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Ductility is one of the most important requirements of RC design besides other requirements such as strength and stiffness. In recent years, concrete beams with a large amount of tensile reinforcement ratio (ρ) have been required in large projects, such as high‐rise buildings and bridges. Using high (ρ) increases the strength and stiffness of the beams and leads to a decrease the ductility. This paper aimed to investigate the effect of using steel fibers reinforced concrete (SFRC) layer in compression zone on the flexural behavior of over‐reinforced concrete beams. Partial replacement of concrete with SFRC layer in compression zone was used to avoid the brittle compression failure of concrete. For this purpose, 12 over‐reinforced concrete beams with a span of 1300 mm and a cross‐section of 120 mm × 180 mm were cast and tested under a three‐point loading. The first beam was used as a reference beam and others as strengthened beams using SFRC layer. The effects of thickness and length of strengthening layer, (ρ), volume fractions of steel fibers, and strengthening methods on flexural performance of tested beams were investigated. The flexural capacity, failure modes, crack patterns, load–deflection relationships, load–strain relationships, ductility index, and toughness were evaluated. The results showed that the suggested technique (SFRC layer in the compression zone) is an effective technique to increase ultimate load, ductility, and toughness by up to 35.72%, 121.01%, and 349.16%, respectively, compared to the reference beam. Furthermore, the failure mode changed from brittle to ductile failure. Also, one of the main advantages of this technique is allows to increase of (ρ) up to 8.55% (4.15ρb) without needing the compressive reinforcement. The results of this study indicate that the using SFRC layer in the compression zone is an appropriate and economical method to provide high flexural capacity and ductility over‐reinforced concrete beams. [ABSTRACT FROM AUTHOR]

Ultra‐high performance concrete (UHPC) prefabricated beams are competitive in accelerated bridge construction. However, their broader application has been hindered by limited large‐scale tests and inaccurate design methods. To fill this gap, the authors conducted an experimental investigation on the shear and flexural performance of UHPC pi‐beams using two full‐scale specimens. One specimen was a precast UHPC beam, while the other was a composite beam with a normal concrete slab on the UHPC beam. The primary focus was on crack propagation, ultimate capacities, and failure modes. To complement the experimental findings, the extended finite element method (XFEM) was developed as a numerical approach. Nevertheless, relying solely on XFEM to understand real structural behavior is prone to misinterpretations. Moreover, the shear and flexural capacities were evaluated using existing codes and compared with the experimental results. The comparisons revealed that the predictions of shear capacities were at least 15% lower than the experimental values, whereas the flexural capacities showed acceptable agreement. To address this, the authors introduced the limit equilibrium method, leading to a more accurate prediction of shear capacity for UHPC beams with a deviation of <2%. [ABSTRACT FROM AUTHOR]

To study the influence of the defects on the flexural behavior of laminated T‐beams, full‐scale beam tests of three reinforced concrete laminated T‐beams with incomplete bonding and one non‐defective reinforced concrete laminated T‐beam were conducted under monotonic loading. The results showed that the failure modes and crack patterns of the defective beams were similar to those of beams without defects. However, horizontal cracks appeared in these defects. Although the peak loads of the four specimens were relatively close, the difference in the maximum deflection was distinct. The deflection span ratio of each specimen exceeded 1/17, and the displacement ductility ratio exceeded 15. The results indicate that internal defects have only a slight influence on the flexural capacity of laminated beams but significantly influence their ductility. [ABSTRACT FROM AUTHOR]

Polyvinyl alcohol‐engineered cementitious composite (PVA‐ECC) exhibits strain hardening and multiple cracking characteristics under tension. Its superior tensile behavior may also influence the flexural behavior of reinforced PVA‐ECC beams. This paper investigates the load capacity and failure mode of reinforced PVA‐ECC beams in bending. Seven beams with different tensile reinforcement ratios, including six PVA‐ECC beams and one conventional concrete beam, were tested in the experimental program. The influence of reinforcement ratio on load capacity and failure characteristics was discussed in detail. Test results showed that with increasing reinforcement ratio, the ultimate load of beams was increased, but the failure mode was changed from fracture of PVA‐ECC in the tension zone to crushing in the compression zone, thereby limiting the full development of beam ductility. An analytical model is proposed to calculate the load and the vertical deflection of beams. In the model, the tension‐stiffening effect of reinforcement after cracking of PVA‐ECC is considered by defining the bond–slip relationship of reinforcement embedded in PVA‐ECC. Comparisons are made between experimental results in the literature and those calculated by using the analytical model to show the accuracy of the model in predicting the load–deflection relationship, the moment–rotation relationship, and the moment–curvature relationship. [ABSTRACT FROM AUTHOR]

In this work, the theoretical model for predicting the flexural behavior of steel‐reinforced basalt fiber‐reinforced concrete (RBFRC) beams was developed and the results were experimentally validated. The experimental results presented two failure modes of the RBFRC beams including flexural failure and flexural‐shear failure. The load‐carrying capacity, deformation ability, and crack resistance of RBFRC beams failing in flexure can be significantly enhanced with the addition of chopped basalt fiber. To verify the theoretical model, the predicted results were compared with the experimental results of RBFRC beams, and the relative error between the two methods is very small. Based on the theoretical method, a parametric study was conducted to identify the influence of several crucial materials and structural parameters on the flexural behavior of RBFRC beams. [ABSTRACT FROM AUTHOR]

The present investigation deals with the flexural behavior of a new type of Hybrid steel, polypropylene Engineered Cementitious Composite (Hf‐ECC) ‐ Lightweight Aggregate Concrete (LWAC) encased Hybrid Steel Truss Composite (HSTC) beams and detailed parametric study of HSTC beams using Abaqus. Eight simply supported beams fabricated with identical hybrid steel truss, but with varying depths and layer arrangement of Hf‐ECC and LWAC were experimentally tested to investigate the effects of Hf‐ECC depth of HSTC beam on the ultimate load‐carrying capacities and failure modes. Test results show that cracking, yield, ultimate moments, and the ductility of HSTC beams are improved by increasing the depth of Hf‐ECC due to the excellent tensile properties of Hf‐ECC. In addition to the above enhancement, it is also found that the combined use of Hf‐ ECC and LWAC could improve the beams' general ductility and considerable energy dissipation capacity due to Hf‐ECC's excellent deformation ability besides reducing beams' weight. In addition to experimental work, a finite element model is used to predict the load‐deflection behavior of Hf‐ECC and LWAC‐encased HSTC beams. [ABSTRACT FROM AUTHOR]

This paper experimentally investigated the flexural and ductile behaviors of ultra‐high‐performance concrete (UHPC) beams. The failure modes, deflection, ductility, concrete strain, and reinforcement strain were tested using eight UHPC rectangular beams. The experimental parameters were the reinforcement ratio, the reinforcement diameter, and the UHPC cover thickness. The experimental results showed that all specimens exhibited flexural failure characterized by the yielding of steel rebars, multiple micro‐cracks, one localized macro‐crack, and slight crushing of UHPC. It was concluded that increasing the reinforcement ratio significantly enhanced the stiffness, flexural capacity, and ductility of the rebar‐reinforced UHPC beams, whereas showed little effect on their cracking load. Meanwhile, both the reinforcement diameter and UHPC cover thickness in the range investigated here had little influence on the flexural performance of UHPC beams in the elastic stage and crack development stage, whereas exhibited different influences in the yield stage. Besides, increasing the reinforcement ratio was in favor of presenting the deflection‐hardening behavior, while the reinforcement diameter and UHPC cover thickness had little influence on the deflection‐hardening behavior. The analytical models were established to predict the yielding load, peak load, and ultimate load of rebar‐reinforced UHPC beams, and the predictions showed good agreement with the experimental results in this study. Also, the steel reinforcement could show a dominant role in the bearing capacity by increasing the reinforcement ratio. A post‐yielding capacity factor λ was proposed, which could reasonably evaluate the deflection‐hardening and deflection‐softening behavior of UHPC flexural members in the present study. Based on other experimental results collected in literature, three different ranges for the post‐yielding capacity factor, namely, λ ≤ 0.7, 0.7 < λ < 0.9, and λ ≥ 0.9, were identified, corresponding to the deflection‐softening behavior, transition stage, and deflection‐hardening behavior, respectively. [ABSTRACT FROM AUTHOR]