RCAAP Repository

O NEPAD - New Partnership for African Development - tem seus primórdios em 1996, proposto pelo atual presidente da África do Sul, Thabo Mbeki e outros líderes africanos, para erradicar a marginalização e o subdesenvolvimento africanos e promover o crescimento econômico, através da integração continental. Seus objetivos, inseridos no contexto da globalização e do African Renaissance, incorpora valores da luta antiapartheid sul-africana, restauração da auto-estima e resgate de valores pré-coloniais. O que o difere de outros planos que não deram certo na África é o vínculo inseparável entre democracia, direitos humanos, paz, governabilidade e o desenvolvimento econômico, as responsabilidades assumidas pelos participantes e a propriedade africana do plano.

A Internet é aqui considerada uma fonte alternativa do estudo da história, sobretudo história das relações diplomáticas. São analisados os sites dos ministérios das relações exteriores pelo mundo: alguns atribuem grande importância à história, com detalhada visão retrospectiva (Brasil, França, México, Rússia, Alemanha, Estados Unidos), outros têm abordagem seletiva ou restrita a determinados períodos (Espanha, Argentina, Itália, Bélgica, Portugal, China, Japão), uns se voltam para o passado, somente com informações históricas que sejam indispensáveis à imagem nacional (Suíça) e outros mostram sua história voltada para o futuro (Grã-Bretanha).

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Abstract The Ultra-High Performance Fiber-Reinforced Concrete is a material with remarkable mechanical properties and durability when compared to conventional and high performance concrete, which allows its use even without the reinforcement. This paper proposes the design of prestressed towers for a 5 MW turbine, through regulatory provisions and the limit states method, with UHPFRC and the concrete class C50, comparing the differences obtained in the design by parametric analysis, giving the advantages and disadvantages of using this new type of concrete. Important considerations, simplifications and notes are made to the calculation process, as well as in obtaining the prestressing and passive longitudinal and passive transverse reinforcement, highlighting the shear strength of annular sections comparing a model proposed here with recent experimental results present in the literature, which was obtained good agreement. In the end, it is estimated a first value within the constraints here made to ensure the economic viability of the use of UHPFRC in a 100 m prestressed wind tower with a 5 MW turbine.

Abstract Self-consolidating concrete is characterized by its high flowability, which can be achieved with the addition of superplasticizer and the reduction of the amount and size of coarse aggregates in the concrete mix. This high flowability allows the concrete to properly fill the formwork without any mechanical vibration. The reduction in volume and particle size of the coarse aggregates may result in lower shear strength of beams due to a reduced aggregate interlock. Therefore, an experimental investigation was conducted to evaluate the influence of the reduction in the volume fraction and the nominal size of coarse aggregate on concrete shear strength of self-consolidating beams. Six concrete mixes were produced, four self-consolidating and two conventionally vibrated. A total of 18 beams, with flexural reinforcement but without shear reinforcement were cast. These beams were tested under a four-point loading condition. Their failure modes, cracking patterns and shear resistances were evaluated. The obtained shear resistances were compared to the theoretical values given by the ACI-318 and EC-2 codes. The results demonstrated a lower shear resistance of self-consolidating concrete beams, caused mainly due to the reduced aggregate size.

Abstract This paper presents the development of an effective numerical formulation for the analysis of steel-concrete composite structures considering geometric and materials nonlinear effects. Thus, a methodology based on Refined Plastic Hinge Method (RPHM) was developed and the stiffness parameters were obtained by homogenization of cross-section. The evaluation of structural elements strength is done through the Strain Compatibility Method (SCM). The Newton-Raphson Method with path-following strategies is adopted to solve nonlinear global and local (in cross-section level) equations. The results are compared with experimental and numerical database presents in literature and a good accuracy is observed in composite cross sections, composite columns, and composite portal frames.

Abstract Over the last few years, comprehensive management programs for the diagnosis and prognosis of alkali-aggregate reaction (AAR) in aging concrete structures were developed in North America, based on a series of laboratory test procedures. Although promising, these lab-procedures presented several parameters whose impacts were not completely understood, which significantly reduced their applicability for the appraisal of deteriorated concrete structures in service. In this context, it has been suggested that two lab-tools, the Stiffness Damage Test (SDT) and the Damage Rating Index (DRI) could reliably assess the condition of concrete affected by AAR. This paper presents the condition assessment of 25, 35 and 45 MPa AAR affected concrete specimens incorporating fine and coarse reactive aggregates and presenting different distress degrees (i.e. expansion levels from 0.05 to 0.30%) through the use of an innovative multi-level approach. Results show that both SDT and DRI are suitable for assessing damage in AAR affected concrete through their output parameters. Yet, they present a complementary character, which illustrates the need for a multi-level approach.

Abstract Green roofs can contribute in many ways to the quality of the environment, being known for reducing the heat transfer to the interior of the buildings. Amongst the available techniques for the execution of this type of covering, the use of light cement blocks which are compatible with the system of extensive modular green roofs is proposed. For the light cement blocks, produced with EVA aggregates (waste from the footwear industry), an additional contribution in the capacity of thermal insulation of the proposed green roof is expected. In the present article, the demonstration of such contribution is intended through measurements carried out in prototypes in hot and humid climates. After characterizing the capacity of thermal insulation of the proposed green roof, with different types of conventional covering as a reference, an additional contribution of the component used in this green roof was identified by making comparisons with measurements collected from another green roof, executed with cement blocks without the presence of the EVA aggregates. In the experiments, external and internal surface temperatures were measured in each of the prototypes' coverings, as well as the air temperatures in the internal and external environments. From the analysis of the data for a typical summer day, it was possible to prove that the proposed green roof presented the lowest temperature ranges, considering the internal air and surface temperatures. The presence of the EVA aggregates in the proposed blocks contributed to the decrease of the internal temperatures.

Abstract This paper describes the adherence behavior of a structural lightweight concrete with EPS beads (SLCEB) in a monotonic loading, based in a bibliographic review and in pull-out tests. The results of these SLCEB tests were compared with those of an ordinary concrete (OC) and with the values based in indications of the Brazilian code ABNT NBR 6118:2014 - Design of concrete structures. The pull-out tests of two batches of SLCEB and one of OC were analyzed, in a total of 60 tests. Mechanical characteristics were determined too, such as: compressive strength and tensile strength in split cylinder test. The calculated results according to the above mentioned standard were very different from those obtained in the tests, indicating that the theoretical values are more conservative than the experimental ones. It was also verified that it is possible to use SLCEB in structures with respect to the adequate adherence of reinforcement in the concrete.

Abstract There are many theories and empirical formulas for estimating the shear strength of reinforced concrete structures without transverse reinforcement. The security factor of any reinforced concrete structure, against a possible collapse, is that it does not depend on the tensile strength of the concrete and the formation of any collapse is ductile, thus giving advance warning. The cracking from tensile stress can cause breakage of the concrete and should be avoided at all cost, with the intent that any such breakage does not incur any type of failure within the structure. In the present research study, experiments were performed in order to analyze the complementary mechanisms of the shear strength of lattice beams of reinforced concrete frames without transverse reinforcement. The experimental program entails the testing of eight frames that were subjected to a simple bending process. Two concrete resistance classes for analyzing compressive strength were considered on the construction of frames, 20 MPa and 40 MPa. To resist the bending stresses, the beams of the frames are designed in domain 3 of the ultimate limit states. Different rates and diameters of longitudinal reinforcement were used, 1.32% and 1.55% with 12.5 mm diameter and 16.0 mm in longitudinal tensile reinforcement. From the obtained results, an analysis was made of the criteria already proposed for defining the norms pertinent to the portion of relevant contribution for the shear resistance mechanisms of concrete without the use of transverse reinforcement and the influence of the concrete resistance and longitudinal reinforcement rates established in the experimental numerical results.

Abstract This research investigates reinforced concrete plates and shells with skew reinforcement whose directions are not aligned with the principal internal forces. Two normal forces, one tangential force, two bending moments, and one twisting moment are defined in the plane of the element. The analysis includes two shear forces in the transverse direction. The membrane and flexural forces are distributed between two panels at the upper and lower faces of the element. The smeared cracking model, equilibrium considerations, and plasticity approach yield the design equations of the skew reinforcement. The slab reinforcement of flat bridges, with and without lateral beams and girder bridges are compared considering different skew angles. The minimum reinforcement criteria of skew meshes are discussed. The results show that skew reinforcement yields higher steel and concrete stresses.

Abstract This paper is a compendium on intumescent paint and its main features regarding chemical composition, thermophysical properties and performance as a fire-retardant material. Some of the main technical publications and lines of research on the subject are presented herein. The purpose of this paper is to show the current stage of the technical research being conducted on the topic and enable a better understanding of this fire-retardant material.

Abstract This work studies the column-base connection by external socket in precast structures. A parametric study of the geometric characteristics of the external socket base with smooth interface is presented. In this parametric study, the consumption of concrete and steel are analyzed. The column cross section, the embedded length of the column in the socket base and the thickness of the wall of the socket base were the variables considered in this study. It was observed that with the increase of the embedded length, the minimum cross section of the main horizontal reinforcement reduces. With this modification, the walls of the socket base that are perpendicular to the direction of the applied loads presented a reduction of their stiffness. Besides the parametric study, this paper presents a verification model. This part of the study shows the possibility to generate abacuses that simplifies the project of the socket base foundation. Moreover, a comparative analysis becomes easier to be accomplished

Abstract The frequent use of flat slabs in building constructions highlights the importance of improving the study of slab-column joints, particularly regarding the verification of the ultimate limit state of punching shear, given the complexity of this phenomenon. This article applies concepts of the Theory of Reliability in order to evaluate the safety of the formulation established by NBR6118: 2014 standard to check punching shear in flat slabs with centered columns. Twelve probabilistic model analysis for C and C' equations were developed, considering the influence that the variation of the slab thickness, the ������ and the shear force eccentricity have on reliability index �� and failure rate ����. Results indicated that formulation of C boundary is reasonably safe, although C'boundary revealed �� index below expectations.

Abstract The Brazilian design code for composite buildings (NBR8800) has never been subject to a reliability-based calibration of the partial factors used in design. As a consequence, the level of structural safety achieved by using these factors is, in general, unknown. This paper presents a study of the reliability of partially encased steel-concrete composite columns, subject to compression and bending. Literature statistics are used to quantify uncertainty in strength of structural materials and in loads. Reliability indexes are evaluated, via FORM, for two ratios between dead and live loads, and for some values of load eccentricity. It was found that larger load eccentricity leads to a reduction in reliability indexes. These values are larger than minimum values recommended in international design codes; hence one concludes that design of such columns using NBR8800 leads to acceptable safety levels.

Abstract This paper describes a LITS (Load Induced Thermal Strain) semi empirical model and two practical applications in simple and reinforced concrete members. The model allows a preliminary and straightforward quantification of the total strain of concrete structures submitted to heating and a sustained compressive load, without the need to use complex numerical analyses. The model takes into account the effect of the thermal expansion restraint due to the boundary conditions (temperature and compressive load) and can be adopted for several types of concretes (conventional, high strength and ultra high performance). In the first example, the total deformations of simple concrete specimens from KHOURY (2006) are determined. In the second example, the total displacement of a reinforced concrete column from SCHNEIDER et al (1994) is calculated. A comparison between the results of the model and the experimental values demonstrated the reliability of the semi-empirical model to obtain a preliminary quantification of the total deformations of concrete.