What Structural Engineers Need to Know

It is a shame that many cargo containers are lying around harbors all over the world and, in other places, rusting and wasting away. Would it not be nice to give these very strong structures new life?

Designing For Yield Based on Anchoring-to-Concrete Provisions

The American Concrete Institute (ACI) standard ACI 318, Building Code Requirements for Structural Concrete, includes provisions to design cast-in reinforcing bars for development, i.e., embedding a bar deep enough to develop the yield strength without splitting failure occurring. Splitting failure refers to cracking and splitting in the concrete around bars in tension. Post-installed reinforcing bars have typically been designed using ACI 318 anchoring-to-concrete provisions, which consider various possible anchor failure modes rather than designing the bars to yield. This article expands the discussion of a design concept introduced in an ACI Structural Journal article by Charney et al. in which anchoring-to-concrete provisions could be used to design post-installed reinforcing bars specifically for yielding.

Using ASCE/SEI 7-22

Designers using the 2022 Edition of the ASCE/SEI standard Minimum Design Loads and Associated Criteria for Buildings and Other Structures (ASCE/SEI 7-22, ASCE, 2022) will find significant changes to the seismic design of diaphragms and their chords and collectors: a new diaphragm design methodology added, an existing methodology expanded, significant changes affecting bare steel deck diaphragms, and more. This leaves the user needing to choose between three methods of diaphragm seismic design and needing to incorporate other updates into their designs. The changes were generated from research and code development efforts that go back years, with contributions from many, including research and guideline development teams and the NEHRP and ASCE 7 update participants. This article provides an overview of these changes to diaphragm seismic design from the designer’s perspective.

Cantilevers in many modern buildings exceed historical precedents and proportions. These cantilevers can be unenclosed balconies and enclosed occupiable rectangular volumes of buildings. Enclosed portions of buildings are found in New York City buildings in which the Owners have purchased air rights over adjacent properties or within property lines and above such ground features as driveways. The cantilevers are typically steel-framed for air rights buildings and integrated with diagonals or Vierendeel trusses that extend into the overall building framing. For enclosed occupiable cantilevered stories constructed within property lines, the protruding structural framing is typically steel and attached to the building framing with beam-to-column connections. The last type of framing is of particular interest. The design of long cantilevers, cantilevered enclosed occupiable stories, and atypical back-span conditions require consideration and caution on the part of the designer. Engineers should carefully review layouts, bracing, stiffness, deflection compatibility, detailing, and vibration that can affect more than one cantilevered floor to avoid problems during construction and the long-term performance of cantilevered structures.

Adoption of IBC 2018 Shakes Up Storm Shelter Requirements

With the 2018 Edition of the International Building Code (IBC) being adopted in more jurisdictions across the country, some designers in storm-prone areas may be surprised that their next project requires a storm shelter. Section 423 of IBC 2018 now requires that structures housing critical emergency operations and certain Occupancy E buildings incorporate storm shelters in accordance with the International Code Council and National Storm Shelter Association’s Standard for the Design and Construction of Storm Shelters (ICC 500). The code requires projects such as police stations and elementary schools (with occupant loads over 50) located in parts of the country with potential tornado wind speeds of 250 mph to incorporate a storm shelter. Although some designers may think their projects are not typically prone to tornados, this requirement affects a large portion of the country, as shown by the dark shaded area in ICC 500-2014, Figure 304.2(1) (Figure 1).

A Stiff Task to Achieve Better Performance and Cost Savings

Wood-framed structural panel shear walls designed using the Force Transfer Around Openings (FTAO) method have become a very popular option for engineers, especially in areas with high lateral force requirements. The need for more affordable housing in metropolitan areas is leading to larger and taller multi-family residential buildings, and these typically wood-framed structures can benefit from the innovative approach behind FTAO design methodology. But do engineers have all the tools they need to accurately determine the stiffness of these walls and the associated lateral force required for their design.

Part 2: Significant Changes to Design and Detailing Requirements

Significant changes were made to the design and detailing requirements for special steel-reinforced concrete structural walls in the 2019 edition of Building Code Requirements for Structural Concrete (ACI 318-19) (hereafter referred to as ACI 318).

Part 1: Significant Changes to the Design and Detailing Requirements

Significant changes were made to the design and detailing requirements for special steel-reinforced concrete structural walls in the 2019 edition of Building Code Requirements for Structural Concrete (ACI 318-19) (hereafter referred to as ACI 318). According to ASCE/SEI 7-16, Minimum Design Loads and Associated Criteria for Buildings and Other Structures, special structural walls are required in buildings with bearing walls, building frames, and dual systems assigned to Seismic Design Category (SDC) D, E, or F.

What Has Changed and Why?

The new ASCE 7-22, Minimum Design Loads for Buildings and Other Structures, ground snow load maps target uniform reliability rather than a uniform hazard (Bean et al., 2021). Previously, the ASCE 7 snow loads used a uniform-hazard 50-year mean recurrence interval (MRI) with a 1.6 load factor. These loads resulted in non-uniform reliability for structures across the country. The site-specific ground snow load determination is no longer tied to a uniform hazard (i.e., X-year recurrence interval) but to the safety or reliability levels stipulated in Chapter 1 of ASCE 7. The new strength level loads are used with a load factor of 1.0, as shown in Equation 1, and were selected to create uniform reliability across the country. These loads are mapped in the new ASCE 7-22 Chapter 7 in the online Hazard Tool and additionally reduced the number of case study regions by 90%.

Advancing First-Generation Performance-Based Seismic Design for Steel Buildings

Part 3: Future Efforts for All Structure Types

Capabilities to conduct a performance-based seismic design (PBSD) of retrofitted existing buildings and new buildings have advanced exponentially over the past 25 years. This progress has augmented our knowledge of building behavior given an earthquake intensity. Still, we must be cautious of considering a PBSD as an exact answer; instead, a PBSD gives us information to support decision-making. There is still much work needed to support PBSD capabilities, and this depends on the type of assessment being conducted. At the same time, a vision for the not-so-distant future must also be established.