May 01, 2013
Blast Topics at 2013 ASCE/SEI Structures Congress!!
by Brian Katz
Be on the lookout for Hinman at this year’s ASCE/SEI Structure’s Congress being held in Pittsburgh, Pennsylvania from May 2 – 4. Here is a sneak peak of Hinman presentations to be on the lookout for!
Presenter: Andy Coughlin (Hinman)
Presentation Time: Friday May 3rd, 3:30-5:00 pm
Topic: Double curtain wall façade systems, where two layers of façade exist on the exterior of a building, have gained popularity in new and retrofit construction due to advantages in thermal performance, sound transmission, and exterior aesthetics. However, when the systems are used on government or high-profile buildings, they are often required to achieve a certain level of blast performance. Common blast engineering practice does not currently have a validated method to determine the pressure wave which may be transmitted due to “piston effects” short of computational fluid dynamics.
The presentation will discuss the results of an analytical study that quantified the important parameters to consider in designing double curtain wall systems. Results are presented in the form of design curves that can be used to develop preliminary blast resistant designs. This allows a quick solution to be presented when determining feasibility or preliminary cost estimates before a more robust design method can be implemented.
Present: Sharon Gallant (Hinman) & Lara Leininger (Lawrence Livermore National Laboratory)
Presentation Time: Friday May 3rd, 3:30-5:00 pm
Topic: This presentation is intended for architects, engineers and curtain wall vendor who are currently employed in the design and construction of blast-resistant curtain walls. We will present structural analysis of an aluminum-backed curtain wall system to inform blast-resistant structural design practice. This analysis focuses on the expected material response of an aluminum curtain wall support to a set of typical blast loadings used in U.S. government criteria for domestic projects. Dynamic experiment test results of aluminum samples are used with a three-dimensional finite element hydro-code to account for over-strength, dynamic strengthening, and post-failure response of aluminum. The analysis shows that a curtain wall member under high-rate (blast) loading that is prescribed to "fail" using the recommended values of yield strength in the criteria documents, actually has very little evolved plastic strain. Further analysis shows that the combination of both the measured quasi-static yield over-strength and dynamic yield strength of specific aluminum evaluated exceeds the design recommendations prescribed in government design criteria in excess of 30% for the 6063 aluminum evaluated. The additional fidelity provided by the more accurate material properties improved the calculated performance of the structural member to the point that a member upgrade would not be required! If anything, we hope attendees walk away with a sense that the use of more pragmatic material properties can save time and money by not triggering a redesign.
Presenter: Jessie Godinho (Hinman)
Presentation Time: Saturday May 4th, 8:30-10:00 am
Topic: The focus of this presentation will be design and detailing concepts of metal stud wall systems for achieving a predictable performance when subjected to air-blast loading effects. These systems are commonly used for exterior cladding and interior partition systems and while they can provide both strength and ductility their performance is highly dependent on proper detailing to minimize buckling effects and connection failure. As a result, current practice assumes more conventional design and detailing methods and penalizes the designer with restrictive deformation limits that leads to labor intensive and costly designs.
Due to lack of available testing data, current practice either restricts metal stud performance to low deformation limits or attempts to yield the section under full tension membrane action. The first approach is limiting in its application under even moderate blast loading without the need for heavy robust sections due to the minimal extent of allowable deformation, typically in the range of 1- to 2-deg. The second approach, while effective in providing high resistance to blast loading due to the absorption of energy through excessive deformation, requires specialized connections that are both costly and difficult to install.
We will focus on the transition region between these two responses, where the metal stud section has yielded and the performance is governed by the behavior of its connections and its ability to maintain stability under buckling effects such as web crippling and lateral torsional buckling. Using a combination of available test data and design examples, this presentation will examine the performance of metal studs within the plastic region. Key takeaways will relate to conventional construction methods and their ability to provide blast resistance, as well as provide design and detailing guidance for architects, engineers, and light gage framing sub-contractors to achieve a high level of performance, while minimizing cost and constructability issues.