Fracture Of Bars Research Articles

Seismic repair of severely corroded precast RC columns with FRP shell and headed steel bars

Corrosion of reinforced concrete bridge columns degrades their seismic performance. A seismic repair strategy for severely corroded reinforced concrete columns is developed. Three specimens were constructed; one served as the control, and two were corroded with a 25% target mass loss of longitudinal steel bar area. The control and one of the corroded columns were tested under cyclic loads, and the remaining corroded column was repaired before being tested. Repair consisted of a carbon fiber reinforced polymer shell filled with concrete and connected to the footing using headed steel bars. All three columns failed due to longitudinal steel bar fracture; the control column failed at 9.0% drift ratio, the severely corroded column failed at 6.0% drift ratio after longitudinal steel bars buckled, and the repaired corroded column failed at 10.0% drift ratio. This demonstrates the effectiveness of the repair method. A numerical model was developed to simulate the seismic performance of the control, the corroded, and the repaired columns, which matched the experimental hysteresis curves and predicted fracture of longitudinal steel bars at the same drift ratio as the experiment. The numerical model is extended for parametric analysis of reinforced concrete columns with varying levels of corrosion and repaired columns.

Tensile behaviour of a novel grouted sleeve splice for high-strength rebars

This study introduces a novel type of grouted sleeve fabricated from a standard low-alloy seamless steel pipe using cold-rolling techniques. The main goal is to achieve an effective connection between the high-strength steel (HSS) reinforcements in the joints of precast concrete structures. To investigate the structural performance of the developed splice under uniaxial tensile loading, 24 coupler specimens configured with 28 mm diameter HRB600 reinforcements were prepared. Two primary parameters, namely the embedded length of the spliced bar and number of inner concentric ribs rolled on the sleeve, were considered. By conducting direct pullout tests, the performance of the developed splices was thoroughly assessed based on the failure mode, bond stiffness, bond ductility, and strength. The test results demonstrated that increasing the bar embedded length and number of inner ribs enhances the initial bond stiffness and ductility of the splice. Increasing the quantity of inner ribs only in the inelastic region of the splice is effective for improving its tensile capacity. For grout splices with large-diameter HSS bars, an embedded length of 8db is recommended to guarantee bar fracture failure and satisfy the specification requirements. This length exceeds that of splices with normal-strength reinforcements. Finally, a formula was proposed to estimate the inelastic region length and tensile strength of the proposed splice.

Shear performance of perfobond leiste (PBL) connectors in engineered cementitious composites (ECC)

Substituting normal concrete with ductile Engineered Cementitious Composites (ECC) is a promising way to address the safety and durability issues caused by cracking in steel-concrete composite structures. To realize a synergistic deformation behavior between steel and ECC, Perfobond Leiste (PBL) shear connectors are preferred to be used owing to their superior shear resistance, shear stiffness, and excellent fatigue performance. This research comprehensively investigated the shear performance of PBL connectors in ECC through experimental, numerical, and analytical approaches. Firstly, the shear load-slip relationships of PBL connectors in ECC and concrete were studied through push-out tests of 36 H-shaped specimens. It indicated that the fracture of penetrating bars dominated the final failure of PBL connectors in ECC, whereas premature concrete spalling happened in concrete specimens. By establishing a refined finite element model, the parametric study was then conducted to clarify the influence of the compressive strength of ECC, hole diameter, penetrating bar diameter, and penetrated plate thickness on the shear characteristics of PBL connectors in ECC. Finally, an analytical model for predicting the shear carrying capacity of PBL connectors embedded in ECC was derived, matching well with the test results.

Effect of high-strength and stainless steel reinforcement on the flexural behavior of UHPC beams

Ultra-high performance concrete (UHPC) is an advanced cement-based composite which shows remarkable properties including very high compressive strength, increased tensile resistance, impressive toughness and excellent durability. One promising application of UHPC is in heavily-loaded beams and slabs where its use can allow for increased design efficiency and improved durability. Conversely, the high bond capacity of UHPC can lead to early bar fracture failures, especially when using low amounts of ordinary steel reinforcement. This paper examines the influence of reinforcement grade on the flexural ductility of UHPC beams. As part of the study, three beams built with either Grade 400 MPa ordinary steel reinforcement, Grade 690 MPa high-strength reinforcement or Grade 520 MPa stainless steel reinforcement, are tested under flexural loading. The key test parameters include the influence of concrete type (UHPC vs. conventional high-strength concrete) and steel type (high-strength or stainless steel vs. ordinary steel). The results show that the flexural strength and ductility of the UHPC beams is influenced by the steel grade/type. The beam with ordinary steel shows a well-defined yield point but fails by bar rupture. Increased resistance by 47% is observed when using high-strength bars, however bar rupture occurs owing to the low strain-capacity of this steel type. Combining UHPC with higher ductility stainless steel does not increase capacity, but leads to remarkable ductility by 75%. As part of the numerical study the behaviour of the beams is predicted using FE modelling and the effects of tension steel ratio, UHPC tensile strength and high-strength or stainless steel type are investigated.

Strain-Based damage model for ductile tearing simulation under combined tensile and shear modes

This paper proposes a strain-based damage model to simulate ductile tearing under combined tensile and shear modes. For tensile mode, the multiaxial fracture strain model depending only on the stress triaxiality is used, determined by analysing smooth bar tensile test and fracture toughness test data. For shear mode, a simple constant fracture strain model is used, determined by analysing smooth bar torsion test and torsion fracture test using a deep surface cracked cylinder specimen. The proposed damage model is applied to simulate circumferential surface cracked pipe made of SUS 304 under combined bending and torsion. Comparison with full-scale surface cracked pipe test data suggests that the use of the combined tensile and shear damage model with the linear interaction rule gives good and conservative prediction results.

Behaviour of Grouted Sleeve Wall Connection under Lateral Load

A grouted sleeve’s efficiency in splicing steel bars makes it a potential choice for connecting precast elements. While most studies have focused on the feasibility of grouted sleeves under tension, only a few have investigated the real response of precast concrete members connected using grouted sleeves. In this study, Tapered Head Sleeves (THS) were utilized as connections for precast walls. The objectives were to examine their behavior under incremental lateral loads and assess the feasibility of THS as a wall connection. Five test specimens and one control specimen were fabricated, each comprising two walls joined by THS. The load was applied 1.8 m above the joint until specimen failure. Specimens that experienced bar fracture failure exhibited a relatively large drift upon failure, while those failing due to bar bond slip showed smaller drift. Factors contributing to wall drift included horizontal slip, rocking displacement, cantilever bending deformation, and compressive settlement. The ultimate load increased by 71% as the embedded length increased from 75 mm to 175 mm, and it increased by 50% as the sleeve diameter decreased from 75 mm to 50 mm. The sleeves' performance was evaluated for feasibility based on the strength ratio, drift ratio, ductility ratio, failure mode, performance ratio, serviceability ratio, and length ratio. Only THS-8 met all the criteria, suggesting that the bar's embedded length should be at least 11 times the bar diameter.

Flexural Performance of Steel-Continuous-Fiber Composite Bar and Fiber-Reinforced Polymer Bar Hybrid-Reinforced Sustainable Sea-Sand Concrete Beams: Numerical and Theoretical Study

To investigate the flexural performance of steel-continuous-fiber composite bar (SFCB) and fiber-reinforced polymer (FRP) bar hybrid-reinforced sea-sand concrete (SSC) beams, a total of 21 SSC beams were numerically studied. The concrete damaged plasticity model (CDPM) and FRP brittle damage model were adopted, and the bond-slip behavior between the reinforcement and concrete was considered. Parametric studies were conducted to study the effects of the SSC strength, sectional steel ratio of the SFCB, core steel bar yield strength of the SFCB, out-wrapped FRP elastic modulus of the SFCB, and the ultimate tensile strength of the SFCB on the flexural performance of the beams. The results indicate that increasing the SSC strength and out-wrapped FRP modulus enhanced the bearing capacity and stiffness but reduced the ductility, shifting failure from concrete crushing to FRP bar fracture. A higher SFCB sectional steel ratio markedly improved the flexural stiffness, transforming the load–deflection curve. Elevated core steel bar yield strength maintained the cracking load and deflection while increasing the yield and ultimate loads. For SFCB fracture, higher ultimate tensile strength in the out-wrapped FRP enhanced the ultimate load and deflection, but not in concrete crushing failure. In addition, three failure modes were defined based on the proper assumption, with the proposed bearing capacity formulas aligning well with the FE results.

Blast retrofit of shear-deficient high-strength concrete beams with ultra-high performance concrete

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%.

Bond behavior between bundled composite bars and concrete using beam-end pullout tests

Bundled reinforcement can improve construction efficiency by reducing the number of connectors required. The steel-fiber reinforced polymer (FRP) composite bar (SFCB) is a novel reinforcement with high strength, moderate modulus of elasticity and good durability. Four groups of pullout tests were carried out, with parameters including the number of bars within each bundle, bonded length, and rebar type (steel bar, BFRP bar, SFCB). The failure modes of bar pullout without or after yielding, rebar fracture, and concrete splitting were observed. Compared to the single-bar specimen, the two-bar and three-bar bundled specimens resulted in approximately 30% and 40% decrease in average bond strength. The yielding slip sy of the three-bar bundled SFCB specimen is 3.8 times that of the single-bar specimen, indicating that bundled reinforcement can effectively control sy. A simplified bond strength prediction method and a bond stress-slip constitutive model based on the equivalent effective area approach are proposed. Finite element (FE) models were established and verified, and the failure modes of bar fracture are obtained by varying the bonded lengths for different bundled reinforcements, the ultimate slip of four-bar bundled BFRP bars increased by 127%. Recommendations for the development length of bundled SFCBs are proposed based on the FE results, which provide enough safety redundancy.

Ramus Frame Dental Implant Functional Survival and Safety in Severely Atrophic Edentulous Human Mandibles.

Ramus frame dental implants were retrospectively studied in 360 adults with severely atrophic edentulous mandibles. Patient records up to 12 years post-treatment were independently reviewed after a single clinician surgically placed titanium long-arm ("Tatum") ramus frame implants and immediately loaded them with a mandibular overdenture. A total of 11 ramus frames were removed at 19 to 109 months post-treatment, mostly due to supramucosal bar fracture (N = 6) or mobility (N = 3). Kaplan-Meier product-limit analysis revealed the post-treatment survival probability for functional ramus frame implants to be 99.3% at 2 years (266 patients), 98.9% at 3 years (223 patients), 97.9% at 4 years (198 patients), 96.9% at 5 years (160 patients), 96.9% at 6 years (123 patients), 95.0% at 7 years (86 patients), 95.0% at 8 years (67 patients), 93.3% at 9 years (43 patients), and 91.1% at 10 years (25 patients). No statistically significant differences in functional ramus frame implant survival were found relative to patient gender, smoking, presence of natural maxillary teeth, or compliance with semi-annual maintenance care. Fracture of endosseous anterior feet/posterior arms was the most frequent implant-related complication on 29 implants, which were left in place, repaired, or replaced in situ without implant removal. At 5 years, the ramus frame implant functional survival probability without any implant-related biological or mechanical complication was 88.9%. Ramus frame dental implants, immediately loaded with a fully implant-borne mandibular overdenture, exhibited a high degree of long-term functional survival and safety in severely atrophic edentulous human mandibles.

Analysis of Catapult-Assisted Takeoff of Carrier-Based Aircraft Based on Finite Element Method and Multibody Dynamics Coupling Method

Catapult-assisted takeoff is the initiation of flight missions for carrier-based aircrafts. Ensuring the safety of aircrafts during catapult-assisted takeoff requires a thorough analysis of their motion characteristics. In this paper, a rigid–flexible coupling model using the Finite Element Method and Multibody Dynamics (FEM-MBD) approach is developed to simulate the aircraft catapult process. This model encompasses the aircraft frame, landing gear, carrier deck, and catapult launch system. Firstly, reasonable assumptions were made for the dynamic modeling of catapult-assisted takeoff. An enhanced plasticity algorithm that includes transverse shear effects was employed to simulate the tensioning and release processes of the holdback system. Additionally, the forces applied by the launch bar and holdback bar, nonlinear aerodynamics loads, shock absorbers, and tires were introduced. Finally, a comparative analysis was conducted to assess the influence of different launch bar angles and holdback bar fracture stain on the aircraft’s attitude and landing gear dynamics during the catapult process. The proposed rigid–flexible coupling dynamics model enables an effective analysis of the dynamic behavior throughout the entire catapult process, including both the holdback bar tensioning and release, takeoff taxing, and extension of the nose landing gear phases. The results show that higher launch bar angle increase the load and extension of the nose landing gear and cause pronounced fluctuations in the aircraft’s pitch attitude. Additionally, the holdback bar fracture strain has a significant impact on the pitch angle during the first second of the aircraft catapult process, with greater holdback bar fracture strain resulting in larger pitch angle variations.

Analysis of the Mechanical Performance of Sleeve Considering the Different Distributions of Grouting Defects

To study the influence of grouting defects on the mechanical properties of grouting sleeves, 49 groups of specimens with different specifications were made considering the length and location of defects, monotonic axial tension tests were carried out to study the influence of grouting defects on its failure process, failure mode, load-displacement curve, bearing capacity and other mechanical properties, and the influence law of different distribution defects on the grouting sleeve was analyzed. This research shows that there are two forms of sleeve failure: steel bar fracture failure and steel bar pullout failure. The bearing capacity of specimens with a defect length of 2D and 3D varies with the defect type. The ultimate displacement of specimens with a defect length of 2D varies with the defect type. The ultimate displacement of specimens with a defect length of 3D increases with the increase in bearing capacity. By moving defects, it is found that if there is a vertical overlap of defects in the upper or middle part of the specimen, the bearing capacity of the specimen will be greatly affected.

Performance of high strength steel bar splice with novel grouted deformed sleeve under tensile load

High-strength steel (HSS) bars can solve bar congestion problem in beam-column joints of monolithic precast concrete frame structure. Unfortunately, its application in precast concrete structures is greatly hindered by few researches on HSS bar grout splice. In this paper, utilizing large-diameter HRB600 reinforcements with specified yield strength of 600 MPa, 34 splice specimens were prepared considering the parameters of embedded length, grout strength and inner cavity structure of sleeve. Through uniaxial tension test, it is shown that the embedment length has the greatest effect on the structural performance of grouted splice. For the d28 bar grout splice, 8db is the minimum embedded length to ensure bar fracture failure, which is longer than the normal-strength steel bar grout splice. For the splices with embedded length not smaller than 5db and concentric ribs not less than five, excessive ribs set on the sleeve cannot significantly increase the tensile strength of the grouted splice, but further adding one rib still can effectively reduce the elastic residual deformation. Similar test results have been observed for the effect of grout strength. As the compressive strength increases from 95.3 MPa to 118.2 MPa, the tensile strength improves only by about 2.52%, but the residual deformation decreases significantly by 11.68% on average. For a high-strength large-diameter bar grout splice, it is recommended to set six concentric ribs at each side of the sleeve, and select 8db as the minimum embedded length to achieve reliable performance.

A Method for Improving Heat Dissipation and Avoiding Charging Effects for Cavity Silicon-on-Glass Structures

Anode bonding is a widely used method for fabricating devices with suspended structures, and this approach is often combined with deep reactive-ion etching (DRIE) for releasing the device; however, the DRIE process with a glass substrate can potentially cause two critical issues: heat accumulation on the suspended surface and charging effects resulting from the reflection of charged particles from the glass substrate. In particular, for torsional bars with narrow widths, the heat accumulated on the suspended surface may not dissipate efficiently, leading to photoresist burning and, subsequently, resulting in the fracture of the torsional bars; moreover, once etching is finished through the silicon diaphragm, the glass surface becomes charged, and incoming ions are reflected towards the back of the silicon, resulting in the etching of the back surface. To address these issues, we proposed a method of growing silicon oxide on the back of the device layer. By designing, simulating, and fabricating electrostatic torsional micromirrors with common cavity silicon-on-glass (SOG) structures, we successfully validated the feasibility of this approach. This approach ensures effective heat dissipation on the suspended surface, even when the structure is over-etched for an extended period, and enables the complete etching of torsional bars without adverse effects due to the overheating problem; additionally, the oxide layer can block ions from reaching the glass surface, thus avoiding the charging effect commonly observed in SOG structures during DRIE.

Experimental study on displacement capacity of reinforced concrete walls with varying cross-sectional slenderness

The utilization of thinner and more slender walls in the design of reinforced concrete shear wall structures has become increasingly popular in Chile and other countries. However, while this approach can lead to increased wall strength if the wall length is increased, it may also result in lateral instability. This study presents experimental results obtained from testing walls with variations in cross-sectional slenderness and their impact on out-of-plane lateral instability, while maintaining wall height, information that in the literature is scarce. Three slender walls were constructed with different cross-sectional dimensions: 160 mm by 900 mm (M1), 100 mm by 900 mm (M2), and 100 mm by 1350 mm (M3). These walls were subjected to a constant axial load and a cyclic lateral load. It was found that the strength of each specimen was consistent with the variation in its cross-sectional dimensions, while maintaining the distribution of steel reinforcement. However, walls with reduced thickness and increased length showed evidence of both local and global lateral instability. Specimen M1 presented concrete crushing, longitudinal bar bucking and fracture, whereas M2 presented a decreased stable confined portion of the wall compared to wall M1, yielding local instability. Wall M3, on the other hand, with a larger wall length, presented larger cracks that favored an unstable out-of-plane behavior of the entire wall section, leading to a sudden strength loss due to its inability to maintain the axial load. As a result, the drift capacity of these walls was found to decrease from 4.2% to 3% with thickness reduction, and to 1.2% with thickness reduction and increased length.

Behaviour of UHPFRC-retrofitted RC beams with varying strengthening configurations under single and repeated blast loading

The objective of this study was to characterize the effects of various UHPFRC strengthening configurations on the blast performance of reinforced concrete (RC) beams. The methodology involved blast tests on eight as-built and UHPFRC-retrofitted RC beams using a pneumatically-driven shock-tube. The 150 mm × 200 mm × 2440 mm beams were first cast with 40 MPa concrete and were retrofitted by replacing the 20 mm cover with UHPFRC. The studied parameters included the influence of UHPFRC applied on the tension face, or in the form of U, Full or localized jackets, under single or repeated blast loads. The first set included one as-built beam and three specimens with tension-sided (T), U-jacket (UJ) or full jacket (FJ) retrofits, and were tested under repeated and gradually increasing blast pressures (Pr = 16, 38 and 50 kPa, for Blasts 1, 2 and 3). The second set included one as-built beam and two specimens with full-jacket retrofits applied over the full span (FJ) or in the middle hinge region (FJ-Hinge). The final beam had a hybrid of the T-sided and FJ-Hinge schemes. These beams were tested under single Blast 3 loads, and then tested under static bending to assess their residual capacity. In the first set, all retrofits resulted in reduced displacements (ranging from 30% to 60%) when compared to the as-built beam; however, the repeated blasts ultimately led to crack localization and rupture of the tension steel bars. In the second set, both the full-span and localized hinge schemes led to reductions in damage and displacements (ranging from 20% to 40%), without bar fracture, along with significant residual capacity. Finite element (FE) modelling using LS-DYNA was used to predict the blast behavior of the beams. After validation, the models were used to study the effects of the longitudinal steel ratio and blast load scenario on the behaviour and failure mode of the beams. Increasing the steel ratio was found to be effective in preventing bar rupture, while this failure mode was more likely under repeated blast loading.

The Use of De-Icing Salts in Post-Tensioned Concrete Slabs and Their Effects on the Life of the Structure

This article expounds on the problem of the use of de-icing salts in the corrosion of steel rebars in bridge decks and their effect on post-tensioning elements. In particular, this paper focuses this problem on structures affected by an aggregate–alkali reaction and without any waterproof treatment using the example of one structure whose repair was carried out in 2020. In this structure, the internal stresses due to the aggregate–alkali reaction caused longitudinal cracks in the upper face of the deck, through which the penetration of chloride ions was concentrated, causing, finally, the brittle fracture of the steel bars and the corrosion of the prestressing elements. This article also explains some conclusions about the most probable mechanisms that resulted in the brittle fracture of the steel bars due to the extraordinary and unexpected nature of this phenomenon.

Experimental study on interfacial shear behavior of PBL shear connector deeply embedded in UHPC

To analyze the shear capacity and failure mechanism of perfobond strip (PBL) connectors in the junction of the steel-UHPC composite pedestrian truss bridge, this study conducted monotonic loading push-out tests on four specimens of PBL shear connector deeply embedded in UHPC and one specimen in normal concrete. The research primarily investigated the interfacial shear behavior of PBL connectors under static load, focusing on the effects of different concrete types, embedded depth of PBL connector, and diameter of transverse reinforcing bar, especially in the situation with a deep 240 mm embedded depth of PBL connectors. The results showed that the shear capacity of PBL connector in UHPC was 76% higher than that in normal concrete specimen. For UHPC specimens with 240 mm embedded depth, the failure mode of the specimens with 16 mm and 25 mm transverse reinforcing bar diameter was steel plate destroy while the specimens with 12 mm transverse reinforcing bar diameter showed transverse reinforcing bar fracture. Reducing the embedded depth of the PBL connector with 12 mm diameter transverse reinforcing bar increased the initial stiffness and shear capacity of PBL connector, but decreased the ductility. In this study, the experimental results were compared with several calculation equations, and a modified equation was proposed for PBL connectors deeply embedded in UHPC based on the force transferring mechanism and different failure modes. The predicted results were in good agreement with the experimental results. Furthermore, some design suggestions for PBL connectors deeply embedded in UHPC were concluded in this paper.

Experimental Study on an Innovative Double-Limb-Thin-Wall Bridge Pier with Longitudinal Replaceable Connecting Beams

Replaceable energy dissipation elements can reduce damage to main structures and improve seismic resistance of bridge structures. However, in existing studies, replaceable energy dissipation elements are mainly arranged in the transverse direction of the bridge structure, while little attention is given to the longitudinal direction of the bridge, which also suffers from serious damage under earthquakes. This paper proposes an innovative double-limb-thin-wall (DLTW) bridge pier, which consists of two thin-limb-wall columns in the longitudinal direction of the bridge and replaceable steel connecting beams (RSCBs) between them. Quasistatic tests of the proposed innovative DLTW pier with RSCBs (DLTW-RSCBs), a conventional DLTW pier, and a DLTW pier with RC connecting beams (DLTW-RCCBs) were conducted to investigate the longitudinal seismic performance of the innovative bridge pier. The test results demonstrate that the use of connecting beams (CBs) can improve the lateral bearing capacity and cumulative dissipated energy of the DLTW pier, while the improved amplitudes are more significant for the DLTW-RSCB specimen, about 21.6% and 13.4%, respectively. Moreover, due to the protection of the CBs, the DLTW-RCCBs and DLTW-RSCBs have lower damage and residual drift ratios than the DLTW-NBs before the failure of the CBs. However, the differences between these three piers gradually disappear with the failure of the CBs, and the piers are finally destroyed as a result of the failure modes of buckling and low-cycle fatigue fracture of the longitudinal bars at the column bottom. Moreover, RSCBs can still be rapidly repaired after damage failure of the DLTW-RSCB specimen. Therefore, setting replaceable steel beams between DLTW piers can effectively improve seismic performance and reduce seismic damage and repair costs of DLTW bridge piers under earthquake loading, which are valuable for sustainability during the service stage. The outcomes of this work can serve as a reference for further development of structural forms for the innovated pier.

Effect of UHPC jacketing on the shear and flexural behaviour of high-strength concrete beams

Ultra-high performance concrete (UHPC) is an advanced material which shows high compressive strength, tensile resistance, toughness and durability when compared to conventional concrete. One of the potential applications of UHPC is in the retrofit of ageing or deteriorated reinforced concrete structures. However, limited research exists on the use of UHPC to strengthen higher strength concrete members (with compressive strength exceeding 80 MPa). This paper examines the ability of UHPC to improve the shear and flexural performance of high-strength concrete (HSC) beams. As part of the tests two shear-deficient HSC beams built without stirrups, and having 15M or 20M bars (steel ratios of 1.6% and 2.4%), were retrofitted with a thin UHPC jacket and tested under four-point bending. The results are compared to a control set of HSC beams built with and without stirrups. The effect of steel ratio in the retrofitted beams was also investigated. The results show that the UHPC jacketing significantly increased the shear capacity by 40–125% in the shear-deficient HSC beams, allowing the beams to reach their full flexural resistance. The UHPC retrofit also allowed for improved flexural performance, with increases of 80–85% in stiffness, 20–35% in flexural strength and 40–180% in ductility when compared to the control beams built with stirrups. The failure mode and ductility in the UHPC retrofitted beams was affected by the longitudinal steel ratio, with the failure transitioning from bar fracture to concrete crushing as the steel ratio in the reference HSC beams was increased from 1.6% to 2.4%. To supplement the engineering case, finite element modelling is used to study the influence of other retrofit types, as well as the shear-span-to-depth ratio.