Strength of circular concrete columns under concentric compression

An experimental study, in which six columns were loaded concentrically toinvestigate the behavior of reinforced normal strength and high strength circular columns underconcentric compression, is described. The concrete strengths of the columns were 30 MPa and 60 MPa.The primary variables considered were the concrete strength and the amount of transversereinforcement. Test results indicate that smaller hoop spacing provides higher column capacity andgreater strength enhancement in a confined concrete core of columns. For the same lateralconfinement, high strength concrete columns develop lower strength enhancement than normal strengthconcrete columns. Both the strength enhancement ratio (f'_(cc) /f'_(co)) and the column capacityratio (P_(test)/P_o) were observed to show linear increase variations with rho_s f_(yt)/f'_c incircular columns.

Effect laws and mechanisms of different temperatures on isothermal tensile fracture morphologies of high-strength boron steel

The fracture behaviour and morphologies of high-strength boron steel were investigated at different temperatures at a constant strain rate of 0.1 s-1 based on isothermal tensile tests. Fracture mechanisms were also analyzed based on the relationship between microstructure transformation and continuous cooling transformation(CCT) curves. It is found that 1) fractures of the investigated steel at high temperatures are dimple fractures; 2) the deformation of high-strength boron steel at high temperatures accelerates diffusion transformations; thus, to obtain full martensite, a higher cooling rate is needed; and 3) the investigated steel has the best plasticity when the deformation temperature is 750 °C.

Study on high speed tension property of B-grade bulletproof steel

In this paper, the high speed tension experiments have been performed on ultra high strength bulletproof steel. The specimen were cut from B-grade bulletproof steel sheet after hard-module quenching with thickness of 2.3 mm. The mechanical properties at strain rates of 0.001 s^-1, 0.01 s^-1, 0.1 s^-1 and 1 s^-1 were carried out on MTSS10, while those at higher strain rates of 200 s^-1, 500 s^-1 and i 000 s^-1 were tested on HTM5020 high speed tension tester and Hopkinson bar. The data from the high speed tension experiments were fitted via Johnson-Cook constitutive equation, and the fracture surface of each specimen was analyzed by scanning electron microscope （SEM）. The results indicate that, the shoot resistance capability of bulletproof steel is closely related to its strength, thickness and flow behaviors under high strain rate. The shoot resistance will be improved in the case of higher strength and better matching between strength and elongation. The Johnson-Cook constitutive equation fitted via experimental data provides fundament to numerical simulation. With the increase of strain rate, the size and depth of dimple trend to decrease and the depth of dimple changes less in steel with lower strength and higher elongation. The SEM analysis of fracture aspect is of benefit for further understanding of deformation and fracture mode under high strain rate.

Flexural response of reinforced concrete beams strengthened with post-poured ultra high toughness cementitious composites layer

Four-point bending tests were conducted up to failure on eleven reinforced concrete (RC) beams and strengthening beams to study the effectiveness of externally pouring ultra high toughness cementitious composites (UHTCC) on improving the flexural behavior of existing RC beams.The strengthening materials included UHTCC and high strength grade concrete.The parameters,such as thickness and length of strengthening layer and reinforcement in post-poured layer,were analyzed.The flexural behavior,failure mode and crack propagation of composite beams were investigated.The test results show that the strengthening layer improves the cracking and ultimate load by increasing the cross section area.Introducing UHTCC material into strengthening not only improves the bearing capacity of the original specimens,but also disperses larger cracks in upper concrete into multiple tightly-spaced fine cracks,thus prolonging the appearance of harm surface cracks and increasing the durability of existing structures.Compared with post-poured concrete,UHTCC is more suitable for working together with reinforcement.The load?deflection plots obtained from three-dimensional finite-element model (FEM) analyses are compared with those obtained from the experimental results,and show close correlation.

Research on the mechanical property test of a new high-strength metal bolt

In order to study how to improve the overall performance of the operational metal bolt, based on the production process of an ordinary metal bolt used in understructure engineering, this paper focused on the existing problems of ordinary metal bolts identified by some survey and analysis. The results show that the structure of operational metal bolts is so unrea- sonable that the bolt tail is easily fractured by low load capacity. Furthermore, a new type of strong big-end metal bolt and its heat treatment and roughing processing technology were introduced. Through bolt tensile and metallographic tests, the property of the new big-end bolt was analyzed. The new findings indicate that after a special processing, the overall strength and plasticity of the bolt is greatly improved, and the grain of the bolt tail structure is refined, which would help build up favorable working conditions for bolt tails.

Investigation of meso-failure behavior of rock under thermal-mechanical coupled effects based on high temperature SEM

It is extremely important to study and understand the deformation behavior and strength characteristics of rocks under thermal-mechanical （TM） coupling effects. Failure behavior and strength characteristics of Pingdingshan sandstone were investigated at room temperatures up to 300℃ in an internally heated apparatus and tensile load through meso-scale laboratory experiments in this work. 33 experiments have successfully been conducted for Pingdingshan sandstone. Experimental results indicated that the tensile strength increased slowly with temperatures from 25℃ to 100℃, and then sharply jumped from 100℃ to 150℃, and finally decreased slightly with temperatures from 150℃ to 300℃. And about 150℃ is the threshold temperature of strength and thermal cracking. At low temperatures （25℃-150℃）, sandstone strength is determined by relatively weak clay cement. However, at higher temperatures （150℃-300℃）, because of the strength enhancement of clay cement, sandstone strength is controlled by both mineral particles and clay cement. The effects of cement clay, micro-cracks closing, and thermal cracking were the possible reasons for our detailed analysis. In addition, the typical fracture position maps and nominal stress-strain curves indicated that the temperature had strong effects on the failure mechanism of sandstone. The fractograph implied that the dominant fracture mechanism tended to transform from brittle at low temperatures to ductile at high temperatures.

Experimental study on mechanical behaviors of pseudo-ductile cementitious composites under biaxial compression

Experimental investigation was conducted to characterize the responses of pseudo-ductile cementitious composites (PDCCs) when subjected to uniaxial and biaxial compression.The PDCCs is a class of fiber reinforced cementitious composites with ultra-high ductility by using a low volume fraction (2%) of polyvinyl alcohol (PVA) fiber.Two different strength grades of PDCC were examined with cubic specimen size of 100 mm in the tests.The specimens were loaded with a servo-hydraulic jack at different stress ratios.The principle stresses and strains of the specimens were recorded,and the failure modes with various stress states were examined.The test results indicated that the ultimate strength of PDCCs increased due to the lateral confinement in the other principal stress direction,and the maximum ultimate strength occurred at the biaxial stress ratio of 0.25,which was very different from common concrete material.For the PDCC specimens,the biaxial strength may be lower than the uniaxial strength when subjected to biaxial compression with the stress ratio of 1.0,and the failure mode showed a shear-type failure because of the bridging effect of fibers.Finally,a failure criterion was proposed for PDCCs under biaxial compression.