Periodic Reporting for period 1 - ASPIRE (Assessing Seismic Performance of Integral bridges for improved Resilience and lifecycle in Earthquake-prone areas)
Période du rapport: 2020-10-01 au 2022-09-30
Integral abutment bridges (or integral bridges) have no expansion joints and bearings. For this reason the maintenance and construction costs are reduced, and they result in having less carbon emissions and less costs during the life-cycle. Integral bridges represent a valid alternative to conventional bridges, especially for short spans.
Because of their particular design, the forces exerted on one abutment by the backfill soil and those acting on the deck are transmitted to the opposite abutment and embankment, thus generating a complex interaction between the bridge structure and the soil. Soil-Structure Interaction (SSI) is a key aspect to understand their response under earthquake. Due to their increased structural redundancy, integral bridges can provide higher structural safety against seismic actions. Despite the increasingly high number of studies regarding their response under earthquake, there is still uncertainty about the dynamic response of IABs including SSI and a lack of standard procedures to evaluate their seismic performance. The new version of the Eurocode 8 Part 2 on bridges (in the approval process) contains important novelties and a new section specifically dedicated to the design of integral bridges.
Project ASPIRE had the main goal to investigate the seismic response of integral abutment bridges, to shade light on the feasibility and performance of this bridge typology in earthquake-prone areas, and to study their life-cycle behaviour. In particular, Specific objectives were the definition of the site-specific seismic hazard; the definition of a numerical simulation strategy to investigate the seismic response of integral bridges including Soil-Structure Interaction; the development of experimental tests to investigate the life-cycle and seismic behaviour; the investigation of the impact of earth pressures on the abutments and find suitable mitigation strategies; the assessment of vulnerability and improved lifecycle performances of integral bridges. The main conclusion are that: 1) Integral Bridges can be suitable for extensive use in earthquake-prone areas, soil-structure interaction should be investigated accurately; 2) attention should be paid to the maximum span length, for longer spans the damage level in the abutment/backfill system can be higher; 3) The comparison with Eurocode 8 provisions can help with the preparation of guidelines for structural design.
Because of their particular design, the forces exerted on one abutment by the backfill soil and those acting on the deck are transmitted to the opposite abutment and embankment, thus generating a complex interaction between the bridge structure and the soil. Soil-Structure Interaction (SSI) is a key aspect to understand their response under earthquake. Due to their increased structural redundancy, integral bridges can provide higher structural safety against seismic actions. Despite the increasingly high number of studies regarding their response under earthquake, there is still uncertainty about the dynamic response of IABs including SSI and a lack of standard procedures to evaluate their seismic performance. The new version of the Eurocode 8 Part 2 on bridges (in the approval process) contains important novelties and a new section specifically dedicated to the design of integral bridges.
Project ASPIRE had the main goal to investigate the seismic response of integral abutment bridges, to shade light on the feasibility and performance of this bridge typology in earthquake-prone areas, and to study their life-cycle behaviour. In particular, Specific objectives were the definition of the site-specific seismic hazard; the definition of a numerical simulation strategy to investigate the seismic response of integral bridges including Soil-Structure Interaction; the development of experimental tests to investigate the life-cycle and seismic behaviour; the investigation of the impact of earth pressures on the abutments and find suitable mitigation strategies; the assessment of vulnerability and improved lifecycle performances of integral bridges. The main conclusion are that: 1) Integral Bridges can be suitable for extensive use in earthquake-prone areas, soil-structure interaction should be investigated accurately; 2) attention should be paid to the maximum span length, for longer spans the damage level in the abutment/backfill system can be higher; 3) The comparison with Eurocode 8 provisions can help with the preparation of guidelines for structural design.
The site-specific hazard was defined both by selection of natural ground motions and by defining an up-to-date method for the generation of simulated ground motions. The method allows to generate a number N of simulated ground motions starting from a few input parameters (Magnitude, Distance, soil type and fault type). A novel software tool was developed allowing to generate spectrum-compatible ground motions.
A numerical model was developed using the OpenSees platform. First, the numerical model of the shaking table test of EU/H2020 SERA/SERENA project was defined. The numerical model, including the model of the bridge and foundations with the piles and the soil domain, takes into account the soil-structure interaction by appropriate interfaces between structural and soil elements. Static and Dynamic analyses were performed, allowing to obtain results in terms of acceleration, frequencies, displacements, bending strains and earth pressures.
The numerical results were compared with the experimental ones. The comparison allowed to validate the numerical strategy, and the earth pressures obtained were compared with the new provisions contained in the new version of Eurocode 8 Part 2 on Bridges, allowing to draw suggestions and guidelines for the application of Eurocodes. The influence of different parameters was investigated, such as the increasing mass of the bridge deck, and the study of the areas of the backfill soil which are more likely to be damaged and therefore need mitigation strategies.
After the definition the earthquake ground motion and the numerical model of real integral bridges, a number of sets of earthquake-bridge samples was defined. A non-linear time history analysis is performed for each of the cases, allowing to obtain a certain damage state for each of the component of the bridge. While generally the damage of a conventional bridge is described by the damage of piers, in the case of integral bridges different damage indicators have to be defined, involving damage to the abutments-backfill system. This allowed to evaluate the vulnerability of such bridges.
The life-cycle performance of integral bridges was investigated by taking part to the experimental campaign of project PLEXUS PLUS funded by UKCRIC and composed by two tests:
- A small-scale pseudo-static test was conducted to simulate the effects of repeated thermal variations on the bridge throughout its lifespan, replicating the soil-structure interaction resulting from seasonal expansion and contraction of the bridge deck, and to assess the effectiveness of various monitoring techniques. By combining data from different instruments, a preliminary evaluation of the soil-structure interaction behaviour of the system was conducted.
- A large-scale pseudo-static experimental campaign (100 cycles) to reproduce the life-cycle thermal variations of integral bridges. It was the first experimental campaign to be carried out in the new National Facility for Soil-Foundation-Structure-Interaction Laboratory (SoFSI) at the University of Bristol.
The 6m x 5m x 4m Soil Pit was used, and settlements, strains and earth pressures were measured on the abutment and in the backfill soil. The large-scale test of Plexus Plus, besides being among the first comprehensive tests of Integral bridges at large scale, featured a number of innovative monitoring techniques including optical fibres, digital image correlation (DIC) and Ground Penetration Radar (GPR).
The results were disseminated through peer-reviewed journal papers (published and submitted). In addition, the results are published in five conference papers which are either published or submitted in major conferences in the field of earthquake engineering.
A numerical model was developed using the OpenSees platform. First, the numerical model of the shaking table test of EU/H2020 SERA/SERENA project was defined. The numerical model, including the model of the bridge and foundations with the piles and the soil domain, takes into account the soil-structure interaction by appropriate interfaces between structural and soil elements. Static and Dynamic analyses were performed, allowing to obtain results in terms of acceleration, frequencies, displacements, bending strains and earth pressures.
The numerical results were compared with the experimental ones. The comparison allowed to validate the numerical strategy, and the earth pressures obtained were compared with the new provisions contained in the new version of Eurocode 8 Part 2 on Bridges, allowing to draw suggestions and guidelines for the application of Eurocodes. The influence of different parameters was investigated, such as the increasing mass of the bridge deck, and the study of the areas of the backfill soil which are more likely to be damaged and therefore need mitigation strategies.
After the definition the earthquake ground motion and the numerical model of real integral bridges, a number of sets of earthquake-bridge samples was defined. A non-linear time history analysis is performed for each of the cases, allowing to obtain a certain damage state for each of the component of the bridge. While generally the damage of a conventional bridge is described by the damage of piers, in the case of integral bridges different damage indicators have to be defined, involving damage to the abutments-backfill system. This allowed to evaluate the vulnerability of such bridges.
The life-cycle performance of integral bridges was investigated by taking part to the experimental campaign of project PLEXUS PLUS funded by UKCRIC and composed by two tests:
- A small-scale pseudo-static test was conducted to simulate the effects of repeated thermal variations on the bridge throughout its lifespan, replicating the soil-structure interaction resulting from seasonal expansion and contraction of the bridge deck, and to assess the effectiveness of various monitoring techniques. By combining data from different instruments, a preliminary evaluation of the soil-structure interaction behaviour of the system was conducted.
- A large-scale pseudo-static experimental campaign (100 cycles) to reproduce the life-cycle thermal variations of integral bridges. It was the first experimental campaign to be carried out in the new National Facility for Soil-Foundation-Structure-Interaction Laboratory (SoFSI) at the University of Bristol.
The 6m x 5m x 4m Soil Pit was used, and settlements, strains and earth pressures were measured on the abutment and in the backfill soil. The large-scale test of Plexus Plus, besides being among the first comprehensive tests of Integral bridges at large scale, featured a number of innovative monitoring techniques including optical fibres, digital image correlation (DIC) and Ground Penetration Radar (GPR).
The results were disseminated through peer-reviewed journal papers (published and submitted). In addition, the results are published in five conference papers which are either published or submitted in major conferences in the field of earthquake engineering.
The main advancements with respect to the existing state of the art are:
- The definition of a novel method to simulate synthetic earthquake ground motions, including a software tool which allows to define site-specific earthquake ground motions and spectrum compatibility with the code spectrum.
- The development of a consolidated strategy for the numerical modelling of Integral Abutment Bridges including Soil-Structure Interaction, based on experimental simulation of the behavior of Integral bridges by means of shaking table tests;
- The accurate evaluation of earth pressures on the abutments using the developed numerical model, allowing the evaluation of weak areas in order to design appropriate mitigation strategies.
- The Comparison of the evaluated earth pressures behind the abutment wall with the new Eurocode 8 provisions;
- The development of new small and large-scale experimental tests to investigate the life-cycle performance due to seasonal variations and evaluation of infrastructure resilience of IABs.
The project will have a strong impact on the application of the new version of Eurocode 8 – Part 2 on Bridges. The extensive use of Integral Bridges in earthquake-prone areas could bring an increased safety of road bridges.
- The definition of a novel method to simulate synthetic earthquake ground motions, including a software tool which allows to define site-specific earthquake ground motions and spectrum compatibility with the code spectrum.
- The development of a consolidated strategy for the numerical modelling of Integral Abutment Bridges including Soil-Structure Interaction, based on experimental simulation of the behavior of Integral bridges by means of shaking table tests;
- The accurate evaluation of earth pressures on the abutments using the developed numerical model, allowing the evaluation of weak areas in order to design appropriate mitigation strategies.
- The Comparison of the evaluated earth pressures behind the abutment wall with the new Eurocode 8 provisions;
- The development of new small and large-scale experimental tests to investigate the life-cycle performance due to seasonal variations and evaluation of infrastructure resilience of IABs.
The project will have a strong impact on the application of the new version of Eurocode 8 – Part 2 on Bridges. The extensive use of Integral Bridges in earthquake-prone areas could bring an increased safety of road bridges.