Prediction of Shear Strength of UHPC Beam with Small Shear Span to Depth Ratios Based on Modified MCFT

Ultra-high performance concrete (UHPC) has been gradually used in structure engineering due to its excellent mechanical performance, however, predicting the shear capacity of the UHPC beams is still a challenge, especially for the beams with small shear span to depth ratios. To address this issue, this paper devotes to developing a rational model to predict the shear capacity of the UHPC beams with stirrups based on the modified compression field theory (MCFT) and plastic theory. The shear force will be balanced by the stirrups, matrix, fibers and shear compression zone. The contribution of stirrups, matrix and fibers on shear capacity can be predicted by MCFT, and the contribution of compression zone is determined based on plastic theory. 12 UHPC beams was designed and tested to validate the proposed model. It can be found that the predictions agree well with test results, while the current design codes, including SETRA-AFGC and SIA, give overly conservative values for UHPC beams when the shear to span is less than 2.5.

Analysis of Dowel Action in Reinforced Concrete Beams with Shear Reinforcement

The shear transfer mechanism was examined to view the contributions of different components of shear transfer such as aggregate interlocking, dowel force and uncracked compression zone. Understanding the role of various shear transfer components with transverse reinforcement provided was complex due to traditional difficulties involved in detail assessment of accompanying kinematics during the failure. In the present paper, the issue was addressed by employing sixteen specimens and grouped under two categories representing conventional beams and beams with preformed cracks and were tested under four - point bending load with a shear span to depth ratio of 1.26 by increasing the characteristic strength of concrete. From the results obtained, empirical formulas proposed were also evaluated and it was concluded that the results were consistent and contribution of shear transfer across uncracked compression zone was maximum in shear resistance with transverse reinforcement provided. Later structural behaviour was also assessed and it was concluded that beams with preformed cracks had exhibited greater stiffness thus nullifying the effect of aggregate interlocking in shear transfer.

Study on Soil Displacement Fields around the Expanded Body of Drill-Expanded Concrete Piles Based on DIC Technique

The soil displacement field around a drill-expanded concrete pile is noticeably different from that of an equivalent section pile placed under axial load due to the mutual embedment between the expanded body and the soil. It is important to study the soil displacement field around drill-expanded concrete piles in order to understand the mechanisms of interaction between the pile and the soil. First, the model test of the half-face pile installed in undisturbed soil and the model test of the half-face pile installed in sand were used to study the soil displacement field around the pile. Then, the entire process of the soil displacement field’s formation and development under the load was observed by using digital image correlation (DIC) techniques. Finally, numerical simulation was used to verify the results of the model tests. The results show that the displacement characteristics of the soil around the pile in the undisturbed soil and sand are basically the same. There is a clear soil compression zone under the expanded body, and the magnitude and density of the displaced soil in the compression zone are much higher than in other areas. Both the vertical displacement and the horizontal displacement gradually decrease as the distance from the expanded body and the burial depth increase. The horizontal displacement of the soil under the expanded body follows a trend of first moving toward the pile body and then moving away from it. The results of the numerical simulation are basically consistent with the results of the model test, indicating that the results of the model test are relatively reliable.

Experimental Ductility of Compression-Controlled Flexural Members Using CFRP Grid to Confine Concrete

Concrete members are typically designed so that flexural failure initiates with steel yielding and ends with concrete crushing in compression in order to take advantage of the yielding property of steel that allows for large deformations prior to any fracture of the material. On the other hand, if a large percentage of steel or linear elastic non-yielding reinforcement (i.e., FRP composite) is used, the member flexural failure typically initiates and ends with concrete crushing in compression. These members are known as compression-controlled members and typically exhibit brittle behavior. This study proposes a new approach in improving the flexural behavior of over-reinforced members through concrete confinement using carbon fiber reinforced polymer (CFRP) grid tubes in the compression zone. The concept was experimentally tested using rectangular beams. Beam 1 (control beam) had no grid reinforcement and beam 2 (tube beam) had two 152 mm grid tubes embedded in its compression zone. Experimental results indicate improvement in the ductility of the tube beam compared to the control beam of approximately 20–30% depending on the criteria used. Considering the low amount and mechanical properties of the CFRP grid, the improvement is significant, which shows that the proposed approach is valid and improves the ductility of compression-controlled members.

MEASUREMENT OF THE LOCAL ELECTRON TEMPERATURE IN SELF-COMPRESSED PLASMA STREAM

The local electron temperature measurements with the double electric probe in the compression zone are presented. Electric probes make it possible to measure the electron temperature with a reasonably good spatial resolution. Double electric probe application for electron temperature measurements in the dense self-compressed plasma stream is discussed. We have shown experimentally that the electric probe operates in a diffusion regime.

Fabrication of Extrudate Filaments from Waste Polyethylene Terephthalate Plastics for 3D Printers

The use of 3D printers for manufacturing processes comes with the challenge of filament replacement for subsequent processes. This aforementioned including the environmental problems posed by plastics wastes formed the basis for the current work which is focused on design and construction of a simple single extruder for the production of filaments from waste polyethylene terephthalate (PET) plastics for rapid prototyping machines and 3D printers. Three Band heaters were used to melt the PET plastics and a screw was used to move the melted PET plastics longitudinally along the barrel. The screw is consisted of three zones namely feed zone, compression zone and metering zone. The temperature of the band heaters is controlled by a Digital temperature controller. This paper describes the design, fabrication and testing of a filament extruder. A 2mm die was used to extrude the filament to1.75 mm. The performance of the system was quantified through relevant tests and the findings reported. When the barrel and die assembly are at 200°C, melting begins to occur and at 230°C, the extrudate begins to appear at the metering zone. The energy efficiency of the system was found out to be 75.2%. Keywords— 3D printer, Design, Extruder, Filament, Polyethylene terephthalate.

Experimental Evaluation on Components of Shear resistance of Reinforced Concrete Beams with Shear Reinforcement Provided

The contribution of aggregate interlocking and dowel force in shear strength of reinforced concrete beams was topic of research for many years. The precise forecasts of shear behavior were challenging to determine due to complication involved. The existing theories had focused on aggregate interlocking force and shear resistance arising due to concrete compression zone, neglecting the contribution of dowel force despite considering as significant constituent in shear transfer mechanism. The present investigation focuses on cogitating all components in shear transfer mechanism by providing shear reinforcement and keeping clear cover and effective span to depth ratio constant. Sixteen specimens were considered for parametric study by employing suitable variables such as increase in strength of concrete and variation in flexural reinforcement. Eight specimens were conventional beams and the remaining eight specimens were provided with preformed cracks. Moment vs. displacement curvature and strain vs. moment curvature were plotted to evaluate shear at uncracked compression zone and accordingly aggregate interlocking force and dowel force were determined based on the empirical formulas proposed. From the result it was confirmed that contribution of aggregate interlocking force and dowel force were insignificant and shear resistance due to uncracked compression zone is the sole contributor in shear transfer mechanism. Structural behavior of concrete beams was also studied and it was confirmed that beams with preformed cracks exhibited better structural behavior when related to conventional beams.

Multi-Scale Simulation of Two-Dimensional Chloride Transport Under the Effect of Bending Load in Concrete

Chloride transport in marine concrete under loading is the main cause of its structural deterioration. The traditional numerical simulation assumes that the coefficient of chloride transport is constant, resulting in a large deviation in the prediction results. Based on the porous medium theory, micromechanics theory, and the idea of equivalent homogenization, a multi-scale model of the effective diffusion variable coefficient of chloride transport under bending load was established, which was calculated and programmed by the numerical analysis. The results show that the prediction values of the two-dimensional variable coefficient model are basically consistent with those in the literature, and the prediction accuracy is significantly improved. In addition, the theoretical simulation proves that the bending load affects the porosity of the cement matrix, and then the diffusion coefficient of chloride is changed in concrete. The compression zone can slow down the chloride transport process, while tension zone will accelerate it. The chloride concentration under tension zone is 42.1% higher than that under compression zone when the diffusion time is 200 days and the concrete depth is 15 mm.

BEHAVIOR OF NON-BRITTLE ROCKS UNDER BENDING CONDITION

Experimental results of determining the bearing capacity of a marble beam are presented. A significant influence of plastic properties on the strength characteristics of the beam is noted. On the basis of a model of strength-different materials, an elastoplastic profile of stresses in a beam is constructed. It is proposed to use elastic stress distribution in the compression zone for rocks and similar heterogeneous materials with different compressive and tensile strengths, and elastic-plastic distribution in the tensile zone. Such a stress diagram makes it possible to explain the high values of bending strength in comparison with the tensile strength of the presented materials.