Search Results (34)

In many densely populated towns and semi-urban areas, masonry buildings often stand close to busy roads, exposing them to blasts from improvised explosives or other localized sources. Such structures are rarely designed to resist sudden explosive forces, making severe damage or even progressive collapse likely. Even moderate-intensity blasts can weaken walls, endanger occupants, and cause significant property loss. Unlike reinforced concrete, masonry is highly susceptible to explosive impact. Therefore, understanding how these buildings behave under blast loads and developing affordable protection methods is crucial. Low-rise unreinforced masonry (URM) structures, usually up to about 13 m in height (roughly 2–4 stories), common in villages, semi-urban regions, and conflict-prone zones, are particularly at risk. In many areas, these poorly constructed buildings lack proper engineering design and are therefore highly vulnerable to blast damage. Non-load-bearing internal dividers and perimeter enclosures are especially prone to lateral displacement, which can initiate instability and, in severe cases, lead to overall structural failure. This research focuses on reducing catastrophic damage in URM walls when exposed to close-proximity blast forces using concrete-based protective coatings, both with and without embedded steel-welded wire mesh. The study references a previously tested laterally supported clay brick wall built with cement–sand mortar as the baseline model, with its behavior validated against experimental findings from existing literature. Two blast cases were considered corresponding to scaled stand-off distances of 2.19 m/kg^1/3 and 1.83 m/kg^1/3, representing moderate flexural-shear cracking and full structural failure, respectively. To replicate the observed behavior, a comprehensive 3D numerical simulation was developed using the ABAQUS/Explicit 2020 solver. The model’s predictions were benchmarked and verified through comparison with reported test data. While both blast intensities were used to confirm computational accuracy, the effectiveness of UHPC and UHPFRC protective coatings with and without embedded wire mesh was specifically evaluated under the more severe collapse scenario (Z = 1.83 m/kg^1/3). Results indicated that at a scaled distance of 1.83 m/kg^1/3, the uncoated URM wall could not withstand the blast because of poor tensile and bending capacity. In contrast, the UHPC- and UHPFRC-coatings provided improved confinement and better stress distribution. When welded wire mesh was embedded, crack control improved further, the interface bond strengthened, and a larger portion of blast energy was absorbed and dissipated. Full article

Strengthening square reinforced concrete (RC) columns with full ultra-high-performance fiber-reinforced concrete (UHPFRC) jacketing is highly effective, but such complete wrapping is often impractical due to architectural or geometric constraints. Previous studies have not systematically examined the performance of partial-coverage UHPFRC patterns for these sections. This study numerically investigates the axial performance of square RC columns strengthened with strategically arranged UHPFRC elements—including horizontal shortcuts, vertical strips, and hybrid configurations—using finite element analysis in ABAQUS. Key parameters include jacket thickness, element dimensions, column height, and reinforcement details. Results show that a 10 mm full UHPFRC jacket more than doubles axial capacity (+105.9% for 800 mm columns), with significant gains in stiffness. Vertical strips enhance strength but reduce ductility; horizontal shortcuts improve post-peak stability; and hybrids offer a balanced response. With full jacketing, internal steel details have minimal impact on peak capacity, while column height chiefly influences energy dissipation. This work establishes that optimized partial UHPFRC layouts—specifically strips, shortcuts, and their combinations—can achieve tailored performance improvements, introducing a novel, practical, and material-efficient design strategy for strengthening square columns where full wrapping is not feasible. Full article

This study presents a reliable methodology for analyzing reinforced ultra-high-performance fiber-reinforced concrete (UHPFRC) elements by linking material behavior to structural performance. A non-linear finite element model (NLFEM) is proposed to simulate the tensile response of reinforced UHPFRC elements, with particular emphasis on shrinkage effects. The model operates in two phases: the first simulates shrinkage during specimen storage and the second simulates the mechanical tensile test, using the internal stresses from the first phase as initial conditions. The model was validated through an experimental program involving reinforced UHPFRC ties. The NLFEM accurately reproduced the load–displacement response using average UHPFRC tensile parameters obtained from a simplified Four-Point bending test Inverse Analysis method (4P-IA). It reliably predicted the shrinkage strain range and its impact on stiffness loss during microcrack initiation and stabilization, where tension-stiffening behavior is critical. Additionally, the simulation from the model captured the transition from microcracking to macrocrack formation and the role of fiber bridging in maintaining stiffness. The predicted shrinkage strain aligns with values reported in the literature and represents a conservative upper bound, neglecting the potential effects of creep and relaxation. Overall, the NLFEM effectively simulates the full tension-stiffening behavior of reinforced UHPFRC, including three-dimensional effects, and provides a reliable tool for structural analysis and design. Full article

Despite extensive research on blast-resistant concrete structures, a clear scientific deficiency remains in the quantitative understanding of how fiber-reinforced concrete slabs behave under blast loading, particularly when experimental and numerical investigations are not conducted together under identical loading conditions. Existing studies often focus on either conventional reinforced concrete or isolated material systems, providing limited validation of comparative blast performance across different fiber-reinforced concretes. This study addresses this gap by investigating the blast resistance performance of four types of reinforced concrete slabs: normal concrete (NC), ultra-high-performance fiber-reinforced concrete (UHPFRC), organic fiber-reinforced high-performance concrete (O-HPC), and basalt FRP-sheet-strengthened slurry-infiltrated fiber concrete (F-SIFCON), using full-scale blast experiments and validated numerical simulations conducted with ANSYS Explicit Dynamics. Blast tests were performed to obtain time histories of reflected pressure, displacement, acceleration, reaction force, and internal energy. The influence of different fiber systems and FRP strengthening on dynamic response and failure mechanisms was systematically analyzed. The numerical models showed good agreement with experimental measurements, confirming their reliability. The results indicate that the normal concrete slab exhibited brittle failure and poor blast resistance, whereas the F-SIFCON slab demonstrated the best overall performance. Compared with the normal concrete slab, the F-SIFCON slab achieved approximately a 47% reduction in maximum displacement, a 56% increase in peak reaction force, and the highest internal energy absorption of 236 kJ. The UHPFRC and O-HPC slabs also showed improved blast resistance, although with different post-peak response characteristics. These findings demonstrate that hybrid fiber reinforcement combined with FRP strengthening can significantly enhance the blast resistance of concrete slabs and that coupled experimental–numerical approaches provide a robust framework for evaluating structural performance under extreme dynamic loading. Full article

Ultra-high-performance fiber-reinforced concrete (UHPFRC) has the characteristics of high strength, toughness, and excellent crack resistance. In order to fully utilize the high-strength properties of UHPFRC and reduce the structural weight and construction cost, solid slabs can be fabricated into hollow-core slabs or composite sandwich slabs. In order to further analyze the mechanical properties and mechanism of action of UHPFRC hollow-core slabs, one solid slab and two hollow-core slabs with the same geometric dimensions, reinforcement, and steel fiber volume content are designed in this paper, and their stress performance under a static load was investigated using a four-point bending test. The research results show that the UHPFRC hollow-core slab is anisotropic, and the bending stiffness of the section with parallel, distributed tubes is slightly smaller than that of the solid slab. The addition of steel fibers can greatly limit the development of cracks on a slab surface, so the elastic limit of a UHPFRC hollow slab is higher than that of a conventional concrete hollow slab. The whole bending process is roughly divided into the elastic stage, the elastic–plastic stage, and the plastic stage; the crack development process on the bottom of the slab can be classified into the cracking stage, the stable crack development stage, and the rapid propagation stage. In the elastic stage, the cross-sectional deformation of the UHPFRC hollow-core slab in the bending process still satisfies the assumption of a flat section. A row of parallel, round tubes on the neutral axis has a little effect on the cracking load, bearing capacity, and deformation capacity of the UHPFRC slab. By conducting the comparative analysis of the hollow rate and bearing capacity, when the hollow rate reaches 13.57%, the comprehensive weight of the solid slab is reduced by 13.16%, the cracking moment is slightly reduced, and the ultimate load is only reduced by 8.78%. Under the premise of meeting the bearing capacity, the hollow rate of the UHPFRC hollow-core slab can be appropriately increased to save money and energy. Full article

Strengthening reinforced concrete (RC) buildings is a critical challenge in the construction industry, pushed by the necessity to address aging infrastructure, environmental degradation, and growing use requirements. Ultra-high-performance fiber-reinforced concrete (UHPFRC) is one of the advanced materials that present a viable solution owing to its exceptional durability and mechanical characteristics, which encompass higher compressive and tensile strengths, low permeability, and resilience against intense environmental as chloride ingress, cycles of freeze–thaw, and chemical assaults. This literature review comprehensively examines UHPFRC as a rehabilitation or strengthening mix material for the RC slabs and beams. Experimental key subjects include the influence of bonding techniques, strengthening configurations, steel fiber ratios, UHPFRC thickness, and reinforcing steel within the UHPFRC layer. In addition, the existing numerical and analytical approaches for forecasting the flexural or shear capability of reinforcing concrete structures retrofitted with UHPFRC were examined and critically assessed. Despite the improvements in the RC structures achieved through experiments utilizing UHPFRC as a reinforcement layer, this study highlights some deficiencies in the existing knowledge, such as the absence of effective ways to address debonding, insufficient research on cyclic loading, and the necessity for economical and sustainable strengthening techniques. This review establishes a basis for future research, intending to create an innovative UHPFRC-based strengthening system that mitigates current limits and improves the overall efficacy, performance, and durability of RC structures. Full article

Buckling-Restrained Braces (BRBs) are widely utilized in structures as an anti-seismic system to enhance performance against lateral excitations. While BRBs are designed to yield symmetrically under both tension and compression without significant buckling, their effectiveness is often limited to moderate seismic events. During high-intensity earthquakes, repetitive yielding can lead to core failure, resulting in the loss of BRB functionality and potentially causing structural collapse. This study proposes an innovative design for BRBs to improve energy dissipation capacity under severe seismic activity. The new design incorporates Ultra-High-Performance Fiber-Reinforced Concrete (UHPFRC) filler and hyper-elastic rubber components as primary load-bearing elements. Through extensive testing and simulation, the proposed Rubber Buckling-Restrained Brace (RBRB) was developed and manufactured by integrating hyper-elastic rubber between the concrete and core to enhance the device’s strength. Additionally, a prototype of the conventional BRB device was fabricated to serve as a benchmark for evaluating the performance of the RBRB. Experimental testing of both the conventional BRB and the proposed RBRB prototypes was conducted using a heavy-duty dynamic actuator to assess the RBRB’s performance under applied loads. Based on the experimental results, an analytical model of the proposed RBRB was formulated for use in finite element modeling and analysis. Furthermore, a specialized seismic design procedure for structures equipped with the RBRB was developed, according to the performance-based design method. This procedure was applied to the design of a seven-story steel structure, and the impact of the RBRB on the seismic response of the structure was investigated through finite element simulations. The analysis results demonstrated that the RBRB significantly improves the loading capacity and energy dissipation capabilities of structures, thereby enhancing their overall performance against earthquake excitations. Full article

Due to their relatively high tensile strength and dense matrix, UHPFRCs have proven to be a highly effective building material for both strengthening existing reinforced concrete structures and constructing new ones. In both cases, the use of fasteners is prevailing, with threaded anchors being frequently employed. The thicknesses of structural components made of UHPFRCs are relatively thin, i.e., at least 30 mm, typically 50 to 100 mm, and exceptionally 100 to 200 mm. Therefore, the aim is to use fasteners with short anchorage lengths. In this study, the structural behavior of a short threaded anchor with a 20 mm diameter and an embedment length of 50 mm (2.5 Ø) in a UHPFRC is investigated using non-linear finite element models. The UHPFRC is assumed to exhibit tensile strain-hardening behavior, with tensile strengths of 7 MPa and 11 MPa, respectively. The modeled anchor was subjected to a continuously increasing uniaxial pull-out force. The results indicate that the fracture mechanism of threaded anchors in UHPFRCs is primarily characterized by the formation of a tensile membrane within the UHPFRC, which acts as the main resisting element against the pull-out force. Additionally, the influence of the UHPFRC’s tensile properties on the pull-out behavior and ultimate resistance of the threaded anchors was determined. Full article

The adoption of prefabricated elements and systems (PBES) in accelerating bridge construction (ABC) and rapidly replacing aging infrastructure has attracted considerable attention from bridge authorities. These prefabricated components facilitate quick assembly, which diminishes the environmental footprint at the construction site, alleviates delays and lane closures, reduces disruption for the traveling public, and ultimately conserves both time and taxpayer resources. The current paper explores the structural behavior of a reinforced concrete (RC) precast full-depth deck panel (FDDP) having 175 mm projected glass-fiber-reinforced polymer (GFRP) bars embedded into a 200 mm wide closure strip filled with ultra-high-performance fiber-reinforced concrete (UHPFRC). Three joint details for moment-resisting connections (MRCs), named the angle joint, C-joint, and zigzag joint, were constructed and loaded to collapse. The controlled slabs and mid-span-connected precast FDDPs were statically loaded to collapse under concentric or eccentric wheel loading. The moment capacity of the controlled slab reinforced with GFRP bars compared with the concrete slab reinforced with steel reinforcing bars was less than 15% for the same reinforcement ratio. The precast FDDPs showed very similar results to those of the controlled slab reinforced with GFRP bars. The RC slab reinforced by steel reinforcing bars failed in the flexural mode, while the slab reinforced by GFRP bars failed in flexural-shear one. Full article

A depth precast deck panel (FDDP) is one element of the prefabricated bridge element and systems (PBES) that allows for quick un-shored assembly of the bridge deck on-site as part of the accelerated bridge construction (ABC) technology. This paper investigates the structural response of full-depth precast deck panels (FDDPs) constructed with new construction materials and connection details. FDDP is cast with normal strength concrete (NSC) and reinforced with high modulus (HM) glass fiber reinforced polymer (GFRP) ribbed bars. The panel-to-girder V-shape connections use the shear pockets to accommodate the clustering of the shear connectors. A novel transverse connection between panels has been developed, featuring three distinct female-to-female joint configurations, each with 175-mm projected GFRP bars extending from the FDDP into the closure strip, complemented by a female vertical shear key and filled with cementitious materials. The ultra-high performance fiber reinforced concrete (UHPFRC) was selectively used to joint-fill the 200-mm transverse joint between adjacent precast panels and the shear pockets connecting the panels to the supporting girders to ensure full shear interaction. Two actual-size FDDP specimens for each type of the three developed joints were erected to perform fatigue tests under the footprint of the Canadian Highway Bridge Design Code (CHBDC) truck wheel loading. The FDDP had a 200-mm thickness, 2500-mm width, and 2400-mm length in traffic direction; the rest was over braced steel twin girders. Two types of fatigue test were performed: incremental variable amplitude fatigue (VAF) loading and constant amplitude fatigue (CAF) loading, followed by monotonically loading the slab ultimate-to-collapse. It was observed that fatigue test results showed that the ultimate capacity of the slab under VAF loading or after 4 million cycles of CAF exceeded the factored design wheel load specified in the CHBDC. Also, the punching shear failure mode was dominant in all the tested FDDP specimens. Full article

As the bridge’s structural component is directly subjected to vehicle loads, the stress performance of the bridge deck has a significant impact on the safety, durability, and driving comfort of the bridge. In order to improve the bending performance of the bridge deck in the negative moment zone, a new type of steel grating–UHPFRC composite bridge deck was proposed in this paper. Firstly, structural details and advantages of the new steel grating-UHPFRC composite bridge deck were introduced. Secondly, the finite element program ABAQUS was used to establish a refined solid finite element model of the new bridge deck. The mathematical program MATLAB (PYTHON) was also used to analyze the effects of the structural parameters on bending bearing capacity and put forward reasonable structural parameters of the new bridge deck, considering the technical and economic indexes. Thirdly, the simplified plasticity theory was applied to analyze the bending bearing capacity of the new bridge deck, and the corresponding formula for bending bearing capacity calculation was derived and verified by numerical model results. In addition, the cost–benefit analysis and environmental impact assessment of the new bridge deck were also conducted. The results show that the bending bearing capacity of the new bridge deck in the negative moment zone increases with the increase of the width of the bridge deck, the thickness of the wing plate, and the height of the web plate, with a trend of increasing and then decreasing when the horizontal inclination of the web plate decreases. The bridge deck width does not have a significant effect on improving the bearing capacity. The bearing capacity calculated by theoretical formulas is close to that calculated by numerical models and the maximum relative deviation is 9.1%. The new steel grating-UHPFRC composite bridge deck proposed in this paper is superior to conventional steel-UHPC composite bridge deck in terms of cost-benefit and environmental impact. Full article

The strengthening of existing columns using additional reinforced concrete (RC) jackets is one of the most popular techniques for the enhancement of a column’s stiffness, load-bearing capacity and ductility. Important parameters affecting the effectiveness of this method are the strength of the additional concrete, concrete shrinkage and the connection between the old and the new concrete. In this study, the application of Ultra-High-Performance Fiber-Reinforced Concrete (UHPFRC) jackets for the structural upgrade of RC columns has been examined. Extensive numerical studies have been conducted to evaluate the effect of parameters such as the thickness of the jacket, concrete shrinkage and the addition of steel bars, and comparisons have been made with conventional RC jackets. The results of this study indicate that the use of UHPFRC can considerably improve the strength and the stiffness of existing reinforced concrete columns. The combination of UHPFRC and steel bars in the jacket leads to the most effective strengthening technique as a significant enhancement in the stiffness and the ultimate load capacity has been achieved. Full article

Ultra-high-performance concrete (UHPC) has been used in building joints due to its increased strength, crack resistance, and durability, serving as a repair material. However, efficient repair depends on whether the interfacial substrate can provide adequate bond strength under various loading scenarios. The objective of this study is to investigate the bonding behavior of composite U-shaped normal strength concrete–ultra-high-performance fiber reinforced concrete (NSC-UHPFRC) specimens using multiple drop-weight impact testing techniques. The composite interface was treated using grooving (Gst), natural fracture (Nst), and smoothing (Sst) techniques. Ensemble machine learning (ML) algorithms comprising XGBoost and CatBoost, support vector machine (SVM), and generalized linear machine (GLM) were employed to train and test the simulation dataset to forecast the impact failure strength (N2) composite U-shaped NSC-UHPFRC specimen. The results indicate that the reference NSC samples had the highest impact strength and surface treatment played a substantial role in ensuring the adequate bond strength of NSC-UHPFRC. NSC-UHPFRC-Nst can provide sufficient bond strength at the interface, resulting in a monolithic structure that can resist repeated drop-weight impact loads. NSC-UHPFRC-Sst and NSC-UHPFRC-Gst exhibit significant reductions in impact strength properties. The ensemble ML correctly predicts the failure strength of the NSC-UHPFRC composite. The XGBoost ensemble model gave coefficient of determination (R²) values of approximately 0.99 and 0.9643 at the training and testing stages. The highest predictions were obtained using the GLM model, with an R² value of 0.9805 at the testing stage. Full article

As the modular industry expands, the most widely used building materials are primarily concrete, steel, and wood. However, the use of wood and steel is severely limited compared to concrete for reasons such as durability and economy. To overcome these shortcomings, we aimed to apply ultra-high-performance fiber-reinforced concrete (UHPFRC), which has excellent compressive strength and tensile strength, high durability, and minimal reinforcement with steel fibers. In this study, research was conducted on the development of unit box-type architectural modules using UHPFRC with a compressive strength of 120 MPa and a tensile strength of greater than 7 MPa. Various amounts of steel fibers (Vf = 1.0, 1.5, and 2.0%) were evaluated to determine the optimal mixing ratio of UHPFRC, in which both the durability and mechanical performance were assessed. The compressive strength and tensile strength of UHPFRC were found to be 132 MPa and 10.1 MPa, respectively, while its resistance to chloride penetration averaged 14.47 coulombs, indicating superior durability compared to conventional concrete. To reduce the weight of the unit components of the architectural modular system, both normal concrete (NC) components and UHPFRC were applied. The main variables in the flexural tests were the cross-sectional thickness, steel fiber content, and presence of an insulation material, comprising a total of three variables for evaluating the flexural performance. The application of UHPFRC with a compressive strength of 120 MPa, a cross-sectional thickness of 120 mm, and a 10 mm diameter reinforcement provided a similar performance to that of NC components while reducing concrete usage by 60% compared to NC components. Additionally, structural analysis was performed to prototype the unit box-type modular structure using UHPFRC. The modular structural system developed in this study was found to reduce construction costs by 18.7% compared to traditional steel structural systems. Further research is necessary to address issues such as floor slab vibration and noise, connections, and expansion to multistory buildings for commercialization of modular structures using UHPFRC. Full article

Curvature-based damage detection has been previously applied to identify damage in concrete structures, but little attention has been given to the capacity of this method to identify distributed damage in multiple damage zones. This study aims to apply for the first time an enhanced existing method based on modal curvature analysis combined with wavelet transform curvature (WTC) to identify zones and highlight the damage zones of a beam made of ultra-high-performance fiber-reinforced concrete (UHPFRC), a construction material that is emerging worldwide for its outstanding performance and durability. First, three beams with a 2 m span of UHPFRC material were cast, and damaged zones were created by sawing. A reference beam without cracks was also cast. The free vibration responses were measured by 12 accelerometers and calculated by operational modal analysis. Moreover, for the sake of comparison, a finite element model (FEM) was also applied to two identical beams to generate numerical acceleration without noise. Second, the modal curvature was calculated for different modes for both experimental and FEM-simulated acceleration after applying cubic spline interpolation. Finally, two damage identification methods were considered: (i) the damage index (DI), based on averaging the quadratic difference of the local curvature with respect to the reference beam, and (ii) the WTC method, applied to the quadratic difference of the local curvature with respect the reference beam. The results indicate that the developed coupled modal curvature WTC method can better identify the damaged zones of UHPFRC beams. Full article