Steel Fiber-reinforced Ultra-high Performance Concrete Research Articles

Experimental Investigation on Shear Behavior of Non-Stirrup UHPC Beams under Larger Shear Span–Depth Ratios

Due to the extraordinary mechanical properties of ultra-high-performance concrete (UHPC), the shear stirrups in UHPC beams could potentially be eliminated. This study aimed to determine the effect of beam height and steel fiber volume content on the shear behavior of non-stirrup UHPC beams under a larger shear span–depth ratio (up to 2.8). Eight beams were designed and fabricated including six non-stirrup UHPC beams and two comparing stirrup-reinforced normal concrete (NC) beams. The experimental results demonstrated that the steel fiber volume content could be a crucial factor affecting the ductility, cracking strength, and shear capacity of non-stirrup UHPC beams and altering their failure modes. Additionally, the height of the beam had a considerable effect on its shear resistance. French standard formulae were more accurate for the UHPC beams with larger shear span–depth ratios, PCI-2021 formulae greatly overestimated the shear capacity of UHPC beams with larger shear span–depth ratios, and Xu’s formulae were more accurate for the steel fiber-reinforced UHPC beams with larger shear span–depth ratios. In summary, French standard formulae were the most suitable formulae for predicting the shear capacity of UHPC beams in this paper.

The Dynamic Mechanical Properties and Damage Constitutive Model of Ultra-High-Performance Steel-Fiber-Reinforced Concrete (UHPSFRC) at High Strain Rates.

A high strain rate occurs when the strain rate exceeds 100 s-1. The mechanical behavior of materials at a high strain rate is different from that at middle and low strain rates. In order to study the dynamic compressive mechanical properties of ultra-high-performance steel-fiber-reinforced concrete (UHPSFRC) at high strain rates, an electro-hydraulic servo universal testing machine and a separate Hopkinson pressure bar (SHPB) with a diameter of 120 mm were used, respectively. A quasi-static compression test (strain rate 0.001 s-1) and impact compression test with a strain rate range of 90~200 s-1 were carried out to study the failure process, failure mode, and stress-strain curve characteristics of UHPSFRC at different strain rates and quantify the strain rate strengthening effect and fiber toughening effect. Based on the statistical damage theory and energy conversion principle, a dynamic damage constitutive model considering the effects of strain rate and fiber content was constructed. The results showed that the rate correlation of UHPSFRC and the fiber toughening properties showed a certain coupling competition mechanism. When the fiber content was less than 1.5%, with an increase in the steel fiber content, the crack initiation and propagation time of the specimen was extended, and the strain rate sensitivity gradually decreased. When the fiber content was 2%, the impact compressive strength of the specimen was optimal. Compared with UHPC, the dynamic increase factor (DIF) of UHPSFRC was significantly lower. The dynamic damage constitutive model established in this paper, considering the influence of strain rate and fiber content, has a good applicability and can describe the mechanical behavior of UHPSFRC at a high strain rate.

Investigation of the corrosion-induced damage mechanism of steel fibers in ultra-high-performance steel fiber-reinforced concrete using X-ray computed tomography

To investigate the corrosion damage mechanism of ultra-high-performance steel fiber-reinforced concrete (UHPSFRC), the electrically accelerated corrosion process of specimens with different steel fiber contents was evaluated using micron-level X-ray computed tomography. The results showed that the grid structure formed by the interconnecting steel fibers was a key factor in inducing corrosion damage in the UHPSFRC. The 1% steel fiber content specimens were strongly corrosion-resistant. Steel fiber corrosion triggered the concrete cover of the UHPSFRC to crack or spall from the outside to the inside, and areas with a higher initial density of steel fibers showed a higher degree of damage.

Behavior of Reinforced Ultra-High Performance Concrete Slabs Under Impact Loading After Exposure to Elevated Temperatures

Steel fiber-reinforced ultra-high performance concrete (UHPC) material is prone to explosive spalling under elevated temperatures. With the addition of polypropylene (PP) fiber, thermal spalling of UHPC can be mitigated and its fire resistance can be improved. This research investigates the impact resistance of steel and PP fiber-reinforced UHPC slabs after exposure to elevated temperatures, and the structural behavior and damage were compared against normal strength concrete (NSC) slabs. Karagozian & Case concrete (KCC) model was adopted to simulate both NSC and UHPC materials. With consideration of thermal hazards, the material damage, equation of state and strain rate sensitivity were adapted. The validity of this numerical model was evaluated against available experimental results. The numerical model was used to investigate the impact resistance of the reinforced UHPC slabs after exposure to fire hazards. The effect of fire exposure time, impact velocity and impact mass on the resistance of the reinforced NSC and UHPC slabs were analyzed. The simulation results revealed that punching shear failure areas in the NSC slabs were 2.5 times, 3.4 times, 3.0 times and 1.2 times larger than the UHPC slabs after exposure to international standardization ISO-834 standard fire for 1[Formula: see text]h, 2[Formula: see text]h, 3[Formula: see text]h and 4[Formula: see text]h, respectively. After exposure to the standard fire ISO-834 for 2 h, the punching shear failure on the bottom side of NSC increased 90.9% with the increase in falling height from 1[Formula: see text]m to 7[Formula: see text]m, while for the UHPC slabs, the increment was around 67.9%. After exposure to the standard fire ISO-834 for 2[Formula: see text]h, the punching shear damage of the NSC slabs increased by 72.9% with the punch weight increased from 100[Formula: see text]kg to 700[Formula: see text]kg, whereas the damage in the UHPC slabs increased by 53.8%.

An overview of progressive advancement in ultra-high performance concrete with steel fibers

A progressive advance in the construction sector is attained by employing ultra-high performance concrete (UHPC) technology. Rigorous efforts have been made in this research domain to have remarkable quality levels with 150 MPa or more strength and significant durability, which was impossible previously. Steel fiber incorporation in UHPC is vital in improving its mechanical characteristics. This review on the incorporation of steel fibers in UHPC evaluates, identifies, and synthesizes research outcomes for creating a summary of current evidence that can contribute to evidence-based practice. This study summarized a review of the literature on steel fibers’ effect on UHPC, intending to explore its essential aspects. The aim is to summarize the literature in this research domain and provide guidance for future research. Moreover, the basic requirements and materials, mixing and casting, mechanical properties, modern applications, advantages and disadvantages, and future perspectives associated with steel fibers reinforced UHPC in the construction sector are discussed. It is revealed from the conducted analysis that the most widely applied keyword is “steel fibers.” Due to the graphical illustration of the contributing studies, the current work may benefit academic scholars in sharing novel techniques and ideas and establishing collaborative efforts. Furthermore, the present work reveals that steel fibers have the potential to enhance the mechanical properties of UHPC; however, the large-scale production and applications of steel fiber-reinforced UHPC are controlled by parameters like fiber content and geometry.

Ultra high performance concrete and C-FRP tension Re-bars: A unique combinations of materials for slabs subjected to low-velocity drop impact loading

In this research work, different combinations of normal strength concrete (NSC), ultra-high-performance concrete (UHPC), and steel fiber-reinforced UHPC (SFR-UHPC) concrete with re-bars of conventional steel and of carbon fiber-reinforced polymer (C-FRP) are used in a two-way square slab of size 1000mm x 1000mm x 75mm subjected to 2500 mm free-fall impact loading. Experimental arrangement consisting of 105 kg dropping weight with the circular flat impacting face of 40 mm diameter used for carrying out impact test is modeled using a high-fidelity physics-based finite element computer code, ABAQUS/Explicit-v.6.15. After validating the experimental results of the NSC slab with steel bars, analyses are extended by replacing NSC and steel bars with UHPC/SFR-UHPC and C-FRP bars, respectively, under the same dropping weight. Only the remote face (tension face) of the slabs is provided with the re-bars. Widely employed and available with the ABAQUS, the Concrete Damage Plasticity model with strain-rate effects has been entrusted for simulating the concrete plastic response. Re-bars of steel are idealized with the Johnson-Cook plasticity damage model. C-FRP re-bars are defined with the classical plasticity model following the elastic-plastic constitutive laws. The impact responses of the slabs consisting of NSC/UHPC/SFR-UHPC concrete with re-bars of steel, and C-FRP combinations considered are discussed and compared. Slabs made of UHPC/SFR-UHPC concrete with the C-FRP re-bars are found to offer a promising combination of materials to withstand low-velocity impact load with little damage and extraordinary impact performance.

Direct tensile behavior of steel fiber reinforced ultra-high performance concrete at high strain rates using modified split Hopkinson tension bar

This paper aims to investigate the dynamic tensile behavior of steel fiber reinforced ultra-high performance concrete (SF-UHPC) under impact loading. The investigated SF-UHPC were designed to have a compressive strength in excess of 200 MPa. A modified split Hopkinson tensile bar (SHTB) has been designed to obtain the dynamic behavior of SF-UHPC with fiber volume fraction of 2% and 4% under high strain rates ranging from 55 to 156 s−1. Wave shaping technique was used to achieve stress equilibrium and constant strain rate during testing. The average dynamic impact factor (DIF) of the tensile strength for SF-UHPC with a fiber volume fraction of 2% and 4% was found to be 3.2 and 1.9 at an average strain rate of 118 s−1 and 131 s−1, respectively. The designed SHTB in combination with high speed digital image analysis of notched specimens was able to measure the stress versus crack opening relationship of the SF-UHPC. Based on the results obtained from the current study and results obtained from twelve other studies, an equation is suggested to calculate the DIF of the tensile strength of SF-UHPC.

Effects of content and length/diameter ratio of PP fiber on explosive spalling resistance of hybrid fiber-reinforced ultra-high-performance concrete

Ultra-high-performance concrete (UHPC) is prone to explosive spalling at high temperatures, which compromises the load-bearing capacity of the structures. In this paper, the effects of the content and length/diameter ratio of polypropylene (PP) fibers on the explosive spalling resistance of the steel and PP hybrid fiber-reinforced UHPC were investigated utilizing experimental method. First, the UHPC specimens were prepared using the conventional curing method. Second, the UHPC specimens were heated using the ISO-834 standard heating curve. Thirdly, the appearances, the first spalling time, the first spalling temperature, and the mass loss of the specimens were used to evaluate the explosive spalling resistance of the UHPC. The results demonstrated that the steel and PP hybrid fiber-reinforced UHPC has much greater explosive spalling resistance than the steel fiber-reinforced UHPC. The explosive spalling resistance of the hybrid fiber-reinforced UHPC is strongly influenced by the content and length/diameter ratio of the PP fibers. Generally, the explosive spalling resistance of the hybrid fiber-reinforced UHPC increases with the increase of the PP fiber content and length/diameter ratio.

Experimental Studies on Seismic Performance of UHPSFRC-Filled Square Steel Tubular Columns

The excellent seismic performance of concrete-filled steel tube (CFST) structures has been widely recognized, but there is a paucity of research on composite columns using UHPC with added steel fibers. This paper presents the experimental studies and numerical analyses with OpenSees on seismic performance of ultra-high performance steel fiber-reinforced concrete (UHPSFRC)-filled square steel tubular columns. Five half-scaled specimens of UHPSFRC-filled square steel tubular columns were tested under a combination of constant axial compression and cyclic horizontal load, with parameters of width-to-thickness ratio (28.5, 19.9 and 14.7) and axial compression ratio (0.133, 0.266 and 0.399) of the steel tube. With the decrease in width-to-thickness ratio, the maximum bending moment capacity increased by 33.5% and 15.3%, and the energy dissipation capacity and ductility increased, while the strength degradation and stiffness degradation reduced. With the increased axial compression ratio, the loading capacity increased from 55.3 to 70.2 kNm (26.94%). The results indicate that UHPSFRC-filled square steel tubular columns improve seismic performance by decreasing the axial compression ratio and by increasing the width-to-thickness ratio. When the width-to-thickness ratio was reduced, the steel tubular was able to provide higher lateral restraint to the internal UHPC; thus, seismic performance was improved. With the increase in the axial compression ratio, the second-order damage effect of the members was greatly affected, and it accelerated the plastic damage. A modified UHPSFRC model considering steel tubular constraints was adopted, and the nonlinear dynamic modeling of the column response using OpenSees led to good agreement with the tested response of the column under cyclic motion. The theoretical calculation model can better predict the bending capacity of the UHPSFRC-filled square steel tubular columns. However, the calculation formulas of initial stiffness and yield bending moment need further research.

Self-healing of slag-cement ultra-high performance steel fiber reinforced concrete (UHPFRC) containing sisal fibers as healing conveyor

This paper presents the results of a research on the influence of sisal fibers on the self-healing capacity of slag-cement UHPFRC reinforced with steel fibers. In order to evaluate the composite healing capacity, specimens were submitted to pre-cracking by tensile test and then to a 3 months of wetting and drying cycles treatment. Treated specimens were resubmitted to tensile test and evaluated by Optical and Electronic microscopy and CT Scan. Results indicate that the sisal fiber works as a healing conveyor improving by about 20% and 15% the tensile stress and post cracking energy of treated specimens, respectively. Sisal fibers played a major role densifying the interface, working as a vehicle for the healing agents into small interface cracks. All specimens with cracks under 80 μm could completely self-seal mainly by calcium carbonate. Wider cracks could not be completely sealed, though the specimens exhibited a recovery of the mechanical behavior essentially due to late slag-cement hydration.

Machine learning prediction of structural response of steel fiber-reinforced concrete beams subjected to far-field blast loading

Owing to its superior mechanical properties, enhanced energy absorption, and improved blast resistance, steel fiber-reinforced cementitious composites are a prime choice for the development of resilient structures. Sizable advancements have recently been made in assessing the blast performance of steel fiber-reinforced concrete (SFRC), high-strength steel fiber-reinforced concrete (HSFRC), and ultra-high-performance steel fiber-reinforced concrete (UHPFRC). However, there is still need for concerted research to explore the effects of fiber parameters under blast loading and to develop simple and robust predictive models. Thus, the present study develops a machine learning model to predict the maximum displacement of SFRC, HSFRC, and UHPFRC beams subjected to far field blast loading. Using Gaussian Process (GP) regression and Conditional Tabular Generative Adversarial Networks, a novel model was developed considering 117 experimental and 300 synthetic datasets. The proposed model was appraised through several statistical performance metrics and compared to existing analytical and numerical methods. The model imparts noteworthy reduction in modeling complexity in terms of static and dynamic material properties. A parametric analysis was conducted using the developed model to investigate the effects of fiber properties for diverse beam configurations. The proposed simplified model achieved highly favorable predictive performance with MAE of 2.75, R2 of 90.32%, and MAPE of 13.8%.

Development of Thermoplastic Composite Reinforced Ultra-High-Performance Concrete Panels for Impact Resistance.

In order to improve flexural and impact performance, thin panels of steel fiber-reinforced ultra-high performance concrete (UHPC) were further reinforced with external layers of continuous fiber-reinforced thermoplastic (CFRTP) composites. CFRTP sheets were bonded to 305 × 305 × 12 mm UHPC panels using two different techniques. First, unidirectional E-glass fiber-reinforced tapes of polyethylene terephthalate glycol-modified (PETG) were arranged in layers and fused to the UHPC panels through thermoforming. Second, E-glass fiber woven fabrics were placed on the panel faces and bonded by vacuum infusion with a methyl methacrylate (MAA) polymer. Specimens were cut into four 150 mm square panels for quasi-static and low-velocity impact testing in which loads were applied at the panel centers. Under quasi-static loading, both types of thermoplastic composite reinforcements led to a 150–180% increase in both peak load capacity and toughness. Impact performance was measured in terms of both residual deformation and change in specimen compliance, and CFRTP additions were reduced both by 80% to 95%, indicating an increase in damage resistance. While both reinforcement fabrication techniques provided added performance, the thermoforming method was preferable due to its simplicity and fewer specialized tool requirements.

Performance evaluation of RC-MRFs with UHPSFRC and SMA rebars subjected to mainshock-aftershock sequences

Although structures are generally subjected to mainshock-aftershock sequences, the current structural design process merely considers the main seismic event. This study aims to compare the performance of Reinforced Concrete Moment Resisting Frames (RC-MRFs) with Shape Memory Alloy (SMA) and Ultra-High-Performance Steel Fiber Reinforced Concrete (UHPSFRC) under the influences of mainshock and aftershock sequence. To achieve this aim, 3, 6, and 8-story five-span frames were simulated considering three different approaches: (i) RC frames; (ii) RC frames with SMA rebars in the plastic hinge length of the beams; (iii) RC frames with UHPSFRC and SMA in the plastic hinge length of the beams.Each frame was analyzed under two different scenarios, with and without considering seismic sequences to assess the post-earthquake performance of damaged RC frames. Time history analyses were conducted using seven real accelerograms. Maximum transient inter-story and roof drifts, as well as residual inter-story drifts, were determined and compared in undamaged and damaged structures to assess the effect of seismic sequence. As the performance evaluation of the damaged structures appears to be essential to make repair policy decisions and rescue operations, damage states were defined according to FEMA-356 based on maximum transient and residual drifts. Numerical results illustrate the salient effect of using SMA and UHPSFRC synergistically in reducing transient and residual drifts and enhancing the functionality of structures in both mainshock and aftershock.

Use of Waste from Granite Gang Saws to Manufacture Ultra-High Performance Concrete Reinforced with Steel Fibers

The purpose of this study is to analyze the feasibility of using the ultra-fine waste coming from the granite cutting waste gang saws (GCW-GS) to manufacture ultra-high performance, steel-fiber reinforced concrete (UHPFRC). These machines cut granite blocks by abrasion using a steel blade and slurry containing fine steel grit. The waste generated by gang saws (GCW-GS) contains up to 15% Fe2O3 and up to 5% CaO. This is the main difference from the waste produced by diamond saws (GCW-D). Although this waste is available in large quantities, there are very few studies focused on recycling it to manufacture any kind of concrete. In this study, the replaced material was the micronized quartz powder of natural origin used in the manufacture of UHPRFC. The properties tested include workability, density, compressive strength, elasticity modulus, flexural strength, and tensile strength. The final conclusion is that this waste can be used to manufacture UHPFRC with a better performance than that from diamond saws given that there is an improvement of their mechanical properties up to a replacement of 35%. Even for higher percentages, the mechanical properties are within values close to those of control concrete with small decreases.

Tensile behaviour of ultra-high-performance steel fiber reinforced concrete

Recent developments in the area of ultra-high-performance steel fiber reinforced concrete (UHP-SFRC) has enabled a reduction in the use of steel reinforcement and has led to enhanced ductility and toughness of structural components owing to its resilient tensile behaviour. This paper presents the results of an experimental study that was conducted to investigate the tensile behaviour of UHP-SFRC. Four commercial mixes and two in-house mixes were evaluated using the procedures prescribed in the 2019 edition of Annex U of CSA-A23.1 and in Annex 8.1 of CSA-S6 2018. The tensile strength of UHP-SFRC was quantified and correlated through the direct tension test, splitting test, inverse analysis of four-point bending tests using either code expressions or nonlinear finite element analysis, and a calibrated empirical expression that links this property to the cylinder compressive strength. In addition, the effect of important parameters on flexural strength including casting methodology, volumetric ratio of steel fibers, and aspect ratio (shear span to depth ratio) of bending prisms have been assessed. The casting methodology affected the fiber distribution, an attribute that directly relates to flexural strength. Prisms containing 1% steel fibers by unit volume failed in a relatively brittle manner and possessed less flexural strength than the prisms containing 2% steel fibers. Prisms with an aspect ratio of 1 tended to develop greater flexural strength than the prisms tested with an aspect ratio of 2. The tensile strength obtained from inverse analysis is generally greater than the strength obtained from the direct tension test, the finite element analysis, and the calibrated empirical expression. Furthermore, it was determined that tensile strength obtained from the splitting test should be multiplied by a correction factor of ≈1/π, to match the strength obtained from the direct tension test. The majority of the mixes tested exhibited a tension hardening behaviour with a hardening ratio greater than 1.1 and an ultimate tensile strain greater than 0.001.

Study of Combined Multi-Point Constraint Multi-Scale Modeling Strategy for Ultra-High-Performance Steel Fiber-Reinforced Concrete Structures.

Compared with normal strength concrete (NSC), ultra-high-performance steel fiber-reinforced concrete (UHPFRC) shows superior performance. The concrete damage plasticity (CDP) model in ABAQUS can predict the mechanical properties of UHPFRC components well after calibration. However, the simulation of the whole structure is seriously restricted by the computational capability. In this study, a novel multi-scale modeling strategy for UHPFRC structure was proposed, which used a calibrated CDP model. A novel combined multi-point constraint (CMPC) was established by the simultaneous equations of displacement coordination and energy balance in different degrees of freedom of interface nodes. The advantage is to eliminate the problem of the tangential over-constraint of displacement coordination equation at the interface and to avoid stress iteration of the energy balance equation in the plastic stage. The expressions of CMPC equations of typical multi-scale interface connection were derived. The multi-scale models of UHPFRC components under several load cases were established. The results show that the proposed strategy can well predict the strain distribution and damage distribution of UHPFRC while significantly reducing the number of model elements and improving the computational efficiency. This study provides an accurate and efficient finite element modeling strategy for the design and analysis of UHPFRC structures.

Steel Fiber Use as Shear Reinforcement on I-Shaped UHP-FRC Beams

In the presented paper, the effectiveness of steel fiber use on the shear and flexure behaviors of ultra-high performance concrete (UHPC) beams and the feasibility of steel fibers in place of shear reinforcement were investigated experimentally. In this framework, a total of four I-shaped UHPC beams were produced for a high tensile reinforcement ratio of 2.2%. While two of them were non-fiber UHPC beams with and without the shear reinforcement to show the contribution of steel fibers, the remaining beams were made from the ultra-high performance steel fiber-reinforced concrete (UHP-FRC) having the short straight fibers with 1.5% and 2.5% by volume. The shear and flexural parameters, such as the load–deflection response, cracking pattern, failure mode, deflection, and curvature ductilities were discussed based on the four-point loading test results. While the reference beam without fiber and shear reinforcement failed by the shear with a sudden load drop before the yielding of reinforcement and produced no deflection capability, the inclusion of steel fibers to the UHPC matrix transformed the failure mode from shear to flexure through the fibers’ crack-bridging ability. It might be deduced that the moderate level of steel fiber use in the UHP-FRC beams may take the place of shear reinforcement in practical applications.

Numerical simulation of SHPB test of ultra-high performance fiber reinforced concrete with meso-scale model

<p indent="0mm">Ultra-high performance steel fiber-reinforced concrete is an innovative cement-based composite material with excellent mechanical properties and outstanding potential in resisting extreme loads. In this study, a meso model of ultra-high performance steel fiber-reinforced concrete specimen, which consists of cement mortar and fibers, is developed to numerically simulate Split Hopkinson pressure bar (SHPB) tests for investigation of behavior of ultra-high performance steel fiber-reinforced concrete material under impact loading. The software LS_DYNA is used to perform the numerical simulation of dynamic tests. A good agreement is observed between the simulated results and experimental results. After the meso model is validated with static compression and split tension tests, SHPB tests are numerically modelled and the stress-strain history is interpreted in the meso-scale level. The influence of fiber on ultra-high performance steel fiber-reinforced concrete in dynamic tests is investigated. Within a reasonable range of steel fiber volume ratio (optimum volume ratio ranges from 0%–2.5% for micro steel fiber), the dynamic strength of ultra-high performance steel fiber-reinforced concrete increases significantly with the increase of steel fiber volume ratio, however, the contributions of fibers to Dynamic Increase Factors (DIF) of ultra-high performance steel fiber-reinforced concrete are constantly lower than those of conventional concrete material. The proposed model qualitatively and quantitatively predicts the material static and dynamic behaviors, and also gives insights on the fiber reinforcement effect in the concrete matrix. In this study, the dynamic constitutive relationships of ultra-high performance fiber-reinforced concrete are derived for predicting the dynamic strength of ultra-high performance fiber-reinforced concrete with different steel fiber volume ratios and strain rates.

Post-earthquake evaluation of damage and residual performance of UHPSFRC piers based on nonlinear model updating

This paper presents an innovative approach for damage and residual performance evaluation of ultra-high performance steel fiber reinforced concrete (UHPSFRC) piers after earthquakes utilizing low-level vibration tests. A nonlinear fiber section element model is constructed in OpenSees to simulate the hysteretic behavior of a UHPSFRC bridge pier. Experimental data from a UHPSFRC column is utilized to verify the accuracy of the nonlinear numerical model. Based on the nonlinear fiber section element model, a new technique of nonlinear finite element model updating involving two updating stages is developed. This new method is designed to incorporate the maximum and minimum strains of section fibers as the updating parameters. By forming the objective function from the modal information, the damage parameters related to the nonlinear material model can be updated by solving the constrained optimization problem. To validate the efficiency of this updating approach, it has been applied to a numerically simulated UHPSFRC pier. With using the updated nonlinear finite element model, the residual axial loading capacity and post-seismic performance of the UHPSFRC pier are examined. The numerical results indicate that the updated nonlinear finite element model can be used not only to assess the current damage state of the UHPSFRC pier but also to predict its future performance after an earthquake. Finally, the noise effect on the proposed method is also investigated. The results reveal that the post-earthquake evaluation approach for UHPSFRC piers based on this study’s updating algorithm is robust to noise.

Mechanical properties of steel fiber-reinforced UHPC mixtures exposed to elevated temperature: Effects of exposure duration and fiber content

In the present study, ultra-high performance concrete (UHPC) mixtures reinforced with varying dosage of steel fibers were considered for studying the effects of exposure duration and fiber content on mechanical properties of the mixtures subjected to a sustained pre-spalling elevated temperature of 300 °C for different durations. Test results showed an increase in compressive strength and modulus of toughness even after exposing to elevated temperature for 5 h. However, modulus of elasticity and flexural strength decreased significantly with increase in exposure duration. The experimental data were statistically analyzed using analysis of variance (ANOVA) method to examine the effects of fiber content and exposure duration on the mechanical properties. Empirical equations were obtained with excellent degrees of fit correlating the mechanical properties of UHPC mixtures with fiber content and exposure duration.