Degree Not Listed / Department of Civil Engineering / Asadollah Esmaeily / This report is contingent upon research and literature reviews, targeting steel fiber reinforced concrete (SFRC). It will explore all aspects involved, detailing both properties and functionality. Historical development of the modern application mix and design procedures will be discussed. A critical investigation based on laboratory testing is examined and a comparative discussion is provided. This report will also highlight the structural uses, benefits, applications and deficiencies acquired by SFRC.

By adding annealed plain carbon steel fibers and stainless steel fibers into Ultra-High Performance Concrete (UHPC), we have increased UHPC’s toughness through optimized thermal processing and alloy selection of steel fiber reinforcements. Currently, steel fiber reinforcements used in UHPCs are extremely brittle and have limited energy dissipation mainly through debonding due to matrix crumbling with some pullout. Implementing optimized heat treatments and selecting proper alternative alloys can drastically improve the post-yield carrying capacity of UHPCs for static and dynamic applications through plastic deformations, phase transformations, and fiber pullout. By using a phase transformable stainless steel, the ultimate flexural strength increased from 32.0 MPa to 42.5 MPa (33%) and decreased the post-impact or residual projectile velocity measurements an average of 31.5 m/s for 2.54 cm and 5.08 cm thick dynamic impact panels.

Master of Science / Department of Civil Engineering / Asadollah Esmaeily / Engineers involved in construction face various challenges. One of them being dealing with cracks in concrete. Naturally, concrete is weak in tension defining its bristle characteristics. To compensate, fiber reinforcement is used in the concrete mixes. Popular fiber types are steel, glass, polypropylene, and carbon fibers. These types of fibers are used to reinforce concrete. These fibers all increase the tensile and flexural strength of concrete. Additionally, they all have their own advantages. This paper is oriented to briefly introduce basic properties of these fibers. This includes the composition, production, advantages, applications, and restrictions of the mentioned fibers.

With the increasing need for commercial and residential buildings, post-tensioned (PT) flat plates have become a preferred choice for floor systems, because of the numerous advantages over non-prestressed slabs such as better efficiency, reduced slab self-weight, as well as crack and deflection control. To improve the competitive advantage of PT flat plates through improved economy and performance, a study was undertaken. This study investigated the performance and behavior of three one-third scale models of a nine-panel two-way unbonded post-tensioned flat plate. One of the slabs had conventional reinforcement with uniform-banded tendon layout, another had conventional reinforcement with banded-banded tendon layout while the last had banded-banded tendon layout reinforced with steel fiber. The specimens were loaded to service limit state, factored load and then to failure, using a whiffle tree loading system that approximated a uniformly distributed load. Experimental results were compared to analytical results from finite element and yield line analysis. The performance of the banded-banded specimens was very similar to the uniform-banded specimens at service and factored load. The failure loads for all specimens were considerably higher than the design factored load of 197 psf. Steel fiber was able to replace conventional reinforcement and the performance of the specimens with steel fibers was satisfactory, and comparable to their corresponding conventional reinforced specimens at service and factored limit state. Analytical results from finite element analysis showed a fairly reasonable agreement with experimental results. The results from the experimental tests showed that the use of steel fiber in post-tensioned flat plates is a viable and safe technology that will lead to improved performance and economy. The experimental results seem to indicate that the requirement of conventional reinforcement may be unnecessary in the negative moment regions and also in the positive moment region if the tensile stress is not more than 3√(f'c ) in this region. ACI 318-19 code design recommendations were provided for design of banded-banded PT system and SFRC post-tensioned flat plate. Additional testing should be conducted before SFRC post-tensioned flat plates are incorporated in the ACI 318 code (ACI 318, 2019) with a maximum allowable tensile stress of 6√(f'c). / Doctor of Philosophy / Over the years, the use of post-tensioned flat plates as flooring system has increased and became popular in residential and commercial buildings. Post-tensioned flat plates are a type of concrete structural slabs typically used for flooring in high-rise building because of the numerous advantages over non-prestressed slabs such as better efficiency, reduced slab self-weight, as well as smaller crack and deflection. This type of slab typically consists of high strength steel strands called tendons, which are stretched to compress the concrete slab in both directions. To improve the performance of this type of slabs a research study was performed. This study investigated the performance and behavior of three one-third scale models of a nine-panel two-way post-tensioned flat plate. One of the slabs was strengthened with conventional steel bars and the tendon layout was uniform-banded tendon, another had conventional steel bar with banded-banded tendon layout while the last had banded-banded tendon layout reinforced with steel fiber. Actual load that will act on the slab when in use was applied and then this load was increased by a factor as specified in the building code, before loading the slab to the point where it cannot carry any more load. Results from the load test were compared to results obtain from analytical software package. The performance of the specimens that had banded-banded tendon layout was very similar to the specimens that had uniform-banded tendon layout, at actual operational load when in use. The failure loads for all specimens were considerably higher than the load they were designed for. The results suggest that steel fiber is a good alternative to conventional steel bars. The results from the load tests suggest that steel fiber can be used to strengthen post-tensioned flat plates which will lead to better performance and reduced cost.

Diploma thesis deals with composite materiál and it is dedicated to steel fiber concreat. The thesis focuses on verification of mechanical parameters of the steel fiber concrete. Especially on the compressive (tensile) strength at first cracking and the compressive strength in cracked state. Testing was conducted on concrete different tensile with 30 kg on m3 steel fibers KrampeHarex DE 50/1,0 N. The thesis is divided into theoretical and experimental part.

Este estudo apresenta os resultados de uma investigação experimental constituída de três séries de ensaio, cada uma envolvendo dois modelos: um pilar básico de concreto armado, representando o pilar a ser reforçado e um pilar reforçado por camisa de concreto de alto desempenho com várias características. Todos os pilares básicos tinham a seção quadrada de 150 mm x 150 mm com altura de 1200 mm. Eles foram produzidos com concreto de 18 MPa de resistência nominal à compressão, armadura longitudinal com quatro barras de 8 mm de diâmetro e armadura transversal com estribos de 6.3mm de diâmetro com espaçamento de 90 mm. Os parâmetros que foram variados nas camisas de reforço foram: a) dois valores de espessura (tj); b) três valores de taxa de armadura transversal (*sw) utilizando telas soldadas ou armadura de estribos; c) adição de fibras curtas de aço. A resistência nominal à compressão do concreto utilizado em todas as camisas foi de 65 MPa, caracterizando-se portanto um concreto de alta resistência. Os pilares foram submetidos à compressão axial por meio de uma máquina hidráulica servo-controlada. Os ensaios foram realizados com controle de deslocamento, adotando-se uma velocidade de 0.005mm/s para o deslocamento do pistão. A força aplicada e as deformações continuaram sendo medidas após o alcance da força de ruína, para se avaliar o comportamento pós-pico, até se atingir uma força residual de cerca de 50% da força de pico. Modelos de cálculo da resistência última dos pilares reforçados foram analisados. Também foram testados modelos de confinamento e ductilidade para os elementos reforçados. / This study presents the results of an experimental investigation in three series of tests, each one involving two models: a basic reinforced concrete column, which represents the column to ge strengthened, and an identical basic column strengthned by a high-performance concrete jacket with variable characteristics. All the basic columns had a 150 mm x 150 mm square section and a 1,200 mm length. They were made of a 18 MPa nominal strength concrete and reinforced with four 8 mm diameter steel bars and 6.3mm diameter stirrups each. The jacket characteristics varied as follows: a) two thickness values(tj); b) three values of transverse reinforcement ratio (*sw) using welded wire steel meshes or ordinary stirrups; c) addition of short steel fibers. The nominal concrete compressive strength used in all the jackets was 65 MPa, therefore a high-strength concrete. The columns were subjected to monotonic axial compression by means of a servo-controlled hydraulic machine. A displacement increasing rate of 0.005 mm/sec at the top of the column was adopted. Load and strain measurements continued after the ultimate load to evaluate the post-peak behavior, up to a residual load-bearing capacity of about 50% of the peak load. Several calculation hypotheses were tested to evaluate the ultime strength of the rehabilitated columns. Also confinement mechanisms and ductility of the members were analyzed.

Este trabalho apresenta um estudo para a previsão de comportamento quanto à fissuração e seu controle pelo uso das fibras de aço, em elementos de superfície de concreto restringidos, ou seja, submetidos às tensões de tração induzidas pela retração restringida. Neste estudo, foi desenvolvido um método analítico para calcular o consumo de um determinado tipo de fibra de aço em função do potencial de retração da matriz de concreto e da máxima abertura de fissura, determinada em função de parâmetros de durabilidade e aceitabilidade sensorial. Posteriormente, foram realizados ensaios para caracterização do potencial de fissuração de matrizes de concreto utilizadas em obras de elementos de superfície, onde testou-se um método de estimativa das tensões induzidas por retração restringida no concreto, no momento da primeira fissura. Na etapa final do trabalho, foi realizado um programa experimental, com a construção de pistas de concreto reforçado com fibras de aço (CRFA), com consumos de fibras de 10 kg/m3, 30 kg/m3 e 60 kg/m3, construídas sobre bases com duas condições de restrição: superfície desempenada e superfície jateada com exposição dos agregados. A fissuração destas pistas, nas primeiras idades, foi monitorada através da medida da abertura e do comprimento das fissuras. Com os resultados desta etapa experimental, foi realizada uma retroanálise do método onde concluiu-se que a consideração de valores característicos na previsão da resistência à tração do concreto era um ajuste necessário e coerente com a observação prática. Com o ajuste, os resultados experimentais de abertura de fissura ficaram dentro da faixa de previsibilidade do método, considerando um intervalo de confiança de 90%. Com o desenvolvimento deste método, buscou-se contribuir para a aplicação do CRFA no controle da fissuração por retração restringida de elementos de superfície, ampliando a fronteira do conhecimento no aspecto da escolha e dosagem da fibra para um determinado desempenho esperado quanto à fissuração. / This work presents a study for crack prediction and use of steel fibers to crack control in concrete surface elements submitted to tension stress induced by restrained shrinkage. In this study, a method was developed where a certain steel fiber type could be quantified, as function of concrete matrix shrinkage potential and maximum crack width, determined from human sensorial and durability criteria. Afterwards, an experimental program was done in order to characterize the crack potential of concrete matrices commonly used in surface elements. In this program, a method to predict tension stress induced by restrained shrinkage, at first crack moment, was tested. In the final step of this work, another experimental program was done, where steel fiber reinforced concrete (SFRC) tracks were built, with fiber contents of 10 kg/m3, 30 kg/m3 and 60 kg/m3, over substrates with two restriction conditions: smooth surface and rough surface, with exposition of surface aggregates. Lengths and widths of the early age shrinkage cracks in the tracks were monitored. The results obtained in this program were useful to analyze the method, adjusting it with the consideration of characteristic values in prediction of tension strength. With this adjust, experimental crack width results were more compatible with 90% confidence interval for crack width values predicted by the method. With this study, the goal was the contribution to use SFRC in the control of restrained shrinkage cracks in surface elements, amplifying the knowledge border in the aspect of fiber selection and proportioning, for a determined and expected performance in terms of crack width.

Concrete is a very weak and brittle material in tension. It has been shown in previous researches that the addition of steel fibers to a concrete matrix can improve this behavior. The ability of fibers to control and redistribute stresses after cracking results in a number of improvements in the structural behaviour of concrete. A review of existing literature shows that the addition of steel fibers enhances concrete’s tensile resistance, crack control properties, ductility and damage tolerance. In beams, fibers can transform brittle shear response into a flexural response and promote ductility, thereby allowing for a full or partial replacement of traditional shear reinforcement. The enhanced shear capacity, ductility and damage tolerance of Steel Fiber Reinforced Concrete (SFRC) can also potentially be used to relax seismic detailing requirements in frames by partially replacing the required transverse reinforcement in the plastic hinge regions of RC beams. One of the drawbacks associated with SFRC is that the addition of steel fibers to a traditional concrete mix at high fiber contents can result in workability problems. The combined use of Self-Consolidating Concrete (SCC) and fibers can solve this problem and facilitate placement for a wider range of structural applications. Although several studies have been conducted on the behaviour of SFRC beams subjected to monotonic loading, there is limited research on the behaviour of SFRC beams under cyclic or reverse-cyclic loading. This thesis presents the results of an experimental and analytical study conducted on nine SFRC beam specimens tested under load reversals. The main objective of this research program was to investigate the effect of fibers on structural behaviour and to examine the ability of steel fibers to replace transverse reinforcement. The experimental and analytical results show that use of fibers results in several improvements in behaviour, including enhanced damage tolerance and post-peak ductility. The results also show that steel fibers can potentially be used to allow for a reduction of transverse reinforcement in beams, however further research is required.

Steel fibers or fibers in general are utilized in concrete to control the tensile cracking and to increase its toughness. In literature, the effects of fiber geometry, mechanical properties, and volume on the properties of fiber reinforced concrete have often been experimentally investigated by numerous studies. Those experiments have shown that useful improvements in the mechanical behavior of brittle concrete are achieved by incorporating steel fibers. This study proposes a simulation platform to determine the influence of fibers on crack propagation and fracture behavior of fiber reinforced concrete. For this purpose, a finite element (FE) simulation tool is developed for the fracture process of fiber reinforced concrete beam specimens subjected to flexural bending test. Within this context, the objective of this study is twofold. The first one is to investigate the effects of finite element mesh size and element type on stress intensity factor (SIF) calculation through finite element analysis. The second objective is to develop a simulation of the fracture process of fiber reinforced concrete beam specimens. The properties of the materials, obtained from literature, and the numerical simulation procedure, will be explained. The effect of fibers on SIF is included by unidirectional elements with nonlinear generalized force-deflection capability. Distributions and orientation of fibers and possibility of anchorage failure are also added to simulation. As a result of this study it was observed that with the adopted simulation tool, the load-deflection relation obtained by experimental studies is predicted reasonably.

Seismic resistance of many buildings in Turkey is insufficient. Strengthening using R/C infills requires huge construction work. Feasible, easy strengthening techniques are being studied in Structural Mechanics Laboratory of METU. In this project, it was aimed to develop an economical strengthening method. This method is based on addition of steel fibers and/or PP fibers in mortar and application of mortar on masonry wall. Project was sponsored by the Scientific and Technical Research Council of Turkey (T&Uuml / BiTAK). Physical properties of cement, aggregate, and mortar used in tests were determined by material tests. After performing flexural strength and compressive strength tests, optimum mortar was obtained. R/C frames strengthened by applying the mortar to brick infilled walls were tested under reversed cyclic loads. Before the frame tests, two series of panel tests were performed to correctly model strengthened infill walls and to gather information about behavior of walls under load. Totally 10 frame tests were done. 4 tests were done as reference tests, and other 6 were done as strengthened frame tests. In the analytical part of study, the plastered hollow brick infill wall strengthened by FRM was modeled as two separate compression struts. First strut was used to model the plastered hollow brick infill wall. Second strut was used to model the FRM. This technique is effective in improving seismic behavior by increasing strength, initial stiffness, energy dissipation, and ductility. Moreover, the method provides strengthening of the buildings without evacuating the structure.