Advanced composites have become one of the most popular methods of repairing and/or strengthening civil infrastructure in the past couple of decades. While the use of Fiber Reinforced Polymer laminates and sheets for the repair and strengthening of reinforced concrete structures is well established, research on the application of FRP composites to steel structures has been limited. The use of FRP material for the repair and rehabilitation of steel members has numerous benefits over the traditional methods of bolting or welding of steel plates. Carbon FRPs (CFRPs) have been preferred over other FRP material for strengthening of steel structures since CFRPs tend to posses higher stiffness. The emergence of high modulus CFRP plates, with an elastic modulus higher than that of steel, enables researchers to achieve substantial load transfer in steel beams before the steel yields. This research investigates both analytically and experimentally, the bond characteristics between ultra high modulus CFRP strengthened steel members and the flexural behavior of these members. A series of double strap joint tests with two different CFRP strip widths are carried out to evaluate the development length of the bond. Both ultra high modulus and normal modulus CFRP laminates are used to compare strengthened member performance. Steel plates reinforced with CFRP laminates on both sides are loaded in tension to evaluate the load transfer characteristics. Debonding under flexural loads is also studied for ultra high modulus CFRP strengthened steel girders. Flexural tests are carried out under 4-point bending on several small scale wide flange beams. This study also introduces the novel ultra high modulus CFRP plate strip panels for strengthening of steel bridge girders. The first field application of ultra high modulus CFRP laminates in strengthening steel bridge girders in the United States is also carried out as part of the research. Full scale load tests carried out before and after the strengthening are utilized to measure the degree of strengthening achieved and checked against the expected results. A finite element model is developed and calibrated using data obtained from the field testing of the bridge. The model is then used to evaluate the behavior of the bridge under different conditions before and after the strengthening process.

The aim of this thesis was to investigate what the relation is between as-quench hardness and final surface hardness for steel beams is, depending on what tempering temperature is used. Also explain how chemistry, dimension and microstructure effects the final mechanical properties of the front axle beam. For this a review of literature concerning the effects was completed.Hardness measurement on the surface was performed on the ends of the beam (bottom and top). This hardness measurement was performed on 6 different front axle articles of the same material (41CrS4) and 2 different front axle articles of another material (40CrMo4). The relation diagram gives an estimation of what type of tempering temperature is needed to achieve the final hardness that is desired. Because the relation was done with some inconsistences it can’t be said to give a perfect answer. The relation diagrams only work for material 41CrS4 and 40CrMo4. For the core hardness test, 2 articles of 41CrS4 and one article of 40CrMo4 was measured on 5 different position on the cross-section, the beams for the respective articles were taken from quenched state and quenched+tempered. The beam dimensions have a significant effect when it comes to cooling down the part and achieve as close to uniform hardness as possible. Even though the Middle point of the I-section sample is one of the closest cores to the surface, it has a softer core compared with the other cores. While there exists hardness difference after quenching between different points in the core they even out after tempering. When comparing the core hardness with the surface hardness it can be said that the surface hardness is not as hard as the core because of decarburization. The microstructure analysis was done on 2 articles of 41CrS4 and one article of 40CrMo4. Samples from the 3 articles is taken from both the as-quenched state and quenched+tempered state. From the optical microscope it could be seen, that the surface of the beams decarbonizes leading to a higher amount of ferrite at the structure and softer surface. Because of this 15 mm into the material is harder than at-surface. Decarburization of the 41CrS4 steels made it so that what should have been a martensite and bainite dominated surface became a ferrite and bainite dominated.To decide the actual amount of retained austenite in the sample an XRD-analysis was performed. The XRD-analysis is done only for one article type of 41CrS4. From the front axle beam three samples of three different locations (bottom, middle, top) was taken for the analysis. For the theoretical calculation of the retained austenite vs the actual amount it can be said that is a very good representation of the total amount of retained austenite in the product. But the theoretical calculation deviates a bit from the actual amount at the top part of the beam. / Syftet med denna avhandling var att undersöka vad relationen är mellan härdat ythårdhet och slut ythårdhet för stålbalkar är, beroende på vilken anlöpnings temperatur som används. Tar också upp hur kemi, dimension och mikrostruktur påverkar de sista mekaniska egenskaperna hos framaxel balken. För detta genomfördes en genomgång av litteraturen om effekterna.Hårdhetsmätning på ytan utfördes på balkens ändar (botten och toppen). Denna hårdhetsmätning utfördes på 6 olika främre axelartiklar av samma material (41CrS4) och 2 olika främre axelartiklar av annat material (40CrMo4). Relationsdiagrammet ger en uppskattning av vilken typ av anlöpningstemperatur som behövs för att uppnå den slutliga hårdheten som önskas. Eftersom förhållandet gjordes med vissa inkonsekvenser kan det inte sägas ge ett perfekt svar. Relationsdiagrammen fungerar endast för material 41CrS4 och 40CrMo4.För kärnhårdhetstestet mättes 2 artiklar av 41CrS4 och en artikel av 40CrMo4 i 5 olika positioner på tvärsnittet, stålen för respektive artiklar togs från härdat tillstånd och härdat + anlöpt. Dimensionerna har en signifikant effekt när det gäller att kyla ner delen och uppnå så nära enhetlig hårdhet som möjligt. Även om mittpunkten i I-sektionsprovet är en av de närmaste kärnorna till ytan, så har det en mjukare kärna jämfört med de andra kärnorna. Det finns hårdhetsskillnad efter härdning mellan de olika punkter men de jämnar ut sig efter anlöpningen. När man jämför kärnhårdheten med ythårdheten kan man säga att ythårdheten inte är så hård på grund av avkolning.Mikrostrukturanalysen gjordes på 2 artiklar av 41CrS4 och en artikel av 40CrMo4. Prover från de 3 artiklarna tas från både härdat tillstånd och härdat + anlöpt tillstånd. Från det optiska mikroskopet kunde man se att stålbalkens yta har blivit utsatt för avkolning vilket leder till en högre mängd ferrit vid strukturen och en mjukare yta. På grund av detta, så är 15 mm in i materialet hårare än vid ytan. Avkolning av 41CrS4 stål gjorde så att det som borde ha varit ett martensit och bainit dominerat yta blev istället ferrit och bainit dominerat.XRD-analysen görs endast för en artikelart av 41CrS4. Från fram axelbalken togs tre prov från tre olika platser (botten, mitten, toppen) för analysen. För att bestämma den verkliga mängden restaustenit i provet utfördes en XRD-analys. För den teoretiska beräkningen av den rest austeniten jämfört med det faktiska beloppet kan man säga det är en mycket bra representation av den totala mängden kvarhållen austenit i produkten. Men den teoretiska beräkningen avviker lite från den faktiska mängden vid stålens övre del.

Intumescent coating fire protection on steel structures is becoming widely popular in the UK and Europe. The current assessment for the fire protection performance method using the standard fire resistance tests is not accurate, owing to the reactive behaviour of intumescent coating at elevated temperature. Moreover, the available intumescent coating temperature assessment method provided in the Eurocode for structural steel at elevated temperature does not incorporate the steel beam's behaviour and/or assessment for partial protection and/or damaged protection. The research work presented provides additional information. on the assessment of partial and/or damaged intumescent coating at elevated temperature. In the scope of the investigation on the thermal conductivity of intumescent coating, it was found that the computed average thermal conductivity was marginally sensitive to the density and emissivity at elevated temperature. However, the thermal conductivity was found to be reasonably sensitive to the differences in initial dft's (dry film thicknesses). In this research, a numerical model was developed using ABAQUS to mimic actual indicative test scenarios to predict and establish the temperature distribution and the structural fire resistance of partial and/or damaged intumescent coating at elevated temperatures. Intumescent coating actively shields when the charring process occurs when the surface temperature reaches approximately 250°C to 350°C. Maximum deflection and deflection failure times for each damage scenario were analyzed by applying specified loading conditions. It was also found that the structural fire resistance failure mode of intumescent coating on protected steel beams was particularly sensitive to the applied boundary conditions. Careful selection of nodes in the element was necessary to avoid numerical instability and unexpected numerical error during analysis. An assessment of various numerical models subjected to a-standard fire with partially protected 1 mm intumescent coating was analysed using ABAQUS. An available unprotected test result was used as a benchmark. The outcome suggests that the fire resistances of the beams were found to be sensitive to the location of the partial and/or damage protection. The overall fire resistance behaviour of intumescent coating at elevated temperature was summarized in a 'typical deflection regression' curve. An extensive parametric analysis was performed on localized intumescent coating damage with various intumescent coating thicknesses between 0.5mm to 2.0mm. It was found that the average deflection was linear for the first 30 mins of exposure for all the variables, damage locations and intumescent thicknesses. It was concluded that a thicker layered intumescent coating may not be a better insulator or be compared to a much less thick intumescent coating at elevated temperature. The use of passive fire protection, however, does enhance the overall fire resistance of the steel beam, in contrast to a naked steel structure. The research work investigated the intumescent coating behaviour with different aspects of protection and damage and the outcome of the assessment provided a robust guide and additional understanding of the performance of intumescent coating at elevated temperature.

This thesis deals with heat treatment of pearlitic steel beams with using of induction heating. The aim of this heat treatment is to improve mechanical properties of steel beams. In theoretical part are described pearlitic steels and theory of induction heating. In experimental part of this thesis analysis of current state of technology with its results was made. Numerical model describing current state of technology was assembled. Then this model was used to recommend adjustments in current technology of heat treatment, which leads to enlargement of heat treated depth. Experiments with adjusted parameters were executed on heat treating machine. Analysis of microstructure using LM and EM, measurement of hardness and fractographic analysis were done. The result of adjustments is enlargement of heat treated depth about half compared with current technology.

No description available.

This paper evaluates the effective width of composite steel beams with precast hollowcore slabs numerically using the finite element method. A parametric study, carried out on 27 beams with different steel cross sections, hollowcore unit depths and spans, is presented. The effective width of the slab is predicted for both the elastic and plastic ranges. 8-node three-dimensional solid elements are used to model the composite beam components. The material non-linearity of all the components is taken into consideration. The non-linear load-slip characteristics of the headed shear stud connectors are included in the analysis. The moment-deflection behaviour of the composite beams, the ultimate moment capacity and the modes of failure are also presented. Finally, the ultimate moment capacity of the beams evaluated using the present FE analysis was compared with the results calculated using the rigid – plastic method.

In steel¿concrete composite beams, the longitudinal shear force is transferred across the steel flange/concrete slab interface by the mechanical action of the shear connectors. The ability of the shear connectors to transfer these longitudinal shear forces depends on their strength, and also on the resistance of the concrete slab against longitudinal cracking induced by the high concentration of shear force. Most of the research in composite construction has concentrated on the more traditional reinforced concrete and metal deck construction, and little information is given on shear capacity of the headed studs in precast hollowcore slabs. In this paper, a standard push test procedure for use with composite beams with precast hollowcore slabs is proposed. Seven exploratory push tests were carried out on headed studs in solid RC slabs to validate the testing procedures, and the results showed that the new test is compatible with the results specified in the codes of practice for solid RC slabs. Once a standard procedure is established, 72 full-scale push tests on headed studs in hollowcore slabs were performed to determine the capacities of the headed stud connectors in precast hollowcore slabs and the results of the experimental study are analysed and findings on the effect of all the parameters on connectors¿ strength and ductility are presented. Newly proposed design equations for calculating the shear connectors¿ capacity for this form of composite construction are also be given.

no / The recently published report on Rethinking Construction in the UK has highlighted the need to reduce on-site activities as part of its drive for greater efficiency, improved quality and greater certainty in the delivery of construction projects. For multi-storey buildings, the use of precast slabs in the floors - particularly if this can be done without the need for in-situ screeds - drastically reduces the volume of on-site concreting required. Although the use of precast hollow core slabs in steel framed buildings are common, their use in composite design with steel beams is relatively new. By designing the steel beams and precast hollow core slabs compositely, a reduction in beam size and overall floor depth can be achieved, which would lead to an overall reduction in construction cost. This paper summarises the recent developments and on-going research on composite construction with precast hollow core slabs.

Experimental testing and elastic buckling studies were performed on 68 C-section cold-formed steel joists with unstiffened rectangular web holes. Four Steel Stud Manufacturers Association (SSMA) cross-section types; 800S200-33, 800S200-43, 1000S162-54, and 1200S162-97, were evaluated to explore the influence of holes on local, distortional, and global bucking failure modes. Hole depth was varied in the tests to identify trends in ultimate strength. Ultimate strength was observed to decrease with increasing hole depth for 800S200-33, 1200S162-97 cross-sections. Due to small number of specimen and unidentified behavior of the beams, a more in depth study of the behavior of 800S200-43 and 1000S162-54 beams are necessary. Local buckling of the unstiffened strip above the hole was observed to accompany distortional buckling at the hole for the locally slender 800S200-33 and 1000S162-54 cross-sections. Thin shell finite element eigen-buckling analysis of each joist specimen, including measured cross-section dimensions and tested boundary and loading conditions, were conducted in parallel with the experiments to identify those elastic buckling mode shapes which influence load-deformation response. The distortional and lateral-torsional buckling moments were observed to decrease with increasing hole depth while a contrasting behavior was captured for local buckling modes. A modification to the AISI Direct Strength Method equations for beams with slotted web-holes was compared against the experimental results with predictions lower than tested strength. Initial cross-section imperfections led to inclined webs which decreased the capacity of the beams. The use of a water-jet cutting process was employed successfully to produce accurate holes sizes and locations in each joist specimen and is recommended for researchers and manufacturers as a method for custom fabrication of cold-formed steel members. / Master of Science

Sistemas mistos de aço e concreto são aqueles em que o elemento de aço trabalha estruturalmente em conjunto com o concreto. Essa associação dos materiais resulta numa melhor utilização de ambos os materiais tanto quanto à capacidade resistente, quanto em caráter construtivo, funcional e estético. O presente trabalho tem como finalidade a análise de vigas de aço e mistas de aço e concreto parcialmente revestidas em situação de incêndio. Esse estudo tem grande importância tendo em vista os incidentes com altas temperaturas em edificações ocorridos ao longo dos anos. O aumento de temperatura nas estruturas é um efeito nocivo, pois prejudica a rigidez e a resistência dos materiais, podendo levar estruturas ao colapso. As análises das vigas mistas aço e concreto parcialmente revestidas em situação de incêndio foram feitas através de análises experimentais que foram realizadas no forno horizontal à gás do Laboratório de Engenharia de Estruturas da EESC/USP. Foram realizados ensaios de flexão em pontos em altas temperaturas e a variável nos ensaios foi o fator de carga aplicado no meio do vão das vigas. Foi possível comparar o comportamento das vigas metálica e mistas, bem como as temperaturas em vários pontos ao longo do elemento por meio de termopares colocados em pontos estratégicos. Transdutores de deslocamento também foram usados para saber o valor de deslocamento nos apoios e no meio do vão das vigas. Uma análise térmica bidimensional através do ABAQUS também foi feita para comparação de resultados. Conclui-se que para uma mesma carga aplicada os deslocamentos foram mais expressivos nos ensaios das vigas em situação de incêndio se comparados aos valores obtidos nos ensaios à temperatura ambiente, observou-se o efeito benéfico do revestimento de concreto ao perfil metálico, responsável por um ganho expressivo de resistência ao fogo quando comparado aos elementos puramente metálicos e por fim obteve-se boa concordância entre as temperaturas encontradas por modelagem numérica através do ABAQUS e dos ensaios experimentais realizados. / Composite steel and concrete systems are those in which the steel element works structurally in conjunction with the concrete. This association of the materials results in a better use of both materials as much as the resistant capacity, as well as in a constructive, functional and aesthetic character. The present work has the purpose of analyzing steel beams and mixed steel and concrete partially coated in a fire situation. This study has great importance in view of the incidents with high temperatures in buildings that have occurred over the years. The increase in temperature in the structures is a harmful effect, as it impairs the rigidity and the resistance of the materials, which can lead to collapse structures. The analyzes of the composite steel and concrete composite beams in a fire situation were made through experimental analyzes that were carried out in the horizontal gas furnace of the Laboratory of Structural Engineering of EESC/USP. Bending tests were performed on points at high temperatures and the variable in the tests was the load factor applied in the middle of the span of the beams. It was possible to compare the behavior of the metallic and composite beams as well as the temperatures at various points along the element by means of thermocouples placed at strategic points. Displacement transducers were also used to know the displacement value in the supports and in the middle of the span of the beams. A two-dimensional thermal analysis through ABAQUS was also done for comparison of results. It was concluded that for the same applied load the displacements were more expressive in the tests of the beams in the fire situation compared to the values obtained in the tests at room temperature, the beneficial effect of the concrete coating was observed on the metallic profile, responsible for a an expressive gain of fire resistance when compared to the purely metallic elements and finally a good agreement was obtained between the temperatures found by numerical modeling through ABAQUS and the experimental tests performed.