Andre R. Barbosa

Application of Reliability-Based Robustness Assessment of Steel Moment Resisting Frame Structures under Post-Mainshock Cascading Events

This paper proposes a reliability-based framework for quantifying structural robustness considering the occurrence of a major earthquake (mainshock) and subsequent cascading hazard events, such as aftershocks that are triggered by the mainshock. These events can significantly increase the probability of failure of buildings, especially for structures that are damaged during the mainshock. The application of the proposed framework is exemplified through three numerical case studies. The case studies correspond to three SAC steel moment frame buildings of three, nine, and 20 stories, which were designed to pre-Northridge codes and standards. Two-dimensional nonlinear finite-element models of the buildings are developed with the Open System for Earthquake Engineering Simulation framework (OpenSees), using a finite length plastic hinge beam model and a bilinear constitutive law with deterioration, and are subjected to multiple mainshock-aftershock seismic sequences. For the three buildings analyzed herein, it is shown that the structural reliability under a single seismic event can be significantly different from that under a sequence of seismic events. The reliability based robustness indicator shows that the structural robustness is influenced by the extent to which a structure can distribute damage.

Deterioration modeling of steel moment resisting frames using finite-length plastic hinge force-based beam-column elements

AbstractThe use of empirically calibrated moment-rotation models that account for strength and stiffness deterioration of steel frame members is paramount in evaluating the performance of steel structures prone to collapse under seismic loading. These deterioration models are typically used as zero-length springs in a concentrated plasticity formulation; however, a calibration procedure is required when they are used to represent the moment-curvature (M−χ) behavior in distributed plasticity formulations because the resulting moment-rotation (M−θ) response depends on the element integration method. A plastic hinge integration method for using deterioration models in force-based elements is developed and validated using flexural stiffness modifications parameters to recover the exact solution for linear problems while ensuring objective softening response. To guarantee accurate results in both the linear and nonlinear range of response, the flexural stiffness modification parameters are computed at the begi...

Viability of Hybrid Poplar in ANSI Approved Cross-Laminated Timber Applications

AbstractThe development of cross-laminated timber (CLT) technology has opened up new opportunities for low-density hardwood species, which have traditionally not been rated as construction-grade materials for structural engineering applications. Several characteristics of CLT, namely thermal performance, seismic behavior, and speed of construction, have raised interest among designers. The CLT technology has recently been used for residential and nonresidential multistory buildings and it has been identified as one of the ways of achieving tall timber building construction. As CLT gains acceptance in the industry, low-density wood species, not specified in current ANSI standards, need to be investigated for potentially successful use in CLT panels. This paper presents a study that demonstrates the viability of a Forest Stewardship Council (FSC) certified sustainable plantation grown low-density species, hybrid poplar (marketed as Pacific Albus), for use in performance-rated CLT panels by following the ANS...

Methodology for Development of Physics-Based Tsunami Fragilities

AbstractTsunamis affect coastal regions around the world, resulting in fatalities and catastrophic damage to communities. Fragility functions form the basis of most risk and resilience analyses at ...

Structural Identification of an 18-Story RC Building in Nepal Using Post-Earthquake Ambient Vibration and Lidar Data

Few studies have been conducted to assess post-earthquake performance of structures using vibration measurements. This paper presents system identification and finite element modeling of an 18-story apartment building that was damaged during the 2015 Gorkha earthquake in Nepal. In July 2016, a few months after the earthquake, the authors visited the building and collected its ambient acceleration response. The recorded data are analyzed and the modal parameters of the structure are identified using an output-only system identification method. A linear finite element model of the building is also developed based on the geometry of the building and its material properties to estimate numerically its dynamic characteristics. The identified modal parameters are compared to those of the model to identify possible shortcomings of the modeling and identification approaches. The identified natural frequencies and mode shapes of the first two vibration modes are in good agreement with the model.

Seismic Performance of High-Strength Steel RC Bridge Columns

AbstractThis paper presents the results of a testing program developed to assess the performance of circular RC bridge columns constructed with ASTM A706 Grade 80 [550] high-strength steel (HSS) reinforcement. Two pairs of columns were tested (four columns in total). The columns were subjected to lateral cyclic loading to determine the effects of steel reinforcement grade (yield strength) and of moment–shear span ratio on column performance. Each pair consisted of one column constructed with Grade 80 [550] HSS reinforcement and a control column constructed with Grade 60 [420] reinforcement. The first pair had a moment–shear span ratio of six (6), and the second pair had a moment–shear span ratio of three (3). All four columns were designed to have similar nominal bending-moment capacities. Results indicate that the columns constructed with Grade 80 [550] HSS reinforcement achieve similar resistance, similar maximum lateral displacements, and similar curvature ductility values when compared with the contro...

Multiple-Hazard Fragility and Restoration Models of Highway Bridges for Regional Risk and Resilience Assessment in the United States: State-of-the-Art Review

AbstractHighway bridges are one of the most vulnerable constituents of transportation networks when exposed to one or more natural hazards, such as earthquakes, hurricanes, tsunamis, and riverine floods. To facilitate and enhance prehazard and posthazard event mitigation and emergency response strategies of transportation systems and entire communities, probabilistic risk and resilience assessment methodologies have attracted increased attention recently. In this context, fragility and restoration models for highway bridges subjected to a range of hazards are essential tools for efficient and accurate quantification of risk and resilience. This paper provides a comprehensive review of state-of-the-art fragility and restoration models for typical highway bridge classes that are applicable for implementation in multihazard risk and resilience analyses of regional portfolios or transportation networks in the United States. An overview of key gaps in the literature is also presented to guide future research.

Probabilistic Seismic and Tsunami Hazard Analysis Conditioned on a Megathrust Rupture of the Cascadia Subduction Zone

This paper presents a framework for a probabilistic hazard assessment for the multi-hazard seismic and tsunami phenomena (PSTHA). For this work, we consider a full-rupture event along the Cascadia Subduction Zone and apply the methodology to the study area of Seaside, Oregon, along the US Pacific Northwest coast. In this work, we show that the annual exceedance probabilities (AEP) of the tsunami intensity measures (IM) are qualitatively dissimilar to the IMs of the seismic ground motion in the study area. Specifically, the spatial gradients for the tsunami IM are much stronger across the length scale of the city owing to the physical differences of energy dissipation of the two mechanisms. Example results of probabilistic seismic hazard analysis (PSHA) and probabilistic tsunami hazard analysis (PTHA) are shown for three observation points in the study area of Seaside. For the seismic hazard, the joint mean annual rate of exceedance shows similar trends for the three observation points, even though there is a large scatter between and . For the tsunami hazard, the joint AEP of hmax and (MF)max shows a high correlation between the two IMs in the study area. The joint AEP at each of the three observation points follows a particular Froude number (Fr) due to the local site-specific conditions locally rather than the distributions of fault slips. The joint probability distribution of hmax and (MF)max throughout the study region falls between 0.1 ≤ Fr < 1.0 (i.e., the flow is subcritical) regardless of return interval (500-, 1,000-, and 2,500-yr). However, the peak of the joint probability distribution with respect to hmax and (MF)max varies with the return interval, and the largest values of hmax and (MF)max were observed with the highest return intervals (2,500 yr) as would be expected. The results of the PSTHA can be the basis for a probabilistic multi-hazard damage assessment and help to understand the uncertainties of the multi-hazard assessments.

Performance of Steel Energy Dissipators Connected to Cross-Laminated Timber Wall Panels Subjected to Tension and Cyclic Loading

AbstractThis paper presents a new alternative energy dissipation solution to be used with cross-laminated timber (CLT) self-centering walls. CLT is a relatively new building product in North America and could potentially be used for high-rise construction. The development of high-performance seismic design solutions is necessary to encourage innovative structures and the design of these structures to new heights. The objective of this paper is to propose a wall-to-floor connection system that is easy to install and replace (structural fuse) after the occurrence of a large damaging event. The proposed energy dissipators are fabricated following concepts used in developing steel buckling restrained steel braces (BRB), having a milled portion, which is designed to yield and is enclosed within a grouted steel pipe. The connection system is investigated experimentally through a test sequence of displacement-controlled cycles based on a modified version of the test method developed by the American Concrete Inst...

Structural Assessment of a School Building in Sankhu, Nepal Damaged Due to Torsional Response During the 2015 Gorkha Earthquake

This paper discusses the structural assessment of a red-tagged four-story school building in Sankhu, Nepal. The building had a masonry-infilled reinforced concrete frame which was severely damaged during the 2015 Gorkha Earthquake. The concentration of damage in the west end of the first story indicates that the frame exhibited torsional response to the ground excitation. The authors visited the structure 2 months after the earthquake, collected LiDAR scans, and recorded the ambient vibrations of the damaged structure. The LiDAR data has been used to create a three-dimensional point cloud of the building which has allowed the identification of the locations and geometry of the major cracks but also the measurement of the permanent deformations of the building. The structure was also instrumented with four unidirectional accelerometers on every floor; two at opposite corners, to capture the translational and torsional motion. The translational and torsional modes have been identified with an operational modal analysis method and have been used to validate a finite element model of the structure. The comparison indicates that the model can capture the modal properties of the structure utilizing the strut modeling approach for the infill panels.