This thesis focuses on the dynamic and static behavior of steel fiber-reinforced concrete (SRFC) beams. As part of this study a total of eighteen (18) beams are tested, including fourteen (14) SFRC beams, and a companion set of four (4) beams built without fibers. Seven (7) of the beams are tested under quasi-static (slowly applied) loading with the remaining eleven (11) beams tested under simulated blast loading using the University of Ottawa shock-tube. The variables considered in this study include: concrete type (SFRC vs. conventional concrete), fiber content, fiber type, as well as the effect of transverse reinforcement. The criteria used to evaluate the blast performance of the beams includes: overall blast capacity, maximum and residual mid-span displacement, secondary fragmentation and damage control. Static results confirm the beneficial effect of fibers on improving the shear and flexural capacity of beams. Dynamic results show that use of steel fibers at a sufficient content can increase shear capacity and effectively replace transverse reinforcement in beams tested under blast loads. The results also show that increasing fiber content can improve the blast response of the beams by reducing maximum and residual mid-span displacement, improving damage tolerance and minimizing secondary blast fragments. However, at high fiber contents, problems with workability of the concrete mix can occur, resulting in a reduction of improvements when compared to SFRC specimens with lower fiber content. The analytical research program aimed at predicting the response of the test beams using dynamic inelastic single-degree-of-freedom (SDOF) analysis. Overall the analytical results demonstrate that SDOF analysis can be used to predict the blast response of beams built with SFRC.

The use of steel fiber reinforced concrete (SFRC hereafter) is becoming more and more common. Building codes and recommendations are gradually including the positive effect of fibers on mechanical properties of concrete. How to take advantage of the higher ductility and energy absorption capacity of SFRC to reduce anchorage lengths when using fibers is not a straightforward issue. Fibers improve bond performance because they confine reinforcement (playing a similar role to that of transverse reinforcement). Their impact on bond performance of concrete is really important in terms of toughness/ductility. The study of previous literature has revealed important points of ongoing discussion regarding different issues, especially the following: a) whether the effect of fibers on bond strength is negligible or not, b) whether the effect of fibers on bond strength is dependent on any other factors such as concrete compressive strength or concrete cover, c) quantifying the effect of fibers on the ductility of bond failure (bond toughness). These issues have defined the objectives of this thesis. A modified version of the Pull Out Test (POT hereafter) has been selected as the most appropriate test for the purposes of this research. The effect of a number of factors on bond stress¿slip curves has been analyzed. The factors considered are: concrete compressive strength (between 30 MPa and 50 MPa), rebar diameter (between 8 mm and 20 mm), concrete cover (between 30 mm and 5 times rebar diameter), fiber content (up to 70 kg/m3), and fiber slenderness and length. The experimental program has been designed relying on the principles of statistical Design Of Experiments. This has allowed to select a reduced number of combinations to be tested without any bias or loss of accuracy. A total of 81 POT specimens have been produced and tested. An accurate model for predicting the mode of bond failure has been developed. It relates splitting probability to the factors considered. It has been proved that increasing fiber content restrains the risk of splitting failure. The favorable effect of fibers when preventing splitting failures has been revealed to be more important for higher concrete compressive strength values. Higher compressive strength values require higher concrete cover/diameter ratios for splitting failure to be prevented. Fiber slenderness and fiber length modify the effect of fiber content on splitting probability and therefore on minimum cover/diameter ratios required to prevent splitting failures. Two charts have been developed for estimating the minimum cover/ diameter ratio required to prevent splitting. Predictive equations have been obtained for estimating bond strength and areas under the bond stress¿slip curve as a function of the factors considered. Increasing fiber content has a slightly positive impact on bond strength, which is mainly determined by concrete compressive strength. On the contrary, fibers have a very important effect on the ductility of bond failure, just as well as concrete cover, as long as no splitting occurs. Multivariate analysis has proved that bond stress corresponding to the onset of slippage behaves independently from the rest of the bond stress¿slip curve. The effect of fibers and concrete compressive strength on bond stress values corresponding to the onset of slips is mainly attributable to their influence on the material mechanical properties. On the contrary, the effect of fibers and concrete cover on the rest of the bond stress¿slip curve is due to their structural role. / García Taengua, EJ. (2013). Bond of Reinforcing Bars to Steel Fiber Reinforced Concrete (SFRC) [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/32952 / TESIS

Load testing was performed on a one-third scale model steel fiber reinforced concrete post-tensioned flat plate. The specimen had nine 10ft x 10ft x 3in. bays along with a 2ft-6in. overhang. Distributed loading was applied with a whiffle tree loading system at each bay and overhang section. Throughout the test, crack widths, crack locations, deflections, concrete strains, and reinforcing bar strains were monitored. The post-tensioned flat plate was designed to just meet the maximum allowable stress requirements of ACI 318. Minimal quantities of hairline cracks were observed after stressing the slab, and up through service-level loads, the cracks grew slightly in length and width. The slab behaved elastically through service-level loading. As factored-level loading was approached, the slab began to behave inelastically as indicated by both the load-deflection plots and the load-strain plots. A total ultimate load of 282psf (174psf of applied load) was reached when concrete crushing occurred. A 0.20in. wide full-length crack was observed running on the bottom surface of the slab between column lines 1 and 2, and a full-length crack was observed at column line 2 on the top surface of the slab. These two cracks were the leading contributors to the slab's failure. The performance of the SFRC post-tensioned flat plate indicated that considerations should be made to remove requirements for negative moment reinforcement in post-tensioned flat plates when SFRC is used. Also, the requirements for positive moment reinforcement should be modified. Additionally, the SFRC post-tensioned flat plate exhibited excellent levels of ductility. More experimentation should be conducted to determine if the maximum tensile stress in ACI 318 can be increased for post-tensioned flat plates with SFRC. / Master of Science / Load testing was performed on a one-third scale model steel fiber reinforced concrete (SFRC) post-tensioned flat plate. Post-tensioned flat plates are a type of concrete structural system typically used as flooring. This system typically employs high-strength steel strands, which are stretched to introduce compression into the concrete, which helps prevent the onset of cracking. The specimen had nine 10ft x 10ft x 3in. bays along with a 2ft-6in. overhang. Distributed loading was applied with a whiffle tree loading system at each bay and overhang section. The whiffle tree loading system was used to allow actuators to spread out the vertical loading on the slab. During the test, crack widths, crack locations, deflections, concrete strains, and reinforcing bar strains were monitored. The post-tensioned flat plate was designed to just meet the maximum allowable stress requirements of the governing standard, ACI 318. Minimal quantities of hairline cracks were observed after stressing the slab, and up through service-level loads, the cracks grew slightly in length and width. As larger loads were applied, the cracks grew and the effects of these cracks on the slab were evidenced in the deflection and strain measurements. A total ultimate load of 282psf (174psf of applied load) was reached when concrete crushing occurred. A 0.20in. wide full-length crack was observed running on the bottom surface of the slab between column lines 1 and 2, and a full-length crack was observed at column line 2 on the top surface of the slab. These two cracks were a driving force in the slab’s failure. The performance of the SFRC post-tensioned flat plate indicated that considerations should be made to change the requirements for negative and positive moment reinforcement in post-tensioned flat plates when SFRC is used. Additionally, the SFRC post-tensioned flat plate exhibited great performance after significant cracking was present. More experimentation should be conducted to determine if the maximum allowable tensile stress in ACI 318 can be increased for post-tensioned flat plates with SFRC.

Composite materials reinforced with particles or fibers are widely used in industrial applications due to their good mechanical, thermal, and electrical properties. Consequently, for the scientific community as well as the industry, an important challenge is to understand the relationship between the microstruture and the macroscopic response in order to design composite materials with optimised properties. In this thesis, we study a class of inclusion-reinforced multi-phase composites. Our main objective is to develop a micromechanical model and the corresponding numerical algorithms which enable the simulation of the rate-independent mechanical response. The proposed model is based on an incremental Hill-type formulation and uses the two-step Mori-Tanaka/Voigt mean-field homogenisation schemes. The crucial issues of the choice of reference comparison materials and Eshelby's tensor computation are examined In parallel, an experimental study consisting in four-point bending tests performed on plain concrete and steel fiber-reinforced concrete (SFRC) specimens, is carried out with the aim of achieving an appropriate modelling of SFRC, and collecting data for the validation of our model predictions. The accuracy and the efficiency of the proposed approach are evaluated through numerical simulations. Several discriminating tests of concrete, metal, and polymer matrix composites are carried out. A two-scale approach is developed in order to simulate, within reasonable CPU time and memory usage, the response of realistic structures under complex loadings. In many cases our estimates are validated against finite element computations and experimental results.

The mitigation of blast hazards on critical reinforced concrete structures has become a major concern in regards to the safety of people and the integrity of buildings. Recent terrorist incidents and accidental explosions have demonstrated the need to study the effects of such threats on structures in order to develop effective methods of reducing the overall impact of blast loads. With the arrival of innovative materials such as steel fibre reinforced concrete (SFRC), ultra-high performance fibre reinforced concrete (UHPFRC) and high strength steel reinforcement, research is required in order to successfully adapt these new materials in blast-resistant structures. Hence, the objective of this thesis to conduct an experimental parametric study with the purpose of investigating the implementation of these innovative materials in reinforced concrete slabs and panels. As part of the study, a total of fourteen one-way slab specimens with different combinations of concrete, steel fibres and steel reinforcement are tested under simulated blast loads using the University of Ottawa Shock-Tube Facility. The test program includes three slabs constructed with normal-strength concrete, five slabs constructed with SFRC and six slabs constructed with UHPFRC. Among these specimens, four are reinforced with high-performance steel reinforcement. The specimens are subjected to repeated blast loading with gradually increasing reflected pressure and reflected impulse until failure. The performance of the slabs is studied using various criteria such as failure load and mode, maximum and residual deflections, as well as tensile cracking, spalling and secondary fragmentation control. The behaviour of all specimens is compared in different categories to determine the effects of concrete type, steel reinforcement type, steel fibre content and steel fibre type on blast performance. As part of the analytical study the response of the slab specimens is predicted using dynamic inelastic single-degree-of-freedom (SDOF) analysis. The dynamic analysis is conducted by generating load-deformation resistance functions for the slabs incorporating dynamic material properties.

When subjected to a combination of moment and shear force, a reinforced concrete (RC) beam with either little or no transverse reinforcement can fail in shear before reaching its full flexural strength. This type of failure is sudden in nature and usually disastrous because it does not give sufficient warning prior to collapse. To prevent this type of shear failure, reinforced concrete beams are traditionally reinforced with stirrups. However, the use of stirrups is not always cost effective since it increases labor costs, and can make casting concrete difficult in situations where closely-spaced stirrups are required. The use of steel fiber reinforced concrete (SFRC) could be considered as a potential alternative to the use of traditional shear reinforcement. Concrete is very weak and brittle in tension, SFRC transforms this behaviour and improves the diagonal tension capacity of concrete and thus can result in significant enhancements in shear capacity. However, one of the drawbacks associated with SFRC is that the addition of fibers to a regular concrete mix can cause problems in workability. The use of self-consolidating concrete (SCC) is an innovative solution to this problem and can result in improved workability when fibers are added to the mix. The thesis presents the experimental results from tests on twelve slender self-consolidating fiber reinforced concrete (SCFRC) beams tested under four-point loading. The results demonstrate the combined use of SCC and steel fibers can improve the shear resistance of reinforced concrete beams, enhance crack control and can promote flexural ductility. Despite extensive research, there is a lack of accurate and reliable design guidelines for the use of SFRC in beams. This study presents a rational model which can accurately predict the shear resistance of steel fiber reinforced concrete beams. The thesis also proposes a safe and reliable equation which can be used for the shear design of SFRC beams.

When subjected to a combination of moment and shear force, a reinforced concrete (RC) beam with either little or no transverse reinforcement can fail in shear before reaching its full flexural strength. This type of failure is sudden in nature and usually disastrous because it does not give sufficient warning prior to collapse. To prevent this type of shear failure, reinforced concrete beams are traditionally reinforced with stirrups. However, the use of stirrups is not always cost effective since it increases labor costs, and can make casting concrete difficult in situations where closely-spaced stirrups are required. The use of steel fiber reinforced concrete (SFRC) could be considered as a potential alternative to the use of traditional shear reinforcement. Concrete is very weak and brittle in tension, SFRC transforms this behaviour and improves the diagonal tension capacity of concrete and thus can result in significant enhancements in shear capacity. However, one of the drawbacks associated with SFRC is that the addition of fibers to a regular concrete mix can cause problems in workability. The use of self-consolidating concrete (SCC) is an innovative solution to this problem and can result in improved workability when fibers are added to the mix. The thesis presents the experimental results from tests on twelve slender self-consolidating fiber reinforced concrete (SCFRC) beams tested under four-point loading. The results demonstrate the combined use of SCC and steel fibers can improve the shear resistance of reinforced concrete beams, enhance crack control and can promote flexural ductility. Despite extensive research, there is a lack of accurate and reliable design guidelines for the use of SFRC in beams. This study presents a rational model which can accurately predict the shear resistance of steel fiber reinforced concrete beams. The thesis also proposes a safe and reliable equation which can be used for the shear design of SFRC beams.

When subjected to a combination of moment and shear force, a reinforced concrete (RC) beam with either little or no transverse reinforcement can fail in shear before reaching its full flexural strength. This type of failure is sudden in nature and usually disastrous because it does not give sufficient warning prior to collapse. To prevent this type of shear failure, reinforced concrete beams are traditionally reinforced with stirrups. However, the use of stirrups is not always cost effective since it increases labor costs, and can make casting concrete difficult in situations where closely-spaced stirrups are required. The use of steel fiber reinforced concrete (SFRC) could be considered as a potential alternative to the use of traditional shear reinforcement. Concrete is very weak and brittle in tension, SFRC transforms this behaviour and improves the diagonal tension capacity of concrete and thus can result in significant enhancements in shear capacity. However, one of the drawbacks associated with SFRC is that the addition of fibers to a regular concrete mix can cause problems in workability. The use of self-consolidating concrete (SCC) is an innovative solution to this problem and can result in improved workability when fibers are added to the mix. The thesis presents the experimental results from tests on twelve slender self-consolidating fiber reinforced concrete (SCFRC) beams tested under four-point loading. The results demonstrate the combined use of SCC and steel fibers can improve the shear resistance of reinforced concrete beams, enhance crack control and can promote flexural ductility. Despite extensive research, there is a lack of accurate and reliable design guidelines for the use of SFRC in beams. This study presents a rational model which can accurately predict the shear resistance of steel fiber reinforced concrete beams. The thesis also proposes a safe and reliable equation which can be used for the shear design of SFRC beams.

The doctoral thesis deals with a non-destructive testing method (NDT) designed to evaluate the uniformity of distribution and determination of the concentration of steel fibres in steel fiber reinforced concrete (SFRC). At present, no non-destructive method is available in the field of diagnostics of building structures to assess the concentration and the homogeneity of SFRC. The Institute of Building Testing (SZK FAST BUT Brno) has several diagnostic devices, but their utility for the evaluation of selected parameters of SFRC has not proven during the research activity. This knowledge led to the design of a new measuring instrument in cooperation with the Institute of Theoretical and Experimental Electrical Engineering of the Faculty of Electrical Engineering and Communication (UTEE FEKT BUT in Brno) and the methodology for evaluation of these parameters. The proposed NDT method has been experimentally tested and verified for its utility for the evaluation of SFRC in building practice.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Steel fibre reinforced concrete (SFRC) is the most prominent fibre reinforced concrete composite that was engineered to enhance the material’s post-cracking behaviour. In certain situations it is utilised to replace conventional reinforcement and considered to be more cost-efficient. The purpose of this research is to characterise the moment redistribution behaviour of a statically indeterminate SFRC structure with varying volumes of fibres, with the focus on the development of the moment redistribution accompanied by the rotation of the plastic hinges at the critical sections in the structure. The material properties were characterised with a series of experimental tests. The compression behaviour was obtained with uniaxial compression tests while the uniaxial tensile behaviour was obtained with an inverse analysis performed according to flexural test results. These properties were utilised to derive a theoretical moment-curvature relation for each SFRC member which supplied the basis for the characterised moment-rotation behaviour and the finite element analyses (FEA) performed on the statically indeterminate structure. Experimental tests were conducted on the statically indeterminate structure in laboratory conditions to validate the theoretical findings. For the different SFRCs the material properties in compression were similar, while it resulted in an increased tensile resistance with an increase in the volume steel fibres. The theoretical momentcurvature and moment-rotation responses also indicated an increased structural capacity and member ductility with an increase in the volume fibres. From the finite element analyses the computational moment redistribution-plastic rotation relations were obtained. It was found that the final amount of moment redistribution decreased with an increase in the fibre volume, but that the rotational capacity increased. It was found that the experimental moment-curvature and moment-rotation results correlate well with the theoretical predictions. Also, unexpected structural behaviour was observed, but the issue was addressed with applicable computational analyses which confirmed the possible causes. It was concluded that the computational moment redistribution approximations were reasonably accurate. A parameter study indicated that the crack band width differed among the different SFRC members. / AFRIKAANSE OPSOMMING: Staal vesel versterkte beton (SVVB) is die mees vooraanstaande vesel versterkte beton mengsel wat ontwikkel is om die materiaalgedrag na kraakvorming te verbeter. In sekere situasies kan dit gebruik word om konvensionele staal te vervang en lei soms to koste vermindering . Die einddoel van die studie is om die moment herverdeling gedrag te karaktiseer vir ‘n statiese onpebaalbare SVVB struktuur deur die invloed van verskillende volumes vesels en die rotasie kapasiteit by die kritieke posisies in ag te neem. Die materiaal eienskappe was geidentifiseer met ‘n reeks eksperimentele toetse. Die druk gedrag was geïdentifiseer deur eenassige druktoetse, terwyl die eenassige trek gedrag bekom is met die implementasie van ‘n inverse analise van die uitgevoerde buig toetse. Hierdie eienskappe is gebruik om die teoretise moment-kromming verhouding vir elke mengsel te bekom. Hierdie verhoudings word as die basis bestempel vir die teoretiese moment-rotasie verhouding en die eindige element analises (EEA) wat op ‘n staties onbepaalbare struktuur toegepas is. Eksperimentele toetse is op hierdie voorgestelde struktuur toegepas om die teoretiese verwagtings te verifieer. Dit is gevind dat die druk gedrag ooreenstem tussen die verskillende mengsels, alhoewel ‘n toename in die trek kapasiteit ervaar is met ‘n toename in die volume vesels. Die teoretiese momentkromming en moment-rotasie verwantskappe stel ook voor dat die strukturele kapasiteit en duktiliteit toeneem met ‘n toename in die volume vesels. Die teoretiese moment herverdeling-plastiese rotasie verwantskapppe is verkry deur middel van die eindige element analises. Dit is gevind dat die aantal moment herverdeling by faling afgeneem het vir ‘n toename in die volume vesels, maar dat dit to ‘n groter rotasie kapasiteit gelei het. Van die eksperimentele resultate is dit afgelei dat die teoretiese moment-kromming en momentrotasie verwantskappe goeie benaderings voorstel. Sekere invloede van die opstelling het daartoe gelei dat onverwagte strukturele gedrag bekom is, maar die moontlike invloede is verifieer met eindige element analises. Dit is afgelei dat die teoretiese beramings van die moment herverdeling gedrag redelik akkuraat is. ‘n Parameter studie het getoon dat die kraak spasiëring verskil tussen mengsels met verskillende volumes vesels.