When a concrete slab is excessively loaded due to an accidental event, compressive membrane action can be activated in order to generate an alternative load transfer to the remaining supports, which can considerably enhance the load‐carrying capacity. This can increase the structural reliability of the components, delay or even prevent a progressive collapse and consequently increase the robustness of concrete structures. Although the beneficial effects of compressive membrane action in reinforced concrete slabs have been recognized for decades, only limited research has been focusing on this effect in prestressed concrete members, like hollow core slabs. Therefore, a novel real‐scale test set‐up has been developed in order to assess this phenomenon in real‐scale hollow core slabs. The results indicate that, despite the presence of the large hollow cores, compressive membrane action can significantly improve the load‐carrying capacity of hollow core slabs under excessive loading. In parallel, a numerical finite element model has been established in order to model the structural behavior (i.e., compressive membrane action) as per the investigated test program. The model was able to correlate the results from the experiments very well, and emphasized the large influence of the concrete tensile strength on the ultimate failure load of concrete hollow core slabs in compressive membrane action.
Although traditionally the fire resistance rating of concrete elements is determined through standardized tests or tabulated data, there is a growing trend towards the use of performance-based approaches to evaluate structural behaviour during or after a fire. The safety format to be applied with these advanced numerical evaluations is however unclear. In this paper, the applicability of the concept of a global resistance factor (GRF) safety format is explored for simply supported concrete slabs exposed to the Eurocode parametric fire curve for a wide range of parameters. The safety of the slab is evaluated in relation to its ability to withstand a complete burnout scenario, i.e. its ability to resist the applied loads throughout the entire duration of a fire including the cooling phase. Using a full-probabilistic model, the required GRF is numerically derived for a specified target safety level in case of fire. Additionally, a calculation method is provided which allows to determine the GRF of fire exposed slabs for any given compartment through the use of a reference compartment and equivalency equations.
Thermal conductivity and specific heat of concrete are highly influential parameters for the heat transfer into the material during fire exposure. Reviewing the available literature has shown that there is a large scatter in the data for these thermal parameters. To quantify that uncertainty, novel probabilistic models for thermal conductivity and specific heat of concrete at elevated temperatures are developed.Analysis of available experimental data indicates that a temperature-dependent Gamma distribution can be recommended for both thermal properties. Closed-form equations for the temperature-dependent mean and standard deviation are derived. Thus, for both the thermal conductivity and the specific heat, a continuous probability distribution as a function of temperature is obtained, which can be easily implemented in numerical simulations. Using the example of the probabilistic analysis of a simply supported concrete slab exposed to the standard fire, the models are compared with the commonly used deterministic representation of the thermal properties. It is shown that the calculated probabilities of failure using the deterministic models are an order of magnitude lower and therefore unconservative. This analysis suggests that accounting for the uncertainty in thermal properties for concrete slabs can have a significant effect on evaluating the safety and therefore should not be ignored in cases of high importance.
ABSTRACT. The fatigue behaviour of concrete has become more important for the design of constructions due to the desire to build slimmer structures, which are more sensitive to fatigue loading. This article aims to evaluate and compare the fatigue crack propagation rate in vibrated concrete for four different stress ratios using the Paris-Erdogan law. The data evaluation in this article is based on crack mouth opening displacement (CMOD) measurements from cyclic three-point bending tests on single edge notched beams and from wedge splitting tests on notched cubes, obtained from experiments at Ghent University. For this study, finite element analysis is used to obtain a mathematical relationship between the CMOD and the relative crack length a/W, as well as a relationship between the stress intensity ratio ∆K and a/W. The obtained mathematical relationships were then combined with the measured CMOD values to correlate the test data to the ParisErdogan law. Herein, the crack propagation rate da/dN is plotted against the corresponding stress intensity range ∆K in a log-log graph. In a final step, the Paris-Erdogan law parameters C and m were obtained through linear curve fitting on the data points from the obtained graphs. The parameters C and m are then used to compare and evaluate the fatigue crack behavior in vibrated Citation: Seitl, S., Thienpont, T., De Corte, W., Fatigue crack behaviour: comparing threepoint bend test and wedge splitting test data on vibrated concrete using Paris' law, Frattura ed Integrità Strutturale, 39 (2017) 110-117.
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