Testing of full-scale concrete bridge deck slabs reinforced with fiber-reinforced polymer (FRP) bars

This paper presents an experimental study investigating the behavior of FRP-reinforced concrete bridge deck slabs under concentrated loads. A total of eight full-scale deck slabs measuring 3000-mm long by 2500-mm wide were constructed. The test parameters were: (i) slab thickness (200, 175 and 150 mm); (ii) concrete compressive strength (35–65 MPa); (iii) bottom transverse reinforcement ratio (1.2–0.35%); and (iv) type of reinforcement (GFRP, CFRP, and steel). The slabs were supported on two parallel steel girders and were tested up to failure under monotonic single concentrated load acting on the center of each slab over a contact area of 600 × 250 mm to simulate the footprint of sustained truck wheel load (87.5 kN CL-625 truck). All deck slabs failed in punching shear. The punching capacity of the tested deck slabs ranged from 1.74 to 3.52 times the factored load (P_f) specified by the Canadian Highway Bridge Design Code (CHBDC) CAN/CSA S6-06. Besides, the ACI 440.1R-06 punching strength equation greatly underestimated the capacity of the tested slabs with an average experimental-to-predicted punching capacity ratio (V_exp/V_pred) of 3.17.     

First documentation of spawning and nest guarding in the laboratory by the invasive fish,the round goby (Neogobius melanostomus)

Although the round goby, Neogobius melanostomus, is widespread in the Great Lakes and has an extended breeding season with a high reproductive rate; its spawning behaviour remains elusive. We present the first reported accounts of spawning by the round goby in the laboratory. By simulating winter conditions and restoring spring conditions, we induced round gobies to spawn in October 2007, March 2008, May 2008, and January 2009. In one case, fanning by the nest-holding male began 10 days before egg deposition and, during this period, the male rubbed secretions along the ceiling of the nest. Males were choosy about which gravid females entered the nest and prevented entry by some females. Spawning involved repeated inversions by females and males releasing gametes on the ceiling of the nest. Males guarded the nest by blocking the entrance, producing agonistic vocalizations and chasing intruders. Inside the nest, eggs were regularly inspected by the males and constantly ventilated using pectoral and caudal fins. Up to three gravid females spawned sequentially in a nest. Peak ventilation occurred after egg deposition and declined with time until the parental male ate the eggs. The decline of parental care and egg cannibalism was likely an artifact of laboratory conditions and small brood size. Our findings offer new information on the reproductive habits of the invasive round goby. Because the reproductive sequence in the laboratory seems easy to disrupt, the procedures may lead to a management tool to control the spread of the species into new areas.     

Neural networks for predicting compressive strength of structural light weight concrete

Neural networks procedures provide a reliant analysis in several science and technology fields. Neural network is often applied to develop statistical models for intrinsically non-linear systems because neural networks behave the advantages of simulating complex behavior of many problems. In this investigation, the neural networks (NNs) are used to predict the compressive strength of light weight concrete (LWC) mixtures after 3, 7, 14, and 28 days of curing. Two models namely, feed-forward back propagation (BP) and cascade correlation (CC), were used. The compressive strength was modeled as a function of eight variables: sand, water/cement ratio, light weight fine aggregate, light weight coarse aggregate, silica fume used in solution, silica fume used in addition to cement, superplasticizer, and curing period. It is concluded that the CC neural network model predicated slightly accurate results and learned very quickly as compared to the BP procedure. The finding of this study indicated that the neural networks models are sufficient tools for estimating the compressive strength of LWC. This undoubtedly will reduce the cost and save time in this class of problems.     

Resonant tunneling through double barriers, perpendicular quantum transport phenomena in superlattices, and their device applications

New results on the physics of tunneling in quantum well heterostructures and its device applications are discussed. Following a general review of the field in the Introduction, in the second section resonant tunneling through double barriers is investigated. Recent conflicting interpretations of this effect in terms of a Fabry-Perot mechanism or sequential tunneling are reconciled via an analysis of scattering. It is shown that the ratio of the intrinsic resonance width to the total scattering width (collision broadening) determines which of the two mechanisms controls resonant tunneling. The role of symmetry is quantitatively analyzed and two recently proposed resonant tunneling transistor structures are discussed. The third section deals with perpendicular transport in superlattices. A simple expression for the low field mobility in the miniband conduction regime is derived; localization effects, hopping conduction, and effective mass filtering are discussed. In the following section, experimental results on tunneling superlattice photoconductors based on effective mass filtering are presented. In the fifth section, negative differential resistance resulting from localization in a high electric field is discussed. In the last section, the observation of sequential resonant tunneling in superlattices is reported. We point out a remarkable analogy between this phenomenon and paramagnetic spin resonance. New tunable infrared semiconductor lasers and wavelength selective detectors based on this effect are discussed.     

Influence of Permeability on Liquefaction-Induced Shear Deformation

Permeability of a liquefiable soil profile may affect the rate of pore-pressure buildup and subsequent dissipation during and after earthquake excitation. Consequently, effective soil confinement and available resistance to shear deformations may be significantly dependent on permeability in many practical situations. If present, spatial variation in permeability may even have a more profound impact on available overall shear resistance. Indeed, case histories and experimental evidence (shake table and centrifuge tests) suggest that spatial permeability variation in stratified liquefiable deposits can highly influence the nature and extent of associated lateral deformation. In such situations, the onset of liquefaction-induced densification may result in water or water-rich thin interlayers trapped below overlying low-permeability strata. The presence of these low-shear-strength interlayers may trigger excessive (or even unbounded) localized shear deformations (flow failure mechanism). In this paper, numerical modeling is employed in order to investigate the influence of permeability and the spatial variation thereof on liquefaction-induced shear deformations. The involved response characteristics are numerically simulated using a fully coupled two-phase (solid–fluid) Finite Element program.     

Mass transfer in electrochemical reactors employing gas evolving mercury pool cathodes

The effect of H₂ evolution on the mass transfer coefficient of the cathodic reduction of potassium ferricyanide at a mercury cathode was studied with the aim of (i) comparing the mass transfer behaviour of a Hg cathode with that of solid electrodes under gas evolving conditions, and (ii) testing the effect of surface active agents on the mass transfer behaviour of a H₂-evolving Hg cathode. For a given H₂ discharge rate the mass transfer coefficient at a mercury cathode was much higher than the value at a solid cathode. The mass transfer coefficient at the H₂-evolving Hg cathode was found to decrease in the presence of Triton X-100 surfactant by an amount ranging from 62.6% to 86.2% depending on H₂ discharge rate and surfactant concentration. A simple mathematical model was formulated to explain the results. The presence of surfactant was found to increase the cell voltage.     

Field-oriented vector control of synchronous motors with additional field winding

This paper presents a new method to control a synchronous motor in such a way to resemble the characteristics of a DC motor. The method suggests including a second field winding to the rotor of a voltage-source-inverter-fed synchronous motor. The angular frequency of the inverter is made equal to the angular rotor speed, (of a self-controlled synchronous motor drive). The added field winding is in space quadrature to the main field winding and is properly excited in such a way as to diminish the direct axis component of the stator current at every load conditions. The motor is controlled to operate with zero power angle from the inverter side and zero direct axis current from the rotor excitation side. Therefore, it operates with minimum stator current and with unity power factor. The addition of the second field winding will not complicate the design because it is just a control winding. This winding may be made with smaller wire cross-section and a larger number of turns. The control on this winding is not complicated and it can be easily created. The synchronous motor along with the added field and the required control loops are simulated and tested extensively. The test results show excellent motor performance in motoring and regenerating modes of operation.     

The role of the mercury-Si Schottky-barrier height in /spl Psi/-MOSFETs

Pseudo-MOSFETs (/spl Psi/-MOSFET) are routinely used for silicon-on-insulator (SOI) material characterization, allowing threshold voltage, electron and hole mobility, doping density, oxide charge, interface trap density, etc. to be determined. The HgFET, one version of the /spl Psi/-MOSFET, uses mercury source and drain contacts. It is a very effective SOI test structure, but its current-voltage behavior is critically dependent on the Hg-Si interface. We have investigated this interface through current-voltage measurements of HgFETs and Schottky diodes and through device modeling. We show that modest barrier height changes of 0.2 eV lead to current changes of up to three orders of magnitude. Etching the Si surface in a mild HF :H/sub 2/O solution can easily change barrier heights and we attribute this behavior to Si surface passivation of dangling bonds. As this surface passivation diminishes with time, the Si surface becomes a more active generation site and the barrier height of the Hg-Si interface changes, taking on the order of 50-100 h at room temperature in air.     

Architectural Engineering Curriculum at Illinois Institute of Technology

Illinois Institute of Technology started a bachelor of science degree program in architectural engineering in the fall of 1995. The program's curriculum requires the students to take 136 semester credit hours during a period of eight semesters, with the option for specialization in one of the three main areas of architectural engineering. To share the experience worldwide with schools that intend to offer similar bachelor degrees, this paper presents the architectural engineering curriculum at Illinois Institute of Technology. It discusses the objectives of the curriculum, the constraints upon its structure, as well as the challenges that face the establishment of an architectural engineering program.