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ABSTRACT Energy retrofit of the envelope of existing historical buildings, due to their historical and cultural value, often includes the addition of an interior insulation layer. The new wall configuration [...]

Byline: H. Hens (KU-Leuven, Department of Civil Engineering, Laboratory of Building Physics, Kasteelpark Arenberg, 40, B-3001 Leuven, Belgium, Hugo.hens@buk.kuleuven.be); A. Janssens (University of Ghent, Section of Architecture and Town Planning [...]

ABSTRACT: This study presents experimental analysis and numerical modeling of hygroscopic moisture buffering by paper and books. First, a literature review of moisture transport properties of paper is presented. Experimental [...]

Abstract In a previous paper [Zheng et al., Hygrothermal Performance, Part I; Const Building Mater, Vol. 18, Issue 1, pp. 49-59], the hygrothermal performances of four well-insulated cold zinc roofs [...]

Abstract In order to investigate the hygrothermal performance and durability of well-insulated cold zinc roofs, a total of four cold zinc roofs with a low U-factor [U Keywords: Metallic roofs; [...]

Seismogenic plate boundaries are posited to behave in a similar manner to a densely packed granular medium, where fault and block systems rapidly rearrange the distribution of forces within themselves, as particles do in slowly sheared granular systems. We use machine learning to show that statistical features of velocity signals from individual particles in a simulated sheared granular fault contain information regarding the instantaneous global state of intermittent frictional stick‐slip dynamics. We demonstrate that combining features built from the signals of more particles can improve the accuracy of the global model and discuss the physical basis behind the decrease in error. We show that the statistical features such as median and higher moments of the signals that represent the particle displacement in the direction of shearing are among the best predictive features. Our work provides novel insights into the applications of machine learning in studying frictional processes occurring in geophysical systems. Records of previous earthquakes do not provide adequate data for scientists to predict future earthquakes with sufficient certainty. In this study, we use computer simulations representing earthquakes as frictional slips and record hundreds of scaled earthquakes. We employ machine learning, an artificial intelligence technique, to estimate the fault friction. In machine learning, the computer is trained to establish a relation between emitted seismic signals and fault friction. Subsequently, when the trained model is applied to new seismic data, it can accurately estimate the fault friction. The similarities between our model and field‐scale observations from real faults suggest that an extension of our approach may have potential of estimating the friction of geological faults leading to prediction of real earthquakes. Machine learning estimates the global state of frictional dynamics from velocity of individual particles in a sheared granular faultCombining statistical features built from the signals of several particles improves the accuracy of estimation of machine learning modelApplication of machine learning to granular models provides useful framework for characterizing frictional processes in geophysical systems

We investigate dynamic wave-triggered slip under laboratory shear conditions. The experiment is composed of a three-block system containing two gouge layers composed of glass beads and held in place by a fixed load in a biaxial configuration. When the system is sheared under steady state conditions at a normal load of 4?MPa, we find that shear failure may be instantaneously triggered by a dynamic wave, corresponding to material weakening and softening if the system is in a critical shear stress state (near failure). Following triggering, the gouge material remains in a perturbed state over multiple slip cycles as evidenced by the recovery of the material strength, shear modulus, and slip recurrence time. This work suggests that faults must be critically stressed to trigger under dynamic conditions and that the recovery process following a dynamically triggered event differs from the recovery following a spontaneous event. In the lab instantaneous dynamic triggering requires fault gouge and dynamic strains exceeding 10-6Following triggering there is a recovery process that takes place over multiple stick-slip cyclesWe posit that similar processes may take place in situ

This paper investigates the effect of roofing systems on the humidityinduced corrosion of zinc sheeting in highly insulated zinc roofs. Ten types of roofing systems (U< 0.25 W/(m2K)) were tested in a hot box–cold box apparatus. The measurements and investigations include the relative humidity under the zinc sheeting, the corrosion type, the corrosion product, and the corrosion rate. The influence of a well performing air-vapor retarder below the insulation on the underside corrosion of zinc sheeting is slight for zinc roofs with a good cavity ventilation, but significant if the ventilation is poor. For nonventilated zinc roofs, installing a perfect air-vapor retarder under the insulation only is not sufficient to control the sheeting underside corrosion. Further introducing a dry capillary and sorption active material between the sheeting and the insulation greatly reduces that corrosion.

The Boltzmann transformation method is used to determine the liquid water diffusivity from moisture content profiles as measured in a capillary water absorption experiment. An inter-laboratory comparison for analyzing the reliability of the determination method showed that the inaccuracy in the liquid water diffusivity is caused by scatter in the transformed data and by uncertainty in the boundary conditions at the intake surface and ahead of the steep moisture front. A methodology is proposed based on (1) the evaluation of the validity of the diffusion approach, (2) a simplified handling of the boundary conditions, (3) smoothing of the scattered data and (4) the evaluation of the quality of the determined liquid water diffusivity. For HAM (Heat-Air-Moisture transport) calculations values of the liquid water diffusivity for moisture contents higher than the capillary moisture content are disregarded. The liquid water diffusivity can be described by an exponential function limited at a lower moisture content bound.To describe the moisture diffusivity including liquid water and water vapour transports, a new parametric description of the moisture diffusivity is presented, which shows sufficient flexibility both in the hygroscopic and overhygroscopic ranges. When permeability is calculated from diffusivity, the permeability should monotonically increase with decreasing capillary pressure. In the hygroscopic region it should coincide with the measured water vapour permeabilities.

Implications of moisture in building and construction are of interest to the international community because of their huge economical consequences, including effects on health, maintenance and repair, retrofitting and conservation, as well as on common welfare. The present day knowledge offers a potential to tackle such problems, both in the design process and during the service life of building. In 2001, the European Commission initiated the project ‘‘HAMSTAD’’ (Heat Air and Moisture Standards Development) to propose a better modelling methodology than the traditional Glaser method. HAMSTAD focused on the development of draft standardisation procedures on determination methods of moisture transfer properties and a draft methodology for certification of advanced moisture modelling codes. To stimulate competitiveness and progress, the project was carried out following an ‘open methodology’ instead of a system of deterministic and prescriptive (pre-) standards. This paper outlines the project and highlights the main outputs, serving as an introduction to the following more detailed research papers resulting from that work.

This paper looks at masonry walls insulated outside with an EIFS system. It applies calculation procedures, laboratory testing and field experience to the selection of the materials and the details of the design. Special attention is given to the thermal and hygric response of the walls and to the durability of EIFS applications. The study shows that calculation procedures and measurements cannot only provide confidence in the prediction of the performances but can also give the fundamental information required for the improvement and optimisation of the design.

Non-local and gradient enhanced damage models are able to properly model localization phenomena in quasi-brittle materials. By the introduction of an internal length scale they avoid mesh-size sensitivity in finite element calculations and are capable of describing size effects. To experimentally determine the internal length scale and other damage model parameters, indirect identification methods have to be used. The method presented is based on the Markov estimation procedure, which also permits to evaluate the accuracy and the well-posedness of the identification problem, characterized by the uniqueness and identifiability of the estimated values. This information offers the possibility to compare and optimize the designs of laboratory tests in order to minimize the effect of errors on the estimated values. The indirect determination of the gradient damage parameters based on global response measurements far from the crack on one-size specimens is sensitive to the problem of ill-posedness due the high correlation between the gradient damage parameters, which dominate the localization process. The size effect method can be used as an accurate identification method for the gradient damage parameters, when information on the tensile behaviour is included and a sufficient size range is considered. Local displacement analysis close to the crack provides sufficient information with respect to the identification problem independent of the size of the specimen and gives the most accurate parameter estimations. Copyright © 1999 John Wiley & Sons, Ltd.

Damage evolution in quasi-brittle materials is a complex process in which heterogeneity plays an important role. This heterogeneity may imply that the exact failure mode can be highly dependent upon the precise spatial distribution of initial imperfections. To model this inhomogeneity stochastic distributions of material properties must be used in numerical simulations. However, the use of a stochastic approach does not resolve the issue of the change of character of the governing differential equations during progressive damage. To avoid such a change of character higher order terms, either in space or in time, must be added to the standard continuum description (regularization techniques). A simulation technique that describes the failure process properly must incorporate both a regularization technique and a stochastic description of the disordered continuum. This statement will be substantiated here by presenting finite element analyses of direct tension tests with a standard local damage model and with a nonlocal damage model. The randomness in the damage process will be introduced by considering the initial damage threshold of the continuum damage model as a random field, characterized by a relevant distribution and autocorrelation coefficient function. The response statistics calculated by the Monte-Carlo technique will be presented for two different levels of finite element discretization. The nonlocal and random field formulations both rely on the introduction of a length parameter: the internal length scale in case of the nonlocal continuum and the correlation length for the random field. The effect of the relative variation of the correlation length and the internal length scale will also be discussed.

Nonlocal continuum damage mechanics and random field theory are used to model the stochastic damage behavior of a strain‐softening material with random field properties. The randomness in the damage process is introduced by considering the initial damage threshold and the local strain‐softening behavior as a bivariate random Nataf field, defined by the marginal distributions and correlation matrix. A key component of the model is the introduction of two different length parameters: the characteristic length of the nonlocal damage model and the correlation distance for the random field. The probabilistic nonlocal damage model is illustrated by presenting finite‐element analyses of direct‐tension tests. It is found that the specimen exhibits a structural behavior representing a nonsymmetrical deformation and nonlinear stress‐displacement curve. The influence of the cross‐correlation coefficient between the initial damage and the strain‐softening behavior is discussed. The probabilistic nonlocal damage model is also capable of describing the deterministic and probabilistic size effect of structures.

Separation of harmonics in pulsed neutron source experiments may be effected by measuring the neutron decay at several points of the medium. A pulse generator allowing for the simultaneous recording of four neutron decay curves with a time analyzer having a single detector input is described.