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This paper presents the results of experimental program focused on change of compressive strength of concrete exposed to elevated temperature. The change of compressive strength was studied for several types of concrete with different properties (common concrete, air-entrained concrete, concrete with polypropylene fibres, high performance concrete with steel fibres and concrete with basalt fibres). The samples were exposed to high temperatures up to 1000 0C at, the compressive strength was measured at the elevated temperature. This paper presents results of this experiment and comparison of experimental results with available data from literature and valid Eurocodes.

This paper presents achievements in the field of the numerical simulation of the fibrere reinforced concrete (FRC) and ultra-high performance fibre reinforced concrete (UHPFRC). The numerical simulations were performed to verify results of two experimental programmes focused on the blast resistance of FRC and UHPFRC. The response of the FRC and UHPFRC slabs to the contact and near-field blast was studied in these two experiments. As the detail behaviour of specimens could not be observed because of the blast load, the numerical models were prepared. The accuracy of the numerical models was evaluated based on the comparison of numerical and experimental results. Different approaches for blast simulation were tested and compared. The results indicate that the various phenomena (e.g. overpressure propagation, stress cumulation, crack propagation and damage extend) can be successfully simulated. However, the comparison of the soffit velocity, measured with the PDV unit and numerical model showed shortcomings of the numerical model. These numerical model inaccuracies are discussed and their reasons presented.

Because of the current geopolitical situation, research on improving the resistance of the civil and transport infrastructure to blast or impact loads has gained considerable attention. This paper presents the results of full-scale blast experiments designed to characterize the resistance of concrete-based composite bridge decks subjected to close-in blast loading. Three composite decks with different degrees of heterogeneity were proposed and tested: a slab with basalt fiber meshes in multiple layers along the depth of the specimen, a slab with recycled textile sheets 100 mm in total thickness, and a typical hollow-core prestressed slab. The dependence of the extent of the blast damage on the material characteristics of the composite material was studied. A detailed study of the damage to the specimen caused by the close-in explosion found apparent delamination of all tested composite specimens. The heterogeneity of the layered composite material converts the blast damage due to internal rebounds into layer delamination.

Because of the current geopolitical situation, research on improving the resistance of the civil and transport infrastructure to blast or impact loads has gained considerable attention in recent years. This paper presents the results of full-scale blast experiments designed to characterize the resistance of steel-fiber-reinforced concrete full-scale bridge decks subjected to near-field blast loading, and its dependence on the material properties of the concrete. The blast performance of reinforced concrete specimens increases with added high-performance steel fibers. An increase in fiber content and in compressive strength up to ultrahigh-performance fiber concrete (UHPFRC) further enhances its blast performance. An attempt was made to further increase the blast resistance of a concrete structure with the use of a basalt mesh. The UHPFRC specimen with a basalt mesh experienced a greater extent of internal damage than a regular UHPFRC specimen. However, the basalt mesh inserted into the concrete cover at the soffit of the UHPFRC specimen improved its blast performance, as expressed by the area of spalling and the volume of debris. This phenomenon was studied numerically, and it was proved that it is caused by the internal rebound of the shock wave, which causes a local increase in the stresses inside the specimen. The heterogeneity of the specimens, which is increased by an internal reinforcement or by a basalt mesh, converts the blast damage due to internal rebounds into layer delamination. The delamination of the concrete specimen can be very effective in dissipating the energy of the blast wave.

The impact of heavy trucks on a bridge substructure can lead to progressive collapse of the bridge superstructure, and to disastrous accidents. This type of load should therefore be taken into consideration, especially in the design of motorway bridges. For some structural arrangements, vehicle impact is the decisive loading for the design of the bridge substructure. This paper presents verification of the detailed procedures given by European standard EN 1991-1-7 for bridge pier impact load – dynamic ana lysis, which is compared with the outcomes from a detailed finite-element model (FEM) of a truck impact prepared using AUTODYN software. A nonlinear material model of concrete with damage and strain-rate effect is used to assess the impact performance of a bridge pier. The paper further presents the results of a numerical study focused on the influence of different types of bridge pier reinforcement arrangement on their resistance to vehicle impact. The performance of various types of reinforcement is analysed and compared. Practical recommendations are drawn for the design of bridge piers which can be subjected to vehicle impacts in an urban environment.

This paper investigates means for increasing the effectiveness of a blast barrier using various types of surfacing. It builds on previous research on the blast effect mitigation properties of rigid concrete blast barriers. Previous research has studied barriers with a smooth surface. The effectiveness of rigid smooth barriers in reducing shock wave overpressure has been proven to be low. Their main contribution is in absorbing flying debris or shrapnel created by an explosion, and thereby reducing the risk of injury to the occupants of a building. This paper suggests ways to achieve greater safety by increasing the blast mitigation properties of barriers. It studies the influence of various materials and shapes on the effectiveness of a barrier, and proposes methods for providing increased overpressure reduction while keeping the same overall dimensions. A barrier of this kind provides additional security for the occupants of a building without disrupting the functionality of the interior with a massive obstacle. The use of a deformable porous material is compared with the use of rigid durable ultra-high performance fibre-reinforced self-compacting concrete (UHPFRSCC), developed by the authors especially for application in blast-resistant structures. The results of an original experimental program are used to determine the influence of barrier shape and barrier material on blast wave mitigation. The effect of uneven barrier surfacing on a shock wave is demonstrated on a finite element numerical model calculated using LS-DYNA. Results of the analysis proved that the use of uneven surface has a positive effect on blast mitigation properties of a barrier without affecting its shrapnel absorption capabilities. All experiments and FEM models consistently proved that a barrier has significant overpressure reduction effect in the area directly behind the barrier. The comparison of experimental measurements of rigid and deformable barrier material showed no drastic increase in mitigation properties of deformable barrier.

This paper reports on numerical assessment of the blast response of a heterogeneous composite structure using LS-DYNA solver. There experimentally observed effect of heterogeneity on the overall response of the structure is numerically assessed. Multiple approaches to the introduction of material heterogeneity are proposed, modelled and tested. The numerical results are confronted with the authors’ original experimental program on a full-scale concrete structure subjected to a near field explosion. Tests were carried out on a total of three specimens. All the specimens were subjected to the same close-in blast loading from 25 kg TNT charges placed on steel chairs in the middle of each slab. The chairs provided 450 mm standoff from the top surface of the slab. Two of the analyzed specimens were reinforced concrete slabs 6 m in length, 1.5 m in width and 0.3 m in thickness. The first specimen contained basalt fiber meshes in multiple layers along the depth of the specimen. The second specimen contained two layers of recycled textile sheets 100 mm in total thickness. The third specimen was a commercial hollow-core precast prestressed panel 6 m in length, 1.2 m in width and 0.32 m in thickness. The paper aims to verify and explain the experimental findings. It was numerically proved that the highly heterogeneous concrete-based composite bridge decks consume the blast energy by layer delamination in the pre-determined damage zones. The findings are supported by PDV measurements.

Nowadays, new types of cementitious composites are increasingly being used for the construction of structural members. This poses a problem regarding the structural fire safety design as the thermal behaviour and mechanical properties at high temperatures of these materials are usually not known. The main aim of this paper is to investigate and present the thermal behaviour, propensity to spalling, and residual strength of various types of cementitious composites exposed to fire. Namely, the following materials are investigated: ordinary normal-weight concrete with or without fibres, light-weight aggregate (LWA) concrete with or without fibres, recycled aggregate concrete with or without fibres, LWA concrete with open structure, and two novel cementitious composites – LWA concrete containing crushed textile and foam plastic, and concrete containing mineral wool insulation shreds. Additional aim of this investigation is to resolve whether widely-used simple transport and material models are suitable for numerical simulations of thermal behaviour of unusual cementitious composites. For the purposes of the investigation, experimental program was proposed and executed, and numerical simulations were performed. The experimental program consisted of fire test of wall-panel specimens and cube specimens in a vertical furnace and of measurement of physical and mechanical properties of the investigated materials. The numerical simulations consisted of finite element analysis of temperature evolutions in the wall-panel specimens. The paper summarizes the results and conclusions of the experimental and numerical investigations. Within the paper, compressive strengths and residual compressive strengths of the investigated materials are presented and discussed. Moreover, experimentally measured thermal behaviour is analysed and compared with the thermal behaviour predicted by numerical simulations. In addition to this, spalling behaviour and surface damage of the specimens made of the investigated materials are presented and discussed. The main conclusion of this paper is that widely-used simple heat transport and material models are suitable for numerical simulations of thermal behaviour of various cementitious composites. Additional important conclusion is that concrete containing mineral wool shreds performs very well when subjected to fire.

This paper presents the results of an experimental program that compares the material properties of various types of cementitious composites subjected to high temperatures. Within this experimental program, measurements of bulk density, porosity, thermal conductivity, specific heat capacity, permeability and compressive strength of the materials were made. All these properties were measured on test samples exposed to high temperatures up to 1000 °C. The results of this experimental investigation are the temperature dependences of the material properties and the relative changes of the properties at high temperatures in relation to their values at room temperature. The paper also presents and compares different methods for measuring the selected properties studied here, and the effect of the measurement methods on the obtained results. All results are compared with values from the valid standards and referenced literature.

Because of the current geopolitical situation, research on improving the resistance of the civil and transport infrastructure to blast or impact loads has gained considerable attention in recent years. This paper presents the results of full-scale blast experiments designed to characterize the resistance of steel-fibre-reinforced concrete full-scale bridge decks subjected to near-field blast loading. Twenty-five kilogrammes of TNT charges were placed on steel chairs in the middle of each slab. The specimens were concrete slabs 6 m in length, 1.5 m in width and 0.3 m in thickness. Following, slabs with multiple placements of basalt mesh were used. The basalt mesh was placed at the half of both upper and lower concrete cover and three times in between both layers of panel reinforcement. To conclude, slabs with deformable layer were used. The layer was made of shredded textiles slabs, 80 mm thick. These slabs were placed in the middle of the slab cross section. The experimental programme was recorded by high-speed cameras, and the recordings were supplemented by PDV (Photon Doppler Velocimetry) measurements of the acceleration of the bottom surface of the studied specimens. Conclusions are drawn from the utilization of the PDV measurements to studying of shock wave propagation through heterogeneous cementitious composites.

Due to its greater ductility, fiber reinforced concrete shows better performance under blast and impact loading than conventionally reinforced concrete. Common purpose-fabricated fibers are quite expensive and the use of more cost-effective waste materials in structures subjected to blast and impact loading should be investigated. This paper presents the results of field experiments focused on the effect of low ductility and low strength waste steel fibers, their combination with poly-propylene fibers on the blast performance of concrete. The combined effect of varied concrete compressive strength is also investigated. The tests were performed using real scale precast slabs (0.3 × 1.5 × 6 m) and 25 kg of TNT charges placed at a distance from the slab. Waste steel fibers added into the concrete mixture had a minimal effect on the blast performance of FRC. The results of the experiments were plotted on the spall and breach prediction curves; the RC specimens show good agreement with the spall and breach prediction curves. A numerical simulation of the experiment was performed. The results obtained from numerical modeling showed good agreement with the experimental results, and prove the preliminary estimates based on material performance.

This paper follows the line of contributions from earlier conferences and informs about more results of experimental program focused on the resistance of plain and fibre reinforced concrete elements against adjacent and contact blast. Concurrently, a detailed analysis of element response is carried out using ultra high speed cameras.

Fiber-reinforced concrete (FRC) has mechanical properties that enhance its suitability for use in structures subjected to high strain rates, e.g. blast or impact loading. The fracture energy value is the decisive material characteristic for assessing the damage to concrete structures due to loadings with high strain rates. An analytical description of the force-deflection diagram of FRC can be a very efficient instrument for making a preliminary estimate of the fracture and mechanical properties of FRC. On the basis of our experiments and experiments from other authors, a tool for an analytical description of the force-deflection diagram for various strength classes, fiber types, etc. is proposed and evaluated.

The paper describes approach for the description of punching-shear resistance of concrete slab specimens subjected to close blast. The procedure is based on a combination of standardized approaches, a rich experimental program and numerical modeling. The approach aims to quantify the close blast behavior in the means of the velocity of the loading, strain-rate dependent material characteristics and simplify it to allow practical use.

Paper compares and discusses two different layouts of testing of mechanical and fracture properties of FRC, the three-point bending test and four-point bending test. The basis is extensive experimental program and analytical and statistical evaluation.

Fiber-reinforced concrete (FRC) has mechanical properties that enhance its suitability for use in structures subjected to high strain rates, e.g. blast or impact loading. The fracture energy value is the decisive material characteristic for assessing the damage to concrete structures due to loadings with high strain rates. This paper summarizes the results of tests focused on the fracture energy of fiber-reinforced concrete of various strength classes, fiber types and fiber contents, subjected to different loading rates. An analytical description of the force–deflection diagram of FRC can be a very efficient instrument for making a preliminary estimate of the fracture and mechanical properties of FRC. On the basis of our experiments and experiments from other authors, a tool for an analytical description of the force–deflection diagram for various strength classes, fiber types, etc. is proposed and evaluated.

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.

Many articles and papers about mitigating the impacts of the transport infrastructure on the environment have pointed out that one of the factors influencing the usage of underbridges for mammal migration is the noise induced by traffic. However, this phenomenon has not yet been properly investigated and verified. This paper describes the influence of the structural arrangement of bridges, mainly the bearings and expansion joints, and the location of the bridge in the countryside, on the noise induced by traffic. The findings come from noise measurements on several structures on the D1 motorway and the R35 expressway in the Czech Republic. The measured noise levels are juxtaposed with the migration potential of the bridge for wildlife.

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, such as governmental buildings and bridges, etc. Due to improved ductility, fiber-reinforced concrete (FRC) shows better performance under blast and impact loading compared to conventionally reinforced concrete. Field tests of FRC and reinforced concrete specimens were performed in cooperation with the Czech Army corps and Police of the Czech Republic in the military training area Boletice. The tests were performed using real scale reinforced concrete precast slabs with varying fiber content and concrete strength class and 25 kg of TNT charges placed in a distance from the slab for better simulation of real in-situ conditions. This paper presents conclusions from two sets of tests and results of their numerical evaluation.

The paper describes the network arches built at the grade separated junction of the II/468 road and the industrial area of Trinec-Baliny in the Czech Republic. A network arch is defined as an arch bridge with inclined hangers where some hangers cross other hangers at least twice. The tie is formed by a concrete slab with longitudinal prestress. Owing to the arrangement of hangers, there is little bending in the tie and the arches. All hangers have the same cross-section. Their connections should be placed equidistantly along the arch; the hangers act like a light web. The two 73·5 m span network arch bridges described in the paper and the adjacent approach ramps work as one articulation system. The paper presents the prestressing arrangement of the prestressed concrete deck, the unique bridge articulation without fixed bearing and the prestressing of the interchange between the arch bridges (the part where the approach ramps turn left and right from the longitudinal axis of the bridges). The activation of the bridge hangers is also described, together with the results of the long-term monitoring (the bridges were put in operation in April 2009).

The arch is the oldest structural shape that mankind has invented. The Romans constructed a large number of stone arch bridges on roads or water supply routes (aqueducts), many of which have survived to the present day. Arch bridges were constructed throughout medieval times; some of them represent masterpieces of the world´s cultural heritage. Buried concrete arch bridges are built with spans from 2 m up to 40 m on roads and railways, both as underbridges or overbridges, and as pre-cast and cast-in-place structures. Owing to low construction costs, great durability and endurance, they are favoured by contractors and owners. This paper focuses on the structure–soil interaction of buried arch bridges both in operation and under construction. Based on analytical derivation, a method of centre-line optimisation of cast-in-place buried concrete arch bridges is proposed and applied on an existing structure. The method leads to reduction of bending moments and deflections, thus making the structural system more effective. The impact of the construction phases on the distribution of internal forces is studied. Based on the acquired knowledge, modifications of the construction process are proposed and evaluated.

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 newly-developed 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 “in-hand” 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.

Many 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...

One of the most demanding topics in blast and impact engineering is the modelling of projectile impact. To introduce this topic, a set of numerical simulations was undertaken. The simulations study the impact of regular and sub-calibre projectile on Czech pre-WW2 military bunkers. The penetrations of the military objects are well documented and can be used for comparison. The numerical model composes of a part from a wall of a military object. The concrete block is subjected to an impact of a regular and sub-calibre projectile. The model is divided into layers to simplify the evaluation of the results. The simulations are processed within ANSYS AUTODYN software. A nonlinear material model of with damage and incorporated strain-rate effect was used. The results of the numerical simulations are evaluated in means of the damage of the concrete block. Progress of the damage is described versus time. The numerical simulation provides good agreement with the documented penetrations.

Impact resistance of plain concrete and FRC composites gains high importance in the present days. This paper presents outcomes of the experiments focused on performance of FRC slabs subjected to impact loading of various strain rates. The FRC slabs, thickness 30, 60 and 120 mm were subjected to various drop-weight impacts. The different drop-hammer weights provided different loading speeds and strain rates. The performance of the slabs was recorded with the use of high speed cameras. The cameras were used for impact speed control and specimen deflection measurement. With the use of the recordings, the force-time response of the slabs could be plotted. The plots correspond to the mechanical behaviour obtained by static load tests (loading speed 0.2 mm/min) but several differences can be found. Several types of FRC (varying fiber material, fiber content, etc.) were tested and evaluated. The experimental program is supplemented by numerical modelling which provides good agreement with the experimental results.

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 impact performance of reinforced concrete specimens subjected to fatigue loading has not been quantified properly yet. This topic is significant in the field of vehicle impact or similar applications. The paper aims to fill this gap by presenting the on-going experimental program. The paper presents outcomes of the experiments focused on the performance of RC beams subjected to drop-weight impact loading. The behaviour of the beams which were prior to the impact testing subjected to cyclic loading was compared to the behaviour of the beams which were not subjected to cyclic loading.