Marek Foglar

Numerical and Experimental Analysis of the Effect of Rigid Barriers on Blast Wave Propagation

AbstractMany terrorist attacks have been carried out in recent years, such as in Oslo, Norway (2011), and more recently in Boston, Massachusetts, and in Volgograd, Russia (both 2013). Terrorist attacks target primarily public facilities, such as railway stations, government buildings, embassies, and the transport infrastructure. Research on the effect of blast loading on structures and interiors has gained considerable attention. Although there are many types of terrorist attacks, this paper focuses specifically on bomb attacks. Two different types of bomb attacks can be distinguished. In Oslo and Boston, the explosion occurred in an open space. In Volgograd, the explosion occurred inside a confined space. This paper primarily focuses on the type of bombing observed in Volgograd by presenting reduced-scale experiments on the effect of rigid barriers on blast wave propagation in the confined space of a railway station. The experimental data set was used for calibrating numerical finite-element models for u...

The blast performance of real-scale reinforced concrete specimens with varying fiber types and content

According to recent publications, from 2005 to 2008 there were more than 13,000 terrorist attacks around the world, which took more than 73,000 human lives. The attacks were targeted mainly on the technical and civic infrastructure, like governmental buildings, bridges, etc. Due to improved ductility, fibrereinforced concrete (FRC) shows better performance under blast and impact loading compared to conventionally reinforced concrete. Also higher concrete strength shows better blast performance. Field tests of FRC and reinforced concrete specimens were performed in cooperation with the Czech Army corps in the military training area Boletice. The test were performed using real scale reinforced concrete precast slabs (6 x 1.5 x 0.3 m) with varying fiber content, fiber type, fiber strength and concrete strength class and 25 kg of TNT charges placed in distance from the slab for better simulation of real in-situ conditions. The paper presents conclusions from three sets of tests from years 2010, 2011 and 2013. Eleven specimens were tested in total. Two specimens were without fibers and had different concrete strength. Polypropylen fibers with length 54 mm and strength of 600 MPa and steel fibers with low ductility 25 mm long and strength 400 MPa were added in different content (0.5% and 1%) to the other nine specimens.

The structural response of a reinforced concrete specimen subjected to adjacent blast loading

The paper presents the results of the field tests of FRC and reinforced concrete specimens which were performed in cooperation with the Czech Army corps in the military training area Boletice. The tests were performed using real scale reinforced concrete precast slabs (6×1.5×0.3 m) with varying fibre content, fibre type, fibre strength and concrete strength class and 25 kg of TNT charges placed at a distance from the slab for better simulation of real in-situ conditions. The slabs were recorded using a high speed framing camera during the blast loading. The instrumentation enabled us to study the propagation of the blast shock wave through the material, propagation of the cracks on the soffit of the specimen and the final collapse of the middle part of the slab exposed to blast loading. The sequence of the structural behaviour is documented in detail and verified by numerical modelling using the LS-DYNA solver.

Experimental and Theoretical Study of the Performance of Reinforced Concrete Specimen Subjected to Cyclic Loading and Aggressive Environment

Because of the progress in cementitious composites material engineering, modern concrete structures are designed as more slender in comparison to previous years. For structures subjected to cyclic loadings it means higher stress ranges and thus higher probability of fatigue failure. These types of structures are often located in places of severe environment (bridges, crane tracks in chemical plants etc.). The paper presents an experimental research focused on the effect of coupled deterioration by aggressive environment and cyclic loading on the concrete specimens. The evaluation of the deteriorative effect of aggressive environment is based on kinetics of chemical reaction between concrete and aggressive solution of hydrochloric acid.

INFLUENCE OF CYCLIC LOADING ON THE DEFLECTION DEVELOPMENT OF CONCRETE SPECIMENS

Durability of the structures is one of the most discussed issues of last decades. It is one of the most easily measured properties for analysis during the structural lifetime. Concrete deflections increase over time due to rheological effects (creep and shrinkage) in addition cyclic creep can be observed on the cyclically loaded structures. The deflection increase due to the cyclic creep is not properly quantified. The fatigue damage function presented in this paper provides an analytical solution for the deflection development due to cyclic loading. The evaluation of the deflection is based on the reduction of the initial modulus of elasticity. Main principles of the function are discussed and compared with the standardized approaches for the fatigue assessment. Experimental verification of the fatigue damage function was carried out on reinforced concrete specimens and on prestressed concrete slab. To improve the standardized approaches, the real stress distribution was considered with the use of newlydeveloped method of partial integration over the height of the specimen compressive zone. The deflection increase due to cyclic loading was measured regularly with inductive displacement transducer. Comparison of the measured values and the values calculated using the presented function shows good agreement. The fatigue damage function can be used easily in “inhand” calculations, or can be inserted into FEM-based software and used in practical applications for assessing the increase in the deformations of concrete structural elements caused by cyclic loading.

Non-Destructive Examination of Cement Based Materials before and after Explosion Tests

The article describes the use of ultrasonic testing methods for examining slabs made from cement based materials. For the detection of cracks, in full-scale slabs before and after the explosion, ultrasonic pulse method was used. Data obtained before the explosion confirm the high quality of the cement based material. Another set of data taken after the explosion shows the scale of cracks in the slabs. The article compares material characteristics of the unreinforced concrete, steel fibre concrete and high performance fibre reinforced concrete on the basis of materials tested by using the passage ultrasonic method after the explosion.