Stirrup Ratio Research Articles

Finite element analysis of the seismic performance of PVC-CFRP confined concrete column-ring beam interior joints

This paper presents a finite element (FE) analysis of the seismic performance of PVC-CFRP confined concrete column-ring beam interior joints (PCCC-RBIJs) under low cyclic loading. Based on the constitutive relationship of materials, a FE model was established using ABAQUS and validated against the experimental results of ring beam joints found in the literature. Then, FE parametric analysis was performed to investigate the influence of studied parameters on the seismic performance of the PCCC-RBIJs. These studied parameters included the axial compression ratio, height-diameter ratio of the ring beam joint, column longitudinal reinforcement ratio, reinforcement ratio and stirrup ratio of ring beam, and joint concrete strength. The FE analysis showed that the seismic performance of PCCC-RBIJ specimens can be enhanced by increasing their axial compression ratio, column longitudinal reinforcement ratio, and ring beam reinforcement ratios or decreasing their height-diameter ratio of the ring beam joint. Although the joint concrete strength and ring beam stirrup ratio have little effect on the seismic performance of the joint, the ring beam stirrup ratio affects the stirrup utilization. The paper also provides design suggestions for PCCC-RBIJs.

Axial compressive behavior of steel reinforced GGBS-RFBP-FA ternary composite geopolymer recycled fireclay brick aggregates concrete columns

In this study, the axial compressive behaviors of steel reinforced ternary composite geopolymer recycled fireclay brick aggregates concrete columns were investigated. The ternary binder material used in this study was produced by the combination of industrial by-products (i.e., granulated blast furnace slag (GGBS), recycled fireclay brick powder (RFBP), and fly ash (FA)) and alkali-activated solution. A total of 60 square steel reinforced composite columns (with a 200-mm side length and 600-mm height) were tested under axial compression. The tested variables included the mix proportion of ternary composite geopolymer concrete with recycled aggregates containing recycled fireclay brick aggregates (GRA-RFBAC), the recycled coarse aggregate replacement ratios (0%, 30%, 50%, 70%, 100%), the longitudinal reinforcement ratios (1.13%, 2.01%), and the hoop stirrup reinforcement ratios (0.81%, 1.62%). Each group contained three identical samples. The ductility, failure mode, and axial load-bearing capacity of the columns were recorded and analyzed. The experimental results revealed that the damage progression and patterns of steel reinforced GRA-RFBAC columns were similar to those of ordinary Portland cement based recycled concrete columns. The ultimate bearing capacity of steel reinforced GRA-RFBAC columns decreased with an increasing replacement ratio of recycled coarse aggregate and increased with an increasing reinforcement ratio of longitudinal and hoop stirrups. Meanwhile, the stress-strain model of steel reinforced GRA-RFBAC columns under axial compression was proposed based on the experimental results. The present study suggests an efficient and environmental-friendly compression member.

Influence of joint forms on the seismic behavior of concrete-filled PVC-CFRP tubular column-RC beam joints connected with core steel tubes

To examine the effects of joint forms on the failure mode, hysteretic behavior, ductility and energy dissipation capacity of concrete-filled PVC-CFRP tubular column-RC beam connected with core steel tubes (“RC beam” for short), low-cycle reversed loading tests on 13 cross-joints and 11 T-joints were designed and conducted. The findings demonstrate that the core regions of both joint types experience normal shear failure. Less flexural cracking is present in the RC beams of T-joints, but the concrete crush failure is severer in the joint core area and mostly occurs on the ends of the cantilever beams. The seismic behaviors of both joint forms alter in the same pattern with an increase in the radius-thickness ratio of the core steel tube, the joint area stirrup ratio and the steel ratio. With a rise in the axial compression ratio, the ductility of the cross joints improves but the energy dissipation capacity shows no evident change, while both decrease for the T-joints. The cross joints show better energy dissipation capacity in the whole test. As the reinforcement ratio of the beam longitudinal reinforcement rises, the cross joints show a decrease in ductility and energy dissipation capacity, while T-joints have the exact opposite effect. The seismic behavior of core steel tube joints throughout the whole test is unaffected by CFRP strip spacing.

Parametric Study on Seismic Performance of Slender T-Shaped RC Walls Subjected to Biaxial Loading

To investigate the effects of parameters on the seismic performance of slender T-shaped RC walls subjected to a biaxial seismic action, a numerical model was established using a fiber-based cross-section and displacement-based beam–column element. The axial load ratio, shear span ratio, flange width to web height ratio, concrete strength grade, stirrup ratio, and longitudinal reinforcement ratio were selected for the parametric study, and the effects of these parameters on the performance degradation under biaxial loading were investigated. Furthermore, a sensitivity analysis of various parameters for the decrease was conducted. The results showed that the bearing and deformation capacities under biaxial loading were both decreased, and the total energy consumption was greater than that under uniaxial loading. The impacts of different parameters and loading paths on the decrease extent were significantly different, and the overall reduction was greater in the flange direction than in the web direction. Under the square loading path, the T-shaped wall had the greatest reduction in its seismic performance, followed by the eight-shaped and cruciform loading paths. The changes in the axial load ratio, shear span ratio, and concrete strength significantly affected the performance degradation under biaxial loading. Accordingly, it is recommended to reasonably consider the values of these three parameters in a multidimensional seismic design to maintain safety redundancy.

Study on restraint coefficient of the stirrups-stiffened square concrete filled double-skin steel tube axial compression stub columns

This paper proposes a novel structural design for stirrups-stiffened square concrete-filled double-skin steel tubular stub columns (SCFDST) that offers high capacity and superior advantages in terms of low consumption of concrete and steel, as well as economic efficiency. The study includes an axial pressure test on two sets of 8 SCFDST columns with varying hollow ratios and stirrup ratios, with a specific focus on the influence of stirrups on mechanical properties. Experimental results demonstrate that stirrups significantly enhance the mechanical properties of SCFDST columns with large hollow ratios, including stiffness, bearing capacity, and ductility, with a more pronounced effect observed as the stirrup ratio increases. A three-dimensional solid finite element (FE) model of the SCFDST columns is developed and validated using ABAQUS software and appropriate constitutive models. Parameter analysis is then conducted based on the FE model, revealing that the stirrups not only restrain the concrete itself but also provide additional restraint by limiting the deformation of the steel tube. This improvement effect was more significant in the middle of steel tubes section. When stirrup ratio was 0.015, the steel tube had the highest constraint efficiency on the concrete. The study introduces a constraint enhancement factor to represent the enhanced restraining effect of stirrups on the steel tube, which is incorporated into a fresh equation for determining the maximum bearing capacity (Nu) of SCFDST columns. The derived formula offers clear physical meaning and high accuracy, building upon the existing formula for CFDST columns.

Experimental and numerical study of stirrup‐confined concrete‐filled L‐shaped steel tube stub column under axial compression

AbstractIn this paper, three concrete‐filled L‐shaped steel tube (CFLST) stub columns subjected to axial compression were tested, with one normal CFLST stub column and two stirrup‐confined specimens. The investigation focused on the effect of the equivalent stirrup ratio on ultimate bearing capacity, axial compression stiffness, ductility factor, and strain ratio of the columns. 3D finite element (FE) models of the specimens were constructed and verified against the tests results and data from literature Parametric analysis was carried out to analyze the influence of different section length–width ratios, steel ratios, material strength grades, and equivalent stirrup ratios on the ultimate bearing capacity. Additionally, the confinement effect of stirrups on the core concrete was analyzed. By generalizing the stress nephogram of the core concrete at the ultimate state and considering the equilibrium of forces, a formula was proposed for calculating the ultimate bearing capacity of the stirrup‐confined CFLST stub column under axial compression using the superposition method. The accuracy of the proposed formula was demonstrated by comparing its results with experimental results, FE model results, and those proposed by other scholars.

Plastic Properties of Prestressed High-Strength Steel Reinforced Concrete Continuous Beams

In this paper, the plastic properties of prestressed high-strength steel reinforced concrete (PHSSRC) beams are studied, by performing static load tests on eight built-in Q460 and Q690 prestressed high-strength steel reinforced concrete continuous beams and one built-in Q355 prestressed steel reinforced concrete (PSRC) continuous beam. The design parameters of the specimens were the steel strength grade, the steel ratio, the comprehensive reinforcement ratio, and the stirrup ratio. The failure mode, load–deflection curve, internal force redistribution ability, curvature ductility, plastic hinge performance, and moment modification coefficient of continuous beams under the influence of various parameters were analyzed to measure the plastic performance of the continuous beams. These results show that after the plastic hinge is formed in the middle support and mid-span of the prestressed high-strength steel reinforced concrete continuous beam, the test beam eventually becomes a rotating mechanism and is destroyed with increasing load. The built-in high-strength steel can significantly improve the bearing capacity of the specimen, and the maximum increase in the bearing capacity is 37.3%. The specimen still has a high bearing capacity after reaching the ultimate bearing capacity. With a decrease in the steel ratio, the degree of internal force redistribution is deepened, the curvature ductility is improved, and the plastic performance is enhanced. Increasing the comprehensive reinforcement ratio and the stirrup ratio can improve the plastic performance of the specimen. The calculation formula of the equivalent plastic hinge zone length is proposed. The calculation formula of the moment modification coefficient, with the relative plastic rotation angle and relative compression zone height as independent variables, is established. When the relative plastic rotation angle is not greater than 0.829 × 10−5, the moment modification coefficient increases with increasing plastic rotation angle and is not greater than 0.37. In the range of 0.3~0.4, the moment modification coefficient decreases with increasing height of the relative compression zone.

Study on the oblique seismic behavior of reinforced concrete L-shaped columns strengthened with carbon fiber reinforced polymer slabs

The oblique seismic performance of reinforced concrete L-shaped columns is an important factor that affecting the safety of structures. However, there is limited research on the oblique seismic performance of reinforced concrete L-shaped columns strengthened with carbon fiber reinforced polymer (CFRP) slabs mounted at the column bottom. In order to address the theoretical gap and meet the practical requirements, finite element analyses were conducted on L-shaped reinforced concrete columns. These analyses considered various parameters, including loading angle, strengthened method, volume stirrup ratio and axial compression ratio. The seismic performance indexes of L-shaped columns such as failure state, hysteretic curve, skeleton curve, carrying capacity, and ductility are investigated. The analyses results show that the failure mode of L-shaped column is bending failure, and the seismic performance of strengthened L-shaped column is better than that of unstrengthened L-shaped column. The CFRP slabs mounted at the column bottom could increase the peak carrying capacity and decrease the ductility coefficient of specimen. Therefore it is suggested to employ the method of strengthening column bottom by CFRP slabs in practical engineering application. Moreover, the peak carrying capacity of specimens under different loading angles is similar. With a higher loading angle, the positive peak carrying capacity of specimen increases, while the negative peak carrying capacity decreases. Finally, this study presents a novel method for determining the compression-bending carrying capacity of reinforced concrete L-shaped column, where the influence of torsion action is taken into account. This method offers valuable insights for the engineering design.

Prediction of fatigue lives for steel beams and steel reinforced concrete beams

With the wide application of steel reinforced concrete (SRC) beams, the problem of fatigue has become increasingly prominent. To deeply understand the fatigue performance of SRC beams, a finite element analysis (FEA) about fatigue failure process of SRC beams was performed. The internal H-steel inside SRC beam (SRCH-steel) was shown to possess similar fatigue failure characteristics to steel beam and exert a deciding influence on the fatigue resistance of SRC beam in previous experiments. Therefore, FEA of fatigue crack growth (FCG) was conducted using a fully-automated remeshing technique for steel beam first. Comparisons were made and a good agreement was found between predicted and experimental fatigue lives. The average value of ratio between predicted and experimental fatigue lives for the five steel beams is 1.149, which verifies the accuracy of FEA model. Then, based on the FEA model of steel beam, rebars and external concrete were included to simulate fatigue failure process of SRC beams. The results suggest that the average value of ratio between predicted and experimental fatigue lives for SRCH-steels inside the thirty-nine SRC beams is 1.191, and the average value for tensile rebars is 1.212, which indicates that the numerical model is accurate and reliable. At last, further analysis about influences of critical parameters on fatigue performance of SRC beams was conducted, such as nominal stress range, steel ratio of SRCH-steel, steel ratio of tensile rebars, fatigue strength of tensile rebars, shear span-to-depth ratio, concrete strength grade and stirrup ratio.

Numeričko ispitivanje učinka uvjeta oslanjanja na posmično ponašanje grede u armiranobetonskim gredama realnih veličina

In studies on beams in the literature, the beam elements are designed and tested as simply supported. Therefore, in this study, the behaviour of reinforced concrete (RC) beams under fixed support conditions was numerically investigated using ANSYS finite element software. The variables used in the study are the shear span/effective depth ratio (a/d) and stirrup spacing of the analysed specimens. In this study, 16 RC beams on a 1/1 scale were analysed in 4-point bending protocol. The a/d ratios were assumed to be 1.0, 2.0, and 3.0, in the test members produced. In addition, as another variable, the lateral reinforcement amount was designed and analysed at f8/75, f8/150 and f8/300 mm spacings without stirrups. Load-displacement and stiffness graphs are drawn based on the numerical results. The numerical results were interpreted and compared based on the graphs drawn for each analysis, stress distribution, and damage occurrence in the experiments. The results indicated that the a/d ratio and number of stirrups had strong effects on the behaviour of the fixed supported beams. The results of the beam analyses obtained using ANSYS finite element software were consistent with the experimental results.

Research on Nonlinear Behavior of Local High-Performance Concrete Beam-Column Connections.

The seismic performance index of prefabricated structures is generally obtained via experimental analysis. However, in experimental research, it is impossible that every influencing factor can be taken into account. Therefore, the finite element analysis method can be used as a supplementary method for experimental research to carry out parametric analysis of joints. Based on this test, a hysteretic model of steel bars is developed on the ABAQUS platform; meanwhile, the model is used to simulate the seismic analysis of the proposed local reinforced joints. The hysteresis curve obtained via simulation exhibits a high degree of coincidence with the experimental results. Based on the validated model, a detailed parameter analysis of prefabricated local reinforced concrete frame joints is carried out. The analysis results illustrate that the axial pressure ratio at the top of the column has a minimal impact on the joint's performance. Decreasing the stirrup ratio within the core region, enlarging the diameter of the PC steel bar, and increasing the concrete strength that is poured in the keyway and the core region can raise the cumulative energy consumption of the joints, thereby reducing the damage degree of other units and improving the maximum bearing capability of the joints.

Experimental study on seismic behavior of RC beams confined by corroded stirrups

PurposeTo understand the seismic behavior of reinforced concrete (RC) beams confined by corroded stirrups, low-reversed cyclic loading tests were carried out on seven RC beam specimens with different stirrup corrosion levels and stirrup ratios to investigate their mechanical characteristics.Design/methodology/approachThe failure mode, hysteresis behavior, skeleton curves, ductility, stiffness degradation and energy dissipation behavior of RC specimens are compared and discussed. The experimental results showed that the restraint of concrete provided by corroded stirrups is reduced, which leads to a decline in seismic performance.FindingsFor the specimens with the same ratios of stirrup, as the corrosion level increased, the load-carrying capacity, stiffness, plastic deformation capacity and energy-dissipation capacity dropped significantly. Compared with the uncorroded specimen, the failure modes of specimens with high corrosion level changed from ductile bending failure to brittle failure. For the specimens with the same levels of corrosion, the higher the stirrup ratio was, the stronger the restraint effect of the stirrups on the concrete, and the seismic behavior of the specimens was obviously improved.Originality/valueIn this paper, a total of seven full-size RC beam specimens at joints with different stirrup corrosion levels and stirrup ratios were designed and constructed to explore the influences of corrosion levels and stirrup ratios of stirrups on the seismic performances. The failure modes, strain of reinforcement, hysteretic curves, skeleton curves, stiffness degradation and ductility factor of RC specimens are compared and discussed.

Effect of different configurations of end stirrups on the seismic performance of RC columns

To improve the seismic performance of reinforced concrete (RC) columns, this paper establishes the equations for the theoretical relationship of bending-shear resistance of RC columns based on the theory of truss and arch. Tests and finite element simulations are carried out on six groups of specimens with the same main reinforcement but different stirrup configurations and stirrup ratios. Based on theoretical calculations, test data, and simulation results, the hysteresis curves, failure modes, compressive deformations, main reinforcement deformations, and deformations at the ultimate limit state of carrying capacity of the RC columns are investigated. Moreover, the feasibility of adjusting the stirrup configurations and stirrup ratio for controlling the damage location at the end of the column is discussed. The comparison of the results shows that the hysteresis curves obtained from the tests and the finite element simulations are in general agreement, verifying the correctness of using the concrete plastic damage model for modeling. In addition, the theoretical results based on the theory of truss and arch are closer to the test results, which also proves the reliability of the theory. By analyzing the results, the relationship between the ratio of the test and theoretical values (Z) and the stirrup ratio (ρw) is summarized through fitting. Under the ultimate limit state of carrying capacity, it can be concluded that the encryption of the stirrup reinforcement at the end of the column can retard the crack development and reduce the shear deformation. Overall, the computational method proposed in this paper has high accuracy in predicting column cracks and detecting the ultimate load-carrying capacity.

Study on seismic performance of prestressed composite joint with CESA columns

Several issues persist in the design and construction of conventional prestressed concrete encased steel (CES) frame structures. This includes the need to strengthen the steel flanges and webs during the passage of prestressed tendons and longitudinal reinforcements through the joint, and insufficient compaction of the concrete cast in the joint core. Therefore, a novel type of prestressed CES frame structure was developed using concrete-encased steel angle (CESA) columns to replace the conventional CES columns. To investigate the seismic shear performance of this new type of prestressed composite joints to propose a method for predicting the shear capacity of joint cores, this study performed tests and nonlinear analysis on three prestressed joints and one non-prestressed joint under low cyclic loading. The failure patterns, energy dissipation, stiffness degradation, deformation recovery performance, and ductility properties were examined for these joints. The effects of prestress level, axial compression ratio, web thickness, stirrup ratio, and steel angle ratio are also discussed. Two formulas are proposed to predict the shear capacity of joint cores based on the fitting of tests and finite element analysis. The results revealed that the oblique crushing of concrete occurred in the joint core at the peak load, resulting in shear failure. Increasing the thickness of the steel web effectively enhanced the horizontal peak load to increase the shear capacity in the joint core. However, an increase in the axial compression ratio may reduce ductility. The formulas developed to predict the shear capacity of the joint core exhibited much higher accuracy, where the simplified practical formula can facilitate convenient design implementation. Overall, these findings demonstrate excellent seismic shear behavior for prestressed composite joints while providing technical support for applications in such types of prestressed frame structures.

Effect of ultra‐high performance concrete repair layer thickness on the behavior of concrete columns

AbstractThe use of ultra‐high‐performance fiber reinforced concrete (UHPFRC) to repair or rehabilitate old concrete structures has been shown to be appropriate due to its properties, such as higher compressive strength, ductility, and durability than conventional concretes. One of the studied strengthening techniques is the reinforced concrete columns jacketing by UHPFRC. Some recent research evaluated some parameters, such as the repair thickness and the volumetric ratio of stirrups. However, other important parameters, such as UHPFRC jacketing thickness in different column cross‐sections and the concrete core compressive strength, need to be addressed. In addition, the analytical models presented in the literature are restricted to only one concrete grade. The present study aims to evaluate the behavior of short reinforced concrete columns strengthened with UHPFRC subjected to centered compression. Numerical analyses of three‐dimensional models were performed using the finite element method, validated, and calibrated using experimental results. The influence of the concrete core compressive strength, the UHPFRC jacketing thickness, and the shape of the cross‐section were evaluated. Numerical simulations concluded that the lower concrete core compressive strength columns showed the best relative increase performance. Moreover, the concrete core strength was inversely proportional to the resistance capacity of the repair system. In addition, the increase in repair thickness contributes to the axial strength of the column. Furthermore, the cross‐section influences the distribution of stresses and strains, showing the best performance for circular sections. Finally, regardless of cross‐section type, the proposed equations accurately predicted the numerical results.

Residual performance of hollow RC piers damaged by rockfall impact

Recently, hollow reinforced concrete (RC) piers have been increasingly utilized in bridge structures located in mountainous regions, owing to their high strength-to-mass ratio and stiffness-to-mass ratio. Among various natural disasters, rockfall poses a major threat to the serviceability and safety of bridge piers, potentially leading to a reduction in bearing capacity or even complete collapse. Given the critical nature of repairing or reinforcing bridges, this paper aims to enhance the understanding of the residual performance of hollow RC piers against rockfall impact. A simulation framework for hollow piers subjected to rockfall impact is developed using LS-DYNA and validated against available experimental data. Utilizing this validated framework, extensive numerical simulations have been conducted to investigate the effect of various parameters such as impact energy, longitudinal reinforcement ratio, stirrup ratio, and axial force ratio on the localized damage patterns and residual capacity of hollow piers. In addition, the relationship between the rupture width of the front panel and the resulting reduction in axial capacity is discussed. These results indicate the impact force and resistance mechanism of hollow piers are governed by the interaction between the rockfall and hollow section. The rupture width of the front panel notably increases with the impact energy, and increasing the stirrup ratio could reduce the concrete spalling. However, the axial force demonstrates minimal influence on the localized damage of the front panel when the rockfall diameter is less than the front panel width. The residual capacity of an impact-damaged hollow pier mainly relies on the rupture width of the front panel. These findings would contribute to the fast prediction of the residual capacity of hollow RC piers after rockfall impact.

Numerical simulation of size effect in concrete-encased high-strength steel columns under axial compression

Concrete-encased steel (CES) columns are extensively utilized in practical engineering due to their outstanding performance. However, there have been limited studies on the size effect of CES columns. To investigate the influences of stirrup ratio, steel ratio, and steel strength grade on the axial capacity and the mechanism of the size effect of members under axial compression, a finite element (FE) analysis model that considers the interaction between the size effect and the confinement effect is established and verified. The study results demonstrate that the nominal stress of CES columns can be remarkably increased by employing high-strength steel and enhancing the steel ratio. However, the nominal stress decreases as the cross-sectional size of specimen increases, indicating the presence of the size effect. Moreover, increasing the steel strength grade, stirrup ratio, and steel ratio can decrease the degree of reduction of the nominal stress. Furthermore, comparison of the FE analysis findings and the calculation results of EN1994–1–1:2010(Europe), AISC360–16 (U.S.), and JGJ138–2016(China) revealed that the three codes fail to accurately assess the axial capacity of CES columns. The accuracy and safety reserve of the codes calculation results are even more inadequate for the larger cross-sectional specimens. Finally, a theoretical formula that considers the size effect and confinement effect is developed to calculate the bearing capacity of CES columns, and its applicability and reliability are verified.

Experimental study of interfacial bonding performance between section steel and ultra high-performance concrete

The key to fully exploiting the benefits of section steel and ultra high-performance concrete (UHPC) is to improve their bonding. The primary goal of this study was to investigate the interfacial bonding performance between these two materials. Section steel - reinforced ultra high-performance concrete (SSRUHPC) and section steel-reinforced concrete (SSRC) specimens were subjected to push-out tests. Failure modes, load-slip (PS) curves, and strain distributions were studied, and the experimental results showed that the PS curves of all specimens have a similar trend: a no-slip stage followed by a slip stage, a failure stage, and a residual stage. By increasing the cover thickness and stirrup ratio and lowering the embedded length, the bond strength between the section steel and UHPC may markedly increase. The results of this study show that the bonding between section steel and UHPC is superior to that between section steel and ordinary concrete. Finally, after carefully considering the experimental results, regression formulae for the SSRUHPC bond strength were developed, and the computed results were found to be accurate. Unlike other bond strength formulae, the formulae in this study consider the influence of the stirrup ratio on the bond strength, and the R2 values range from 0.763 to 0.961.

Reliability-based design method for shear capacity of steel reinforced engineered cementitious composites (ECC) beams

Engineered cementitious composites (ECC) is famous for its excellent tensile deformability and crack width control ability. Steel reinforced ECC beams under shear loading exhibit brittle behaviors, which leads to a lack of structural safety. The reliability-based shear capacity model of steel reinforced ECC beams needs to be established for ensuring the structural shear safety. In this research, a test database of steel reinforced ECC beams under shear loading was constructed based on the given selecting principles. Through considering the shear resistance provided by fibers, the shear capacity model of steel reinforced ECC beams was preliminary established. The statistical characteristics of random variables were described and determined, and reliability index was calculated through Monte Carlo simulation. It is found that reliability index increases with increasing ECC strength, while decreases with increasing stirrup strength or stirrup ratio, especially at the high partial factor of ECC. For different target reliability indexes, the recommended partial factors of ECC are obtained through calibration. This research supplies a useful reference for the shear design of steel reinforced ECC beams in the actual engineering.

Shear performance evaluation of damaged RC beams strengthened with cast-in-place U-shaped UHPFRC shell

The shear behavior of reinforced concrete (RC) beams may degrade during service, necessitating effective strengthening interventions for these shear-degraded RC members. This study aims to investigate the shear performance of damaged RC beams strengthened by a cast-in-place U-shaped ultra-high performance fiber reinforced concrete (UHPFRC) shell. Four-point flexural tests were performed on one un-strengthened and four UHPFRC shell-strengthened damaged RC beams. In this study, different pre-damage levels for the RC beams (55%, 70%, and 85%) and stirrup ratios within the UHPFRC shell (0.7% and 1.34%) were considered. The failure mode, ultimate capacity, and ductility of these tested RC beams were assessed. The results indicate that the shear capacity of the strengthened beams can be greatly improved by a U-shaped UHPFRC shell, reaching 2.7–3.0 times that of the un-strengthened beams. As the stirrup ratio increased from 0.7% to 1.34%, the failure mode of the strengthened beams changed from shear compression failure to flexure failure, and the ductility increased from 1.56 to 1.96. However, the shear capacity of strengthened beams is slightly influenced by the pre-damage level of the RC beams. Moreover, planting steel rebars at the UHPFRC-RC interfaces effectively improved the interfacial bonding performance. Finally, the shear capacity of the strengthened beams was evaluated by a truss arch model, and the calculated results of the truss arch model are safe as the lower limit of shear capacity.