Durability Design Of Structures Research Articles

Comparison of different local design concepts for the structural durability assessment of welded offshore K-nodes

The structural durability design of complex welded structures should not rely only on one single design method but should apply different methods for assuring the reliability of the assessment. In this context the application of the structural stress (hot-spot), notch stress, notch strain and crack-propagation concepts are discussed through the example of K-nodes used in energetic offshore constructions like oil platforms or wind power plants, presenting the state of the art. While the hot-spot, notch stress and crack-propagation concepts show a good agreement between calculated and experimental results and do not differ significantly from each other, the notch strain concept fails significantly.

Service Life Prediction for Concrete Structures by Time-Depth Dependent Chloride Diffusion Coefficient

This paper uses the time-depth dependent chloride diffusion coefficient obtained from the analytical solution of the nonlinear chloride diffusion equation at nonsteady state to propose a new life prediction model of concrete structures exposed to a chloride environment. The proposed theoretical model treats the chloride diffusion coefficient as a variable dependent on time, depth, and chloride content of concrete rather than a constant as normally assumed. Detailed step-by-step guides to the practical application with this model are provided. Based on the illustrated example, the comparison of the service life prediction calculated by this model and the well-known LightCon model is addressed. However, the proposed model should remain to be verified by using long term field data for the potential failure impacts in the durability design of concrete structures.

Optimization of RC structure performance in marine environment

As a result of extensive research work performed on durability design and long-term performance of concrete structures in marine environments, new procedures for probability-based durability design have been shown to provide a more realistic basis for the analysis. This approach has been successfully applied to several new concrete structures, where requirements for a more controlled durability and service life have been specified. It is commonly assumed that the dominant degradation mechanism for reinforced concrete structures in a marine environment is the corrosion of the reinforcement due to the presence of chlorides. A design approach based on the verification of the serviceability (durability) limit states has been suggested, examples of which are depassivation of reinforcement, cracking and spalling due to corrosion, and collapse due to cross section loss of reinforcement. With this design approach the probability of failure, i.e. the probability of not verifying the limit state, can be determined as a function of time. In the present paper, a probability-based durability performance analysis is used in order to demonstrate the importance of the durability design approach of concrete structures in marine environments. In addition, the sensitivity of the various durability parameters affecting and controlling the durability of concrete structures in a marine environment is studied. Results show that the potential of this approach to assist durability design decisions making process is great. Based on the procedure shown, it is possible to prolong the service life of structures while simultaneously optimizing the final design solution.

Constitutive model for aging thermoviscoelasticity of reacting concrete II: results and discussion

The present paper deals with the aging thermal creep of the reacting elastic concrete. In Part I of the Paper, the theoretical formulation and significance of the proposed unified constitutive model have been presented. This Part II of the Paper focuses on its empirical validation and practical relevance. Theoretical predictions for the creep, recovery and relaxation of hydrating concrete, young cement paste and leaching concrete subjected to different stress or strain histories have been found to be satisfactory. Different observed effects of ambient constant temperature on creep of concrete have been accurately predicted. Absence of any substantial effect of grade of concrete on creep coefficients has been confirmed. The proposed constitutive model is expected to be relevant for creep and durability design of concrete structures. Depending upon the environmental exposure conditions and ambient temperatures, different creep coefficients have been suggested for concrete. Possible areas of future theoretical and experimental research in this field have been identified.

Durability design of concrete structures, Part 2: Modelling and structural assessment

This paper is a sequel to [19] where the theoretical foundations were given for the analysis of durability of concrete structures. An overview of some approaches to modeling the durability of RC structures is given in the paper. Experiences resulting from experimental and numerical research of some influential parameters leading to corrosion of the reinforcement, cracks and delaminating of the surrounding concrete, which leads to the decrease of service life of the RC structure's elements, are described in details. Methodologies of structure evaluation presented in this paper are based on assessment of critical influential parameters and represent a methodology of reasonable maintenance of an engineering construction, i.e. reasonable service life of the structure. The methods are based on analysis of conditions and performance (Condition Rating Method and Performance Rating Method). The results of ratings of concrete structures in the industrial zone of the city of Tuzla are presented in the final part of the paper.

Structural durability assessment of welded offshore K-nodes by different local design concepts

The structural durability design of complex welded structures should not rely only on one single design method but should apply different methods for assuring the reliability of the assessment. In this context the application of the structural stress concept, notch stress concept and crack propagation concept are discussed through the example of K-nodes used in energetic offshore constructions like oil platforms or wind power plants, presenting the state of the art.

Nonlinear relationships between parameters of simplified diffusion-based model for service life design of concrete structures exposed to chlorides

Abstract This paper presents an approach toward performance-based durability design of concrete structures based on a simplified diffusion-based model, which overcomes some of the limitations of the current prescriptive rules of existing design standards. Numerical nonlinear relationships and relative sensitivities between the four parameters that govern the time to corrosion initiation of reinforced concrete structures are determined, including chloride diffusion coefficient, chloride threshold value of reinforcement, concrete cover and surface chloride exposure condition. To achieve a specified design life, it is found that in aggressive chloride-laden environments: (i) increasing the minimum concrete cover is more effective than selecting a corrosion-resistant steel; (ii) it is necessary to use both high-performance concrete and corrosion-resistant steel; (iii) a relative decrease in the concrete cover has to be compensated by a much greater increase in the corrosion resistance of steel; and (iv) the variations in chloride diffusion coefficient have a large impact on required concrete cover and chloride threshold value, especially in increasingly aggressive environments. These relationships can be used to identify the most relevant parameters and serve as a guide for service life-based design for durable concrete structures.

Long-term analysis of bending moment resistance on pre-cast concrete beams

Durability design of structures is an important part of the design process. A possible method for the durability design is the probabilistic approach considering changes of structural resistance and the load effect during a certain time period. In order to determine stochastic parameters of structural resistance as a function of time, deterioration of materials and the decrease of structural sizes due to environmental effects must be predicted. This paper is mainly focusing on the analysis of the bending moment resistance of pre-cast concrete beams as a function of time. The effect of creep, shrinkage, relaxation, carbonation induced corrosion and deterioration of cross-sectional sizes on the mean value and standard deviation of bending moment resistance were considered. The performed calculation method is illustrated by numerical example on a pre-cast, prestressed concrete beam. In case of the presented beam, the mean value of bending moment resistance decreases 4-6% and its standard deviation increases 200- 350% after 100 years depending on the relative ambient humidity. Results concerning mean value and standard deviation of structural resistance can be used for the purposes of probabilistic durability design. Considering the same safety level as in Eurocode 2, the introduced probabilistic design method delivers about 10% higher load carrying capacity as the application of relevant Eurocode 2 standard in case of the presented beam.

Improving Durability Performance of Reinforced Concrete Structures with Probabilistic Analysis

In recent years, much research work has been performed on durability design and long-term performance of concrete structures in marine environments. In particular, the development of new procedures for probability-based durability design has been shown to provide a more realistic basis for the analysis. This approach has been successfully applied to several new concrete structures, where requirements for a more controlled durability and service life have been specified. For reinforced concrete structures in a marine environment, it is commonly assumed that the dominant degradation mechanism is the corrosion of the reinforcement due to the presence of chlorides. The design approach is based on the verification of durability limit states, examples of which are: depassivation of reinforcement, cracking and spalling due to corrosion, and collapse due to cross section loss of reinforcement. With this design approach the probability of failure can be determined as a function of time. In the present paper, a probability-based durability performance analysis is used in order to demonstrate the importance of the durability design approach of concrete structures in marine environments. In addition, the sensitivity of the various durability parameters affecting and controlling the durability of concrete structures in a marine environment is studied. Results show that the potential of this approach to assist durability design decisions making process is great. Based the crucial information generated, it is possible to prolong the service life of structures while simultaneously optimizing the final design solution.

Numerical Analysis of Moisture Influential Depth in Concrete and Its Application in Durability Design

Determining the moisture influential depth in concrete under drying-wetting cycles is of great interest for investigation of chloride ion transport and thus the initiation of reinforcement corrosion. In this paper, the moisture transport processes during drying and wetting are modeled by diffusion and absorption. A predictor-corrector implicit scheme of finite difference method is used to solve the partial differential equations. The stability of moisture influential depth is then analyzed with the available numerical tool for both initially saturate and unsaturated concretes. The concept of equilibrium time ratio is proposed for drying-wetting cycles by the balance between water loss and intake during drying and wetting. According to this time ratio, drying-wetting cycles are classified into drying-dominated, wetting-dominated, and equilibrium ones. For drying-dominated cycles, the drying front will penetrate gradually into material while the influential depth is determined by wetting; for wetting-dominated cycles, the wetting front will progress into material while the influential depth is determined by drying. This classification has strong engineering implication and can give a more rational division of convection and diffusion zones of chloride ion transport. The case of concrete in marine splash zone is investigated to illustrate the application of influential depth in durability design of concrete structures.

미세균열이 콘크리트의 염소이온 침투에 미치는 영향 III; 배합조건 특성에 따른 미세균열의 특성

초록·키워드 목차 오류제보하기 등록된 정보가 없습니다. ABSTRACT1. 서론2. 실험 프로그램3. 결과 및 고찰4. 결론참고문헌요약

Effect of freeze-thaw cycles on bond strength between steel bars and concrete

The effect of freezing and thawing cycles on mechanical properties of concrete (compressive, splitting tensile strength) was experimentally investigated. According to the pullout test data of three kinds of deformed steel bars, the bond stress-slip curves after freezing and thawing were obtained. The empirical equations of peak bond strength were proposed that the damage accounted for effects of freezing and thawing cycle. Meanwhile, the mechanism of bond deterioration between steel bars and concrete after freezing and thawing cycles was discussed. All these conclusions will be useful to the durability design and reliability calculation of RC structures in cold region.

An Integrated Approach to Durability Design of Steel Structures Against Atmospheric Corrosion

To develop a durability design procedure based on lifetime safety factor method, different dose-response functions based on both ISO standards and the literature are presented for the prediction of the thickness loss due to atmospheric corrosion in metal structures. Finally, serviceability and ultimate limit states are defined for the durability design against corrosion.

Theoretical Approach to Calculate Surface Chloride Content C<sub>s</sub> of Submerged Concrete under Sea Water Laden Environment

The ingress of chloride ions plays a crucial role for service life design of reinforced concrete structures. In view of durability design of concrete structures under marine environment, one of the most essential parameters is the surface chloride content of concrete. With the social and technical backgrounds, the research approach of this study starts with the calculation of the amount of chloride ingredients in normal sea water. The capillary pore structure is modeled by numerical simulation model HYMOSTRUC and it is assumed to be completely saturated by the salt ingredients of seawater. In order to validate this approach, the total chloride content of the mortar and concrete slim disc specimen was measured after the immersion into the artificial sea water solution. Additionally, the theoretical, the experimental and in-situ investigation results of other researchers are compiled and analyzed. Based on this approach, it will follow to calculate the maximum surface chloride content of concrete in the tidal zone, where the environment can be considered as subjected to dry-wetting cycles.

Integration of durability with structural design: An optimal life cycle cost based design procedure for reinforced concrete structures

The durability design of concrete structures is traditionally based on implicit and prescriptive requirements for materials, material constituents and structural dimensions. With the use of such rules, it is however not possible to visualize an explicit relationship for durability over the lifetime of a structure and determine what constitutes acceptable durability at an optimum cost. An explicit durability design procedure for the design of reinforced concrete structural elements is presented in this paper. The procedure attempts to directly integrate considerations of durability into the structural design process while ensuring lifetime cost optimization. The evaluation of durability is made on the basis of service life which is determined based on the principle of exceedance of defined limit states – a concept commonly used in structural design. Two limit states for corrosion of reinforcement induced by chloride ingress from sea water are used. The service life decides the magnitude and timing of future costs incurred during the design life of the structure. Tradeoffs between initial costs and future costs are examined to determine the optimum design alternative from a life cycle cost perspective. Further the influence of various design and environment variables on the life cycle cost and hence durability of the structure is also evaluated.

Concepts and requirements of durability design for concrete structures: an extensive review of CCES01

Acquiring enough durability for concrete structures in their design phase is a crucial step against unexpected deterioration during their service life. This article gives an extensive and in-depth review of the first Chinese national guide, CCES01-2004, destined exclusively for durability design of concrete structures. Based on the state-of-art knowledge on durability and in place experiences, this guide formulates its durability requirements from several fundamental concepts: environmental action, durability limit state and structure service life. For each environmental class and expected service life, the guide details its requirements on raw material constituents, concrete curing conditions, material performance as well as structure details, in particular the concrete cover to reinforcement steel. The relevant quantitative requirements are compared with those from other codes such as EuroCode2, EN206, ACI318 and CSA. As a special case, the durability of post-tensioned prestressed concrete structures is treated separately and a multi-layer, environment-based strategy is proposed for the prestress tendon and anchorage protection. At the end, the remaining crucial questions are brought forth for durability design of concrete structures.

Fatigue testing under variable amplitude loading

There are many publications about variable amplitude test results. However, very often information on load–time histories, spectra and testing details are missing. This fact does not allow the interpretation of test results with regard to fatigue lifing and structural durability design. Therefore, this paper aims at presenting how spectra and test conditions should be clearly described and how statistics can be applied when variable amplitude test results are presented.

Structural durability design optimisation and its reliability assessment

Mechanical fatigue subject to external and inertia transient loads in the service life of mechanical systems often leads to structural failure due to accumulated damage. A structural durability analysis that predicts the fatigue life of mechanical components subject to dynamic stresses and strains is a computer-intensive, multidisciplinary simulation process, since it requires the integration of several computer-aided engineering tools and large amounts of data communication and computation. Uncertainties in geometric dimensions result in the indeterministic fatigue life of a mechanical component. Uncertainty propagation to structural fatigue under transient dynamic loading is not only numerically complicated but also extremely expensive. It is, therefore, a challenge to develop a durability-based design-optimisation process and reliability analysis to ascertain whether the optimal design is reliable. The objective of this paper is to develop an integrated CAD-based computer-aided engineering process to effectively carry out design optimisation for structural durability, yielding a manufacturable, durable, and cost-effective product. In addition, a reliability analysis is executed to assess the reliability of the deterministic optimal design.

Prediction of diffusivity of concrete based on simple analytic equations

Proposed is a simple analytic model that can predict realistically the diffusivities of concrete and mortar. The basic concept of the model comes from the relation between the diffusivities and the microstructure of concrete. The microstructure that affects the diffusivity includes the interfacial transition zone (ITZ) between aggregates and cement pastes as well as the microstructure of cement paste itself. The general effective media (GEM) equation was introduced to derive the diffusivity of cement paste. The effective diffusivity of concrete is derived on the basis of the composite sphere assemblage model, which considers the diffusivities of both ITZ and cement paste. The main parameters in the proposed model are the microstructural properties of cement paste such as capillary porosity and pore structure parameter, solid phase diffusivity, aggregate volume fraction, and interfacial zone properties. To validate the proposed model, many series of concrete and mortar specimens have been tested to measure the diffusivities. The major test variables include the water-to-binder ratios, the types and amount of mineral admixtures on the diffusivities. The effects of compressive strength, water-to-binder ratio, and mineral admixtures have been investigated comprehensively. The comparison of the proposed theory with the test data exhibits reasonably good correlation. The proposed model allows more accurate prediction of diffusion process and, thus, more realistic durability design of concrete structures.

コンクリート内の温・湿度状態に及ぼす環境条件の影響に関する基礎的研究

Durability design of concrete structures is now one of the main issues in the field of structural engineering. Since the durability depends mainly on the pore structures of concrete and the environment to which concrete is exposed, data of concrete temperatures and moisture content are essential for the durability design. For collecting the data, concrete specimens with different water-cement ratios were exposed in the open-air. In this paper, the experimental results of the temperatures and moisture content in concrete are reported and they are briefly discussed in relation to the climatic conditions, the sheltered condition and the pore structure.