Academic literature on the topic 'Precast concrete'

Orientadores: Newton de Oliveira Pinto Junior, Monica Pinto Barbosa<br>Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo<br>Made available in DSpace on 2018-08-13T07:24:31Z (GMT). No. of bitstreams: 1 Ferraz_AndreLuizNonato_D.pdf: 9941000 bytes, checksum: 30542f4364161961a9bfdb7bfe736ac0 (MD5) Previous issue date: 2009<br>Resumo: Foram avaliados neste trabalho, teórica e experimentalmente, o comportamento reológico e mecânico do concreto auto-adensável (C.A.A.), em específico suas características frente as deformações lentas, retração e fluência, e sua aplicabilidade em peças pré-moldadas. Foram desenvolvidos duas composições de concreto de classes de resistência distintas, 35 e 55 MPa. Na etapa de dosagem foram utilizados os procedimentos do método REPETTE-MELO, onde nas pastas e argamassas, foram realizados ensaios reométricos, ensaios de fluidez e Mini-Slump, e na definição do traço do C.A.A., ensaios de controle, tais como Slump-Flow, Funil em V, caixa em L, caixa em U e tubo em U, assim como ensaios das propriedades mecânicas tais como resistência à tração, resistência à compressão, e módulo de elasticidade. A avaliação do comportamento dos concretos frente a fluência se deu nas idades de 7, 14, 28, e 56 dias, segundo a NBR 8224 (ABNT, 1983), e frente a retração de acordo com a norma MERCOSUL NM 131:9. Os resultados experimentais foram comparados com valores de concretos convencionais disponíveis na literatura. Todos os ensaios foram realizados no Laboratório CESP de Engenharia Civil, e no Laboratório de Hidrologia da UNESP em Ilha Solteira-SP. No estudo da deformação rápida, ensaios de tração na flexão foram realizados aos 28 e 56 dias. Os coeficientes de fluência foram calculados quer seja através dos valores experimentais como pela NBR 6118 e comparados entre si, apresentando boa correlação, com diferenças menores que 10% para toda as idades. A composição do concreto auto-adensável foi implantada para fins de avaliação, junto a empresa de Pré- Moldados Protendit de São José do Rio Preto-SP, onde foram moldadas vigas, em escala real, as quais apresentaram melhor acabamento e se mostraram 50% mais economicas, em relação a mão-de-obra, quando comparada com a viga de concreto convencional. Os resultados obtidos mostram que as composições de concreto auto-adensável apresentam maiores valores de retração e fluência quanto comparados com concretos convencionais de mesma resistência mecânica. O C.A.A. de resistência à compressão igual a 55 MPa apresentou menor retração e fluência básica que o C.A.A. de resistência 35 MPa.<br>Abstract: This project analyzed, theoretically and experimentally, the mechanical and rheological behavior of the selfcompacting concrete (C.A.A.), specially its features according to slow deformation, shrinkage and creep, and its applicability in precast elements. Two compositions of concrete of different classes of resistance were developed, 35 MPa and 55 MPa. In the stage of the dosage, the procedures of the method REPETTE-MELO were used, rheometrical tests, fluidness tests and Mini-Slump were carried out on the pastes and the mortars, and control tests, such as Slump-Flow, funnel V test, box L, box U and tube U, and mechanical properties tests, such as tensile strength, compression strength and elasticity module were used to define the C.A.A. feature. The evaluation of the concrete behavior by creep happened at ages of 7, 14, 28, and 56 days, according to NBR 8224 (ABNT, 1983), and by shrinkage according to MERCOSUL NM 131:9. The experimental results were compared with values from conventional concrete available in the literature. All tests were performed at CESP Civil Engineer Laboratory, and at Hydrology Laboratory of the UNESP in Ilha Solteira-SP. In the fast deformation study, traction tests in flexion were performed at 28 and 56 days. The creep coefficients were calculated either through experimental values as by the NBR 6118 and compared each other, showing a good correlation, with differences smaller than 10% for all ages. The composition of self-compacting concrete was established for evaluation, in partnership with precast elements company Protendit of São José do Rio Preto-SP, where were shaped beams, in real scale, which showed better finishing and they showed themselves 50% more economical regarding labor, when compared with conventional concrete beam. The results reached show that the compositions of self-compacting concrete present higher values of shrinkage and creep when compared with conventional concrete of same strength. The C.A.A. that presented compression strength equal to 55 MPa showed a lower shrinkage and basic creep that C.A.A. strength of 35 MPa.<br>Doutorado<br>Edificações<br>Doutor em Engenharia Civil

The following thesis presents the results of four full scale beams tests as part of a research program conducted at McGill University. The purpose is to study the applicability of existing design provisions, in the American Association of State Highway and Transportation Officials (AASHTO) specifications, for the use of self-consolidating concrete (SCC) in precast pretensioned bridge girders. The test specimens had an overall length of 31 ft (9.4m) with a center-to-center span of 29 ft (8.8m). They were cast in four batches with different concrete attributes: two non air-entrained SCC mixtures and two high-performance concretes. For each type, compressive strengths of 8,000 and 10,000 psi (55.2 and 69 MPa) with release strengths of 5,000 and 6,250 psi (34.5 and 43 MPa) at 18 hours, respectively, were tested. Each girder was prestressed with eight Grade 270 seven-wire low-relaxation prestressing strands of 0.6 in (15.2 mm) diameter. Six of the strands were straight and two were harped twice, 4’-11” (1.5 m) from mid-span. The specimens were supported on neoprene bearing pads at their ends, and were tested with two equal point loads located 4’-11” (1.5 m) from mid-span. This research project demonstrated that the shear failure of the girders exceeded the predicted nominal shear resistance given by the 2004 AASHTO Specifications. The experimental flexural resistance also exceeded the predicted nominal resistance.<br>Le présent mémoire expose les résultats de quatre poutres pleine grandeur faisant partie intégrante d’une étude effectuée à l’Université McGill. Le but de cette étude est de valider l’applicabilité des provisions de conception existantes, de l’Association Américaine des Autoroutes d’État et des Officiers de Transport (norme AASHTO), pour l’usage de béton autoplaçant (BAP) dans les poutres précontraintes et préfabriquées de ponts.Les spécimens testés ont une longueur maximale de 31 pieds (9.4 m) avec une distance du centre au centre de 29 pieds (8.8 m). Les poutres ont été coulées une à la fois avec différentes sortes de béton: deux d’entres-elles à partir de béton autoplaçant sans air entrappé, et deux avec du béton haute-performance. Pour chaque sorte, une résistance compressive de 8,000 et 10,000 psi (55.2 et 69 MPa) avec une résistance, avant de précontraindre le béton, de 5,000 et 6,250 psi (34.5 et 43 MPa) à 18 heures, respectivement, ont été testées. Chaque poutre était précontrainte avec huit tendons, grade 270, de 0.6 in (15.2 mm) de diamètre. Six de ces tendons étaient horizontaux alors que deux étaient inclinés 59 pouces (1.5 m) de chaque bord de l’axe central. Les spécimens étaient supportés aux deux extrémités sur des pads de néoprène et étaient testés avec deux charges concentriques situées 59 pouces (1.5 m) de l’axe central.Cette recherche à démontrer que la capacité en cisaillement des poutres testées excédait les valeurs nominales prévues par les normes AASHTO 2004. Les valeurs expérimentales de la résistance à la flexion des poutres aussi excèdent les valeurs nominales prédises.

This thesis describes a new technique for studying the non-linear behaviour of reinforced concrete frames with flexible joints. The method is based on the concept of establishing an equilibrium deflected shape of a structure. The computations involve two basic levels of iteration. First, starting with an assumed nodal deformation, equilibrium deflected shapes and end forces of individual members in a structure are calculated using moment-thrust-curvature relations. The out of balance forces are computed by considering equilibrium of member forces at nodal points. In the second level of iteration based on a numerically computed nonlinear stiffness matrix, the nodal deformation are updated until the out of balance forces are negligible. The interaction of torsion with flexure has been assumed to be independent and further, the members are assumed to behave linearly in torsion. The influence of floors and cladding is ignored and only the skeleton frame is considered in the analysis. The associated computer program SWANSA based on the above method can be used as a design tool for sway and nonsway concrete frames with or without flexible joints. An interactive data entry facility allows the user to enter data by answering simple questions or by returning default values. Full scale experiments were carried out on eight column beam subframes to validate the computer program. Each subframe consisted of a two storey column with a short length of a typical mid-storey beam. Four types of connection commonly used in precast construction were selected to connect the beam to the column at mid height. Two sets of subframes were made for each connection, one each of a pair of subframes was tested for upward and downward rotations. The numerical technique is further validated with results published in literature, including experiments and the finite element method. All the comparisons show that the analysis developed in this thesis can be used to predict the behaviour of precast and other reinforced concrete frames for deflections, strains and for the ultimate loads. Finally, it is shown how a computer program based on the new numerical method can be used as an alternative method of designing rigid jointed or semi-rigid jointed precast concrete 3-dimensional frames, taking into account material and geometrical nonlinearities.

Bibliography: leaves 69-72.<br>Modern fast track construction methods increasingly favour the use of precast concrete elements. Precast box culverts are structurally significant units, subject to an important combination of bridge loadings. Culverts occasionally in contact with water pose a high durability risk. Despite this, the current specifications allow a reduction in cover to reinforcing steel for precast culverts to only 20 mm from at least 40 mm for cast-in-place culverts.

Multi-span precast concrete segmental bridges are commonly constructed using the balanced cantilever method, which essentially involves sequentially extending precast segments outwards from each pier in a balanced manner. A gap of 100 to 200 mm wide is usually provided around the mid-span location between the last two approaching segments to facilitate erection. In-situ concrete is then cast to ‘stitch’ the segments together, thus making the bridge deck continuous. In the current practice, the in-situ concrete stitches are usually designed to be capable of sustaining considerable sagging moment but only minimal hogging moment. Failure of stitches may occur under exceptional circumstances that may potentially trigger a progressive collapse. However, relatively little research in this area has been carried out. In view of this, the author is motivated to undertake an extensive study of the behaviour of in-situ concrete stitches and the effects of their performance on the robustness of typical segmental bridges. Experimental study is carried out to examine the behaviour of in-situ stitches under different combinations of internal forces. Series of stitch specimens of different configurations are tested. Subsequent parametric studies are conducted numerically to examine the effects of various parameters on the load-displacement characteristics of the stitches. Formulae for strength estimation are proposed based on the results. A study of robustness involves analyzing the collapse behaviour of a structure in an extreme event and the analysis should be carried out up to and then well beyond the state of peak strength of structural members. A finite element programme for post-peak analysis is therefore developed for the present study. As the ability of a member section to sustain large inelastic deformation can ultimately affect the robustness of a structure, an investigation is conducted to examine the effects of steel content, yield strength and prestressing level on the ductility and deformability of prestressed concrete sections. Using the programme developed, the formation of collapsing mechanisms of a multi-span segmental bridge deck in an extreme event is examined. A typical bridge deck is subject to prescribed accidental load on its span in order to analyze the sequence of failure. Substantial redistribution of internal forces along the deck is observed as failures initiate, thus causing subsequent failures of other deck sections even though they have been designed to resist the internal forces at the ultimate limit state. The results indicate that any span of a multispan bridge may become a temporary end-span in the event of collapse of an adjacent span and the strength of the sections must be designed accordingly to prevent progressive failure. As a span becomes a temporary end-span, the in-situ concrete stitches may experience substantial moment and shear, and their failure could potentially trigger progressive collapse of the entire bridge deck. Towards the end of the thesis, important design considerations that can enhance the performance of in-situ concrete stitches and robustness of precast concrete segmental bridges are presented.<br>published_or_final_version<br>Civil Engineering<br>Doctoral<br>Doctor of Philosophy

Precast concrete structures are not widely used in severe seismic regions due the limited knowledge of the response of these systems to reversed cyclic loading. A series of four precast concrete wall panels were tested to evaluate their response to reversed cyclic loading. These units represent the wall panels of a typical single storey precast concrete structure. In order to achieve improved ductility and energy absorption characteristic, it was found that the horizontal sliding of the wall panel along the grout-wall interface must be controlled. Due to the reversed cyclic loading and the increased wall panel participation from limiting the horizontal sliding of the wall, it was determined that shear reinforcement of each precast specimen was separated into three separate component parts, joint rotation, wall panel deformations and horizontal wall panel sliding, to compare and evaluate the seismic performance of the wall panels.

Experimental research, engineering analysis and theoretical developments comprise a study in which various interactions between ductile moment resisting frames and precast prestressed hollow core flooring have been examined. The most critical interaction tested involves support behaviour, and the ability of reinforcing details to provide control against loss of support and possible catastrophic flooring collapse under dilation effects. Plastic hinge dilation, also known as elongation or growth, is an inherent property of ductile concrete members when subjected to cyclic plastic deformations. Hence, the performance of floor support details is enveloped by the general design philosophy of seismic resisting structures. In the experimental phase, emphasis was placed on testing support construction joints from contemporary building practice, for direct comparison with special support tie details of known capabilities. The contemporary details were found to exhibit seriously flawed behaviour under monotonic and cyclic loading regimes. Corroborative experiments were undertaken to establish direct shear capacities between typical composite bond surfaces. In particular, these tests addressed the discrepancy that has emerged between direct shear and shear flow strengths. Also, the continuity response of conventional and proposed support detail types was examined. A composite section model was analysed to demonstrate the likely influence of prestressing steel on beam bending strength within a ductile frame environment. Likewise, the probable effects of prestressing steel on beam plastic hinge development were examined, but on a more theoretical basis. Other elements of theory have been presented. These mainly concern the general topic of elastic-plastic response in reinforced concrete elements. The particular focus of this work has been to demonstrate a rational basis to stiffness transition and plastic buckling analysis. The important role of stiffness degradation in dynamic analysis has also been examined. Although ductile moment resisting concrete frames have been emphasised, it is considered that the findings of this thesis are applicable to other structural systems, such as dry joint "hybrid" precast concrete frames and spring connected steel frame structures.

Structural engineering is facing an extraordinarily challenging era. These challenges are driven by the increasing expectations of modern society to provide low-cost, architecturally appealing structures which can withstand large earthquakes. However, being able to avoid collapse in a large earthquake is no longer enough. A building must now be able to withstand a major seismic event with negligible damage so that it is immediately occupiable following such an event. As recent earthquakes have shown, the economic consequences of not achieving this level of performance are not acceptable. Technological solutions for low-damage structural systems are emerging. However, the goal of developing a low-damage building requires improving the performance of both the structural skeleton and the non-structural components. These non-structural components include items such as the claddings, partitions, ceilings and contents. Previous research has shown that damage to such items contributes a disproportionate amount to the overall economic losses in an earthquake. One such non-structural element that has a history of poor performance is the external cladding system, and this forms the focus of this research. Cladding systems are invariably complicated and provide a number of architectural functions. Therefore, it is important than when seeking to improve their seismic performance that these functions are not neglected. The seismic vulnerability of cladding systems are determined in this research through a desktop background study, literature review, and postearthquake reconnaissance survey of their performance in the 2010 – 2011 Canterbury earthquake sequence. This study identified that precast concrete claddings present a significant life-safety risk to pedestrians, and that the effect they have upon the primary structure is not well understood. The main objective of this research is consequently to better understand the performance of precast concrete cladding systems in earthquakes. This is achieved through an experimental campaign and numerical modelling of a range of precast concrete cladding systems. The experimental campaign consists of uni-directional, quasi static cyclic earthquake simulation on a test frame which represents a single-storey, single-bay portion of a reinforced concrete building. The test frame is clad with various precast concrete cladding panel configurations. A major focus is placed upon the influence the connection between the cladding panel and structural frame has upon seismic performance. A combination of experimental component testing, finite element modelling and analytical derivation is used to develop cladding models of the cladding systems investigated. The cyclic responses of the models are compared with the experimental data to evaluate their accuracy and validity. The comparison shows that the cladding models developed provide an excellent representation of real-world cladding behaviour. The cladding models are subsequently applied to a ten-storey case-study building. The expected seismic performance is examined with and without the cladding taken into consideration. The numerical analyses of the case-study building include modal analyses, nonlinear adaptive pushover analyses, and non-linear dynamic seismic response (time history) analyses to different levels of seismic hazard. The clad frame models are compared to the bare frame model to investigate the effect the cladding has upon the structural behaviour. Both the structural performance and cladding performance are also assessed using qualitative damage states. The results show a poor performance of precast concrete cladding systems is expected when traditional connection typologies are used. This result confirms the misalignment of structural and cladding damage observed in recent earthquake events. Consequently, this research explores the potential of an innovative cladding connection. The outcomes from this research shows that the innovative cladding connection proposed here is able to achieve low-damage performance whilst also being cost comparable to a traditional cladding connection. It is also theoretically possible that the connection can provide a positive value to the seismic performance of the structure by adding addition strength, stiffness and damping. Finally, the losses associated with both the traditional and innovative cladding systems are compared in terms of tangible outcomes, namely: repair costs, repair time and casualties. The results confirm that the use of innovative cladding technology can substantially reduce the overall losses that result from cladding damage.