Concrete Crushing Research Articles

A new Distinct Element meso‐model for simulating the rocking‐dominated seismic response of RC columns

AbstractThe rocking‐dominated seismic response of reinforced concrete (RC) columns is a complex mechanism that entails P‐Δ effects, concrete crushing and spalling, rupture and dislocation of steel bars and stirrups, as well as combined localized failures causing splitting and shear‐flexure cracking. In this paper, we present a new meso‐scale numerical modeling strategy for the detailed simulation of the rocking response of slender RC columns under seismic actions. This work advances the current state‐of‐the‐art by exploring the unprecedented use of the Distinct Element Method (DEM), originally conceived for geotechnical studies and whose applicability in earthquake engineering has been primarily limited to the assessment of unreinforced masonry sub‐structures. To decrease analysis time and enable the use of DEM for RC problems, concrete is herein idealized as an assembly of solid macro‐block layers of size directly proportional to their distance from expected plastic hinges. These layers are connected by nonlinear interface springs to simulate tensile and shear cracking via a simplified Mohr‐Coulomb criterion. Crushing of concrete in deformable blocks is modeled using the Feenstra and De Borst strain‐softening linearized compression law, while confinement and combined failures are accounted for numerically through the explicit representation of longitudinal and transversal reinforcement bars, idealized as link elements. Previous experimental static and dynamic tests on full‐scale RC column specimens and results from fiber‐based Finite Element and sectional analysis models are used to evaluate DEM results and quantify the influence of key modeling parameters, including block number and deformability, as well as the amount of damping. The agreement between simulated failure modes and force and displacement capacities and their experimental counterparts demonstrate the applicability of the proposed approach, while demonstrating the pros and cons of simplified numerical methods.

Flexural Capacity of Concrete Beams with Basalt Fiber-Reinforced Polymer Bars and Stirrups.

The flexural properties of six 120 × 300 × 4500 mm concrete beams reinforced with bars made from basalt fiber-reinforced polymer (BFRP) basalt fibers and concrete stirrups were investigated. The beams contained different concrete compositions (with or without basalt fibers). Steel and BFRP bars were used as longitudinal and shear reinforcement. As expected, all the beams failed by the crushing of the concrete in the top compression fibers because of using BFRP bars. Beams with BFRP bars should be designed to fail by concrete crushing because it is safer than a brittle failure of the bars. The beams with composite reinforcement were characterized by the greatest number of cracks with the largest crack width. The use of basalt fibers resulted in slightly reduced cracks in beams. The most significant deflections were recorded for the beams with BFRC composite reinforcement, the smallest for FRC beams. Adding basalt fibers to the concrete resulted in slightly reduced deflection of FRC beams compared to RC beams and significantly reduced deflection compared to BFRC beams. Results showed that introducing basalt fibers to the concrete increased curvature ductility of these beams. A theoretical analysis of flexural capacity showed that the ACI standard design is more similar to experimental values (0.87). A more restrictive standard, as it turns out, is the fib Model Code (0.68).

Flexural behavior of reinforced concrete beams strengthened with high-strength stainless steel wire rope meshes reinforced ECC

In this study, the flexural behavior of reinforced concrete (RC) beams strengthened with high-strength stainless steel wire rope (HSSSWR) meshes reinforced Engineered Cementitious Composite (ECC) was investigated. In total, six strengthened beams and one control beam were manufactured and tested taking into account of test variables including the reinforcement ratio of longitudinal HSSSWR, nominal diameter of HSSSWR, and formula of ECC. The test results showed that the flexural capacity, ductility, stiffness, and toughness of the strengthened beams were sufficiently improved, and the development of crack including maximum width and spacing was delayed by using the strengthening system of HSSSWR meshes reinforced ECC, and the failure mode of the strengthened beams was concrete crushing, which was followed by the local debonding along the interface and rupture of reinforcement layer except for the beam with the relatively high reinforcement ratio of longitudinal HSSSWRs. The calculation models with high accuracy were proposed to predict the flexural capacity and stiffness for the RC beams strengthened by the HSSSWR meshes reinforced ECC, which were verified by test results in this study and existing study.

Cyclic behavior of polypropylene fiber reinforced concrete beams with prestressed CFRP tendons and nonprestressed steel bars

The main purpose of this paper is to evaluate the cyclic behavior of polypropylene fiber-reinforced concrete (FRC) beams with a hybrid reinforcement system of prestressed carbon fiber reinforced polymer (CFRP) tendons and nonprestressed steel bars. A total of six beams are tested, including four beams prestressed with CFRP tendons, one prestressed with steel tendons and one reinforced with steel bars. The experimental variables include the partial prestressing ratio, amount of CFRP tendons, and jacking stress level. The test results are presented in terms of failure mode, hysteretic response, flexural capacity, self-centering capability, ductility, stiffness degradation and energy dissipation. The results show that the CFRP prestressed beam failing due to concrete crushing exhibits much higher ductility and dissipated energy than the beam failing due to CFRP rupture. An increase in the partial prestressing ratio or a decrease in the jacking stress has a favorable effect on the ductility. A numerical moment–curvature analysis procedure is applied to perform a parametric analysis of the ductility and deformability of the hybrid FRC section. It is recommended that the reinforcing index should be sufficient to ensure compression failure, but should not be greater than 0.35 to ensure reasonable ductility and deformability.

Global stability of axially loaded partially encased composite column with L-shaped section

The partially encased composite (PEC) section consists of steel component and concrete partially encased between flanges. This paper investigates the global stability of partially encased composite column with L-shaped section (L-PEC column). Firstly, two experiments of the L-PEC column with unequal-leg under axially compressive load is reported. Their failure modes are mainly flexural buckling, concrete crushing and spalling. Secondly, the elastic buckling of the L-PEC columns is demonstrated through the buckling analysis of the FE models, and it is proved to be feasible that the normalized slenderness ratio λv is used to evaluate the reduction factors φ of L-PEC columns within the length-to-thickness ratio less than 4 instead of λuvω which is corresponding to flexural-torsional buckling mode. The elastic buckling of axially compressed members with L-shaped thick-walled PEC and homogeneous section is also discussed. Moreover, the parameter analysis of the nonlinear stability of the L-PEC columns is conducted, and the results indicate that the aspect ratio of the cross-section and length-to-thickness ratio of the shorter leg are also key factors affecting the stability of the L-PEC columns. Based on that, the design formulas are proposed, which take into account the effect of the aspect ratio and length-to-thickness ratio of the shorter leg. The formulas can be used to calculate the load-bearing capacity of the L-PEC columns with both equal- and unequal-leg L-shaped sections.

Numerical investigation into the effects of corrosion on the shear performance of pretensioned bridge girders with cast-in-place slabs

Corrosion and shear cracking are frequently observed near supports of pretensioned bridge girders in coastal climates, so non-linear finite element analysis was used to study the effect of corrosion on shear performance in a real case study. Varying degrees of corrosion and various locations (top strands, bottom strands, vertical stirrups and girder-slab interface) were considered. The analyses included construction phases, concrete creep and shrinkage, and the effects of corrosion on the properties of prestressing and reinforcing steel, concrete, and the bond between concrete and reinforcement. The study shows that high (20%) corrosion in the bottom layer of strands can modify the failure mode from concrete crushing in the web to strand slippage or crushing of concrete in the support zone with limited cracking. Although severe strand corrosion significantly compromises girder capacity and ductility, failure occurs only when there is overloading. The predicted failure mode was also sensitive to material parameters, in particular the corrosion-induced crack widths used for modelling the reduced concrete strength. Nevertheless, some similarities were noticed between observed and predicted cracking occurrence. For moderate corrosion (10%), girder capacity was limited by strand fracture, but extensive flexure and shear cracking would appear before failure. 20% corrosion in the vertical stirrups in the web seems to have potentially smaller effect on the shear capacity than 20% corrosion in the strands in support, while corrosion in the top strands or stirrups in the girder-slab interface did not affect the girder capacity.

Finite element analysis of the effect of type, number, and installation angle of FRP sheets on improving the flexural strength of concrete beams

Using FRP material to strengthen concrete beams is one of the best methods to prevent cracks propagation in the tensile zone. In this article, a concrete beam is modeled using the finite element software Abaqus. In order to investigate the effects of type, number, and installation angle of FRPs, a total number of 25 numerical models are considered. In these models, 3 types of covers made of GFRP, CFRP, and AFRP materials, including 6 and 12 sheets, are used at the installation angles of 30, 45, 60, and 90 degrees. Also, at the bottom of the beam in all the models, FRP layers are used to prevent the growth of cracks. After applying a constant load of 60 kN on all models, the stresses produced in the beam together with displacement at the middle of the beam, are investigated. The results showed that with an equal number of sheets and equal distance of installed sheets, the effect of FRP sheets on reducing displacement is greater at an installation angle of 45 degrees compared to that of a 60-degree angle. Also, this effect is greater at an installation angle of 60-degree angle compared to that of a 90-degree angle. Furthermore, by the addition of plates, the maximum lateral strain at the middle of the beam span is reduced up to 12.5 %. Also, CFRP material had a better performance compared to the two other types of fibers. The addition of prestressed FRP sheets to the specimens increases their strength. The load increase continues to the point wherein the beam fails due to the crushing of the compressive concrete. Adding the prestressed FRP sheets to the specimens increases the strength against the ultimate load from 5.4 % to 26.4 %, compared to the beam, which has internal confinement by the inner rebars.

Seismic performance of earthquake-damaged corroded reinforced concrete beam-column joints retrofitted with basalt fiber-reinforced polymer sheets

This present research conducted an experimental study on the influence of different earthquake damages on the seismic performances of aged reinforced concrete (RC) beam-column joints retrofitted with basalt fiber-reinforced polymer (BFRP) sheets under cyclic loadings. Six beam-column joints included one benchmark specimen, one uncorroded specimen retrofitted with BFRP sheets, and four earthquake-damaged corroded specimens with the corrosion rates of 0% and 9% retrofitted with BFRP sheets. Test results demonstrated that the seismic performances of earthquake-damaged corroded specimens effectually improved after retrofitting with BFRP sheets, and the retrofitting effectiveness was significantly affected by the earthquake-damaged levels. The bucking of stirrups, spalling and crushing of concrete of retrofitted specimens were effectually postponed, while the ductility of corroded and uncorroded specimens under the earthquake damages increased after retrofitting with BFRP sheets. The total cumulative energy dissipation and final stiffness of retrofitted specimens considerably improved with the maximum increase of 22.3% and 14.3% comparing to those of benchmark specimen, respectively. Besides, the models for predicting the shear strength of RC beam-column joint cores considering the influences of earthquake damage, reinforcement corrosion, and FRP retrofitting were proposed.

Cyclic tests on steel truss-embedded steel plate-concrete composite walls

This paper performed five cyclic tests to investigate seismic performances of novel steel truss-embedded steel plate-concrete composite wall (STSCW) specimens with different prepared parameters. The studied key parameters included the cross-section size of chord member, truss-to-wall ratio, and steel–concrete interface without studs. The STSCWs experienced progressive failures of steel faceplate buckling, vertical weld fracture in the bottom corner, concrete crushing, and steel faceplate tensile fracture. Moreover, the failure modes of embedded steel truss consisted of flange necking or fracture under tension and local buckling under compression. The effects of these key parameters on seismic behaviors of STSCWs were analyzed and discussed. They showed that increasing the truss-to-wall ratio and cross-section size of the chord member improved the lateral shear resistance and deformation capacity of STSCWs. Welding studs to the flange had a negligible effect on the lateral shear resistance but reduced the deformation capacity of STSCWs. Moreover, welding studs to the flange improved the deformation compatibility between the wall and steel truss. A theoretical model was developed and validated, indicating that the predicted lateral resistances agreed well with test results.

Behaviour and design of composite walls under axial compression

An extensive investigation on the axial behaviour of composite walls was carried out with the main aim of developing design recommendations. Firstly, in order to investigate the slenderness limit for different steel grades, an experimental programme was conducted comprising six concrete filled composite panels (CF-CPs) with four shear studs symmetrically welded on one steel plate, incorporating both mild steels, high- and ultra-high-strength steels. The second set of experiments included thirteen concrete filled composite walls (CF-CWs), in which different connector types and arrangements were utilised together with mild steels, high- and ultra-high-strength steels. In parallel with the experimental tests, numerical models were developed, involving element deletion and concrete damage properties to simulate concrete crushing. Extensive parametric study was conducted based on the validated models against the test results with detailed discussions. Innovative method (both experimentally and numerically) was adopted to separate the loads carried by exterior steel plates and the infilled concrete to assist the following design recommendations. The validity of the proposed design recommendations was demonstrated through comparisons with the present test and numerical results as well as the data collected in the literature.

Intermediate Crack Debonding of Externally Bonded FRP Reinforcement-Comparison of Methods.

Many researchers around the world have made extensive efforts to study the phenomenon of fiber-reinforced polymer (FRP) debonding. Based on these efforts, code provisions and various models have been proposed for predicting intermediate crack (IC) debonding failure. The paper presents a comparison of seven selected models: fib bulletin 14 approach, Teng et al. model, Lu model, Seracino et al. model, Said and Wu model, Elsanadedy et al. model and ACI 440. The accuracy of each model was evaluated based on the test results of 58 flexural specimens with IC debonding failures of externally bonded (EB), carbon FRP plates or sheets found in the existing literature. The experimental database was prepared to include a wide range of parameters affecting the issue under consideration. A comparison of the measured and predicted load capacity values was made to evaluate the prediction accuracy of the considered models. The analysis included the limitation of the load capacity estimated based on IC debonding models as well as concrete crushing and FRP rupture types of failure. The results indicate that the latest models proposed for direct implementation in design guidelines—the Said and Wu model and the Elsanadedy et al. model—offer the best accuracy in predicting the load capacity. In contrast, the fib bulletin 14 approach shows a wide dispersion of predictions and a large proportion of highly overestimated results.

Experimental and numerical modelling studies of slender reinforced concrete walls with single-layer reinforcement in Peru

The deficit in affordable residential construction in Lima has generated the construction of several mid to high-rise buildings using the structural system of Slender Reinforced Concrete (RC) Walls. In Peru, this system is known as ‘walls of limited ductility’ and their main characteristics are a fast construction time and an affordable price. Due to the expected non-ductile behaviour, Peruvian RC slender wall buildings follow the same seismic design criteria as traditional RC wall buildings but with a smaller reduction factor of elastic seismic forces and minor permissible story displacement drift. However, there is limited experience of the seismic response of such buildings in severe earthquakes and seismic design criteria have been obtained from just a few experimental tests. This work presents an experimental program of cyclic in-plane testing, developed at the Pontificia Universidad Católica del Perú (PUCP) to obtain more knowledge about the lateral behaviour of typical Peruvian slender walls. According to quasi-static tests, the slender walls reached a maximum story drift of 1.27% after damage occurred, including diagonal tension, diagonal compression, sliding shear, concrete crushing, and buckling of the vertical reinforcement. Experimental results for the slender RC walls were computed to obtain the Damage States, Equivalent Lateral Stiffness (Keff), Ductility (μ), Equivalent Damping Ratio (ξeq) and Bending/Shear/Sliding deformations. In this work, a calibration process on numerical models was developed using OpenSees software. This work shows that slender RC walls in Peru show the typical hysteretic response of structural walls until a maximum drift of 1.27%, despite their deficiencies in slenderness, squat geometry, and the absence of confinement zones.

Low cycle fatigue crack propagation and damage evolution of concrete beams reinforced with GFRP bar

This paper studies the low cycle fatigue (LCF) behavior of glass fiber-reinforced polymer (GFRP) reinforced concrete (RC) beams by utilizing experimental and analytical investigation. Static and LCF three-point bending tests were carried out on 12 over-reinforced GFRP RC beams and six under-reinforced steel RC beams. The failure modes, fatigue lives, load-deflection, strain, and crack propagation were analyzed. The fatigue life of the steel RC beam with the same maximum stress level was lower than the GFRP RC beam, while the GFRP RC beam illuminated a larger failure mid-span deflection. For GFRP RC beams, the average fatigue lives with the maximum stress levels Sσmax=0.85Pu, 0.70Pu, and 0.65Pu, were 896, 8491, and 19949, respectively (Pu = the ultimate static flexural loading capacity). The average fatigue life of the highest stress level (0.85Pu) was approximately 22 times the lowest stress level (0.65Pu). Bending shear failure, and concrete crush were the dominant fatigue failure mode for GFRP and steel RC beams. The relationship between fatigue stress range and fatigue life was investigated based on fitting and reliability analysis. The stress intensity factor of the type I crack of the GFRP RC beam was deduced theoretically. The fatigue crack clarified a three-stage development trend (crack initiation, stable crack propagation, unstable crack propagation). When the crack continued to expand until it ran through the whole section, the beam was damaged. The fatigue crack propagation was fitted according to the experimental data. The deflection, dynamic stiffness, and damage evolution law of steel and GFRP RC beams were deducted. The fatigue life prediction models based on crack propagation and damage evolution were derived.

Experimental study of a new assembled integral concrete–steel open-web sandwich plate composite bridge

This study introduces a new type of bridge structure—the assembled integral concrete–steel open-web sandwich plate composite bridge (COSPB), which is composed of a concrete slab,steel Vierendeel beams (SVBs, with top chords, bottom chords and shear keys), and studs (used for connecting SVBs and concrete slab). The bi-directional SVBs form a spatial steel grid structure, which can be used as the formwork for concrete slab casting, and divided into prefabricated units to allow on-site assembly after prefabrication in factory, leading to the reduction of on-site construction workload and the acceleration of the construction schedule. To understand the flexural behavior of this kind of structure, a static experiment was conducted on a 10-m-span full-scale test specimen with simply supported boundaries to investigate the deflection, strain distribution, and failure mode. The test results showed that there was still a large safety reserve for the flexural capacity of the section after the bottom chord of the steel–concrete composite Vierendeel beam (SCVB) began to yield. The ratio of the ultimate load to the yield load was 1.56. No concrete crushing and large area cracking were observed during loading, and the structure had good ductility. The ultimate flexural capacity of the SCVB was analyzed by the method of cross-sectional analysis, and the results were in good agreement with the test results. Finally, based on the test results, the ultimate flexural capacity and stiffness of the bridge were discussed using the Chinese Highway Bridge Design Code.

Parametric study on the residual compressive strength of RC columns subjected to different standard fire durations and load ratios

PurposeSince columns are critical structural elements, they shall withstand hazards without any considerable damage. In the case of a fire, although concrete has low thermal conductivity compared to other construction materials, its properties are changed at elevated temperatures. Most critically, the residual compressive strengths of reinforced concrete columns are significantly reduced after fire exposure. Validation of the worthiness of rehabilitating concrete structures after fire exposure is highly dependent on accurately determining the residual strengths of fire-damaged essential structural elements such as columns.Design/methodology/approachIn this study, eight reinforced-concrete columns (200 × 200 × 1,500 mm) that were experimentally examined in a prior related study have been numerically modelled using ABAQUS software to investigate their residual compressive strengths after exposure to different durations of standard fire (i.e. one and two hours) while subjected to different applied load ratios (i.e. 20 and 40% of the compressive resistance of the column). Outcomes of the numerical simulations were verified against the prior study's experimental results.FindingsIn a subsequent phase, the results of a parametric study that has been completed as part of the current study to investigate the effects of the applied load ratios show that the application of axial load up to 80% of the compressive resistance of the column did not considerably influence the residual compressive strength of the shorter columns (i.e. 1,500 and 2,000-mm high). However, increasing the height of the column to 2,500 or 3,000 mm considerably reduced the residual compressive strength when the load ratio applied on the columns exceeded 60 and 40%, respectively. Also, when the different columns were simulated under two-hour standard fire exposure, the dominant failure was buckling rather than concrete crushing which was the typical failure mode in most columns.Originality/valueThe outcomes of the numerical study presented in this paper reflect the residual compressive strength of RC columns subjected to various applied load ratios and standard fire durations. Also, the parametric study conducted as part of this research on the effects of higher load ratios and greater column heights on the residual compressive strength of the fire-damaged columns is practical and efficient. The developed computer models can be beneficial to assist engineers in assessing the validity of rehabilitating concrete structures after being exposed to fire.

Experimental study on out-of-plane flexural behavior of steel-concrete-steel composite walls

In this study, six steel-concrete-steel composite wall (SCSCW) specimens have been designed and manufactured, and their out-of-plane flexural behaviors under combined axial and horizontal loads are experimentally studied. The study parameters include the connector arrangement scheme and applied axial load. The effects of these parameters on the failure modes, experimental load–displacement curves, bearing capacities, ductility coefficients, stiffness, energy dissipation capacities, and strain distributions of the specimens are analyzed. All specimens exhibit sectional flexural failure. The failure phenomena include the out-of-plane local buckling, concrete crushing, and welding fracture of the steel plates. These specimens show excellent ductility with an average ductility coefficient 2.27. The strength degradation coefficients of the specimens are >0.85. Increasing the number of connectors can restrict the local buckling of external steel plates, and the bearing capacities of the specimens are also improved. The connector arrangement scheme and axial load significantly influence the secant stiffness of the specimens during the initial stage of the experiments. When the connector arrangement schemes are identical, the higher the axial load, the better the energy dissipation capacity of the specimens. A simplified calculation model for the flexural capacity of SCSCWs is proposed considering the effects of local buckling and side plates, which has high accuracy and efficiency, and average ratio between the calculated and experimental peak loads is 0.96. A brief design example for the SCSCWs is provided to illustrate the design process considering the axial and out-of-plane loads.

Flexural behavior of prefabricated composite beam with cast-in-situ UHPC: Experimental and numerical studies

Steel-concrete composite beams, which consist of steel beams, reinforced concrete slabs, as well as headed shear studs, are getting widely used in engineering structures. This paper proposed an innovative prefabricated composite beam consisting of two full-depth precast concrete (FDPC) slabs with extending rebars and reversed grooves, an H-shaped steel beam with welded shear studs, the additional transverse rebars and the cast-in-situ ultra-high performance concrete (UHPC). Compared with conventional steel–concrete composite beams, the innovative prefabricated composite beam retains the advantages of rapid assembly and construction, while maintaining favorable flexural performance and reducing the excessive costs and potential construction challenges due to application of the FDPC slabs and cast-in-situ UHPC. Experimental study was carried out to investigate the flexural behavior of prefabricated composite beam. Failure modes, flexural capacity, deformation characteristics, and crack propagation were observed. Refined finite element (FE) models were established, calibrated against test results and then adopted to simulate the load-carrying capacity of the proposed prefabricated composite beam. The effects of critical design parameters such as cast-in-situ concrete strength, steel beam strength and section height, shear stud diameter and interval on the flexural behavior of prefabricated composite beam were investigated. The analysis results indicated that the proposed prefabricated composite beam exhibited excellent and expected flexural behavior, and the failure mode was concrete crushing and steel beam yielding. The prefabricated composite beam is regarded as partially connected composite beam. Through geometrical parameters correlation analysis, the prediction formulas of flexural capacity and bending stiffness of the partially connected composite beam were deduced and validated, which provided a fundamental basis for further study and application.

Experimental investigation on the flexural behavior of coarse aggregate reactive powder concrete (CA-RPC) bridge deck

The high mechanical characteristics of reactive powder/ ultrahigh performance concrete have promoted its application in the bridge industry. Nonetheless, its employment in full structural components in bridges is hindered by the high cost and inconsistencies in the design guidelines. The addition of small-size coarse aggregate has been advocated by many researchers in pursuit of accomplishing a cost-effective and high-performance concrete. This paper introduces an innovative application of coarse aggregate reactive powder concrete (CA-RPC) and presents a comprehensive experimental investigation on the flexural behavior of a full-size prefabricated (CA-RPC) slab. The test results validated the sustained performance of RPC with the inclusion of coarse aggregate. The slab exhibited high capacity and excellent ductility, achieving an ultimate deflection to span ratio of about 1/8, accredited to the fibers and the appropriate reinforcement ratio. The resulting ductility was characterized by multiple micro-cracking at early stages, stable multiple macro-cracking prior to localization, slow localized crack growth and gradual concrete crushing. A detailed exploration of the cracking development and failure progression is provided, and a general evaluation of the performance of the slab under cyclic loading is also presented.

Experimental investigation and numerical analysis of precast reinforced concrete shear walls with shoe bolt connections

An innovative shoe bolt connection for precast concrete (PC) structures that features resilience is proposed in this study. In this connection, a steel washer plate that could be easily replaced after an earthquake serves as the “fuse” element, and the bolt passing through the horizontal joints serves as the self-centring element. To validate the reliability of the proposed connection, quasi-static tests were conducted on two PC shear wall specimens. One specimen was designed with a conventional wall shoe bolt connection (S-1). The other specimen was designed with the proposed connection (S-2). The crack pattern, failure mode, hysteresis curve, skeleton curve, ductility and energy dissipation capacity of the specimens were studied. Furthermore, finite element (FE) analysis was conducted to reproduce the test and facilitate an in-depth understanding on the mechanism of the specimens. The test and analysis results indicated that S-1 exhibited brittle failure, while the failure of S-2 was governed by concrete crushing and fuse plate yielding and reflected a remarkable self-centring capacity; only minor shear slips of the horizontal joints occurred, even for the specimen S-1 with a smaller axial load ratio, indicating that the joints had enough shear resistance; the proposed three-dimensional FE model could predict the skeleton curve and the failure mode of the specimens with acceptable accuracy; for the specimen with proposed connection, the failure mode was significantly influenced by the thickness of the fuse plate.

Effect of overlay thickness, fiber volume, and shrinkage mitigation on flexural behavior of thin bonded ultra-high-performance concrete overlay slab

This study investigated the flexural performance of 10 reinforced concrete slabs rehabilitated using thin ultra-high-performance concrete (UHPC) bonded overlay. The performance was compared to two slabs repaired using latex-modified concrete (LMC) that is widely used for bridge deck rehabilitation. Test parameters included the overlay thickness (25, 38, and 50 mm), fiber volume (2% and 3.25%), and shrinkage mitigation methods for the UHPC. The overlay slab specimens were stored outdoor for 30 months before conducting the four-point bending test. Experimental results indicated that the overlay slabs exhibited flexural failure pattern with yield of reinforcing steel, concrete crushing of the reinforced concrete substrate, and multiple cracks in the overlay. The use of UHPC thin bonded overlay enhanced cracking load by 295%–395% and flexural capacity by 35%–75% compared to the LMC overlay slabs. The maximum crack width of UHPC overlay slabs at the stage of the yield of reinforcement was less than 0.1 mm compared to 0.25–0.3 mm for the LMC overlay slabs. No slip occurred at the interface between the UHPC overlay and substrate, whereas the slip initiated following LMC overlay cracking. The increase of overlay thickness from 25 to 50 mm and fiber volume from 2% to 3.25% enhanced the flexural load capacity of the UHPC overlay slabs by 30%–40% and 10%–25%, respectively. These two strategies also reduced crack opening and propagation before the yield of reinforcing steel. The use of pre-saturated lightweight sand and CaO-based expansive agent was effective in mitigating autogenous and drying shrinkage without significantly influencing the flexural capacity of UHPC overlay slab.