Safety Assessment Of Concrete Structures Research Articles

Analytical method for predicting mode I crack propagation process of concrete under low-cycle fatigue loading

The fatigue failure of concrete structures is preceded by the formation of microcracks and the propagation of macrocracks. Therefore, the fatigue fracture properties of concrete should be investigated thoroughly to guarantee the safety of structures. In this paper, an analytical method for predicting the mode I crack propagation in concrete under low-cycle fatigue loading is proposed according to the fictitious crack model, where the fatigue tension-softening constitutive relationship is introduced, and the initial fracture toughness-based crack propagation criterion is applied. The fatigue crack propagation process can be determined by solving two governing equations. To validate the effectiveness of the method, the fatigue crack propagation in three-point bending (TPB) beams is calculated, and the results are compared with the simulated and experimental results. It is shown that, although the linearization assumption of the crack opening displacement (COD) along the depth direction leads to slight differences between the analytical and simulated results, there is still a reasonable agreement between the analytical and experimental results. The effectiveness of the analytical method is verified. Therefore, when Young’s modulus, initial fracture toughness, and fatigue tension-softening constitutive relationship are determined, the mode I fatigue crack propagation in concrete can be predicted based on the analytical method. It is expected that the method will contribute to the safety assessment of concrete structures under low-cycle fatigue loading.

A hybrid FE-based predictive framework for ASR-affected structures coupled with accelerated experiments

Engineers are often confronted with the challenge of performing a rigorous safety assessment of concrete structures affected by alkali silica reaction (ASR). Such an endeavor is often accompanied by accelerated expansion tests to simulate the aging process. This paper proposes an integrative framework to link test results with finite element analyses in order to predict future response. This hybrid approach is further enhanced through a probabilistic framework.As a vehicle for this approach, tests performed on large reinforced concrete panels subjected to accelerated ASR expansion are used, and predictive response made through an uncertainty quantification paradigm. Finally, safety is quantified through developed fragility functions. The proposed methodology could be expanded as a prognosis tool to other applications where future response of ASR affected structures is sought.

Safety analysis and reliability assessment of engineering structures – The success story of SARA

AbstractThe concept for the safety assessment of concrete structures integrating nonlinear finite element analysis with stochastic and reliability technology into an advanced engineering tool is presented. The basic aim of the stochastic nonlinear analysis is to calculate the safety index (and failure probability) of an existing engineering structure, which characterizes its reliability. The nonlinear solution enables a realistic estimation of the structural response statistics to be obtained (failure load, deflections, cracks, stresses, etc.). The development of possibility of randomization for such computationally intensive problems was part of the project Safety Analysis and Reliability Assessment of Engineering Structures (SARA). Latin hypercube sampling has been used in SARA in order to keep the number of required simulations at an acceptable level. Statistical correlation, which is important for a realistic solution, was also imposed in SARA by using a stochastic optimization technique called simulated annealing. The sensitivity of results to random input parameters can be evaluated using nonparametric rank‐order correlation coefficients. The presented project SARA focusing on the safety assessment of engineering structures supersedes the usual methods based on simplified formulas. SARA supports a higher level of decision‐making process in bridge administration and maintenance of transport macrostructure. The object of this article is to present the diverse developments of the project SARA and to honor Professor Konrad Bergmeister, who was the frontrunner and chair of SARA and was mainly responsible for the SARA project initiation and its fruitful and amazing developments.

Outline of “Assessment Guideline for the Local Failure of Structures Subjected to Impact Actions” and “Safety Assessment of Concrete Structures Subjected to Explosion” by JSDFE

Outline of “Assessment Guideline for the Local Failure of Structures Subjected to Impact Actions” and “Safety Assessment of Concrete Structures Subjected to Explosion” by JSDFE

Probabilistic design of fibre concrete structures

Advanced computer simulation is recently well-established methodology for evaluation of resistance of concrete engineering structures. The nonlinear finite element analysis enables to realistically predict structural damage, peak load, failure, post-peak response, development of cracks in concrete, yielding of reinforcement, concrete crushing or shear failure. The nonlinear material models can cover various types of concrete and reinforced concrete: ordinary concrete, plain or reinforced, without or with prestressing, fibre concrete, (ultra) high performance concrete, lightweight concrete, etc. Advanced material models taking into account fibre concrete properties such as shape of tensile softening branch, high toughness and ductility are described in the paper. Since the variability of the fibre concrete material properties is rather high, the probabilistic analysis seems to be the most appropriate format for structural design and evaluation of structural performance, reliability and safety. The presented combination of the nonlinear analysis with advanced probabilistic methods allows evaluation of structural safety characterized by failure probability or by reliability index respectively. Authors offer a methodology and computer tools for realistic safety assessment of concrete structures; the utilized approach is based on randomization of the nonlinear finite element analysis of the structural model. Uncertainty of the material properties or their randomness obtained from material tests are accounted in the random distribution. Furthermore, degradation of the reinforced concrete materials such as carbonation of concrete, corrosion of reinforcement, etc. can be accounted in order to analyze life-cycle structural performance and to enable prediction of the structural reliability and safety in time development. The results can serve as a rational basis for design of fibre concrete engineering structures based on advanced nonlinear computer analysis. The presented methodology is illustrated on results from two probabilistic studies with different types of concrete structures related to practical applications and made from various materials (with the parameters obtained from real material tests).

Modelling of the compressive strength development of cement mortar with furnace slag and desulfurization slag from the early strength

Replacing natural resources with renewable materials is a very important research topic for sustainable development. Several recycled materials such as furnace slag (S) and desulfurization slag (D) were widely used and applied in concrete or cement mortar. The compressive strength at the 28th day was usually used as design strength for structure. Thus, an assessment of the compressive strength of cement mortar with furnace slag and desulfurization slag from the early strength is desirable to develop. In this study, desulfurization slag that could pass through a No. 4 sieve and furnace slag with a fineness of approximately 4000cm2/g were used to replace the fine aggregate (0%, 10%, 20% or 40%) and cement (0%, 10%, 20% or 40%), respectively, through a volumetric method. The cement mortar thus formulated was then put through a series of compressive strength tests in which the samples were cured at a 23–25°C room temperature and a 75°C high temperature. According to the test results, the compressive strength decreased as the replacement rate of desulfurization slag increased, but increased as that of the furnace slag increased. Using the test results when the replacement rates of D were 0%, 10% and 20%, a hyperbolic function was used to perform a multivariate non-linear regression analysis, thus establishing a compressive strength prediction model for cement mortars of other ages based on the early strength at the age of 7days. From the confirmatory analysis, when the replacement rate of desulfurization slag D=40%, the MAPE (mean absolute percentage error) value of the test sample cured at high temperature was found to be 6.13%, while that for the test sample cured at room temperature was 11.32%. Moreover, when D was 0%, 10% and 20%, the MAPE value for the test sample cured at high temperature was 3.05%–4.47%, respectively, while that for the test sample cured at room temperature was 7.83%–9.17%. Generally speaking, the results delivered by the analytical model established in this study were satisfactory under different conditions. As it is capable of performing a predictive analysis of the compressive strength of cement mortar at other ages based on the early strength at the age of 7days, this model could contribute to the safety assessment of concrete structures during the construction phase.

A numerical method for predicting Young’s modulus of heated cement paste

The evaluation of the mechanical properties of heated cement paste is essential to the safety assessment of concrete structures exposed to elevated temperatures. A numerical method is developed in this paper for predicting the Young’s modulus of heated cement paste with or without silica fume up to 600°C. The initial volume fractions of various constituents and the thermal decomposition of hydration products in cement paste are approximately estimated. A two-phase composite sphere model is then built and a two-step approach is applied to evaluating the Young’s modulus of heated cement paste with thermal decomposition and microcracking effects. Finally, the validity of the proposed numerical method is verified with three sets of experimental data collected from the literature.

Global Safety Factor or Nonlinear Design of Concrete Structures

Abstract The paper focuses on different approaches to the safety assessment of concrete structures designed using nonlinear analysis. The method based on the concept of partial factors recommended by Eurocodes, and methods proposed by M. Holicky, and by the author of this paper are presented, discussed and illustrated on a numerical example. Global safety analysis by M. Holicky needs estimation of the resistance coefficient of variation from the mean and characteristic values of resistance, and requires two separate nonlinear analyses. The reliability index value and the sensitivity factor for resistance should be also identified. In the method proposed in this paper, the resistance coefficient of variation necessary to calculate the characteristic value of resistance may be adopted from test results and the resultant partial factor for materials properties, and may be calculated according to Eurocodes. Thus, only one nonlinear analysis from mean values of reinforcing steel and concrete is required

Structural assessment and reliability analysis for existing engineering structures, theoretical background

The concept presented for the safety assessment of concrete structures integrates nonlinear finite element analysis with stochastic and reliability technology into an advanced engineering tool. The basic aim of the stochastic nonlinear analysis is to calculate the safety index of an existing engineering structure, which characterizes its reliability (and failure probability). The nonlinear solution enables a realistic estimation of the structural response statistics to be obtained (failure load, deflections, cracks, stresses, etc.). The possibility of randomization for such computationally intensive problems is shown. Latin hypercube sampling is used in order to keep the number of required simulations at an acceptable level. Statistical correlation, which is important for a realistic solution, is imposed by using a stochastic optimization technique called simulated annealing. The sensitivity of results to random input parameters can be evaluated using nonparametric rank-order correlation coefficients. The safety index of the analysed structure is calculated from the stochastically obtained structural resistance and expected load distribution using appropriate reliability techniques. The presented approach for the safety assessment of engineering structures supersedes the usual methods based on simplified formulas. It can lead to considerably improved results since the structure is analysed more precisely. Therefore, it supports a higher level of decision-making process in bridge administration and maintenance of transport macrostructure.