About

Larry A. Fahnestock holds a B.S. in civil engineering and architectural engineering from Drexel University, an M.S. and Ph.D. in civil engineering from Lehigh University. He has been a faculty member in the Department of Civil and Environmental Engineering at the University of Illinois since 2006. His research interests include earthquake engineering, steel structures, seismic building design, structural stability, connection behavior, bridge performance under service and extreme loading, and progressive collapse mitigation. His projects employ large-scale laboratory experiments, field monitoring, and numerical simulations, supported by grants from organizations such as the National Science Foundation, American Institute of Steel Construction, Illinois Center for Transportation, Illinois Tollway, and DARPA. Dr. Fahnestock has held various academic positions at Illinois, including Associate Dean for Facilities and Capital Planning, Director of the Newmark Structural Engineering Laboratory, and Chair of the Structures Group. He has also served as an Education Innovation Fellow and an invited professor at Ecole Polytechnique Montreal. His professional activities include memberships in the American Institute of Steel Construction, the Earthquake Engineering Research Institute, and the Structural Stability Research Council, where he served on the executive committee and as chair. He is a licensed professional engineer in Illinois and California and has received numerous awards for teaching, advising, and research, including the ASCE Walter L. Huber Civil Engineering Research Prize and being named a Fellow of ASCE and the Structural Engineering Institute of ASCE.

Research topics

• Mathematics
• Engineering
• Structural engineering
• Civil engineering
• Materials science
• Composite material

Selected publications

• Point Cloud Processing for Damage Characterization of Steel I-Sections

  Journal of Structural Engineering · 2026-03-26

  articleSenior author

  When structural members experience impact damage, understanding their geometry is a critical step for assessing damage severity and determining how to maintain functionality and structural safety. Traditional methods for characterizing damage severity require hand measurements of displacement at discrete points along the member length. Terrestrial laser scanning (TLS) offers several advantages over manual measurements, such as more comprehensive data, improved accuracy, reduced need for lane closures, and avoiding work at height. However, TLS point cloud data are unstructured and must be processed to extract displacements. Existing methods for point cloud displacement measurements rely on manual techniques, where a point cloud is carefully manipulated to select individual points, but these approaches are impractical for obtaining a global member displacement curve. This paper presents a new semiautomated modular procedure for processing laser scan point cloud data of steel I-sections to obtain bottom-flange displacement curves along the length of a span. Several existing point cloud processing techniques are incorporated, including outlier removal, voxelization, cross-sectional slicing, and random sample consensus (RANSAC) regression. The proposed procedure measures horizontal and vertical displacements at three cross-sectional locations—the left corner, centerline, and right corner of the bottom-flange surface—so that the flange displacement and tilt can be accurately characterized. A person who has been trained can capture hundreds of measurements along a member length in less than an hour of postprocessing time, whereas existing methods would likely require several workdays to produce the same number of measurements. The procedure was developed using TLS data from steel I-girders damaged in overheight vehicle strikes on highway bridges. Laser scan data from a damaged steel-girder highway bridge in Mt. Vernon, Illinois, are used as a case study, and results from three other steel-girder highway bridges are also presented. The measurement procedure has been designed for implementation in structural engineering practice.

  PublisherDOI

• Explainable machine learning for predicting the load-carrying capacity of damaged steel girders after over-height vehicle strikes

  Engineering Structures · 2026-03-12

  articleOpen access

  Steel bridge girders are often subjected to strikes by over-height vehicles that exceed the allowable vertical clearance underneath a bridge. Such strikes may affect the serviceability of a bridge structure and can significantly reduce the load-carrying capacity of damaged girders. Although finite element analyses are commonly used to estimate the residual capacity of damaged girders, developing and analyzing such models for every strike incident is computationally intensive and time-consuming. To address these limitations, this paper presents a new explainable machine learning methodology that can accurately and efficiently predict the residual load-carrying capacity of damaged steel I-girders. The methodology is conducted in five main stages: (1) data collection, (2) data analysis and preprocessing, (3) model training, (4) model validation, and (5) model interpretation. Five machine learning models were developed and trained to predict the residual capacity of damaged girders. Results show that the eXtreme Gradient Boosting (XGBoost) algorithm outperformed all other models, achieving R 2 and MAPE scores of 95.4% and 3.21%, respectively, on the unseen test set. Moreover, the SHapley Additive exPlanations framework (SHAP) was used to explain the global performance of the XGBoost model and interpret its individual predictions. SHAP values revealed that predicted residual capacity is reduced by increases in girder span length and observed horizontal and vertical damage deflections. The proposed machine learning models are expected to provide bridge engineering researchers and practitioners with an efficient and explainable method for assessing the residual capacity of damaged steel I-girders without relying on time-consuming and computationally intensive simulations. • A dataset of simulated damaged steel I-girders was created using FE analysis. • Relationships between girder attributes and load-carrying capacity were investigated. • Several ML models were trained to predict residual capacity of damaged steel girders. • K-fold cross-validation was used to confirm the generalizability of ML models. • SHAP values were employed to interpret XGBoost model outputs of predicted capacities.

  PublisherDOI

• Analytical studies and pseudo-dynamic testing of an earthquake-resistant buckling-restrained braced frame

  2026-02-04

  article1st authorCorresponding

  Due to the recent attention that buckling-restrained braced frames (BRBFs) have received in the United States and the resulting need for knowledge about system behavior and performance, an integrated analytical and large-scale experimental research program on BRBFs has been initiated at the ATLSS Center, Lehigh University. Nonlinear time-history analyses were performed on a 4-story prototype BRBF using a suite of earthquake ground motions. The ground motions were scaled to two seismic input levels: the design basis earthquake (DBE) and the maximum considered earthquake (MCE). Good performance was observed at both input levels and the analytical studies were used to plan the large-scale experimental program. The laboratory experiments were conducted using the pseudo-dynamic testing method to simulate seismic input. Tests were conducted at various seismic input levels, including the DBE and MCE. Good performance was observed in the experimental program and the significant ductility capacity of BRBFs was verified.

  PublisherDOI

• Seismic Collapse Performance of Multitiered Ordinary Concentrically Braced Frames

  Journal of Structural Engineering · 2025-01-13 · 2 citations

  articleSenior author

  In tall, single-story buildings with steel concentrically braced frame (CBF) lateral force resisting systems, it is more efficient to replace a single brace or pair of braces between the base and the story (roof) level with multiple bracing panels or tiers, leading to a multitiered braced frame (MT-BF). MT-BFs lack intermediate out-of-plane supports at the tier levels, and most of the building mass is concentrated at the story level, so their seismic behavior is more complex than typical multistory CBFs. Inelastic response in MT-BFs during a seismic event can cause drift concentration in an individual frame tier and increase the propensity for column instability due to combined axial and flexural demands. These unique conditions have been the focus of studies that support the first-generation of MT-BF design requirements introduced in the 2016 AISC Seismic Provisions. Requirements for multitiered ordinary concentrically braced frames (MT-OCBFs), which is the focus of this paper, were based on a limited investigation, and the primary feature of the requirements is an axial force amplification (150% of the overstrength horizontal seismic load effect), intended to account for induced in-plane flexural demands. Prior to the introduction of design requirements specific to MT-OCBFs, they were designed as multistory frames without considering flexural demands. This study uses detailed nonlinear models to assess the seismic performance of a comprehensive set of MT-OCBF designs. The results show that potential for column instability in MT-OCBFs is reduced in designs considering the new axial force amplification, and frame collapse probabilities are within acceptable limits. The 2016 AISC Seismic Provisions also introduced an out-of-plane notional load requirement (0.6% of the vertical component of the compression brace force at each tier), which was intended to account for effects from buckling compression braces. Since this requirement does not influence column proportioning appreciably, and since performance was acceptable for MT-OCBFs, where the columns were designed without an out-of-plane notional load, this study suggests that it can be removed. MT-OCBF column instability is primarily related to axial force and in-plane moment, and the axial force amplification that accounts for this combination in a simple fashion is satisfactory.

  PublisherDOI

• Special Issue: Large‐Scale Testing of Earthquake‐Resistant Structures: Accomplishments and Future Challenges

  Earthquake Engineering & Structural Dynamics · 2025-08-20

  articleSenior author

  Summary Advanced experimental techniques for dynamic and quasi‐static testing Quantification of system‐level effects via physical experimentation Robust identification of dynamic and mechanical properties of structures via state‐of‐the‐art instrumentation Techniques for robust data storage and curation that enable data reuse for contemporary research Effective use of experimental data and methods for the further advancement of earthquake engineering

  PublisherDOI

• Field and Numerical Evaluations of Static and Dynamic Live Load Response in Skewed Steel I-Girder Bridges with Stub and Integral Abutments

  Journal of Bridge Engineering · 2025-04-24 · 1 citations

  article

  The behavior of skewed steel I-girder bridges under live load is complex and challenging to interpret due to sparse existing field data; predictions used in the design process can include oversimplifications regarding superstructure load distribution and girder lateral response. To further understand the static and dynamic live load response of skewed steel I-girder bridges with different abutment conditions, two continuous-span steel I-girder bridges, one of skew 41° with stub abutments and the other of skew 45° with integral abutments, were evaluated in the field under isolated (single truck) live load as full and temporary half (during staged construction) bridges. Tests were conducted at 3, 32, and 56 km/h (2, 20, and 35 mi/h, respectively) for multiple load paths; data acquisition systems measured field response at 20 Hz. Girders and cross-frames were instrumented with strain gauges, girder end rotations were measured with tiltmeters, and bridge end movements were monitored with displacement transducers. Field instrumentation provides insight into superstructure behavior and data for validation and refinement of three-dimensional numerical simulation approaches (e.g., representation of abutment and bearing conditions, proper inclusion of structural components, and modeling of connections). The simulation approaches were then adopted for assessing bridge live load behavior beyond the range of field measurements, which can also be used in other research with limited access to field information. The live load distribution factor for girder strong-axis bending in standard line girder analysis was observed to be conservative, especially for interior girders when considering loading from the isolated test truck. Girder bottom flange lateral bending stress along the bridge span (in-span) was more significant for interior than exterior girders under the live load tests, whereas the lateral bending stress near bridge supports was mostly uniform for all girders (and of smaller magnitude than the in-span stress). Truck live load generally induced the most critical response on adjacent girders and cross-frames, except when loading close to an exterior girder—considerable bottom flange lateral bending response was observed on multiple adjacent interior girders for the exterior loading, with peak stresses away from the directly loaded bridge obtuse corners. Dynamic live load effects were evaluated by calculating dynamic load allowance (DLA) based on field measurements; the DLA used in standard practice for strength limit states was generally acceptable but slightly unconservative for an integral abutment bridge exterior girder.

  PublisherDOI

• Data Paper: E‐Defense Shake‐Table Tests on a Steel Moment‐Resisting Frame Supplemented With Spines and Force‐Limiting Connections

  Japan Architectural Review · 2025-01-01

  articleOpen access

  ABSTRACT This data paper presents data obtained from E‐Defense shake‐table tests of a full‐scale, steel moment‐resisting frame (MRF) supplemented with Spines. Herein, the Spines were pin‐based columns with sufficient stiffness and strength to distribute plastic deformation evenly over the height of the MRF. The specimen was tested under two configurations: first, with the Spine rigidly connected to the MRF; second, with the Spine connected to the MRF through force‐limiting connections (FLCs). Each specimen configuration underwent earthquake simulations using ground motions with two scale factors. The tests demonstrated the expected benefits of Spines as well as the disadvantage of inducing large floor accelerations in the structure and large shear forces in the Spines. The tests also demonstrated how the FLCs can mitigate these disadvantages. This data paper reports an overview of the tests, data archive structure, and potential use of the data. The data can be used, for example, to reproduce the observations presented by the authors, to compare the dynamic response of the specimen with building specimens tested in other shake‐table test programs, to validate numerical models against the measured specimen response, or to formulate classroom exercises on system identification of linear and nonlinear systems.

  PublisherOA PDFDOI

• Parametric Assessment of Structural Behavior of Integral Abutment Bridge Approach Slabs When Subjected to Live Load and Thermal Effects

  Journal of Bridge Engineering · 2025-04-10

  articleSenior author

  Integral abutment bridges (IABs) have gained increasing popularity in the United States owing to their relatively low cost, simpler construction, greater service life, and better seismic performance. However, elimination of the joints in IABs raises concerns about distress to the structural system induced by live loads and thermal effects. IAB approach slab cracking has been a frequent example of such distress in Illinois. This paper presents validated numerical simulations of IAB approach slabs in Illinois based on typical design and construction practices, as well as on 2.5 years of thermal effect conditions obtained from field monitoring of two instrumented IAB approach slabs. Various approach slab parameters, boundary conditions, and loadings are examined in the simulations. From this parametric study, it is suggested that such approach slabs would generally not be prone to cracking from truck live loads, although certain skews and widths can increase the chances of cracking. However, when an approach slab is subjected to the combined effects of low temperature and solar radiation, the principal stress can reach the concrete modulus of rupture—and its distribution confirms some crack patterns observed in the field, especially for highly skewed approach slabs. Increasing the slab thickness and/or releasing restraint at the approach slab–abutment interface may aid in mitigating structural distress from live load and/or thermal effects for IAB approach slabs in Illinois.

  PublisherDOI

• Field-data-driven assessment of an in-service skewed integral abutment bridge assisted by deep learning

  Bridge Structures · 2025-02-01 · 1 citations

  articleSenior author

  Integral abutment bridges (IABs) exhibit complex and evolving structural behavior due to their interaction with the foundation and surrounding soil. Long-term effects, such as backfill soil ratcheting and cumulative in-plan superstructure rotation, can lead to unexpected structural responses that are not fully understood. This study analyzes more than 3 years of superstructure displacement, abutment rotation (tilt), and temperature data, collected at 0.5 Hz, from an in-service two-span skewed (45°) steel I-girder bridge with integral abutments and staggered-X-cross-frames. The study advances the understanding of IAB behavior, including behavioral anomalies, which could assist in the interpretation of stress deviations reported in previous studies. Findings show that the monitored IAB presents changing behavior, as well as an accumulation of transverse displacement and abutment tilt over time. Analysis indicates that boundary condition representation in finite element models should incorporate the flexibility provided by soil and pile deformation to accurately reflect field behavior. It is further observed that abutment tilt data displays different trends over short and long periods. Discrepancies between these trends underscore the complexity of IAB behavior under varying temperature conditions. Deep learning techniques, particularly long short-term memory models, assisted in identifying these behavioral patterns. This application demonstrates their potential for detecting subtle deviations in bridge response.

  PublisherDOI

• Short-Term Structural Response of Integral Abutment Bridge Approach Slabs Subjected to Live Loading and Thermal Effects

  Journal of Bridge Engineering · 2024-01-17 · 5 citations

  articleSenior author

  Integral abutment bridges (IABs) are prevalent in the US due to their lower maintenance and construction costs, as well as longer service life. However, approach slabs at IABs experience complex demands owing to the fact that there are no expansion joints between the ends of a bridge and its approach slabs. To provide comprehensive field data on the response of IAB approach slabs, a four-lane IAB cast-in-place approach slab and a three-lane IAB precast approach slab were instrumented during construction to elucidate approach slab structural behavior due to live load and thermal effects. Static truck load tests were conducted at various traffic lanes and shoulder locations on each of the instrumented approach slabs. Finite-element analysis (FEA) models were developed to simulate slab behavior under controlled live loading and thermal effects. Numerical modeling of slabs subjected to truck loads is used to estimate the modulus of subbase support under the approach slab. The strain and stress results from numerical modeling are consistent with the truck-induced behavior measured in the field, validating key assumptions of approach slab boundary conditions. A nonlinear thermal gradient profile is proposed to improve the ability of the FEA models to properly capture slab behavior under thermal effects. Solar radiation is found to introduce peak stresses greater than the live load stresses. It is also observed that simplified structural analysis in practice (neglecting parapets) can significantly underestimate stresses in approach slab edge regions.

  PublisherDOI

Recent grants

• Innovative Self-Centering Braces for Advanced Seismic Performance

  NSF · $149k · 2009–2012

• NEESR: Reserve Capacity in New and Existing Low-Ductility Steel Braced Frames

  NSF · $716k · 2012–2017

• Collaborative Research: Frame-Spine System with Force-Limiting Connections for Low-Damage Seismic Resilient Buildings

  NSF · $840k · 2019–2026

Frequent coauthors

• James M. LaFave

  University of Illinois Urbana-Champaign

  45 shared

• Eric M. Hines

  23 shared

• Richard Sause

  22 shared

• James M. Ricles

  Lehigh University

  19 shared

• Robert Tremblay

  17 shared

• Cameron R. Bradley

  Tufts University

  16 shared

• Christopher Stoakes

  Engineering Arts (United States)

  15 shared

• Joshua S. Steelman

  14 shared

Awards & honors

• ASCE Raymond C. Reese Research Prize (2009)
• AISC Faculty Fellowship (2009)
• University of Illinois Campus Distinguished Promotion Award…
• ASCE Walter L. Huber Civil Engineering Research Prize (2014)
• Fellow of the Structural Engineering Institute of ASCE (2017…