Why Is Everyone Talking About Performance-Based Multi-Hazard Design?

The design for multi-hazard mitigation is a new subprinciple of structural engineering, aiming to protect structures from hazards (earthquakes, winds, tsunamis, snowfalls, floods, wild-fire, etc.). This is done by anticipating damage, minimizing consequence losses, and targeting fast recovery in the event’s aftermath. Recurring hazards may be independent or interrelated (concurrent or successive). Earthquakes and winds are typical examples of independent actions, while heavy rain and high winds, main earthquake shocks, and aftershocks are examples of concurrent and successive events, respectively.

…

Before the 2016 version of the American Society of Civil Engineer’s ASCE 7 Load Standard, Minimum Design Loads for Buildings and Other Structures, all snowdrifts were two dimensional. The height and width (horizontal extension) of the leeward roof step drifts were taken to be constant all along the roof step. The same holds for windward roof step drifts, parapet wall drifts, and over-the-ridge gable roof drifts. As such, the wind direction of interest was nominally perpendicular to the geometric irregularity, i.e., perpendicular in plan to the roof step, the parapet wall, or the gable roof ridgeline. …

On March 18^th, 2020, a moderate earthquake of magnitude 5.7 hit Magna, Utah, at 7:09 am. In the downtown area, the strongest shaking lasted 4-6 seconds; however, the shaking was strong enough to be felt for about 20 seconds. For people living in high-rise buildings in downtown Salt Lake City, 17 miles from Magna, the shaking seemed to last much longer. Fortunately, due to the Covid-19 pandemic and the early hour at which the earthquake occurred, most people were still at home and in bed. The earthquake was reportedly felt as far away as 66-miles from the epicenter. …

Is the Wind Blowing in the Right Direction?

The ASCE 7-16, Minimum Design Loads for Buildings and Other Structures, has been published in accordance with the International Building Code (IBC 2018), incorporating updates regarding wind load calculations from ASCE 7-10. This article relates to wind uplift on flat and gable roofs of major logistic centers with slopes ≤ 7 degrees and buildings ≤60 feet in height. The article focuses on the wind uplift loads on the roof elements of joists and girders. For joist wind uplift loads, the method of Components and Cladding in Chapter 30 of ASCE 7 is adopted. For girders, considering the effective wind area is larger than 700 square feet for typical major logistic centers, the Main Wind Force Resisting System (MWFRS) method in Chapter 27 is adopted. …

As structural engineers, our approach to structural fire safety in supertall buildings has evolved along with overall fire and life safety goals. Structural systems have progressed from the early steel frame towers of the 1970s to current practice incorporating concrete and composite steel/concrete structural elements. This article looks at the relationship between structural engineering practices for tall buildings and how these practices have influenced fire safety strategies for passive and active protection systems in tall buildings over the last 50 years. …

Masonry Damage and Modeling

On June 13, 2018, at approximately 10:00 PM, an EF-2 tornado passed over Wilkes-Barre, Pennsylvania, causing an estimated $18,000,000 in property damages and severely impacting commercial and retail buildings within its 600-foot-wide (183 meters) by 2.9-mile-long (4.7 kilometers) path (Figure 1). Losses to affected buildings ranged from complete or partial collapse to superficial damage to the fenestration. …

Part 2

Part 1 of this series discussed background information relative to the issues, including an overview of current codes and standards (STRUCTURE, July 2019). …

Part 1

Articles recently appearing in major newspapers and features run on other media outlets have called into question the seismic performance of buildings designed using U.S. seismic codes and standards. The primary criticism appears to be that, while the codes and standards prevent the collapse of buildings in strong earthquakes and even provide life safety by allowing people to evacuate safely, they do not ensure the continued functioning of the buildings or the community. …

It is common to overlook Structural Clay Units (SCU) as a viable, and often more desirable, solution during discussions of structural masonry. It seems that the default solution to most structural masonry design challenges is Concrete Masonry Units (CMU). Unfortunately, in many instances, this is due to lack of information. There are some areas of the U.S. and Canada, and some individual practitioners, who are unfamiliar with SCU as a viable structural solution. If properly evaluated, practitioners may find that SCU is the best structural masonry solution to satisfy the design criteria/demand. …

How Collapse Potential is Affected by the Method of Considering Accidental Torsion

Structural Engineers have long observed that torsional building response is an indicator of earthquake collapse risk. The Building Code’s explicit treatment of torsion dates back at least to the 1961 Uniform Building Code (UBC), which introduced the requirement of adding 5% eccentricity to any inherent torsion when distributing lateral earthquake forces to the vertical seismic force-resisting elements. Although today’s code includes additional penalties for torsionally irregular structures, the treatment of “accidental torsion” remains much the same. This often-maligned but critically important provision prohibits the design of cruciform-type structures without any torsional strength. It also offers increased collapse protection by indirectly accounting for the non-uniform degradation of the vertical seismic force-resisting elements that occur in the true non-linear response of structures. …