Experimental study on vibration serviceability of cold-formed thin-walled steel floor

Bin Chen,Liang Cao,Faming Lu,Y. Frank Chen 국제구조공학회 2023 Steel and Composite Structures, An International J Vol.46 No.4

In this study, on-site testing was carried out to investigate the vibration performance of a cold-formed thin-walled steel floor system. Ambient vibration, walking excitation (single and double persons), and impulsive excitation (heel-drop and jumping) were considered to capture the primary vibration parameters (natural frequencies, damping ratios, and mode shapes) and vertical acceleration response. Meanwhile, to discuss the influence of cement fiberboard on structural vibration, the primary vibration parameters were compared between the systems with and without the installation of cement fiberboard. Based on the experimental analysis, the cold-formed thin-walled steel floor possesses high frequency (> 10 Hz) and damping (> 2%); the installed cement fiberboard mainly increases the mass of floor system without effectively increasing the floor stiffness and may reduce the effects of primary vibration parameters on acceleration response; and the human-structure interaction should be considered when analyzing the vibration serviceability. The comparison of the experimental results with those in the AISC Design Guide indicates that the cold-formed thin-walled steel floor exhibits acceptable vibration serviceability. A crest factor βrp (ratio of peak to root-mean-square accelerations) is proposed to determine the root-mean-square acceleration for convenience.

A simplified method for determining the acceleration amplitudes of long-span floor system under walking/running loads

Liang Cao,Y. Frank Chen 국제구조공학회 2020 Structural Engineering and Mechanics, An Int'l Jou Vol.75 No.3

Modern long-span floor system typically possesses low damping and low natural frequency, presenting a potential vibration sensitivity problem induced by human activities. Field test and numerical analysis methods are available to study this kind of problems, but would be inconvenient for design engineers. This paper proposes a simplified method to determine the acceleration amplitudes of long-span floor system subjected to walking or running load, which can be carried out manually. To theoretically analyze the acceleration response, the floor system is simplified as an anisotropic rectangular plate and the mode decomposition method is used. To facilitate the calculation of acceleration amplitude aP, a coefficient αwmn or αRmn is introduced, with the former depending on the geometry and support condition of floor system and the latter on the contact duration tR and natural frequency. The proposed simplified method is easy for practical use and gives safe structural designs.

Experimental study on the seismic performance of concrete filled steel tubular laced columns

Zhi Huang,Lizhong Jiang,Y. Frank Chen,Yao Luo,Wang-Bao Zhou 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.26 No.6

Concrete filled steel tubular (CFST) laced columns have been widely used in high rise buildings in China. Compared to solid-web columns, this type of columns has a larger cross-section with less weight. In this paper, four concrete filled steel tubular laced columns consisting of 4 main steel-concrete tubes were tested under cyclic loading. Hysteresis and failure mechanisms were studied based on the results from the lateral cyclic loading tests. The influence of each design parameter on restoring forces was investigated, including axial compression ratio, slenderness ratio, and the size of lacing tubes. The test results show that all specimens fail in compression-bending-shear and/or compression-bending mode. Overall, the hysteresis curves appear in a full bow shape, indicating that the laced columns have a good seismic performance. The bearing capacity of the columns decreases with the increasing slenderness ratio, while increases with an increasing axial compression ratio. For the columns with a smaller axial compression ratio (< 0.3), their ductility is increased. Furthermore, with the increasing slenderness ratio, the yield displacement increases, the bending failure characteristic is more obvious, and the hysteretic loops become stouter. The results obtained from the numerical analyses were compared with the experimental results. It was found that the numerical analysis results agree well with the experimental results.

Practical formula for determining peak acceleration of footbridge under walking considering human-structure interaction

Liang Cao,Hailei Zhou,Y. Frank Chen 국제구조공학회 2022 Structural Engineering and Mechanics, An Int'l Jou Vol.83 No.6

In this paper, an analytical formulation is proposed to predict the vertical vibration response due to the pedestrian walking on a footbridge considering the human-structure interaction, where the footbridge and pedestrian are represented by the Euler beam and linear oscillator model, respectively. The derived coupled equation of motion is a nonlinear fourth-order partial differential equation. An uncoupled solution strategy based on the combined weighted residual and perturbation method) is proposed to reduce the tedious computation, which allows the separate integration between the bridge and pedestrian subsystems. The theoretical study demonstrates that the pedestrian subsystem can be treated as a structural system with added mass, damping, and stiffness. The analysis procedure is then applied to a case study under the conditions of single pedestrian and multi pedestrians, and the results are validated and compared numerically. For convenient vibration design of a footbridge, the simplified peak acceleration formula and the idea of decoupling problem are thus proposed.

Vibration performance of composite steel-bar truss slab with steel girder

Jiepeng Liu,Liang Cao,Y. Frank Chen 국제구조공학회 2019 Steel and Composite Structures, An International J Vol.30 No.6

In this study, on-site testing was carried out to investigate the vibration performance of a composite steel-bar truss slab with steel girder system. Ambient vibration was performed to capture the primary vibration parameters (natural frequencies, damping ratios, and mode shapes). The composite floor possesses low frequency (< 10 Hz) and damping (< 2%). Based on experimental, theoretical, and numerical analyses on natural frequencies and mode shapes, the boundary condition of SCSC (i.e., two opposite edges simply-supported and the other two edges clamped) is deemed more reasonable for the composite floor. Walking excitations by one person (single excitation), two persons (dual excitation), and three persons (triple excitation) were considered to evaluate the vibration serviceability of the composite floor. The measured acceleration results show a satisfactory vibration perceptibility. For design convenience and safety, a crest factor βrp describing the ratio of peak acceleration to root-mean-square acceleration induced from the walking excitations is proposed. The comparisons of the modal parameters determined by ambient vibration and walking tests reveal the interaction effect between the human excitation and the composite floor.

Accurate computational design of multipass transmembrane proteins

Lu, Peilong,Min, Duyoung,DiMaio, Frank,Wei, Kathy Y.,Vahey, Michael D.,Boyken, Scott E.,Chen, Zibo,Fallas, Jorge A.,Ueda, George,Sheffler, William,Mulligan, Vikram Khipple,Xu, Wenqing,Bowie, James U. American Association for the Advancement of Scienc 2018 Science Vol.359 No.6379

<P><B>Membrane protein oligomers by design</B></P><P>In recent years, soluble protein design has achieved successes such as artificial enzymes and large protein cages. Membrane proteins present a considerable design challenge, but here too there have been advances, including the design of a zinc-transporting tetramer. Lu <I>et al.</I> report the design of stable transmembrane monomers, homodimers, trimers, and tetramers with up to eight membrane-spanning regions in an oligomer. The designed proteins adopted the target oligomerization state and localized to the predicted cellular membranes, and crystal structures of the designed dimer and tetramer reflected the design models.</P><P><I>Science</I>, this issue p. 1042</P><P>The computational design of transmembrane proteins with more than one membrane-spanning region remains a major challenge. We report the design of transmembrane monomers, homodimers, trimers, and tetramers with 76 to 215 residue subunits containing two to four membrane-spanning regions and up to 860 total residues that adopt the target oligomerization state in detergent solution. The designed proteins localize to the plasma membrane in bacteria and in mammalian cells, and magnetic tweezer unfolding experiments in the membrane indicate that they are very stable. Crystal structures of the designed dimer and tetramer—a rocket-shaped structure with a wide cytoplasmic base that funnels into eight transmembrane helices—are very close to the design models. Our results pave the way for the design of multispan membrane proteins with new functions.</P>

Analytical solution for free vibration of multi-span continuous anisotropic plates by the perturbation method

Jie-Peng Liu,Liang Cao,Y. Frank Chen 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.69 No.3

Accurately determining the natural frequencies and mode shapes of a structural floor is an essential step to assess the floor’s human-induced vibration serviceability. In the theoretical analysis, the prestressed concrete floor can be idealized as a multi-span continuous anisotropic plate. This paper presents a new analytical approach to determine the natural frequencies and mode shapes of a multi-span continuous orthotropic plate. The suggested approach is based on the combined modal and perturbation method, which differs from other approaches as it decomposes the admissible functions defining the mode shapes by considering the intermodal coupling. The implementation of this technique is simple, requiring no tedious mathematical calculations. The perturbation solution is validated with the numerical results.

Design Aid for Moment Strength of Built-up Crane Runway Girders

Wei T. Hsu,Dung M. Lue,Y. Frank Chen 한국강구조학회 2012 International Journal of Steel Structures Vol.12 No.3

The evaluation of elastic moment for built-up crane runway girders is not an easy task as the difficulty involves the calculation of torsional properties including warping constant, the coefficient of monosymmetry, and torsion constant. To date,all AISC specifications offer no specific formulas for determining the elastic critical moment for WC (W-shape with Cap channel) or SC (S-shape with Cap Channel) girders. They provide only the approximate formulas which were derived from singly symmetric I-sections. Based on this study, the AISC approximate formulas would underestimate the elastic critical moment of WC/SC girders by 6-25% depending upon the unbraced length. This paper first summarizes the theoretical and AISC formulas for WC/SC girders. Theoretical torsional properties and relevant design parameters for WC/SC girders are computed and arranged in tabular form for design purposes. With these design values made available, engineers can perform more rational evaluation of WC/SC girders more conveniently. Lastly, a simplified but rational design approach is proposed for all available WC and SC girders listed in the AISC design manuals.

Experimental and Numerical Study on Complex Multi-planar Welded Tubular Joints in Umbrella-Type Space Trusses with Long Overhangs

Jinfeng Jiao,Xiao Ma,Honggang Lei,Y. Frank Chen 한국강구조학회 2018 International Journal of Steel Structures Vol.18 No.5

A test rig with multi-functional purposes was specifi cally designed and manufactured to study the behavior of multi-planar welded tubular joints subjected to multi-planar concurrent axial loading. An experimental investigation was conducted on full-scale welded tubular joints with each consisting of one chord and eight braces under monotonic loading conditions. Two pairs or four representative specimens (two specimens for each joint type) were tested, in which each pair was reinforced with two kinds of diff erent internal stiff eners at the intersections between the chords using welded rectangular hollow steel sections (RHSSs) and the braces using rolled circular hollow steel sections (CHSSs) and welded RHSSs. The eff ects of different internal stiff eners at the chord–brace intersection on the load capacity of joints under concurrent multi-planar axial compression/tension are discussed. The test results of joint strengths, failure modes, and load–stress curves are presented. Finite element analyses were performed to verify the experimental results. The study results show that the two diff erent joint types with the internal stiff eners at the chord–brace intersection under axial compression/tension signifi cantly increase the corresponding ultimate strength to far exceed the usual design strength. The load carrying capacity of welded tubular joints decreases with a higher degree of the manufacturing imperfection in individual braces at the tubular joints. Furthermore, the interaction eff ect of the concurrent axial loading applied at the welded tubular joint on member stress is apparent.

Debonding defect quantification method of building decoration layers via UAV-thermography and deep learning

Xiong Peng,Xiong Peng,Anhua Chen,Chao Zhao,Canlong Liu,Y. Frank Chen 국제구조공학회 2021 Smart Structures and Systems, An International Jou Vol.28 No.1

The falling offs of building decorative layers (BDLs) on exterior walls are quite common, especially in Asia, which presents great concerns to human safety and properties. Presently, there is no effective technique to detect the debonding of the exterior finish because debonding are hidden defect. In this study, the debonding defect identification method of building decoration layers via UAV-thermography and deep learning is proposed. Firstly, the temperature field characteristics of debonding defects are tested and analyzed, showing that it is feasible to identify the debonding of BDLs based on UAV. Then, a debonding defect recognition and quantification method combining CenterNet (Point Network) and fuzzy clustering is proposed. Further, the actual area of debonding defect is quantified through the optical imaging principle using the real-time measured distance. Finally, a case study of the old teaching-building inspection is carried out to demonstrate the effectiveness of the proposed method, showing that the proposed model performs well with an accuracy above 90%, which is valuable to the society.