Moment Redistribution in Continuous Externally CFRP Prestressed Beams with Steel and FRP Rebars

This paper assesses the impact of adopting carbon- or glass-fiber-reinforced polymer (CFRP or GFRP) instead of steel rebars on the redistribution of moments in prestressed concrete beams (PCBs) with external CFRP tendons. A numerical program is introduced, and numerical simulations are performed on two-span continuous beams with steel, CFRP or GFRP rebars of various areas, i.e., Ar2 = 360–3560 mm2, and Ar1/Ar2 = 1.5, where Ar1 and Ar2 are areas of tensile rebars over the positive and negative moment zones, respectively. The results show the moment redistribution is contributed by concrete cracking only for the beams with fiber-reinforced polymer (FRP) rebars, and by concrete cracking and steel yielding for the beams with steel rebars. As a result, the use of FRP rebars leads to a substantially lower moment redistribution than in steel rebars. It is also demonstrated that Eurocode 2, CSA A23.3-04 and ACI 318-19 fail to reflect the rebar influence on moment redistribution in PCBs with external tendons. A simplified equation for the quantification of moment redistribution in externally PCBs with steel and FRP rebars is recommended, which yields accurate and conservative predictions.

Dragondrop: a novel passive mechanism for aerial righting in the dragonfly

Dragonflies perform dramatic aerial manoeuvres when chasing targets but glide for periods during cruising flights. This makes dragonflies a great system to explore the role of passive stabilizing mechanisms that do not compromise manoeuvrability. We challenged dragonflies by dropping them from selected inverted attitudes and collected 6-degrees-of-freedom aerial recovery kinematics via custom motion capture techniques. From these kinematic data, we performed rigid-body inverse dynamics to reconstruct the forces and torques involved in righting behaviour. We found that inverted dragonflies typically recover themselves with the shortest rotation from the initial body inclination. Additionally, they exhibited a strong tendency to pitch-up with their head leading out of the manoeuvre, despite the lower moment of inertia in the roll axis. Surprisingly, anaesthetized dragonflies could also complete aerial righting reliably. Such passive righting disappeared in recently dead dragonflies but could be partially recovered by waxing their wings to the anaesthetised posture. Our kinematics data, inverse dynamics model and wind-tunnel experiments suggest that the dragonfly's long abdomen and wing posture generate a rotational tendency and passive attitude recovery mechanism during falling. This work demonstrates an aerodynamically stable body configuration in a flying insect and raises new questions in sensorimotor control for small flying systems.

Turbocharger Axial Turbines for High Transient Response, Part 2: Genetic Algorithm Development for Axial Turbine Optimisation

In a previous paper [1], a preliminary design methodology was proposed for the design of an axial turbine, replacing a conventional radial turbine used in automotive turbochargers, to achieve improved transient response, due to the intrinsically lower moment of inertia. In this second part of the work, the focus is on the optimisation of this preliminary design to improve on the axial turbine efficiency using a genetic algorithm in order to make the axial turbine a more viable proposition for turbocharger turbine application. The implementation of multidisciplinary design optimisation is essential to the aerodynamic shape optimisation of turbocharger turbines, as changes in blade geometry lead to variations in both structural and aerodynamics performance. Due to the necessity to have multiple design objectives and a significant number of variables, genetic algorithms seem to offer significant advantages. However, large generation sizes and simulation run times could result in extensively long periods of time for the optimisation to be completed. This paper proposes a dimensioning of a multi-objective genetic algorithm, to improve on a preliminary blade design in a reasonable amount of time. The results achieved a significant improvement on safety factor of both blades whilst increasing the overall efficiency by 2.55%. This was achieved by testing a total of 399 configurations in just over 4 h using a cluster network, which equated to 2.73 days using a single computer.

Highway Bridge Load-Bearing Capacity Assessment Under Chinese and British Methodologies

The purpose of assessment of structures is to check their adequacy for specific loading levels and to identify those bridges that have an unacceptable risk of failure, either in part or complete collapse, under extreme circumstances of loading and material condition [1]. In this study, a comparison was made between new Chinese bridge load-bearing capacity assessment method and The British Highway Agency method. Load-bearing capacity assessment results were generated for bridges super structure and analyzed for moment and shear load effect. Also the study included a comparison of the main component of load-bearing capacity calculation, factored live load, factored dead load, and factored capacity. The comparison shows that the British Method produced lower moment and shear bridges carrying capacity factor than Chinese Method.

An invariant of finitary codes with finite expected square root coding length

Let p and q be probability vectors with the same entropy h. Denote by B(p) the Bernoulli shift indexed by ℤ with marginal distribution p. Suppose that φ is a measure-preserving homomorphism from B(p) to B(q). We prove that if the coding length of φ has a finite 1/2 moment, then σ2p=σ2q, where σ2p=∑ ipi(−log pi−h)2 is the informational variance of p. In this result, the 1/2 moment cannot be replaced by a lower moment. On the other hand, for any θ<1, we exhibit probability vectors p and q that are not permutations of each other, such that there exists a finitary isomorphism Φ from B(p) to B(q) where the coding lengths of Φ and of its inverse have a finite θ moment. We also present an extension to ergodic Markov chains.

The crystallography and paramagnetic anisotropy of potassium ferricyanide

Single crystal X-ray analyses of the structure of potassium ferricyanide at ca. 300 and 95° K are reported. Least-squares refinements within the monoclinic space group, P 2 1 / c , have converged with the residuals R 300°K = 0·092 and R 95°K = 0·077. The unit cell dimensions at 300°K are: a = 7·06, b = 10·38, c = 8·40 Å, β = 107·0°, and at 95°K are: a = 7·03, b = 10·31, c = 8·35 Å, β = 107·2°. The coordination octahedra are only slightly distorted, both analyses independently revealing a small tetragonal elongation of the molecule along Fe-CN bonds lying nearly perpendicular to the crystallographic c axis. The principal crystal paramagnetic susceptibilities are characterized by an essentially unique, and lower, moment parallel to the c axis. These two observations are to be reconciled only in relation to the role of second-nearest neighbour effects of either antiferromagnetic or crystal-field character. Exchange is ruled out by earlier e.s.r. work and the present susceptibility dilution experiments. The crystal anisotropy appears to be dominated by the coulombic field set up by adjacent potassium ions in the lattice. While all potassium ions in the structure will play some role in this second-order perturbation, those forming ‘chains’ with the octahedra parallel to the c axis are likely to be the more important. A simple crystal-field approach, using symmetry-adapted, zero-order wavefunctions on the iron atoms, has shown how the correct direction and relative magnitudes of the crystal magnetic anisotropies may be predicted by this model. The splitting of the ground 2 T 2g term of the complexion is estimated as 150 to 300 cm -1 .

Some 5- and 6-coordinate base adducts of Bis(acetylacetonato)manganese(II)

From diaquobis(acetylacetonato)manganese(II) we have obtained mono- and bis(pyridine)acetylacetonatomanganese(II), corresponding 4-methylpyridine compounds, bis-2-methylpyridine-, aquo-2-methylpyridine-, and o-phenanthroline- derivatives and some compounds in which all or part of the water is replaced by ethanol. All these compounds have magnetic moments which are normal for spin-free d5 complexes, but anhydrous bis(acetylacetonato)manganese(II) has a slightly lower moment. Molecular weight determinations show that the anhydrous compound is trimeric; the adducts with one molecule of base, though monomeric and 5-coordinate in freshly prepared benzene solutions, slowly decompose in solution, probably to condensed 6-coordinate species; the bispyridine, bis-4-methylpyridine, and o-phenanthroline adducts also dissociate in solution, an indication that manganese(II) forms unstable complexes with nitrogen as donor atom. The dark colour of these solutions appears to be due to manganese(IV) oxide.