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This study aims to establish a complete theoretical model for the nominal flexural strength of concrete beams reinforced with steel-fiber composite bars (SFCB-RC), and determine an optimized range for the ratio of the diameter of the steel core to the diameter of SFCBs (η). Firstly, flexural failure modes for SFCB-RC beams were determined through theoretical analysis, and two failure modes including concrete crushing (compression failure) and FRP in SFCBs rupturing (tension failure) were recommended. It was confirmed that there exists a transition region between the failure modes of tension and compression, where both modes are possible. By conducting a statistical analysis of a database including 57 SFCB-RC beams, an upper-limit reinforcement ratio was recommended for SFCB-RC beams in the transition region. Simplified equations to predict the nominal flexural strength for compression-controlled SFCB-RC beams were proposed by directly using the constitutive model of SFCBs. The flexural strength equations for tension-controlled concrete beams reinforced with fiber reinforced polymer bars (FRP-RC) were confirmed to be also suitable for SFCB-RC beams. Validation of these equations was conducted using the assembled database. Furthermore, the parametric analysis revealed an optimal range of the ratio η (0.77–0.87). This suggested range can serve as a basis for standardizing the production specifications of SFCBs. • Design methods and recommendations for flexural SFCB-RC beams were proposed. • The upper-limit reinforcement ratio of the transition region for flexural SFCB-RC beams was determined. • Simplified equations for predicting the nominal flexural strength of SFCB-RC beams were proposed. • An optimized range for the ratio of the steel core diameter to the SFCB diameter was determined. [ABSTRACT FROM AUTHOR]

Digital twin (DT) is capable of managing, simulating, and future performance prediction of existing infrastructures by integrating three-dimensional (3D) geometric model and finite element (FE) model. This study aims to automatically generate geometric DT of existing RC members using point clouds and incorporate damages detected from images into FE models. An edge-based modeling method was proposed to extract sharp features for geometry reconstruction with incomplete point clouds, and an automated procedure was established for registering images to point clouds, mapping cracks detected in images to FE models, and assigning reduced material properties. Four RC beams were tested in a laboratory to validate the proposed method. Existing cracks were found to have a significant effect on structural capacity and failure mode. The results also showed that the developed FE model produced a good agreement between experimental and predicted failure loads while providing a more efficient and time-saving assessment protocol. [Display omitted] • Automated gDT generation of existing RC beams using incomplete point clouds. • DT-driven structural assessment through FE modeling by fusing point clouds and images. • Automated algorithms for incorporating existing cracks into FE model. • Effects of existing cracks on structural capacity and failure mode. [ABSTRACT FROM AUTHOR]

This research presents a novel joint design for wall-type concrete filled steel tube (WCFTC) beams, integrated with high-strength double-side plates, resolving the problem of traditional side plate extending from the wall and interfering with wall panel installation. The study synthesizes a reliable finite element (FE) model corroborated by previous experimental analyses, enabling a detailed parametric study on the dimensions of the side plates. Comprehensive analysis assessed the impact of steel plate thickness and material strength on the joint's seismic properties, uncovering that the innovative joint design reduces steel usage while maintaining load capacity. Subsequent full-scale testing of prototypes under cyclic loading revealed the failure modes and hysteresis responses, which exhibited notable energy dissipation reflected in ductility coefficients exceeding 3.0. The study also identifies the plastic hinge location to be at a distance ranging from 1.0 to 1.5 times the beam's height from the column's edge, validating the efficacy of the joint design categorized as full-strength or rigid. Furthermore, comparative assessments of Q690D and Q460C steel plates indicated similar performance, suggesting a flexibility in high-strength material choice without loss of joint integrity. The culmination of the study is the proposal of a clear and actionable design method, predicated on the synthesized findings, offering a pragmatic reference for designers and engineers in the field. This method aims to streamline the adoption of this advanced joint construction for enhanced seismic resilience in structural applications. • WCFTC-beams joint with high-strength steel double-sided plate. • The proposed joint exhibits good seismic performance while using less steel and achieving better building's functionality. • The design method of the joint is proposed. • The findings of the study are expected to improve the design theory of the joints. [ABSTRACT FROM AUTHOR]

With the aim to develop and assess an effective reinforcement technique for concrete beams, the approach of the combination of ultra-high ductility magnesium phosphate cement-based composites (UHDMC) and carbon fiber reinforced polymer (CFRP) was analyzed and established based on the measured parameters, including failure mode, load-deflection curve and feature points. The results showed that, for specimens reinforced by UHDMC alone or the combination of UHDMC and CFRP, several cracks in the concrete layer and multi-cracks in the UHDMC layer were both shown, presenting a ductile failure and three distinct stages in the load-deflection curve. Moreover, compared with the specimens reinforced by CFRP alone and UHDMC alone, the ultimate load and ultimate deflection both were improved in the specimens reinforced by UHDMC and CFRP. Furthermore, the strain distribution of CFRP was symmetrical along both sides of the test specimen, presenting a general law of large in the middle and small in the two ends, and its more and more obvious phenomenon with the increase of the number of CFRP layer. To some extent, the inclination trend of the overall strain of CFRP can be used to determine the location of the weak surface. • An effective method to strength the flexural performance of concrete was developed. • Multi-cracks characteristic and thus ductile failure in the UHDMC layer was shown. • Ultimate load and ultimate deflection both were improved by the combination of UHDMC and CFRP. • The inclination trend of the overall strain of CFRP predicted the location of the weak surface. [ABSTRACT FROM AUTHOR]

This study presents an experimental investigation of the failure characteristics, interface slip, strain distribution, and load-deflection response of adhesively bonded timber-concrete composite (TCC) beams fabricated using wet or dry processes. A total of six adhesively bonded TCC beams were produced with a span of 3.2 m and subjected to four-point bending tests. Wet and dry fabricated TCC beams revealed distinct failure modes. The results emphasized the critical role of bonding integrity in ensuring effective composite action and shared contribution mechanism. Wet-fabricated TCC beams exhibited a rigid bonding characterized by a consistent neutral axis alignment and load distribution along the beam span, while dry-fabricated beams experienced interface separation and compromised load-shared contribution, resulting in a significant reduction of the ultimate bending capacity of TCC beams. The outcomes showed that wet and dry TCC beams exhibited comparable load-to-mid-span deflection responses before failure, highlighting uniform behaviour and alignment with fully composite characteristics under the imposed loads. Furthermore, an analytical model for calculating TCC beams is presented and validated. The foundation of the analytical model is established upon the γ-method derived from Eurocode 5. The analytical model is compared with experimental results, highlighting its reliability and precision. Load-deflection responses, bending strain distributions, and ultimate failure loads are accurately captured, affirming the model's capability to anticipate the TCC beam behaviour. • Reliability of glue connection in TCC structures. • Performance insight in wet vs. dry TCC beams. • Analytical model for TCC design. • TCC Structural performance and environmental impact. [ABSTRACT FROM AUTHOR]

Civil structures and buildings may be subjected to accidental impact load scenarios to which the response is still a research subject. Impact failure mode and resistance of concrete structures have shown to be rather different from those under quasi-static loading, due to the influence of strain-rate modification of material properties, development of inertia forces leading to variable sectional forces' distributions and local damage mechanisms. A high sensitivity to develop shear-related failures of reinforced concrete beams under impact loading has been observed experimentally, with a complex shear-bending interaction difficult to be modelled numerical and analytically. Shear force-bending moment (M-V) interaction diagrams have been traditionally employed to provide the combination of sectional forces leading to failure. Thus, the availability of such diagrams for impact scenarios would be very useful for the engineering practice. In the present paper, an experimental investigation is presented to analyze the impact resistance of reinforced concrete beams with different span-to-depth ratios in order to determine possible envelope M-V interaction curves in impact regime. Sectional forces are tracked with the help of Digital Image Correlation (DIC) supported with High-Speed Video (HSV). Impact tests have covered beam specimens with and without shear reinforcement to understand the different failure modes. Envelope interaction diagrams are proposed taking into account the curvature rate from the experiments, which allows considering the particular strain-rate conditions of the tests. • Fully-instrumented impact experiments on RC beams have been completed. • Envelope dynamic shear force-bending moment interaction diagrams have been derived. • Analytical formulation including the curvature rate and M-V interaction is proposed. [ABSTRACT FROM AUTHOR]

Few studies have reported on the flexural behavior of multi–span reinforced concrete (RC) structures strengthened using externally–bonded (EB) systems such as fiber–reinforced polymer (FRP) and fiber–reinforced cementitious matrix (FRCM) systems. This paper introduces a theoretical model that can accurately predict the flexural behavior of such structures with a focus on their rotational capacity (curvature) and their moment redistribution response between critical sections. Unlike the available models, the proposed model accounts for the variation in the structure's stiffness during loading including that of the strengthened section. The model can precisely determine the failure mode, the rotational capacity of the formed plastic hinges and estimate the moment redistribution ratio (MRR) between the critical sections at any applied load. The efficiency of the model was validated against the experimental results of eleven FRCM–strengthened two–span RC beams (including two control beams) previously tested by the authors. A good agreement between the experimental and the theoretical results was obtained with average experimental–to–theoretical ratios of 1.0 and 0.99 for the load carrying–capacity and MRR, respectively. To accurately determine the mid–span deflections of continuous EB–strengthened structures, a new reduction parameter was incorporated in the CSA–A23.3–19 (2019) formulations to account for the variation in stiffness of the strengthened section. The new formulations substantially enhanced the prediction of the deflection capacity of the strengthened structures with an average experimental–to–theoretical ratio of 1.02 versus 1.7 when CSA formulations were used. • New model is proposed to predict the nonlinear flexural behavior of multispan RC structures strengthened using FRCM systems. • The model was validated against experimental results previously tested by the authors. • The model accurately predicted the moment capacity and the moment redistribution ratios of all beams. • New deflection parameter is incorporated in the CSA equation to account for stiffness variation due to strengthening. [ABSTRACT FROM AUTHOR]

Ultra-high performance concrete (UHPC) is usually embedded with reinforcing bars to avoid localized cracking, when adopted to strengthen existing reinforced concrete (RC) structures. In this case, indoor test is the most common way to evaluate the strengthening efficiency of UHPC overlay, which is inadequate to describe the real mechanical and degeneration states of existing structures. In this study, seven existing RC beams were first detached from a 15-year-old bridge. Then, three of them were strengthened with GFRP-reinforced UHPC overlay (named GFRP-strengthened beams), other three of them were strengthened with steel-reinforced UHPC overlay (named steel-strengthened beams), and the rest one was used as control beam. The effects of rebar type and reinforcement ratio were studied by in-situ four-point bending tests. Results indicated that the failure modes of steel-strengthened beams were predictable ductile failure, whereas sudden brittle failure was observed in GFRP-strengthened beams. The rebar type within the UHPC layer has little effect on the cracking loads of strengthened beams. When compared to steel-strengthened beams, GFRP-strengthened beams exhibited faster stiffness degradation and crack width development, with fewer crack number and wider crack spacing. Regardless of rebar type, the flexural capacity, stiffness and cracking resistance of existing RC beams were increased with the increase of reinforcement ratio. • Flexural performance of service RC beams repaired with UHPC was in-situ evaluated. • The capacity, stiffness and ductility of UHPC-strengthened beams were investigated. • Strengthening mechanism of UHPC layers with different rebar ratios was obtained. [ABSTRACT FROM AUTHOR]

This research investigated the behavior of RC slabs subjected to four points loading with five different CFRP sheet numbers (1, 2, 3, 4, 5) and three different anchorage systems (Type 1 used CFRP strips in the transverse direction, Type 2 used galvanized steel end plates without grooving, Type 3 used galvanized steel end plates with grooving). A total of twenty reinforced concrete (RC) solid slabs were cast to fulfill the study objectives. Results showed that the presence of CFRP strips enhanced the slab's ultimate load capacity by 102 %, reduced mid-span deflection by 12 %, also improved energy absorption capacity and stiffness by 36 % and 32 %, respectively. Type 2 anchorage system without grooves and type 3 anchorage system with grooves both used galvanized steel end plates and enhanced the flexural capacity of the slabs by 119 % and 125 %, respectively, also improved the RC slab properties and shifted the failure mode from delamination to a CFRP strips rupture. The introduced anchorage system without grooving was found to be an efficient and easily applied technique with high efficiency in terms of capacity and serviceability. • The noticed mode of failure of the control RC slab was due to flexural failure. • The debonding between concrete parent and fiber is a significant major failure mode for FRP. • Develop effective strengthening techniques for RC slabs. • Increasing the number of CFRP strips increased the toughness. [ABSTRACT FROM AUTHOR]

guidelines require an adequate overlap length for reinforcing bars, especially in extended spans of elements constructed from Reinforced Concrete (RC). Insufficient overlap can have adverse effects on key characteristics like bending strength and deformability of RC beams. The potential danger of failure in such elements is a significant concern as is considered a potential threat, and this study addresses it through experimental identification and numerical analysis to be mitigated carefully in this study to enhance the safety and sustainability of buildings to mitigate the risk of failure. The current investigation is centered on investigating the structural behavior of cantilevered RC beams exhibiting inadequate overlap between reinforcing bars in the hogging moment region. These beams have been strengthened through the application of ferrocement layers of Engineered Cementitious Composite (ECC). The experimental study consisted of eleven beams, which were categorized into four groups and subjected to bending loads until they reached failure. The research assessed various factors, such as the casting method (whether cast-in-situ or precast), the installation technique (involving the use of epoxy, or epoxy with anchors), and the length of the ECC layer. This layer was configured to have a length of 30Ø, 40Ø, and 50Ø, with Ø representing the diameter of the reinforcing bars along the zone subjected to hogging moments. According to findings, strengthening of specimens exhibiting insufficient steel overlap through an ferrocement ECC layer exhibited an improved overall structural behavior compared to the defective control beam. The most significant enhancement in both failure mode and load-deflection behavior was observed in beams strengthened through the incorporation of a cast-in-situ ECC layer with anchor bolts. Additionally, augmenting the strengthening length not only increased the initial stiffness of the reinforced beams but also enhanced their energy absorption capacity. Furthermore, the study involved the construction of a numerical simulation employing the Finite Element Method (FEM) simulating the observed behavior in experimentally tested beams. The model's precision was validated through a comparison of its results with the experimental data, revealing a satisfactory level of accuracy. • ECC layers enhance cantilevered RC beams with inadequate lap spliced reinforcement. • Beams strengthened with ECC layers exhibit enhanced failure mode and load-deflection behavior. • Anchor bolts with cast-in-situ ECC layers improves failure mode. • FE Models accurately predict beam behavior, offering insights for further research. [ABSTRACT FROM AUTHOR]

A hybrid strengthening system, comprising a carbon fiber reinforced polymer (CFRP) sheet combined with fiber reinforced concrete (FRC) layer is proposed in this study as a mitigatory solution to brittle debonding problems. Five reinforced concrete (RC) beams, comprising both control cases and those strengthened with the hybrid CFRP-FRC system at various FRP reinforcement ratios, were fabricated and tested to assess the system's effectiveness. A comprehensive finite element (FE) model was also developed to complement the experimental campaign and extend it into a parametric investigation on the effects of FRP reinforcement ratio (ρ f), fiber percentage in FRC (v f), and FRC layer thickness (t FRC). Compared with beams strengthened with FRP alone, using the FRC layer increased the ultimate load (P ult.) of FRP-strengthened beams by 29–59%, depending on ρ f and v f. The ductility of the hybrid FRP-FRC strengthened beams also increased by more than twice compared to the beams strengthened with only FRP. For the FRP reinforcement ratio (ρ f) of 0.18%, use of an FRC layer with v f = 2% yields the highest increase in P ult. and ductility for the hybrid system. Ultimately, the brittle FRP debonding failure was successfully eliminated using the FRC layer, leading to desirable FRP rupture. Built with capabilities to capture material nonlinearity, contact, and debonding phenomena, the FE model predictions excellently matched those of the test results in terms of the beam's capacity, failure modes as well as load-deflection and load-strain responses. • A hybrid strengthening using CFRP sheets combined with FRC layer is proposed. • Performance was evaluated using tests on RC beams at various FRP reinforcement ratios. • A comprehensive finite element model was developed to complement the experiment. • FRC layer serves as a mitigatory solution to brittle FRP debonding and leads to desirable FRP rupture. • Compared with FRP only strengthening, FRC layer increased the capacity by 29–59% along with up to twice the ductility realized by using FRP alone. [ABSTRACT FROM AUTHOR]

This paper investigates the behavior of reinforced concrete (RC) arch beams with shear weaknesses strengthened with fiber-reinforced polymer (FRP) composites, using two different methods: the externally bonded reinforcement (EBR) and grooving method (GM) in the form of externally bonded reinforcement on grooves (EBROG) method. Additionally, two different patterns of shear strengthening including two-sided and U-shaped were utilized. Nine arch beam specimens were tested, each having a square cross-section of 150 mm and a span length of 947 mm. Among these, two specimens were strengthened using the EBR method, while six specimens were strengthened using the EBROG method. The paper explores the impact of the strengthening method and pattern on the load-carrying capacity, failure mode, energy dissipation, and strain distribution of the specimens. The results indicate that the EBROG method significantly increased the load-carrying capacity of the arch beams compared to the EBR method in both patterns. The results also show that the U-shaped pattern was more effective than the two-sided pattern in increasing the load-carrying capacity of the specimens. The specimen with intermittent U-shaped FRP demonstrated 34.8% and 47.3% higher load-carrying capacity than the non-strengthened specimen when using the EBR and EBROG methods, respectively. The paper also introduces an analytical approach to estimating internal forces, such as flexural moment, axial force, and shear force, along the arch beam. The comparison between the experimental and theoretical results confirms the accuracy of the analytical approach. • The behavior of RC arch beam with shear weakness was investigated. • EBR and EBROG methods were adopted for strengthening of the arch beam. • PIV method was utilized to obtain the strain distribution, validate the displacements, etc. • An analytical procedure was conducted to validate the experimental results and investigate the performance of the strengthening methods. [ABSTRACT FROM AUTHOR]

• The failure models and collapse mechanisms of self-centering PC frames were analyzed. • Effects of different design parameters on failure modes were evaluated. • Reasonable optimization measures were suggested to reduce the concrete damage. • Collapse mechanism of self-centering PC frames were compared with RC frames. • Calculation model was proposed to predict the progressive collapse resistance. In this study, the refined finite element (FE) models for the collapse resistance of self-centering precast concrete (PC) frames with and without infill walls were established. Based on the validated FE models, the effects of different design parameters on the failure modes at the beam ends as well as the collapse resistance of the structures were evaluated. Correspondingly, the reasonable optimization measures were suggested to reduce the concrete damage at the beam ends. The results indicated that the insufficient stirrup spacing may cause the concrete failed prematurely along the edge of the steel jackets due to stress concentration. Decreasing the thickness of steel angles could reduce the failure area of concrete at the beam ends, but also caused a significant reduction in the initial stiffness and vertical resistance of the structures. The thickness of steel jackets mainly influenced the size of failure area at the beam ends. The position of horizontal bolts and longitudinal bolts had effects on the failure modes of concrete at the beam ends as well as the collapse resistance of the structures, while the latter was particularly evident. Compared to the cast-in-place reinforced concrete (RC) frames with the same size and reinforcement ratio, the damage extent at crucial locations of the optimized self-centering PC frame structures was lower, while exhibiting similar collapse resistance. A calculation model considering the resistance contribution of structural and non-structural infill wall members was proposed to predict the vertical resistance of self-centering PC frame structures in the compressive arch action (CAA) stage. The accuracy of the calculation model was verified by comparing 23 FE models with different design parameters. [ABSTRACT FROM AUTHOR]

An experimental program was conducted to examine the seismic performance of flexural beam members strengthened with carbon fiber-reinforced polymer (CFRP) sheet and anchored using carbon fiber splay anchors. This research study extends the use of carbon fiber anchors to secure the top and bottom CFRP flexural sheets under cyclic loading. In this study, low strength concrete is examined, with lightly reinforced steel ratio (0.0034) to test full-scale rectangular beams. Five reinforced concrete beams were cast, strengthened, and tested under reversed cycles of four-point bending to failure. The beams were categorized into a control specimen, strengthened specimens with thin sheets with and without fiber anchors, and strengthened specimens with thick sheets with and without fiber anchors. They were tested cyclically under displacement control according to the AC 125 loading protocol. The failure modes ranged from classical ultimate failure for the control beam to rupture and intermediate crack (IC) debonding for the beam with unanchored thin CFRP sheets. On the other hand, debonding took place for the thicker sheets with no anchors, while the thicker sheets with fiber anchors underwent cover delamination failure mode despite the fact that the sheets were extended very close to the simple supports. The hysteresis response loops were compared for the different specimens and the analytical envelop curves were predicted resulting in a close agreement to the experimental finding. • Seismic performance of flexural beams CFRP strengthened with and without carbon fiber anchors is successfully examined. • Thicker CFRP sheets yield lower energy dissipation, ductility, but higher strength and seismic pinching. • Failure modes varied from sheet debonding to CFRP rupture and cover delamination. • The use of anchors at sheet ends was not very effective in extending the hysteretic cycles beyond those without anchors. • The need to apply fiber anchors along the entire shear span to harness improved behavior is clearly evident. [ABSTRACT FROM AUTHOR]

With the construction and development of intelligent roads, an increasing number of sensors are being embedded into the road structures. Portland cement concrete (PCC) pavement is one of the main forms of road pavement, but the mechanical behaviors of the PCC pavement with sensor embedding are less studied. In this study, the damage mechanism of PCC pavement is investigated by using the three-point beam bending test, considering the sensor embedding and the coating of the sensor surface. The effect of sensor embedding on the flexural mechanical properties and the damage failure modes of concrete beams are evaluated by using the acoustic emission (AE) technique and the digital image correlation (DIC) technique. Moreover, the concept of degree of coupling (DC) is introduced to reveal the collaborative bearing mechanism between sensor and concrete, and is characterized by an evaluation model considering ultimate bearing capacity, critical instability point, collaborative bearing capacity, AE ring counts, and AE energy. The findings can provide valuable insights in the packaging design of sensor to guarantee the coupling between the sensor and the surrounding concrete for accurately monitoring the long-term performance of road infrastructure. • The damage evolution of concrete beam implanted with sensor with different surface coating were conducted through three-point bending test. • The acoustic emission (AE) data and digital image correlation (DIC) data of concrete beam embedded with sensor or not were discussed. • The degree of coupling (DC) is introduced to reveal the collaborative bearing mechanism between sensor and concrete. [ABSTRACT FROM AUTHOR]

• CFRP-strengthened RC beams exposed to natural hygrothermal environment for six years. • The fatigue life decreased due to the degradation of CFRP-concrete interface. • A fatigue life prediction model for beams exposed to nature was developed using FEM. Exploring the durability of Carbon Fiber Reinforced Plastic (CFRP) strengthened concrete structures is a significant focus in the field of civil engineering. The majority of the present durability studies, which investigate the combined effects of external and environmental loading on CFRP-strengthened concrete structures, are conducted in accelerated aging environments. Nevertheless, this method fails to accurately reflect the real service conditions experienced by these structures in natural hygrothermal environments. In this study, a 6-year-long natural exposure experiment is conducted on CFRP-strengthened reinforced concrete (RC) beams under sustained loads. Additionally, the static and fatigue behavior of the exposed beam is investigated through both experimental and theoretical methods. The results indicated that the ultimate load of CFRP-strengthened RC beam remained unchanged after 6 years of natural exposure, as compared to that of non-exposed beams. However, noticeable changes were observed in their fatigue performance. The fatigue life decreased by 30 %, 75 %, and 86 % at loading levels of 0.60, 0.65, and 0.72, respectively. The fatigue limit decreased by 10 % and exhibited a dense distribution of cracks. Meanwhile, a fatigue life prediction model for RC structures strengthened with CFRP after long-term exposure to natural hygrothermal environment was established. In this model, the degradation of the CFRP-concrete interface behavior was considered. Through finite element analysis, two failure modes were predicted: fracture of the main reinforcement and the CFRP-concrete interface debonding failure under fatigue load. The corresponding fatigue life times were calculated. This model agrees well with the experimental findings. [ABSTRACT FROM AUTHOR]

This research has investigated the ability of ultra-high performance concrete (UHPC) to improve the blast performance of high-strength concrete (HSC) beams. As part of the study 4 shear-deficient HSC beams built without stirrups and with dimensions of 125 mm × 250 mm × 2440 mm were retrofitted with a UHPC jacket and tested under simulated blast loads using a shock-tube. The retrofit involved replacing the existing cover with a cast in-situ UHPC jacket (with thickness of 20–40 mm). A companion set of beams was also tested under quasi-static four-point bending. The results from the blast and static tests are compared to a control set of HSC beams built without and with stirrups to examine the ability of UHPC to increase shear and flexural resistance, respectively. The effect of steel ratio (ρ = 1.6% or 2.4%), an important parameter which affects the behavior of HSC and UHPC beams, was also investigated in beams with 15M and 20M bars. Under static loading, the results show that the UHPC jacket was able to prevent shear failure, and improve flexural performance by increasing strength by 40–125%, stiffness by 80–100% and overall toughness by 56–144%, when compared to the companion HSC beams. Under blast loading, the UHPC increased shear capacity, prevented shear failure and improved blast performance by reducing displacements, increasing overall blast capacity and improving damage tolerance. For example, in the 20M set, the UHPC-retrofitted beam showed reductions of 26–63% in maximum displacements, and 88–100% in residual displacements under varying blast intensities. The steel ratio was found to play an important role on the failure mode of the retrofitted beams under static loading, with bar fracture observed in the beam with lower steel ratio of 1.6%. As part of the numerical study, the blast response of the UHPC retrofitted beams was predicted using 3D finite element (FE) modeling. The FE models were able to predict the failure modes and maximum displacements of the control and UHPC retrofitted beams, with an average numerical-to-experimental displacement ratio of 1.03 and an average error of 8%. • Ability of UHPC to improve shear/flexural response of HSC beams under static/blast loads is investigated. • UHPC prevented shear failure and promoted flexural response in shear-deficient beams under static and static/blast loads. • Compared to beams with stirrups, the UHPC retrofit increased blast capacity and reduced blast-displacements. • The UHPC further increased damage tolerance and prevented formation of blast fragments. • FE modeling of the beams was conducted with LS-DYNA with good predictions of displacements and damage modes. [ABSTRACT FROM AUTHOR]

This research investigated using waste polyethylene terephthalate (PET) bottle fibres in concrete. Experimental tests were conducted to evaluate the mechanical properties of PET fibre-strengthened concrete. The effects of the fibre volume fraction and fibre length were studied to obtain optimal values. Moreover, a thorough statistical analysis was performed to identify the parameter that impacts the inclusion of PET fibres in concrete. Furthermore, the study explored the effect of PET fibres on reinforced concrete beams of shear failure mode. The results showed that incorporating PET fibres significantly enhances the ductility of the concrete material and reduces shrinkage. It also promotes the initial stiffness, the inelastic absorbed energy and the ductility of steel-reinforced concrete beams. [Display omitted] • The influence of PET plastic fibres in concrete mechanical properties, ductility and shrinkage. • Experimental work to select the optimised volume fraction and length of the fibres. • Statistical analysis to define the parameter that impacts the inclusion of PET fibres in concrete. • Exploring the effect of PET fibres on reinforced concrete beams of shear failure mode. • PET fibre enhancement in the initial stiffness, energy capacity and ductility of the RC beams. [ABSTRACT FROM AUTHOR]

The high incidence of debonding as a failure mode in FRP-strengthened structures highlights the importance of regular inspections of the bond layer for any discontinuity. In contrary to most previous studies, which focus on the linear features of waves like amplitude and velocity, the present study utilises a novel collinear wave mixing technique for the generation of mixed harmonics of surface guided waves for debond characterisation. Experimental study is conducted in which a particular surface guided mode, sensitive to bond layer, is excited using wedge transducers. A three-dimensional finite element model is developed to understand the nonlinear interaction of surface guided waves with debonding, and the results obtained are compared with those obtained from the experimental results in both time and frequency domains. The numerical results are found to be in good agreement with the experimental ones. Later, extensive parametric studies are conducted on the validated model by changing the debond size. A damage index is proposed that rely on the band frequency amplitude of fundamental and higher order mixed harmonics paving the way for baseline-free debond quantification. The damage index (DI) exhibited a consistently increasing trend with debond size. Finally, a sensitivity analysis is conducted by increasing the debond size and comparing the relative parameter values of linear features (scattered amplitude and change in time of arrival) with the proposed damage index. The analysis results revealed that the proposed DI is more sensitive to the debond size than the conventional linear parameters that also requires pristine condition data. Thus, the study offers valuable insights into the collinear wave mixing phenomenon in FRP strengthened RC structures and proposes an efficient and practical technique for debond detection in the field. • Nonlinear features of surface guided waves are used for debond characterisation in FRP-strengthened RC beams. • A damage index, based on fundamental and combined harmonics is proposed. • The proposed damage index is more sensitive than conventional linear features. • This technique does not require baseline data for debond detection and quantification. • Wedge transducers offer more convenient field applications than PZT patch transducers. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study of full-scale steel-concrete composite beams using truss-type shear connectors. The connector geometry is original and effective. It is made from traditional steel rebar used in reinforced concrete structures. When compared with the stud-shear connector, the truss-type shear connector has several advantages, including low cost, ease of installation, and high resistance, among others. Previous research on the truss-type shear connector has made use of the popular push-out test, a reduced-scale physical model. However, for a better understanding of the truss-type shear connector behavior and to make it reliable for engineering practice, the truss-type shear connector must be studied under more realistic working conditions. In that sense, this research presents an experimental study in which three full-scale tests of steel-concrete composite beams, using truss-type shear connectors, are carried out. In the experimental program, different shear connection degrees are considered. The experimental results showed that when the shear connection degree is decreased, there is a rise in slippage between the steel beam and the concrete slab and a drop in the ultimate load. In the tests, the measured values of the uplift separation between the steel beam and the concrete slab were in compliance with the Eurocode-4 specifications. The failure modes of the specimens were characterized by excessive yielding of the steel beam or by a combination of this and the failure of the connections. The resistance of the truss-type shear connector was successfully predicted using the equation developed by the authors. • Truss-type shear connectors are evaluated experimentally in full-scale steel-concrete composite beams. • It was experimentally found that the truss-type connector complies with Eurocode-4 specifications. • An equation for the shear resistance strength of the truss-type connector was verified experimentally. • The effectiveness of the truss-type shear connector and its potential to applications were demonstrated in this research. [ABSTRACT FROM AUTHOR]

Plate end debonding is a common failure mode for fiber reinforced polymer (FRP) strengthened beams. FRP sheets and shape memory alloy (SMA) composites can effectively slow down plate end debonding and improve beam ductility owing to the anchorage effect of SMA wires on the FRP ends. This work aims to comprehensively study the anchorage performance of FRP/SMA composite strengthened beams through both model analysis and experimental investigation. The plate end debonding strength models of existing FRP strengthened beams were initially summarized and analyzed, and an improved model was proposed to predict the debonding strength of FRP/SMA composite strengthened beams at the plate end. Moreover, the anchorage performance and flexural behavior of beams strengthened with carbon fiber reinforced polymer (CFRP) and SMA composites were studied through experiments. The failure mode of the FRP sheet strengthened beams was plate end debonding failure, while the plate end debonding failure of the CFRP/SMA composite strengthened beams occurred at the strengthening zone end, and the peeling failure was delayed owing to the anchorage effect of SMA wires on the ends of the strengthening CFRP sheets. The recovery effect of SMA wires could successfully introduce prestress into CFRP sheets. Moreover, the CFRP strain corresponding to plate end debonding increased because of the anchorage of SMA wires on the CFRP sheet in the strengthening zone. The strength and ductility of the CFRP/SMA composite strengthened beam significantly improved. The proposed model for predicting the plate end debonding strength of FRP/SMA composite strengthened beams was validated through experiments. • An improved model is proposed to predict the debonding strength of beams strengthened with FRP/SMA composites at the plate ends. • The debonding failure was delayed due to the anchorage effect of SMA wires on CFRP sheets in the strengthening zone. • The strength and ductility of the beam strengthened with CFRP/SMA composites have been significantly improved. • The proposed model for predicting the plate end debonding strength of FRP/SMA composite strengthened beams was validated through experiments. [ABSTRACT FROM AUTHOR]

Revision of design standards, new regulations, and planned/unplanned increases in loadings potentially make buildings vulnerable to changes in capacity demands. This may result in some structural components of an existing structure requiring strength or stiffness improvement. Strengthening of capacity deficit members is widely recognised as the preferred and sustainable choice in terms of conserving resources and minimising the carbon footprint. Strengthening techniques such as Reinforced Concrete (RC) jacketing, steel jacketing and Fibre Reinforced Polymer (FRP) wrapping have been explored and widely used. However, when adopted solely, each scheme has its drawbacks. RC jacketing results in a considerable rise in the dead load, influencing the loading on the foundation and restricting the functional space available post-jacketing. Steel jacketing often lacks flexibility as a significant effort is required for installation. FRP improves the flexural strength response but produces low stiffness enhancement and lesser ductility. A hybrid strengthening option, i.e. a combination of the above strengthening methods, presents a viable option to address the limitations cost-effectively. This paper presents a pioneering attempt focused on improving the flexural performance of RC beams using a hybrid strengthening scheme comprising of RC jacketing and FRP. Four large-scale RC beams were prepared, and three of them were strengthened. The first was strengthened by RC jacketing, the second by a combination of RC jacketing and flexural FRP, and the last by the combination of RC jacketing, flexural FRP and FRP 'U wrap' in the shear zones. The specimens were tested using the four-point bending test. The flexural behaviour was assessed in terms of the peak moment capacity, flexural stiffness, load-displacement response, crack pattern and failure modes. The test results confirmed that hybrid strengthening leads to strength gain and stiffness gains of 105% and 90% respectively, as compared with the unstrengthened beam. The efficacy of the theoretically predicted strengths against the test strengths is assessed. • Development of hybrid strengthening scheme for capacity deficit RC beams. • Various combinations of strengthening schemes were explored. • Large-scale tests conducted to determine the efficacy of the strengthening schemes. • Feasibility of combining RC jacketing & FRP for strength/stiffness gains is confirmed. • Theoretically predicted strengths match with the test strengths with sufficient accuracy. [ABSTRACT FROM AUTHOR]

The use of fiber-reinforced polymer (FRP) anchors to enhance the efficiency of externally bonded (EB) FRP systems has received considerable attention in recent years. However, their widespread application has been constrained by the challenges associated with their installation due to complexity in anchor detailing. To date, there has been limited research aimed at simplifying anchor detailing while maintaining its efficiency. This paper presents an extensive experimental study involving 88 tests on concrete beams with anchored FRP material, with variations in the number of FRP strips, anchor material ratio (AMR), fan length, and rounding radius of the anchor hole. The study focuses primarily on different aspects of the anchor configuration. The first part of the study compares the performance of two anchor details, while the second part assesses the impact of different FRP patch arrangements on enhancing the performance of the anchors. The efficiency of the newly suggested end anchor detail was found to be equivalent to the previously used end anchor detail. The use of FRP patches over anchors proved very effective in certain cases but ineffective in others. • Effectiveness and efficiency of end FRP anchors with simplified detail. • Impact of AMR on performance and failure mode of FRP anchor. • Effect of different FRP patch arrangements on FRP anchor strength and performance. [ABSTRACT FROM AUTHOR]

This paper investigated both experimentally and numerically the flexural performance of two–span beams after being strengthened with polyparaphenylene benzobisoxazole (PBO) fiber–reinforced cementitious matrix (FRCM) systems at different hogging–to–sagging (H/S) strengthening ratios. The test results revealed that the enhancement in the flexural response of the strengthened beams was highly dependent on the strengthening configuration and the number of layers used in both the hogging and sagging sections. The H/S ratio had a notable effect on the failure modes of the hogging sections only whereas the sagging sections showed similar failure modes regardless of the H/S used. Strengthening the sagging sections governed the ductility of the tested beams with a slight effect of the H/S ratio on their ductility. Despite strengthening, the hogging sections were capable to redistribute up to 37% of their moments to the sagging sections, which represented 93% of the redistribution capacity of the unstrengthened sections. This finding suggests the revision of the CSA and ACI formulations that prohibit any moment redistribution in the design of externally–bonded strengthened elements. The developed finite element model accurately predicted the experimental results in terms of the failure modes, the load–carrying capacity, the ductility, and the moment redistribution ratios between the critical sections. • Using different H/S strengthening ratios change the failure modes of the hogging sections rather than the sagging sections. • Strengthening the sagging sections governed the ductility of the beams rather than the hogging strengthening. • Strengthened beams can redistribute between 23% and 37% of the moments between their critical sections. • It is important to consider the continuity of the FRCM–strengthened structures in the design equations of ACI 549.4 R (2020). • The numerical model reasonably predicted the moment redistribution ratios of the beams. [ABSTRACT FROM AUTHOR]

Risk analyses addressing consequences of progressive collapse have shown that, due to the small probabilities of element loss due to abnormal loads, structural strengthening for alternate load paths has negative cost-benefit for most buildings subjected to typical threats. This study addresses optimal risk-based design of reinforced concrete beams subjected to supporting column removal, with specific focus on reinforced concrete behavior. Nonlinear finite element analysis (NLFEA) is carried out, allowing both compressive arch and catenary actions to be predicted under large deflections. NLFEA results are compared to experimental data, showing good agreement and allowing quantification of model errors. Risk optimization results show that optimal beam designs change significantly with local damage probability, which is considered an independent parameter. More importantly, the study shows how different failure modes compete for limited construction and strengthening budgets. In case of intact structure, optimal design is governed by serviceability displacements, bending failure at midspan, and bending-shear failure at beam ends. Optimal design of the damaged structure is controlled by shear failure at beam ends and tensile rupture of steel rebar due to either catenary action or snap-through instability. Results highlight that, under significant column-loss probabilities, progressive collapse resistance is reached by larger beam depth, greater reinforcement area and reduced stirrup spacing. Such design measures against progressive collapse also provide greater safety margins against all failure modes of the intact structure. • Optimal designs strongly dependent on probability of local damage, P LD. • Probability of local damage is the focal point of epistemic uncertainty. • Under usual loading condition, optimal design controlled by serviceability, beam bending and shear. • Under column loss condition, optimal design controlled by steel rupture in catenary action. • Design with 3-legged stirrups shows better performance against progressive collapse. [ABSTRACT FROM AUTHOR]

• A series of 3 full-scale bending tests on cellular and Angelina girders is reported. • 4-pt bending arrangements of beam from 7.5 m to 11 m span were chosen so as to maximize the occurrence of lateral torsional buckling. • Careful measurements on material properties (tensile tests) and geometrical imperfections are reported. • Besides, dedicated non-linear shell F.E. models were developed and validated against the experimental data. • As excellent agreement between experimental and numerical sources is evidenced, the numerical models are found fit to be used in extensive numerical parametric studies aimed at characterizing in detail the structural response of cellular beams. This paper deals with the response of so-called "cellular members" against lateral torsional buckling. These beams comprising regularly-spaced circular web openings are especially used for their high resistance-to-weight ratio, the possibility to integrate service pipes within their height, and for aesthetics. Such profiles usually exhibit a complex behaviour and many potential failure modes, including interactional local/global instability modes. Regarding global instability, the members are usually designed by means of approximate design rules, which often lead to an unduly conservative solution, with beams sometimes showing up to 150 % resistance reserves. The present research works aim at improving this situation, through the development of adequate design formulae. In this respect, the present paper reports on investigations led towards improved solutions for cellular members at the experimental and numerical levels. This first paper focuses on experimental activities and on the development and validation of dedicated shell F.E. models. The results of three bending tests on members spanning from 7.5 m to 11 m are reported. Cross-sectional dimensions, material properties and accurate initial geometrical imperfections were measured for each specimen and further introduced in the corresponding F.E. models, which are shown to provide predictions in close agreement with the experimental results. The companion paper [1] further makes use of the F.E. models within extensive parametric studies and proposes a new set of design rules that could be proposed for integration in Eurocode 3. [ABSTRACT FROM AUTHOR]

After using Ultra-High Performance Concrete (UHPC), the mechanical properties of the composite beams have significant differences compared to those of the steel-normal concrete composite beams. To investigate the effect of reinforcement ratio on the force behavior of steel-UHPC composite beams, tests on the flexural performance of steel-UHPC composite beams with different reinforcement ratios under negative moments were carried out, and reasonable design of the composite beams was analyzed by using a numerical simulation method. In addition, the existing crack calculation methods for composite beams were validated. The results showed that the failure modes of the composite beams with different reinforcement ratios were similar. Increasing the reinforcement ratio from 2.01% to 2.98%, the ultimate capacity of the steel-UHPC composite beams was increased by 4% and the ultimate deflection was reduced by 7%, while the ductility was reduced by 11%. The cracking load was not enhanced, but the higher reinforcement ratio had a controlling effect on crack development and crack width in the late loading stage. For steel-UHPC composite beams, the appropriate reinforcement ratio should be less than 4%. Furthermore, the crack calculation formulas in the existing steel-concrete composite beam codes do not apply to steel-UHPC composite beams, and the calculation results were much smaller than the measured values. Among the related formulas for reinforced UHPC members, the calculated value of the formula in NF P 18–710 was closer to the measured value but the overall error was still large, so further research is needed. • Compares the flexural behavior of stee-UHPC composite beams under negativebending moment. • Analyzes the effect of reinforcement ratio on the development of cracks and the width of the main cracks. • Investigates the appropriate reinforcement ratio of steel-UHPC composite beams. • Investigates the variation in the contribution ratio of UHPC tensile strength during the loading process. • Compares and verifies the existing formulas for cracking of composite beams. [ABSTRACT FROM AUTHOR]

This paper proposes a new design concept for a steel truss-reinforced concrete box girder which incorporates a steel truss instead of longitudinal bars and stirrups. A comprehensive assessment of the flexural and shear behavior of the proposed steel truss-reinforced concrete box girders was conducted through the testing of twelve girders until failure. All test specimens had the same concrete depth and width of 400 mm and 300 mm, but the length of concrete in the shear and flexural specimens were 3300 mm and 3100 mm, respectively. Moreover, the reinforcing steel truss configuration and member sizes were different. The effects of the angle steel size of the lower chord, vertical webs spacing, shear span ratio and presence of diagonal webs on the cracking, yield and ultimate loads, crack patterns, failure modes, vertical load-deflection curves and strain distribution of these steel truss-reinforced concrete box girders were studied. The test results showed that the flexural capacity of the steel truss-reinforced concrete box girder increases with the increase of angle steel size of the lower chord. Moreover, the spacing of vertical webs and presence of diagonal webs have little effect on the flexural capacity of steel truss-reinforced concrete box girders tested. With the decrease of the shear span ratio and vertical webs spacing, the shear capacity of the steel truss-reinforced concrete box girder increases. Finally, simplified formulae for calculating the flexural and shear capacities of steel truss-reinforced concrete box girders were proposed, showing good agreement with the experimental results. • A novel steel truss-reinforced concrete box girder with steel truss chords instead of steel bars is proposed. • The flexural and shear behaviors of the proposed steel truss-reinforced concrete box girder have been investigated. • Formulae for the flexural and shear capacities of the proposed box girder have been developed. [ABSTRACT FROM AUTHOR]

This paper conducted design and experimental study on frame specimen equipped with steel-HPEC (Hollow-core partially encased composite) spliced beams (SHS beam in short). SHS beams are comprised of two bare steel beams and an HPEC beam with thinner flange plates, present similar deformation and bearing capacity to traditional I-shaped steel structure, in addition to the benefits of good lateral stiffness and steel saving. Lateral low-cyclic loading tests were conducted on a bare steel frame and a frame with SHS beams to investigate their failure modes, seismic performance, and evaluate the feasibility of implementing SHS beams in frame structures. The frame specimen with SHS beams exhibited similar failure modes as those observed in steel frame specimen. Due to the higher stiffness of SHS beams, which effectively limited out-of-plane deformation in frame, SHS beam frame presented higher initial lateral stiffness, ultimate bearing capacity and energy dissipation capacity when contrast with bare steel frame. For calculations, SHS beams could be construed as stepped beams with variable rigidity. Finally, the calculation methods and formulas for initial lateral stiffness and ultimate bearing capacity of both the frames with SHS beams and bare steel frames were proposed, and the calculated results agreed well with the experimental values. • The SHS beam has reliable connections and similar deformation and bearing capacity to that of steel beam. • SHS beam has superior stiffness and effectively constrains out-of-plane deformation of frame structure. • The frame with SHS beams has higher stiffness, bearing capacity and energy dissipation. • The calculation methods of frame with SHS beams are simple and similar to that of bare steel frames. [ABSTRACT FROM AUTHOR]