Simpson Gumpertz & Heger Inc. (SGH) is a privately held ENR 500 engineering firm that designs, investigates, and rehabilitates structures and building enclosures. Their work encompasses commercial, institutional and residential buildings, transportation, water/wastewater, nuclear, science, and defense structure projects throughout the U.S. and over twenty foreign countries. SGH has 625 employees at eight offices in Atlanta, Boston, Chicago, Houston, New York City, Oakland, Southern California and Washington, D.C.
Train-induced ground vibrations can propagate into pile foundations, potentially causing undesirable vibration in nearby buildings, laboratories housing vibration-sensitive equipment, and manufacturing facilities for high-precision processes. This paper presents an innovative method for predicting building vibration from free-field ground vibration measurements at locations away from the tracks during train pass-bys. The proposed method accounts for site-specific soil profiles and train-soil-pile-structure interactions and is implemented in four steps. In Step 1, train-induced vibration transmission into the ground is estimated using an axisymmetric finite element model that simulates wave propagation through layered soils from the tracks to free-field ground locations. Step 2 estimates free pile head vibration using a three-dimensional finite-element model that captures the ground-borne transmission of track inputs through soil layers to the pile. Step 3 estimates vibration at the junction of the pile head and depot column base using a finite-element model to estimate the pile head impedance and an analytical impedance model for the depot structures supported by the pile. In Step 4, estimates of column-base vibration that transmits into over-track buildings are compared to measured column-base vibration levels obtained during train pass-bys. The method was applied at a metro depot in China, where tracks were in close proximity to columns supporting over-track buildings. Ground and column base vibration levels were measured during multiple train pass-bys. The estimated vibration levels at the base of depot columns closely agreed with the measured vibration levels at the columns during six-car train pass-bys. It demonstrated the potential effectiveness of this hybrid method for assessing vibration transmission into structures atop existing railway tracks. By integrating field measurements, finite element simulations, and analytical impedance models, the proposed hybrid method provides a framework for evaluating the transmission of the train-induced vibration to nearby building structures.
Hybrid Isolated-Rocking (HIR) columns comprising precast concrete segments, unbonded post-tensioning tendons, and lead rubber bearings offer promising seismic performance by enabling rocking motion, self-centering, and energy dissipation. This study presents a novel two-dimensional finite element framework for simulating the seismic behavior of HIR columns. A modified bearing element was developed in OpenSees to account for the coupled effects of axial load and bending moment on shear behavior. The proposed model was validated against detailed three-dimensional simulations conducted in ABAQUS. A comprehensive parametric study was carried out to evaluate the key design parameters, including the maximum achievable shear strain, number and location of bearings, and their characteristic strength. Furthermore, the effect of vertical earthquake excitation was assessed using time-history analyses under far-field ground motions. The results indicated that increasing the characteristic strength of the bearings (Qd) can enhance the column's effective damping up to 20 %, thereby reducing its seismic demands. Additionally, the results indicated that positioning the bearings within the upper third of the column height enhances energy dissipation and reduces lateral displacements. Notably, the vertical component of far-field earthquake excitation has a negligible influence on the seismic response of HIR columns, due to the dominant role of axial loads from gravity and post-tensioning.
The objective of this paper is to evaluate the seismic design parameters for modular metal building systems in high seismic zones in the United States using the FEMA P695 (ATC, 2009) methodology. Modular metal buildings, commonly used for large open spaces such as warehouses and data centers, combine traditional built-up tapered steel frames with intermediate gravity-only columns. A suite of archetype buildings with varying spans, heights, and number of modules was developed in collaboration with industry and analyzed using nonlinear static and dynamic procedures. High-fidelity shell finite element models, validated against component and shake table tests, capture key failure modes, including local and global buckling. Results from pushover and quasi-static cyclic analyses were used to calibrate nonlinear single-degree-of-freedom models for subsequent incremental dynamic analyses against the FEMA P695 earthquake suite. The study demonstrates that modular metal buildings designed with a response modification factor R = 3.5 meet the FEMA P695 collapse performance criteria, provided that lateral bracing systems are designed to meet both strength and stiffness requirements of AISC 360. Buildings using traditional strength-only bracing exhibited limited ductility due to premature column buckling, whereas AISC-compliant bracing achieved stable post-peak response and improved collapse margins. A collapse drift limit of 6% is proposed based on system flexibility and observed behavior. The findings confirm the adequacy and applicability of current ASCE 7 ordinary moment frame provisions for modular metal building systems, with important implications for design practice in high-seismic regions.
The objective of this paper is to explore the seismic performance of metal building systems when they are designed as steel ordinary moment frames (OMFs), but have wall and roof dead loads that exceed prescriptive limits in the United States loads standard (ASCE 7). A set of archetype frames — spanning both clear span and modular metal building system geometries — was developed in collaboration with industry and subjected to a FEMA P-695-based seismic assessment. At the core of the assessment is an advanced shell finite element model of the metal building systems, exercised through a nonlinear hysteretic protocol to accurately capture the response of the system. The shell finite element models inform the calibration of nonlinear single-degree-of-freedom models used in incremental dynamic analyses under the FEMA P-695 ground motion suite. The results show that heavier roof and wall loads can reduce system ductility and collapse margins in certain configurations. However, all archetypes that satisfy a set of simple frame member proportioning criteria, achieve acceptable performance under the evaluated seismic demands. These findings support the extension of OMF-based designs to heavier wall and roof loads if the additional proportioning requirements are included.
While rate and scale effects influence the strength and inelastic behavior of geomaterials, their interplay in borehole failure problems remains largely unexplored, posing challenges for assessing the stability of small-diameter boreholes in time-sensitive rocks. This work proposes a nonlocal gradient viscoplastic model to numerically investigate this issue. Within the model, the viscoplastic shear strain is linked to a nonlocal variable through a non-standard balance equation, whose analogy to the heat equation enables a straightforward numerical implementation of the coupled governing equations. At the integration point level, the classical fully implicit integration scheme is extended to incorporate both rate dependence and nonlocal gradient regularization. The improved applicability of this framework over standard approaches is demonstrated through numerical examples. Simulations of loading-induced borehole failure, validated against experimental data, reveal that hole strength decreases as the system scale to material length scale ratio increases, indicating pronounced scale effects. Meanwhile, the failure pattern changes from a homogenous type to shear-bands-dominated one. Higher loading rates increase hole strength and attenuate scale effects, as evidenced by reduced discrepancies in strength and failure modes across different borehole sizes. Under creep conditions, smaller boreholes require higher far-field pressures to induce delayed failure. When subjected to identical, sufficiently high far-field pressures, larger boreholes fail in shorter creep times, while increasing the pressure mitigates these differences.
