Several of our engineers ventured to Denver, CO, to present their papers, studies and projects at this year’s Structures Congress. The congress is organized annually by the Structural Engineering Institute of the American Society of Civil Engineers.
An overview of the M7.8 April 16, 2016 Ecuador Earthquake
Moderator: Ramon Gilsanz, PE, SE, F.SEI, F.ASCE, Gilsanz Murray Steficek
Speakers: Eduardo Miranda, PhD, Stanford University; Xavier Vera, Ph.D., Universidad Católica Santiago de Guayaquil; Ramon Gilsanz, PE, SE, F. SEI, F.ASCE, Gilsanz Murray Steficek; Virginia Diaz, PE, Gilsanz Murray Steficek; Adrian Tola, PE, Virginia Tech
On April 16, 2016 a M7.8 struck along the subduction trench on western Ecuador near the town of Muisne in the province of Esmeraldas. The earthquake caused the collapse of hundreds of buildings some as far as Guayaquil, Ecuador’s largest city located 260 km southeast of the epicenter leading to 663 deaths, more than 27,000 injured and approximately 30,000 displaced residents living in public shelters. The largest death tolls occurred in the cities of Pedernales, Portoviejo and Manta where 82% of the casualties occurred.
Very severe ground motions were recorded in the city of Pedernales located approximately 20 miles south of the epicenter where peak ground acceleration in excess of 1.5g and peak ground velocities in excess of 100 cm/s (40 in/s) were recorded which greatly exceeded design spectra in the Building Code of Ecuador.
The earthquake produced the collapse of the control tower in the Manta international airport which led to the shutdown of the airport and caused massive liquefaction and damage in the port of Manta leading to a reduced operation. The Caras bridge, Ecuador longest and most important bridge which was recently built using seismic isolation had an excellent seismic performance and remained fully operational. The earthquake caused a large impact to the hospital infrastructure in the provinces of Manabi and Esmeralda where more than 25% of the hospitals beds were not available after the earthquake, primarily as a result of damage to nonstructural components. A strong relationship between damage and soil condition was observed in several cities, particularly in Guayaquil where soft clay deposits lead to strong amplifications of the ground motions that lead to the collapse of an RC bridge structure and collapse of 6 buildings.
Just after two-days of the earthquake a rapid evaluation of structures was initiated by Ecuadorian engineers organized and lead by the Ministry of Urban Development and Housing (MIDUVI by its initials in Spanish) with the main goal of getting people back to residence and business that are safe to be reoccupied. Similarly to how it is done in the U.S. using the Applied Technology Council’s ATC-20, structures were tagged into three categories: (1) safe to reoccupy; (2) restricted use; and (3) unsafe. All building inspected were geo-referenced and evaluations were gathered and stored in a central database. At its peak more than 450 volunteered joined this effort and more than 11,000 structures were evaluated.
The presentation was made by three ASCE members, who conducted earthquake reconnaissance trips in the days following this large seismic events; Ramon Gilsanz, PE, SE, F. SEI, F.ASCE, Gilsanz Murray Steficek; Virginia Diaz, PE, Gilsanz Murray Steficek; Andrew S. Whittaker, PE, SE, PhD, University at Buffalo. The presentation summarized the performance of bridges, dams, electrical substations, highways, ports, airports and buildings.
Politics and Public Policy for Civil Engineers
Moderator: Jessica Mandrick, PE, SE, LEED AP, M.ASCE, Gilsanz Murray Steficek
Civil and structural engineers help shape society through the development of codes and standards and technical advances in design and construction. It is critical to extend this influence to shaping political decisions at the local and national levels, particularly in key areas such as infrastructure, sustainability, and licensing. This session discussed areas where civil and structural engineers are currently influencing public policy, why engineers should serve as advocates, and how they can become more actively involved. Speakers and their presentation topics included Jessica Mandrick – Political Activity of Engineering Professional Organizations, Andy Herrmann – ASCE Report Card 2017, Aaron Castelo – ASCE Government Relations, Brady Doyle – ACEC Legislative Process, Mike Griffeth – Your Representative Needs You, and Ross Corotis – The Engineer as Political Decision Maker and Political Leader
Column Transfers at 75 Rockefeller Plaza
75 Rockefeller Plaza is a landmarked 34 story steel moment frame building constructed in 1947 for John D. Rockefeller’s Standard Oil Company. New ownership began a full repositioning of the building in 2014. This work included a reconfiguration of the lobby and the removal of four columns at the ground floor, three of which supported existing transfer girders. This paper and presentation provided a case study on the transfer of these four columns from early schematic concept through their removal.
Multi-story transfer trusses and removal of each column from the top down were among the schemes considered before the final design of a composite box girder was selected. Design challenges faced included specifying a composite box girder (for which both AISC 360 and AASHTO codes were consulted), eccentrically reinforcing existing columns, and modifying the existing partially-restrained wind frame.
Of particular note were the constructability challenges of erecting and preloading a new steel box girder around an existing transfer girder to effectively extend that transfer to the next column line. A scaled 3D model was printed to help communicate the design concept to the steel fabricator and the owner. To preload the girders, a solution was developed that maintained redundancy throughout the entire loading procedure and did not require any temporary structure. Effects of column shortening, elongation, and resistance from the steel moment frame above were all considered during the loading process.
Simplified Alternative Load Path Analysis Guidelines
Ramon Gilsanz, PE, SE, F.SEI, F.ASCE, Gilsanz Murray Steficek; John Abruzzo, PE, Thornton Tomasetti; Akbar Mahvashmohammadi, Ph.D, Gilsanz Murray Steficek; Joshua Peng, Ph.D, Gilsanz Murray Steficek; Sarah Orton, Ph.D, University of Missouri Columbia; Ross Cussen, PE, Thornton Tomasetti; Joseph Gannon, PE, Walter P. Moore; Min Liu, Ph.D, The Catholic University of America; Nabil Rahman, Ph.D, PE, The Steel Network
Based on the experimental and numerical studies performed by the National Institute of Standards and Technology (NIST), an Alternative Load Path Analysis (ALPA) guideline is being developed by the Disproportionate Collapse Technical Committee of ASCE to provide design, analysis and modeling methods for engineers in practice to reduce the vulnerability of steel and concrete structures to disproportionate collapse. This paper presents a summary of chapter 3 of this guideline, titled Simplified Analysis to Predict Collapse Resistance. Chapter 3 focuses on simplified analysis methods that can be applied in form of spreadsheets or closed form solutions to predict the collapse resistance capacity of steel and concrete buildings.
Disproportionate Collapse Analysis using Structural Analysis and Design Software
Karl Rubenacker, PE, SE, Gilsanz Murray Steficek; Brett Agee, Bluescope Steel; Peter Barrett, CAE Associates; Gustavo Cortes, LeTourneau University; Larry Faria, CH2M; Joseph Gannon, PE, Walter P. Moore; Joshua Peng, Ph.D, Gilsanz Murray Steficek; Macarena Schachter, Thornton Tomasetti; Halil Sezen, Ohio State University; John Wade, AECOM.
This presentation gave an overview of Chapter 4 of the new Alternative Load Path Analysis Guidelines, which are being developed by the Disproportionate Collapse Technical Committee of ASCE-SEI. Chapter 4 presents how commercial structural analysis and design software can be used to determine if a structure is likely to resist disproportionate collapse. It covers the analysis methodologies, software capabilities, for various typical structures for design using the alternative load path method against disproportionate collapse.
Structural Integrity of Flat Slabs: Building Code Comparison using Alternative Load Path Analysis
This paper presented a comparison of results of disproportionate collapse analysis for reinforced concrete flat slabs; the analysis was performed using simplified techniques as well as finite element and applied element analysis. The slabs were designed according to the New York City Building Code, which contains structural integrity requirements for concrete flat plate slabs beyond those required by the ACI-318. These requirements enhance the slab’s performance after extreme event scenarios by adding local robustness and providing additional overall system redundancy, therefore increasing the overall post-punching shear failure capacity of the slab. This paper explained the concepts behind these additional requirements. Examples showed the amount of steel added to meet the requirements and how the additional steel can be accommodated in complex connections, where the reinforcing is interrupted by the mechanical, electrical, and plumbing systems.