Fiber-reinforced Concrete Slabs Research Articles

Mesoscale Modeling of Spallation Failure in Fiber-Reinforced Concrete Slab due to Impact Loading

AbstractIn this paper, a model for damage and fracture, considering the heterogeneity of material properties, is validated and used to investigate the mechanism of spallation in fiber-reinforced concrete (FRC) slabs with various fiber and aggregate contents under impact loading. Numerical simulations show that there is a marked difference in the failure patterns among slabs with various fiber and aggregate contents, and the fibers can remarkably improve the tensile strength of the concrete slab, effectively prevent the initiation and propagation of cracks, and inhibit the occurrence of spallation. Moreover, numerical simulations capture the whole process of the propagation of incident compressive stress waves in the FRC and the reflection of stress waves upon concrete surfaces and the spallation failure of FRC induced by the reflected tensile stress wave, which is obviously different from the failure pattern of FRC under static loads. The results of this study can also provide a valuable reference for stu...

Soil-Structure Interaction of Steel Fiber Reinforced Concrete Slab Strips on a Geogrid Reinforced Subgrade

Performance of slabs on grade is governed mainly by the mutual coupled performance of the slab stiffness and the subgrade support. The use of reinforcement geogrids to increase the stiffness and structural capacity of the subgrade support can be potentially advantageous, but is currently poorly understood, especially under frequent transient loading conditions. The objective of this experimental study is to investigate the beneficial use of geogrids as a reinforcing material in a loose subgrade. This paper presents the results of large scale laboratory tests on slab strips (300 mm wide × 150 mm thick × 2,500 mm long) supported on a reinforced subgrade. The slab strips contained either steel fibers or were reinforced with welded wire fabric (WWF), and are compared with earlier tests on an unreinforced subgrade. All slab strips were tested under a central point load and were restrained from uplift at the ends. Both monotonic and cyclic loads are considered. The geogrid increases the bottom surface cracking load of the slab strip, does not affect the top surface cracking load, and increases the ultimate load carrying capacity. The use of steel fiber reinforced concrete (SFRC) was successful in providing post-cracking strength to maintain slab integrity when compared to the WWF reinforced slab strip used in this investigation. A simplified analysis of beams on grade is carried out for the elastic and post-cracking regions, and predicted values for the SFRC slab strip under monotonic load are compared to the measured load-deformation response. The comparison indicates that the theoretical response underestimates the capacity of the SFRC slab strip.

Characterization of Load Transfer Behavior for Bonded Concrete Overlays on Asphalt

A bonded concrete overlay on asphalt (BCOA) is a rehabilitation method for moderately distressed asphalt pavements by relatively thin plain cement concrete or fiber-reinforced concrete slabs. The joint load transfer behavior for BCOAs plays a significant role in the long-term performance. Poor load transfer across the joints of the concrete slabs initiates debonding of the asphalt layer from the concrete slabs, which promotes the development of corner cracks or longitudinal cracks. However, because of the tediousness involved in characterizing the joint load transfer behavior of BCOAs, this important aspect is not accounted for in many available mechanistic–empirical BCOA design procedures. The influences of joint load transfer behavior on the performance of BCOA are discussed. The joint load transfer behavior for BCOAs with 1.52- × 1.83-m (5- × 6-ft) slabs and 1.22- × 1.22-m (4- × 4-ft) slabs is analyzed with the finite element method. The load transfer contributed by the asphalt layer, as well as the concrete slab, is characterized as a function of the BCOA design features. Finally, a method is proposed to determine the nondimensional joint stiffness (AGG*) for BCOAs as a function of the structural design features of the pavement section. The AGG* is significant in that it is the factor commonly used to characterize joint load transfer behavior when pavements are designed with a mechanistic-based design approach.

Hybrid FRP–UHPFRC composite girders: Part 2 – Analytical approach

A companion paper shows the experimental testing and numerical analysis of composite girders consisting of hybrid carbon/glass fiber-reinforced polymer (HFRP) I-girders topped with precast ultra-high-performance fiber-reinforced concrete (UHPFRC) slabs. This paper presents derivations of analytical equations to examine the composite behavior of the HFRP–UHPFRC girders with varying levels of interaction at the slab/girder interface. The derived equations to predict interfacial slip strain, curvature, and deflection of the composite girders were validated by the experimental data. An equation to determine the effective moment of inertia of the HFRP–UHPFRC composite girders with partial interaction is proposed and compared against the experiment. A fairly good agreement between the experimental and analytical results was found. The derived/proposed equations can simply and reliably evaluate the composite behavior between the HFRP I-girder and the UHPFRC slab.

Hybrid FRP-UHPFRC composite girders: Part 1 – Experimental and numerical approach

This paper presents experimental testing and numerical analysis of durable composite girder systems consisting of hybrid carbon/glass fiber-reinforced polymer (HFRP) I-girders and precast ultra-high-performance fiber-reinforced concrete (UHPFRC) slabs. Epoxy adhesive and/or bolt shear connectors (SCs) were used to transfer horizontal shear forces from the UHPFRC slabs to the HFRP I-girders. Push-out tests were performed to evaluate the shear interaction at the slab/girder interface. The results of the push-out tests were used to design five large-scale composite girders. The experimental variables included two types of bolt SCs (straight and inclined bolt SCs) and different slab geometries. The composite behavior between the HFRP I-girder and the UHPFRC slab was examined. The test results showed that the combined use of the bolt SCs and the epoxy adhesive was essential to achieve a full interaction between the HFRP I-girder and the UHPFRC slab. The use of the epoxy adhesive resulted in improving the strength and stiffness of the composite girders, reducing the stress concentration around the bolt-holes, and increasing the shear strength of the bolt SCs. The girders with the inclined bolt SCs showed a more ductile behavior than those with the straight headed bolt SCs. A three-dimensional finite element (FE) analysis of the HFRP-UHPFRC composite girder was carried out that considered slip effects at the slab/girder interface and the nonlinear behavior of the bolt SCs. Comparisons between the experimental results and the FE analysis were performed and a fairly good agreement was found. A companion paper shows derivations of analytical equations to predict composite behaviors of the HFRP-UHPFRC girders with varying levels of interaction at the slab/girder interface.

Innovative Timber-Concrete Composite Structures with Prefabricated FRC Slabs

This paper concerns the development of innovative composite floor systems, comprising timber beams and prefabricated concrete slabs. For the development of this new system, two properties were regarded as vital, as follows: (1) good stiffness, and (2) a high degree of prefabrication. Shear connection systems installed using completely dry processes were used. Innovative and very efficient materials, such as fiber-reinforced concrete (FRC) and modified wood, were used for the manufacture of the specimens. The research reported in this paper was conducted in two phases, as follows: (1) the mechanical properties of different shear connectors were investigated (Phase A), and (2) on the basis of these experiment’s results a second investigation was carried out in order to study the behavior of full-scale timber-concrete composite slabs (Phase B). During Phase A four different configurations, with a total of eight specimens, were laboratory tested in shear. During Phase B two full-scale floor elements, each with a different shear connection system, were laboratory tested in bending. The two shear connector systems used in the investigation were (1) shear anchor-keys of furfurylated wood, and (2) inclined steel tubes. Both of the proposed connection systems performed more than satisfactorily, showing a very high degree of composite action even at load levels close to the failure load. Moreover, it appeared that the assembling of the prefabricated fiber-reinforced concrete slab with the underlying beams occurred in an extremely easy manner.

Shrinkage and cracking of restrained ultra-high-performance fiber-reinforced concrete slabs at early age

In this study, the combined effect of shrinkage-reducing admixture (SRA) and expansive admixture (EA) on the shrinkage and cracking behaviors of restrained ultra-high-performance fiber-reinforced concrete (UHPFRC) slabs was investigated. For this investigation, six full-scale UHPFRC slabs with three different thicknesses (h=40, 60, and 80mm) were fabricated using two different mixtures. Test results indicated that the combined use of 1% SRA and 7.5% EA is beneficial to improve the mechanical strengths and to reduce the free shrinkage strain of approximately 36–42% at 7days. Regardless of SRA and EA contents, the slabs with the lowest thickness of 40mm showed shrinkage cracking at a very early age, while the slabs with higher thicknesses of 60 and 80mm showed no cracking during testing. However, the UHPFRC slab including 1% SRA and 7.5% EA exhibited a shallow crack with a very small maximum crack width of below 0.04mm, while the slab without SRA and EA showed through cracks with a large maximum crack width of 0.2mm.

Post-Cracking Steel Fiber Reinforced Concrete Slabs with Subsoil Interaction

The aim of the paper is to investigate the flexural behavior and property changes of concrete structures reinforced by steel fibers (SFRC) and to use the results for carrying capacity assessment of SFRC post-cracked slab on ground structure with subsoil interaction effect. Because the national codes cover neither design nor assessment of SFRC structures the investigation is generally based on the nonlinear fracture mechanics models to establish the stress-crack opening and load-crack mouth opening displacement relationship. Then the flexural tensile strength and residual flexural tensile strength of the post-cracked SFRC structure is determined with respect to subsoil interaction.

Behavior of Steel Fiber-Reinforced Concrete Slabs under Impact Load

Seven intermediate-scale slabs were constructed and tested to failure under sequential drop-weight impacts. The slabs contained longitudinal reinforcing bars and were constructed with steel fiber contents ranging from zero (that is, conventional reinforced concrete) to 1.50% by volume. The data from the testing program were used to further assess the performance of steel fiber-reinforced concretes in impact-resistant applications and to provide a well-documented dataset pertaining to a research area which is currently limited within the literature. The test results showed that the addition of the steel fibers was effective in increasing slab capacity, reducing crack widths and spacings, and mitigating local damage under impact. Although the slabs in the program were designed to be flexure-critical under static loading conditions, the development of inertial forces under impact loading conditions led to observed responses and failure modes that were governed by shear.

The Stress Analysis of the Industrial Fiber-Reinforced Concrete Slab on Elastic Subgrade Loaded by the Operational Loading

Floors which are used for factory building are usually located in an environment where is expected to be used heavy vehicles and also heavy supplies stored on the floor. What means that these structures have to be designed to withstand the action of the forces. For that reason it is useful to do a numerical simulation followed by stress analysis and evaluation of results. The parametric study was done to compare the influence of different thickness and different characteristics of the subgrade on the values of stress in a concrete slab. It was loaded by forklifts and structures used for storage of material and products.

Push-out tests for shear connections between UHPFRC slabs and FRP girder

This paper presents an experimental investigation on the shear connections between carbon/glass Fiber-Reinforced Polymer I-girder and Ultra-High Performance Fiber-Reinforced Concrete (UHPFRC) slabs. Effects of straight/inclined bolt shear connectors and effective embedment depth-to-bolt diameter (hef/d) ratios were investigated. Fourteen push-out tests were conducted to evaluate the load–slip behavior and the ultimate resistance of the bolt shear connectors. With the use of the UHPFRC, the hef/d ratio needed for obtaining a shear connector failure mode was 2.7 times lower than that obtained from 43 push-out tests in the literature for normal weight and lightweight concrete slabs. The inclined bolt shear connectors showed a more ductile behavior than the straight bolt shear connectors. The experimentally obtained ultimate resistance of the bolt shear connectors was compared against the equations provided by ACI 318-11, AISC 2011, AASHTO LRFD 2010, PCI 2004, and EC-4 2004. An empirical equation to predict the ultimate shear connector resistance was proposed and validated by the experimental data. Idealized load–slip models and equations to predict the load versus slip relationship for all push-out tested specimens were proposed. Curve fitting was performed to find fitting parameters for all tested specimens and the results showed a very good correlation with the experiments.

Hybrid Fiber-Reinforced Polymer Girders Topped with Segmental Precast Concrete Slabs for Accelerated Bridge Construction

The behavior of composite girders made of hybrid fiber-reinforced polymer (HFRP) I-girders, topped with precast ultra-high-performance, fiber-reinforced concrete (UHPFRC) slabs is presented in this paper. HFRP I-girders were manufactured under the pultrusion process in which unidirectional carbon fibers and bidirectional fiberglass fabric or continuous strand mat were used. Four large-scale composite girders were tested under four-point flexural loading. In the first composite girder, the HFRP I-girder was topped with a full-length precast UHPFRC slab. Twelve precast UHPFRC segments were used in each slab of the other three composite girders. Either epoxy or mortar connections were used to connect the precast UHPFRC segments. The test results showed that the flexural stiffness of the composite girder with the epoxy-connected segmental precast slabs was similar to that of the full-length precast composite girder. The mortar-connected girder exhibited more ductile behavior than the epoxy-connected girder. All the composite girders exhibited significant improvements in strength and stiffness compared with the HFRP I-girder without the UHPFRC slab. The HFRP–UHPFRC composite girders were shown to provide a promising and sustainable solution for accelerated bridge construction.

An Experimental Study on the use of Fiber-Reinforced Concrete in Bridge Approach Slabs

Fiber-reinforced concrete is well known for crack control by bridging cracks in the concrete. Short, discontinuous fibers are added into plain concrete to provide post-cracking ductility to the fiber-reinforced concrete. Although fiber-reinforced concrete has been used in various civil engineering applications, the practical application of fiber-reinforced concrete in bridge approach slabs is rarely found. In this paper, steel fibers, serving as macro-fibers, and polyvinyl alcohol fibers, serving as micro-fibers, were added to the approach slab concrete for crack control purpose. This paper describes flexural tests of four fiber-reinforced concrete beams and loading test of a full scale fiber-reinforced concrete approach slab. Results from the flexural beam test show that the addition of fibers greatly improves the fracture toughness of the concrete. Results from the loading test show that the overall performance of the slab is comparable to conventional reinforced concrete approach slabs, and the surface cracks on the slab due to negative moment can be adequately controlled by the addition of steel and polyvinyl alcohol fibers into concrete, even without top reinforcement mat.

Influence of steel fibers and fiber-reinforced polymers on the impact resistance of one-way concrete slabs

In this study, to estimate the impact resistance of steel fiber-reinforced concrete slabs strengthened with fiber-reinforced polymer sheets, a series of 50 × 100 × 350 mm3 sized slabs with 0.5%–1.5% (by volume) of steel fibers and two types of fiber-reinforced polymer sheets were impact-tested using drop-weight impact test machine. From the test results, the maximum impact load, dissipated energy and the number of drops before failure were all increased, whereas the maximum deflection and support rotation were reduced by strengthening the steel fiber-reinforced concrete slabs with externally bonded fiber-reinforced polymer sheets in the tensile zone. It was noticed that the impact resistance of the steel fiber-reinforced concrete slabs was substantially improved by externally strengthening the fiber-reinforced polymer sheets. In addition, the dynamic response of the steel fiber-reinforced concrete slabs strengthened with fiber-reinforced polymer sheets under a low-velocity impact load was analyzed using explicit code LS-DYNA with strain rate-dependent material models and debonding failure analysis. These numerical analyses were verified by comparing with the experimental results.

Flexural Behavior of Hybrid Composite Beams

This paper presents the development of composite beams, which consist of hybrid carbon and glass fiber-reinforced polymer (FRP) I-beams and precast, ultra-high-performance, fiber-reinforced concrete (UHPFRC) slabs. Hybrid FRPs (HFRPs) provide the advantage of high resistance to corrosion, while UHPFRC has great strength and durability. The combination of these two materials is expected to benefit structures subjected to severe environmental conditions and to respond to the need for accelerated bridge construction. Three full-scale composite beams with varied UHPFRC slab width were tested under four-point flexural loading. Bolt shear connectors with and without epoxy bonding were used in the tested beams. The bolt shear connectors and epoxy were used to resist the horizontal shear flow at the interface between the HFRP I-beam and the UHPFRC slab. The composite action between the HFRP I-beam and UHPFRC slab was investigated. The test results showed that all of the composite beams exhibited significant improvements in stiffness and strength properties, above those of single HFRP I-beams without a UHPFRC slab. A fiber model was developed to predict the strength and stiffness of the composite beam, and the model accuracy was verified. Good agreement was found between the experimental and analytical results. The high tensile strength of a carbon FRP in an HFRP tensile flange could be used effectively, and the delamination failure of an HFRP compressive flange could be prevented through the addition of a UHPFRC slab on the top flange of the HFRP I-beam. The study revealed that HFRP–UHPFRC beams were efficient and could provide a competitive, cost-effective, and sustainable solution to bridge structures.

Experimental Investigation of Ultra-high Performance Fiber Reinforced Concrete Slabs Subjected to Deformable Projectile Impact

Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) is currently one of the biggest challenging issues in modern concrete technology. The UHPFRC represents a concrete with improved durability and strength, which is significantly higher than in conventional normal strength concrete. This may result in reduced cross-sections and as a consequence smaller dead-load of the structure. The uniaxial compressive cylinder strength of UHPFRC used in this study exceeded 150MPa and the uniaxial direct tensile strength exceeded 10MPa. Several UHPFRC mixtures with different content of fibers were subjected to deformable projectile impact. The ogive-nose projectile weighed 8.04 grams and its average velocity was determined to be 710 m/s. It was shown that plain UHPC specimen failed in the brittle manner which caused that the slab split into several pieces. Further, it was demonstrated that addition of steel micro fibers enhanced the resistance to deformable projectile impact and it was specified that specimens containing 2% of fibers by volume have optimal resistance against impact loading. In addition, response of slabs made of conventional fiber reinforced concrete (FRC) and normal strength concrete (NSC) was studied for comparison. The magnitude of the damage was assessed based on the penetration depth, crater diameter and mass loss. Experimental results clearly showed that implementation of high strength steel micro fibers significantly increased the resistance to projectile impact. It was stated, that UHPFRC has much better resistance to projectile impact in comparison to conventional FRC.

New wood composite bridges

ABSTRACT This research explores the possibilities of wood composite structures with a view to designing durable lightweight composite decks. The paper examines a new wood structure technology in which an ultra-high-performance fiber-reinforced concrete (UHPFRC) slab is fastened to glulam beams. Fasteners representing most existing groups are first experimentally investigated on small beams (span one meter). The modes of functioning of each type and the various failure modes are identified. The paper proposes a method for assessing the interface shear stiffness. This method is based on analysis of flexural test results using a slip versus shear stress relation. It is shown that glued assembly of the two materials yields the best shear stiffness and highest ultimate strength. The practical aspects of surface preparation before gluing are considered. The results of a bending test carried out on a composite structure having a span of three meters, made of UHPFRC glued to two glulam beams, validate this fastening technique.

Design Aspects on Steel Fiber-Reinforced Concrete Pavements

A numerical study on the fracture behavior of steel fiber-reinforced concrete (SFRC) slabs on grade for industrial pavements is presented. Finite element analyses have been carried out by using a commercial finite element code where user subroutines based on nonlinear fracture mechanics have been implemented to describe the progressive cracking behavior of SFRC. The model is capable of simulating both primary and secondary cracks when they occur in concrete and it has been validated by comparing numerical predictions with experimental observations of full-scale tests on slabs on elastic subgrade under point loads in different positions. A real pavement with contraction or construction joints has been numerically simulated to investigate the stress and the strain fields for the most significant positions of point loads.

COMPARISON OF BLAST RESISTANCE WITH VARIOUS FIBER-REINFORCED CONCRETES

In this study, the contact detonation tests were conducted on six kinds of fiber-reinforced concrete slabs, and then spall damages created in them were compared with those in S-PEFRC (fiber-reinforced concrete with polyethylene fiber of strand type) slabs. The main results obtained are as follows: 1) all of fiber-reinforced concretes investigated in this study were effective in reducing spall damage as compared with normal concrete; 2) total damage depths in various fiber-reinforced concrete slabs could be generally estimated by formula for estimating that in the S-PEFRC slab; and 3) in case the modified-scaled concrete thickness was small, the S-PEFRC had somewhat better blast resistance than other fiber-reinforced concretes of which flexural toughness was equal to that of the S-PEFRC.

Punching shear strength of interior concrete slab–column connections reinforced with steel fibers

Abstract A theoretical study was performed to investigate the punching shear strength of interior slab–column connections made of steel fiber reinforced concrete (FRC). In the steel FRC slab–column connection, the shear force applied to the critical section is resisted by both the compression zone and the tension zone at the critical section. The shear capacity of the compression zone was defined by considering the interaction between the shear and the normal stresses developed at the critical section. The shear capacity of the tension zone was defined by considering the post-cracking tensile strength of FRC. By using the shear capacity, a new strength model for the punching shear strength of steel FRC slab–column connections was developed. The proposed strength model was verified using existing test results and showed very good accuracy. For convenience in design, a simplified design equation was also developed.