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-concreto, denominado ensaio APULOT, para estimativa da resistência à . In NBR [7], the bond stress (τu) is given by the follo-. A complete example using the expressions of the Brazilian code for the design of reinforced concrete structures, NBR, is also presented. PDF | The Brazilian code, NBR , recommends the usage of truss (θ) e do tirante transversal (α) para o dimensionamento de vigas de concreto.

Sorry, but Javascript is not enabled in your browser! How to cite. MARC format. OAI DC format. Master's Dissertation. Este trabalho apresenta o dimensionamento de pilares, de acordo com a nova NBR Columns Computing Instability Normalization Reinforced concrete. This work presents the computing of columns, in accordance with the new NBR It's considered the ultimate limit state of instability, possible to occur in equilibrium configuration of reinforced concrete columns submitted to normal loads. This study has been fundamental to make possible to propose safe and economically reasonable structural solutions, in order to supply the questionings that can appear to the designers of structures and professionals of the area, beyond to constitute a basic bibliography of consultation with regard to this subject. The objective is research details related to the columns project, and investigate the validity of the approached processes, through examples enclosing the possible situations inside the application field, to created a content of "Recommended Practice", more accessible to the professionals of the area and involving practice criterions of computing, placing to the disposal a summary of that exists in the norm and what is important to be followed. Initially, will be showed the calculation of the equivalent length of the column while isolated element and the limit of the index of slenderness, below of which reveals that the second order effects can be rejected. This document is only for private use for research and teaching activities. Reproduction for commercial use is forbidden.

A good choice of materials as well an investigation of effects of employed technologies, associated with a structural system improvement are important factors to ensure safety conditions.

In general, safety in structural design is introduced by safety partial factors that takes account inevitable imprecisions in load estimations or variability of mechanical properties of materials.

Besides that, safety incorporates imperfections due to simultaneous actions that structure must support, but it also be included in these uncertainties the errors resulting from simplified design conception or capacity of redistribute action produced by eventual damages.

When this aspects and coefficients are not addressed, neglected or verified, there is an increase of non-conformity cases and, thus, should be investigated. Case studies in non-conformity of concrete. It is noteworthy that safety assessment of non-conformity structural concrete includes many stages and methods, which include extraction of concrete cores and design review with the obtained concrete compressive strength Silva Filho; Helene, This paper aims to review some of the main factors involved in the analysis of non-conformities in concrete.

Aspects of variability of axial compressions test results, concrete acceptance criteria and compressive strength evolution in terms of long time effects are addressed. This review is complemented with a case study of a composite structure, with concrete-filled steel columns, which showed a lower compressive strength than the specified by the designer. With this analysis of long time effects on concrete compressive strength, is intended to contribute in decision making in the analys of nonconformities in concrete structures.

One possible approach to the assessment of structural safety consists in the analysis of long time behavior of concrete during time considering effects of strength evolution and long lasting load.

Compressive strength evolution over time can be calculated by using mathematic models related to the compressive strength at 28 days. Klemczak et al , It is well knowed that this evolution varies depending on the cement type, ambient temperature and curing conditions CEB, Compressive strength at t days;. Coefficient that depend on cement type: Compressive strength of concrete under sustained load, at j days, in MPa;.

Potential compressive strength at time age t 0 just before application of long lasting load, MPa;.

Another factor to be verified is the variability of compressive strength test results. Table 1 shows main factors that can affect compressive strength test results, as well the maximum variability of each factor.

Adapted from Helene and Terzian Indeed, this variability is true, as we can see in data from research and laboratorial tests. Santiago compiled technological control data of more than six thousand test specimens, coming from nine Brazilian states.

Another aspect to be considered is concrete receiving and acceptance. Observing the main Brazilian national and international concrete standards, it appears diverging aspects regarding method and acceptance criteria. In partial concrete sampling, only some of the total batches is sampled. In total concrete sampling, all batches are sampled and the acceptance criterion is that none of the individual sample presents compressive strength below than the characteristic strength.

Despite the high cost, this sampling method is widely used in Brazil Pacheco; Helene, The American standard, ACI Building Code Requirements for Structural Concrete , establish three different criteria: Additionally, the standard does not provide total concrete sampling, establishing minimum criterion of only one sample per day to each m 3 of concrete or each m 2 of builded area.

abnt nbr 6118 pdf

Pacheco; Helene, Specification, performance, production and conformity , presents different criterion according to the period of production: Larrossa et al conducted a comparison of the above mentioned sampling criteria to 32 concrete batches.

In conformity control realized in a building construction, by following procedures of NBR ABNT, , concrete compressive strength f c of three batches of 8m 3 presented test results below than the f ck of 40 MPa, specified by designer.

As the building presents obstacles to extraction of concrete cores, since the structure is made of concrete-filled steel columns, a study of concrete compressive strength evolution was made, in order to helps in the safety assessment of structure.

It is noteworthy that this analysis is complementary and must be performed together with other verifications, as the design review with the obtained concrete compressive strength and realization of non-destructive tests.

Concrete mix proportions are presented in table Table 2. On specified dates, compressive tests were made at certified laboratory, following standards procedures. Results are presented in Table 3. In this case, NBR states that the acceptance criterion is when all of the individual samples meet the f ck specified by designer.

As can be seen in Table 3 , the potential strength, at 28 days, does not show strength above or equal than the 40 MPa specified. Another pointed aspect is strength evolution after 28 days. In a study conducted by concrete supplier, in a year, the concrete presented a strength gain of From test results, it was performed an analysis of concrete compressive strength gain.

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Values are presented in Table 5. For verification of safety in this study case, it was calculated the design compressive strength of concrete f cd, according to Equation 4, using coefficients defined in Table 5.

Results are presented in Table 6. The values obtained showed that only when considering exclusively cement CPV ARI the final stress obtained is below than the expected. Table 1 shows main factors that can affect compressive strength test results, as well the maximum variability of each factor. Indeed, this variability is true, as we can see in data from research and laboratorial tests.

abnt nbr pdf - PDF Files

Santiago compiled technological control data of more than six thousand test specimens, coming from nine Brazilian states. Observing the main Brazilian national and international concrete standards, it appears diverging aspects regarding method and acceptance criteria. In partial concrete sampling, only some of the total batches is sampled.

In total concrete sampling, all batches are sampled and the acceptance criterion is that none of the individual sample presents compressive strength below than the characteristic strength. Despite the high cost, this sampling method is widely used in Brazil Pacheco; Helene, Additionally, the standard does not provide total concrete sampling, establishing minimum criterion of only one sample per day to each m3 of concrete or each m2 of builded area.

Pacheco; Helene, Larrossa et al conducted a comparison of the above mentioned sampling criteria to 32 concrete batches.