Current practice is mostly focused on prescriptive design approaches where the performance of the structure in case of fire is assessed based on its performance in standardized fire tests. Those tests indicate whether the structural member can withstand standardized ISO 834 fire exposure for a certain code specified time. This method however does not provide an explicit safety level. This issue is enlarged even more by the fact that the ISO 834 fire exposure does not represent a natural fire exposure, but a pseudo-worst-case exposure, making the correlation between the standardized fire test results and real-life behaviour of structural members exposed to fire questionable. However, there has been a century-old tradition of standardized fire tests with a lot of experience and infrastructure based on it. For that reason, here, a methodology is presented to obtain more information on the behaviour of structural members exposed to a natural fire from the standardized fire test results by using a Bayesian framework. As an example structure, a simply supported concrete slab is considered. Its failure during the standardized fire test is modelled and the parameters affecting the time when it fails (i.e., parameters affecting the nominal fire resistance time) are determined. The model is then used in a Markov chain Monte Carlo procedure to update parameter distributions based on the measured fire resistance time. Using these updated distributions, a full probabilistic calculation of the performance of the slab considering a natural fire exposure is then conducted to assess the failure probability.
No abstract is provided for this article.
No abstract is provided for this article.
In a finite element formulation for dynamic soil-structure interaction, an absorbing boundary condition is needed to model wave propagation in an unbounded problem domain. When the soil is saturated, its dynamic behaviour can be modelled by means of Biot's poroelastic theory. Based on an analytical study of wave propagation in a saturated poroelastic medium, a frequency-dependent local absorbing boundary condition can be obtained at the expense of spurious reflections for oblique incident waves. Reflection curves are presented for all types of incident wave and varying dimensionless frequencies. Alternatively, the effective energy ratio allows the definition of a measure for the overall efficiency of the absorbing boundary condition. Based on these analytical investigations, good wave-absorbing capabilities of the absorbing boundary condition have been revealed. Encouraged by these results, the absorbing boundary condition is implemented in an irreducible finite element formulation for a compressible pore fluid, as discussed in Part II (Degrande, G. & De Roeck, G., Soil Dynamics & Earthquake Eng., 1993, 12(7), 423-32).
The vibro-acoustic response of built-up structures, consisting of stiff components with low modal density and flexible components with high modal density, is sensitive to small imperfections in the flexible components. In this paper, the uncertainty of the response is considered by modeling the low modal density master system as deterministic and the high modal density subsystems in a nonparametric stochastic way, i.e., carrying a diffuse wave field, and by subsequently computing the response probability density function. The master system’s mean squared response amplitude follows a singular noncentral complex Wishart distribution conditional on the subsystem energies. For a single degree of freedom, this is equivalent to a chi-square or an exponential distribution, depending on the loading conditions. The subsystem energies follow approximately a chi-square distribution when their relative variance is smaller than unity. The results are validated by application to plate structures, and good agreement with Monte Carlo simulations is found.
No abstract is provided for this article.
With double-leaf wall systems such as plasterboard walls, a high sound insulation can potentially be achieved with a relatively low weight. The accurate sound transmission analysis of this type of wall is challenging since the leafs are usually coupled to a common frame, and since the finite dimensions play a role at lower frequencies. Existing analytical models for sound insulation prediction account for the deformation of the wall in an approximate way, while detailed numerical models are computationally very demanding. In this work, a sound insulation prediction model that achieves a high prediction accuracy at a low computational cost is developed. The wall components that display low geometrical complexity, such as the wall leafs and the cavity, are modelled in an analytical way. Sound absorbents in the cavity are modelled as equivalent fluids. The metal studs, which have a highly deformable cross section, are modelled in full detail with finite elements. The sound fields in the sending and receiving rooms are modelled as diffuse; they are rigorously coupled to the deterministic wall model by employing a hybrid deterministic-statistical energy analysis framework. With the resulting room-wall-room model, the airborne sound insulation is predicted for a range of double-leaf plasterboard walls with single, double and triple plating and with different cavity depths. The obtained transmission losses are validated against the results of an extensive set of experimental tests. A very good agreement between predicted and measured transmission loss values is observed. The single number ratings for the airborne sound insulation for nearly all walls differ from the experimental values by 0–2 dB, which is close to the average experimental reproducibility. At the same time, the computational cost is more than three orders of magnitude lower than for recently proposed models of similar accuracy.
This paper deals with the dynamic analysis of multispan simply supported railway viaducts subjected to moving trains. In the analysis, the Sesia viaduct is considered, which is a composite railway bridge consisting of seven isostatic spans. An experimental analysis shows that the modes of adjacent spans are connected because of the weak coupling through the ballast and rails. In this case, a model of the entire viaduct is needed for an accurate prediction of the dynamic response of the bridge during the passage of the train. To reduce the computational cost, two alternatives are investigated: a single-span model with adjusted boundary conditions and a component mode synthesis (CMS) reduced-order model comprising all seven spans. The two models are subsequently used for dynamic train-bridge interaction analysis. The predicted dynamic responses of the viaduct during a train passage with both models are in good agreement with the experimental results. Compared with the single-span model, the coupling between adjacent spans is better represented by the CMS model of the entire viaduct. In practical engineering design, however, the single-span model with adjusted boundary conditions can be used to obtain a reasonably good representation of the dynamic behavior of the bridge.
In this paper, Smeulders' modification of Biot's saturated poroelastic theory is used to account for the presence of a small amount of air in the pores of an unsaturated medium. The influence of the gas phase on the compressibility of the generalized pore fluid is accounted for by a complex effective bulk modulus of the gas phase. This modification is introduced in a spectral element formulation, enabling to model transient wave propagation in layered dry, saturated and unsaturated poroelastic media. The extended application area of the method is illustrated by a numerical example.
The free wave characteristics, i.e. propagation constants and free waves, characterize the dynamic behaviour of periodic structures.For this reason, they may therefore provide a viable alternative to modal characteristics for finite element model updating.The sensitivities of the free wave characteristics to model parameters are required when using a gradient-based optimization algorithm for model updating.This paper investigates the sensitivity of the free wave characteristics to the model parameters.In this paper, an analytical expression of the sensitivities is derived and verified by comparison to results obtained by finite differences in a case study.The resulting sensitivities are compared to those of the modal characteristics to check their use in finite element model updating.In the case considered, the sensitivities of free wave characteristics are higher than those of the corresponding modal characteristics, indicating that free wave characteristics may be an alternative for model updating.
