Browsing by Author "Fang, YS"

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Closure to "Passive earth pressure with critical state concept" by Yung-Show Fang, Ying-Chieh Ho, and Tsang-Jiang Chen
(2003-10-01)
Fang, YS
;
Ho, YC
;
Chen, TJ
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土木工程學系
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Department of Civil Engineering
Dissociation of energy-selected c-C2H4S+ in a region 10.6-11.8 eV: Threshold photoelectron-photoion coincidence experiments and quantum-chemical calculations
(2005-08-01)
Fang, YS
;
Lin, IF
;
Lee, YC
;
Chiang, SY
;
應用化學系
Dissociation of energy-selected c-C2H4S+ was investigated in a region of 10.6-11.8 eV with a threshold photoelectron-photoion coincidence technique and a synchrotron as a source of vacuum ultraviolet radiation. Branching ratios and average releases of kinetic energy in channels of formation of c-C2H4S+, CH3CS+, and HCS+ were obtained from well-resolved time-of-flight peaks in coincidence mass spectra. Measured average releases of kinetic energy for channel CH3CS++H of least energy are substantial and much greater than calculated with quasiequilibrium theory; in contrast, small releases of kinetic energy near the appearance onset for channel HCS++CH3 agree satisfactorily with statistical calculations. Calculations of molecular electronic structures and energetics of c-C2H4S+ and C2H3S+ isomers and various fragments and transition states were also performed with Gaussian 3 method to establish dissociation mechanisms. A predicted dissociation energy of 11.05 eV for c-C2H4S -> HCS++CH3 agrees with a linearly extrapolated threshold at 10.99 +/- 0.04 eV and a predicted dissociation mechanism that c-C2H4S+ isomerizes to CH3CHS+ before dissociating to HCS++CH3 supports the experimental results. The large releases of kinetic energy for channel CH3CS++H might result from a dissociation mechanism according to which c-C2H4S+ isomerizes to a local minimum CH3CSH+ and then dissociates through a transition state to form CH3CS++H. (C) 2005 American Institute of Physics.
Dissociation of energy-selected c-C3H6S+ studied with threshold photoelectron-photolon coincidence experiments and calculations
(2006-05-10)
Chiang, SY
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Fang, YS
;
Lin, CN
;
應用化學系
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Department of Applied Chemistry
The dissociation of energy-selected c-C3H6S+ was investigated in a region 10.2-10.9 eV with a threshold photoelectron-photoion coincidence technique. Branching ratios and average releases of kinetic energy for channel c-C3H6S+ -> H2CS+ + C2H4 were derived from coincidence mass spectra. The measured small releases of kinetic energy near the appearance onset agree with statistical calculations; a linearly extrapolated threshold at 10.39 +/- 0.01 eV agrees with a predicted energy 10.35 eV with the GAUSSIAN-3 method. We discuss plausible mechanisms for c-C3H6S+ dissociating to CH3CS+ + CH3 based on G3B3 calculations to rationalize the absence of CH3CS+ signal in these experiments. (c) 2006 Elsevier B.V. All rights reserved.
Earth pressures with sloping backfill
(1997-03-01)
Fang, YS
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Chen, JM
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Chen, CY
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交大名義發表
;
土木工程學系
This paper presents experimental data of earth pressure acting against a vertical rigid wall, which moved away from or toward a mass of dry sand with an inclined surface. The instrumented retaining-wall facility at National Chiao Tung University (NCTU) Taiwan, was used to investigate the variation of earth pressure induced by the translational wall movement. Based on experimental data, it has been found that the earth-pressure distributions are essentially linear at each stage of wall movement. Both the wall movement required for the backfill to reach an active state and the wall movement needed for the backfill to reach a passive state increase with an increasing backfill inclination. The experimental active and passive earth-pressure coefficients for various backfill sloping angles are in good agreement with the values calculated by Coulomb's theory. It may not be appropriate to adopt the Rankine theory to determine either active or passive earth pressure against a rigid wall with sloping backfill.
Earth pressures with sloping backfill - Closure
(1998-11-01)
Fang, YS
;
Chen, JM
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Chen, CY
;
土木工程學系
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Department of Civil Engineering
Effect of initial shearing on shear modulus and damping of sand
(1995)
Fang, YS
;
Guo, JS
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交大名義發表
;
National Chiao Tung University
Experimental and quantum-chemical studies on dissociative photoionization of c-C2H4S
(2005-06-01)
Chiang, SY
;
Fang, YS
;
應用化學系
;
Department of Applied Chemistry
The dissociative photoionization of thiirane (c-C2H4S) in a region similar to 9-20 eV was investigated with photoionization mass spectroscopy and calculations of molecular energies with the Gaussian-3 method. An adiabatic ionization energy of 9.051 eV for c-C2H4S agrees with a prediction of 9.07 eV for formation of c-C2H4S+; predictions of energies of formation of ring-opened isomers CH3CHS+, CH2CHSH+ and CH2SCH2+ are 8.85, 8.91 and 9.37 eV, respectively. Major fragment ions C2H3S+, C2H2S+, HCS+, H2S+ and C2H3+ were observed with their respective appearance energies at 10.71, 13.07, 11.13, 11.96 and 12.58 eV. Based on comparison of determined appearance energies and predicted reaction energies, we established six dissociation channels c-C2H4S+ -> CH3CS+ + H, HCS+ + CH3, H2S+ + C2H2, C2H3+ + HS, CH2CS+ + H-2 and CHCSH+ + H-2. Ring-opening and H migration are involved in these processes. (c) 2005 Elsevier B.V. All rights reserved.
Experimental and quantum-chemical studies on photoionization and dissociative photoionization of CH2Br2
(2004-02-15)
Chiang, SY
;
Fang, YS
;
Sankaran, K
;
Lee, YP
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應用化學系
The dissociative photoionization of CH2Br2 in a region similar to10-24 eV was investigated with photoionization mass spectroscopy using a synchrotron radiation source. An adiabatic ionization energy of 10.25 eV determined for CH2Br2 agrees satisfactorily with predictions of 10.26 and 10.25 eV with G2 and G3 methods, respectively. Observed major fragment ions CH2Br+, CHBr+, and CBr+ show appearance energies at 11.22, 12.59, and 15.42 eV, respectively; minor fragment ions CHBr2+, Br+, and CH2+ appear at 12.64, 15.31, and 16.80 eV, respectively. Energies for formation of observed fragment ions and their neutral counterparts upon ionization of CH2Br2 are computed with G2 and G3 methods. Dissociative photoionization channels associated with six observed fragment ions are proposed based on comparison of determined appearance energies and predicted energies. An upper limit of DeltaH(f,298)(0)(CHBr+)less than or equal to300.7+/-1.5 kcal mol(-1) is derived experimentally; the adiabatic ionization energy of CHBr is thus derived to be less than or equal to9.17+/-0.23 eV. Literature values for DeltaH(f,298)(0)(CBr+)=362.5 kcal mol(-1) and ionization energy of 10.43 eV for CBr are revised to be less than 332 kcal mol(-1) and 9.11 eV, respectively. Also based on a new experimental ionization energy, DeltaH(f,298)(0)(CH2Br2+) is revised to be 236.4+/-1.5 kcal mol(-1). (C) 2004 American Institute of Physics.
Experiments and calculations on photoionization and dissociative photoionization of CH2CO
(2004-08-01)
Chiang, SY
;
Fang, YS
;
Bahou, M
;
Sankaran, K
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應用化學系
The dissociative photoionization of molecular-beam cooled CH2CO in a region of similar to10-20 eV was investigated with photoionization mass spectrometry using a synchrotron radiation as the light source. Photoionization efficiency curves of CH2CO+ and of observed fragment ions CH2+, CHCO+, HCO+ C2O+ CO+, and C2H2+ were measured to determine their appearance energies. Relative branching ratios as a function of photon energy were determined. Energies for formation of these observed fragment ions and their neutral counterparts upon ionization of CH2CO are computed with the Gaussian-3 method. Dissociative photoionization channels associated with six observed fragment ions are proposed based on comparison of determined appearance energies and predicted energies. The principal dissociative processes are direct breaking of C=C and C-H bonds to form CH2+ + CO and CHCO+ + H, respectively; at greater energies, dissociation involving H migration takes place.
Modification of Mononobe-Okabe theory
(1995-03-01)
Fang, YS
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Chen, TJ
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交大名義發表
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National Chiao Tung University
Passive earth pressure with critical state concept
(2002-08-01)
Fang, YS
;
Ho, YC
;
Chen, TJ
;
土木工程學系
;
Department of Civil Engineering
This paper presents experimental data of earth pressure acting against a vertical rigid wall, which moved toward a mass of dry sand. The backfill had been placed in lifts to achieve relative densities of 38, 63, and 80%. The instrumented retaining-wall facility at National Chiao Tung University in Taiwan was used to investigate the effects of soil density on the development of earth pressure. Based on the experimental data, it has been found that the Coulomb and Terzaghi solutions calculated with the peak internal friction angle significantly overestimated the ultimate passive thrust for the retaining wall filled with dense sand. As the wall movement S exceeded 12% of the wall height H, the passive earth thrust would reach a constant value, regardless of the initial density of backfill. Under such a large wall movement, soils along the rupture surface had reached the critical state, and the shearing strength on the surface could be properly represented with the residual internal-friction angle. The ultimate passive earth pressure was successfully estimated by adopting the critical state concept to either Terzaghi or Coulomb theory.
Properties of soilcrete stabilized with jet grouting
(2004)
Fang, YS
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Kuo, LY
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Wang, DR
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土木工程學系
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Department of Civil Engineering
In this paper. mechanical properties of jet-grouted soilcrete are investigated. Jet grouting (JSG) was conducted to improve ground properties for the construction of a cross-passage between a sewerage tunnel and a manhole of the Taipei Sewer Sub-main System. Soils treated were silty sand and sandy silt. Cylindrical specimens were drilled from the site and tested in the laboratory. Experimental results show that the elastic wave velocities, modulus of elasticity, and uniaxial compressive strength of soilerete increase with increasing dry density. Poisson's ratio of soilcrete varies from 0.05 to 0.29, which is very close to the ratio for concrete. Brazilian tensile strength of soilcrete varies from 1/7 to 1/28 of its uniaxial compressive strength. The cohesion of jet-grouted soilcrete varies from 0.40 to 4.22 MPa, and the internal friction angle varies from 20degrees to 44degrees. The design internal friction angle phi = 0degrees recommended by the JSG Association appears to be conservative.
Reduction of boundary friction in model tests
(2004-01-01)
Fang, YS
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Chen, TJ
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Holtz, RD
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Lee, WF
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土木工程學系
To model plane-strain conditions in the laboratory, the frictional resistance between the soil and side walls of the soil box should be reduced as much as possible. Methods commonly employed for this purpose include a latex sheet with silicon grease ("grease method") or multiple layers of thin plastic sheeting ("plastic sheet method"). Interface friction angles are often measured by direct shear-type tests. In this paper, a new sliding block testing device for measuring the friction at the interface between soil and different materials at low stress conditions is described. Interface friction angles for eight different methods for reducing boundary friction were investigated using the proposed testing method. Test results indicated that the friction angle obtained with the plastic sheet method is nearly independent of the normal stress. On the other hand, the interface friction angle of the grease method was quite high under low normal stress conditions. Thus, the plastic sheet method appears to be a more appropriate technique under low normal stress conditions to reduce the boundary friction for laboratory scale model tests. As compared with the grease method, advantages of the plastic sheet method include constant friction angles, less time for preparation and cleanup, and lower cost. To investigate their applicability, both lubrication systems were used in some large-scale laboratory-retaining wall experiments. Earth pressure measurements obtained near the sidewalls indicated that, under a low normal stress, the plastic sheet method was more effective in reducing sidewall friction.
Retaining walls damaged in the Chi-Chi earthquake
(2003-12-01)
Fang, YS
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Yang, YC
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Chen, TJ
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土木工程學系
;
Department of Civil Engineering
This paper investigates the failure of three gravity walls due to the 1999 Chi-Chi earthquake. Characteristics of the damaged walls were carefully recorded and backfill materials behind the damaged walls were collected and tested in the laboratory. Both the simplified analysis based on the Mononobe-Okabe method and the simplified dynamic analysis based on the Richards-Elms method were adopted. For the first case, the sliding of concrete wall blocks along the construction joint was observed. It was found that, during the earthquake, the frictional resistance at the untreated construction joint was not sufficient to resist the dynamic lateral thrust. For the second case, the retaining wall settled significantly and tilted about its toe. Seismic analysis of the wall indicated that, under the same horizontal acceleration, the factor of safety against bearing capacity failure was lower than that against overturning and sliding. A stability check against bearing capacity failure for the retaining wall should never be neglected. For the third case, the retaining wall built on top of the Che-Lung-Pu fault was severely damaged by the fault rupture. During the earthquake, the vertical displacement of the hanging wall uplifted the backfill, causing the wall to overturn. Horizontal displacement of the hanging wall caused the wall to slide and the soil in front of the toe to heave.