Home About us Contact
|
Home About us Contact | ||
|
|
||
Fundamental Mode (fundamental + mode)
Selected AbstractsApplicability of pushover methods for the seismic analysis of single-column bent viaductsEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 8 2008Tatjana Isakovi Abstract An overview of the applicability of a typical single-mode pushover method (the N2 method) and two typical multi-mode pushover methods (the modal pushover analysis (MPA) and incremental response spectrum analysis (IRSA) methods) for the analysis of single column bent viaducts in the transverse direction is presented. Previous research, which was limited to relatively short viaducts supported by few columns, has been extended to longer viaducts with more bents. The single-mode N2 method is accurate enough for bridges where the effective modal mass of the fundamental mode is at least 80% of the total mass. The applicability of this method depends on (a) the ratio of the stiffness of the superstructure to that of the bents and (b) the strength of the bents. In short bridges with few columns, the accuracy of the N2 method increases as the seismic intensity increases, whereas in long viaducts (e.g. viaducts with lengths greater than 500,m) the method is in general less effective. In the case of the analyzed moderately irregular long viaducts, which are common in construction design practice, the MPA method performed well. For the analysis of bridges where the modes change significantly, depending on the seismic intensity, the IRSA method is in principle more appropriate, unless a viaduct is torsionally sensitive. In such cases, all simplified methods should be used with care. Copyright © 2008 John Wiley & Sons, Ltd. [source] The role of soil in the collapse of 18 piers of Hanshin Expressway in the Kobe earthquakeEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 5 2006George Mylonakis Abstract An investigation is presented of the collapse of a 630 m segment (Fukae section) of the elevated Hanshin Expressway during the 1995 Kobe earthquake. The earthquake has, from a geotechnical viewpoint, been associated with extensive liquefactions, lateral soil spreading, and damage to waterfront structures. Evidence is presented that soil,structure interaction (SSI) in non-liquefied ground played a detrimental role in the seismic performance of this major structure. The bridge consisted of single circular concrete piers monolithically connected to a concrete deck, founded on groups of 17 piles in layers of loose to dense sands and moderate to stiff clays. There were 18 spans in total, all of which suffered a spectacular pier failure and transverse overturning. Several factors associated with poor structural design have already been identified. The scope of this work is to extend the previous studies by investigating the role of soil in the collapse. The following issues are examined: (1) seismological and geotechnical information pertaining to the site; (2) free-field soil response; (3) response of foundation-superstructure system; (4) evaluation of results against earlier studies that did not consider SSI. Results indicate that the role of soil in the collapse was multiple: First, it modified the bedrock motion so that the frequency content of the resulting surface motion became disadvantageous for the particular structure. Second, the compliance of soil and foundation altered the vibrational characteristics of the bridge and moved it to a region of stronger response. Third, the compliance of the foundation increased the participation of the fundamental mode of the structure, inducing stronger response. It is shown that the increase in inelastic seismic demand in the piers may have exceeded 100% in comparison with piers fixed at the base. These conclusions contradict a widespread view of an always-beneficial role of seismic SSI. Copyright © 2005 John Wiley & Sons, Ltd. [source] A preliminary prediction of seismic damage-based degradation in RC structuresEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 7 2001Vinay K. Gupta Abstract Estimation of structural damage from a known increase in the fundamental period of a structure after an earthquake or prediction of degradation of stiffness and strength for a known damage requires reliable correlations between these response functionals. This study proposes a modified Clough,Johnston single-degree-of-freedom oscillator to establish these correlations in the case of a simple elasto-plastic oscillator. It is assumed that the proposed oscillator closely models the response of a given multi-degree-of-freedom system in its fundamental mode throughout the duration of the excitation. The proposed model considers the yield displacement level and ductility supply ratio-related parameter as two input parameters which must be estimated over a narrow range of ductility supply ratio from a frequency degradation curve. This curve is to be identified from a set of recorded excitation and response time-histories. Useful correlations of strength and stiffness degradation with damage have been obtained wherein a simple damage index based on maximum and yield displacements and ductility supply ratio has been considered. As an application, the proposed model has been used to demonstrate that ignoring the effects of aftershocks in the case of impulsive ground motions may lead to unsafe designs. Copyright © 2001 John Wiley & Sons, Ltd. [source] Dual-band N-shaped patch antenna loaded by lumped elementsMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 11 2009Asmaa H. Moustafa Abstract This article presents a dual-band circular N-shaped microstrip patch antenna loaded by a shorting pin and lumped R-C circuit, hence a resonant R-L-C circuit is introduced. Loading by shorting pin excites the zero fundamental mode of the circular patch antenna (TM010), and it shifts the first fundamental mode (TM110) to higher one. N-shaped microstrip patch antenna is used as a modified circular microstrip patch antenna with reduced size. The proposed antenna is designed and fabricated on two-layered substrate. A comprehensive parametric study has been carried out on values of R and C to optimize the antenna performance. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2534,2537, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24673 [source] GSM850/900/1800/1900/UMTS coupled-fed planar ,/8-PIFA for internal mobile phone antennaMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 4 2009Chih-Hua Chang Abstract A coupled-fed planar PIFA (planar inverted-F antenna) operated in its one-eighth wavelength (,/8) mode, different from the traditional one-quarter wavelength (,/4) mode, as the fundamental mode for mobile phone application is presented. The proposed PIFA comprises two radiating strips, both of slightly different lengths and close to about ,/8 at 900 MHz. By incorporating the use of the coupling feed, a wide operating band formed by the two ,/8 modes is excited at about 900 MHz for the antenna to cover GSM850/900 operation. Two ,/4 modes are also generated at close frequencies to from a wide operating band centered at about 1950 MHz to cover GSM1800/1900/UMTS operation. The proposed antenna hence can cover GSM850/900/1800/1900/UMTS penta-band operation for application in the mobile phone. In addition, the antenna has a simple structure and can be printed on a thin FR4 substrate of size 1.6 × 7 × 40 mm3 as a surface-mountable chip antenna. Details of the proposed antenna are presented and discussed. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1091,1096, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24214 [source] MOST, photometry of the RRd Lyrae variable AQ Leo: two radial modes, 32 combination frequencies and beyondMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007Michael Gruberbauer ABSTRACT Highly precise and nearly uninterrupted optical photometry of the RR Lyrae star AQ Leo was obtained with the MOST (Microvariability and Oscillations of Stars) satellite over 34.4 d in 2005 February,March. AQ Leo was the first known double-mode RR Lyrae pulsator (RRd star). Three decades after its discovery, MOST observations have revealed that AQ Leo oscillates with at least 42 frequencies, of which 32 are linear combinations (up to the sixth order) of the radial fundamental mode and its first overtone. Evidence for period changes of these modes is found in the data. The other intrinsic frequencies may represent an additional non-radial pulsation mode and its harmonics (plus linear combinations) which warrant theoretical modelling. The unprecedented number of frequencies detected with amplitudes down to mmag precision also presents an opportunity to test non-linear theories of mode growth and saturation in RRd stars. [source] Mode-selective stereomutation tunneling as compared to parity violation in hydrogen diselenide isotopomers 1,2,3H280Se2ISRAEL JOURNAL OF CHEMISTRY, Issue 3-4 2003Michael Gottselig We present quantitative calculations of the mode-selective stereomutation tunneling in the chiral hydrogen diselenide isotopomers X2Se2 with X = H, D, and T. The torsional tunneling stereomutation dynamics were investigated with a quasi-adiabatic channel quasi-harmonic reaction path Hamiltonian approach, which treats the torsional motion anharmonically in detail and all remaining coordinates as harmonic (but anharmonically coupled to the reaction coordinate). We also investigated the influence of the excitation of fundamental modes on the stereomutation dynamics and predict which modes should be promoting or inhibiting. Our stereomutation dynamics results and the influence of parity violation on these are discussed in relation to our recent investigations for the analogous molecules H2O2, HSOH, H2S2, and Cl2S2. The electronic potential energy barrier heights for the torsional motion of hydrogen diselenide are similar to those of HSOH, whereas the torsional tunneling splittings are similar to the corresponding values of HSSH. The ground-state torsional tunneling splittings calculated here for D2Se2 are of the same order as the parity-violating energy difference reported by Laerdahl and Schwerdtfeger (Phys. Rev. A 1999, 60, 4439), whereas for T2Se2 the corresponding tunneling splitting is about three orders of magnitude smaller. [source] Analysis of structure and vibrational spectra of 2,5-dihydroxybenzoicacid based on density functional theory calculationsJOURNAL OF RAMAN SPECTROSCOPY, Issue 4 2010V. Krishnakumar Abstract The spectra of 2,5-dihydroxybenzoic acid (DHBA) have been recorded using Fourier transform-infrared spectroscopy (FT-IR) and FT-Raman measurements. The total energy calculations of DHBA were evaluated for various possible conformers. The spectra were interpreted with the help of normal coordinate analysis based on density functional theory (DFT) using standard B3LYP/6,31G* method for the most optimized geometry. The effect of intramolecular hydrogen bonding was discussed. Normal coordinate calculations were performed with the DFT force field corrected by a recommended set of scaling factors, yielding fairly good agreement between observed and calculated frequencies. On the basis of the comparison between calculated and experimental results, assignments of fundamental modes were examined. Copyright © 2009 John Wiley & Sons, Ltd. [source] Study of the vibrational spectra of (CH3)3GeCl from experimental and DFT calculationsJOURNAL OF RAMAN SPECTROSCOPY, Issue 11 2009María Lorena Roldán Abstract New infrared (for gas and liquid phase) and Raman (for liquid) spectra were measured for the chlorotrimethylgermane to obtain a complete assignment of its fundamental modes. The measurement of the low-temperature infrared spectrum together with the application of Fourier self-deconvolution to the Raman spectra resolves the CH vibrational modes into their components. The Rauhut and Pulay scaled quantum mechanical (SQM) force field methodology and the wavenumber-linear scaling (WLS) method were used to predict the vibrational spectra as a guide to the assignment of the fundamental bands. A quantum mechanical analysis was carried out to obtain the harmonic force field. Copyright © 2009 John Wiley & Sons, Ltd. [source] | |||||||||||||