Toughness Of Beams Research Articles

3D mesoscale model of steel fiber reinforced concrete based on equivalent failure of steel fibers

Steel fiber reinforced concrete (SFRC) is widely used in civil engineering. Investigating the mechanical properties and failure mechanisms of SFRC materials using mesoscopic models holds significant theoretical and practical importance. The bond-slip interaction between steel fibers and the cementitious matrix is crucial, yet current computational capabilities struggle to simulate the interactions among the numerous components within concrete containing a large number of steel fibers. This paper establishes an equivalent failure model to replace the bond-slip interaction. Based on this model, a multiphase mesoscopic model (including aggregates, the interfacial transition zone (ITZ), mortar, and steel fibers) is developed to predict the mechanical properties and failure modes of SFRC. The accuracy and validity of the model are verified by comparing the simulation results with the experimental results from four-point bending tests on SFRC beams, focusing on load-displacement curves, failure modes, and crack propagation. The results indicate that under load, the ITZ at the sharp edges of large aggregates in the SFRC beam is the first to be damaged, forming microcracks. Subsequently, these cracks bypass the large particles and propagate towards weaker regions with fewer steel fibers, forming macrocracks. At this stage, the steel fibers take over the load from the cementitious matrix and limit crack propagation. The simulated crack propagation trend and crack width during the loading process of the SFRC multiphase mesoscale model match well with the experimental observations. A higher fiber content can mitigate stress concentration within SFRC beams and enhance the fiber bridging effect, significantly improving the flexural load-bearing capacity and toughness of the beams. A smaller steel fiber inclination angle can effectively inhibit the propagation of vertical cracks, thereby increasing the load-bearing capacity and toughness of SFRC beams and extending the service life of the structure.

Evaluating the flexural behavior of green copper slag-contained steel fiber reinforced SCC beams with/without initial notches

Nature-friendly concrete composites containing hooked-end steel fibers (SF) and copper slag (CS) aggregates can play important roles in sustainable construction, preventing the nature destruction, reducing brittle fracture and improving formability of concrete elements. To this end, effects of SF (0.1, 0.3, and 0.5%) and CS (20, 30, 40, 50 and 60%) on the compressive strength and microstructure of concrete composites were examined and the flexural behavior and toughness of beams with/without notches were evaluated and compared with the control design (no SF/CS) using Post Crack Strength (PCS), CECS 13, ASTM C1018, JSCE-SF4, ASTM C1609 and JG/T 472 models. Same laboratory setup and specimen dimension were used for accurate evaluations and results showed that CS aggregates improved the properties of fresh concrete and its workability was reduced by high SF volumes. Increasing the latter from 0.1 to 0.5% increased the optimal CS from 20 to 50% to achieve better compressive strength, and increasing the CS volume up to 30% strengthened the microstructure of SF-reinforced composites. Compared with notched (N) specimens, unnotched (UN) ones had higher peak loads and lower flexural strengths. At the lowest fiber volume, CS effects on both flexural behavior and fracture toughness were greater, and JG/T 472 method calculated the flexural toughness better than the other mentioned methods because of separating the pre- and post-peak load areas in the load–displacement curve and also using the flexural strength (which is affected by peak load).

Ductility and Toughness of Unsymmetrical CFRP Strengthening of Reinforced Concrete Beams

The use of externally bonded composite materials such as carbon fiber reinforced polymers (CFRP) sheets is a modern and convenient way for strengthening and repairing reinforced concrete (RC) beams. This study presents experimental investigations on the flexural behavior of reinforced concrete beams strengthened by unsymmetrical CFRP sheets with various configurations. Effects of number of which strengthened faces of strengthening and fiber direction on the flexural strength of RC beams are examined. Six RC beams with dimensions of 100 mm * 220 mm were casted and tested under two points loading. One beam considered as a reference (unstrengthened) beam. Five residual beams were strengthened using CFRP sheets with various configurations. From the results, it was observed that all strengthened beams showed higher ultimate load capacity than that of the control beam. On the other hand, it was found that a progressive reduction in flexural ductility and toughness of beams with strengthening in one face and two faces with horizontal fiber direction. The highest decrease in flexural ductility and toughness for strengthened beams with horizontal fiber direction in comparison to control beam were 63% and 54%, respectively. On the contrary, the flexural ductility and toughness of strengthened beams increased with strengthening by vertical fiber direction. Additionally, the maximum percentage of increase in flexural ductility and toughness were 41% and 54%, respectively in comparison with control beam.

Brittleness toughness and thermal shock resistance of tungsten-copper composite : K.Mu et al. (Central Iron and Steel Research Inst., Beijing, China.)

This paper presents the results of an investigation conducted on steel fibre reinforced concrete beams in pure torsion. The main parameters of the study were the volume fraction and aspect ratio of fibres. It was found that inclusion of fibres in concrete improved the ultimate torsional strength and imparted considerable ductility and toughness to the beams. The strength and toughness of beams were found to increase with increasing volume fraction and aspect ratio of fibres. A comparison of test results with torsion theories indicated that a satisfactory prediction of ultimate torque could be obtained by using plastic theory.

Steel fibre reinforced concrete beams in pure torsion

This paper presents the results of an investigation conducted on steel fibre reinforced concrete beams in pure torsion. The main parameters of the study were the volume fraction and aspect ratio of fibres. It was found that inclusion of fibres in concrete improved the ultimate torsional strength and imparted considerable ductility and toughness to the beams. The strength and toughness of beams were found to increase with increasing volume fraction and aspect ratio of fibres. A comparison of test results with torsion theories indicated that a satisfactory prediction of ultimate torque could be obtained by using plastic theory.