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This paper investigates the shear performance of corroded reinforced concrete (RC) beams with different stirrup corrosion rates and strengthening interventions. In this work, eight corroded beams strengthened with various interventions, including U‐shaped stirrup, bonded steel plate, and anchored steel plate strengthening techniques, were tested under static loading. The experimental shear capacity, load–deflection response, and failure modes of the unstrengthened and strengthened specimens were carefully studied. Three shear capacity models based on GB50010‐2010, ACI 318‐08, and Eurocode 2 codes were proposed and discussed. The results showed that all specimens have the same failure mode, that is, the shear–compression failure. The shear capacities are improved by 17.36%–23.61% and 23.76%–38.46% by these interventions for the specimens with 10% and 20% stirrup corrosion rates, respectively. The anchored steel plate technique provides the maximum improvement in the shear capacity. Additionally, the increased stiffness of corroded specimens with strengthening interventions is apparent when the corrosion rate is 10% but not obvious when the corrosion rate is 20%. The models based on GB50010‐2010 and ACI 318‐08 codes were proved to have higher accuracy but may overestimate the shear capacity. In contrast, the Eurocode 2‐based model comes with relatively low prediction accuracy but conservative results, and it is recommended for engineering design. [ABSTRACT FROM AUTHOR]

Glued-laminated timber arches are widely used in gymnasiums, bridges, and roof trusses. However, studies on their mechanical behaviours and design methods are still insufficient. This paper investigates the in-plane loading capacity of circular glued-laminated timber arches made of Douglas fir. Experiments were conducted on four timber-arch models with different rise-to-span ratios under concentrated loads at mid-span and quarter-point locations. The structural responses, failure modes, and loading capacity of the timber arch specimens were obtained. The results show that the timber arches presented symmetric and antisymmetric deformation under mid-point and quarter-point loading conditions, respectively. The downward shifting of the neutral axis of the cross section was observed under mid-point loading condition, which contributes to higher loading capacity compared to that under quarter-point loading condition. The loading condition significantly affects the ultimate loads and the strain distribution in the cross section. Based on the design formula in current standards for timber structures, an equivalent beam-column method was introduced to estimate the loading capacity of the laminated timber arches under vertical concentrated loads. The moment amplification factor in the formula was compared and discussed, and the value provided in the National Design Specification for Wood Construction was recommended with acceptable accuracy. [ABSTRACT FROM AUTHOR]

• Twelve rectangular UHPC solid beams subjected to pure torsion are fabricated and tested. • The additional steel fibers substantially improved the torsional behavior. The failure modes of UHPC members, including two different modes, are identified, and the definitions of these failure modes evolve with new connotations. • The effective reinforcement ratio (1.32%) is proposed in this paper, which is mainly directly depended upon the steel fibre volume fraction. • A formula was proposed to predict the ultimate torsional strength for UHPC rectangular solid beams, and the application was verified by the experimental data available in reference and a reliability analysis. This study presents an experimental investigation of the loading capacity and failure mechanism of ultra-high-performance concrete (UHPC) beams under pure torsion. Twelve rectangular solid beams were fabricated and tested. The investigated parameters include the volumetric fraction of steel fibers (1.5%, 2.5%, and 3.5%), the longitudinal reinforcement ratio (0–1.54%), and the stirrup ratio (0–1.29%). The torsional behavior, including the crack propagation and failure modes, torque–twist curves, torque–strain curves, cracking and ultimate strengths, and effectiveness of steel fibers were evaluated and presented. Considering the UHPC high tensile strength, a formula for UHPC solid beams was proposed and verified by a reliability analysis. The results showed that compared to conventional concrete beams, the UHPC beams exhibited similar suitably reinforced, partially over-reinforced, and over-reinforced failure modes. Additionally, two different failure modes (type-I and type-II barely reinforced) were identified for UHPC beams. The additional steel fibers improve the torsional properties and directly determine the effective reinforcement ratio. Moreover, the steel fibers with 1.5% or higher volume fractions were proven to be sufficient to replace stirrups, and the proposed formula is effective in predicting the torsional strength of UHPC rectangular solid beams. [ABSTRACT FROM AUTHOR]

Limited studies have been conducted on the torsional performance of ultra-high-performance fiber-reinforced concrete (UHPFRC) hollow beams. This paper presents experimental investigations on eight UHPFRC hollow beams with various cross-sectional dimensions, wall thicknesses, and cross-section types. Their torsional responses, including the failure modes, torque−twist curves, torque−strain curves, torsional stiffness, and ductility indexes, are presented. Theoretical methods were employed to evaluate the cracking and ultimate torques. The results indicated that the UHPFRC hollow beams with and without flange plates exhibited a similar failure model, with the main cracks penetrating spirally. The cross-sectional dimensions, wall thicknesses, and cross-section types significantly affected the ultimate torque, whereas the cracking torque was affected only by the cross-sectional dimensions. A comparison of the experimental and theoretical results indicated that the American Concrete Institute code provisions provided good predictions for the cracking torque, whereas the existing theoretical methods offered unsatisfactory predictions for the ultimate torque. Thus, the equivalent wall thickness of UHPFRC hollow beams must be evaluated with a higher accuracy. [ABSTRACT FROM AUTHOR]

• Electrospun nanofiber veils were first proposed to enhance the bond performance of CFRP-steel epoxy-bonded interfaces. • Effects of areal density of nanofiber veils and CFRP bond length on the bond behavior of nanofiber veil-modified CFRP-steel epoxy-bonded interfaces were investigated. • Bond-slip models of nanofiber veil-modified CFRP-steel epoxy-bonded interfaces were established and compared with those of neat epoxy-bonded interfaces. • Bond strengths of CFRP-steel epoxy-bonded interfaces modified with different nanomaterials were compared. The epoxy-bonded interfaces between carbon fiber reinforced polymer (CFRP) and steel usually have insufficient strength and toughness, and the toughening of bonded interface is a key problem for the usage of CFRP in steel structures. In this study, electrospun nanofiber veils were first proposed to enhance the bond performance of CFRP-steel epoxy-bonded interfaces. Firstly, shear tests were conducted on neat epoxy and nano-modified single-lap aluminum-aluminum joints to determine the optimal areal density and number of layers of nanofiber veils, as well as the optimal curing processes. Then, a series of neat epoxy and nano-modified CFRP-steel double-lap joints with different bond lengths were tested to investigate the size effect of the bond behavior. The displacement and strain field evolution of the joints were captured by the digital image correlation (DIC) technique, allowing for visualization of the detailed failure process. The failure modes, load-displacement curves, CFRP strain distributions, and bond-slip relationships of the CFRP-steel joints were obtained. Both the tests on aluminum-aluminum and CFRP-steel joints show that the optimal modification strategy is incorporating 3 layers of nanofiber wels with an areal density of 4.5 g/m2, with 5 h room-temperature and 2 h 80 °C high-temperature curing. The primary failure mode of CFRP-steel joints is CFRP delamination accompanied by CFRP-adhesive interface or steel-adhesive interface debonding. The bond strengths of the modified joints with 3 layers of 1.5 g/m2 and 4.5 g/m2 nanofiber veils are increased by 7 % and 25 % compared to those of un-modified joints, respectively. The 4.5 g/m2 nanofiber veils modified bonded interface has an effective bond length of about 152 mm, with a corresponding ultimate bearing capacity of 117 kN. Different from the triangular (brittle) shape of most neat epoxy interfaces, the nano-modified interfaces have trapezoidal (ductile) bond-slip relationships, providing superior cracking resistance. Moreover, a comparison with the bond strength of SiO 2 nano-particles and carbon nanotubes (CNTs) modified joints revealed that nanofiber veil modification comes to higher bond strength in most cases. The proposed electrospun nanofiber veil modification technique provides a great insight into the interfacial toughening of CFRP-steel composite structures. [ABSTRACT FROM AUTHOR]

• Fatigue failure mechanisms of the CFRP-steel adhesively bonded joints was investigated. • The S-N curves based on the mean and local bond stress range were established and compared. • The P-S-N curves with different reliability levels were established based on four statistical models. • The P-S-N curves based on the two-parameter Weibull model were recommended for engineering design. In this study, fatigue tests were conducted on a series of carbon fiber reinforced polymer (CFRP)–steel double lap shear joints. The fatigue failure mechanisms were investigated based on the failure modes, load–displacement relationships, and stiffness degradation. Inherent scatter characteristics of the fatigue life were discussed using probabilistic S-N (P-S-N) curves based on four statistical models (ISO 12107, ASTM E739-91, two-parameter Weibull, and Gumber models). The results indicate that the fatigue life decreased dramatically with the increase of the load level, and interface debonding is the primary failure mode of fatigue joints. Stable debonding and accelerated debonding of the bonded interface are initiated when the joint stiffness degrades to approximately 98% and 82–86% of the initial stiffness, respectively. The S-N curve based on the mean bond stress range shows a better fit than that based on the local bond stress. Based on the comprehensive evaluation of the performance of the P-S-N curves, the two-parameter Weibull model is recommended for fatigue life design as it can well-constrain fatigue data without excessive safety redundancy. [ABSTRACT FROM AUTHOR]