Technical Considerations for Engineers

Prescriptive Performance-Based Design: An Innovative Approach to Retrofitting Soft/Weak-Story Buildings (STRUCTURE, September 2019) describes the approach contained in the Federal Emergency Management Agency (FEMA) P-807 guideline. P-807 is a method to retrofit a weak first story of wood buildings to mitigate side-sway pancake-type collapse, as depicted in the Figure. The hazard posed by such buildings was underscored by their damage in the 1989 Loma Prieta earthquake affecting the San Francisco Bay area, as well as in the 1994 Northridge earthquake in the Los Angeles region. Some cities in California have enacted ordinances mandating retrofit of soft-story buildings. …

The structural design of buildings and bridges is currently based on the Load and Resistance Factor Design (LRFD) method. The main structural design philosophy is to maintain the factored resistance (the strength of the entire structure and all its elements) above the maximum demand from the worst possible combination of loads on the structure. The ratio of the strength to the demand represents the safety of the structure, where the nominal resistance is reduced by multiplying factors < 1.0, while the loads are increased by multiplying factors >1.0. These multipliers are the safety factors prescribed by the design codes and specifications for both building and bridge structures. For simplicity, all strength-reducing or load-demand-increasing factors are called safety factors in this article. …

Challenges and Opportunities for Structural Engineers

Architecture 2030 (architecture2030.org) reports that, between now and 2060, growth in the world’s population will require a doubling in the amount of building floor-space, equivalent to building an entire New York City every month for 40 years. Much of the carbon footprint of these new buildings will take the form of embodied carbon – the carbon emissions associated with building construction, including extracting, transporting, and manufacturing materials. As a result, owners, designers, engineers, and contractors are turning their attention to building materials and seeking information on these products so they can make more environmentally informed and smarter choices. …

Developers, owners, general contractors, and subcontractors all face a similar dilemma. How can fantastic projects be created when they cost so much? Competition for land, difficult entitlements, and rising construction costs remain ongoing challenges facing the mandate to build, particularly housing. Material and equipment scarcities, code and regulation intensifications, and the lack of available skilled labor all contribute to decreased productivity. Inadequate housing and transportation create shortages of local labor while insatiable demand continues to outpace supply, all leading to soaring construction costs. …

Upgrading Highway Bridge Infrastructure

There is general agreement that the country’s infrastructure is in critical condition. With available funding that pales in comparison to the amount needed, engineers working on infrastructure-related projects have a professional obligation to produce high-efficiency projects to ensure maximum impact is obtained from the available funding. …

A successful engineer is, in all likelihood, an unknown engineer. Short of significant failures, the general public is unaware of the time and thought that goes into a good design. Most assume the success of our infrastructure is due to building codes or architects, without any knowledge of the layers of security provided by structural engineers. This lack of awareness has far-reaching consequences for the profession, the most significant of which is a decided undervaluing of structural engineering. Structural engineering, as a profession, needs a marketing plan. …

This article is a follow-up from the author’s article, Code Requirements for Residential Roof Trusses, in the March 2019 issue of STRUCTURE. (The terms in this article beginning with capital letters are defined in Section 2.2 of ANSI/TPI 1-2014, National Design Standard for Metal Plate Connected Wood Truss Construction, published by the Truss Plate Institute (TPI) – www.tpinst.org). …

Measure the distance between two points using a ruler, and you may read “12 inches.” This implies that the relative accuracy is to the nearest inch. If I write “12.00 inches,” then this implies accuracy to nearest 1/100^th of an inch. For a foundation, the accuracy of ± ½ an inch may be appropriate. The tools of that construction trade do not have a high level of precision (i.e., a backhoe, shovel, or excavator). In contrast, for an Aircraft Wing on a fighter jet, the accuracy may be measured in Mills (0.001 inches) or 1/1000^th of an inch. Understanding the level of accuracy required for a given task involves familiarity and judgment. …

Structural engineers frequently provide special or extra services without receiving appropriate additional compensation. Does this phenomenon seem familiar? It can be due to scope creep, which is a malady that afflicts nearly all practitioners. If profits do not meet expectations, scope creep is usually part of the problem. …

Kurt Vonnegut, whose father and grandfather were architects, imagined a computer program called “Palladio” in his novel Timequake (1997). Palladio, the story went, could perform a complete building design according to basic user inputs about the intended use, size, location, architectural style, and even the aesthetic of surrounding buildings. The program output full working drawings – down to “plans for the wiring and plumbing” (presumably structural as well) – in less than half an hour. …