Shear Behavior of Reinforced Post-Filling Coarse Aggregate Concrete Beams Produced by Creative Construction Process

Different from the traditional concrete mixing procedure, the innovative post-filling coarse aggregate concrete (PFCC) reduces the cost of pumping concrete by increasing the coarse aggregate content and reducing the usage of cement. Previous studies have shown that PFCC enhances the compressive strength, elastic modulus, and flexural strength of concrete. In this paper, the shear behavior of 13 post-filling coarse aggregate concrete beams and 3 control beams was tested to determine the relationships between the shear performance of the beam and the post-filling coarse aggregate ratio, concrete strength grade, shear span ratio and stirrup reinforcement ratio. The results showed that the ultimate shear capacity of beam specimen increases first and then decreases with the increase in post-filling coarse aggregate ratio, reaching the maximum at 15% post-filling ratio. The results also indicated that the ultimate shear capacity of the beam increases with the increase in concrete strength grade and stirrup ratio. However, experimental results exhibited that the ultimate shear capacity decreases as the shear span ratio increases. This study provides a reference for the application of post-filling coarse aggregate concrete in engineering practice.

Numerical Analysis on Flexural Behaviors of Prestressed Reinforced Concrete Beams Strengthened with NSM CFRP Strips

This paper presents the numerical analysis of prestressed reinforced concrete (PRC) beams strengthened with near-surface mounted (NSM) carbon fiber reinforced polymers (CFRP). ABAQUS finite element software was used to simulate the existing test beams to investigate the flexural behaviors of PRC beams strengthened with NSM CFRP strips. The finite element model of beams strengthened with NSM CFRP strips was established. The finite element calculation results were compared with the experimental results to verify the accuracy and effectiveness of the model. Based on this model, the influences of concrete strength grade and amount of CFRP strips on the flexural behaviors of directly strengthened beams and the cycle numbers and overload amplitude on the flexural behaviors of damaged strengthened beam were further analyzed, and the load-carrying capacity calculation formula of PRC beam strengthened with NSM CFRP strips was established. The results showed that the simulation results and the theoretical calculation were consistent with the test results. With the increase of concrete strength grade and amount of CFRP strips, the ultimate load of directly strengthened beams increased significantly, with a maximum increase of 21.3% and 23.0%, respectively. When the concrete strength grade exceeded C50, the improvement of the ultimate load was limited. When the overload amplitude was less than 60% of the ultimate load, the cycle numbers (within 500 times) had little effect on the yield load, ultimate load, and deformation. When the overload amplitude was higher than 60% of the ultimate load, the deformation increased, and the ultimate load decreased with the increase of the cycle numbers. The larger the overload amplitude, the smaller the ultimate load, and the larger the deformation under the same cycle numbers.

Bearing Capacity of Recycled Self-Compacting Concrete-Filled Circular Steel Tubular Long Columns Subjected to Axial Load

To investigate the ultimate bearing capacity and deformation of the recycled self-compacting concrete-filled circular steel tubular (RSCCFCST) long columns subjected to axial load, nine specimens with different recycled self-compacting concrete (RSCC) strength grades and slenderness ratios are tested. The experimental results indicate that the lateral deflection dominates the buckling failure of the specimens. The ultimate bearing capacity of the specimens is enhanced gradually as the RSCC strength grade increases but decreases as the slenderness ratio rises. The load-strain curves are linear and basically coincide at the elastic stage. The decrease in the slenderness ratio or increase in the RSCC strength grade contributes to the improvement of the stiffness and ultimate circumferential and axial strains of the columns gradually. Based on the combined tangent modulus theory and bearing capacity of the RSCCFCST short columns, two estimation models are presented to predict the ultimate bearing capacity of the RSCCFCST long columns. Additionally, comparisons between the calculation results of the ultimate strength demonstrate that the prediction models established in this study are more accurate than the other specifications mentioned.

Research of influence of heat treatment on metallophysical properties of metal of welded seams

Цель настоящего исследования - оценка влияния локальной термической обработки (нормализации и закалки с отпуском для продольных сварных соединений труб, сваренных контактной сваркой токами высокой частоты, а также высокотемпературного отпуска и термического отдыха для кольцевых стыков трубопроводов, сваренных дуговой сваркой) на показатели механических свойств и металлургического качества металла сварных соединений. Для проведения исследований в области продольных сварных соединений использовались трубы диаметром 530 мм с толщиной стенки 10 мм класса прочности К56, для оценки свойств металла кольцевых стыков были выбраны катушки длиной 500 мм с односторонней симметричной разделкой кромок с углом скоса 30°, изготовленные из труб диаметром 219-530 мм с толщиной стенки 8-15 мм из сталей класса прочности К42, К48, К56. В частности, показано, что высокий отпуск повышает пластичность, снижает уровень остаточных сварных напряжений (более чем на 30 %), твердость и прочность. Термический отдых сварных стыков способствует снижению уровня остаточного водорода в металле сварных соединений, что позволяет повысить свариваемость трубной стали при проведении ремонтных работ. В целом сделан вывод о том, что локальная термообработка позволяет оптимизировать показатели механических свойств металла сварных соединений и при необходимости получать требуемый уровень механических свойств. The purpose of this study is to assess the effect of local heat treatment (normalizing and quenching with tempering for longitudinal welded joints of pipes welded through contact welding with high frequency currents, and high-temperature tempering and cooling for arc welded circular joints of pipelines) on the mechanical properties and metallurgical quality of welded joint metal. To carry out research in the field of longitudinal welded joints, pipes with a diameter of 530 mm and a wall thickness of 10 mm with the K56 strength grade were used; to assess the metal properties of ring joints, 500 mm long spools with unilateral symmetrical beveling with a bevel angle of 30°, made of pipes with a diameter of 219-530 mm with wall thickness of 8-15 mm made from K42, K48, K56 strength grade steel, were used. In particular, it is shown that high tempering increases ductility, reduces the level of residual weld stresses (by more than 30 %), hardness and strength. Cooling of welded joints helps to reduce the level of residual hydrogen in the welded joint metal, which increases the weldability of pipe steel during repair works. In general, it is concluded that local heat treatment allows to optimize the indicators of mechanical properties of the welded joint metal and, if necessary, to obtain the required level of mechanical properties.

Comprehensive Analysis of Cold-Cracking Ratio for Flux-Cored Arc Steel Welds Using Y- and y-Grooves

This study investigates various factors that influence the cold-cracking ratio (CCR) of flux-cored arc welds through Y- and y-groove tests. Factors affecting the CCR include the alloy component, diffusible hydrogen content, microstructure, hardness, and groove shape. In weld metals (WMs; WM375-R and WM375-B) of a low-strength grade, the diffusible hydrogen content has a more significant effect on the CCR than the carbon equivalent (Ceq) and microstructure. However, the combined effects of the microstructure and diffusible hydrogen content on the CCR are important in high-strength-grade WM. The CCR of the WM increased upon increasing Ceq and the strength grade because hard martensite and bainite microstructures were formed. Moreover, y-groove testing of the 500 MPa grade WM revealed a more significant CCR than that of the 375 MPa grade WM. Therefore, in high-strength-grade WMs, it is necessary to select the groove shape based on the morphology in the real welds.

RESEARCH OF THE DEPENDENCE OF THE GRAIN SIZE COMPOSITION AND GRADE OF CRUSHABILITY OF RECYCLED CRUSHED STONE ON THE STRENGTH OF THE ORIGINAL RECYCLED CONCRETE

The results of the study of the grain-size composition and the grade of crushability of recycled crushed stone and their dependence on the strength of the original recycled concrete are presented. It is found that recycled crushed stone obtained from the original concrete of classes B10 - B30 does not meet the requirements of GOST 8267-93 for total residues on Ø25, Ø20, Ø5 and Ø2.5 sieves. Regardless of the strength of the original concrete, the main fraction of recycled crushed stone is grains with sizes from 12.5 to 20 mm. The strength (grade in terms of crushability) of the recycled crushed stone increases with an increase in the strength of the original concrete. The study of the main parameters of recycled crushed stone at the current moment has been carried out in an insufficient (for widespread introduction into production) volume and requires further study for the subsequent development of independent regulatory and technical documentation (or additions to the current regulatory and technical documents).

Study on the Performance of Synergistic Preparation of Sulphoaluminate Based Recycled Concrete by RP and RCA

In this paper, the properties of sulphoaluminate based recycled concrete, with high workability and low and medium strength, prepared by recycled powder (RP), recycled coarse aggregate (RCA), and high belite sulphoaluminate cement (HBSAC), were systematically studied. Under the condition of a water binder ratio of 0.45, sulphoaluminate based recycled concrete, with different mix proportions, was prepared by replacing sulphoaluminate cement with RP and natural coarse aggregate (NCA) with RCA. The workability, mechanical properties, durability, and hydration products of the prepared concrete were analyzed. The results showed that when RP and RCA were used together, the workability of recycled concrete could fully meet the pumping demand in actual construction. When the mass replacement rate of RP was less than 30% and that of RCA was less than 20%, the strength of recycled concrete could completely reach the design strength grade, while those that did not reach the design strength grade could reach the next grade. The durability performance was also good.

Sensitivity Analysis of Steel-Plate Concrete Containment against a Large Commercial Aircraft

Due to the excellent impact resistant performance of steel-plate concrete (SC) structure compared with the conventional reinforced concrete (RC) structure, SC structure is preferred to be used in the design of external walls of nuclear island buildings for new nuclear power plants (NPPs). This study aims at evaluating the effect of material and geometric parameters of SC containment on its impact resistant performance, thus the numerical simulation and sensitivity analysis of SC containment subjected to malicious large commercial aircraft attack are conducted based on the force time-history analysis method. The results show that: (1) the impact resistant performance of full SC containment is better than that of half SC containment; (2) for relatively thin full SC containment, the impact response and concrete damage can be significantly reduced by the enhancing of concrete strength grade or the increasing of steel plate thickness; (3) for the thicker full SC containment, concrete strength grade has only a slight influence on the impact displacement response, and the increasing of steel plate thickness has no significant effect on mitigating the impact displacement response. However, the increasing of steel plate thickness can effectively reduce its plastic strain, and the decreasing of strength grade of steel plate may obviously increase its plastic strain; and (4) concrete thickness plays a decisive role on the improvement of impact resistance, which is more effective than the enhancing of concrete strength grade. Resultantly, this paper provides a reference and guidance for the design of SC structure external walls of nuclear island buildings against a large commercial aircraft.

Blastability and Ore Grade Assessment from Drill Monitoring for Open Pit Applications

Blasting performance is influenced by mechanical and structural properties of the rock, on one side, and blast design parameters on the other. This paper describes a new methodology to assess rock mass quality from drill-monitoring data to guide blasting in open pit operations. Principal component analysis has been used to combine measurement while drilling (MWD) information from two drill rigs; corrections of the MWD parameters to minimize external influences other than the rock mass have been applied. First, a Structural factor has been developed to classify the rock condition in three classes (massive, fractured and heavily fractured). From it, a structural block model has been developed to simplify the recognition of rock classes. Video recording of the inner wall of 256 blastholes has been used to calibrate the results obtained. Secondly, a combined strength-grade factor has been obtained based on the analysis of the rock type description and strength properties from geology reports, assaying of drilling chips (ore/waste identification) and 3D unmanned aerial vehicle reconstructions of the post-blast bench face. Data from 302 blastholes, comprised of 26 blasts, have been used for this analysis. From the results, four categories have been identified: soft-waste, hard-waste, transition zone and hard-ore. The model determines zones of soft and hard waste rock (schisted sandstone and limestone, respectively), and hard ore zones (siderite rock type). Finally, the structural block model has been combined with the strength-grade factor in an overall rock factor. This factor, exclusively obtained from drill monitoring data, can provide an automatic assessment of rock structure, strength, and waste/ore identification.

MEEHANITE GC275

Meehanite GC275 is a pearlitic gray cast iron that has a minimum tensile strength of 275 MPa (40 ksi) when determined on test pieces machined from separately cast, 30 mm (1.2 in.) diameter, test bars. This intermediate-tensile-strength grade has a fine, close-grained structure that is ideal for finishing cuts. It is used for a wide variety of applications on account of its useful combination of good all round properties with adaptability to production of small and large volumes. This datasheet provides information on physical properties, hardness, and tensile properties as well as fatigue. It also includes information on heat treating, machining, and joining. Filing Code: CI-78. Producer or source: Meehanite Metal Corporation.