25 Years On
In the early morning of January 17, 1994, the ground shook hard in the northern San Fernando Valley area of Los Angeles. The structural engineering profession was shaken hard too. That was 25 years ago, and how have things changed! …
Part 1: A 32-year Déjà-vu
Mexico City’s geoseismic design challenges arise from its unique local geology combined with high tectonic activity. This article discusses the challenges that continue to grow, as the center of the ruins of the Aztec capital has turned into the most prominent modern metropolis of Latin America, with economic growth that demands taller buildings. The response of the regional soils has repeatedly and destructively materialized in the form of soil basin amplification phenomena (one- and two-dimensional) that manifested as seismic waves propagating through the natural valley’s topography. …
The usual investigation of a fire incident consists of an effort to establish the origin and causes of the fire. More detailed investigations may be expanded to estimate the fuel quantity, the heat developed, and its duration. Building re-occupancy may take place only after a structural engineering assessment of the effect of the fire on the existing structural system. …
Wood studs designed to resist wind loads in either loadbearing or non-loadbearing tall wall applications are good examples of resilient design. Tall walls can be defined as those exceeding the International Residential Code (IRC) prescriptive limit of 10 feet for loadbearing walls. Proper design of wood structures to resist such wind loads also requires correct use of wind load provisions. Minimum design loads must be in accordance with the governing building code or, where applicable, other recognized minimum design load standards such as American Society of Civil Engineers’ ASCE 7 Minimum Design Loads for Buildings and Other Structures. …
Part 2: Settlement Profile Convergence Method
In Part 1 (STRUCTURE, November 2018) of this 2-part series, the definition of the modulus of subgrade reaction was presented and the current state of design with regard to its use was discussed. That article further described some potential shortcomings of the simplified theory of subgrade reaction. This article continues to describe the settlement profile convergence method and how it can be implemented into a new design. …
The world of Structural Engineering is in one of the most significant transitions we have seen in recent history. As we exit the more recent Great Recession and establish new normal economic conditions, we are also dealing with rapidly changing technology, the effects of a more global economy, and ever-evolving contract structures and delivery methods. The growth of the economy in the last few years has provided new opportunities and filled the backlog of most firms, but we still see pricing pressures. BIM, finite element modeling, and the growing sophistication of computer programs are changing workflows. Where we used to compete against a small group of local firms that we knew, we are now finding ourselves competing with firms across the country and even internationally. …
One day, I learned that our firm had been awarded the Oregon Zoo Elephant Lands project, a new 6-acre development to replace the existing, old exhibit that housed a herd of seven Asian elephants. Suddenly, the reality of having to design structures to withstand abuse from elephants standing 14 feet tall and weighing 14,000 pounds settled in. Not finding “Elephants” listed in Table 4-1 of ASCE 7-10, it became quickly apparent that this was not going to be like any other project I had designed. As it turned out, the elephants repeatedly reminded me of many great things about our profession, lessons that serve to inspire me at work to this day. …
In 2016, AISI S100, North American Specification for the Design of Cold-Formed Steel Structural Members (or Specification), was updated with an entirely new layout which is parallel in format with ANSI/AISC 360, Specification for Structural Steel Buildings. Also, the Direct Strength Method has been integrated into the body of AISI S100, which enables engineers to design cold-formed steel members with unconventional cross-sections. …
Recurring Structural Failures
Forensic practice in structural engineering typically entails seeking technical causes of failures. Occasionally, discussions of technical causes are disseminated through publications or conference presentations. However, the underlying or root causes of failures are seldom disseminated, because they are rarely sought. …
Understanding and Minimizing Footfall Vibrations
Humans are restless creatures, always moving. They also tend to congregate and enjoy being restless together. Locate all this restlessness in just the wrong spot in a susceptible structure, and the structure is likely to join in – by vibrating in resonance. Structural amplification of human footfalls – walking, jogging, running, jumping, dancing – can be annoying at best and dangerous at worst. …