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Papers by Christoph Roller

Research paper thumbnail of High-velocity impact experiments and quantitative damage evaluation for finite ultra-high-performance concrete targets

International Journal of Protective Structures, Dec 10, 2023

Research paper thumbnail of Experimental and Analytical Investigation of Point Fixed Corrugated Metal Sheets Subjected to Blast Loading

Engineering Transactions, Feb 14, 2019

Besides the primary threats of a blast loading scenario, flying fragments from nonstructural elem... more Besides the primary threats of a blast loading scenario, flying fragments from nonstructural elements could be a further threat to exposed humans. Point fixed corrugated metal sheets are often applied as facade elements. This paper focuses on the analysis of the dynamic bearing resistance and related pull-out behaviour of such elements. In a first step, the dynamic bearing capacity is investigated by an experimental study. Different sheet thicknesses and dimensions are examined for different loading levels using shock tube experiments. Based on the experimental results an engineering model is applied to predict the overall bearing capacity of the investigated corrugated metal sheet elements using mathematical optimisation methods. In a second step, the comparison to an analytical approach to quantify the prognostic capacity of the theoretical assessment method is addressed. Obtained results enable fast and effective quantification of expected damage effects and can be integrated into an overall risk and resilience analysis scheme.

Research paper thumbnail of Influence of the Projectile Shape on the Dynamic Tensile Characterization of Concrete Using a Split Hopkinson Bar

WIT Transactions on the Built Environment, Sep 19, 2022

Research paper thumbnail of Pre-Stressed Reinforced Concrete Elements Under Blast Loading: Numerical Analysis and Shock Tube Testing

WIT Transactions on the Built Environment, Sep 19, 2022

Research paper thumbnail of Blast-induced dynamic responses of reinforced concrete structures under progressive collapse

Magazine of Concrete Research, Jan 26, 2022

To study the response of reinforced concrete structures under progressive collapse induced by an ... more To study the response of reinforced concrete structures under progressive collapse induced by an actual blast event, an experimental programme on reinforced concrete frames subjected to contact detonation was conducted. The tested structure included a double-span beam with a middle joint, side columns and beam extensions connected to external restraints. The experimental programme employed similar geometry, reinforcing arrangement, material properties and boundary restraints from previous quasi-static as well as free-fall dynamic test series, which focused on the effects of horizontal restraint conditions on the mobilisation of catenary action. Compared to the corresponding static and free-fall tests conducted previously, the blast-induced tests simulated the condition of a progressive collapse event triggered by an explosive charge which is close to actual accidental/terrorist situations. As a result, initial effects/damages created by the initial blast effects – that is uplift of the double-span beam and blast pressure on beam and column – were witnessed and well captured. Damage patterns and failure modes from the blast tests were compared with those from related quasi-static and free-fall tests to emphasise the actual behaviour of structures under realistic explosive attacks. Finally, the blast tests also indicated the limitations of some simplified dynamic assessment methods when applying the single column removal assumption.

Research paper thumbnail of Resilience management processes in the offshore wind industry: schematization and application to an export-cable attack

Environment Systems and Decisions

Offshore wind energy (OWE) production is a crucial element for increasing the amount of renewable... more Offshore wind energy (OWE) production is a crucial element for increasing the amount of renewable energy. Consequently, one can observe a strong and constant rise of the OWE industry, turning it to an important contributor of national energy provision. This trend, however, is accompanied by increasing pressure on the reliability, safety, and security of the OWE infrastructure. Related security threats are characterized by high uncertainty regarding impact and probability leading to considerable complication of the risk assessment. On the other hand, the resilience concept emphasizes the consideration of the system’s response to such threats, and thus, offers a solution for dealing with the high uncertainty. In this work, we present an approach for combining the strengths of risk and resilience management to provide a solution for handling security threats in OWE infrastructures. Within this context, we introduce a quality assessment enabling the quantification of the trustworthiness...

Research paper thumbnail of Pre-Stressed Reinforced Concrete Elements Under Blast Loading: Numerical Analysis and Shock Tube Testing

WIT Transactions on The Built Environment

Research paper thumbnail of Influence of the Projectile Shape on the Dynamic Tensile Characterization of Concrete Using a Split Hopkinson Bar

WIT Transactions on The Built Environment

Research paper thumbnail of Blast-induced dynamic responses of reinforced concrete structures under progressive collapse

Magazine of Concrete Research, 2022

To study the response of reinforced concrete structures under progressive collapse induced by an ... more To study the response of reinforced concrete structures under progressive collapse induced by an actual blast event, an experimental programme on reinforced concrete frames subjected to contact detonation was conducted. The tested structure included a double-span beam with a middle joint, side columns and beam extensions connected to external restraints. The experimental programme employed similar geometry, reinforcing arrangement, material properties and boundary restraints from previous quasi-static as well as free-fall dynamic test series, which focused on the effects of horizontal restraint conditions on the mobilisation of catenary action. Compared to the corresponding static and free-fall tests conducted previously, the blast-induced tests simulated the condition of a progressive collapse event triggered by an explosive charge which is close to actual accidental/terrorist situations. As a result, initial effects/damages created by the initial blast effects – that is uplift of ...

Research paper thumbnail of Validation of two different analysis techniques to obtain dynamic mechanical properties of concrete using a modified Hopkinson Bar

International Journal of Impact Engineering, 2021

Research paper thumbnail of Residual load capacity of exposed and hardened concrete columns under explosion loads

Engineering Structures, 2013

Research paper thumbnail of Hugoniot Data and Equation of State Parameters for an Ultra-High Performance Concrete

Journal of Dynamic Behavior of Materials, 2021

This work aims at the characterization of a modern concrete material. For this purpose, we perfor... more This work aims at the characterization of a modern concrete material. For this purpose, we perform two experimental series of inverse planar plate impact (PPI) tests with the ultra-high performance concrete B4Q, using two different witness plate materials. Hugoniot data in the range of particle velocities from 180 to 840 m/s and stresses from 1.1 to 7.5 GPa is derived from both series. Within the experimental accuracy, they can be seen as one consistent data set. Moreover, we conduct corresponding numerical simulations and find a reasonably good agreement between simulated and experimentally obtained curves. From the simulated curves, we derive numerical Hugoniot results that serve as a homogenized, mean shock response of B4Q and add further consistency to the data set. Additionally, the comparison of simulated and experimentally determined results allows us to identify experimental outliers. Furthermore, we perform a parameter study which shows that a significant influence of the a...

Research paper thumbnail of Attenuation of Blast Effects from Underwater Explosions in Built Structures

Structures Under Shock and Impact XV, Jun 4, 2018

The paper provides reassessment and new design of shock-absorbing retrofit systems for water-fill... more The paper provides reassessment and new design of shock-absorbing retrofit systems for water-filled ducts based on experimental investigations. In a first step, tests were conducted in a 2.0-meter-high circular cylinder tank made of steel. The axisymmetric geometry of the tank offered an ideal environment for validation of the theoretical work. A number of parameter variations (water level, charge location, retrofit system) provided further insight into potential and limitations of the concepts. In a second step, a reinforced concrete shaft plus relief pool will used for scaled experiments. This will serve for a realistic representation of the phenomena in a water duct and thus enabled investigations of more complex processes (multiple reflections, tunnel effect) and practical proof of concept. Regarding retrofit systems, three concepts have been identified with respect to their impedances mismatch with water: a single layer concept made of polyvinyl chloride (PVC) foam and polyurethane (PUR) foam respectively as well as a bubble curtain. The significant potential of all investigated measures has been confirmed during the test campaign. Maximum reduction of peak-overpressure down to 0.3% for PVC, 3.2% for PUR and 1.6% for the bubble curtain compared to unmitigated setup (100%) have been determined. Thus, the developed concepts have been successfully validated and may be applied to all areas where safety and security of structures filled with or covered by fluids. Examples include among others power plants, chemical industry, port facilities and canal constructions.

Research paper thumbnail of Dynamic bearing capacity of ductile concrete plates under blast loading

International Journal of Impact Engineering, 2014

ABSTRACT For chosen infrastructural buildings, the occurrence of an intentional or accidental bla... more ABSTRACT For chosen infrastructural buildings, the occurrence of an intentional or accidental blast loading has to be considered. These infrastructures building components have to withstand the loading in order to avoid fatal debris ejection and to ensure the integrity and stability of the construction under such extraordinary loading situations. To ensure a sufficient resistance in a slender construction, advanced concrete based materials are known to have high protection potential (i.e. Roller 2010). This paper investigates systematically the bearing resistance of plate elements made of the ductile concrete DUCON® under blast loading conditions. Therefore, a series of shock tube tests has been conducted to investigate different configurations of ductile concrete plates with varying thickness and degree of reinforcement. Based on the results, a mathematical description of the resistance behavior of ductile concrete has been derived. Iso-damage curves are calculated using the derived resistance function in a Single-Degree-of-Freedom model. Applying similarity analysis for non-dimensionalized formulation enables the transfer of the experimental results to arbitrary (similar) plate dimensions. Results and findings of the paper are finally compared and discussed in relation to normal strength reinforced concrete.

Research paper thumbnail of Residual load capacity of exposed and hardened concrete columns under explosion loads

Engineering Structures, 2013

ABSTRACT The resistance behavior of columns subjected to contact or close-range detonation loadin... more ABSTRACT The resistance behavior of columns subjected to contact or close-range detonation loading is the topic of the present paper. For this purpose, a test series with columns made of normal strength concrete and advanced concrete materials is conducted. Thereby, the experiments on standard reinforced concrete (RC) columns are the starting point and form the reference tests. Those are compared with investigations on columns with different constructive strengthening. Approaches for both retrofitting of existing columns and design of new constructions, are considered. A comparison of load-carrying capacity of exposed and undamaged columns for all examined elements leads to statements about the effectiveness of each protective measure. For the determination of original and residual strength static compression tests are used. The results demonstrate the positive influence of the different strengthening methods. A thin extra layer of absorbing material leads to an enormous increase of residual load capacity compared to unprotected reinforced concrete columns. Moreover, using strengthened design for a new construction results in increase of general load-carrying capacity.

Research paper thumbnail of High-velocity impact experiments and quantitative damage evaluation for finite ultra-high-performance concrete targets

International Journal of Protective Structures, Dec 10, 2023

Research paper thumbnail of Experimental and Analytical Investigation of Point Fixed Corrugated Metal Sheets Subjected to Blast Loading

Engineering Transactions, Feb 14, 2019

Besides the primary threats of a blast loading scenario, flying fragments from nonstructural elem... more Besides the primary threats of a blast loading scenario, flying fragments from nonstructural elements could be a further threat to exposed humans. Point fixed corrugated metal sheets are often applied as facade elements. This paper focuses on the analysis of the dynamic bearing resistance and related pull-out behaviour of such elements. In a first step, the dynamic bearing capacity is investigated by an experimental study. Different sheet thicknesses and dimensions are examined for different loading levels using shock tube experiments. Based on the experimental results an engineering model is applied to predict the overall bearing capacity of the investigated corrugated metal sheet elements using mathematical optimisation methods. In a second step, the comparison to an analytical approach to quantify the prognostic capacity of the theoretical assessment method is addressed. Obtained results enable fast and effective quantification of expected damage effects and can be integrated into an overall risk and resilience analysis scheme.

Research paper thumbnail of Influence of the Projectile Shape on the Dynamic Tensile Characterization of Concrete Using a Split Hopkinson Bar

WIT Transactions on the Built Environment, Sep 19, 2022

Research paper thumbnail of Pre-Stressed Reinforced Concrete Elements Under Blast Loading: Numerical Analysis and Shock Tube Testing

WIT Transactions on the Built Environment, Sep 19, 2022

Research paper thumbnail of Blast-induced dynamic responses of reinforced concrete structures under progressive collapse

Magazine of Concrete Research, Jan 26, 2022

To study the response of reinforced concrete structures under progressive collapse induced by an ... more To study the response of reinforced concrete structures under progressive collapse induced by an actual blast event, an experimental programme on reinforced concrete frames subjected to contact detonation was conducted. The tested structure included a double-span beam with a middle joint, side columns and beam extensions connected to external restraints. The experimental programme employed similar geometry, reinforcing arrangement, material properties and boundary restraints from previous quasi-static as well as free-fall dynamic test series, which focused on the effects of horizontal restraint conditions on the mobilisation of catenary action. Compared to the corresponding static and free-fall tests conducted previously, the blast-induced tests simulated the condition of a progressive collapse event triggered by an explosive charge which is close to actual accidental/terrorist situations. As a result, initial effects/damages created by the initial blast effects – that is uplift of the double-span beam and blast pressure on beam and column – were witnessed and well captured. Damage patterns and failure modes from the blast tests were compared with those from related quasi-static and free-fall tests to emphasise the actual behaviour of structures under realistic explosive attacks. Finally, the blast tests also indicated the limitations of some simplified dynamic assessment methods when applying the single column removal assumption.

Research paper thumbnail of Resilience management processes in the offshore wind industry: schematization and application to an export-cable attack

Environment Systems and Decisions

Offshore wind energy (OWE) production is a crucial element for increasing the amount of renewable... more Offshore wind energy (OWE) production is a crucial element for increasing the amount of renewable energy. Consequently, one can observe a strong and constant rise of the OWE industry, turning it to an important contributor of national energy provision. This trend, however, is accompanied by increasing pressure on the reliability, safety, and security of the OWE infrastructure. Related security threats are characterized by high uncertainty regarding impact and probability leading to considerable complication of the risk assessment. On the other hand, the resilience concept emphasizes the consideration of the system’s response to such threats, and thus, offers a solution for dealing with the high uncertainty. In this work, we present an approach for combining the strengths of risk and resilience management to provide a solution for handling security threats in OWE infrastructures. Within this context, we introduce a quality assessment enabling the quantification of the trustworthiness...

Research paper thumbnail of Pre-Stressed Reinforced Concrete Elements Under Blast Loading: Numerical Analysis and Shock Tube Testing

WIT Transactions on The Built Environment

Research paper thumbnail of Influence of the Projectile Shape on the Dynamic Tensile Characterization of Concrete Using a Split Hopkinson Bar

WIT Transactions on The Built Environment

Research paper thumbnail of Blast-induced dynamic responses of reinforced concrete structures under progressive collapse

Magazine of Concrete Research, 2022

To study the response of reinforced concrete structures under progressive collapse induced by an ... more To study the response of reinforced concrete structures under progressive collapse induced by an actual blast event, an experimental programme on reinforced concrete frames subjected to contact detonation was conducted. The tested structure included a double-span beam with a middle joint, side columns and beam extensions connected to external restraints. The experimental programme employed similar geometry, reinforcing arrangement, material properties and boundary restraints from previous quasi-static as well as free-fall dynamic test series, which focused on the effects of horizontal restraint conditions on the mobilisation of catenary action. Compared to the corresponding static and free-fall tests conducted previously, the blast-induced tests simulated the condition of a progressive collapse event triggered by an explosive charge which is close to actual accidental/terrorist situations. As a result, initial effects/damages created by the initial blast effects – that is uplift of ...

Research paper thumbnail of Validation of two different analysis techniques to obtain dynamic mechanical properties of concrete using a modified Hopkinson Bar

International Journal of Impact Engineering, 2021

Research paper thumbnail of Residual load capacity of exposed and hardened concrete columns under explosion loads

Engineering Structures, 2013

Research paper thumbnail of Hugoniot Data and Equation of State Parameters for an Ultra-High Performance Concrete

Journal of Dynamic Behavior of Materials, 2021

This work aims at the characterization of a modern concrete material. For this purpose, we perfor... more This work aims at the characterization of a modern concrete material. For this purpose, we perform two experimental series of inverse planar plate impact (PPI) tests with the ultra-high performance concrete B4Q, using two different witness plate materials. Hugoniot data in the range of particle velocities from 180 to 840 m/s and stresses from 1.1 to 7.5 GPa is derived from both series. Within the experimental accuracy, they can be seen as one consistent data set. Moreover, we conduct corresponding numerical simulations and find a reasonably good agreement between simulated and experimentally obtained curves. From the simulated curves, we derive numerical Hugoniot results that serve as a homogenized, mean shock response of B4Q and add further consistency to the data set. Additionally, the comparison of simulated and experimentally determined results allows us to identify experimental outliers. Furthermore, we perform a parameter study which shows that a significant influence of the a...

Research paper thumbnail of Attenuation of Blast Effects from Underwater Explosions in Built Structures

Structures Under Shock and Impact XV, Jun 4, 2018

The paper provides reassessment and new design of shock-absorbing retrofit systems for water-fill... more The paper provides reassessment and new design of shock-absorbing retrofit systems for water-filled ducts based on experimental investigations. In a first step, tests were conducted in a 2.0-meter-high circular cylinder tank made of steel. The axisymmetric geometry of the tank offered an ideal environment for validation of the theoretical work. A number of parameter variations (water level, charge location, retrofit system) provided further insight into potential and limitations of the concepts. In a second step, a reinforced concrete shaft plus relief pool will used for scaled experiments. This will serve for a realistic representation of the phenomena in a water duct and thus enabled investigations of more complex processes (multiple reflections, tunnel effect) and practical proof of concept. Regarding retrofit systems, three concepts have been identified with respect to their impedances mismatch with water: a single layer concept made of polyvinyl chloride (PVC) foam and polyurethane (PUR) foam respectively as well as a bubble curtain. The significant potential of all investigated measures has been confirmed during the test campaign. Maximum reduction of peak-overpressure down to 0.3% for PVC, 3.2% for PUR and 1.6% for the bubble curtain compared to unmitigated setup (100%) have been determined. Thus, the developed concepts have been successfully validated and may be applied to all areas where safety and security of structures filled with or covered by fluids. Examples include among others power plants, chemical industry, port facilities and canal constructions.

Research paper thumbnail of Dynamic bearing capacity of ductile concrete plates under blast loading

International Journal of Impact Engineering, 2014

ABSTRACT For chosen infrastructural buildings, the occurrence of an intentional or accidental bla... more ABSTRACT For chosen infrastructural buildings, the occurrence of an intentional or accidental blast loading has to be considered. These infrastructures building components have to withstand the loading in order to avoid fatal debris ejection and to ensure the integrity and stability of the construction under such extraordinary loading situations. To ensure a sufficient resistance in a slender construction, advanced concrete based materials are known to have high protection potential (i.e. Roller 2010). This paper investigates systematically the bearing resistance of plate elements made of the ductile concrete DUCON® under blast loading conditions. Therefore, a series of shock tube tests has been conducted to investigate different configurations of ductile concrete plates with varying thickness and degree of reinforcement. Based on the results, a mathematical description of the resistance behavior of ductile concrete has been derived. Iso-damage curves are calculated using the derived resistance function in a Single-Degree-of-Freedom model. Applying similarity analysis for non-dimensionalized formulation enables the transfer of the experimental results to arbitrary (similar) plate dimensions. Results and findings of the paper are finally compared and discussed in relation to normal strength reinforced concrete.

Research paper thumbnail of Residual load capacity of exposed and hardened concrete columns under explosion loads

Engineering Structures, 2013

ABSTRACT The resistance behavior of columns subjected to contact or close-range detonation loadin... more ABSTRACT The resistance behavior of columns subjected to contact or close-range detonation loading is the topic of the present paper. For this purpose, a test series with columns made of normal strength concrete and advanced concrete materials is conducted. Thereby, the experiments on standard reinforced concrete (RC) columns are the starting point and form the reference tests. Those are compared with investigations on columns with different constructive strengthening. Approaches for both retrofitting of existing columns and design of new constructions, are considered. A comparison of load-carrying capacity of exposed and undamaged columns for all examined elements leads to statements about the effectiveness of each protective measure. For the determination of original and residual strength static compression tests are used. The results demonstrate the positive influence of the different strengthening methods. A thin extra layer of absorbing material leads to an enormous increase of residual load capacity compared to unprotected reinforced concrete columns. Moreover, using strengthened design for a new construction results in increase of general load-carrying capacity.