Our research works are experimentally and theoretically oriented. Experimental works are conducted at the full-scale and laboratory scale. The full-scale experiments are related to investigations of size effects in concrete and reinforced concrete beams, stability problems in large metal silos with horizontally corrugated curved sheets strengthened by vertical columns, management and control of heat supply into and heat extraction from external walls containing embedded pipes in a residential house and fatigue in steel beams. The beams in size effect tests are separately scaled along with the length or height to induce different failure mechanisms. The effect of varying beam dimensions and longitudinal and transverse reinforcement ratios are analysed. In a full-scale metal silo, we investigate flow patterns and loads exerted on walls with the different bulk solids, solid densities, outlet diameters, outlet locations and vertical stiffeners’ shape and size. In a residential house, the following systems are tested and monitored: thermal barrier, hidden solar collector, ground heat storage system and a natural ventilation system. Measured are: temperature (in the ground and water), ground humidity, air temperature, relative air humidity, air velocity, barometric pressure, wind speed, wind direction and solar net radiation. The fatigue phenomenon is investigated in welded steel beams of a different length. In laboratory tests, the following problems are investigated: strength, brittleness and fracture in concrete elements, autogenous coupled dynamic-acoustic effects during confined granular silo flow and hydro-mechanical fluid flow in rocks. The fracture experiments are performed for the different element sizes during bending and compression. The effect of the different aggregate volume, size, shape and roughness on cracking is explored. In tests, we utilize a micro-CT system, digital image correlation (DIC) technique and scanning electron microscope. The laboratory silo tests are carried out with the different silo shape, outlet diameter, filling height, solid and wall stiffness. We measure wall pressures, accelerations and sound pressures.
Theoretically, we use different numerical tools such as finite element method (FEM), discrete elements method (DEM), material point method (MPM) and computational fluid dynamics (CFD) to solve different problems. For describing a fracture process in concrete and reinforced concrete elements at the macro-level, we use FEM, based on a coupled elasto-plastic-damage model with non-local softening and cohesive elements. We use also XFEM. To reproduce fractures in concrete at the meso-level, we use FEM with cohesive elements and DEM. Concrete is described as a 4-phase material composed of aggregates, mortar, interfacial transitional zones and voids. The concrete meso-structure is obtained with the aid of micro-CT images. One-phase DEM is also used for reproducing fractures in rocks. To describe the flow behaviour of granular materials in silos, we apply MPM, based on a hypoplastic constitutive model with non-local softening and DEM. The silos include also flow correcting inserts to promote mass flow. The focus is on simulations of shear localization and dynamic effects. The combined dynamic-acoustic effects are investigated with a fully coupled DEM/CFD. The combined thermo-hydro-mechanical phenomena during hydraulic fracturing in rocks are also explored with a fully coupled DEM-CFD model.
Key words:
civil engineering structures; fracture mechanics; mechanics of granular materials; mechanics of bulk solids; building physics; FEM and DEM; thermo-hydro-mechanics
