Secondary transfer length and residual prestress of fractured strand in post-tensioned concrete beams

An experimental study is performed on five post-tensioned concrete beams to explore the effects of different fracture positions on secondary transfer length and residual prestress of fractured strand.A numerical model is developed and used to predict the secondary transfer length and residual prestress of fractured strand in post-tensioned concrete beams.The model change interaction,which can deactivate and reactivate the elements for simulating the removal and reproduction of parts of the model,is used to reproduce the secondary anchorage of fractured strand.The numerical model is verified by experimental results.Results shows that the fractured strand can be reanchored in concrete through the secondary anchorage,and the secondary transfer length of fractured strand with the diameter of 15.2 mm is 1133 mm.The residual prestress of fractured strand increases gradually in the secondary transfer length,and tends to be a constant beyond it.When the fractured strand is fully anchored in concrete,a minor prestress loss will appear,and the average prestress loss is 2.28%in the present study.

On the Exploitation of Secondary Fibre Transfer： The Use of Flock Fibres as a Tracer

Objective Flock fibres are proposed as a tracer in cases where secondary transfer of the tracer is needed. Methods The research was carried out following a case in which people were suspected to commit large numbers of burglaries. Fibres were applied to the vehicle of the suspects and collected from later crime scenes. A device was developed to assist in the appli- cation of fibres and a number of experiments on secondary transfer were carried out. Results The device can be used to apply many fibres homogeneously in a short time. A single contact will not fully deplete the first surface from flock fibres. 1%~15% of the fibres are transferred to the 3rd surface representing the crime scene. The actual number of transferred fibres is dependent on variables such as the choice of surfaces. Conclusion The results indicate that, given the selected parameters, it is realistic to expect that relatively large numbers of fibres are transferred to a crime scene and can be collected.

he Design of Efficient Heat Transfer Based on Flat Plate Solar Water Heater

This is an improved design based on the existing plate type solar water heaters. It aims at making full use of solar energy. To fully absorb radiation, it absorbs coating selectively by adopting the magnetron sputtering technology AL-N/AL. this design conduct heat through aluminum material which can reduce the cost meanwhile conduct heat effectively. To ensure the quality of the water at the same time improve the utilization rate of solar energy, this design use phase change for second heat exchange. Take Shanghai for example, where this design and heat transfer model are applied, the average efficiency of water heaters can achieve 68%, which has proven the feasibility of the design. In a word, this design can achieve the goal of energy conservation and emissions reduction and has broad market prospects.

Transfer of Fibres onto Knife Blades in Stabbing Events: Distribution and Determination of the Stabbing Sequence

Knives are among the weapons most frequently involved in criminal cases.They represent the most encountered category of weapons in Swiss homicide cases(completed and attempted homicides considered)and are also frequently employed in assault cases,notably bodily injuries.Whenever a knife is involved in a stabbing event,DNA and fingerprints may be sought.When garments are damaged,fibres can also be investigated.Fibres from the victim's garments might transfer onto the blade of the knife used in the assault and can thus provide useful infbnnation to determine whether a particular weapon could have be used to stab the victim.This study simulates vertical stabbings into garments with the use of a special holding device.Different types ofknives and blades straight or serrated were used as weapons.Two garments presenting different shedding capacities and garment structures were also considered for the simulations.The distribution of fibres transferred onto the blade(number and position)was recorded for each simulation performed.Sequences of stabbings into the two garments were also carried out to assess whether the order of the stabs could be determined.Several parameters were considered,notably the distribution of fibres transferred onto the blade.The transfer of fibres inside the stab damage ballistic soap was used in this study and on the area near the second damage was also investigated.This study provides new insight into the interpretation of fibres transferred onto knives after a single stab or a sequence of stabbings and into determining the stabbing sequence.Finally,the study brings some guidelines for the search and recovery of fibres on the crime scene and on the blades ofknives.

Flow and Heat Transfer Characteristics in Rotating Two-pass Channels Cooled by Superheated Steam

In a modern gas turbine,using superheated steam to cool the vane and blade for internal convection cooling is a promising alternative to traditional compressor air.However,further investigations of steam cooling need to be performed.In this paper,the three-dimensional flow and heat transfer characteristics of steam are numerically investigated in two-pass square channels with 45° ribbed walls under stationary and rotating conditions.The investigated rotation numbers are 0 and 0.24.The simulation is carried out by solving the Reynolds averaged Navier-Stokes equations employing the Reynolds stress turbulence model,especially considering two additional terms for Coriolis and rotational buoyancy forces caused by the rotating effect.For comparison,calculations for the air-cooled channels are done first at a Reynolds number of 25 000 and inlet coolant-to-wall density ratio of 0.13.The results are compared with the experiment data.Then the flow and heat transfer in steam-cooled channels are analyzed under the same operating conditions.The results indicate that the superheated steam has better heat transfer performance than air.Due to the combined effect of rotation,skewed ribs and 180° sharp turn,the secondary flow pattern in steam-cooled rotating two-pass channels is quite complex.This complex secondary flow pattern leads to strong anisotropic turbulence and high level of anisotropy of Reynolds stresses,which have a significant impact on the local heat transfer coefficient distributions.