DESIGN AND FABRICATION OF CONCRETE-REINFORCED FLOATING PLATFORM FOR CANAL AND RIVER-SHORE PROTECTION

Erosion of canal and river-shore causes problems on agriculture activities and soil environment. This paper devotes to develop a floating platform to protect the shores. A concrete-reinforced floating platform was designed and fabricated in this study. Mechanical simulation was performed to ensure the design viability. The concrete-reinforced floating platform consists of three main parts: (1) steel structure, (2) foam-cement material, and (3) connecting joints. The dimension of the cement foam floating platform is 1.2 m in width, 3 m in length and 0.4 m in thickness. The cement used in this research is resistant to corrosion of sulfate and chloride from saltwater. Foam with density of 12 kg/m3 is mixed with concrete matrix so that the floating platform can float 60% or 0.16 m above the water surface. The foam cement material has the maximum compression stress of 1,951 kg ± 266.59 kg for the material density of 427.30 kg/m3 ± 19.30 kg/m3. The connecting joint part has the ultimate tensile load of 1,564 kg. The assemble floating platform has the compressive stress of 543.33 kg/m2 with the maximum vertical deformation of samples of 1 mm under the distribution load of 1,571 over the samples. Finally, from simulation with data from the material testing, the designed floating platform had a safety factor 3.46 which was higher than the design criteria of 3.

Study of Static and Dynamic Properties of Sand under Low Stress Compression

The aim of this work was to investigate a wide range of grain sizes of sand in the pre-yield regime during compression through the combined study of ultrasound (US) wave speed and acoustic emission (AE). The specific study was performed using modified oedometer and uniaxial compression experimental set-ups. The studied samples were natural dune sand (poorly graded on the poorly graded sand (SP) index) as well as its three extracted fractions as follows: 2.36–0.6 mm, 0.6–0.3 mm and 0.3–0.075 mm. The maximum compression stress during the modified oedometer experiments was <150 kPa, while during the modified uniaxial compression experiments, it was <400 kPa. Each sample was loaded while measuring the US pressure (P) wave speed and AE at each loading stage. The results show that the stiffer the soil is, the higher the value of the P wave speed measured, resulting in similar P wave velocity values achieved at a much lower applied stress during the oedometer experiments in comparison with the uniaxial compression tests. Regarding the AE results, it is seen that the higher the stress level is, causing more friction between the sand particles, the more AE events there are during their movement. The following parameters of AE were shown to be the most sensitive to the stress increase: the number of AE hits and the signals’ energy.

Optimization of Cold Pressing Process Parameters of Chopped Corn Straws for Fuel

Pressed condensation is a key process before the reclamation of loose corn straws. In this study, the effects of stabilization time on the relaxation density and dimensional stability of corn straws were studied firstly, and then the stabilization time was determined to be 60 s by comprehensively considering the compression effect, energy consumption, efficiency and significance. On this basis, the effects of the water content (12%, 15%, 18%), ratio of pressure maintenance time to stabilization time (0, 0.5, 1), maximum compression stress (60.4, 120.8, 181.2 kPa) and feeding mass (2.5, 3, 3.5 kg) on the relaxation density, dimensional stability coefficient, and specific energy consumption of post-compression straw blocks were investigated by the Box–Behnken design. It was found that the water content, ratio of pressure maintenance time to stabilization time, maximum compression stress, and feeding mass all very significantly affected the relaxation density, dimensional stability coefficient and specific energy consumption. The interaction between water content and maximum compression stress significantly affected both relaxation density and specific energy consumption. The interaction between the ratio of pressure maintenance time to stabilization time and feeding mass significantly affected the dimensional stability coefficient. The factors and the indices were regressed by quadratic equations, with the coefficients of determination larger than 0.97 in all equations. The optimized process parameters were water content of 13.63%, pressure maintenance time of 22.8 s, strain maintenance time of 37.2 s, maximum compression stress of 109.58 kPa, and raw material feeding mass of 3.5 kg. Under these conditions, the relaxation density of cold-pressed straw blocks was 145.63 kg/m3, the dimensional stability coefficient was 86.89%, and specific energy consumption was 245.78 J/kg. The errors between test results and predicted results were less than 2%. The low calorific value of cold-pressed chopped corn straw blocks was 12.8 MJ/kg. Through the situational analysis method based on the internal and external competition environments and competition conditions (SWOT analysis method), the cold-pressed chopped corn straw blocks consumed the lowest forming energy consumption than other forming methods and, thus, are feasible for heating by farmers. Our findings may provide a reference for corn straw bundling, cold-press forming processes and straw bale re-compressing.

An innovative approach for the assessment of masonry bridges based on two new limit analysis theorems

<p>The structural safety of a masonry arch bridge is usually assessed using the so-called kinematic approach. In this paper it is proved that the adoption of the dual static method can be more convenient, since a recent theorem (the <i>Minimum Equilibrated Compression </i>theorem) makes its application straightforward for any kind of arch. Computations are checked via the kinematic method by locating the plastic hinges (as many as needed to form a collapse mechanism) in the sections with maximum compression stress. Thanks to the <i>Consecutive Plastic Hinges </i>theorem, the kinematic multiplier may be then evaluated, using familiar moments of forces, without computing the virtual displacements due to the vertical and horizontal loads acting on the arch.</p>

Mechanical properties and characteristics of wheat straw and pellets

Wheat straw pellets can be easily handled, transported and stored with reduced costs as compared with the raw material. The effect of pelletization process and densification parameters on the properties of the mixture of wheat straw powder and 40% epoxy 1092 as a binder was investigated. The samples were compressed into pellets using the lab-scale hydraulic press under various compacting pressures of 10, 12 and 15 bars and different die shapes and sizes (two cylindrical dies with diameters 10 and 18 mm (S1, S2), respectively, and a new hexagonal die of side length (s) = 6 mm (S3)). It was found that the pelleting process increased the fixed carbon content from 7.14% to 17.36%, the heating value from 15,600 kJ kg−1 to 27,800 kJ kg−1 and the bulk density 10 times when compared to a raw wheat straw powder. It was also found that type S2 at pressure 15 bar is the densest pellet and it had the maximum compression stress that reached 2798.54 kg m−3 and 70.02 MPa, respectively. The cylindrical pellet (type S1) of D = 18 mm at a pressure of 15 bar had the lowest water permeability of 2.35%. Pelletizing process had improved combustion characteristic parameters compared to raw biomass where combustion temperature ranges became higher, maximum weight loss rates and residues became lower that led to a higher combustion efficiency. Thermogravimetric analysis of wheat straw before and after pelleting process was analyzed to evaluate the combustion properties. Scanning electron microscopy images showed that the particle bonding was formed mainly from solid bridges, areas of cohesive failure due to lignin flow, and inter-diffusion between neighboring biomass particles. Images were investigated to explore the importance of compaction process. The images also showed that as the pressure decreases, the gap between the particles increases and produces the less durable pellet. It was found that the slagging index equals 0.38, which indicates that the pellet has a medium slagging inclination and for the fouling inclination (1.79), the wheat straw pellet has a relatively high fouling inclination.

Effect of Rare Earth Ce Addition on Microstructure and Properties of WCu Contact Materials

In order to clarify the effect of rare earth Ce on the microstructure and properties of WCu contact materials, different contents of Ce were introduced into W skeleton, and the relative density and compression stress of the pre-sintered W skeletons were tested. Subsequently, WCu contact materials with different contents of Ce were prepared by infiltration method. The hardness, electrical conductivity and the compression stress of WCu contact materials were tested, and the microstructure and composition were characterized by a scanning electron microscope equipped with an energy dispersive spectrometer. The results show that rare earth Ce can purify W/W interface and promote the densification of W skeleton, enhance the bonding of Cu/W, and improve the integral properties of WCu contact materials. In the range of experiments, WCu contact materials with 0.30wt%Ce addition has the maximum hardness of 215HB and the maximum compression stress of 900N/mm2, which are respectively increased by 23.60% and 57.20% in comparison with that without Ce addition.

Effect of La Addition in W Skeleton on Microstructure and Properties of WCu Alloy

In order to improve properties of WCu alloy, the different La were introduced into W skeleton during sintering process. The hardness, electrical conductivity and the compression stress were tested, and the microstructure and composition were characterized by a scanning electron microscope. The results show that an appropriate rare earth La addition can purify W/W interface, enhance the bonding of W /W, and improve the densification and the integral properties of WCu alloy. In the range of experiments, WCu alloy with 0.3wt% La addition has the largest hardness value of 198HB and the maximum compression stress of 823N/mm2. In comparison with that without La addition, 0.3wt%La addition decreases the electrical conductivity slightly, but improves the hardness and the maximum compression stress significantly, which are increased by 23.6% and 57.2%, respectively.

Compression Deformation Behavior of AZ91D Magnesium Alloy in Semi-Solid State

The semi-solid compression deformation behavior of the AZ91D alloy with non-dendritic structure, which was obtained under the semi-solid isothermal treatment condition of 570°C×60min, was studied by means of Gleeble-1500 thermal-mechanical simulator. When the compression strain was lower than 0.7, along with the compression strain increasing, the compression stress firstly increased rapidly, then decreased rapidly, and finally kept a constant stress level gradually. Under the condition of different deformation temperatures and deformation rates, the maximum compression stress was obtained simultaneously when the compression strain value was 0.025 approximatively. Furthermore, when the deformation rate kept a constant, the compression stress decreased along with the deformation temperature increasing, and when the deformation temperature kept a constant, the compression stress increased along with the deformation rate increasing.