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The use of back-to-back built-up channel beams in cold-formed steel (CFS) structures is steadily rising. The growing demand for CFS sections as a cost-effective design solution has driven the development of these CFS built-up sections. Despite this, there has been limited research on the performance of mild steel (MS) based CFS at high temperatures, particularly regarding its flexural behavior. This study thoroughly explores the behavior of MS-based CFS beams with different spans under high temperatures, followed by cooling with air or water. It assesses the impact of thermal loading and evaluates the effectiveness of these cooling methods. Experimental findings are validated and analyzed in conjunction with Finite Element Modeling (FEM) using ABAQUS and the Direct Strength Method (DSM). The study also conducts a parametric analysis to determine how the varying span that affects flexural capacity of beam. Among beams heated to the same temperature, those cooled with water exhibit slightly lower load capacities than those cooled with air. The maximum load observed is 91.21 kN for the reference specimen, while the minimum load is 39.82 kN for the specimen heated for 90 min and cooled with water, resulting in a 78.45% difference between these values. Additionally, as heating duration increases, ductility of beam also increases. Various failure modes are observed based on different heating and cooling conditions across different beam spans. This study offers valuable insights into the performance of MS-based CFS beams under thermal stress and different cooling conditions, providing important data for structural design and safety in construction. [ABSTRACT FROM AUTHOR]

Concrete-filled fiber tubes (CFFT) are gaining prominence as a feasible alternative to traditional materials for a variety of structural applications. However, research on structural performance of CFFT beams is still scarce. This paper presents a finite-element (FE) analysis of CFFT beams validated by experimental results from literature. Then, a parametric study investigating structural performance of post-tensioned (PT CFFT) beams was conducted using 34 FE models using ANSYS nonlinear FE software program. The parametric study results showed that both normal-strength concrete (NSC) and high-strength concrete (HSC) filled PT CFFT exhibit identical nonlinear responses. Increasing the prestressed and non-prestressed reinforcement ratio significantly improved the overall performance of PT CFFT beams. Placing the PT tendons at the bottom of PT CFFT beams enhanced the cracking, yielding, and ultimate load-carrying capacities by 7.98%, 12.32%, and 9.03% for NSC-filled PT CFFT beams, respectively. Doubling the axial stiffness of the tube laminate structure increased the ultimate load, energy absorption capacity (EAC), pre-yielding stiffness (Kpre), and post-yielding stiffness (Kpos) by 18.5%, 12.15%, 9.21%, and 8.2%, respectively for NSC-filled PT CFFT beams. Beams with straight PT tendons exhibited increased cracking, yielding, and ultimate load capacity by 10.85%, 14.60%, and 13.58% more than those with curved-profile tendons. The ductility of PT CFFT beams is more sensitive to the amount of prestressed reinforcement ratio and concrete strength has a minimal effect on the structural performance of PT CFFT beams. [ABSTRACT FROM AUTHOR]

This research presents an experimental, analytical, and numerical study to predict the flexural behavior of reinforced concrete hidden and wide beams embedded in slabs. The experimentally studied parameters of testing eight specimens include beam depth, beam width, and beam eccentricity from the column. The obtained test results were compared to the predictions of finite element analysis using the ANSYS program. A numerical parametric study was conducted by the ANSYS program to explore other parameters affecting the ultimate flexural strength of beams. The studied parameters encompass concrete compressive strength, steel reinforcement strength, bottom reinforcement ratio, top-to-bottom reinforcement ratio, and web reinforcement ratio. The results revealed that an increase in beam depth led to higher ultimate load and secant stiffness, along with a decrease in deflection. The increase in beam width significantly affected beam depth, resulting in increased ultimate load and secant stiffness and a slight decrease in deflection. The increase in beam eccentricity from the column resulted in a decrease in ultimate load and secant stiffness while increasing the deflection. Comparisons between experimental and numerical results were made against calculations based on the ECP 203-2017 and ACI 318-19 codes, and the comparison yielded satisfactory results. [ABSTRACT FROM AUTHOR]

Composite slab has extensive application in building industrialization. In this study, a novel composite slab with a joint was proposed, where the precast planks with bent-up rebar are only partially prefabricated along the thickness direction at the joint for cast-in-site pouring of concrete, and the rest is fully prefabricated in the factory. The flexural performance of the composite slab was compared with that of a traditional cast-in-site slab with the same geometric dimensions through four-point bending test. The results demonstrate that the bending performance of the composite slab, including cracking load, yield load, and ultimate load, is basically consistent with that of the cast-in-site slab, and can meet the engineering requirements. Based on experimental results, numerical research was conducted on the composite slabs. The effects of slab thickness, diameter of steel bar, concrete strength of precast plank, and slab span on the flexural behavior of composite slab were investigated. The numerical results show that the cracking load, yield load, and load corresponding to the deflection limit of the specimen increase with the increase in slab thickness and decrease with the increase in slab span. Increasing the steel bar diameter can increase the load corresponding to the deflection limit and yield load, while the effect on the cracking load is almost negligible. The concrete strength of precast plank has no significant effect on the flexural behavior of the composite slab. [ABSTRACT FROM AUTHOR]

Reinforced concrete beam bridges are usually retrofitted by a steel plate or FRP. However, these two methods tend to result in disadvantages, e.g., construction complexity and debonding failure, owing to the corresponding material properties. In this study, a steel- and CFRP-based method is proposed to achieve the merits of typical retrofitting methods by combining a CFRP plate, a steel plate, and angle steel. To investigate the effect of the cooperative strengthening, six full-scale beam specimens were designed and are evaluated through a monotonic four-point bending test. The failure mode, load–deflection relationship, critical parameters, and crack development are systematically and sequentially analyzed. Finally, a predicting method is proposed to calculate the flexural capacity. The retrofitted beam is characterized by an acceptable load-bearing capacity and deformation capacity. With continuous retrofitting, the crack load and ultimate load can be improved up to 84.9% and 4.41 times, respectively. The steel plate and angle steel function in both the load bearing and the anchorage to the CFRP plate contributes more to the ultimate bearing capacity after the steel components yield. Finally, a calculating model is shown to accurately predict the ultimate bearing capacity after retrofitting, with an average error of 4.03%. [ABSTRACT FROM AUTHOR]

The impact of treated waste crushed brick on shear behavior regarding reinforced concrete beams (RCBs) has been the primary focus of the presented work. A total of 12 concrete beams of 240 mm in height, 1100mm in length, and 130mm in width were used for that purpose. A total of 3 Normal Concrete Beams (HNCB) and 3 Solid Normal Concrete Beams (SNCB) comprise 6 Normal Concrete Beams (NCB) models. In addition, there are 3 Hollow Recycled Brick Concrete Beams (HRBCB) and 3 Solid Recycled Brick Concrete Beams (SRBCB) among the 6 Recycled Brick Concrete Beams (RBCB) models. The obtained crushed brick from building demolition wastes is incorporated in the concrete mixes at these percentages of 0%, and 50% as a replacement by the weight of coarse aggregate. Samples have been tested for bending at four points. The maximum deflection happened at mid-span of the beam. In the test, diagonal cracking load, as well as ultimate shear strength, were assessed to examine the behavior of the beam concrete with the waste material. The purpose of this experiment has been to ascertain how crushed brick affected the mechanical characteristics of RCBs. Furthermore, the outcomes demonstrate that the addition of crushed brick enhanced the mechanical characteristics of samples and enhanced shear behavior regarding the concrete beams made of crushed brick in comparison to control samples. The findings contribute to the understanding of the mechanical behavior and failure mechanisms of such beams and provide valuable insights into the potential use of recycled brick aggregates in structural applications. [ABSTRACT FROM AUTHOR]

Fiber-reinforced polymers (FRPs), which are resistant to corrosion, are used as reinforcement material for concrete. However, the flexural behavior of concrete members reinforced with FRPs can vary depending on the properties of FRPs. In this study, the flexural behavior of one-way concrete slab specimens reinforced with a new grid-type carbon-fiber-reinforced polymer (CFRP) (carbon grid) manufactured by bonding pultruded CFRP strands to an adhesive was investigated. The experimental results indicated differences in the load–deflection relationships of the specimens depending on the carbon grid reinforcement amount. Specimens in which the carbon grids were over-reinforced or reinforced close to the balanced reinforcement ratio reached the maximum load due to concrete crushing and exhibited ductile failure. The specimen under-reinforced with the carbon grid exhibited brittle failure. Specimens with carbon grid reinforcement close to a balanced reinforcement ratio exhibited maximum loads ranging from 0.43 to 0.61 times the calculated flexural strength, which resulted in becoming 0.86–1.00 lower in the specimens with a wider width of the CFRP strands. This study proposes coefficients to estimate the stiffness of carbon-grid-reinforced concrete flexural members after cracking. Applying these coefficients resulted in stiffness calculations that reasonably simulated the behavior of the specimens reinforced with carbon grids after crack formation. [ABSTRACT FROM AUTHOR]

Ultra‐high‐performance cementitious composite (UHPCC) incurs higher economic costs and resource wastage due to its high cement/silica fume (SF) content. The paper aims to achieve sustainability and environmental friendliness of UHPCC by substituting cement/SF with glass powder (GP). The influence of various GP particle sizes and substitution levels on the mechanical properties of UHPCC was investigated. X‐ray diffraction and scanning electron microscopy were employed to analyze the impact of GP on the hydration process of UHPCC from a microscopic perspective. In addition, the internal damage pattern of GP‐UHPCC was simulated by the RFPA3D program. The results show that the addition of GP could achieve superior fluidity than GP‐0. Compared to conventional UHPCC, GP‐20 exhibits improved strength, initial flexural toughness, and residual flexural toughness. Furthermore, finer GP particle sizes contribute to enhanced matrix strength and flexural energy absorption capacity to some extent. Additionally, the incorporation of 5%–20% GP leads to an increase in the characteristic peaks of hydrated lime and C‐S‐H gel, which are beneficial to improving the internal microstructure of the matrix. Based on the RFPA3D program, the crack area, principal stress distribution, and acoustic emission energy of specimens with 15%–25% GP substitution levels were significantly higher than those of specimens with low substitution levels (0%–10%). Generally speaking, a GP substitution level of 15%–25% is found the most effective range for improving strength, and toughness behavior in this study. [ABSTRACT FROM AUTHOR]

Geopolymer concrete (GC) is an innovative and sustainable type of composite resulting from the chemical reaction between waste materials containing and alkaline activators. The researchers have been focused to reduction of the greenhouse‐gas release, especially during the production of cement. Although numerous studies have been conducted on alkali‐activated cement or GC at the material level, there is limited research in the literature on the structural performance of reinforced GC members. The aim of this study is to investigate the effect of fiber combination on the shear and flexural performance of RC beams with maximum and minimum reinforcement ratio. To investigate the shear and flexural behavior of GC beam, four‐point and three‐point tests were performed on 12 GC with hybrid fibers, 4 GC with trio fibers, and 2 GC fiber‐free as references beams. The test parameters were the combination of fibers (steel, glass, carbon, and basalt), the longitudinal reinforcement ratio, and loading type. The key test results include the load‐deflection behavior, characteristics of the cracks, the effect of fiber type on the shear and flexural performance, ductility and stiffness properties, microstructure, the strain in the concrete, and the bars and code predictions. The test results showed that as expected, reducing the longitudinal reinforcement ratio decreased the strength, but the decrease in strength was tolerated by using different types of fibers. The use of trio fibers in beams under bending increased the strength capacity, considerably. Finally, the capacity prediction performance of current codes, that is, GB50010, EuroCode‐2, TS500, and ACI318, were also examined, and the calculations resulted that the current code equations had a percentage error of approximately 25% and 82% on average for flexural and shear, respectively, although EuroCode‐2 equations performed slightly better. [ABSTRACT FROM AUTHOR]

To investigate the flexural behavior of hybrid reinforced concrete (Hybrid‐RC) beams with Basalt fiber‐reinforced polymer (BFRP) bars and steel bars, this paper designed 14 Hybrid‐RC beams and studied the effect of different reinforcement forms on the flexural behavior of Hybrid‐RC beams. The research results indicated that when ρ≈2.28%$$ \rho \approx 2.28\% $$, an increase in Af/As$$ {A}_{\mathrm{f}}/{A}_{\mathrm{s}} $$ leads to a decrease in the cracking moment, ultimate moment, and ductility of Hybrid‐RC beams, the maximum crack width and deflection will increase. When ρ≈0.86%$$ \rho \approx 0.86\% $$, an increase in Af/As$$ {A}_{\mathrm{f}}/{A}_{\mathrm{s}} $$ will lead to a decrease in the cracking moment, deflection, and ductility of the Hybrid‐RC beams, while the maximum crack width and ultimate moment will increase. In addition, when ρ≤1.87%$$ \rho \le 1.87\% $$, the area of BFRP bars (the area of steel bars remains unchanged) should be changed to improve the flexural behavior of the Hybrid‐RC beams; When ρ>1.87%$$ \rho >1.87\% $$, the Hybrid‐RC beams should change the area of steel bars (the area of BFRP bars remains unchanged) to improve the flexural behavior of the beams. In addition, the ductility index prediction equation for Hybrid (BFRP and steel)‐RC beams was fitted based on the results of the theoretical model research. [ABSTRACT FROM AUTHOR]

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Concrete-filled steel tube (CFST) beams have shown their flexural effectiveness in terms of stiffness, strength, and ductility. On the other hand, composite bridge girders demand durable and ductile girders to serve as tension members, while the concrete deck slab resists the compression stresses. In this study, six composite CFST beams with concrete slab decks with a span of 170 cm were investigated under a four-point bending test. The main variables of the study were the compressive strength of the concrete deck, the size of CFST beams, and the composite mechanism between the CFST girder and the concrete deck. The results showed that the flexural strength and ductility of the composite system increased by 20% with increasing concrete compressive strength. The study revealed that the higher-strength concrete slab deck enabled the CFST beam to exhibit improved flexural behavior with reduced deflections and enhanced resistance to cracking. The findings also highlighted the importance of considering the interactions between the steel tube and concrete slab deck in determining the flexural behavior of the composite system revealed by strain distribution along the composite beam profile as determined using the digital image correlation DIC technique, where a 40% increase in the flexural strength was obtained when a channel section was added to the joint of the composite section. [ABSTRACT FROM AUTHOR]

This study develops an innovative multifunctional concrete sandwich shell based on a combined experimental and finite element (FE) study on its flexural behavior. The sandwich shell is made up of inner and outer concrete layers connected by connectors, with a middle functional layer that provides various functions such as insulation, acoustic, and vibration control. Bending tests were conducted on four groups of specimens, including three groups of sandwich shells with different types of connectors, that is, truss, grid, and plate connectors, and one reference group of solid shells. Loads, displacements, and strains were recorded during the tests. The FE analysis showed good correlation with the experimental results. Furthermore, a parametric study was conducted using the FE model to evaluate the influence of different parameters, such as middle layer thickness and number of connectors. The results show that the performance of the sandwich shell is comparable to, and in some cases better than, that of the solid shell, depending on the type of connectors used. This study provides a proof of concept for the sandwich shell and establishes a prototype structure for future research. [ABSTRACT FROM AUTHOR]

This manuscript presents a comprehensive investigation into the tensile strength and flexural behavior of steel fiber‐reinforced concrete (SFRC), utilizing a robust dataset comprising 457 meticulously selected data points, including 54 instances of self‐tested experimental data. The study establishes an empirical relationship governing the tensile strength of steel fiber concrete (SFC) based on the fiber reinforcement index (FRI) and the grade of concrete. The experimental study has extended its scope by testing an additional 27 full‐scale SFRC beams (rectangular cross‐sectioned) under monotonic loading to quantify the impact of tensile strength on the overall structural performance. The beam specimens feature continuous longitudinal and transverse reinforcement throughout their span, with steel fibers strategically positioned below the neutral axis. The steel fiber content was systematically varied from 0% to 2% in intervals of 0.25%. This work introduces modifications to the design of SFRC flexural members, emphasizing the consideration of tensile contribution below the neutral axis. The study integrates both experimental and analytical methodologies, providing diverse insights into the flexural behavior of SFRC beams. The proposed design methodology considers the tensile strength contribution from SFC, effectively predicting flexural capacity, particularly in scenarios involving higher volume fractions. Its applicability extends to structural design, offering insights into evaluating structural capacity for both newly designed and existing structures. [ABSTRACT FROM AUTHOR]

Cold-formed steel (CFS) sections, increasingly favored in the construction industry due to their numerous advantages over hot-rolled steel, have received limited attention in research concerning the flexural behavior of galvanized iron (GI)-based CFS at elevated temperatures. Understanding how these materials and structures behave under elevated temperatures is crucial for fire safety. The authors have performed experimental studies previously on GI-based CFS under elevated temperatures. In that study, CFS sections made of GI of grade E350 of 1.5 m long and 2 mm thickness were used. Built-up beam sections were tested under two-point loading after heating to 60 and 90 min durations and subsequently cooling them down using air and water. This study aims to uncover the influence of different stiffener configurations on the load carrying capacity of sections under elevated temperature parametrically. With the experimental study results from previous studies as a reference, authors used FEM analysis to comprehensively study the behavior of GI-based CFS sections under fire. Vertical, horizontal, and not providing a stiffener were the configurations selected to study the beams parametrically. Parametric analysis confirmed that different stiffener configurations did not alter the predominant failure mode, which remained distortional buckling across all specimens. Beams with vertical stiffeners demonstrated superior performance compared to those with horizontal stiffeners in parametric analysis. Lateral–torsional buckling was observed in the reference specimen, lacking stiffeners due to inadequate restraint at the supports. [ABSTRACT FROM AUTHOR]

To enhance the Young's modulus (E) and strength of titanium alloys, we designed titanium matrix composites with interconnected microstructure based on the Hashin-Shtrikman theory. According to the results, the in-situ reaction yielded an interconnected microstructure composed of Ti2C particles when the Ti2C content reached 50vol%. With widths of 10 and 230 nm, the intraparticle Ti lamellae in the prepared composite exhibited a bimodal size distribution due to precipitation and the unreacted Ti phase within the grown Ti2C particles. The composites with interconnected microstructure attained superior properties, including E of 174.3 GPa and ultimate flexural strength of 1014 GPa. Compared with that of pure Ti, the E of the composite was increased by 55% due to the high Ti2C content and interconnected microstructure. The outstanding strength resulted from the strong interfacial bonding, load-bearing capacity of interconnected Ti2C particles, and bimodal intraparticle Ti lamellae, which minimized the average crack driving force. Interrupted flexural tests revealed preferential crack initiation along the {001} cleavage plane and grain boundary of Ti2C in the region with the highest tensile stress. In addition, the propagation can be efficiently inhibited by interparticle Ti grains, which prevented the brittle fracture of the composites. [ABSTRACT FROM AUTHOR]

This study introduces a novel non-prestressed concrete precast bottom slab with a section steel and two ribs, designated as NPBS2R. The research aimed to evaluate the effect of section steel form and steel trusses on the flexural performance of NPBS2R. A comprehensive analysis, including three-point static loading tests and numerical simulations, was conducted on five full-scale specimens. The findings reveal that all NPBS2R specimens satisfy the free support construction requirements. Compared to conventional non-prestressed precast bottom slabs with steel trusses (NPB), the NPBS2R's cracking moment improved by 43.5–59.5%. The section steel, remaining unyielded in tests, demonstrates potential for reuse, with its form exerting minimal impact on the overall flexural stiffness of NPBS2R. The presence of steel trusses was observed to marginally enhance the flexural behavior, contributing to a 15.0% increase. The numerical study highlights that the section size of the section steel, the chord diameter of the steel truss, and the truss quantity significantly influence NPBS2R's flexural performance. The theoretical values derived from the study closely align with the experimental and numerical outcomes, confirming the established calculation formula's accuracy and reliability for practical engineering applications. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation of the flexural behavior of reinforced concrete one-way slabs with longitudinal hollows. Hollow ratios (weight reductions) used in this work are 11.43% and 22.86%. Two longitudinal reinforcement ratios (ρ = 0.58 % and 1.03 %) and four steel fibers volumetric ratios (Vf = 0, 0.2, 0.4, and 0.8%), were used. Results show that slabs with longitudinal hollows having weight reduction up to 22.86%, show reductions in strength (ultimate load) up to 32% and toughness (energy absorption) up to 45% and higher deflections compared to corresponding solid slabs. However, these reductions lowered to 27.5% and 24.5%, respectively using 0.8% steel fibers or 6.3% and 25.5%, respectively by increasing longitudinal reinforcement from 0.58% to 1.03%. Furthermore, increasing longitudinal reinforcement from 0.58% to 1.03% along with using 0.4% steel fibers in a hollow slab gives a strength gain of 17.5% with a reduction in toughness of only 9.8% compared to reference solid slab with 0.58% longitudinal reinforcement and 0% steel fibers. Results also showed that hollow slabs offer stiffer load deflection behavior (lower deflections) and less maximum crack width as longitudinal reinforcement and/or steel fibers. [ABSTRACT FROM AUTHOR]

Abstract This research presents an experimental, analytical, and numerical study to predict the flexural behavior of reinforced concrete hidden and wide beams embedded in slabs. The experimentally studied parameters of testing eight specimens include beam depth, beam width, and beam eccentricity from the column. The obtained test results were compared to the predictions of finite element analysis using the ANSYS program. A numerical parametric study was conducted by the ANSYS program to explore other parameters affecting the ultimate flexural strength of beams. The studied parameters encompass concrete compressive strength, steel reinforcement strength, bottom reinforcement ratio, top-to-bottom reinforcement ratio, and web reinforcement ratio. The results revealed that an increase in beam depth led to higher ultimate load and secant stiffness, along with a decrease in deflection. The increase in beam width significantly affected beam depth, resulting in increased ultimate load and secant stiffness and a slight decrease in deflection. The increase in beam eccentricity from the column resulted in a decrease in ultimate load and secant stiffness while increasing the deflection. Comparisons between experimental and numerical results were made against calculations based on the ECP 203-2017 and ACI 318-19 codes, and the comparison yielded satisfactory results.

The flexural behavior of lightweight concrete two-way slabs is investigated in this work, with a focus on the strengthening or repairing method of externally attaching carbon fiber-reinforced polymer (CFRP) sheets. Five 1000 mm by 1000 mm by 120 mm reinforced lightweight concrete slab slabs were used in the experiment. Tested one specimen with no strengthening and another with CFRP sheet strengthening and repaired the rest with a single layer of CFRP at damage ratios of 50%, 60%, or 70% of the ultimate load, consciously making each slab crack under bending loads while keeping the exact measurements. As to the experiment findings, the ultimate load capacity increased by 30.3% at the strengthened specimen, 17.7% at the 50% damage level, 12.6% at the 60% damage level, and 10.9% at the 70% damage level. As degradation increases, so does the carrying capacity of LWC slabs. The amount of damage LWC slabs sustain influences their stiffness and flexibility. Effectively repairing the sample, CFRP sheets raised the reinforced concrete slabs� failure stress and stopped the fractures from growing. Reinforced concrete slab failure was increased, and CFRP sheet repairs of the specimens successfully stopped crack propagation.

Recently, a new proposed technique named; Externally Bonded Reinforcement on Grooves (EBROG) has been presented as a strengthening method to postpone or eliminate the undesirable debonding failure mode that is accompanying to Externally Bonded Reinforcement (EBR) method. This paper introduces an experimental and analytical study to evaluate the validity and accuracy of the formulas that were introduced by the standard codes and researchers, in estimating the ultimate load of RC continuous beams strengthened with carbon fiber reinforced polymer (CFRP) sheets in flexure. The experimental program includes testing of ten RC beams with cross section of (200×130) mm and two equal spans, each span has a 1050 mm length. The comparison between the ultimate load collected from the test results and that predicted using ten different analytical models is conducted. It is found that the ACI 440.2R-17 and most of other analytical models well predicted the ultimate load of RC beams strengthening with one layer of CFRP sheets using EBR, but most of these models significantly underestimate the ultimate load of tested beams that were strengthened using EBROG method. ACI, Shehata el. al., and Teng et al. models give close predicted load to the experimental results in case of EBR beams strengthened with two layers.

This paper presents a strengthening technique using a high-performance fibre-reinforced cement-based composite (HPFRCC) mixture. To evaluate the performance of this approach, two types of concrete mixtures were used one high performance and other high strength in strengthening process and compared to strengthening using CFRP laminate. The results showed that the strengthening was in the proportions (42 %, 58.03 %, 74.32 %) for (Mhs, Mcfrp, Mhp), respectively, Where the strengthening improved the bending capacity for beam (Mhp) to a greater extent of the other types and it reduced the appearance of cracks in the beam when loading until occur failure. As appeared failure modes in all elements were due to rupture in the flexure region and crush in the compression region. In addition, ductility index of the strengthened beams was acceptable and energy absorption of the strengthened samples high if compared to the reference beam Therefore, it can be said that this technology may provide a safer alternative for flexural strengthening of RC beams.

The primary aim of this study was to determine the influence of CuO-decorated graphene oxide nanoplatelets (CuO@GONPs) loading (0.05, 0.1, 0.3, 0.5, and 0.7 wt.%) on the flexural and wear properties of epoxy-matrix nanocomposites. It is worth noting that the Copper (II) chloride (CuCl2) was used as a nano-CuO generator on the surface of the GONPs in the presence of NaOH. Various analyses such as X-ray diffraction (XRD), Atomic-force microscopy (AFM), Raman spectra, and energy dispersive X-ray (EDX) confirmed the successful synthesizing of the CuO@GONPs hybrid. The results of the flexural tests revealed that the highest obtained flexural strength and flexural modulus belonged to the specimens containing 0.3 wt.% and 0.5 wt.% CuO@GONPs, with 51.8% and 21.3% enhancements respectively, as compared to the neat epoxy. The wear test results showed that adding 0.5 wt.% CuO@GONPs into the epoxy matrix was caused to decrease the wear rate and friction coefficient by 87.4% and 29.6%, respectively. Additionally, the CuO@GONPs/epoxy nanocomposite denoted better flexural and wear behaviors than the pristine GONPs/epoxy one. Overall, the controlled introduction of the CuO@GONPs hybrid into the epoxy matrix was found to be an effective strategy for enhancing its flexural and wear properties. [ABSTRACT FROM AUTHOR]

To enhance the mechanical and constructional performance of the ultra‐high performance concrete (UHPC) beams, the steel plate placed at the bottom surface of the UHPC beam is utilized to replace the ordinary steel rebars. In this paper, four 3.2 m UHPC T‐shaped beams with different reinforcement patterns of ordinary steel rebars and external steel plate were fabricated and comparatively tested under flexure loading. Their damage patterns, load versus deflection behavior, flexural capacity, load versus strain behavior, moment versus curvature behavior, stiffness, and crack development were investigated. The flexural experiments indicated that the external steel plate, positioned at the bottom surface of the UHPC members, could resolve the difficulty of installing ordinary steel rebars in slender UHPC components and improve its constructional performance. Compared with the inside steel rebar reinforcement, the employment of the steel plate at the bottom surface of the UHPC beam can effectively increase the distance from the neutral axis to the tensile reinforcement at the serviceability and ultimate states, thereby improving its flexural capacity and stiffness. Additionally, the configuration of the external steel plate was beneficial to reduce the tensile stress level of the tensile reinforcement and limit the opening of UHPC crack width, and thus their crack resistance can be effectively enhanced. Moreover, increasing the thickness of the steel plate or rebar ratio can also significantly improve the flexural capacity, stiffness, and cracking resistance of UHPC beams. [ABSTRACT FROM AUTHOR]

This paper presents the experimental study on the reinforced concrete (RC) beam strengthened with externally bonded carbon fiber reinforced polymer (EB-CFRP) laminate and engineered cementitious composites (ECC) material. A total of six beams were tested under the four-point bending test to investigate the influence of strengthening scheme, type of CFRP laminate and the width of CFRP plate on the flexural response. The results revealed that hybrid strengthened beam with the technical of EB-CFRP and ECC transition layer significantly enhanced the crack load (29.0%–133.3%), yield load (50.9%–96.5%) and ultimate load (50.0%–81.9%) of the beams relative to the control beam. The employment of ECC material was an ideal transition layer for delaying the interfacial debonding of CFRP laminate, where the ultimate tensile strain of CFRP plate in hybrid strengthened beams was 13.2%–33.33% higher than that of beam merely strengthened with EB-CFRP plate. Beams strengthened with CFRP sheet had the greater flexural performance and higher utilization of CFRP than its counterparts strengthened with CFRP plate. Moreover, the predicted model associated with ultimate bearing capacity of the hybrid beams was provided based on ACI 440.2R-08, which was relatively conservative with a margin for the ultimate load of the hybrid strengthened beams. [ABSTRACT FROM AUTHOR]

To improve the brittleness characteristics of magnesium phosphate cement-based materials (MPC) and to promote its promotion and application in the field of structural reinforcement and repair, this study aimed to increase the toughness of MPC by adding jute fiber, explore the effects of different amounts of jute fiber on the working and mechanical properties of MPC, and prepare jute fiber reinforced magnesium phosphate cement-based materials (JFRMPC) to reinforce damaged beams. The improvement effect of beam performance before and after reinforcement was compared, and the strengthening and toughening mechanisms of jute fiber on MPC were explored through microscopic analysis. The experimental results show that, as the content of jute fiber (JF) increases, the fluidity and setting time of MPC decrease continuously; When the content of jute fiber is 0.8%, the compressive strength, flexural strength, and bonding strength of MPC at 28 days reach their maximum values, which are increased by 18.0%, 20.5%, and 22.6% compared to those of M0, respectively. The beam strengthened with JFRMPC can withstand greater deformation, with a deflection of 2.3 times that of the unreinforced beam at failure. The strain of the steel bar is greatly reduced, and the initial crack and failure loads of the reinforced beam are increased by 192.1% and 16.1%, respectively, compared to those of the unreinforced beam. The JF added to the MPC matrix dissipates energy through tensile fracture and debonding pull-out, slowing down stress concentration and inhibiting the free development of cracks in the matrix, enabling JFRMPC to exhibit higher strength and better toughness. The JF does not cause the hydration of MPC to generate new compounds but reduces the amount of hydration products generated. [ABSTRACT FROM AUTHOR]

The combination of glass fiber–reinforced polymer (GFRP) and ultrahigh-performance concrete (UHPC) to form structural members has generated significant interest due to their excellent durability and mechanical properties. This paper presents the flexural behavior and design methodology of GFRP-reinforced UHPC beams. Eight reinforced UHPC beams were tested to failure, varying in longitudinal reinforcement type (steel and GFRP), flexural reinforcement ratio, and steel fiber volume fraction (1% and 2%). Two flexural failure modes, including crack localization followed by rupture of GFRP (tension failure) and progressive crushing of UHPC followed by rupture of GFRP (compression failure), were observed in the tested GFRP-reinforced beams. Substitution of steel bars with GFRP bars resulted in delayed crack localization and a significant improvement in flexural strength by 54.9% and ultimate displacement by 55.7%. Increasing the GFRP reinforcement ratio showed a trend of increased flexural capacity, ultimate deformation, and energy dissipation capacity. Increasing the steel fiber volume in UHPC improved the flexural capacity of the tension failure–controlled beam, but had a slight effect on the flexural capacity of the compression failure–controlled beam. In addition, two different models were used to calculate beam deflection, and were compared with experimental results at the service load levels. Considering the fiber-bridging mechanism, a flexural strength model for GFRP-reinforced UHPC beams was developed. Finally, a minimum reinforcement ratio was proposed to ensure progressive failure of GFRP-reinforced UHPC beams. [ABSTRACT FROM AUTHOR]

This research presents an experimental program for flexural strengthening of reinforced concrete (RC) full-scale girders with externally bonded carbon fiber–reinforced polymer (CFRP) sheets secured with fiber anchors. The testing program consisted of five RC T-girders strengthened with identical CFRP sheets anchored with different numbers of CFRP fiber bundles. The main objective of this study is to address the effectiveness of the CFRP fiber anchors in controlling premature failure of the CFRP sheets due to debonding. To evaluate the experimental results, a simplified design model was introduced to predict the effective CFRP maximum strain limit associated with a given number of fiber anchors in the shear span. The test results show that using CFRP fiber anchors significantly delayed the failure of the CFRP sheet beyond the classical intermediate crack (IC) debonding failure mode. In addition, the presented design model agrees reasonably well with the experimental findings as it pertains to the various numbers of anchors. Nevertheless, an anchor efficiency factor is proposed herein to reflect the fiber anchor group effect based on the experimental findings. Practical Applications: This paper presents an experimental program and a design model to capture the efficiency improvements of the response of carbon fiber–reinforced polymer (CFRP) strengthened full-scale reinforced concrete T-girders secured with increasing number of carbon fiber anchors along the shear span. Both the equivalent debonding strain and load capacity were improved owing to the use of increasing numbers of fiber anchors per shear span. This study showed that the ultimate failure of the girders can be controlled by the number of fiber anchors used to secure the CFRP sheets. Sectional analysis may not be strictly applicable once the progression of debonding starts. However, it is shown to capture a reasonably accurate measure of the maximum CFRP debonding strain without the need to resort to higher-order analysis that does not lend itself to design practice. [ABSTRACT FROM AUTHOR]

This paper studied the flexural behavior of bridge deck link slabs made with polyvinyl alcohol–strain-hardening cementitious composites (PVA-SHCC). The tensile and flexural properties of the self-compacting PVA-SHCC with four volume fractions, i.e., 0%, 1%, 1.5%, and 2%, were evaluated first. Next, using the similarity theory, composite models with a geometric similarity ratio of 1:5 were designed to represent the bridge deck with the link slabs. The models considered three materials for link slabs, including concrete, cement mortar, and self-compacting PVA-SHCC, and two different curing ages at 7 and 56 days. Bending tests were performed to investigate the flexural behavior of the models. Based on the fractal theory, the cracking characteristics of the models with different types of link slabs were compared, and the relationship between fractal dimensions and the flexural behavior of the models was studied. Numerical models were built to correlate with the results from the bending tests. It was illustrated that the flexural behavior of the self-compacting PVA-SHCC link slab is better than that of concrete and cement mortar link slabs, where the crack initiation and propagation can be postponed. The results can provide theoretical support and design guidance for the self-compacting PVA-SHCC bridge deck. [ABSTRACT FROM AUTHOR]

Cold-formed steel (CFS) sections have become popular in construction due to several advantages over structural steel. However, research on the performance of galvanized iron (GI)-based CFS under high temperatures, especially regarding its flexural behavior, has been limited. This study extensively investigates how GI-based CFS beams with varying spans behave under elevated temperatures and subsequent cooling using air and water. This study examines the impact of temperature loading and compares the effectiveness of air- and water-cooling methods. Experimental results are validated and analyzed alongside findings from finite element modeling (FEM) using ABAQUS (2019_09_13-23.19.31) and the Direct Strength Method (DSM). Additionally, this study conducts a parametric investigation to assess how beam span influences flexural capacity. Among beams heated to the same temperature, those cooled with water show slightly lower load capacities compared to those cooled with air. The highest load capacity observed is 64.3 kN for the reference specimen, while the lowest is 26.2 kN for the specimen heated for 90 min and cooled with water, a 59.27% difference between them. Stiffness decreases as heating duration increases, with the reference section exhibiting significantly higher stiffness compared to the section heated for 90 min and cooled with water, with a 92.76% difference in stiffness. As heating duration increases, ductility also increases. Various failure modes are observed based on different heating and cooling conditions across different beam spans. This study provides insights into how GI-based CFS beams perform under temperature stress and different cooling scenarios, contributing valuable data for structural design and safety considerations in construction. [ABSTRACT FROM AUTHOR]

Textile-reinforced concrete (TRC) is a composite concrete material that utilizes textile reinforcement in place of steel reinforcement. In this paper, the efficacy of the partial replacement of steel reinforcement with textile reinforcement as a technique to boost the flexural strength of reinforced concrete (RC) beams was experimentally investigated. To increase the tensile strength of concrete, epoxy-coated carbon textile fabric was used as a reinforcing material alongside steel reinforcement. Beams were cast by partially replacing the steel reinforcement with carbon fabric. Partially replaced carbon fabric-reinforced concrete beams of size 1000 × 100 × 150 mm3 were cast by placing the fabrics in different layers. A four-point bending test was used to test cast beams as simply supported until failure. Then, 120 ohm strain gauges were used to study the stress–strain behavior of the control and TRC beams. Based on this experimental study, it was observed that 50% and 25% of the steel replaced with carbon fabric beams performed better than the conventional beam. ABAQUS software was used for numerical investigation. For the load deflection characteristics, a good agreement was found between the experimental and numerical results. Based on the experimental analysis carried out, a prediction model to determine the ultimate load-carrying capacity of TRC beams was created using an Artificial Neural Network (ANN). [ABSTRACT FROM AUTHOR]

The external bonding (EB) of fiber-reinforced polymer (FRP) is a usual flexural reinforcement method. When using the technique, premature debonding failure still remains a factor of concern. The effect of incorporating multi-wall carbon nanotubes (MWCNTs) in epoxy resin on the flexural behavior of reinforced concrete (RC) beams strengthened with basalt fiber-reinforced polymer (BFRP) sheets was investigated through four-point bending beam tests. Experimental results indicated that the flexural behavior was significantly improved by the MWCNT-modified epoxy. The BFRP sheets bonded by the MWCNT-modified epoxy more effectively mitigated the debonding failure of BFRP sheets and constrained crack development as well as enhanced the ductility and flexural stiffness of strengthened beams. When the beam was reinforced with two-layer BFRP sheets, the yielding load, ultimate load, ultimate deflection, post-yielded flexural stiffness, energy absorption capacity and deflection ductility of beams strengthened using MWCNT-modified epoxy increased by 7.4%, 8.3%, 18.2%, 22.6%, 29.1% and 14.3%, respectively, in comparison to the beam strengthened using pure epoxy. It could be seen in scanning electron microscopy (SEM) images that the MWCNTs could penetrate into concrete and their pull-out and crack bridging consumed more energy, which remarkably enhanced the flexural behavior of the strengthened beams. Finally, an analytical model was proposed for calculating characteristic loads and characteristic deflections of RC beams strengthened with FRP sheets, which indicated a reasonably good correlation with the experimental results. [ABSTRACT FROM AUTHOR]

The influence of the curing methods on the flexural performances of the milling steel fiber reinforced ultra-high-performance concrete (UHPC) with a high fiber content was systematically evaluated in this study, alongside the flowability and compressive strength. The UHPC specimens were subjected to standard curing and steam curing, employing three steel fiber reinforcing schedules: single milling fiber, single straight fiber, and a combination of both. The flowability of the UHPC was found to be less affected by the milling fiber compared to the straight fiber. Steam curing significantly enhanced the compressive strength but had a slight negative effect on the flexural behavior. However, this adverse effect could be mitigated as the fiber content increased. The flexural strength and toughness of the UHPC with milling fiber were minimally influenced by steam curing, suggesting that standard curing was sufficient for the milling fiber-reinforced UHPC. Conversely, steam curing exhibited an improvement in the flexural behavior of the UHPC containing a hybrid combination of milling and straight fibers. In addition to developing an empirical model for compressive and flexural strengths, we proposed a data-driven model called Gaussian process regression (GPR) to predict the flexural behaviors of the UHPC with varying fiber content, types, and curing methods. The data-driven model demonstrated high accuracy, with an R2 value of 1.0 when compared to the experimental data. [ABSTRACT FROM AUTHOR]

Regarding the damage incurred by aluminum alloy latticed shells under fire loads, a crucial aspect in assessing structural integrity is examining the residual bearing capacity of aluminum alloy gusset (AAG) joints. Consequently, this paper conducted experimental and numerical analyses on the post-fire flexural behavior of AAG joints. Initially, twelve AAG joints underwent post-fire tests, revealing that the failure patterns differed between thin-plate joints (exhibiting block tearing of gusset plates) and thick-plate joints (exhibiting member buckling). Notably, the initial stiffness approximately remained constant, while a trilinear relationship emerged between the ultimate flexural bearing capacity and the maximum post-fire temperature. Subsequently, finite element (FE) analysis was carried out, and the accuracy of FE models was verified by comparing the FE results with the test results. A comprehensive parametric analysis, considering various plate thicknesses, post-fire temperatures, and aluminum alloy brands, was then conducted. Ultimately, employing statistical regression, theoretical equations were formulated to estimate both bending stiffness and bearing capacity for AAG joints after exposure to fire. [ABSTRACT FROM AUTHOR]

This article presents an experimental analysis on the use of carbon fiber reinforced polymer (CFRP) sheets to enhance the flexural performance of lightweight concrete slabs. The study found that repairing the slabs with CFRP sheets increased their load capacity and prevented crack propagation. However, the effectiveness of the rehabilitation decreased with increasing damage. The article also provides a list of references related to the behavior and performance of various types of concrete structures, which can be valuable for researchers and engineers in the field. [Extracted from the article]

In this study, the structural performance of a new type of lightweight composite cold-formed steel and timber (CFST) flooring system has been investigated by conducting four-point bending tests on 13 specimens. A bare cold-formed steel system without timber sheathing was also tested to provide a benchmark response to which the strength and stiffness of the composite system were compared. This paper presents key findings on the flooring system's structural behavior and performance parameters, such as ultimate bending capacity, load-deflection response, load-slip response, and failure modes, by categorizing 13 specimens into four subgroups based on shear connector types and spacings. In the proposed composite CFST flooring system, 45-mm thick structural plywood panels were connected to the 2.4-mm thick cold-formed steel C-section joist using self-drilling screws, coach screws, and nuts and bolts. The performance of different types of shear connectors on the composite action is experimentally investigated and compared with the theoretical plastic section. Furthermore, the load-carrying capacity, effective bending stiffness, and deflection of composite CFST beams were computed theoretically using elastic theory and compared to experimental results, which showed good agreement. [ABSTRACT FROM AUTHOR]

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Box beams constructed earlier were prone to inadequate bending capacity owing to low construction standards, overloading, and environmental degradation. To resolve the challenge, three full-scale box slab beams in service for 15 years were strengthened with a high-strength mortar layer and an ultra-high-performance concrete (UHPC) layer in this paper. The flexural performances of unstrengthened beams (control beam) and strengthened beams (mortar beam, UHPC beam) were investigated by in situ four-point bending tests and numerical simulations. The experimental results showed that the cracking of box beams, strengthened with high-strength mortar and UHPC layers, was effectively mitigated. In comparison to the control beam, the cracking load of the mortar beam and the UHPC beam increased by 20%, and the ultimate load increased by 23.5% and 35.3%, respectively. The high-strength mortar layer had little influence on the elastic-phase stiffness of box beams. In contrast, the stiffness of the elastic phase of the box beam, strengthened by the UHPC layer, increased by 32.9%. In the numerical simulations, the load-deflection curves obtained from finite elements and tests coincided well. The characteristic loads showed relatively good agreement with the test results, with errors below 10%. Combined with the tests and numerical analyses, the proposed equations for predicting the ultimate bearing capacities of the control beam, mortar beam, and UHPC beam were presented with a better prediction accuracy. [ABSTRACT FROM AUTHOR]

Prestressing basalt‐fiber‐reinforced polymer (BFRP) bars and three types of fibers were used to enhance precast slabs during construction. Experimental investigation was conducted on one control slab and three reinforced slabs, while equations for the flexural behavior of slabs and optimization were performed. The results demonstrated that the addition of fibers had minimal impact on the compressive strength of concrete, but significantly improved its flexural strengths by up to 36%. Fibers and BFRP bars with a prestress level of 40% enhanced the cracking load by a range of 506% to 584%, and the ultimate load by a range of 28% to 48%, while exerting minimal influence on the yield load. Reinforced slabs exhibited a reduction in yield deflection ranging from 57% to 67%, along with a decrease in ultimate deflection ranging from 33% to 42%. Prestress played a crucial role in controlling slab cracks, whereas fiber type had only minor effects. The equation derived for predicting experimental results regarding normal section cracking moment showed a maximum deviation not exceeding 5%. Material utilization can be improved by reducing slab thickness or the number of prestressing bars, followed by lowering prestress levels and truss numbers. Prioritizing reduction in slab thickness is recommended from a construction perspective. [ABSTRACT FROM AUTHOR]

This 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. [ABSTRACT FROM AUTHOR]

The orthotropic steel bridge deck (OSBD) has been widely used in recent decades, benefiting from its advantages of lightweight and easy assembly. However, the longitudinal and transversal stiffeners of OSBDs are connected to the top flange plate through dense welds, which will easily introduce fatigue cracks. Hence, the composite bridge deck (CBD) system was proposed, adding a concrete layer over a steel plate to increase the sectional stiffness of OSBDs and reduce the fatigue stress amplitude. Furthermore, some new materials with extraordinary properties such as ultra-high-performance concrete (UHPC) and engineering cementitious composites (ECC) were used to replace the normal concrete, to improve the bearing capacity and crack resistance of CBDs. In this review, four kinds of bridge deck systems with different structural types including OSBD, steel-concrete, steel-UHPC, and steel-ECC CBDs were discussed. The flexural performance of four systems under sagging and hogging moments was reviewed, and close attention was paid to the crack resistance of the CBD system. In addition, the shear connection used in the CBDs was concentrated, and the shear behavior of some connectors including studs, perforated rib (PBL), and modified clothoid (MCL) shape shear connectors was investigated. The CBD structure assembled by duplicate profile steel parts proposed recently was introduced and discussed. [ABSTRACT FROM AUTHOR]

The cracking resistance was a significant factor influencing the design load of composite beams. According to previous studies, the cracking load reached only 14–40% of the ultimate load when steel-UHPC composite beams in the hogging moment, and the risk of cracking remained. A new perfobond rib shear (PBL) connector was proposed further to improve the cracking resistance of steel-UHPC composite beams. Bending behaviors were researched by analyzing the crack distribution, failure mode, and load-deflection curve for composite beam. At failure, the steel beam flange buckled significantly, and three cracks penetrated through the UHPC board at the pure bending section. Additionally, the excellent slip resistance of the new PBL connector was validated in a push-out test. The failure mode of the push-out specimens was the fracture of the perforated reinforcement. During the push-out test, no cracks were observed on the UHPC boards. Besides conducting experiments, exploring the influence of the headed stud and new PBL connector on the composite beam by numerical analysis. The numerical results proved that the new PBL connector could release tensile stresses in the UHPC slabs and enhance the cracking properties of composite beams. [ABSTRACT FROM AUTHOR]

An experiment was conducted on a prestressed concrete (PC) composite girder bridge with steel truss webs to investigate its flexural performance. The mechanical characteristics and failure modes of a PC composite girder bridge with steel truss webs was clarified. Finite element (FE) analysis was carried out, and the influence of the girder height-to-span ratio and eccentric loading effect on the flexural performance of a composite beam bridge with a steel truss web was discussed. The method for calculating the cracking bending moment, the bending moment at the rebar yield stage, and the ultimate bending moment of a PC composite girder with steel truss webs was proposed. Key findings include that, in both the elastic and cracking elastic stages, the strain of the bottom and top conforms to the plane-section assumption. Throughout the loading process, there was no occurrence of joint failure or local buckling failure in the steel truss webs; the composite girder ultimately fails due to excessive deformation, indicating that the overall mechanical performance of the composite beam is good. The deflection and stress in the mid-span section decrease with an increasing height-to-span ratio, and there are significant impacts of eccentric loading on deflection and stress. Compared with the results of the FE analysis and test, the calculation methods of the cracking moment, reinforcement yield moment, and ultimate moment of PC composite girders with steel truss webs presented in this paper have a high accuracy. [ABSTRACT FROM AUTHOR]

Partially encased composite beams (PECBs) have advantages over conventional steel–concrete composite beams in load-carrying capacity, flexural stiffness and fire resistance. In order to determine whether the shearing force is sufficient to ensure the yield of the tensile reinforcement in the case of a large tensile reinforcement ratio, as well as the influence of encasing concrete strength and the addition of studs on the steel web, three PECB specimens were tested under bending. The results show that, in the case of a 5% tensile reinforcement ratio, natural bonding and friction forces ensure the yield of tensile reinforcement whether studs are added on the steel web or not. The encasing concrete strength and the addition of studs on the steel web have no obvious effect on both the elastic and plastic bending resistance of PECBs. The addition of studs on the steel web significantly slows down the stiffness deterioration of PECBs within the elastoplastic stage, while the flexural stiffness is not obviously affected by the strength of encasing concrete. The simplified plastic theory is proved to be applicable to predict the flexural capacity of PECBs with a large tensile reinforcement ratio. It is also indicated by calculation that, by increasing the tensile reinforcement ratio from 2% to 5%, the flexural capacity of PECBs has a significant increase, by about 32%. [ABSTRACT FROM AUTHOR]

The use of back-to-back built-up channel beams in cold-formed steel (CFS) structures is steadily rising. The growing demand for CFS sections as a cost-effective design solution has driven the development of these CFS built-up sections. Despite this, there has been limited research on the performance of mild steel (MS) based CFS at high temperatures, particularly regarding its flexural behavior. This study thoroughly explores the behavior of MS-based CFS beams with different spans under high temperatures, followed by cooling with air or water. It assesses the impact of thermal loading and evaluates the effectiveness of these cooling methods. Experimental findings are validated and analyzed in conjunction with Finite Element Modeling (FEM) using ABAQUS and the Direct Strength Method (DSM). The study also conducts a parametric analysis to determine how the varying span that affects flexural capacity of beam. Among beams heated to the same temperature, those cooled with water exhibit slightly lower load capacities than those cooled with air. The maximum load observed is 91.21 kN for the reference specimen, while the minimum load is 39.82 kN for the specimen heated for 90 min and cooled with water, resulting in a 78.45% difference between these values. Additionally, as heating duration increases, ductility of beam also increases. Various failure modes are observed based on different heating and cooling conditions across different beam spans. This study offers valuable insights into the performance of MS-based CFS beams under thermal stress and different cooling conditions, providing important data for structural design and safety in construction.