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Compression yielding structural system. (a) CY block cast into an RC beam; (b) test results of CY beams.
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Safety margin and construction costs are two conflicting goals for a structure. By providing a fuse in a structure that is triggered at a certain level of over-loading, further increase of loading is prohibited and failure of the structure is changed to a safer mode. As overloading is controlled and a safer failure mode is enforced, a fused structu...
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Context 1
... biggest challenge in realizing compression yielding (CY) was to find a suitable CY material. Material scientists have claimed that such a material does not exist. After extensive research works, an ideal material for CY, slurry infiltrated fiber concrete (SIFCON) with perforation ( Fig. 2(a)), was made [22]. SIFCON is an existing material that is much more ductile than other cement materials [23], as shown in Fig. 3. However, it still cannot satisfy the excessive ductility demand of a CY system [24]. By providing perforation (holes) inside a SIFCON block, the material becomes an ideal CY material as shown by the SIFCON ...
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... perforation (holes) inside a SIFCON block, the material becomes an ideal CY material as shown by the SIFCON P-block in Fig. 3. More details of the CY material can be found in Ref. [22]. Experimental, numerical and analytical studies on CY beams and columns demonstrated that this new method is not only feasible but also highly effective ( Fig. 2(b)) that can lead to potentially unlimited ductility ...
Context 3
... before the tension reinforcement reaches its fracture stress. Apart from providing ductility, the CY block can also act as a fuse in the structural system. When accidental excessive loading occurs, the fuse can be designed to activate and force the structural system to deform excessively but in a ductile manner in the fuse location, as shown in Fig. 2(b). When excessive deflection is observed, further overloading can be stopped and subsequent dangerous failure modes such as abrupt FRP rupture, concrete crushing, or shear failure can be ...
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This paper investigates the axial behaviour of square and circular concrete specimens confined by externally bonded Fibre Reinforced Polymer (FRP) jackets. Axial compression tests were performed on 96 regular and rubberised concrete specimens. The parameters considered were rubber content (0% and 60%), section shape (circular and square), FRP type...
Citations
... Based on a fundamental understanding of plastic deformation, a new concept named compression yielding was proposed by Wu et al. [12] (Figure 1c), which can effectively meet the ductility requirement of FRP-RC beams. The ductility of the structure can be achieved by a special component with adequate strength and ductility in the compression area [13], i.e., CY block ( Figure 2). When an overload occurs, the CY block will force the structure to deform in a plastic manner to avoid the abrupt rupturing of the FRP bar or the crushing of concrete. ...
... Based on Equations (2)- (13), at the onset of M m , the FRP tension force (F f ) and the curvature κ m of the CY beam are provided as follows: ...
Fiber-reinforced polymers (FRPs) provide promising prospects for replacing steel bars in traditional reinforced concrete structures. However, the use of FRP as tension bars in concrete beams leads to insufficient ductility because of its elastic characteristics. A newly developed compression-yielding (CY) beam has successfully solved this issue. Instead of tensile reinforcement yield, the ductile deformation of a CY beam is realized by the compression yield of a CY block in the compressive region. Another important feature is that the CY block is also the fuse of the beam, where material damage to the beam is concentrated in the CY block region and can be easily replaced. As a load-bearing recoverable and ductile structure, it is necessary to conduct a reliability-based design analysis and recommend reduction factors for this new structure. In this study, the function for calculating the failure probability of CY beams is proposed, semi-probabilistic design recommendations are presented, and Monte Carlo simulation (MCS) is adopted as a reliability analysis method. This study discusses the influence of the possible characteristics of the critical variables on reliability and provides the reliability index with different reduction factors to guide the design of the CY beam. These analyses indicate that the reliability index can be improved from the material design of the CY block in greater strength fb, smaller depth, smaller coefficient of variation of fb, and yield modulus ratio ξ. This study also shows that compared with the design of FRP concrete beams, the ductile failure mode of the CY beams allows a lower safety factor to meet safety requirements, which significantly reduces construction costs and avoids over-designing the load-bearing capacity.
... This is because the flexural capacity of the sections containing the block is decreased by the decreased compressive yield strength, so that the damage mainly falls inside the section with the block as shown in Fig. 19(b). A similar concept has also been proposed by Wu et al. [41], in which the CY block is suggested to be designed as a structural fuse to absorb the damage and thus to enhance the flexural ductility. In summary, when the flexural capacity of P peak , Δ peak : Loading capacity and corresponding deflection, numbers in brackets indicate improvement or reduction; K uc , K cr : Uncracked and cracked stiffness; E uc , E cr : Energy absorption at uncracked stage and after cracking until failure. ...
Fibre-reinforced polymer (FRP) bars are used in concrete structural members to tackle the corrosion problem of steel bars. However, the brittle rupture of FRP bars results in relatively low ductility of such concrete members. This paper numerically investigates the feasibility of using compression yielding (CY) block to enhance the ductility of FRP bar reinforced concrete beams. A finite element model is developed to study the behaviour of beam adopting the CY block, followed by a parametric analysis on the effects of material properties and geometry of the CY block. The results indicate that the adoption of CY block changes the failure mode of the beam from brittle concrete crushing to ductile compression yielding, increasing both the loading capacity and ductility of the beam. Increasing the compressive yield strength of the CY block can effectively increase the loading capacity but decrease the ductility of beams. A higher compressive ultimate strength of the CY block also increases the loading capacity but has limited effect on the beam ductility. In addition, the beam ductility can be increased by reducing the yielding and ultimate strains of the CY block, while the loading capacity can be enhanced by higher yielding strain or lower ultimate strain. It is revealed that sufficient CY block is required to prevent concrete crushing in the compression zone, and an increase in CY block height improves the beam ductility. The CY block length should cover at least the pure bending zone when the section with the block has higher flexural capacity than that without the block, otherwise the length can be controlled as the theoretical plastic hinge length.
... It can be seen from Figure 19 that under the same r, a CY block with a larger h value can reach a much higher ultimate bearing capacity compared with that of a CY block with a smaller h, but the elastic limit of the two cases is close. For example, it can be found that the CY block with h = 0.8 can obtain a larger yield strength-to-peak strength ratio than the CY block with h = 1.0, which is more in line with the ideal requirement of CY block used as the structural fuse [26]. Thus, it can be inferred that a smaller h will further reduce the yield strength-to-peak strength ratio. ...
On one hand, the nature of linear elastic up to brittle rupture hinders the application of fiber-reinforced polymer (FRP) bars as reinforcement in the concrete member due to the displacement ductility demand of structures. On the other hand, FRP bars are equipped with many irreplaceable advantages as reinforcement in concrete structures. To resolve this contradiction, a possible solution is to use the so-called compression yield (CY) structural system and the ductility of a concrete beam incorporating a CY system comes from the compressive side rather than the tensile side. Thus, the development of material in the compressive side (CY material) with well-designed mechanical properties (strength, stiffness, and ductility) is a key challenge. In this study, the CY material is developed by perforating the mild steel block and then substantiated by the test results. Then, experimentally calibrated finite element models are used to conduct systematic parametric studies, based on which parametric equations are proposed to predict the stiffness and ultimate strength of the CY material. Finally, theoretical constitutive models are developed to predict the stress–strain response of perforated steel block under compression and a reasonably acceptable agreement is reached between the model predictions and the test results.
... Thus, holes arranged in a manner of an isosceles triangle (h = 1) will result in a much larger ultimate stress to yield stress ratio. Using the concepts of CY material [11] and structural fuse [15], holes arranged in a manner of an isosceles triangle (h = 0.886) will be better in terms of maintaining strength under an extraordinarily large strain. In a CY structural system, if the stress continuously increases with strain in a CY material, though the member deformation can be enhanced, the resultant stresses in the longitudinal reinforcement and adjacent area of the CY block will also increase. ...
... Notably, during the whole deformation process of the CY material, the strength should be maintained or only fluctuate within a small range. For a ductile CY block used as a structural fuse, ductility performance is another important index to evaluate [15]. The stress at the elastic limit is defined as σ y , and the strain corresponding to this point is ε y . ...
One key obstacle restricting the application of fiber-reinforced polymer (FRP) bars from being used as reinforcement in structural concrete is the significantly reduced ductility because FRP under tension is linear elastic up to brittle rupture at small strain. Recently, a new structural concept, compression yielding (CY), has been proposed as a way to overcome the insufficient ductility of concrete structures reinforced with FRP bars or other non-ductile materials. In the CY structural system, the compression-zone of normal concrete is replaced by a ductile material within the plastic hinge. This enables the flexural deformation to be achieved by the compressive deformation of CY material rather than a tensile deformation of longitudinal reinforcing bars. To this end, an ideal CY material requires strength to be maintained during the extraordinarily large deformation process. This study tries to identify methods for developing this kind of CY material by designing and optimizing perforations inside a mild steel block. The effects of key parameters, including ratio, diameter, and arrangement of perforations on the stiffness, strength, and ductility of CY materials were experimentally investigated. In addition, a finite element (FE) model was developed to predict the behavior of the proposed CY material.
Fibre reinforced polymer (FRP)-reinforced concrete beams usually encounter brittle failure due to the linear behaviour of FRP. To solve this issue, compression yielding (CY) concept was proposed recently to improve the ductility of FRP-reinforced concrete beams. However, because of the complexity of the compression yielding mechanism, the calculation of flexural capacity and ductility of FRP-reinforced concrete beam with CY block (CY beam) is challenging, especially for the CY beam with T section due to the lack of closed form solution. In this study, an integrated model is proposed based on machine learning method to evaluate the moment capacity and ductility of the CY beam with T section. To improve the prediction accuracy of the artificial neural network model for moment capacity, different activation functions are tested. The section effectiveness of CY beam with T section is evaluated using the proposed support vector machine model, which combines different kernel functions. Gaussian process regression is then employed to predict the ductility of CY beam with T section. It demonstrates that the developed integrated model can produce highly accurate predictions. In addition, a genetic algorithm (GA) is developed for identifying optimal CY beam section design solutions. Finally, the robustness of the model in the optimisation design for the CY beams with rectangular section and T section is demonstrated by using two numerical examples.
Concrete elements reinforced with fibre reinforced polymers (FRPs) have been increasingly applied in civil engineering structures. However, these structural elements are usually suffering from brittle failure caused by either concrete crushing or the sudden rupture of FRP. To solve this common issue, a compression yielding (CY) mechanism was recently developed with the aim of enhancing the ductile behaviour of FRP-reinforced concrete beams. In the present study, the flexural resistance of FRP-reinforced concrete beam with a CY block in the compression zone (CY beam) is analysed, and a closed-form solution is derived for the moment capacity of CY beam. The influence of the uncertainties of the mechanical properties of CY material on the flexural resistance of CY beam are quantified. Engineering reliability analysis is then conducted to obtain the reduction factor for CY beam under different load combinations. A reduction factor of 0.75 for building structural members and 0.70 for bridge structural members are recommended for engineering design. In addition, a reduction factor table is provided considering a wider range of statistical parameters.
