Browsing by Author "Yang, Y. B."

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A Novel Approach for Buckling Analysis of Pretwisted Spatially Curved Beams by State Equations
(2016-06)
Kuo, S. R.
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Yang, Judy P.
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Yang, Y. B.
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土木工程學系
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Department of Civil Engineering
Based on force equilibrium and rigid body considerations, a novel approach is proposed for deriving the state equations and then the buckling equations of pretwisted spatially curved beams. Based on statical consideration of an infinitesimal element from the last calculated configuration C-1 to the current configuration C-2, a set of condition equations for the state matrix is derived. Next, by enforcing the rigid body rule for the beam, another set of condition equations for the state matrix is derived. From these two sets of equations, the state matrix of the beam is derived that leads directly to the buckling differential equations. The merit of the proposed approach is that it only requires simple differential and matrix operations. No hidden errors are possible because no higher-order terms need to be treated. In addition, a direct link is established between the straight and curved beam theories. Finally, examples are provided to demonstrate the application of the theory to the buckling analysis of various curved beams, including the helical ones.
A qualified plate theory for rigid rotation in postcritical nonlinear analysis
(2018-12-10)
Kuo, S. R.
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Yang, Judy P.
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Yang, Y. B.
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土木工程學系
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Department of Civil Engineering
A new, simple method is presented for deriving the instability potential of thin plates, based on the equilibrium conditions and constitutive law for incremental forces considering the geometric nonlinear effect. First, the equations of equilibrium are established for the plate at the last calculated C-1 and current deformed C-2 states, from which the equilibrium equations for the incremental forces at C-2 are derived. Then, the incremental forces are derived as the summation of two parts: (1) the part from the increase of the Cauchy stresses at C-1 to the 2nd Piola-Kirchhoff stresses at C-2, which are related to the strain increments and derivable from the linear constitutive; and (2) the part by the difference between the 2nd Piola-Kirchhoff and 1st Piola-Kirchhoff stresses, which are related to the cross-sectional forces at C-1 and rigid displacements. Based on the previous concept, the rigid body rule and coordinate indifference of tensor expressions, the constitutive law for incremental forces including the geometric nonlinear effect is derived. Further, by the variational principle, the following instability potentials are derived: delta U-GB caused by the balance conditions for initial forces, delta U-GC caused by the constitutive law for incremental forces, and delta U-GR caused by the rotation of boundary moments. Consequently, the total instability potential is presented for the plate in the virtual work form. The present approach is self-explanatory, which requires only simple integration operations. Moreover, the two essential conditions are satisfied: equilibrium conditions for incremental forces and rigid body rule. Numerical examples are presented to demonstrate the rationality of the present plate theory compared with the conventional one.
Resonance and Cancellation in Torsional Vibration of Monosymmetric I-Sections Under Moving Loads
(2018-09-01)
Yang, Y. B.
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Li, Mei
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Zhang, Bin
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Wu, Yuntian
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Yang, Judy P.
This paper is concerned with the lateral and torsional coupled vibration of monosymmetric I-beams under moving loads. To this end, a train is modeled as two subsystems of eccentric wheel loads of constant intervals to account for the front and rear wheels. By assuming the lateral and torsional displacements to be restrained at the two ends of the beam, both the lateral and torsional displacements are approximated by a series of sine functions. The method of variation of constants is adopted to derive the closed-form solution. For the most severe condition when the last wheel load is acting on the beam, both the conditions of resonance and cancellation are identified. Once the condition of cancellation is enforced, the resonance response can always be suppressed, which represents the optimal design for the beam. Since the condition for suppressing the torsional resonance is exactly the same as that for the vertical resonance, this offers a great advantage in the design of monosymmetric I-beams, as no distinction needs to be made between the suppression of vertical or torsional resonance.
Seismic Analysis of Twin Tunnels by a Finite/Infinite Element Approach
(2017-09-01)
Lin, Szu-Yun
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Hung, Hsiao-Hui
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Yang, Judy P.
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Yang, Y. B.
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土木工程學系
The two-dimensional (2D) dynamic response of horizontally aligned, cylindrical twin tunnels subjected to vertically incident seismic waves was simulated by a finite/infinite element approach. A rational approach was proposed for imposing the earthquake forces using free-field recorded data. First, the earthquake motion recorded on the free field was transferred to that on the boundary of the near field using the one-dimensional (1D) wave theory. Second, the motion data were computed as the equivalent seismic forces and applied on the near-field boundary in the frequency domain. In this study, the data from the 1999 Chi-Chi earthquake recorded at the TAP003 station were adopted. The accuracy of the procedure for imposing the free-field earthquakes was first verified. Then, a parametric study was performed to investigate the effects of spacing between the twin tunnels, depths of tunnels, and stiffness of tunnel lining under seismic excitation. The results of the analysis indicate that although the depth and spacing of the twin tunnels have less effect on ground response, they are important parameters for the seismic responses of the tunnels. (C) 2017 American Society of Civil Engineers.
Seismic analysis of underground tunnels by the 2.5D finite/infinite element approach
(2016-06)
Lin, K. C.
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Hung, H. H.
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Yang, Judy P.
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Yang, Y. B.
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土木工程學系
A procedure for the seismic analysis of underground tunnels using recorded free-field earthquakes based on the 2.5D finite/infinite element approach is presented. The near and far fields of the half space are modeled by finite and infinite elements, respectively. Using the 1D wave theory, the nodal force and displacement on the near-field boundary are computed for each spectral frequency of the earthquake. Then, equivalent seismic forces are computed for the near-field boundary for the earthquake spectrum. By assuming the soil-tunnel system to be uniform along the tunnel axis, the 2.5D approach can account for the wave transmission along the tunnel axis, which reduces to the 2D case for infinite transmission velocity. The horizontal and vertical components of the 1999 Chi-Chi Earthquake (TCU068) are adopted as the free-field motions in the numerical analysis. The maximal stresses and distribution patterns of the tunnel section under the P- and SV-waves are thoroughly studied by the 2.5D and 2D approaches, which should prove useful to the design of underground tunnels. (C) 2016 Elsevier Ltd. All rights reserved.
State-of-the-Art Review on Modal Identification and Damage Detection of Bridges by Moving Test Vehicles
(2018-02-01)
Yang, Y. B.
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Yang, Judy P.
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土木工程學系
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Department of Civil Engineering
In 2004, Yang and co-workers proposed the extraction of bridge frequencies from the dynamic response of a moving test vehicle [Y. B. Yang, C. W. Lin and J. D. Yau, Extracting bridge frequencies from the dynamic response of a passing vehicle, J. Sound Vib. 272 (2004) 471-493] and verified the technique by a field test [C. W. Lin and Y. B. Yang, Use of a passing vehicle to scan the bridge frequencies - An experimental verification, Eng. Struct. 27(13) (2005) 1865-1878]. This technique was extended to construction of mode shapes [Y. B. Yang, Y. C. Li and K. C. Chang, Constructing the mode shapes of a bridge from a passing vehicles: A theoretical study, Smart Struct. Syst. 13(5) (2014) 797-819] and damage identification of bridges. It was referred to as the indirect method for bridge measurement because no vibration sensors are needed for installation on the bridge, but it only requires one or few vibration sensors on the test vehicle. When compared with the conventional direct method that relies fully on the response of the bridge fitted with vibration sensors, the advantage of the indirect method is clear: mobility, economy, and efficiency. Over the past years, many research studies were conducted along the lines of the indirect method for bridge measurement. Significant advances have been made on various aspects of application. This paper represents a state-of-the-art review of the related research works conducted worldwide. Comments and recommendations will be made at proper places, while concluding remarks including future research directions will be presented at the end of the paper.
Wave Number-Based Technique for Detecting Slope Discontinuity in Simple Beams Using Moving Test Vehicle
(2017-08-01)
Yau, J. D.
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Yang, Judy P.
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Yang, Y. B.
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土木工程學系
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Department of Civil Engineering
The wavelength characteristic is a useful clue for locating and assessing the severity of slope discontinuity in beams. In this study, the slope discontinuity of a beam is represented by an internal hinge restrained by elastic springs, and the wavelength of the beam is calculated indirectly from the vertical response of a test vehicle during its travel over the beam. The key parameters of the problem at hand are first unveiled using an approximate, closed-form solution for the response of the vehicle moving at low speeds over the bridge. Then a two-beam element model with slope discontinuity is formulated for the vehicle-bridge interaction (VBI) system for use in numerical simulation. In the examples, the wavenumber-based response of the test vehicle is used to identify the location and severity of the discontinuity in the beam. It is demonstrated that the wavelength-based technique presented herein by using the moving test vehicle as a moving sensor system offers a promising, alternative approach for damage detection in girder type bridges.