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.

Often Overlooked and Misunderstood

For over 40 years, the traditional pour strip in concrete construction has been an issue of contention between the engineer of record (EOR) and the contractor, and this challenge continues today. The EOR desires a high-quality slab, which requires more pour strips that are left open longer. The contractor wants faster construction, which requires fewer pour strips and pouring them back sooner. Shrinkage and restraint-to-shortening (RTS) are at the core of this age-old dilemma, and EORs should not have to sacrifice quality for cost and schedule.

Advancing First-Generation PBSD for Steel Buildings

Part 2: Case Studies

Implementing performance-based seismic design (PBSD) procedures for assessing existing buildings has generated interest in using similar approaches to design new buildings. The advantage of using these procedures is that designers can go outside the more prescriptive requirements of traditional design and have a more direct connection between expected performance and the design process (i.e., performance targets are explicitly defined upfront). This results in the engineer easily communicating the anticipated performance to the client and targeting a design that achieves beyond-code performance if desired. However, as PBSD was gaining popularity in practice approximately a decade ago, there had been limited published information into the relationship between standards for seismic design of new buildings and the seismic assessment of existing buildings.

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

Part 1: Background and Motivation

First-generation performance-based seismic design (PBSD) principles are outlined in the latest edition of the American Society of Civil Engineers and the Structural Engineering Institute’s ASCE/SEI 41-17: Seismic Evaluation and Retrofit of Existing Buildings referred to herein as ASCE 41. These PBSD principles have evolved since being introduced in the Federal Emergency Management Agency’s FEMA 273: National Earthquake Hazards Reduction Program (NEHRP) Guidelines for the Seismic Rehabilitation of Buildings (FEMA 1997). ASCE 41 provides analytical procedures and performance criteria to evaluate an existing building for a defined performance objective and to design seismic retrofit strategies if the criteria are not satisfied. This ability to explicitly define a performance objective and then assess a building against that objective has led practitioners to adopt ASCE 41 for use in new building designs to meet the intent of ASCE 7: Minimum Design Loads for Buildings and Other Structures, of which the latest edition is ASCE/SEI 7-16.

A Review of Design Considerations

Grout pockets are man-made holes in concrete structures (pre-installed before concrete placement or drilled after concrete placement) to allow the installation of anchors. The main benefit of using grout pockets is to allow equipment or structures to be installed after the concrete placement, providing more construction/installation schedule flexibility. In many non-modular projects, the equipment/machinery packages are typically completed and arrive at the construction site after most of the civil works at the site (including foundations) are completed. The grout pockets also provide extra installation tolerances and eliminate the risk of cast-in-place anchor movement during a foundation placement.