Pavel Beran

The impact of stone shape to the thermal stress of ashlar masonry

The design of repair mortars for renovation of historic objects depends on many aspects. One of these aspects is the impact of the difference of thermal expansion coefficient between mortar and stone. This paper is focused on thermal stress close to the corners of the stones. Three 3-D detail finite element models of masonry which have different radius of curvature in the corners of stone were used for computation of thermal stress. The main result is that shape of stones in ashlar masonry significantly affects the values of thermal stress. The higher radius of curvature of the stones in corners causes significant decrease of thermal stress values in the corners of stone.

The impact of the coefficient of absorption of solar radiation on the state of stress in heterogeneous masonry

The masonry is heterogeneous material created from stones and mortar. The material characteristics of masonry components may differ in many aspects. The intention of this paper is the description of the thermal stresses which are generated by different values of coefficient of solar radiation absorption. The results were obtained by means of the 3-D finite element model of masonry. The difference of absorption coefficient between stone and mortar may cause increase of pressure thermal stress.

Salt attack in parking garage in block of flats

In recent years many new block of flats with parking garages placed inside the buildings were constructed. This tendency brings beyond question benefits for residents and also for city planning, but it requires new design and structural approaches and advanced material and construction solutions. The analysis of plaster damage on partition wall in parking garage in one of these buildings is presented in the paper. The damage of studied plaster is caused by the salts which are transported together with snow on cars undercarriage into garage area during winter. The snow melts and water with dissolved salts is transported by the capillary suction from concrete floor into the rendered partition wall. Based on the interior temperature, adsorbed water with dissolved chlorides evaporates and from the over saturated pore solution are formed salt crystals that damages the surface plaster layers. This damage would not occur if the partition wall was correctly isolated from the floor finish layer in the parking garage.

EVALUATION OF THE APPLICATION OF A THERMAL INSULATION SYSTEM: IN-SITU COMPARISSON OF SEASONAL AND DAILY CLIMATIC FLUCTUATIONS

The current outdated state of many institutional and administrative buildings in the EU region poses a significant burden from the energy sustainability point of view. According to the contemporary EU requirements on the energy efficiency of buildings maintenance, an evaluation of performed improvements is essential for the assessment of expended investments. This paper describes the effect of building envelope reconstruction works consisting in the installation of a thermal insulation system. Here, a long-term continuous monitoring is used for the extensive assessment of the seasonal and daily temperature and relative humidity fluctuations. The obtained results include temperature and relative humidity profiles in the wall cross-section as a response to the changing exterior climatic conditions. The analysis of measured data reveals substantial improvements in thermal stability of the analyzed wall during temperature peaks. While the indoor temperatures exceeding 28 °C are recorded during summer before application of the thermal insulation layer, the thermal stability of the indoor environment is distinctly upgraded after performed improvements. Based on the complex long-term monitoring, a relevant experience is gained for the future work on energy sustainability and fulfilment of the EU directives.

Methodology for assessment of amount and amplitude of thermal stress cycles in masonry

Analysis of amount and amplitude of thermal stress cycles in historic masonry has been made by means of combination of three 2-D numerical models of heterogeneous ashlar masonry. The numerical models were used to simulate thermal stress cycles during June, July and August in reference climatic year valid for Prague Castle, Czech Republic. For evaluation of amplitude and amount of the thermal stress cycles the effective stress in selected point in masonry was used. Afterwards rainflow method was used to count the amplitude and amount of the stress cycles. The results show that during summer quite a lot of significant thermal stress cycles originate in masonry, especially during sunny hot days. The results presented in this paper confirm the significant fatigue character of the thermal stress cycles and the method presented here could be suitable to evaluate thermal stress in building materials and structures.

Comparison of 3-D finite element model of ashlar masonry with 2-D numerical models of ashlar masonry

3-D state of stress in heterogeneous ashlar masonry can be also computed by several suitable chosen 2-D numerical models of ashlar masonry. The results obtained from 2-D numerical models well correspond to the results obtained from 3-D numerical model. The character of thermal stress is the same. While using 2-D models the computational time is reduced more than hundredfold and therefore this method could be used for computation of thermal stresses during long time periods with 10 000 of steps.

The impact of air flow to the distribution of heat transfer coefficient on circular cylinder

To study the temperature effects which cause degradation of building materials in exterior is necessary to know the coefficient of heat transfer on its surface during the cross-flow. In this paper the values of heat transfer coefficient on circular cylinder for the cross-flow of air characterized by Reynolds number 78 200 were determined. The values of heat transfer coefficient were obtained by comparing numerically computed temperatures in several points in cylinder with measured values of temperatures during experiment.