Search

Search Results

• 11. [Article] Achieving Operational Seismic Performance of RC Bridge Bents Retrofitted With Buckling-Restrained Braces

  Typical reinforced concrete (RC) bridges built prior to 1970 were designed with minimum seismic consideration, leaving numerous bridges highly susceptible to damage following an earthquake. In order to ...

  Citation × Citation Citation Abstract Copy Title: Achieving Operational Seismic Performance of RC Bridge Bents Retrofitted With Buckling-Restrained Braces Author: Bazáez Gallardo, Ramiro Andrés Gabriel Year: 2017 Typical reinforced concrete (RC) bridges built prior to 1970 were designed with minimum seismic consideration, leaving numerous bridges highly susceptible to damage following an earthquake. In order to improve the seismic behavior of substandard RC bridges, this study presents the seismic performance of reinforced concrete bridge bents retrofitted and repaired using Buckling-Restrained Braces (BRBs) while considering subduction zone earthquake demands. In order to reflect displacement demands from subduction ground motions, research studies were conducted to develop quasi-static loading protocols and then investigate their effect on structural bridge damage. Results suggested that subduction loading protocols may reduce the displacement ductility capacity of RC bridge columns and change their failure mode. The cyclic performance of reinforced concrete bridge bents retrofitted and repaired using BRBs was experimentally evaluated using large-scale specimens and the developed loading histories. Three BRB specimens were evaluated with the aim of assessing the influence of these components on the overall performance of the retrofitted and repaired bents. Additionally, subassemblage tests were conducted in an effort to study the response of these elements and to allow for refined nonlinear characterization in the analysis of the retrofitted and repaired systems. The results of the large-scale experiments and analytical studies successfully demonstrated the effectiveness of utilizing buckling-restrained braces for achieving high displacement ductility of the retrofitted and repaired structures, while also controlling the damage of the existing vulnerable reinforced concrete bent up to an operational performance level. Title: Achieving Operational Seismic Performance of RC Bridge Bents Retrofitted With Buckling-Restrained Braces Author: Bazáez Gallardo, Ramiro Andrés Gabriel Year: 2017 Typical reinforced concrete (RC) bridges built prior to 1970 were designed with minimum seismic consideration, leaving numerous bridges highly susceptible to damage following an earthquake. In order to improve the seismic behavior of substandard RC bridges, this study presents the seismic performance of reinforced concrete bridge bents retrofitted and repaired using Buckling-Restrained Braces (BRBs) while considering subduction zone earthquake demands. In order to reflect displacement demands from subduction ground motions, research studies were conducted to develop quasi-static loading protocols and then investigate their effect on structural bridge damage. Results suggested that subduction loading protocols may reduce the displacement ductility capacity of RC bridge columns and change their failure mode. The cyclic performance of reinforced concrete bridge bents retrofitted and repaired using BRBs was experimentally evaluated using large-scale specimens and the developed loading histories. Three BRB specimens were evaluated with the aim of assessing the influence of these components on the overall performance of the retrofitted and repaired bents. Additionally, subassemblage tests were conducted in an effort to study the response of these elements and to allow for refined nonlinear characterization in the analysis of the retrofitted and repaired systems. The results of the large-scale experiments and analytical studies successfully demonstrated the effectiveness of utilizing buckling-restrained braces for achieving high displacement ductility of the retrofitted and repaired structures, while also controlling the damage of the existing vulnerable reinforced concrete bent up to an operational performance level. Close

• 12. [Article] GPS Constraints on the Mw = 7.5 Ometepec Earthquake Sequence, Southern Mexico: Coseismic and Post-Seismic Deformation

  We use continuous GPS measurements from 31 stations in southernMexico to model coseismic slip and post-seismic deformation from the 2012 March 20 Mw = 7.5 Ometepec earthquake, the first large thrust earthquake ...

  Citation × Citation Citation Abstract Copy Title: GPS Constraints on the Mw = 7.5 Ometepec Earthquake Sequence, Southern Mexico: Coseismic and Post-Seismic Deformation Author: Graham, Shannon E., DeMets, Charles, Cabral-Cano, Enrique, Kostoglodov, Vladimir, Walpersdorf, Andrea, Cotte, Nathalie, Brudzinski, Michael, McCaffrey, Robert, Salazar-Tlaczani, Luis Year: 2014 We use continuous GPS measurements from 31 stations in southernMexico to model coseismic slip and post-seismic deformation from the 2012 March 20 Mw = 7.5 Ometepec earthquake, the first large thrust earthquake to occur below central Mexico during the modern GPS era. Coseismic offsets ranging from ∼280 mm near the epicentre to 5 mm or less at sites far from the epicentre are fit best by a rupture focused between ∼15 and 35 km depth, consistent with an independent seismological estimate. The corresponding geodetic moment of 1.4 × 1020 N·m is within 10 per cent of two independent seismic estimates. Transient post-seismic motion recorded by GPS sites as far as 300 km from the rupture has a different horizontal deformation gradient and opposite sense of vertical motion than do the coseismic offsets. A forward model of viscoelastic relaxation as a result of our new coseismic slip solution incorrectly predicts uplift in areas where post-seismic subsidence was recorded and indicates that viscoelastic deformation was no more than a few per cent of the measured post-seismic deformation. The deformation within 6 months of the earthquake was thus strongly dominated by fault afterslip. The post-seismic GPS time-series are well fit as logarithmically decaying fault afterslip on an area of the subduction interface up to 10 times larger than the earthquake rupture zone, extending as far as 220 km inland. Afterslip had a cumulative geodetic moment of 2.0 × 1020 N·m, ∼40 per cent larger than the Ometepec earthquake. Tests for the shallow and deep limits for the afterslip require that it included much of the earthquake rupture zone as well as regions of the subduction interface where slow slip events and non-volcanic tremor have been recorded and areas even farther downdip on the flat interface. Widespread afterslip below much of central Mexico suggests that most of the nearly flat subduction interface in this region is conditionally stable and thus contributes measurable transient deformation to large areas of Mexico south of and in the volcanic belt. Title: GPS Constraints on the Mw = 7.5 Ometepec Earthquake Sequence, Southern Mexico: Coseismic and Post-Seismic Deformation Author: Graham, Shannon E., DeMets, Charles, Cabral-Cano, Enrique, Kostoglodov, Vladimir, Walpersdorf, Andrea, Cotte, Nathalie, Brudzinski, Michael, McCaffrey, Robert, Salazar-Tlaczani, Luis Year: 2014 We use continuous GPS measurements from 31 stations in southernMexico to model coseismic slip and post-seismic deformation from the 2012 March 20 Mw = 7.5 Ometepec earthquake, the first large thrust earthquake to occur below central Mexico during the modern GPS era. Coseismic offsets ranging from ∼280 mm near the epicentre to 5 mm or less at sites far from the epicentre are fit best by a rupture focused between ∼15 and 35 km depth, consistent with an independent seismological estimate. The corresponding geodetic moment of 1.4 × 1020 N·m is within 10 per cent of two independent seismic estimates. Transient post-seismic motion recorded by GPS sites as far as 300 km from the rupture has a different horizontal deformation gradient and opposite sense of vertical motion than do the coseismic offsets. A forward model of viscoelastic relaxation as a result of our new coseismic slip solution incorrectly predicts uplift in areas where post-seismic subsidence was recorded and indicates that viscoelastic deformation was no more than a few per cent of the measured post-seismic deformation. The deformation within 6 months of the earthquake was thus strongly dominated by fault afterslip. The post-seismic GPS time-series are well fit as logarithmically decaying fault afterslip on an area of the subduction interface up to 10 times larger than the earthquake rupture zone, extending as far as 220 km inland. Afterslip had a cumulative geodetic moment of 2.0 × 1020 N·m, ∼40 per cent larger than the Ometepec earthquake. Tests for the shallow and deep limits for the afterslip require that it included much of the earthquake rupture zone as well as regions of the subduction interface where slow slip events and non-volcanic tremor have been recorded and areas even farther downdip on the flat interface. Widespread afterslip below much of central Mexico suggests that most of the nearly flat subduction interface in this region is conditionally stable and thus contributes measurable transient deformation to large areas of Mexico south of and in the volcanic belt. Close

• 13. [Article] Cyclic Behavior of Reinforced Concrete Bridge Bent Retrofitted with Buckling Restrained Braces

  The cyclic behavior of a deficient reinforced concrete bridge bent retrofitted using buckling restrained braces (BRBs) was experimentally evaluated using large scale experiments and quasi-static cyclic ...

  Citation × Citation Citation Abstract Copy Title: Cyclic Behavior of Reinforced Concrete Bridge Bent Retrofitted with Buckling Restrained Braces Author: Bazaez, Ramiro, Dusicka, Peter Year: 2016 The cyclic behavior of a deficient reinforced concrete bridge bent retrofitted using buckling restrained braces (BRBs) was experimentally evaluated using large scale experiments and quasi-static cyclic loading that reflected subduction zone earthquake demands. The retrofitted reinforced concrete bent specimen consisted of two circular cross section columns, a rectangular cap beam and a buckling restrained brace in a diagonal configuration. The brace was secured to the bent using steel gusset plates and post-installed adhesive anchors. The retrofitted bent was designed to perform elastically or with minor damage under different seismic hazards design levels. Two BRB designs were considered in an effort to assess the influence of the BRB design on the overall bent performance. The data from these large-scale experiments were analyzed considering bent hysteretic response, observed damage, component curvatures, internal member loads, as well as the overall stiffness and energy dissipation characteristics. The results successfully demonstrated the effectiveness of utilizing buckling restrained braces for achieving high displacement ductility of the retrofitted structure, while also controlling the damage of the existing vulnerable reinforced concrete bent. No damage was observed in the connection regions of the brace throughout the loading history, leaving the potential for rapid replaceability of the sacrificial BRB element. Title: Cyclic Behavior of Reinforced Concrete Bridge Bent Retrofitted with Buckling Restrained Braces Author: Bazaez, Ramiro, Dusicka, Peter Year: 2016 The cyclic behavior of a deficient reinforced concrete bridge bent retrofitted using buckling restrained braces (BRBs) was experimentally evaluated using large scale experiments and quasi-static cyclic loading that reflected subduction zone earthquake demands. The retrofitted reinforced concrete bent specimen consisted of two circular cross section columns, a rectangular cap beam and a buckling restrained brace in a diagonal configuration. The brace was secured to the bent using steel gusset plates and post-installed adhesive anchors. The retrofitted bent was designed to perform elastically or with minor damage under different seismic hazards design levels. Two BRB designs were considered in an effort to assess the influence of the BRB design on the overall bent performance. The data from these large-scale experiments were analyzed considering bent hysteretic response, observed damage, component curvatures, internal member loads, as well as the overall stiffness and energy dissipation characteristics. The results successfully demonstrated the effectiveness of utilizing buckling restrained braces for achieving high displacement ductility of the retrofitted structure, while also controlling the damage of the existing vulnerable reinforced concrete bent. No damage was observed in the connection regions of the brace throughout the loading history, leaving the potential for rapid replaceability of the sacrificial BRB element. Close

• 14. [Article] Geostatistical Examination of the Geotechnical Portland BES Databases with Emphasis on Silt

  Willamette Valley silt deposits from historical catastrophic flood events present a difficult problem for subsurface engineers practicing in the Portland, Oregon area. Silts exhibit behavior of two very ...

  Citation × Citation Citation Abstract Copy Title: Geostatistical Examination of the Geotechnical Portland BES Databases with Emphasis on Silt Author: Baumann, Alex K. Year: 2015 Willamette Valley silt deposits from historical catastrophic flood events present a difficult problem for subsurface engineers practicing in the Portland, Oregon area. Silts exhibit behavior of two very well-documented soil types, but publications containing mechanical properties for silts are scant, especially for local silts. Thus, the need for links between real Portland site investigation data and silt properties is high. To further exemplify the need for documented knowledge of local silts, this project reveals the evolving state of practice to incorporate more Pacific Northwest seismic analyses in preparation for a subduction zone earthquake. The geotechnical Portland BES databases contain thousands of private sector (PrS) and public sector (PbS) geotechnical documents from sites in the Portland area. The PrS database includes approximately 7,000 geotechnical documents for PrS projects dating primarily from the mid 1900’s to 2009 for a range of project types. A statistically significant random sample of 1,500 documents from the PrS database was organized and analyzed. The approximate 1,000 documents in the PbS database containing boring logs can be linked to location through a pre-existing GIS layer. The statistically significant sample from the PrS database and the GIS layer from the PbS database were compared spatially to reveal clusters of documented geotechnical projects. An isolated cluster of 80 full geotechnical reports in the Downtown, Portland area from reputable practitioners was examined for standard penetration blow counts, equipment information, groundwater table depths, soil descriptions, unit weights, drill dates, and moisture contents to capture a range of correlated peak effective friction angles for different compositions of silt. The project types and report contents from the PrS database were analyzed in the Downtown area, and conclusions were made on the percentages of project types and apparent chronological trends in report content. Title: Geostatistical Examination of the Geotechnical Portland BES Databases with Emphasis on Silt Author: Baumann, Alex K. Year: 2015 Willamette Valley silt deposits from historical catastrophic flood events present a difficult problem for subsurface engineers practicing in the Portland, Oregon area. Silts exhibit behavior of two very well-documented soil types, but publications containing mechanical properties for silts are scant, especially for local silts. Thus, the need for links between real Portland site investigation data and silt properties is high. To further exemplify the need for documented knowledge of local silts, this project reveals the evolving state of practice to incorporate more Pacific Northwest seismic analyses in preparation for a subduction zone earthquake. The geotechnical Portland BES databases contain thousands of private sector (PrS) and public sector (PbS) geotechnical documents from sites in the Portland area. The PrS database includes approximately 7,000 geotechnical documents for PrS projects dating primarily from the mid 1900’s to 2009 for a range of project types. A statistically significant random sample of 1,500 documents from the PrS database was organized and analyzed. The approximate 1,000 documents in the PbS database containing boring logs can be linked to location through a pre-existing GIS layer. The statistically significant sample from the PrS database and the GIS layer from the PbS database were compared spatially to reveal clusters of documented geotechnical projects. An isolated cluster of 80 full geotechnical reports in the Downtown, Portland area from reputable practitioners was examined for standard penetration blow counts, equipment information, groundwater table depths, soil descriptions, unit weights, drill dates, and moisture contents to capture a range of correlated peak effective friction angles for different compositions of silt. The project types and report contents from the PrS database were analyzed in the Downtown area, and conclusions were made on the percentages of project types and apparent chronological trends in report content. Close

• 15. [Article] Seismic Retrofit Benefit Considering Statewide Transportation Assessment

  The purpose of this study was to identify and demonstrate a methodology to prioritize bridges for retrofit in the State of Oregon. Given the limited resources available, retrofitting all vulnerable bridges ...

  Citation × Citation Citation Abstract Copy Title: Seismic Retrofit Benefit Considering Statewide Transportation Assessment Author: Mehary, Selamawit Tesfayesus, Dusicka, Peter Year: 2015 The purpose of this study was to identify and demonstrate a methodology to prioritize bridges for retrofit in the State of Oregon. Given the limited resources available, retrofitting all vulnerable bridges in the foreseeable future would not be practical. Instead, a retrofit strategy needs to be developed to prioritize the inventory and enumerate the retrofit cost. In this study, a prioritization methodology used a holistic assessment of overall roadway system to consider highway route segments, rather than individual bridges. The overall assessment was based on a cost-benefit analysis including retrofit cost, expected economic loss (with or without retrofit) and social loss caused by system wide travel time delays. A review of 2010 ODOT bridge inventory suggested that a continuous concrete girder bridge (CCGS) with three spans could be utilized to represent a sizeable portion of vulnerable inventory for Oregon highways bridges. After reviewing several potential retrofit measures, carbon fiber composite material was selected for retrofit of vulnerable columns representing those built from the 1950s to mid-1970s. Four full-scale typical square columns were tested to failure. The results showed that despite the intentionally selected square geometry of the reinforced concrete columns, the CFRP composite material showed to be an effective retrofit measure and could be deployed for to address this deficiency. The software package REDARS2 was used for seismic risk analysis (SRA) of the highway network in this study. This platform was adopted to simulate the impact of scenario earthquakes in an effort to assess the expected benefit considering direct bridge costs as well as social costs from traffic induced delays resulting from seismic retrofitting of a particular bridge type. The assessment considered three scenario Cascadia Subsection Zone earthquakes of magnitudes 9.0, 8.5 North, and, 8.5 South. The study area included all highway routes west of the I-5 corridor, highway routes in the Portland area, the entire length of US-101 and extending partially east on I-84 Columbia River Highway. Due to the considerations of a single bridge type and other limitations identified in the seismic analysis software (REDARS2), the retrofit assessment outcomes should be regarded as a first order estimate. Title: Seismic Retrofit Benefit Considering Statewide Transportation Assessment Author: Mehary, Selamawit Tesfayesus, Dusicka, Peter Year: 2015 The purpose of this study was to identify and demonstrate a methodology to prioritize bridges for retrofit in the State of Oregon. Given the limited resources available, retrofitting all vulnerable bridges in the foreseeable future would not be practical. Instead, a retrofit strategy needs to be developed to prioritize the inventory and enumerate the retrofit cost. In this study, a prioritization methodology used a holistic assessment of overall roadway system to consider highway route segments, rather than individual bridges. The overall assessment was based on a cost-benefit analysis including retrofit cost, expected economic loss (with or without retrofit) and social loss caused by system wide travel time delays. A review of 2010 ODOT bridge inventory suggested that a continuous concrete girder bridge (CCGS) with three spans could be utilized to represent a sizeable portion of vulnerable inventory for Oregon highways bridges. After reviewing several potential retrofit measures, carbon fiber composite material was selected for retrofit of vulnerable columns representing those built from the 1950s to mid-1970s. Four full-scale typical square columns were tested to failure. The results showed that despite the intentionally selected square geometry of the reinforced concrete columns, the CFRP composite material showed to be an effective retrofit measure and could be deployed for to address this deficiency. The software package REDARS2 was used for seismic risk analysis (SRA) of the highway network in this study. This platform was adopted to simulate the impact of scenario earthquakes in an effort to assess the expected benefit considering direct bridge costs as well as social costs from traffic induced delays resulting from seismic retrofitting of a particular bridge type. The assessment considered three scenario Cascadia Subsection Zone earthquakes of magnitudes 9.0, 8.5 North, and, 8.5 South. The study area included all highway routes west of the I-5 corridor, highway routes in the Portland area, the entire length of US-101 and extending partially east on I-84 Columbia River Highway. Due to the considerations of a single bridge type and other limitations identified in the seismic analysis software (REDARS2), the retrofit assessment outcomes should be regarded as a first order estimate. Close