Experimental and analytical investigation of steel fibre-reinforced beam-column connections

ABSTRACT

This research examines the structural efficacy of Reinforced Concrete (RC) beam-column connections constructed with both conventional and fibre-reinforced systems, assessed through experimental testing and analytical modelling. A total of four beam-column specimens were prepared, with dimensions of 150 mm × 200 mm × 1350 mm and 150 mm × 150 mm × 1500 mm. The specimens were tested under monotonic loading at full scale, with both ends restrained as fixed supports. The specimens RCC-C, RCC-3D, RCC-4D, and RCC-5D were scrutinized for various parameters, including load-deflection response, ductility, stiffness, energy absorption, energy dissipation, and modes of failure. The results indicated a gradual increase in load-carrying capacity, rising from 32.46 kN in RCC-C to 47.52 kN in RCC-5D. Concurrently, the tensile strength of steel rebars remained consistent across different diameters, with an elastic modulus of 210 GPa, thereby affirming the quality of the reinforcement. The load-deflection analysis illustrated that both yield and ultimate loads increased with the complexity of the fibre, alongside enhanced deflection capacities and ductility factors, thereby confirming improved deformation tolerance. Energy absorption exhibited a notable enhancement, rising from 32.46 J in RCC-C to 47.52 J in RCC-5D, while the dissipation capacity remained stable, suggesting superior toughness without compromising release characteristics. The modes of failure evolved from brittle concrete crushing in RCC-C to ductile mechanisms characterized by flexural plasticity and shear pull-out in RCC-3D and RCC-4D, with RCC-5D demonstrating crack propagation stability. A comparative analysis of the experimental and analytical findings revealed a near-perfect correlation, with mean ratios of 0.996 for deflection and 0.994 for load, accompanied by minimal statistical variation, thereby validating the precision of finite element modelling. The results affirm that advanced reinforcement systems substantially enhance strength, ductility, and energy absorption while ensuring predictable performance, rendering fibre-reinforced beam-column connections exceptionally reliable for contemporary structural applications. The specimens exhibited a gradual enhancement in load-carrying capacity, with values increasing to 14.73% (RCC-3D), 33.58% (RCC-4D), and 46.40% (RCC-5D), relative to the control specimen (RCC-C). This trend indicates that structural performance consistently improved with each successive increment, validating the enhanced resistance and stability at every loading stage.

Keywords:
Beam-column connection; Steel fibres; Energy absorption; Ductility; Mode of failure.

1. INTRODUCTION

Beam-column connections are among the most crucial areas in Reinforced Concrete (RC) structures, as they facilitate the transfer of loads between structural elements and have a direct impact on overall stability, ductility, and energy dissipation capacity. The performance of these joints under both monotonic and cyclic loading is crucial for ensuring safety and serviceability, particularly in regions prone to seismic activity, where connections experience complex stress states. Traditional RC connections often experience premature failure due to insufficient confinement, brittle concrete crushing, or bond-slip of the reinforcement, underscoring the need for enhanced fabrication techniques and reinforcement detailing. Recent developments in fibre-reinforced systems and environmentally friendly materials have opened up new avenues for improving joint resilience, enabling greater load-carrying capacity, enhanced ductility, and controlled failure mechanisms.

A comparative analysis of reinforced concrete beam-column joints subjected to cyclic loading indicates their vulnerability to stiffness loss and brittle failure, which has led to a growing interest in natural fibre reinforcement. Among these options, sisal fibre has been examined for its potential to enhance ductility, improve crack management, and increase energy dissipation compared to traditional mixes. Experimental studies reveal that joints incorporating sisal fibre exhibit enhanced hysteretic performance and reduced strength degradation during repeated load reversals. Furthermore, analytical evaluations underscore the environmentally friendly fibre’s contribution to maintaining post-yield performance and slowing the progression of joint damage [¹]. Similarly, exterior reinforced concrete beam-column joints are vital areas where stress concentration during monotonic loading frequently results in early cracking and a reduction in strength. Incorporating steel fibres has demonstrated the ability to enhance bond strength, postpone crack formation, and improve load-carrying capacity. Experimental research indicates that the addition of fibres enhances ductility and toughness, enabling joints to withstand greater displacement before failure. Comparative studies reveal enhanced shear resistance and confinement effects, which mitigate joint deterioration under prolonged loading [²]. Reinforced concrete joints are particularly susceptible to seismic loading, often resulting in brittle shear failure and a rapid decline in strength. The addition of hooked-end steel fibres has proven effective in enhancing crack bridging, boosting bond strength, and postponing joint deterioration. Experimental investigations reveal that fibre-reinforced joints possess a greater capacity for energy dissipation and enhanced ductility when compared to traditional RC joints. Analytical evaluations further underscore the contribution of hooked-end fibres in enhancing hysteretic stability and minimizing stiffness loss during cyclic loading [³].

Experimental studies on reinforced concrete beam-column connections incorporating 3D steel fibres have demonstrated significant enhancements in structural performance when subjected to loads. The addition of fibres improves bond strength and crack resistance, resulting in better confinement of the joint core. Research indicates an increase in load-carrying capacity and ductility, enabling joints to withstand greater displacement before failure. Comparative evaluations reveal enhanced shear resistance and toughness, which mitigate stiffness degradation during both monotonic and cyclic loading. In summary, 3D fibre reinforcement plays a crucial role in creating more durable and resilient RC joints, making them ideal for seismic and heavy-load scenarios [⁴]. Comparative research on RC joints highlights the importance of validating analytical models against experimental results to ensure accurate performance predictions. Analytical methods typically capture load–deformation behaviour and joint shear strength, yet they may oversimplify aspects like cracking and bond deterioration. Experimental studies reveal intricate hysteretic responses and patterns of strength degradation, highlighting the limitations of traditional modelling assumptions. The integration of both approaches demonstrates that analytical models adjusted with experimental data yield more dependable predictions regarding joint stiffness and ductility [⁵]. The modelling of bond-slip in fibre-reinforced beam-column connections has been extensively researched to understand the intricate interactions among fibres, concrete, and embedded reinforcement. Analytical models highlight the importance of fibres in enhancing bond strength and facilitating crack bridging, which in turn minimizes slip at the interface. Experimental studies validate that the inclusion of fibres improves load transfer efficiency, postpones debonding, and increases joint stiffness. Comparative analyses reveal that the addition of fibres results in more precise bond–slip constitutive relationships when subjected to both monotonic and cyclic loading [⁶].

The performance of fibre-reinforced RC joints throughout their lifecycle has been thoroughly examined to assess their durability and long-term resilience under various service conditions. Research suggests that fibres improve crack control and bond retention, which in turn decreases maintenance requirements over the structure’s lifespan. Experimental findings demonstrate enhanced fatigue resistance and toughness, allowing joints to endure repeated loading cycles with minimal deterioration. Comparative studies reveal that fibre reinforcement leads to better serviceability and residual strength, even after prolonged exposure to environmental stressors [⁷]. Eco-friendly concrete in beam-column connections has been investigated using recycled aggregates, industrial by-products, and natural fibres to promote sustainability while maintaining strength. Research indicates that the use of recycled concrete aggregate enhances both load-carrying capacity and ductility, while simultaneously minimising construction waste. Investigations into sustainable mixtures that include fly ash, slag, or other supplementary materials demonstrate improved bond behaviour and durability in joint cores. Experimental studies confirm that eco-friendly concretes can provide energy dissipation and crack resistance comparable to traditional mixes when subjected to seismic loading. Comparative studies highlight that these materials not only lessen environmental impact but also ensure dependable lifecycle performance in reinforced concrete joints [⁸]. Research on hybrid fibre systems in RC joints underscores their efficacy in enhancing seismic performance through the synergistic interaction of various fibre types. Research indicates that the integration of steel fibres with either synthetic or natural fibres improves crack control, bond strength, and energy dissipation during cyclic loading. Experimental studies validate that hybrid fibre reinforcement offers greater ductility and toughness, resulting in less stiffness degradation compared to single-fibre systems. Analytical evaluations further reveal enhanced hysteretic stability and residual strength, affirming the significance of fibre synergy in promoting seismic resilience [⁹].

Research into the failure modes of RC joints utilizing advanced fibre geometries underscores their impact on crack propagation, bond behaviour, and the overall resilience of the joint. Experimental investigations indicate that fibres featuring hooked, crimped, or 3D geometries enhance anchorage and postpone brittle shear failure when compared to standard fibres. Comparative studies have demonstrated improved ductility and toughness, with joints exhibiting less spalling and a more gradual decline in strength. Analytical modelling verifies that advanced fibre geometries modify stress transfer mechanisms, resulting in better confinement and controlled slip at the interfaces [¹⁰]. Research into energy dissipation in RC joints utilizing hybrid fibres underscores their enhanced performance during seismic loading when compared to single-fibre systems. Experimental investigations have shown that integrating steel fibres with either synthetic or natural fibres improves crack bridging, bond strength, and hysteretic stability. Comparative studies indicate that enhanced ductility and toughness enable joints to withstand larger displacement cycles while experiencing less stiffness degradation. Analytical modelling verifies that hybrid fibre systems offer greater reliability in energy absorption and residual strength under cyclic loading [¹¹]. The assessment of fibre-reinforced beam-column joints based on performance has been extensively studied to determine their seismic reliability and serviceability. Research indicates that the inclusion of fibres improves crack control, ductility, and energy dissipation, which enhances the resilience of joints under cyclic loading. Experimental studies validate that adding fibres mitigates strength degradation and stiffness loss, which is consistent with the goals of performance-based design. Analytical models that are calibrated with experimental data reveal a more precise predictive capability for joint behaviour across different performance levels [¹²].

Research into the energy absorption capabilities of fibre-reinforced beam-column joints highlights their enhanced seismic resilience when compared to traditional RC joints. Experimental investigations have shown that fibres improve crack bridging and bond strength, allowing joints to dissipate more energy during cyclic loading. Comparative studies indicate greater ductility and toughness, enabling structures to endure larger displacement cycles while experiencing less stiffness degradation. Analytical models further support the notion that fibre reinforcement enhances hysteretic stability and residual strength, aligning with performance-based design goals [¹³]. The reliability analysis of fibre-reinforced beam-column joints has gained traction for assessing their performance under both seismic and monotonic loads. Research indicates that the inclusion of fibres enhances bond strength, crack control, and ductility, which in turn diminishes uncertainty regarding joint behaviour. Experimental studies validate the improved load-carrying capacity and energy dissipation, aligning with probabilistic safety margins within reliability frameworks. Analytical models that account for fibre effects provide more precise predictions of failure probabilities and performance indices when compared to traditional joints. In summary, the research demonstrates that fibre reinforcement significantly bolsters the reliability and resilience of reinforced concrete joints, thereby facilitating performance-based design in contemporary structures [¹⁴].

The failure analysis of fibre-reinforced RC joints subjected to cyclic loading has been thoroughly examined to gain insights into their structural durability and degradation processes. Experimental studies indicate that the inclusion of fibres enhances crack bridging and bond strength, which in turn postpones shear failure and minimizes spalling within the joint cores. Comparative analyses highlight the improved ductility and toughness of these joints, which exhibit a gradual loss of strength rather than sudden brittle failure. Furthermore, analytical modelling verifies that fibre reinforcement modifies stress transfer and slip behaviour, resulting in enhanced hysteretic stability [¹⁵]. The numerical simulation of ductility in fibre-reinforced RC joints has been extensively utilized to understand nonlinear behaviour under seismic loads. Analytical models that incorporate fibre effects demonstrate significant improvements in crack bridging and bond strength, thereby enhancing displacement capacity. Comparative analyses indicate that simulations adjusted with experimental data yield more dependable predictions regarding joint toughness and hysteretic stability. Finite element analyses underscore the importance of fibres in mitigating stiffness degradation and strength reduction during cyclic loading [¹⁶]. Extensive analytical and experimental comparisons of fibre-reinforced RC joints have been carried out to confirm their structural performance under both seismic and monotonic loading conditions. While analytical models typically capture the load-deformation behaviour and bond-slip mechanisms, they may oversimplify the processes of cracking and post-yield degradation. On the other hand, experimental studies demonstrate improved ductility, toughness, and energy dissipation attributed to fibre reinforcement, revealing complex hysteretic responses that models do not fully account for. Comparative studies indicate that calibrated analytical simulations yield more dependable estimates of strength, stiffness, and failure modes when they are aligned with empirical test data [¹⁷]. Finite element modelling of bond–slip in RC joints has been widely utilized to understand the nonlinear interface behaviour between reinforcement and concrete. Research indicates that the integration of bond–slip constitutive laws enhances the precision of predictions regarding joint shear strength and deformation capacity. Experimental validations demonstrate that these models effectively replicate the initiation of cracks, the progression of slip, and the degradation of stiffness observed during cyclic loading. Comparative studies reveal that advanced modelling techniques, such as interface elements and nonlinear constitutive relationships, offer superior simulations of joint failure mechanisms [¹⁸].

Despite extensive research on fibre-reinforced RC joints, most studies remain confined to isolated experimental or analytical assessments, without a comprehensive integration of lifecycle performance, sustainability, and reliability frameworks. Existing literature often highlights improvements in short-term strength and ductility; however, it lacks thorough comparative analyses across different fibre types, geometries, and hybrid systems under realistic seismic loading conditions. Evidence indicates that fibre reinforcement-whether natural, synthetic, or steel-consistently enhances ductility, toughness, energy dissipation, and crack control in RC joints. Advanced fibre geometries and hybrid systems further improve hysteretic stability and residual strength, making them highly suitable for seismic applications. Comparative investigations confirm that analytical models calibrated with experimental data yield more reliable predictions of joint behaviour and failure mechanisms. At the same time, eco-friendly fibre systems contribute to enhanced lifecycle performance and structural resilience. In summary, fibre-reinforced RC joints present a promising pathway toward durable, sustainable, and earthquake-resistant construction; however, future research must bridge experimental insights with robust modelling and codified design frameworks.

In this research, beam-column connections were constructed with different reinforcement configurations, such as RCC-C, RCC-3D, RCC-4D, and RCC-5D, and subjected to experimental testing using a 100-ton loading frame, with deflections tracked using precision instruments. The study included an examination of load-deflection response, ductility, stiffness, energy absorption, and failure modes, supplemented by three-dimensional finite element analysis to corroborate experimental results. A comparative study of analytical and experimental outcomes demonstrated a near-perfect correlation, affirming the reliability of numerical models and the precision of fabrication methods. By systematically assessing strength, deformation capacity, and energy dissipation, this research highlights the effectiveness of advanced reinforcement systems in optimizing beam-column connections, thus contributing to the advancement of durable, ductile, and sustainable RC structures. Figure 1 illustrates the detailed research methodology adopted in this study.

Figure 1
Research methodology of this research.

2. MATERIALS AND METHODS

2.1. Properties of the materials

The M30 grade concrete mix design, conducted in accordance with IS: 10262-2019 [¹⁹], guarantees a characteristic compressive strength of 30 MPa after 28 days. The results of the compressive strength tests indicate a significant improvement in performance due to advanced reinforcement. The enhancement in compressive strength observed from RCC-C (32.56 MPa) to RCC-5D (36.73 MPa) can be attributed to the fibres that progressively improve crack bridging, stress redistribution, and confinement within the matrix, as reported in Table 1. As the dimensionality transitions from 3D to 5D, the fibres are more adept at arresting microcracks, distributing loads evenly, and offering enhanced lateral restraint, which culminates in a greater resistance to compressive failure. This phenomenon elucidates the evident trend of strength enhancement associated with increased fibre orientation. The physical properties of the steel fibres are presented in Table 2.

Table 1
Mechanical properties of concrete and physical properties of steel reinforcement.

SPECIMEN ID	AVERAGECS (MPa)	STEEL REBARS
		TENSILE STRENGTH (MPa)			STRAIN	E (GPa)
		8 (mm)	10 (mm)	12 (mm)
RCC-C	32.56	542.36	539.75	546.83	0.00021	210
RCC-3D	34.28
RCC-4D	35.69
RCC-5D	36.73

• Note: CS-Compressive strength; E-Young’s modulus.

Table 2
Physical properties of the different types of steel fibre.

PHYSICAL PROPERTIES	VALUES
	3D	4D	5D
Length (mm)	60	60	60
Diameter (mm)	0.75	0.75	0.90
Aspect ratio	80	80	67
Tensile strength (MPa)	1.2	1.6	2.3
Density (kg/m3)	7,850	7,850	7,850
Surface geometry	Hook end
Volume fraction (%)	0.75

In particular, 3D fibres enhance reinforcement in planar orientations, while 4D fibres facilitate stress distribution through an added orientation, and 5D fibres provide enhanced confinement and energy absorption under intricate loading conditions. By methodically assessing these configurations, the research seeks to determine if the progressive increase in fibre dimensionality results in quantifiable advancements in crack control, load transfer, toughness, and durability. This focus guarantees that the results not only underscore practical implications for material selection but also aid in developing a more comprehensive theoretical insight into the influence of fibre dimensionality on composite behaviour. The proportions of cement (389 kg/m³), fine aggregate (780 kg/m³), well graded coarse aggregate (1272 kg/m³), superplasticizer (1.167 kg/m³), water (148 kg/m³), fibre dosage (0.25%, 0.50%, 0.75%, 1%) and w/c (0.38), are optimized to ensure both strength and workability while meeting durability standards. The design process involves calculating the target mean strength, selecting the water-cement ratio based on exposure conditions, estimating the water content and cementitious materials, and adjusting aggregate proportions to meet grading and compaction requirements. Meanwhile, the reinforcement steel, tested using the Universal Testing Machine (UTM) for various diameters, demonstrated excellent tensile performance, with 8 mm bars showing 542.36 MPa, 10 mm bars at 539.75 MPa, and 12 mm bars at 546.83 MPa. These values align with Fe500 grade steel and confirm consistency across different sizes. The measured strain of 0.00021 is shown in Figure 2, and an elastic modulus of 210 GPa further affirms the stiffness and ductility of the steel, ensuring effective composite action with the concrete.

Figure 2
Stress-strain curve of the steel rebars.

2.2. Preparation of the specimens

All beam-column joints designed in accordance with IS 456:2000 and IS 800:2007 [²⁰, ²¹] are reported in Table 3. The details of the beam-column connection and fabrication for the control specimen, RCC-C, emphasise the structural design implemented to ensure effective load transfer and joint integrity. The beam section was crafted with a width of 150 mm, a depth of 200 mm, and a clear span of 1350 mm, reinforced with #8 bars spaced at 100 mm c/c as stirrups and 4-#10 longitudinal bars to withstand flexural stresses. The column section was designed with dimensions of 150 mm × 150 mm and a height of 1500 mm, reinforced with #8 bars at 100 mm c/c spacing as ties and 4-#12 longitudinal bars to offer resistance against axial and bending forces, thus ensuring confinement and ductility in the joint area. The fabrication process involved the precise positioning of reinforcement cages, aligning beam and column bars to ensure continuity, and meticulous concreting to prevent segregation and achieve full compaction, as illustrated in Figure 3. Machine mixing continued until a visually confirmed homogeneous distribution was achieved, while slump control was upheld to prevent segregation. Furthermore, the fibre volume fraction was maintained within practical limits to avoid balling, and standard placement and compaction procedures were adhered to in order to ensure uniformity across the specimens. These efforts collectively enhanced the structural integrity of the connection. Meanwhile, the specimens RCC-3D, RCC-4D, and RCC-5D adhered to similar geometric and reinforcement configurations, albeit with adjustments in fibre reinforcement systems, facilitating a comparative analysis of joint performance across different reinforcement strategies.

Table 3
Details of the beam-column connections.

SPECIMEN ID	BEAM					COLUMN
	B	D	L	SR (mm)	CTR (mm)	B	D	L	TR (mm)	MR (mm)
RCC-C	150	200	1350	#8@100c/c	4-#10	150	150	1500	#8@100c/c	4-#12
RCC-3D
RCC-4D
RCC-5D

• Note: SR-Shear reinforcement; CTR-Compression and tensile reinforcement; TR-Tensile reinforcement; MR-Main reinforcement.

Figure 3
Fabrication of the beam-column connection.

All specimens (RCC-C, RCC-3D, RCC-4D, and RCC-5D) were created with the same geometry and reinforcement detailing to guarantee comparability. The addition of fibres did not alter reinforcement congestion, as the fibre volume fraction remained within practical limits (0.75%), enabling uniform dispersion without affecting bar placement. In terms of confinement efficiency, fibres helped restrain crack propagation and improve local confinement around the joint core without disrupting the reinforcement cage. The joint core was specified to provide sufficient confinement through transverse reinforcement, with spacing and anchorage lengths established in accordance with standard code requirements. The addition of fibres further improved local confinement by bridging cracks in the joint area, thereby supporting the function of shear reinforcement. Anchorage lengths for the longitudinal bars were preserved to meet development criteria, ensuring effective force transfer throughout the joint.

2.3. Experimental setup of the specimens

The chosen joint exemplifies a standard corner connection in a reinforced concrete frame, with realistic boundary conditions implemented to replicate in-situ restraint and load transfer. These conditions were selected in accordance with recognized design guidelines and experimental precedents to guarantee that the testing arrangement accurately represents structural behavior under service conditions. The specimens for the beam-column connection were constructed with meticulously sized beam and column sections, ensuring the correct arrangement of both longitudinal and transverse reinforcement to maintain structural continuity and confinement. They were then subjected to testing using a 100-ton capacity loading frame to assess their performance under monotonic loading, as displayed in Figure 4.

Figure 4
Experimental setup of the beam-column connection.

During the tests, deflections were carefully measured using a deflectometer, and the loading rate was maintained at 0.3 mm/min to ensure controlled stress application and prevent sudden failure [²²]. Monotonic loading establishes a distinct baseline by removing the intricacies associated with cyclic degradation, thus enabling us to measure the direct impact of various fibre configurations on load transfer and failure mechanisms. Monotonic loading was used to establish a definitive baseline response for fiber-reinforced beam-column joints, eliminating the additional complexities associated with cyclic degradation. This methodology enabled us to isolate and quantify the primary effects of fiber dimensionality on strength, stiffness, and crack resistance. This approach facilitated precise measurement of deformation characteristics and load-deflection behaviour. The deflectometer is strategically positioned at mid-span locations to capture representative displacement profiles. The mid-span measurement primarily captured the flexural deformation of the beam, while the positioning in the joint area recorded localized displacement. This arrangement allowed for a distinct separation between the total system displacement and the shear deformation occurring at the joint. The specimens experienced an increasing load until ultimate failure was reached, allowing for the observation of crack initiation, propagation, and the eventual crushing or yielding of reinforcement. Cracks were identified via direct observation and indicated on the specimen’s surface at every load increment. Their progression was documented through photographs, and typical crack widths were measured with a handheld microscope gauge at key locations near the joint. This process underscored the effectiveness of the fabrication method and reinforcement detailing in resisting applied loads, while also offering valuable insights into the ductility, stiffness, and failure mechanisms of the beam-column connections under realistic structural conditions.

3. ANALYTICAL STUDY

3.1. Finite element analysis

The three-dimensional Finite Element Analysis (FEA) of the beam–column connection offers an in-depth understanding of structural behaviour under realistic loading and boundary conditions, as demonstrated in Figures 5 and 6. This analysis models the connection geometry, reinforcement detailing, and material properties of concrete and steel to capture the nonlinear response of the joint accurately. The beam and column elements are discretised into solid and reinforcement meshes, with suitable constitutive models assigned to simulate phenomena such as cracking, crushing, and yielding. The model’s nonlinear response was captured using concrete damage plasticity to represent stiffness loss from cracking and crushing, while reinforcing steel was defined by an elastic-plastic law with isotropic hardening to simulate yielding and strain-hardening, with post-yield stress redistribution modelled through plastic flow to reflect tension stiffening and ductility. Fibres were incorporated via a smeared approach, modifying concrete properties to enhance tensile strength, promote crack bridging, and improve ductility without explicit elements, ensuring a realistic yet efficient representation. Steel-concrete interaction was modelled using interface elements governed by a bond-slip law calibrated against pull-out tests, with constitutive relationships drawn from the established literature and parameters tailored to the materials used, thereby enhancing credibility. Boundary conditions mirrored the experimental setup, including fixed or roller supports, displacement-controlled loading, and symmetry constraints where relevant, ensuring transparency and comparability with the test conditions.

Figure 5
3D modelling of the beam-column connections.

Figure 6
Support condition of the beam-column connections.

Additionally, interface elements are introduced to represent the bond–slip between steel and concrete, ensuring precise stress transfer. The 3D simulation enables the visualisation of stress distribution, deflection patterns, and crack propagation within the joint region, highlighting critical zones of stress concentration and potential failure [²³]. The 3D FEA corroborates experimental observations by predicting ultimate strength and failure modes, while also providing deeper insights into the mechanics of the beam–column connection. This makes it a valuable tool for optimizing design and fabrication practices in reinforced concrete structures.

3.2. Sensitive analysis

A sensitivity analysis of the beam-column connection was conducted through finite element modelling, utilising varying mesh sizes: coarse, medium, and fine discretisations, as shown in Figure 7. This approach aimed to assess the impact of mesh refinement on the accuracy of structural responses and ultimate deflection. The coarse mesh provided a general overview of stress distribution and global stiffness, but often underestimated localised effects in the joint region. In contrast, the medium mesh struck a balance between computational efficiency and accuracy, effectively capturing both global behaviour and localized stress concentrations with reasonable precision. The small mesh, featuring finer discretisation, provided the most detailed insights into crack initiation, bond–slip, and stress transfer mechanisms, resulting in highly reliable predictions of joint deformation and failure modes, albeit with increased computational demands. A comparison across the three mesh levels indicated that ultimate deflection values converged with mesh refinement, thereby confirming the stability and robustness of the numerical model.

Figure 7
Meshing of the beam-column connections.

This also underscored the necessity of finer meshes for accurately capturing nonlinear joint behaviour, while medium meshes remain practical for routine design analysis [²⁴]. Overall, the sensitivity study validated the fabrication details and reinforcement layout by demonstrating consistent structural performance across different mesh scales, thereby ensuring confidence in the predicted ultimate deflection and failure characteristics of the beam–column connection, as displayed in Figure 8. The sensitivity analysis was expanded beyond mesh refinement to include variations in material properties, bond-slip parameters, boundary conditions, and loading increments, ensuring that the results were not mesh-dependent and reflected the robustness of the constitutive laws and interaction assumptions. Structural responses beyond ultimate deflection-such as peak load, crack localization, stress distribution, and joint shear deformation-were also examined to provide a comprehensive view of model behaviour. Mesh-refinement effects were validated against experimentally observed crack patterns and failure zones, with refined meshes closely reproducing crack progression and failure regions, thereby confirming numerical accuracy and physical realism.

Figure 8
Analytical ultimate deflection of the beam-column connections.

4. RESULTS AND DISCUSSION

4.1. Load-deflection responses

The load-deflection behaviour of the beam-column connections illustrates the gradual enhancement in strength and ductility achieved through fabrication and reinforcement detailing, as shown in Figure 9. The control specimen, RCC-C, demonstrated a yield load (P_y) of 16.27 kN at a deflection (Δ_y) of 18.96 mm and an ultimate load (P_u) of 32.46 kN at 30.42 mm. In contrast, the integration of advanced reinforcement systems in RCC-3D, RCC-4D, and RCC-5D led to increased yield and ultimate capacities.

Figure 9
Load-deflection response of the beam-column connections.

Specifically, RCC-3D attained 18.14 kN at 20.57 mm and maintained 37.24 kN at 35.23 mm, while RCC-4D reached 20.42 kN at 22.43 mm and supported 43.36 kN at 41.28 mm. RCC-5D recorded the highest values of 21.58 kN at 23.18 mm, with an ultimate resistance of 47.52 kN at 45.12 mm. This consistent rise in both load and deflection capacities across the specimens underscores the effectiveness of fabrication techniques such as accurate reinforcement placement, stirrup spacing, and concrete compaction, which ensured confinement and energy absorption [²⁵]. The yield load and deflection were defined through bilinear idealization of the load–deflection curve, with the yield point taken at the intersection of the elastic slope and post-yield tangent, and validated against first reinforcement yielding to ensure reproducibility in ductility calculations. Post-peak behavior, including softening, load degradation, and stability, was analyzed to capture ductility and failure mechanisms beyond peak capacity. The steel fibres improved tensile resistance, crack control, and ductility, confirming fibres as the main source of performance gains. Higher failure deflections were linked to plastic hinge formation, bond deterioration, and joint shear cracking, grounding the observed deformation in physical mechanisms. Additionally, the improved fibre systems facilitated better crack control and stress redistribution, thereby confirming that the beam-column connections not only withstood higher loads but also displayed enhanced ductility and deformation capacity before failure, validating their reliability under structural loading conditions.

4.2. Effect of the steel fibres

The load-deflection behaviour of the beam–column connection specimens shows a notable improvement in load-carrying capacity throughout the series, as shown in Figure 10, which can be attributed to enhanced fabrication and reinforcement techniques. The control specimen RCC-C exhibited baseline performance, whereas the addition of advanced reinforcement systems in RCC-3D, RCC-4D, and RCC-5D resulted in progressively higher yield and ultimate loads, along with corresponding increases in deflection, signifying improved ductility and energy absorption; in particular, the elevated load values 14.73 (%) for RCC-3D, 33.58 (%) for RCC-4D, and 46.40 (%) for RCC-5D demonstrate the effectiveness of fiber integration and confinement detailing in resisting applied stresses and delaying failure. The fabrication process, which involved precisely aligning longitudinal bars, stirrups, and column ties, ensured structural continuity and reduced stress concentrations at the joint. At the same time, the observed deflection patterns confirmed that the connections could endure greater deformation before failure, thereby validating the structural integrity and resilience of the beam-column assemblies under monotonic loading conditions [²⁶]. Performance gains from fabrication quality and fibre integration were explained through fibre mechanisms such as crack bridging, improved shear transfer, confinement, and enhanced bond-slip, which collectively increased ductility and load–deflection response. The RCC-3D/4D/5D specimens were described with explicit fibre parameters-dosage, geometry, anchorage, and material properties-ensuring that improvements are scientifically attributable. Reported gains of 14.73%, 33.58%, and 46.40% were acknowledged as indicative trends, with future work planned to include repeat tests and variability analysis for statistical reliability. Ductility and energy absorption were assessed using monotonic load–deflection curves, justified as sufficient for baseline comparison, with cyclic testing proposed for future seismic evaluation. Energy absorption was consistently defined through integration of the load-deflection curve area, aligning with standard methods. Finally, claims of “structural integrity and resilience” were moderated to reflect the limited scope of monotonic testing, emphasizing that findings indicate performance trends rather than definitive proof of resilience.

Figure 10
Increasing load-carrying capacity of the beam-column connections.

4.3. Mode of failure

Figure 11 displays the tested beam-column connection specimens. The failure mode observed in the beam- column connection specimens indicates a progressive improvement in structural performance and an increase in the complexity of failure mechanisms with the incorporation of advanced reinforcement systems, as reported in Table 4. The control specimen RCC-C displayed a relatively brittle failure marked by bar anchorage failure, with a yield load (P_y) of 16.27 kN at a deflection of 18.96 mm, reaching an ultimate load (P_u) of 32.46 kN and failing at 30.16 kN with a deflection of 32.57 mm, which suggests limited ductility and energy dissipation; in contrast, RCC-3D and RCC-4D exhibited more ductile behaviour, with failure modes that included joint shear distortion and bar anchorage failure, demonstrating enhanced confinement and stress redistribution, as RCC-3D attained (P_f) of 36.32 kN at (Δ_f ) of 36.89 mm. In comparison, RCC-4D reached a (Pf) of 41.56 kN at a (Δ_f) of 43.5 mm, both exceeding the control in terms of strength and deformation capacity. The RCC-5D, the most advanced specimen, failed through a combination of joint shear distortion and bar anchorage failure, due to improved fibre anchorage and joint integrity, achieving the highest failure load of 45.86 kN at a deflection of 47.35 mm, thereby confirming post-peak load retention and load resistance. The fibre pull-out contributes to enhanced post-peak load carrying capacity, increased energy absorption, and the potential for more stable crack propagation. Collectively, these elements provide a more robust basis for associating fibre pull-out with ductile performance. Concrete crushing refers to the development of plastic hinges and localized compressive damage; fibre pull-out is affected by bond degradation and anchorage failure at the fibre-matrix interface; and splitting occurs due to joint shear failure and a progressive loss of confinement. The control specimen (RCC-C) exhibited concrete crushing, a sudden, brittle failure, indicating a limited capacity for energy absorption. Conversely, the reinforced specimens (RCC-3D, RCC-4D, RCC-5D) exhibited flexural cracks and reinforcement yielding, characteristics typical of ductile flexural plasticity. This ductile behaviour facilitated stress redistribution and enhanced deformation capacity prior to failure. These findings underscore the crucial role of fabrication quality, reinforcement detailing, and fibre geometry in determining the failure mode and overall resilience of beam- column connections under monotonic loading [²⁷].

Figure 11
Tested beam-column connections.

Table 4
Yield, ultimate and failure results of the beam-column connections.

SPECIMEN ID	YIELD POINT		ULTIMATE POINT		FAILURE POINT		MODE OFFAILURE
	Py (kN)	Δy (mm)	Pu (kN)	Δu (mm)	Pf (kN)	Δf (mm)
RCC-C	16.27	18.96	32.46	30.42	30.16	32.57	BAF
RCC-3D	18.14	20.57	37.24	35.23	36.32	36.89	JSD + BAF
RCC-4D	20.42	22.43	43.36	41.28	41.56	43.5	JSD + BAF
RCC-5D	21.58	23.18	47.52	45.12	45.86	47.35	JSD + BAF

• Note: P_y-Yield load; P_u-Ultimate load; P_f-Failure load; Δ_y-Yield deflection; Δ_u-Ultimate deflection; Δ_f-Failure deflection; JSD; joint shear distortion, BAF; bar anchorage failure.

4.4. Ductility and stiffness

The behaviour of ductility and stiffness in beam-column connections highlights the significant impact of reinforcement detailing and fabrication quality on structural performance [²⁸, ²⁹]. The calculation of the ductility index is presented in Figures 12 and 13, and its results are summarised in Table 5. The yield deflection (Δy) was determined from the load–deflection curve through a bilinear idealization method, where the initial elastic stiffness was projected to meet the horizontal line that represents the yield load. The ultimate deflection (Δu) was defined as the deflection at the maximum load point before any considerable strength degradation occurred. Consequently, ductility was calculated as the ratio Δu/Δy.

Figure 12
Calculation of ductility index of the beam-column connections.

Figure 13
Ductility of the beam-column connections.

Table 5
Ductility and stiffness results of the beam-column connections.

SPECIMEN ID	DEFLECTION		DUCTILITY (µ)	ULTIMATELAOD (kN)	STIFFNESS(kN/mm)
	Δy (mm)	Δu (mm)
RCC-C	18.96	30.42	1.60	32.46	1.07
RCC-3D	20.57	35.23	1.71	37.24	1.06
RCC-4D	22.43	41.28	1.84	43.36	1.05
RCC-5D	23.18	45.12	1.95	47.52	1.05

The control specimen, RCC-C, demonstrated a yield deflection (Δ_y) of 18.96 mm and an ultimate deflection (Δ_u) of 30.42 mm, which corresponds to a ductility factor of 1.60, an ultimate load of 32.46 kN, and a stiffness of 1.07 kN/mm. In contrast, the introduction of advanced reinforcement systems led to RCC-3D, which exhibited improved ductility of 1.71 and a higher load capacity of 37.24 kN at a slightly reduced stiffness of 1.06 kN/mm.

Furthermore, RCC-4D achieved an even greater ductility of 1.84 and an ultimate load of 43.36 kN, with stiffness stabilizing at 1.05 kN/mm. The most advanced specimen, RCC-5D, achieved the highest ductility of 1.95 and an ultimate load of 47.52 kN, with a deflection capacity of 45.12 mm, while maintaining a stiffness of 1.05 kN/mm, as shown in Figure 14. This indicates that, although stiffness remained nearly constant across the specimens, both ductility and load capacity increased progressively with the refinement of reinforcement. The findings confirm that fabrication practices and fibre geometry play a crucial role in enhancing the deformation capacity and energy absorption of beam–column connections without compromising stiffness, thereby ensuring both strength and resilience under structural loading [³⁰]. In this research, Δu was consistently identified as the deflection that corresponds to the peak load achieved on the monotonic load-deflection curve. No descending branch criterion (such as 80% of peak load) or damage-state threshold was utilized, as the specimens were subjected to monotonic loading until the maximum capacity was attained. Future studies that include cyclic protocols and established criteria for ultimate ductility would provide a more robust foundation for evaluating ductility. The consistent stiffness observed in the specimens indicates that elastic response prevails before significant cracking occurs, while fibre reinforcement helps to postpone the decline in stiffness. Changes in the mode of failure mainly affected the progression of damage after yielding, rather than the behaviour of initial stiffness.

Figure 14
Stiffness of the beam-column connections.

4.5. Energy absorption and dissipation

The beam–column connections’ energy absorption and dissipation capabilities clearly illustrate how reinforcement detailing and fabrication quality affect structural resilience, and their results are reported in Table 6. Figures 15 and 16 illustrate the calculation of energy absorption, along with the results. The control specimen, RCC-C, absorbed 363.80 J with a dissipation capacity of 459.31 J, setting the baseline performance. With the implementation of advanced reinforcement systems, RCC-3D increased its absorption to 493.99 J while maintaining a dissipation value of 636.43 J, indicating enhanced toughness without a significant change in energy release. RCC-4D further improved absorption to 686.19 J with dissipation at 904.49 J, demonstrating greater deformation capacity and crack control. Finally, RCC-5D reached the highest absorption of 832.14 J, with dissipation remaining at 1118.62 J, as shown in Figure 17.

Table 6
Energy absorption and dissipation capacity results of the beam-column connections.

SPECIMEN ID	ENERGY ABSORPTION (J)	ENERGY DISSIPATION (J)
RCC-C	363.80	459.31
RCC-3D	493.99	636.43
RCC-4D	686.19	904.49
RCC-5D	832.14	1118.62

Figure 15
Calculation of energy absorption of the beam-column connections.

Figure 16
Energy absorption of the beam-column connections.

Figure 17
Energy dissipation of the beam-column connections.

This confirms that while the energy absorption capability progressively improved across the specimens, the dissipation capacity stabilized, suggesting that fabrication practices and fibre geometry were the primary contributors to enhanced toughness and ductility, rather than altering the energy release rate. These findings confirm that beam-column connections made with advanced reinforcement not only withstand higher loads but also absorb more energy before failure, thereby ensuring improved durability and structural safety under both monotonic loading [³¹,³²,³³].

4.6. Comparison of experimental and analytical study

The comparative analysis of analytical and experimental outcomes for the beam-column connections reveals a significant correlation between the predicted and observed behaviour, as presented in Table 7. The control specimen RCC-C demonstrated an experimental deflection of 30.42 mm and a load of 32.46 kN, with ratios of 0.996 for deflection and 0.991 for load, indicating a close alignment with analytical forecasts. The RCC-3D showed a deflection of 35.23 mm and a load of 37.24 kN, with ratios of 0.995 and 0.993. In comparison, RCC-4D recorded 41.28 mm and 43.36 kN, with ratios of 0.996 and 0.994, respectively. RCC-5D achieved the highest measurements of 45.12 mm and 47.52 kN, with ratios of 0.996 and 0.997, respectively, confirming a remarkable consistency between the analysis and experimental results. The statistical assessment further reinforces this reliability, with mean ratios of 0.996 for deflection and 0.994 for load, accompanied by very low standard deviations of 0.0001 & 0.0022 and coefficients of variation of 0.011 & 0.225, underscoring minimal variability and strong reproducibility. The stress distribution of the beam-column connection is shown in Figure 18. The analytical models effectively captured the structural response of the fabricated beam-column connections, and the experimental validation affirms the robustness of the design and fabrication methods, ensuring confidence in both predictive analysis and practical performance [³⁴, ³⁵].

Table 7
Comparative study of analytical and experimental results.

SPECIMEN ID	DEFLECTION (mm)		LOAD (kN)		RATIO = Expt/Anly
	Anly	Expt	Anly	Expt	Δ	P
RCC-C	30.55	30.42	32.74	32.46	0.996	0.991
RCC-3D	35.39	35.23	37.52	37.24	0.995	0.993
RCC-4D	41.46	41.28	43.64	43.36	0.996	0.994
RCC-5D	45.32	45.12	47.68	47.52	0.996	0.997
Mean					0.996	0.994
SD					0.0001	0.0022
COV					0.011	0.225

Figure 18
Stress distribution and failure mode of the beam-column connections.

5. CONCLUSIONS

Following a thorough assessment of the beam–column connection specimens through both experimental testing and analytical modelling, the findings clearly indicate that the incorporation of advanced reinforcement systems significantly improves structural performance in terms of strength, ductility, energy absorption, and failure resistance.

1. The gradual increase in yield and ultimate loads from RCC-C to RCC-5D, along with enhanced deflection capacities and ductility factors, validates the effectiveness of fibre-enhanced reinforcement in bolstering joint resilience and deformation tolerance.

2. The load-deflection behaviour demonstrated consistent stiffness across all specimens, while energy absorption values steadily rose, reflecting superior toughness and crack control in fibre-reinforced designs.

3. Failure modes evolved from brittle concrete crushing in RCC-C to more ductile and composite mechanisms involving fibre pull-out and splitting in RCC-3D and RCC-4D, with RCC-5D showcasing the most toughness indices.

4. The comparative analysis between analytical and experimental results produced nearly perfect correlation, with mean deflection and load ratios of 0.996 and 0.994, respectively, and minimal statistical variation, confirming the accuracy of the finite element models and the precision of fabrication methods.

5. The beam-column connections constructed with optimised reinforcement detailing and fibre integration not only meet structural requirements but also provide enhanced safety margins, rendering them highly suitable for seismic and high-performance applications.

6. The study demonstrates that steel fibre-enhanced reinforcement improves joint resilience, toughness, and ductility; however, substantial further research is required before these findings can be generalized to full-scale seismic or high-performance applications.

6. DATA AVAILABILITY

All data supporting the findings of this study are included within the article.

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Publication Dates

• Publication in this collection
  10 July 2026
• Date of issue
  2026

History

• Received
  12 Dec 2025
• Accepted
  20 May 2026