Numerical study on coupled thermo-mechanical processes in Äspö Pillar Stability Experiment

This paper presents a study of the full three-dimensional thermo-mechanical (TM) behavior of rock pillar in Äspö Pillar Stability Experiment (APSE) using a self-developed numerical code TM-EPCA^3D. The transient thermal conduction function was descritized on space and time scales, and was solved by using cellular automaton (CA) method on space scale and finite difference method on time scale, respectively. The advantage of this approach is that no global, but local matrix is used so that it avoids the need to develop and solve large-scale linear equations and the complexity therein. A thermal conductivity versus stress function was proposed to reflect the effect of stress on thermal field. The temperature evolution and induced thermal stress in the pillar part during the heating and cooling processes were well simulated by the developed code. The factors that affect the modeling results were discussed. It is concluded that, the complex TM behavior of Äspö rock pillar is significantly influenced by the complex boundary and initial conditions.     

Analysis of Äspö Pillar Stability Experiment: Continuous thermo-mechanical model development and calibration

The paper describes an analysis of thermo-mechanical (TM) processes appearing during the Äspö Pillar Stability Experiment (APSE). This analysis is based on finite elements with elasticity, plasticity and damage mechanics models of rock behaviour and some least squares calibration techniques. The main aim is to examine the capability of continuous mechanics models to predict brittle damage behaviour of granite rocks. The performed simulations use an in-house finite element software GEM and self-developed experimental continuum damage MATLAB code. The main contributions are twofold. First, it is an inverse analysis, which is used for (1) verification of an initial stress measurement by back analysis of convergence measurement during construction of the access tunnel and (2) identification of heat transfer rock mass properties by an inverse method based on the known heat sources and temperature measurements. Second, three different hierarchically built models are used to estimate the pillar damage zones, i.e. elastic model with Drucker–Prager strength criterion, elasto-plastic model with the same yield limit and a combination of elasto-plasticity with continuum damage mechanics. The damage mechanics model is also used to simulate uniaxial and triaxial compressive strength tests on the Äspö granite.     

The Äspö pillar stability experiment: Part I—Experiment design

The Äspö pillar stability experiment was carried out to examine the failure process in a heterogeneous and fractured rock mass when subjected to coupled excavation-induced and thermal-induced stresses. The rock pillar was created by the excavation of two adjacent large-diameter boreholes. The pillar was loaded by a combination of excavation-induced stresses and heating of the surrounding rock by a rectangular heater pattern. The experiment was designed using the observation design method. The characterzation of the experiment volume showed that the experiment was located in a fractured water-bearing rock mass that was considered typical for the Äspö Hard Rock Laboratory (Äspö HRL) and for the Fenno-Scandinavian shield. Scoping calculations using two- and three-dimensional elastic stress analyses were carried out to reduce the uncertainty for the far-field in-situ stresses, establish the geometry for the access tunnel that would provide a elevated uniform stresses in the floor of the tunnel, and determine the optimum width of the pillar. It was concluded, based on the rock mass characteristics, that a 1 m-wide pillar formed by two 1.75 m diameter boreholes would meet the design objectives. Thermal modelling showed that thermally induced stresses in the pillar were adequate to elevate the pillar stresses above the stress magnitude required to initiate failure.Acoustic emission, displacement, and thermal monitoring systems were installed according to the experiment design without problems. No sensors were lost over the three month duration. After the experiment was completed, a laser scan of the pillar revealed the extent of the damaged pillar. The experiment commenced in January 2002 and was successfully completed in 2006.     

Numerical modeling for the coupled thermo-mechanical processes and spalling phenomena in spPillar Stability Experiment (APSE)

In this paper, the coupled thermo-mechanical (TM) processes in the sp Pillar Stability Experiment (APSE) carried out by the Swedish Nuclear Fuel and Waste Management Company (SKB) were simulated using both continuum and discontinuum based numerical methods. Two-dimensional (2D) and three-dimensional (3D) finite element method (FEM) and 2D distinct element method (DEM) with particles were used. The main objective for the large scale in situ experiment is to investigate the yielding strength of crystalline rock and the formation of the excavation disturbed/damaged zone (EDZ) during excavation of two boreholes, pressurizing of one of the boreholes and heating. For the DEM simulations, the heat flow algorithm was newly introduced into the original code. The calculated stress, displacement and temperature distributions were compared with the ones obtained from in situ measurements and FEM simulations. A parametric study for initial microcracks was also performed to reproduce the spalling phenomena observed in the APSE.     

The dynamic response of structures subject to excitation by moving mass systems: part 1—basic formulation

A brief review is presented of methods of analysis of dynamic systems, including direct integration methods and mode superposition techniques and concepts associated with these methods. The component element method is then employed to model the problem of masses moving over continuous structures. The time-varying relationships between the moving masses and the structures are expressed via component elements, e.g. springs, dampers, stops, etc., connecting the two. Central to the analysis is a change of basis whereby the generalized masses of the structure are uncoupled, and an explicit numerical scheme for direct integration of the equations of motion. The validity and accuracy of this approach are demonstrated by analyses of comparatively simple systems. Its generality and versatility are demonstrated by combining it with finite element techniques. By incorporating finite element methods, the analysis of very complex structures subjected to complex systems of live loads is possible.     

“Virtual Design Studio”—Part 2: Introduction to overall and software framework

The “Virtual Design Studio (VDS)” is a software platform for integrated, coordinated and optimized design of building energy and environmental systems. It is intended to assist management, architectural and systems design teams throughout the early to detailed building design stages as analyzed in Part 1 (DOI: 10.1007/s12273-013-0110-2). This paper presents an overview of the VDS design and method of software implementation, including system composition, architecture, graphical user interface (GUI), and simulation solver integration. A VDS user workflow is also illustrated with a simplified design example.     

Study of convective phenomena inside cavities coupled with heat and mass transfers through porous media—application to vertical hollow bricks—a first approach

Building structures often contain cavities or strips of air. Because of this, it is difficult to describe the transfer phenomena that are in fact heat transfers (conductive, convective and radiative), as well as mass transfers through porous media. Numerous studies have dealt with each of these transfers separately but few have managed to describe the interrelation between them. This paper represents an initial approach to the problem, by attempting to describe the influence of the moisture level on heat transfers occuring through hollow vertical terra-cotta bricks. A theoretical modeling of exchanges has been carried out in order to determine radiative and convective exchanges coefficients. A mass exchange coefficient has then been deduced. The results obtained show a high sensitivity of the heat flux to the moisture level of the surroundings.     

A damage model to predict the durability of bonded assemblies – Part II: Parameter identification and preliminary results for accelerated ageing tests

A new damage model has been developed in order to predict the durability of adhesively bonded joints. This model, whose theoretical basis is outlined in a previous paper (part I), takes into account both bulk and interfacial damaging behaviours as well as their interactions. The present paper (part II) is dedicated first to describing a parametric study in which we attempted to understand the physical meaning of the model parameters and second to elaborating on an identification procedure for the theoretical parameters. Preliminary results are presented for accelerated ageing tests.     

Occupant Tenability in Single Family Homes: Part I—Impact of Structure Type,Fire Location and Interior Doors Prior to Fire Department Arrival

This paper describes an experimental investigation of the impact of structure geometry, fire location, and closed interior doors on occupant tenability in typical single family house geometries using common fuels from twenty-first century fires. Two houses were constructed inside a large fire facility; a one-story, 112 m², 3-bedroom, 1-bathroom house with 8 total rooms, and a two-story 297 m², 4-bedroom, 2.5-bathroom house with 12 total rooms. Seventeen experiments were conducted with varying fire locations. In all scenarios, two bedrooms had doors remaining open while the door remained closed in a third bedroom immediately adjacent to the open door bedrooms. Temperature and gas measurement at the approximate location of a crawling or crouching trapped occupant (0.9 m from the floor) were utilized with the ISO 13571 fractional effective dose (FED) methodology to characterize occupant tenability up to the point of firefighter intervention. The FED values for the fire room were higher for heat exposure than for toxic gases, while target rooms reached highest FED due to CO/CO₂ exposure. The closed interior door decreased FED significantly, with the worst case scenario resulting in a 2% probability of receiving an incapacitating dose compared to the worst case scenario for an open bedroom of 93% probability of receiving an incapacitating dose. In fact, in 7 of the 17 experiments, the closed interior door resulted in a less than 0.1% chance of an occupant receiving an incapacitating dose prior to firefighter ‘intervention.’     

New Housing in Old Beijing:a Comparative Survey of Projects Completed to Date——Beijing’s Old and Dilapidated Housing Renewal(Part.V)

This article summarizes a study of eight neighbor-hood renewal projects implemented in the old city of Beij-ing The survey aimed to review the actual constructionand inhabitation emerging from Beijing’s housing renew-al program.The selection of project case studies was bas-ed on their being partially or fully completed and occu-pied,thus allowing signeficant observation of the envi-ronment as actually used and discussed by the residents.They include examples of early experimental pilot proj-ects completed before 1991 as well as large projects builtunder Phase I of the broadened renewal program.Inmost cases,later phases of the projects are still underconstruction.Despite the early and incomplete status ofthe program,certain trends have emerged.This articledraws attention to some critical differences between theinitial expersmental approach and the more recent,larg-er—scale approach reflected in the Phase I projects com-pleted so far.