January 30, 2024
Case Study: Treetop Trail at the Minnesota Zoo
Thomas Root, PE, Minnesota Zoo; Fraser Reid, PE, CEng., MICE, Buro Happold; Jon Wacker, PE, HGA; Michael Osowski, PCL Construction; Craig Huhtala, PE, MBJ
Moderator: Jonathan Wacker
The Minnesota Zoo Treetop Trail opened in the summer of 2023, becoming the world’s longest continuous elevated pedestrian loop. Constructed on top of a decommissioned 1970s monorail track, the 1.25-mile-long trail necessitated an innovative and original engineering and construction approach. In this seminar, project participants will share the challenges and solutions encountered in design and construction that made this one-of-a-kind project a reality.
February 6, 2024
Pushing the Mass Timber Envelope
Jordan Komp, PE, SE, Thornton Tomasetti; Erica Fischer, PhD, PE, Oregon State University; Shiling Pei, PhD, PE, Colorado School of Mines
Moderator: Stephen Clark
This seminar presents three topics to help expand our understanding and use of mass timber. Jordan Komp will discuss the Ascent Tower in Milwaukee, WI, currently the tallest mass timber building in the world. Erica Fischer will present on the structural performance of wood during all phases of a fire. And Shiling Pei will describe the TallWood project, the shake table testing of a full-scale, 10-story mass timber building.
Ascent: The Evolution of Mass Timber Construction:
Jordan Komp, Thornton Tomasetti
This presentation will cover the design and construction of the Ascent Tower, currently the tallest mass timber building in the world. The Ascent Tower has broken a world record for mass timber construction, and has doubled the height of the next tallest timber building in the US. This presentation outlines the process that made these achievements possible. We will discuss the design principles of the Ascent Tower, the permitting process, the construction process, and new innovations in Mass Timber.
Introduction to Mass Timber and Fire: Current practice and state-of-the-art research
Erica Fischer, Oregon State University
In the United States, wood is a common building material in low-rise residential construction. Recently, several technical and regulatory barriers have been eliminated through research and innovation to establish wood products as a viable building material for structures beyond low-rise residential structures. However, the consensus among stakeholders is that some major technical challenges remain in the structural performance of wood during all phases of a fire. This presentation will summarize current fire safety design methods for buildings and the current technical barriers thereby increasing the use of wood products in construction in the United States.
NHERI TallWood Project: Seismically Resilient Tall Wood Buildings
Shiling Pei, Colorado School of Mines
Mass timber construction is a relatively new way of utilizing wood material for modern, high performance buildings at both large and small scales, and gives rise to the idea of wooden sky-scrapers. The Natural Hazards Engineering Research Infrastructure (NHERI) TallWood project aims to prove the resilience of tall timber buildings by simulating a series of large earthquakes on a full-scale, 10-story mass timber building. The building features a post-tensioned rocking wall system built from mass timber panels, along with a variety of nonstructural systems, including four exterior façade assemblies, a number of interior walls, and a 10-story stair tower. This presentation will introduce the design, construction, and testing of the NHERI TallWood building and share preliminary test results.
February 13, 2024
Case Study: The Chirajara Bridge
Thomas Murphy, PhD, PE, SE, Modjeski and Masters
Moderator: Arielle Ehrlich
The Chirajara Bridge is part of a highway project located about 40 mi to the southeast of Bogota, Colombia. The collapsed structure was a cable-stayed bridge consisting of two diamond-shaped towers, with a main span length of 940 ft and two side spans of 262 ft. On January 15, 2018, while under construction and with only 164 ft of the floor system remaining to be constructed between the towers, the western tower suddenly collapsed, destroying that part of the bridge. The other tower remained standing, approximately in the same construction stage as the collapsed tower. Modjeski and Masters was engaged one week after the collapse to conduct a forensic investigation that included: an in situ inspection of the collapsed structure, analytical studies, an evaluation of the design, a review of the construction documentation, and testing of materials from critical structural components. Global analyses were performed to determine the loading effects in the bridge before collapse, and refined nonlinear analyses were conducted to estimate the capacity of the tower and to identify the failure mode. The investigation was concluded 4 months after the collapse and, based on the resulting data, the cause of the collapse was determined to be a deficiency in the strength of the tower. The design erroneously assumed that the reinforcing along most of the height of the diaphragm between the lower legs of the tower was effective to resist the horizontal tensile force caused by the tower’s geometry, as opposed to typical practice which utilizes a tension tie at the change in direction of the tower legs. In addition to the discussion about the bridge, Dr. Murphy is involved in ongoing research for the American Association of State Highway and Transportation Officials (AASHTO) to revise the provisions that address robustness in the bridge design specifications to use a risk based approach. Given the failure of the Chirajara Bridge was a design failure, he will show what is being done now to prevent similar disasters here.
February 20, 2024
Shear-Reinforced Concrete Breakout: A New Design Methodology and Pour Strips - Designing for Construction Productivity and Safety
Ben Worsfold, PhD, University of Minnesota; Jared M. Reigstad, PE, PEng., Reigstad Engineers
Moderator: Alireza Mokhtarzadeh
This webinar will consist of two presentations: Shear-Reinforced Concrete Breakout: A New Design Methodology and Pour Strips - Designing for Construction Productivity and Safety.
Shear-Reinforced Concrete Breakout: A New Design Methodology
Ben Worsfold, University of Minnesota
Connections between reinforced concrete structural members often rely on the yielding of reinforcing bars to resist forces and dissipate energy. Development length provisions are commonly used to ensure bar yielding. Recent physical tests have demonstrated that groups of reinforcing bars developed into a receiving member can fail prematurely in a concrete breakout mode before bar yielding. This failure mode is not routinely checked in design even though it can potentially cause premature failure of connections from beams to columns, columns to foundations, coupling beams to walls, and other connections where groups of bars are relied upon to transfer forces. Recent physical tests and finite element simulations have suggested that distributed shear reinforcement throughout the concrete breakout cone region can increase the connection strength and displacement capacity. The ACI 318-19 building code currently does not allow engineers to add the strength contribution of reinforcement to the concrete breakout strength. A novel design methodology is proposed to calculate the shear- reinforced breakout strength. Detailing recommendations are discussed.
Pour Strips – Designing for Construction Productivity and Safety
Jared M. Reigstad, Reigstad Engineers
Pour strips are designed to control shrinkage, creep and elastic shortening in post-tensioned and cast-in-place concrete but they add extra costs, construction delays, and safety issues. Engineers can reduce these problems, provide for higher quality, and increase productivity by being mindful of forming, shoring, reshoring, and backshoring when designing pour strips.
In this presentation, we will discuss the issues with restraint to shortening, and best practices for designing pour strips in post-tensioned and cast-in-place concrete. We will demonstrate how pour strip placement and design can be done to reduce costs, accelerate construction, and improve safety, which increases overall project productivity. We will also discuss different slab-to-slab connectors on the market that eliminate pour strips.
February 27, 2024
Column Base Connections and Structural Engineering Lessons from Failures
Amit Kanvinde, SE, University of California, Davis; David B. Peraza, PE, Exponent
Moderator: Jeffrey Gutzman
This webinar will consist of two presentations: Column Base Connections: Research, Design, and a Look to the Future and Structural Engineering Lessons from Failures.
Column Base Connections: Research, Design, and a Look to the Future and Lessons for Structural Engineers from Failures
Amit Kanvinde, University of California, Davis
Column base connections are arguably the most important connections in steel buildings, transferring loads from the entire structure into the foundation. At the interface of steel and concrete, these connections are complex in terms of behavior, design, as well as structural interactions with the building frame. The lecture will present our current understanding of these connections based on numerous studies, with an emphasis on AISC-funded studies conducted over the last 15 years. Exposed, slab-overtopped, and embedded connections will be discussed, addressing their response (strength, failure modes, stiffness, and deformation characteristics). Implications for the design of the connections as well as the building will be presented. Prospective developments in base connection design will be foreshadowed, including a revision of the AISC Design Guide One, and the use of dissipative base connections in seismic design.
Structural Engineering Lessons from Failures
David B. Peraza, Exponent
This presentation highlights the lessons learned from failures that were caused partially or wholly by an error or omission on the part of the structural engineer. The presentation uses landmark cases that resulted in a dramatic failure, and also little known cases of high importance.
For each case, the consequences of the failure are presented, the failure itself is described, and the technical causes are discussed. The presentation attempts to place the audience members “in the shoes” of the engineer.
March 5, 2024
Conflict of Interest in professional practice and its ethical entanglements
Tara Hoke, BA, JD, American Society of Civil Engineers; Scott A. Civjan, PhD, PE, University of Massachusetts
Moderator: Bill Arockiasamy
This seminar will discuss ethical issues related to conflicts of interest. What are the psychological drivers that can lead us into these entanglements and when do conflicts rise to the level of ethical transgressions? Background information as well as case studies will be used to untangle this topic, including decisions of when conflicts of interest should be disclosed, when they violate ethical and professional standards, why perception can matter as much as reality, and why this is an important and relevant topic for the profession.