Kirk A. Marchand

Alternate Path Method in Progressive Collapse Analysis: Variation of Dynamic and Nonlinear Load Increase Factors

AbstractIn performing alternative path analyses for checking the potential of a structure to progressive collapse, most designers often choose static procedures, which tend to be simpler and less labor demanding. As progressive collapse is a dynamic and nonlinear event, the load cases for the static procedures require the use of factors to account for inertial and nonlinear effects. A number of inconsistencies have been identified in the way the existing guidelines applied dynamic and nonlinear load factors to their static approaches. As part of an existing effort to update the existing guidelines, this study looked into the behavior of a variety of reinforced-concrete and steel moment-frame buildings to investigate the magnitude and variation of the dynamic and nonlinear load increase factors. The study concluded that the factors in the existing guidelines tend to yield overly conservative results, which often translate into expensive designs and retrofits. This study identified new load increase factors...

Blast-resistant Highway Bridges: Design and Detailing Guidelines

This paper presents preliminary results and observations from blast tests on concrete bridge columns conducted during a U.S. national study to develop design and detail guidelines for blast-resistant highway bridges.

Approximation of blast loading and single degree-of-freedom modelling parameters for long span girders

In this paper, the modelling of long-span girders under blast loads is presented. Specifically, spans in the range of 80–160 feet, on the order of those used for typical highway girder bridges, are considered. Topics addressed in this paper include (1) applicability of a uniform equivalent load to model blasts acting on long spans, (2) mathematical development of resistance functions and dynamic transformation factors for beams subjected to multiple distributed loads, and (3) comparisons of dynamic single degree-of-freedom analyses using both a work-equivalent uniform load and an approximation using three distributed loads of variable lengths relative to a detailed representation of the blast load profile as a function of position and time using finite element analyses. Analytical studies showing the sensitivity of the results to variations in the assumptions used to determine the magnitude and length of the loading pattern are provided. Based on these studies, a new method for approximating the response of long-span girders subjected to blasts with small scaled standoffs is proposed, which differs from the equivalent uniform load approach that is typically utilized. The new method is used to carry out parametric studies of bridge superstructure response predictions as part of research work performed for a state pool-funded bridge security project and an NCHRP project involving blast-resistant bridges.

Analysis of blast loads on bridge substructures

The design of structures to resist blast loads has traditionally been considered only for essential government buildings, military structures, and petrochemical facilities. Until recently, however, little attention has been given to bridges. One strategically placed truck bomb on a critical bridge could result in significant loss of life, severe structural damage, and devastate an economy. Recent terrorist threats to bridges in California and New York have demonstrated the vulnerability of our transportation infrastructure and reinforced the need for bridge security. This paper summarizes the results of ongoing research to develop performance-based blast design standards tailored specifically for bridges. The goal of the research is to investigate economical, unobtrusive and effective methods to mitigate the risk of terrorist attacks against critical bridges. The potential effects of blast loads on bridge substructures are presented, and structural design and retrofit solutions to counter these effects are discussed. Case studies demonstrate the use of simple models to analyze concrete piers. The modeling concept, determination of peak overpressures, and inherent assumptions are described, and empirical deformation-based damage criteria that are used to estimate the level of damage are presented.

Design and Detailing Guidelines for Bridge Columns Subjected to Blast and Other Extreme Loads

Data collected from intentional acts of terrorism, as well as tragic accidents leading to bridge collapse, have demonstrated the significant impact the loss of a key highway component can have on a community, region, or even nationally, both in terms of financial implications and societal concerns. Such events, while infrequent, need to be considered by structural engineers in order to provide safe and resilient bridges for the travelling public. This paper presents design and detailing guidelines for reinforced concrete bridge columns subjected to blast loads. The guidelines are based on an extensive research program involving half-scale bridge columns subjected to close-in blasts as well as detailed finite element modeling. To evaluate how design approaches for other loading cases respond when subjected to blast, column specimens included those based on typical seismic detailing in addition to gravity-only cases. Furthermore, columns designed specifically for blast were also tested. Based on the findings from this research, design provisions for columns subjected to extreme loads have been developed.

Blast Analysis of Integrated Framing Assemblies at Openings in Insulated Concrete Form Wall Construction

Insulating concrete forms (ICF) have become increasingly common in commercial projects. In ICF wall construction, wall sections are built by stacking blocks atop each other prior to pouring concrete. A block consists of two foam panels with a cavity between connected by plastic webbing. ICF wall construction has several advantages over traditional assemblies of CMU and stick-frame walls, including: improved structural performance (demonstrated by wind projectile tests, ICF homes surviving hurricanes, and preliminary blast testing), energy efficiency, and speed of construction. STALA® integrated framing assemblies (IFA) were developed by STALA® Integrated Assemblies, LLC to streamline framing of openings in ICF wall construction. The IFAs act as the opening formwork and reinforcement. Protection Engineering Consultants (PEC) and STALA® performed an analytical study to evaluate IFAs used to frame ICF wall, door and window openings subjected to blast loads. The main goal was to develop design guidance for ICF walls with IFAs for Department of Defense (DoD) loads while meeting the DoD low level of protection (LLOP) response criteria (UFC 04-010-01). PEC developed a non-composite resistance function for each ICF wall and IFA combination for use in single-degreeof-freedom (SDOF) analysis program, specifically SBEDS v4.0. Design tables were constructed for DoD charge weights and standoffs based on the results of the SDOF analyses. The design tables illustrate how IFAs impact ICF wall blast performance as a function of opening width and clear spacing. In general, IFAs improve the performance of the typical ICF wall, such that all cases analyzed meet the DoD LLOP response criteria when subjected to DoD charge weights at conventional construction standoffs. This paper presents a summary of our assumptions, analyses, results, and recommendations for future work. INTRODUCTION The Insulating Concrete Form Association (ICFA) demonstrated the blast resistance of insulating concrete form (ICF) walls at the Force Protection Equipment 1 Structures Congress 2012

High Strength Glass Testing and Model Validation for Static and Dynamic Loading

Abstract : The Glass Failure Prediction Model (GFPM) is the basis for ASTM E1300 which is used across the nation for window glass design. ASTM E1300 states that the model is valid only for annealed (AN) glass but, ASTM E1300 does incorporate heat strengthened (HS) or fully tempered (FT) glass through the use of multiplication factors. Rather than multiplication factors, this paper will address modifying the GFPM to incorporate these types of higher strength glass. Designers can then incorporate the model into common design methods such as single degree of freedom (SDOF) and finite element analysis (FEA) to analyze dynamic performance of glazing layups. To validate the modified GFPM, both static and dynamic testing of high strength glass was completed and comparisons to analysis predictions will be provided in the paper. The paper also illustrates how to use the modified GFPM in window design for both static and dynamic applications through the use of Single-degree-of-freedom Blast Effects Design Spreadsheet for Windows (SBEDS-W), a SDOF design tool to be released by the U.S. Army Corps of Engineers Protective Design Center (USACE PDC). Dynamic window analysis tools like SBEDS-W will be utilized more frequently due to the new threat-based requirements for windows and doors in the Unified Facilities Criteria (UFC) 4-010-01 DoD Minimum Antiterrorism Standards for Building (9 February 2012). Also, an understanding of the failure prediction capabilities of SBEDS-W is important for engineers performing the dynamic glazing analyses.