Robby Caspeele

Development of reinforced and posttensioned glass beams: review of experimental research

The use of structural glass in buildings is a growing trend, especially with glass beams, which are increasingly used to support roofs, floors, and glazed facades. However, beams consisting of glass laminates only expose a brittle behavior. To overcome this, research has been performed during the last decade to create structural glass beams with enhanced failure behavior. Among a variety of developments, the application of concepts obtained from concrete construction is very promising. Reinforced and posttensioned glass beams were developed and investigated, yielding good results with respect to failure behavior. This paper gives an overview of the research performed on both types up till now. For reinforced glass beams, categorization is made according to the different reinforcement materials. Although remarkable differences in structural performance exist between the different approaches, the majority of the concepts illustrated an enhanced failure behavior, characterized by significant postfracture strength and sufficient ductility. This enhanced robustness on element level is a huge step forward for the application of structural glass beams in practice. However, additional research and optimization is still required to arrive at practical application.

Full-Probabilistic Analysis of Concrete Beams During Fire

Asimplified full-probabilistic calculation tool is developed which is capable of calculating the bending moment capacity of simply supported beams exposed to fire. It is found that the uncertainty with respect to the reduction factors for the material properties at elevated temperatures and the uncertainty with respect to the concrete cover have a negative effect on the safety level corresponding to the design value of the bending moment capacity calculated according to the Eurocode. Furthermore, the model allows an objective comparison of different design alternatives with respect to the safety level.

Influence of Design Parameters on Tensile Membrane Action in Reinforced Concrete Slabs

Abstract Reinforced concrete slabs are traditionally designed to carry a specified design load for adequate capacity at ultimate limit state (ULS). In case of an accidental event, however, tensile membrane action can be activated to establish an alternative load path, which will delay or prevent the collapse of the structure. As such, this tensile action increases the bearing capacity, safety and, hence, the robustness of structures. However, research on this important strength reserve is scarce and the residual capacity is commonly not taken into account during the design. In previous contributions of the authors, a unique test set-up was developed and described to investigate the tensile behaviour of slabs under large deformations because of the accidental removal of a support. A set of three real-scale reinforced concrete slabs of a total length of 14 m was tested. The experiments provided a unique set of data that was subsequently used to develop and validate a numerical model. In this study, this numerical model was used to perform a parameter study to identify the influence of the most important design parameters: span length, slab thickness and reinforcement (ultimate strain and geometric ratio); the results of the analysis are presented in this article. Further, the boundary conditions were shown to have an important influence on the development of tensile membrane action and this effect was investigated considering different restraint conditions as well as using the finite element model analysis of a frame.

An adjusted partial factor method for temporary structures compatible with the Eurocode framework

The Eurocodes currently do not provide a coherent, straightforward framework for the semi-probabilistic design of temporary structures. Besides the need for suitable target reliability levels, a coherent definition of partial factors is needed in order to adjust them according to the chosen target reliability level and the intended reference period of the temporary structure. Further, attention should be given to the coherency with current Eurocodes in order to avoid conceptual discrepancies between the design of long-term and temporary structures. A framework is presented here in order to derive appropriate partial factors for temporary structures, considering a simplified level II approach. The target reliability level and the reference period are considered as parameters and can be adjusted, so the framework remains valid under alternative economic considerations or requirements for human safety. Further, a set of easy-to-use graphs are provided for implementing the proposed procedure in practical standards. Finally, a framework is presented to adjust the target reliability index, considering human safety and economic criteria in case of temporary structures.

Assessment of the Safety Level of Concrete Slabs during Fire

During the last decades research has provided many new insights in the structural behavior of concrete structures subjected to fire. However, most studies and also the semi-probabilistic design methods in the Eurocode EN 1992-1-2 focus on the maximum time of fire resistance, without mentioning the impact of fire on the safety level of the structure. In order to assess the effect of fire on the safety level of concrete slabs, a full-probabilistic model is developed, using Monte Carlo simulations for modeling the uncertainty regardind the bending moment capacity. Results indicate that the calculated safety level is highly sensitive to the uncertainty of temperature effects on material properties. Furthermore, it is shown that the safety level at the fire resistance time is not the same for all the design approaches mentioned in EN 1992-1-2. Also, a generalized target value for the safety index beta during fire is proposed, which allows for an objective comparison of the fire resistance time for different design alternatives.

Modelling of Long-Term Loading Tests on Reinforced Concrete Beams

During the period 1967-1985 the Magnel Laboratory for Concrete Research participated in an extensive Belgian research campaign with respect to the influence of creep and shrinkage on the long-term behaviour of reinforced and prestressed concrete beams. This research campaign, jointly conducted at several Belgian research institutes, comprised the investigation of concrete and reinforced concrete beams (phase 1), prestressed concrete beams (phase 2) and partially prestressed concrete beams (phase 3). The main aim of the research campaign was the determination of the long-term behaviour subjected to permanent loads, considering the influence of the magnitude of the loads, different reinforcement ratios and/or prestressing degrees and/or different cross-sectional shapes. These results were obtained by a joint collaboration of 4 Belgian research institutes, each focussing on a different reinforcement ratio and reinforcement arrangement. With respect to the reinforced concrete beams (phase 1), at each institute 12 beams were tested in a 4point bending configuration, namely 2 static tests at 28 days and 10 long-term tests with a duration of 2 to 4 years, considering different loading levels. In this contribution some results of the reinforced concrete beams (phase 1) will be documented and analysed, comprising the results obtained on 48 reinforced beam specimens with a length of 3.4 m (span of 2.8 m) and cross-section of 0.28 m x 0.15 m. A cross-sectional calculation tool developed at our department – incorporating the current creep and shrinkage models in standards and guidelines – will be employed in order to investigate the accuracy of the available models with respect to their ability to predict the structural behaviour of the documented reinforced concrete beams.

Quantitative comparison of estimation methods for determining the in situ characteristic concrete compressive strength

Abstract When assessing existing concrete structures, the estimation of the characteristic strength values from limited data is a difficult, but important task. Currently, there are different methods available in order to obtain such an estimate. First of all, the classical coverage method can be used for determining the characteristic in situ compressive strength. Otherwise, based on the ISO 12491, ISO 13822 and ISO 2394, the characteristic strength may also be determined using a prediction method which is referred to as a “Bayesian procedure with vague prior distributions”. Finally, the assessment can also be based on the rather recent European standard EN 13791. The performance of these three different estimation methods is compared and evaluated in a probabilis tic way, using numerical Monte Carlo simulations. Furthermore, some suggestions for improvement with respect to the European Standard EN 13791 are provided and evaluated.

Contemporary Analysis and Numerical Simulation of Revisited Long-Term Creep Tests on Reinforced Concrete Beams from the Sixties

The stresses and deformations in concrete change over time as a result of the creep- and shrinkage deformations of concrete. Different material models are available in literature in order to predict this time-dependent behaviour. These material models mostly have been calibrated on large datasets of creep specimens. In order to verify the accuracy of the contemporary material models with respect to the prediction of the creep behaviour of reinforced concrete beams, a cross-sectional calculation tool which employs the age-adjusted effective modulus has been developed and used to analyse an original set of 4 year-long creep data on reinforced beams from the 1960’s. Six commonly used material models for the prediction of creep and shrinkage are considered in the current investigation: CEB-FIP Model Code 1990–1999, fib Model Code 2010, the model of EN1992-1-1, model B3, the Gardner Lockmann 2000 model, and ACI 209. The data on reinforced beams relates to an experimental investigation in collaboration with six major research institutes in Belgium. From 1967 until 1972 thirty-two reinforced beams with different reinforcement ratios were subjected, up until 4.5 years, to different stress levels in a four point bending configuration with a span of 2.8 m. In this paper a comparison between the measurements and the calculated deflections and strains is reported. Further, the deflections were also predicted using the contemporary creep models in combination with the nonlinear creep correction factor provided in EN1992-1-1, since the maximum concrete stresses in the beams were outside the service stress range of each of the models. Correcting for the nonlinearity of the creep coefficient significantly improves the calculated deflections. The most accurate predictions of the deflections at early age were obtained by the model of fib Model Code 2010. The Gardner Lockmann 2000 model exhibits the highest accuracy with respect to deflections at the end of loading and with respect to the creep rate.

A Parametric Study on Concrete Columns Exposed to Biaxial Bending at Elevated Temperatures Using a Probabilistic Analysis

Concrete columns exhibit a loss of both strength and stiffness during fire. The current contribution focusses on the fire performance of concrete columns subjected to biaxial bending in combination with axial loads, as such information is rarely available in literature. First, the second-order effects are quantified using a numerical tool. In Eurocode 2, the most important parameters which influence second-order effects of columns during fire are the slenderness ratio, fire duration as well as the magnitude of the axial loading. The influences of these parameters are investigated using a parametric study. Additionally, from the viewpoint of fire safety and structural reliability, uncertainties should be incorporated in the second-order analysis in order to achieve reliability-based design guidelines. Hence, the numerical tool is further developed in order to take into account uncertainties. Furthermore, the tool is validated using the Eurocode provisions and existing experimental data, while considering an ISO 834 standard fire. Finally, examples are given for the fire resistance design of concrete columns.

Decision support tool on investments in life safety based on sampling theory

Abstract For decisions related to investments in societal safety and health, it is often difficult to balance the discretionary competence of decision-makers with theoretical optimum levels of investment. While removing day-to-day decisions about risk from the political arena would arguably result in better decisions, a full depoliticisation is not desirable since public and private risk preferences cannot simply be neglected without negatively affecting the perception of risk and inducing a democratic deficit. Therefore, a decision-making tool has been developed which allows for narrowing the scope of possible decisions for the decision-maker, based on predetermined maximum acceptable deviations from the theoretic optimum investment level. These maximum acceptable deviations should be established upfront on a general basis and may subsequently be applied on a case-by-case basis. In this paper, the basic calculation concepts are explained and a detailed example study is presented in which limits for the target safety level of concrete slabs are determined under some specific considerations.