Search Results (4)

A high strain rate occurs when the strain rate exceeds 100 s⁻¹. The mechanical behavior of materials at a high strain rate is different from that at middle and low strain rates. In order to study the dynamic compressive mechanical properties of ultra-high-performance steel-fiber-reinforced concrete (UHPSFRC) at high strain rates, an electro-hydraulic servo universal testing machine and a separate Hopkinson pressure bar (SHPB) with a diameter of 120 mm were used, respectively. A quasi-static compression test (strain rate 0.001 s⁻¹) and impact compression test with a strain rate range of 90~200 s⁻¹ were carried out to study the failure process, failure mode, and stress–strain curve characteristics of UHPSFRC at different strain rates and quantify the strain rate strengthening effect and fiber toughening effect. Based on the statistical damage theory and energy conversion principle, a dynamic damage constitutive model considering the effects of strain rate and fiber content was constructed. The results showed that the rate correlation of UHPSFRC and the fiber toughening properties showed a certain coupling competition mechanism. When the fiber content was less than 1.5%, with an increase in the steel fiber content, the crack initiation and propagation time of the specimen was extended, and the strain rate sensitivity gradually decreased. When the fiber content was 2%, the impact compressive strength of the specimen was optimal. Compared with UHPC, the dynamic increase factor (DIF) of UHPSFRC was significantly lower. The dynamic damage constitutive model established in this paper, considering the influence of strain rate and fiber content, has a good applicability and can describe the mechanical behavior of UHPSFRC at a high strain rate. Full article

This work investigates the effect of various sand fractions on the ballistic resistance of ultra-high-performance steel-fibre-reinforced concrete (UHP-SFRC) samples. We specifically investigated replacing expensive and generally inaccessible microsands with commonly available sands. The tests and the measured values show that replacing part of the microsand with the more commonly and economically acceptable 0/2 mm aggregate fraction minimises the resulting mechanical properties and ballistic resistance. The most common type of ammunition was used to test all sample bodies, which is a 7.62 × 39 mm calibre with an all-metal jacket and a mild steel core. The damage’s extent and mode were determined using a 3D scanner operating on photogrammetry. Full article

The excellent seismic performance of concrete-filled steel tube (CFST) structures has been widely recognized, but there is a paucity of research on composite columns using UHPC with added steel fibers. This paper presents the experimental studies and numerical analyses with OpenSees on seismic performance of ultra-high performance steel fiber-reinforced concrete (UHPSFRC)-filled square steel tubular columns. Five half-scaled specimens of UHPSFRC-filled square steel tubular columns were tested under a combination of constant axial compression and cyclic horizontal load, with parameters of width-to-thickness ratio (28.5, 19.9 and 14.7) and axial compression ratio (0.133, 0.266 and 0.399) of the steel tube. With the decrease in width-to-thickness ratio, the maximum bending moment capacity increased by 33.5% and 15.3%, and the energy dissipation capacity and ductility increased, while the strength degradation and stiffness degradation reduced. With the increased axial compression ratio, the loading capacity increased from 55.3 to 70.2 kNm (26.94%). The results indicate that UHPSFRC-filled square steel tubular columns improve seismic performance by decreasing the axial compression ratio and by increasing the width-to-thickness ratio. When the width-to-thickness ratio was reduced, the steel tubular was able to provide higher lateral restraint to the internal UHPC; thus, seismic performance was improved. With the increase in the axial compression ratio, the second-order damage effect of the members was greatly affected, and it accelerated the plastic damage. A modified UHPSFRC model considering steel tubular constraints was adopted, and the nonlinear dynamic modeling of the column response using OpenSees led to good agreement with the tested response of the column under cyclic motion. The theoretical calculation model can better predict the bending capacity of the UHPSFRC-filled square steel tubular columns. However, the calculation formulas of initial stiffness and yield bending moment need further research. Full article

Ultra-high-performance steel-fibre-reinforced concrete (UHP-SFRC) is a technologically advanced composite with a high ability to absorb and dissipate mechanical energy. This work investigates the possibility of increasing ballistic resistance by adding different percentages of corundum and basalt aggregate into this type of concrete. The most common type of ammunition, a 7.62 mm × 39 mm calibre with a full-metal jacket and a mild-steel core (FMJ-MSC), was used to test all samples. The size of the damage and the mode of failure were determined using a 3D scanner operating on the principle of photogrammetry. The experimental campaign showed that the addition of basalt and, especially, corundum aggregate has a positive effect on ballistic resistance. In particular, the increase in compressive strength and the slight decrease in depth of penetration (DOP) was observed in the case of the usage of the corundum aggregate. Full article