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An important characteristic of self-healing concrete is its ability to regain liquid tightness after it has been damaged. This ability can be tested using water permeability setups. However, a lack of standardized test methods makes it difficult to compare results between different studies. Additionally, the large variation on crack widths between specimens results in a large spread of the permeability results. This, together with all other factors (e.g. internal crack geometry) contributing to the variability of permeability results, should be clearly assessed in order to develop a standardized permeability test. In this study a new active crack width control technique has been developed to significantly reduce the variation on the crack width within a series of specimens, resulting in more consistent permeability results. By analysing permeability results of specimens from test series with different nominal crack widths the factors contributing to variability could be assessed. The two main contributors are the variability on the mean crack width at the crack mouth and the variability on the internal crack geometry. The variability of the mean crack width can induce a 3 times higher variability of the permeability results. In contrast to the crack width, the internal geometry of a crack cannot be determined directly, yet it can cause a difference in permeability of more than 25% for specimens with an identical nominal surface crack width. It can be concluded that when crack widths are actively controlled, the main source of variability on permeability results is the internal geometry which cannot be controlled, regardless of the chosen cracking technique. In order to reduce the variance on the mean permeability, it is proposed to use at least six specimens per series.

Glass is increasingly used to produce structural elements for buildings. For the case of glass beams, a lot of hybrid glass concepts, in which glass is combined with another material (e.g. steel, reinforced concrete, fibre reinforced polymers) were developed and successfully tested to overcome the material’s brittle nature and hence provide post-fracture capacity. Being one of the most widely tested concepts, the reinforced laminated glass beam demonstrates satisfactory load-carrying behaviour, both for statically determinate and indeterminate support conditions, for a variety of environmental conditions (temperature, humidity, etc.) and for several reinforcement percentages and beam sizes. Contemporary building codes do not only require sufficient structural safety and robustness for individual components, but also for parts -or the entire structural system- of a building. For the reinforced glass beam concept, component safety is demonstrated by post-fracture strength and ductile ultimate collapse behaviour. System action can be achieved through plastic hinge formation and stress redistribution. Additional system safety and robustness can be provided through the activation of membrane action in case of horizontal restraints at the beam ends. When a support is (accidentally) removed, membrane action can provide an additional safety mechanism which prevents collapse of the beam system. This paper presents an experimental program to assess the potential of activating membrane action for reinforced laminated glass beams. Statically indeterminate five-point bending tests with horizontal restraints, with or without intermediate support, are performed on 4.3 m long beam specimens. In addition, the effect of reinforcement percentage is investigated.

Recent research has shown that the compressive membrane action (CMA) significantly enhances the load bearing capacity of FRP strengthened concrete beams. It is of great interest to investigate the effect of CMA on the structural reliability of such beams and how to incorporate the benefits of CMA into partial factor based design. Following a CMA model and the probabilistic models of its corresponding design variables, the effect of CMA on the reliability indices of FRP strengthened concrete beams was investigated. A parameter study as well as a sensitivity analysis were also conducted with parameters including properties of FRP and steel reinforcement, concrete properties and geometrical properties. The reliability indices with respect to load ratios i.e. ratios of the variable load to the total loads is selected to quantify the effect of CMA. The results show that the CMA effect significantly improves the structural reliability of FRP strengthened concrete beams. The parameter study indicates that an increase of the concrete strength and yield strain has positive effect on the structural reliability while an increase of FRP ratio, FRP modulus, steel ratio as well as the concrete ultimate strain has an adverse effect. Furthermore, it is found that the variations of the concrete strength, the FRP Young’s modulus as well as the concrete cover have a significant influence on the reliability index; the variations of the ultimate strain of FRP, the yield strain of steel reinforcement and the ultimate strain of concrete have a moderate influence on the reliability index. Finally, an adjusted partial factor for the FRP strength is derived for cases where CMA would already be considered in the design stage.

This study focuses primarily on examining the compressive membrane action (CMA) in FRP (fibre reinforced polymer) strengthened reinforced concrete (RC) beams or one-way slabs. Considering a rigid-plastic mechanism, in combination with strain compatibility and force equilibrium, a model is proposed to predict the load bearing capacity of FRP strengthened RC members when considering CMA. Comparison with experimental tests proves the proposed model to be realistic and effective. A parametric study has been undertaken and an enhancement factor was used to qualify the CMA effect in FRP strengthened RC members. The parameters include the properties of FRP, steel reinforcement and concrete, and the span to depth ratio. The results indicate that CMA can effectively enhance the load bearing capacity of FRP strengthened RC members. Results also indicate that the effect of CMA increases with the increase of FRP area, steel reinforcement ratio, strength and ultimate strain of concrete but decreases with increasing span to depth ratio.

A lot of ‘hybrid’ structural glass beam concepts were developed in the past years to overcome the brittle failure behaviour of glass. These beams possess a safe failure behaviour through post-fracture strength and ductility. Promising is the concept of reinforced laminated glass beams in which stainless steel reinforcement sections are included in the glass laminate and provide a post-fracture load-carrying mechanism. This type of beams was extensively tested in three- and four-point bending for a variety of environmental conditions (e.g. temperature and humidity), geometrical scale, reinforcement percentage and element robustness. The concept proved to be satisfying. In addition to element safety, today’s buildings also require significant system safety. This paper presents an experimental test programme in which the load-carrying behaviour of statically indeterminate reinforced laminated glass beams is investigated. The beam specimens were tested in five-point bending (three supports and two load points) at 23 °C and 60 °C, at a humidity level of 55%. In addition, two different reinforcement percentages were investigated. The beams illustrated satisfying failure behaviour in all cases, proving the effectiveness of applying reinforced laminated glass beams in statically indeterminate systems. The effect of temperature is primarily observed in the fractured and plastic phases. There, the specimens at 60 °C illustrated lower bending stiffness and slip of reinforcement, which resulted in a lower post-fracture strength. The temperature effect was larger for the beams with high reinforcement percentage. The load-carrying behaviour and load redistribution were highly dependent on the reinforcement percentage. A higher reinforcement percentage resulted in higher bending stiffness in all phases of the model. In addition, a higher initial failure load, yield point and post-fracture strength was achieved. Finally, also a different collapse mechanism was observed for both tested reinforcement percentages.

In case of existing concrete structures, the estimation of the characteristic strength values from limited data is a difficult, but important task. There are currently different commonly used estimation methods available, among which the classical coverage method, a Bayesian procedure with vague prior distributions (as mentioned in EN 1990) and the method described in EN 13791. There exists however currently no comprehensive framework in order to quantify the influence of these concrete strength estimation methods on the safety assessment of existing structures. In order to analyse this effect, a previously developed semi-probabilistic partial factor approach for the evaluation of existing structures is considered herein, namely the Adjusted Partial Factor Method. The influence of the different concrete strength estimation methods on the safety level of existing concrete columns is investigated, considering both the application of unchanged partial factors compared to new structures and partial factors adjusted according to the Adjusted Partial Factor Method. The performance of the different estimation methods are evaluated and compared using Monte Carlo simulations and FORM analyses. The relative performance of the estimation methods seem to be rather independent of the partial factor approach applied, however the Adjusted Partial Factor Approach allows to achieve a coherent performance with respect to a target reliability index and alternative reference period. The performance of the classical coverage method and a Bayesian method with vague prior information are comparable and yield a higher safety level when more than 5 test samples are considered. In case only very few concrete samples are used for the assessment (i.e. 3–5), the EN 13791 yields a comparable safety level, mainly due to the reduced variability with respect to the estimation error. Finally, the analysis also showed that for the investigated situation, taking more than about 8 test samples into account does not lead to an increase in assessed safety level.

Bayesian statistics can be used in order to determine the characteristic value of an unknown distribution based on a limited number of test samples. In cases where no previous test results are available, most often a Bayesian method based on vague prior information is used. The assumption of a vague or uniform prior results in a conservative approach in cases where only a limited number of test results are available. However, in case of concrete, prior information on concrete strength can be found in literature or country-specific prior information can be determined. Therefore, the use of a combined vague–informative prior is of particular interest, more specifically in the form of scaled inverse- χ 2 distributions that can be used for updating the standard deviation of the strength distribution of concrete. The differences between the use of a vague and a combined vague–informative prior are investigated through Monte Carlo simulations. Because prior information is taken into account, the uncertainty regarding the standard deviation of the predictive strength distribution is significantly reduced.