John L. Gross

Novel Extreme Value Estimation Procedures: Application to Extreme Wind Data

The past two decades have seen the development of a large body of extreme value theory based on the application of the Generalized Pareto Distribution (GPD) to the excess of the extreme variate over a fixed threshold. For sufficiently large values of the extreme variates, the GPD with tail length parameters c > 0 and c < 0 is equivalent, respectively, to the Type II (Frechet) and Type III (reverse Weibull) distribution of the largest values. The Type I (Gumbel) distribution is equivalent to the limit of the GPD as c→0. Owing to these equivalences, the GPD can be used to model extreme data obtained by either the ’peaks over threshold’ approach or the epochal approach.

A connection model for the seismic analysis of welded steel moment frames

An analytical approach is described for performing seismic evaluation of welded steel moment frame buildings constructed prior to the 1994 Northridge earthquake. The approach is based on an analytical model that captures the possibility of connection fracture and the subsequent loss of strength and stiffness. This connection model was developed and calibrated on the basis of laboratory experiments. It was employed in the seismic analysis of a 13-story building which experienced fractured connections in the Northridge earthquake and for which there are seismograph records and a damage survey. Results from several analyses indicate that the inelastic and fracture models are capable of predicting the behavior of steel moment frame buildings and of estimating the level of damage.

Distribution of earthquake input energy in structures

In developing an energy-based design approach and assessing the damage potential of structures, one must know the distribution of earthquake input energy among energy components: kinetic, elastic strain, hysteretic, and damping. This report examines the influences of the ground motion characteristics: intensity, frequency content, and duration of strong motion and the structural properties: ductility, damping, and hysteretic behavior on the distribution of input energy for a oneand a five-story building using 20 accelerograms, ten with short and ten with long duration of strong motion. Results indicate that for certain damping ratios, ductility has a significant influence on input energy and its distribution among energy components in a structure. For a given ductility ratio, small damping ratio (less than 5%) has a minor effect on input energy, but a major influence on the energy distribution. Damping ratios larger than 5% have a significant influence on the input energy and its distribution. Three energy ratios that relate to hysteretic energy were computed: the maximum ratio of hysteretic to input energy (Eh/Eir)m, the ratio of the maximum hysteretic energy to the maximum input energy Ehm/Eirm, and the equivalent number of yield excursions Neq=Ehm/(Fy.up) where Fy is the yield strength, and up is the plastic deformation. It is found that (Eh/Eir)m generally reflects the energy demand for the largest yield excursion, and Ehm/Eirm and Neq reflect the energy demand for the entire duration of accelerogram. The study shows that (Eh/Eir)m is independent of the duration of strong motion and period of structure; however, Ehm/Eirm is independent of both only for periods less than 1 s. Results indicate that as the duration becomes longer the equivalent number of yield excursions Neq increases indicating more structural damage. The influence of ground motion characteristics and structural properties on the distribution of energy parameters for a five-story building with fixed-base, base-isolation, supplemental damping, and semi-active control are examined using the 20 accelerograms. The results show that: 1) the distribution of energy through the height of the building is mostly independent of the frequency content and the duration of strong motion, 2) baseisolation, supplemental damping, and semi-active control reduce the damage potential by reducing the input and hysteretic energy demands and have significant influences on the distribution of energy through the height of the building.

Behavior of Unrestrained and Restrained Bare Steel Columns Subjected to Localized Fire

AbstractReal fires start from localized burning and will not develop to flashover in an open space or in large open-plan compartments. Temperatures of gas and exposed steel columns in localized fires are not uniform. Current structural fire design methods are based on uniform heating and, therefore, do not account for temperature gradients in real fires. This paper presents a numerical investigation of the behavior of bare steel columns subjected to a localized fire. The buckling behaviors of steel columns surrounded by and adjacent to a localized fire are investigated. Simple approaches are provided to calculate the temperatures of steel columns surrounded by and adjacent to a localized fire. Sequentially coupled thermal-mechanical simulations were conducted. Unrestrained, axially restrained, and rotationally restrained steel columns of various load ratios and dimensions subjected to different heating conditions were considered. The study found that the behavior of steel columns subjected to a localized ...

Inelastic response of the cypress viaduct to the Loma Prieta earthquake

Abstract The inelastic damage evaluation of a typical double-deck bent of the Cypress Viaduct which collapsed during the 1989 Loma Prieta earthquake is presented. A model of the bent consisting of spread plasticity-based beam-column elements to represent the piers and d deck, and shear panel elements to represent the pedestal region was developed. To accurately determine beam and column moment-curvature relationships, separate computer analyses using an element fibre model were conducted. In addition, a smeared-crack approach finite element analysis was employed to determine the lateral load-deformation relationship of the pedestal regions. The model of the Cypress Viaduct was subjected to the O Oakland Outer Harbor Wharf ground acceleration record in the plane of the bent. The analytical model was calibrated using static lateral load tests, ambient and forced vibration tests, and observed performance. The results of time-history analyses, which include a prediction of member damage, indicate that collapse was initiated by a shear failure of the pedestal regions.

Report of the NIST Workshop on Automated Steel Construction

The Building and Fire Research Laboratory of the National Institute of Standards and Technology, in cooperation with the American Institute of Steel Construction, sponsored a workshop on automated steel construction. The purpose of the workshop was to investigate the development of new technologies to facilitate automating the steel construction process. Desired outcomes included a clear definition of issues and constraints, the identification of candidate breakthrough technologies, and the development of a research roadmap. A description of the workshop structure, agenda, and preliminary results are presented.

An integrated interactive visualization and analysis environment to study the impact of fire on building structures

In order to move away from the current prescriptive design methods towards performance based methods for the design of structures under fire, we need validated computer models. The next section describes our approach for modeling and analysis.

STRUCTURAL RESPONSE OF WTC 7 FLOOR SYSTEMS TO FIRE

The WTC 7 investigation by the National Institute of Standards and Technology (NIST) identified several factors that alone, or in combination, led to fire-induced failures of the floors, and subsequently, total collapse of the 47-story WTC 7 building. At the present time, a sensitivity study is being conducted to determine the relative contribution of the identified factors, which includes the presence or absence of shear studs on girders, connection types, asymmetric framing, and bay span lengths. The technical basis for the identified structural factors is presented in this paper.

Final report on the collapse of the Dallas Cowboys indoor practice facility, May 2, 2009

........................................................................................................................................................ v Table of