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Hinman Pulse

April 13, 2015

ASCE Structures Congress 2015

by Kim Gayo

Headed to ASCE's Structures Congress on April 23-25 in Portland? Be sure to catch our very own Hinman Engineers throughout the conference presenting the latest in protective design. Get the scoop on our Engineers and topics here!

Computational Analysis for Blast Loads: Single-Degree-of-Freedom Assumption Limits
Presenter: Taka Yokoyama, PE, Senior Engineer
Date: Thursday, April 23
Time: 8:00am - 9:30am
Location: Room C121 & C122

Design professionals use Single-Degree-of-Freedom (SDOF) models to analyze blast effects on components. It is common knowledge that the SDOF method is an approximation, and is not suitable for large charges with short distances (lower scaled distance – Z). Current design guidelines establish the limit of Z=3ft/lbs1/3 for using SDOF methodologies for blast-loaded components, which is equivalent to a peak pressure of 727 psi; however, this limit may be significantly higher in Z-value (or lower in peak pressure). Higher blast pressure and impulse combinations cause hinges to form before the assumed deflected shape dominates the response. Because transformation factors for SDOF are derived using static deflected shapes and the static collapse mechanism, the factors may not produce accurate or conservative responses for blast loading at lower scaled distances. A Finite Element (FE) model is used to validate the accuracy of SDOF transformation factors for large scaled distances, and to show that the deflected shape assumptions do not apply at higher peak pressures and impulses. Limits to SDOF are established based on the equivalent transformation factors. The limits established based on SDOF assumptions can be influenced by damping and mass. The study quantifies the effect of these variables on the SDOF assumption limits. This presentation is geared towards practicing engineers and researchers in the blast field to help understand the analytical limitations of the SDOF standard of practice.

Simple Methods for Evaluating Localized Collapse & Falling Debris under Column Loss Scenarios
Presenters: Jessie Godinho, PE, Associate Managing Engineer & Leslie Quiter, EIT, Engineer
Date: Friday, April 24
Time: 8:30am - 10:00am
Location: Room C121 & C122

The ability of a structure to accommodate the loss of a column has traditionally been referred to as its ability to resist “progressive collapse.” Recent guidelines, however, have begun to focus on the relative consequence or magnitude of the collapse rather than the manner in which it occurs, often referred to in industry as “disproportionate collapse.” This distinction is important as it allows for a structure to sustain localized failure, provided the resulting damage is proportionate to the initiating event and that it does not result in subsequent collapse and instability of the remaining structure. While designing structures to resist disproportionate collapse provides potential cost-savings, it requires accounting for structural debris in the collapsed area that may fall and impact floor levels below.

This study presents a simplified approach for modeling the impact of falling debris on a structure below. An approach is presented to determine the initial conditions of a beam subjected to impact from falling debris utilizing basic principles of energy and engineering mechanics and the resulting response of the structure is evaluated using three simplified analysis methods. A design example is also presented for comparison and validation of each analysis approach.

Performance-Based Engineering Framework for Fire Following Earthquake
Panel Member: Aerik Carlton, EIT, Engineer
Date: Saturday, April 25
Time: 8:00am - 9:30am
Location:  Room B113

The presentation will deliver a proposed framework for the interaction between earthquake and subsequent fire following earthquake as multiple hazards, or cascading hazards. Fire codes in the United States are largely empirical and prescriptive in nature. The reliance on prescriptive requirements makes quantifying sustained damage due to fire difficult. The very nature of fire behavior (ignition, growth, suppression, and spread) is fundamentally difficult to quantify due to the inherent randomness present in each stage of fire development. The study of interactions between earthquake and fire is in its infancy with essentially no available empirical testing results. A generalized PBE framework for earthquake and subsequent FFE is presented along with a comparative hazard probability to performance objective matrix.

Strength, Stability, and Out-of-Plane Failure of RC Bearing Walls Under One-Sided ASTM E119 Fire
Presenter: Kevin Mueller, EIT, Engineer
Date: Saturday, April 25
Time: 10:00am - 11:30am
Location: Room C124

Full-scale experiments of reinforced concrete (RC) bearing wall structures were conducted under fire and service-level gravity loads as part of an NSF-funded research project at the University of Notre Dame. This presentation describes the behavior of seven planar wall test specimens, with details applicable to bridge piers. Two of the wall specimens failed at fire durations much shorter than the current prescriptive fire resistance ratings for concrete structures (e.g., ACI 216). The results presented can help with the development of performance-based fire design requirements and analysis guidelines for RC bridge piers, including recommendations for improved reinforcement details to achieve higher performance under fire loading.



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