Height of Water Pool in the Roll Nip of Secondary Cooling Zone in Continuous Slab Caster: Application of Open Channel Hydraulics

In continuous casting of steel, the strand is cooled in the upper part of the secondary cooling zone with water sprayed by nozzles towards the strand surface. The water accumulates in the nip of the lower roll of a roll pair, forming a water pool which then drains off towards the ends of the roll. In the present work, open channel hydraulics was applied for computation of the water pool height in the nip between roll and strand in continuous slab casting. The differential equation describing the change of pool height for the spatially varied flow with increasing discharge was solved with the Runge–Kutta technique using as boundary condition the pool height at the end of the nip. The effects of the Manning friction factor n and the energy coefficient α were determined in sets of computation. It was shown that the hydraulic theory could predict water profiles in the nip of continuous casting rolls to a good approximation.

An analytical method for full-range mechanical behavior of continuous slab-deck in multi-span simply supported concrete bridges

Connecting the ends of girders with a continuous slab-deck to make a multiple-span simply supported girder bridge provides many benefits, but there is no suitable nonlinear analysis model which considers continuous slab-deck cracking under tension and bending. In this article, the rotational spring model is further refined to replace the restraining effects at both ends of the girder by the simplified mechanical model associated with axial stiffness, bending stiffness, and shear stiffness. Then, it is introduced into the analysis of continuous slab-deck. The more accurate rotations and displacements of both ends of continuous slab-deck are obtained to investigate the more precise moment and tension of the continuous slab-deck. Furthermore, this article presents an improved nonlinear analysis model of continuous slab-deck based on a detailed boundary rotational spring model. The displacements of important positions and the strain of key components in continuous slab-deck after cracking are investigated by numerical analysis and full-scale model test to verify the accuracy of the proposed nonlinear analysis model. The result shows that the nonlinear analysis model presented in this article could successfully evaluate the depth of cracks and the stress of rebars in continuous slab-deck, and it is instructional in predicting the cracking state of the continuous slab-deck and the reinforcement design.

Wheel Flats in the Dynamic Behavior of Ballasted and Slab Railway Tracks

Wheel flats induce high-impact loads with relevance for the safety of the vehicle in operation as they can contribute to broken axles, hot axle boxes, and damaged rolling bearings and wheels. The high loads also induce damage in the track components such as rails and sleepers. Although this subject has been studied numerically and experimentally over the last few years, the wheel flat problem has focused on ballasted tracks, and there is a need to understand the phenomena also for slab tracks. In this research, a numerical approach was used to show the effects of the wheel flats with different geometric configurations on the dynamic behavior of a classical ballasted track and a continuous slab track. Several wheel flat geometries and different vehicle speeds were considered. The nonlinear Hertzian contact model was used because of the high dynamic variation of the interaction of the load between the vehicle and the rail. The results evidenced that, for the same traffic conditions, the dynamic force was higher on the slab track than on the ballasted one, contrary to the maximum vertical displacement, which was higher on the ballasted track due to the track differences regarding the stiffness and frequency response. The results are useful for railway managers who wish to monitor track deterioration under the regulatory limits.

Gullies on Mars and seasonal ices visualised using the Colour and Stereo Surface Imaging System (CaSSIS)

<p>Young gullies on Mars were first reported by Malin and Edgett in 2000 and were hailed as evidence of recent liquid water flows on Mars. Since that time, monitoring of gullies has revealed they are active today at times of year when the martian surface is at its coldest and when carbon dioxide ice is condensed on to the surface. In order to further explore the relationship between surface frosts and gully-activity we focus on Sisyphi Cavi near the south pole of Mars, where gully-activity has already been studied and CaSSIS obtained a dense temporal coverage in 2018. We identified the following sequence of events:</p><p>1) In winter frost covers all surfaces and dark spots and flows can be seen across the slopes with gullies and preferentially around the gully channels. This is consistent with previous observations and has been interpreted to be the surface expression of gas-jets generated by the sublimation of CO<sub>2</sub> underneath a continuous slab of CO<sub>2</sub> ice on the surface. The jets occur when the pressure fractures the slab ice and the pressurized gas can escape with entrained particles.</p><p>2) As the surface temperature increases towards 200 K, the top of the slopes are the first to defrost followed by sun facing parts of the alcoves and channels.</p><p>3) As the surface temperature approaches and exceeds 250 K and the surrounding terrain is completely defrosted, the last parts of the gully to remain frost covered are the fans. We interpret this to be a result of the fans having slightly lower thermal inertia than the surrounding materials. This lower thermal inertia could be because the fans have a lower content of water ice (i.e. a thicker lag on top of the ice-table), because of recent depositional events. It is at this time of year when gullies are most active. Hence, we infer that gully activity increases when there is both frosted and defrosted surfaces available to drive vigorous sublimation of the CO<sub>2</sub> ice.</p><p>4) Finally, once defrosting has almost fully completed and surface temperatures have reached their seasonal maximum of ~270 K the only remaining surface frosts are in pole-facing niches at the base of gully-alcoves.</p><p>Our study has underlined that the colour capability of the CaSSIS instrument is particularly suited to studying and monitoring changes in surface ices. Our observations reveal that gully-alcoves defrost before the fans and gullies defrost later than surrounding terrain – suggesting activity is driven by the availability of “hot” sediment to trigger more efficient sublimation. Further work will examine whether surface frost patterns differ between gullies that have been shown to be active and inactive since spacecraft observations began.</p>

Numerical analysis of the impact of removing a corner column in a continuous slab-column structure in relation to the experimental model

The paper presents the numerical analysis of the impact of removing a corner column on the behavior of a continuous slab-column structure. The model uses the minimal reinforcement amount compliant with Eurocodes. The basis for numerical modelling was the experimental research of a piece of a slab-column structure with the dimensions of 3.0×3.0 m in column axes. The article includes a detailed description of the assumed conditions of the model support, the method of loading and reading of the results. The paper also compares the obtained results of numerical calculations with experimental results.