Ultimate Deflection Research Articles

Structural behavior of RC one-way slabs strengthened with ferrocement and FRP composites

Existing research lacks focus on the structural behavior of reinforced concrete (RC) one-way slabs reinforced with ferrocement, and there's a notable absence of comparative studies between fiber-reinforced polymers (FRPs) and ferrocement strengthening methods for these slabs. Given the cost-effectiveness and widespread use of ferrocement in structural reinforcement, this study aimed to address these gaps through an experimental program. Three sizes of wire mesh, categorized as Type-I (small), Type-II (medium), and Type-III (large), were employed in this study. Chemical or mechanical anchors were used to attach ferrocement jackets. Moreover, 6, 12, or 18 anchors were used to assess the effect of anchor configuration. The goal was to enhance the structural performance of slabs and compare them with slabs reinforced using FRP jackets. The study focused on preventing debonding of the strengthening layers, employing either mechanical or chemical anchors. All slabs exhibited ductile failure with flexural cracks. The peak load and ultimate deflection were enhanced by up to 49.00% and 109.07%, respectively, by the application of ferrocement jackets, whereas the dissipated energy was increased by up to 174.00 %. Notably, the use of chemical anchors demonstrated a superior ability to delay debonding and enhance ductility compared to mechanical anchors. Slabs reinforced with glass FRP (GFRP) showed delayed debonding relative to carbon FRP (CFRP) reinforced slabs, indicating the superior performance of chemical anchors with GFRP layers. Moreover, the type and size of wire mesh significantly influenced performance, with small and medium-sized mesh configurations enhancing ductility, while large-sized mesh exhibited relatively earlier debonding. The orientation of the wire mesh also played a crucial role, with parallel orientation to the longitudinal axis of slabs yielding better performance.

Cyclic shear testing of artificially corroded reinforced concrete short circular piers

Chloride-induced deterioration of reinforced concrete (RC) structures is an increasingly vital topic among asset management and structural maintenance fields, as many RC bridges and other structures are reaching the end of their initial design lives. Deterioration of the transverse reinforcement in RC piers leads to the direct loss of shear and confinement-related mechanical properties as degradation advances with time. This research investigates the seismic response of fourteen short RC circular piers subjected to artificial chloride-induced corrosion. Each pier is designed to trigger a shear-dominated failure and artificially corroded at two current densities. A maximum average mass loss of 10.5% and 43.0% was measured in the longitudinal and spiral reinforcement, respectively. The influence of confinement effectiveness, spiral diameter, and aspect ratio on the rate of shear capacity degradation are included as test parameters in this study. Results indicate that shear deformation begins to govern performance at moderate to severe deterioration, which precedes the onset of brittle shear-dominated failure modes. Ultimate deflection is more adversely affected by increasing corrosion than all other measured properties, with a maximum observed reduction of 70.9% compared to a maximum 37.5% reduction observed in peak shear capacity. Several existing theoretical models are introduced and evaluated on their ability to predict the shear capacity of the experimental tests. Based on the results, those models directly evaluating the circular section without needing an equivalent section transformation offer the most accurate and reliable predictions.

Numerical investigation of the effect of longitudinal steel reinforcement ratio on the ductility of concrete beams

Abstract This research aims to use numerical methods to analyze concrete beams with different reinforcement ratios. Two software packages – ABAQUS and OpenSeesPy – were employed to achieve this task. Empirical stress–strain relationships were utilized to forecast the concrete’s stress–strain behavior. The numerical analysis results were compared with previously published experimental results, and the findings showed a reasonable similarity. The results were consistent with the published laboratory results, particularly for ultimate and yield loads, with no more than 10% differences. However, the ultimate deflection variation was higher. For the first control beam, denoted as B 2−12, ABAQUS predicted a 24.64% difference in ultimate deflection, while OpenSeesPy predicted a 35.83% difference for the second beam, sampled as B 2–16. However, the ultimate deflection for the remaining beams differed by less than 10%. Meanwhile, the difference in yield deflection was greater than in ultimate deflection, with OpenSeesPy showing a maximum difference of 18.51%. The maximum ductility was found to occur at a reinforcement ratio equal to 0.0016. Additionally, OpenSeesPy was faster than ABAQUS in computation while still producing satisfactory agreement with experimental results.

Flexural behavior of reinforced concrete beams strengthened with gradually prestressed near surface mounted carbon fiber-reinforced polymer strips under static and fatigue loading

The near surface mounted (NSM) carbon fiber-reinforced polymer (CFRP) strengthening technique, combined with gradually anchored prestressed technique, is utilized to delay the occurrence of concrete cover separation (CCS) and enhance the ductility of reinforced concrete beams. The load-carrying capacity of fully prestressed beams and gradually prestressed beams are investigated under both static and fatigue loading conditions. The study focused on the effect of gradient prestress on flexural behavior of strengthened beams, analyzed the failure mode, characteristic load, ductility, and stress distribution at CFRP-concrete interface under both prestress and load conditions. Results indicate that gradually prestressed beams outperform fully prestressed ones in restraining crack development, delaying yield of tensile reinforcement, improving bearing capacity and avoiding CCS failure. Bearing capacity was significantly increased by up to 35.48%, while ductility was greatly improved by 100.33% with ultimate deflection for gradually prestressed beams compared to fully prestressed ones. The fatigue life of gradually prestressed beams, which experienced a transition from CCS failure mode to fatigue fracture of tensile reinforcement, was significantly extended. Additionally, their ductility at failure was also greatly enhanced, thus confirming the effectiveness of gradually prestressed NSM CFRP strengthening technique.

Improvements in lightweight concrete T beams CFRP strengthened and anchored with U‐wraps

AbstractThis research provides a study for an experimental program using sand‐perlite‐lightweight reinforced concrete (RC) beams strengthened and anchored with carbon fiber reinforced polymer (CFRP) materials. The main objective of this work is to showcase the efficiency of using U‐wrap anchors to secure the externally applied CFRP sheets on lightweight RC beams. A series of six full‐scale T‐beams with an increasing number of CFRP U‐wraps per shear span was prepared and tested. The use of U‐wrap anchorage enhanced the flexural performance of the sand‐lightweight concrete beams by progressively delaying the premature debonding of CFRP sheets as a direct function of the number of U‐wraps used per shear span. The beam flexural capacity gradually improved from 116 kN without the use of U‐wrap anchors to 182 kN when using six U‐wraps per shear span, which reflects a significant enhancement. Similarly, the ultimate deflection gradually improved from 56 mm for the beam without U‐wrap anchors to 94 mm when applying six U‐wraps per shear span. A design model established earlier, for normal weight concrete, has been successfully qualified to yield accurate findings against the experimental results. Also, the outcome of this study interestingly showed that the ultimate strength results of the anchored beams were close to their counterparts of normal weight concrete conducted on identical beams. This finding shows that U‐wrap anchors performed efficiently despite the lack of coarse aggregate interlock in the concrete mix.

Experimental Study on the Flexural Behavior of I-Shaped Laminated Bamboo Composite Beam as Sustainable Structural Element

Laminated bamboo (LB) is considered a promising environmentally friendly material due to its notable strength and advantageous lightweight properties, making it suitable for use in construction applications. LB I-beams are a prevalent component in bamboo structures due to their ability to fully utilize their material properties and enhance efficiency when compared to beams with rectangular solid sections, while the characteristics of connections should be further studied. This paper presents an experimental investigation of the flexural behavior of I-shaped LB beams that are connected using self-tapping screws and LB dowels. Compared with glued beams of the same size, the findings of the study reveal that the primary failure modes observed in those two types of components were characterized by the separation of the component and web tensile fracture. The screw beam and dowel beam exhibited a reduced ultimate capacity of 43.54% and 30.03%, respectively, compared to the glued beam. Additionally, the ultimate deflections of the screw beam and dowel beam were 34.38% and 50.36% larger than those of the glued beam, respectively. These variations in performance can be attributed to the early breakdown of connectors. Based on design codes, it can be observed that the serviceability limits were in close proximity, whereas the ultimate strains of the top and bottom flanges were significantly lower than the ultimate stresses experienced under uniaxial loading conditions. As a result of the slip and early failure of connectors, the effective bending stiffness estimated by the Gamma method achieved better agreements before elastic proportional limit. Therefore, in future investigations, it would be beneficial to enhance the connector and fortify the flange as a means of enhancing the bending characteristics of an I-shaped beam.

Flexural behavior of RC beams externally reinforced with CFRP composites using various strategies

Abstract The external composite material bonding is an effective and practical method for flexural strengthening of reinforced concrete (RC) beams, providing a large opportunity to develop high-performance and cost-effective structures. Numerous uses exist for carbon fiber-reinforced polymer (CFRP) materials as RC-member strengthening methods. However, issues with bonding and de-bonding continue to be a barrier to this technique's accomplishment. In this research, the CFRP sheets were integrated as an external strengthening material to evaluate their contribution to the flexural performance and so determine how well the CFRP sheets are being used. The experimental work includes one control beam and ten RC beams with CFRP sheets as external strengthening. All beams have the same dimensions: a length of 1.7 m and a sectional area of 20 cm × 25 cm. Experimental tests were carried out with varying CFRP types, lengths, numbers, and arrangements. Each beam’s performance was evaluated in terms of failure mode, ultimate load capacity, ultimate deflection, and a load–deflection curve. The findings demonstrate the effectiveness of CFRP strengthening by demonstrating a considerable improvement in the majority of the study variables. Furthermore, the CFRP strengthening offered an exterior crack-arresting mechanism.

Behavior of Reinforced Concrete Corbels Strengthened with CFRP Strips Subjected to Monotonic and Repeated Loading

Concrete corbels are short cantilevers subjected to monotonic and repeated loads. Repeated loads generally negatively affect the concrete structural members' strength as they decrease the resistance to external loads. To increase these loads, strengthening with carbon fiber reinforced polymer (CFRP) strips as an externally bounded technique is used. This paper studies the behavior and strength of strengthened corbels subjected to monotonic and repeated (constant and incremental) loads. The experimental program included the casting and testing of twelve double-concrete corbels. All specimens have been kept constant for corbel dimensions and main and secondary reinforcement. Nine were strengthened with CFRP strips using different patterns, while the others were left un-strengthened as control corbels. The results showed that both repeated loads' types, i.e., constant and incremental, affected the ultimate load capacity of corbels. Compared to monotonic loading, a reduction occurred in ultimate load and ultimate deflection for corbels subjected to five repeated loading cycles. For corbels strengthened by externally bounded CFRP strips under any applied loads, the ultimate load significantly increased, while the ultimate deflection decreased compared to un-strengthened at the same applied load. All corbels failed by de-bonding the CFRP strips.

Behavior of shallow concrete beams strengthened using low-cost GCSM and mechanical anchors

<p>This study aimed to evaluate the shear strengthening capabilities of reinforced concrete (RC) shallow beams constrained by externally bonded glass chopped strand mat (GCSM) sheets and metallic mechanical anchors. The research investigated the effectiveness of GCSM sheets, known for their cost-effectiveness, ease of installation, and absence of specialized labor requirements, in improving the shear capacity, energy dissipation, and deformation capacity of RC beams. Experimental results revealed that GCSM sheets significantly enhanced the deformation capability, ultimate shear strength, and energy dissipation of RC shallow beams. Beams with GCSM applied to both the sides and bottom (SB) configuration demonstrated higher load-bearing capacity and energy dissipation compared to beams with GCSM only on the sides. The incorporation of a metallic mechanical bolt anchorage (MBA) system reduced the load-carrying capacities of beams with SB and beams with GCSM applied to only side by 28% and 5%, respectively, due to the drilling required for installation. However, the MBA system significantly improved the deflection performance, with beam B-S-A (GCSM on sides only and supplemented with MBA exhibiting the highest ultimate deflection of 23.92 mm. Overall, beams equipped with the MBA system showed superior ultimate deflection compared with those without it. Despite some reductions in load-bearing capacity, GCSM sheets combined with MBA systems proved highly effective in enhancing the shear strength, energy dissipation, and deformation capabilities of RC shallow beams, making them a valuable alternative for shear strengthening applications.</p>

Flexural behavior of steel fiber reinforced slag- based geopolymer concrete beams

This study includes tested nine reinforced concrete beams. It’s designed to fail in flexural under two-point load. All beams are classified according to the type of concrete and the percentage of PVA into three groups. The first group including four reinforced geopolymer concrete beams with percent of PVA was 0.2 %; second group including four reinforced geopolymer concrete beams with percent of PVA was 0.75 % and third group including one reinforced normal concrete beam. The results showed when comparing the geopolymer concrete beam with the normal concrete beam, noticed that the ultimate strength is equivalent to many times the normal concrete. The best percentage for improving the ultimate load for beam NO.6 (GSSB10) where the percentage of increase was 132% this beam is reinforced by steel bars 2ɸ12mm at top and 2ɸ16mm at bottom. As for the other beams, the percentage increase in ultimate load was for beam NO.1 (46%), beam NO.2 (99%), beam NO.3 (13%), beam NO.4 (60%), beam NO.5 (58%), beam NO.7 (32%) and beam NO.8 (66%). The maximum deflection in all samples was high compared with the normal concrete, where the ultimate deflection reached 30 mm, while in the normal concrete it was 9.65 mm.

Eight-year natural environmental exposure and sustained-loading of reinforced concrete beams with iron-based shape memory alloys

Low-cost iron-based shape memory alloys (Fe-SMA) are recently proving to be favorable alternatives for strengthening reinforced concrete (RC) members. Unlike carbon fiber reinforced polymers (CFRP), Fe-SMAs eliminate the need for labor-intensive anchorages and exhibit plastic behavior similar to reinforcing steel, rendering them especially promising for prestressed near-surface mounted (NSM) applications. However, due to their recent development, not many long-term experimental studies have been yet available and thus the long-term durability of Fe-SMA-strengthened RC members remains relatively unexplored. To this end, the structural behavior of two RC beams strengthened with NSM Fe-SMA were investigated, exposed to a natural environmental conditions and sustained loading above their cracking load level for 8 years, followed by four-point bending until failure. Results were compared with a previous investigation of identical beams and Fe-SMA strips without exposure to environmental factors or sustained loading. Additionally, a comprehensive cross-section analysis (CSA) was conducted for both long-term exposure and four-point bending. Despite notable creep effects caused by the 8 years of sustained loading that accounted to approximately 55% of the total mid-span deflections, no significant differences were observed in terms of load-carrying capacity, ultimate deflections, or strains, compared to the unexposed beams. The employed CSA effectively captured the long-term and bending behavior. Additionally, a parameter study and global sensitivity analysis were conducted to identify influential parameters affecting structural performance, concrete compressive strength was found as the most dominant influencing parameter.

Ohmic heating curing of carbon fiber concrete beam in realistic cold weather: The influence of electrically insulated steel rebars

This work attempted to investigate the on-site application of ohmic heating curing method on the structural concrete with steel reinforcement. The steel reinforced carbon fiber concrete beams were cured by ohmic heating method in the realistic severely cold weather. It was found that steel rebars disturbed the electrically conductive network formed by carbon fibers, resulting in a reduced curing duration of 48 h and an abnormal temperature distribution with high corner temperature and low core temperature. Electrical insulation treatments (epoxy resin coating and heat-shrink tubing) were taken and evaluated based on the ohmic heating features and mechanical properties. The results showed that the epoxy resin coating had a limited insulation effect, with an electrical resistance of 3.9 Ω, which displayed a similar temperature distribution with the uninsulated beam. On the contrary, the heat-shrink tubing had a significant insulation effect with an electrical resistance of 36.5 Ω, leading to an average core temperature of 23.6 ℃ during 7 days of curing period. The average rebound strength of beams with epoxy resin coating and heat-shrink tubing was 34.0 MPa and 41.6 MPa, respectively, and the ultimate deflection of beams was 34.37 mm and 49.18 mm, respectively, which was in correspondence with the temperature distribution. Besides, the heat-shrink tubing increased crack spacing width of beam, while the epoxy resin had little influence on crack pattern. This work emphasized the importance of electrically conductive path of concrete for ohmic heating curing method and gained practical experience of this method on the structural concrete.

Predicting failure process of precast deck joints using physics-guided LSTM model

The performance of precast deck joints is critical to the structural response and service life of precast segmental bridges, while the design of joints is faced with problems of high structural complexity and a large number of influencing factors. Meanwhile, current methods for evaluating joint performance are costly and time-consuming. In this research, a novel method for failure process prediction of deck joints is proposed. Based on the bending tests, finite element analysis (FEA) of the joints was performed and verified. Parametric analysis was then conducted to obtain an extensive failure process database. Further, a physics-guided long short-term memory (PG-LSTM) neural network was constructed for accurate sequence-to-sequence prediction of the failure process. Finally, the prediction results of the model were validated by supplementary tests, which showed good agreement. The method proposed in this study combines conventional methods with machine learning techniques to predict the failure process of deck joints and consequently obtain vital indexes such as initial stiffness, ultimate deflection, failure mode, and ultimate bearing capacity, thus offering an effective tool for the design of joints. It can also be extended to the prediction of other structural behaviors, opening up fresh perspectives for the advancement of intelligent design.

Influences of the bond-slip on the flexural performance of CFRP plate-strengthened damaged steel beams with intermediate debonding: A numerical study

The interfacial intermediate debonding between the steel beam and CFRP (carbon-fiber-reinforced polymer) is a considerable issue for a CFRP plate-strengthened damaged steel beam. The interfacial bond-slip property determines the interfacial debonding and thus affects the strengthening efficiency. To comprehend the influence laws of the bond-slip behavior, this study conducted a finite element (FE) modelling to assess the strengthening efficiency of the damaged steel beam using CFRP plates. The triangular and trapezoidal cohesive zone models were considered in parametric investigations. The comparisons of FE and experimental results verify the developed FE models. The FE modelling shows that the interfacial fracture energy is the most important bond-slip parameter affecting the flexural strengthening efficiency, relative to the maximum bond stress, elastic and plastic slips. The flexural capacity, ultimate deflection, and debonding load of the damaged steel beam are significantly increased with an increase in the interfacial fracture energy. However, changing the maximum bond stress, elastic slip or plastic slip only produce a minor influence under the same interfacial fracture energy. The selection of the adhesive type is critical for strengthening the damaged steel beam using CFRP plates. In this study, the debonding load, flexural capacity, and ultimate deflection are increased by 75.0%, 51.0%, and 131.1%, respectively, when Araldite-2015 adhesive with the trapezoidal bond-slip model is used instead of Sikadur-30 adhesive with the triangular bond-slip model. Moreover, the debonding load and flexural capacity are hardly increased but the ductility can be considerably improved with an increasing CFRP plate length.

Studying the Efficiency of Composite Longitudinal and Transverse Reinforcement for Increasing the Strength and Rigidity of Flexible Eccentrically Compressed Reinforced Concrete Poles

Introduction. In recent years, the use of composite materials for improving the operational properties of the building constructions within the restoration process is gradually replacing the methods, developed for this purpose in the middle of the XXth century and implying the use of reinforced concrete and metal. However, the regulatory framework stipulating the process of strengthening the loadbearing structures of buildings and structures was developed based on the insufficient amount of experimental data. Due to this fact, the large number of structures, exceeding the normative limits, cannot be strengthened with the composite materials, or such strengthening incurs significant economic costs. Thus, nowadays, the experimental studies on strengthening the reinforced concrete structures with composite materials are considered to be forward-looking and relevant. The aim of this study is to analyse the results of a number of experiments conducted to investigate the use and efficiency of composite materials in construction. Materials and Methods. To determine the level of stress in composite carbon materials of the external reinforcement of the eccentrically compressed reinforced concrete poles, the tests were carried out with four specimens. All specimens were strengthened using different reinforcement schemes. The strain gauges with 2cm active measuring grid length were installed in the zones of the most evident work of the composite materials to measure the changes of relative deformation at each load level during testing of the specimens. From 10 to 16 strain gauges were installed at each structure, depending on the importance of the zones for determining the deformations.Results. The work presents the results of the study on determining the efficiency of composite longitudinal and transverse reinforcement for increasing the rigidity and strength of flexible eccentrically compressed reinforced concrete poles. The experimental data on the composite materials’ strength, deflections and relative deformations, obtained during testing of four reinforced concrete poles, is presented. The efficiency of composite reinforcement at ultimate strength and ultimate deflections is assessed. The relative deformations in composite materials are determined and the inclusion of the reinforcement system in the work of the strengthened reinforced concrete specimens is assessed.Discussion and Conclusion. Based on the obtained results, the analysis of the composite reinforcement efficiency has been carried out, and proposals have been developed on designing the reinforcement systems of the flexible eccentrically compressed reinforced concrete poles working with the large eccentricities of the load application.

Study on mechanical properties and microstructure of green ultra-high performance concrete prepared by recycling waste glass powder

Ultra-high performance concrete (UHPC) encounters hindrance in pursing carbon neutrality and extended applications due to the dosage of cementitious materials and high energy consumption. To address this problem, this study utilized WGP to replace placement in the production of UHPC-WGP and invested its impact on workability, mechanical properties, and microstructure. The research results showed that incorporating WGP improved the flowability of UHPC and reduced its early-age mechanical properties but significantly enhanced the later-age mechanical properties. When the WGP content is 20 %, the sample's compressive strength after 28 days increases by 8.6 %. The specimens with 28 days exhibited the highest flexural strength and ultimate deflection, reaching 24.8 MPa and 0.809 mm, respectively, and the UHPC specimens (90 d) demonstrated the lowest total porosity, reduced by 14.6 % compared to the reference group. Furthermore, scanning electron microscopy (SEM) observations revealed that WGP had a good micro-aggregate filling effect and pozzolanic effect improved the microstructure. Finally, low cost and energy consumption characteristics further promote the sustainable application of WGP-based UHPC.

Monotonic and cyclic behaviour of deficient reinforced concrete slabs retrofitted with externally bonded carbon fibre reinforced polymer

Fibre reinforced polymer (FRP) retrofitting of reinforced concrete (RC) slabs has been widely investigated; however, the flexural behaviour of deficient RC slabs retrofitted with FRP under cyclic loading are limitedly explored. Towards this aim, this study experimentally and theoretically investigated the behaviour of RC slabs retrofitted with carbon fibre reinforced polymer (CFRP) under monotonic/cyclic loadings. Seven full-scale RC slabs, including one control slab and six slabs retrofitted by 1/2 and one CFRP layer, namely retrofitting types I and II, were tested under monotonic and cyclic loadings until failure. The results indicated that FRP retrofitted slabs failed by CFRP debonding while the control slab failed by steel yielding. CFRP retrofitted slabs exhibited tri-linear behaviour. CFRP retrofitting types I and II improved the yield load-carrying capacity by 43.5% and 83.5%, and the maximum load-carrying capacity by 81.9% and 217.4% compared with the capacity of the control slab, respectively. The stiffness of the retrofitted slabs increased significantly, leading to a substantial reduction in the deflection capacity. Although the ductility decreased, the safety factors based on load-carrying capacity of CFRP retrofitted slabs were much higher than the safety factor of the control slab. Cyclic loading caused a marginal strength degradation while it slightly reduced the ultimate deflections. Finally, a model to compute the moment capacity of CFRP retrofitted slabs was proposed, which can be useful for engineers in practice due to its simplicity and reasonable accuracy.

The influence of prestress level on the behavior of prefabricated precast concrete bridge deck panel systems with different overlay thicknesses

The bond properties and the excellent performance of the applied protecting overlay in segmental bridge deck panels are essential to ensure the overall quality of the bridge system. This research investigates the role of deck panels overlaying in a prefabricated fully-depth precast bridge using the NLFEA simulation approach under various overlaying thicknesses and prestressing levels. Using the NLFEA approach helps reduce the required time, save cost, study the effect of more factors, and demonstrate any behavior at a given load value at a given position in the investigated system. The NLFEA simulation was firstly validated against a published experimental work, and then it was extended into thirty-two prefabricated full-depth bridge systems composed of precast panels under various prestressing levels. The studied prestressing levels were related to the minimum and maximum prestressing levels as follows; (1.38 MPa (σP, Min), 2.76 MPa (2σP, Min), 4.14 MPa (3σP, Min), and 5.52 MPa (σP, max = 4σP, Min)). In addition, the effect of overlaying thickness on the original bridge thickness was also studied (to/ts) of 0.00 (Without), 0.06, 0.12, 0.18, 0.24, 0.30, 0.36, and 0.42). It has been highlighted that concrete overlying has a significant role in improving the system's overall behavior due to its good bonding with the deck panel, including the stiffness, toughness, cracking load, ultimate strength, and ultimate deflection. In addition, the produced stress by the AASHTO HS20 truck is less than the bond strength at the overlying interface. The maximum and minimum practical values for the overlaying thickness were proposed under different prestressing levels, aiding in getting the guidance of mitigating the detachment problem under the effect of the AASHTO HS20 truck and impact loading.

Performance of circular concrete-filled steel tube beams under monotonic and cyclic loadings

This study explored the performance of concrete-filled steel tube (CFST) beams under monotonic and cyclic loadings. Experiments were performed on nine simply-supported 140-mm-diameter CFST beams, which were classified into three groups by the diameter-to-thickness (D/t) ratios of 56.0, 46.7, and 40.0, conforming to Eurocode 4. The experimental results indicated that CFST beams exhibited high ductility. The buckling of steel tubes governed the plastic behavior and the ultimate state of CFST beams. The deformation and curvature concentrated in the middle region of the beams, forming a plastic hinge. The yield load, ultimate load, and yield and plastic stiffness slightly increased when D/t decreased from 56.0 to 46.7. However, by further decreasing D/t to 40.0, the ultimate and yield loads were significantly increased by ∼100%, the elastic stiffness by up to 58.2%, and the plastic stiffness by at least 187.5%. With a decrease in D/t ratio, the yield deflections slightly increased, whereas the ultimate deflection significantly decreased by up to 56.3%. The strength degradation was more pronounced for CFST beams with a D/t ratio of 40.0. Decreasing D/t ratio increased the plastic-to-yield stiffness ratios. The absorbed energy increased linearly with the increase in deflection in the plastic range. The cyclic loading effect caused an average degradation of 1.7%/cycle for both loading and unloading stiffness, whereas it marginally impacted on strength degradation. A decoupling concept and simplifications were employed to propose a simple model for rapidly estimating the moment capacity of CFST beams, which can be useful in designing and evaluating CFST beams.

Behavior of Steel–Lightweight Self Compacting Concrete Composite Beams with Various Degrees of Shear Interaction

This study investigated the use of lightweight self-compacting concrete (LWSCC), which represents a trend in producing high-performance concrete, as slabs in steel-concrete composite beams with headed studs as shear connectors. Three push-out test specimens were fabricated and tested to assess the shear strength and behavior of M16-headed stud connectors embedded in LWSCC. Based on the push-out test results, six steel-LWSCC composite beams were manufactured and tested as simply supported composite beams. In addition, a steel-normal weight self-compacting concrete (NWSCC) composite beam specimen with full shear interaction was manufactured and tested for comparison. The main variables taken into account in this study were the degree of shear interaction and regions of bending moment (sagging or hogging). It was observed that the increase in degree of shear interaction from 50 to 100% improved the ultimate carrying capacity, the service load, and the stiffness of the tested steel-LWSCC beam specimens by a ratio reached to 96, 95, and 122%, respectively, when subjected to sagging bending moments and by a ratio reached to 57, 59, and 134%, respectively, when subjected to hogging bending moments. In addition, it was noted that the deflection and the end slip values for steel-LWSCC specimens under a sagging bending moment are smaller than those under a hogging bending moment, which have the same degree of shear interaction and at the same load level. Moreover, the experimental results show that the ultimate carrying capacity, service load, and stiffness values for the steel-NWSCC composite beam were higher than those for the steel-LWSCC beam specimens that have the same properties, while the ultimate deflection and end slip were smaller. Doi: 10.28991/CEJ-2023-09-11-04 Full Text: PDF