prevented efficiently if only horizontal stiffeners were provided at the copedregion. Both the test and the numerical results showed that the horizontal stiffeners at the cope displaced lateraly due to grossweb distortion. Based on the results of the parametric study of coped beams with diferent configurations of horizontal andvertical stiffeners, it was found that for cope depth to beam depth ratio (dc/D)≥0.3, both horizontal and vertical stiffeners arerequired in order to prevent local web buckling at the cope region. A preliminary recomendation for the design of copedbeams with both horizontal and vertical stiffeners was proposed according to the key findings of the investigation.

Photocatalytic Degradation of Gaseous Formaldehyde by Sol-Gel TiO₂Thin Film Coated on Glass

W.H. Ching,Michael Leung,W.C. Yam,S.P. Ng,Lilian L.P. Vrijmoed 한국태양에너지학회 2004 한국태양에너지학회 학술대회논문집 Vol.- No.-

An algorithm for quantifying dynamic buckling and post-buckling behavior of delaminated FRP plates with a rectangular hole stiffened by smart (SMA) stitches

Ghazaleh Soltanieh,Michael C.H. Yam 국제구조공학회 2021 Smart Structures and Systems, An International Jou Vol.28 No.6

Dynamic buckling of structure is one of the failure modes that needs to be considered since it may result in catastrophic failure of the structure in a short period of time. For a thin fiber-reinforced polymer (FRP) plate under compression, buckling is an inherent hazard which will be intensified by the existence of defects like holes, cracks, and delamination. On the other hand, the growth of the delamination is another prime concern for thin FRP plates. In the current paper, reinforcing the plates against buckling is realized by using SMA wires in the form of stitches. A numerical framework is proposed to simulate the dynamic instability emphasizing the effect of the SMA stitches in suppressing delamination growth. The suggested algorithm is more accurate than the other methods when considering the transformation point of the SMA wires and the modeling of the cohesive zone using simple and yet reliable technique. The computational design of the method by producing the line by line orders leads to a simple algorithm for simulating the super-elastic behavior. The Lagoudas constitutive model of the SMA material is implemented in the form of user material subroutines (VUMAT). The normal bilinear spring model is used to reproduce the cohesive zone behavior. The nonlinear finite element formulation is programmed into FORTRAN using the Newmark-beta numerical time-integration approach. The obtained results are compared with the results obtained by the finite element method using ABAQUS/Explicit solver. The obtained results by the proposed algorithm and those by ABAQUS are in good agreement.

Behaviour insights on damage-control composite beam-to-beam connections with replaceable elements

Xiuzhang He,Michael C. H. Yam,Ke Ke,Xu-Hong Zhou,Huanyang Zhang,Zi Gu 국제구조공학회 2023 Steel and Composite Structures, An International J Vol.46 No.6

Connections with damage concentrated to pre-selected components can enhance seismic resilience for moment resisting frames. These pre-selected components always yield early to dissipate energy, and their energy dissipation mechanisms vary from one to another, depending on their position in the connection, geometry configuration details, and mechanical characteristics. This paper presents behaviour insights on two types of beam-to-beam connections that the angles were designed as energy dissipation components, through the results of experimental study and finite element analysis. Firstly, an experimental programme was reviewed, and key responses concerning the working mechanism of the connections were presented, including strain distribution at the critical section, section force responses of essential components, and initial stiffness of test specimens. Subsequently, finite element models of three specimens were established to further interpret their behaviour and response that were not observable in the tests. The moment and shear force transfer paths of the composite connections were clarified through the test results and finite element analysis. It was observed that the bending moment is mainly resisted by axial forces from the components, and the dominant axial force is from the bottom angles; the shear force at the critical section is primarily taken by the slab and the components near the top flange. Lastly, based on the insights on the load transfer path of the composite connections, preliminary design recommendations are proposed. In particular, a resistance requirement, quantified by a moment capacity ratio, was placed on the connections. Design models and equations were also developed for predicting the yield moment resistance and the shear resistance of the connections. A flexible beam model was proposed to quantify the shear resistance of essential components.

Energy factor of high-strength-steel frames with energy dissipation bays under repeated near-field earthquakes

Ke Ke,Michael C.H. Yam,Xu-Hong Zhou,Fuming Wang,Fei Xu 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.40 No.3

This investigation contributes to quantification of the inelastic seismic demands for high strength steel moment resisting frames equipped with energy dissipation bays (HSSF-EDBs) subjected to seismic sequences composed of repeated near-field ground motions. The emphasis is placed on the energy factor demand. A statistical examination of a database with more than eighty million energy factor demands of single-degree-of-freedom (SDOF) oscillators representing HSSF-EDBs responding in different yielding stages is conducted. The research findings show that in the damage-control stage, the energy factor which quantifies the peak seismic demand of a HSSF-EDB structure is insensitive to the repeated near-field earthquake motions. In contrast, a remarkable elevation of the energy factor is observed when oscillators characterising HSSF-EDBs progress into the ultimate stage. In addition, an increasing post-yielding stiffness ratio of the nonlinear force-displacement response in the damage-control stage may produce a detrimental effect on HSSF-EDBs progressing into the ultimate stage under repeated near-field earthquakes due to the corresponding evident increase of seismic demands. A nonlinear regression model quantifying the mean energy factor demand of the system under repeated near-field earthquake motions is proposed to facilitate performance-based seismic design of HSSF-EDBs.

Energy-factor-based damage-control evaluation of steel MRF systems with fuses

Ke Ke,Michael C.H. Yam 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.22 No.3

The primary objectives of this research are to investigate the energy factor response of steel moment resisting frame (MRF) systems equipped with fuses subject to ground motions and to develop an energy-based evaluation approach for evaluating the damage-control behavior of the system. First, the energy factor of steel MRF systems with fuses below the resilience threshold is derived utilizing the energy balance equation considering bilinear oscillators with significant post-yielding stiffness ratio, and the effect of structural nonlinearity on the energy factor is investigated by conducting a parametric study covering a wide range of parameters. A practical transformation approach is also proposed to associate the energy factor of steel MRF systems with fuses with classic design spectra based on elasto-plastic systems. Then, the energy balance is extended to structural systems, and an energy-based procedure for damage-control evaluation is proposed and a damage-control index is also derived. The approach is then applied to two types of steel MRF systems with fuses to explore the applicability for quantifying the damagecontrol behavior. The rationality of the proposed approach and the accuracy for identifying the damage-control behavior are demonstrated by nonlinear static analyses and incremental dynamic analyses utilizing prototype structures.

Collapse resistance of steel frames in two-side-column-removal scenario: Analytical method and design approach

JingZhou Zhang,Michael C.H. Yam,Ghazaleh Soltanieh,Ran Feng 국제구조공학회 2021 Structural Engineering and Mechanics, An Int'l Jou Vol.78 No.4

So far analytical methods on collapse assessment of three-dimensional (3-D) steel frames have mainly focused on a single-column-removal scenario. However, the collapse of the Federal Building in the US due to car bomb explosion indicated that the loss of multiple columns may occur in the real structures, wherein the structures are more vulnerable to collapse. Meanwhile, the General Services Administration (GSA) in the US suggested that the removal of side columns of the structure has a great possibility to cause collapse. Therefore, this paper analytically deals with the robustness of 3-D steel frames in a twoside- column-removal (TSCR) scenario. Analytical method is first proposed to determine the collapse resistance of the frame during this column-removal procedure. The reliability of the analytical method is verified by the finite element results. Moreover, a design-based methodology is proposed to quickly assess the robustness of the frame due to a TSCR scenario. It is found the analytical method can reasonably predict the resistance-displacement relationship of the frame in the TSCR scenario, with an error generally less than 10%. The parametric numerical analyses suggest that the slab thickness mainly affects the plastic bearing capacity of the frame. The rebar diameter mainly affects the capacity of the frame at large displacement. However, the steel beam section height affects both the plastic and ultimate bearing capacity of the frame. A case study on a sixstorey steel frame shows that the design-based methodology provides a conservative prediction on the robustness of the frame.

A numerical framework of the phenomenological plasticity and fracture model for structural steels under monotonic loading

Qun He,Michael C. H. Yam,Zhiyang Xie,Xue-Mei Lin,Kwok-Fai Chung 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.44 No.4

In this study, the classical J2 flow theory is explicitly proved to be inappropriate to describe the plastic behaviour of structural steels under different stress states according to the reported test results. A numerical framework of the characterization of the strain hardening and ductile fracture initiation involving the effect of stress states, i.e., stress triaxiality and Lode angle parameter, is proposed based on the mechanical response of structural steels under monotonic loading. Both effects on strain hardening are determined by correction functions, which are implemented as different modules in the numerical framework. Thus, other users can easily modify them according to their test results. Besides, the ductile fracture initiation is determined by a fracture locus in the space of stress triaxiality, Lode angle parameter, and fracture strain. The numerical implementation of the proposed model and the corresponding code are provided in this paper, which are also available on GitHub. The validity of the numerical procedure is examined through single element tests and the accuracy of the proposed model is verified by existing test results.

A re-examination of the current design rule for staggered bolted connections

Xue-Mei Lin,Michael C. H. Yam,Ke Ke,Binhui Jiang,Qun He 국제구조공학회 2023 Steel and Composite Structures, An International J Vol.46 No.3

This paper summarised and re-examined the theoretical basis of the commonly used design rule developed by Cochrane in the 1920s to consider staggered bolt holes in tension members, i.e., the s 2 /4g rule. The rule was derived assuming that the term two times the bolt hole diameter (2d0) in Cochrane’s original equation could be neglected, and assuming a value of 0.5 for the fractional deduction of a staggered hole in assessing the net section area. Although the s 2 /4g rule generally provides good predictions of the staggered net section area, the above-mentioned assumptions used in developing the rule are doubtful, in particular for a connection with a small gauge-to-bolt-hole diameter (g/d0) ratio. It was found that the omission of 2d0 in Cochrane’s original equation appreciably overestimates the net section area of a staggered bolted connection with a small g/d0 ratio. However, the assumed value of 0.5 for the fractional deduction of a staggered hole underestimates the staggered net section area for small g/d0 ratios. To improve the applicability of the above two assumptions, a modified design equation, which covers a full range of g/d0 ratio, was proposed to accurately predict the staggered net section area and was validated by the existing test data from the literature and numerical data derived from this study. Finally, a reliability analysis of the test and numerical data was conducted, and the results showed that the reliability of the modified design equation for evaluating the net section resistance of staggered bolted connections can be achieved with the partial factor of 1.25.

Fracture Behaviour and Design of Steel Tensile Connections with Staggered Bolt Arrangements

Feng Wei,Cheng Fang,Michael C. H. Yam,Yanyang Zhang 한국강구조학회 2015 International Journal of Steel Structures Vol.15 No.4

This paper presents an experimental, numerical, and reliability study on the fracture behaviour of bolted steel tensile connections with various bolt arrangements. A total of 36 full-scale specimens were tested under tension until fracture. The main test parameters included the geometric pattern of the connections and the connection details such as pitch, gauge, edge distance and material. The test results show that the predictions of the ultimate capacity based on the s2/4g rule can be conservative, which may be mainly due to the ‘reinforcement’ effect of the biaxial stress state that exists between the bolt holes. However, for the specimens fabricated using higher strength steel with lower ductility, the conservatism is reduced substantially. Moreover, the test efficiency, which is defined as the ratio of the test ultimate capacity over the theoretical capacity of the gross section, was also examined. A higher test efficiency can be found when the hole spacing/edge distance is decreased/increased, although substantial increase in the edge distance can be ineffective. In addition, less ductile steel can lead to lower test efficiency. Furthermore, a numerical study was undertaken, where good agreements were observed between the numerical and the test results. With available test data, reliability analysis was finally performed to re-examine the rationale behind the resistance factors used in the current design codes.