The effect of sampling volume size on the apparent stiffness of jointed rock mass

Overall mechanical properties of a jointed rock mass are strongly affected by discontinuities – fractures – that naturally occur in rocks. Stochastically-generated discrete fracture network (DFN) modeling, which uses a probabilistic approach to describe the spatial distribution of fractures, such as position, size, or orientation, offers an explicit way to describe geometry of the fracture system. Many in-situ measurements and analyses presented in literature indicate that fractures’ sizes can be adequately represented by the power law probability distribution. The parallel plate model of individual fractures combined with an averaging technique makes it possible to estimate the overall compliance or stiffness of jointed rock mass (Oda et al. [1]). In the present study, a series of numerical simulations of jointed rock mass modeled by DFN and Oda’s approach were conducted to analyze the effect of different sizes of the sampling volume on the overall elastic moduli. The results of the numerical study show that the variance as well as the average of the apparent stiffness decrease as the size of sampling element grows

A General Interpretation of Transition in the Czech Republic (1989-1993)

Fundamental changes in the Czech Republic since Nov 1989 are contended to be brought about by the interplay of the drama of the erosion of the old regime with that of the birth of a new order. When the old order was partly dismantled, society found itself in transitional anomie, which made it possible to gradually build a new order. This transitological view sees transition as a provisional state of affairs constructed by many individuals, groups, communities, & organizations. This provisional situation is characterized by a rich dynamic of social problems, together with an unbalanced & changing distribution of gains & losses. The resulting conflicts become - in successful cases - part of the universe of myth, in which the conflicts are seen as a series of crises/tests that push the society indirectly from the old to the new order. The transition ends when the participants cease to see the current events as provisional. The main task then becomes the normalization of the new order, enforcing its regime & coping with the formerly provisional arrangements that were 'justified' by the apparent anomie

A Simplified Analysis of the Post-buckling Behavior of a Compressed Reinforcing Bar

Recently, a computational methodology based on a sequential multiscale approach, which facilitates numerical simulation of an R/C building demolition has been developed. In this type of analysis, it is necessary to capture the behavior of compressed reinforcement bars until complete rupture, which occurs due to extensive bending in the post-buckling regime. To this end, a simplified analytical model of the post-buckling behavior of a compressed bar is proposed. The simplification consists namely in considering rigid-plastic material behavior, neglecting axial contraction of the central line, and approximating the shape of the deformed central line in the plastic hinges by a circular arch. Consequently, the axial loading force, bar end displacement, and extreme strain can be expressed in relatively simple closed forms. The results obtained with the proposed model show very close agreement with those obtained by a detailed and realistic finite element analysis, which justifies the use of the simplifying assumptions.

Finite element simulation of shear and compact tension tests on timber

The non-linear finite element simulation of the ASTM shear and pre-stressed compact tension tests was conducted. Tested specimens were cut from the glued laminated timber made of European spruce (Picea abies) with the lamina thickness of 10.5 mm and 45 mm. The 2D homogeneous orthotropic constitutive model of the tensile-shear fracture in timber, which has been proposed by the authors, was used. The model calibration was adopted from the authors’ recent experimental study. The numerical results show that the model can adequately reproduce both the experimental response and the crack pattern, which in certain cases comprises of cracking parallel or perpendicular to fibers. Furthermore, the results confirm that the value of the parameter fASTMxy , obtained from ASTM shear test as the maximum attained force divided by the shearing area, represents the averaged stress at the failure plane, while the extreme stress experienced by the material is much higher

Analysis of tunnel excavation based on linear DFN-FEM modelling

Simulations of tunnel excavations have to take into account the natural occurrence of joints and faults in the surrounding rock mass, which dominantly control its mechanical response. In this paper, we present work in progress toward 3D finite element analysis of excavation using equivalent rock-mass properties derived from stochastically generated discrete fracture networks (DFNs). The equivalent stiffness is determined by volume averaging. Presently, we solve the problem linearly for an incremental change of the stress state. The fracture’s stiffness is assumed to depend on the initial normal stress acting in direction normal to it. However, within the solved incremental step, we assume the fracture’s stiffness to be constant. This assumption is acceptable for small stress changes. Since the fractures represented in the DFN model have preferred directions, the equivalent stiffness is anisotropic

RESPONSE AND DAMAGE EVOLUTION OF SINGLE EDGE NOTCHED TIMBER BEAMS UNDER THREE-POINT BENDING

Two groups of small-size single edge notched beams (SENB) made of European spruce (Picea abies) were tested in three-point bending (3PB) until failure under displacement control. The first group comprised of eight solid and two glued laminated (GL) timber beams manufactured with (a) the single edge notch at the bottom of the mid-span and (b) the reduced ligament depth. The second group consisted of four GL timber beams with the single edge notch only. We employed digital image correlation (DIC) to quantify strains and displacements, capture the damage evolution, and track the sequence of failure patterns. In this work, we present response of the beams in terms of load vs. crosshead displacement of the moving crosshead and load vs. crack tip opening displacement (CTOD)

Optimal (Comfortable) Operative Temperature Estimation Based on Physiological Responses of the Human Organism

Problems following the application of optimal operative temperatures estimated on the basis of PMV and the necessity to apply correct values in the new Czech Government Directive No. 523/2002 Code led to experiments based on the physiological human body response instead of solely people’s feelings in a given environment. On the basis of experiments on 32 subjects (university students) it has been possible to estimate: a) the total balance of hygrothermal flows between the human body and the environment, b) the optimal operative temperature as a function of the subject’s activity, c) the thermoregulatory range for each optimal operative temperature, i.e. maximal (category Cmax) limited by the onset of sweating, minimal (category Cmin) limited by the onset of shivering (category C can be applied to naturally ventilated buildings), optimal (comfort level – category A) defined by time constant 0.368 (can be applied to air conditioned buildings), and submaximum (decreased comfort level – category B) defined by time constant 0.632 (can be applied to buildings with basic air conditioning systems).

Finite Element Analysis of Building Collapse during Demolition

A computational strategy that employs a multi-level approach to model the physical phenomena that occur during a structural collapse is used to simulate demolition of a multi-story precast concrete building. The building is modeled by means of beam elements, whose rigidity relations have been derived from a fracture mechanics-based model of cracked RC panels and joints. The motion and deformation of the collapsing building are solved as a transient dynamic problem in the finite displacements/ rotations range. The presented approach appears as an efficient way to verify whether a proposed demolition method leads to the desired mechanism of building collapse. By simulating various blasting scenarios, the most suitable demolition procedure is identified

Technique of uncertainty and sensitivity analysis for sustainable building energy systems performance calculations

Sustainable buildings design process is typical for modeling and simulation usage. The main reason is because there is generally no experience with such buildings and there is lot of new approaches and technical solutions to be used. Computer simulation could be supporting tool in engineering design process and can bring the good way for reducing energy consumption together with optimalization algorithm. For the optimization process we have to know which most sensitive input parametr from many of them has to be investigate. Therefore at first is necessary to perform the sensitivity analysis and find out the "strongest" input parametrs which most affecting the results under observation. Also still the simulation tools are mainly using to predict energy consumption, boiler and chiller loads, indoor air quality, etc. before the building is build. The information about the building envelope, schedule and HVAC components are unclear and can bring large uncertainty in results by setting this inputs to the simulation tools. Paper presents preview of uncertainty and sensitivity analysis. This techniques are shown on case study concretely BESTEST case600 with DRYCOLD climate conditions. Also systems VAV (variable volume of air) and water fancoil system are compared. For this prototype the simulation tool IES was chosen