removal of roofing materials from more than 25% of the roof area of a building assigned to Seismic Design Category D, E, or F that has parapets constructed of unreinforced masonry or appendages such as cornices, spires, towers, tanks, signs, statuary, etc., the work shall include installation of bracing to resist out-of-plane seismic forces, unless an evaluation demonstrates compliance of such items. For the purpose of design, reduced seismic forces shall be permitted.” Seismic and Structural Observations The importance of structural observations has been underscored, with the 2021 IBC now requiring structural observations for all Risk Category III facilities and above, previously only being required for Category IV facilities. Structural observations are now required for the Seismic Design Category E buildings more than two stories. Where structural observations are required by the code, Section 1704.6 introduces some more definitive language on what should be fulfilled during a structural observation. The code now states that “the observer shall visually observe representative locations of structural system, details and load paths” for conformance. Although the term load paths is not yet defined in the IBC, it is generally used in the engineering community to describe a complete path that loads must take from their source until being resolved into the foundations of the structure. The addition of this term may indicate a trend towards more frequent observation from structural engineers to ensure complete load paths from foundation to roof are observed and conform to the approved documents. Frost Protection at Exits Section 1809.5.1 introduces a significant update: the requirement for frost protection for all exterior landings at required meansof-egress doors. This change aims to prevent concrete landings from heaving and compromising the operation of egress doors. Frost protection is only required as needed to prevent the obstruction of exit doors. ACI 318-19 Adoption and Shear Force Amplification IBC 2021’s adoption of ACI 318-19 brings in substantial updates to structural components, notably requiring the increased amplification of earthquake shear forces for design and introducing new requirements for shear lugs and anchorage to concrete. Although amplification of forces is not new to concrete seismic design, ACI 318-19 now introduces amplification factors to shear walls based on wall height to wall length aspect ratios and then again amplified based on the number of stories. As a result, tall and slender shear walls supporting several levels may now be required to resist up to three times the design level forces. This can lead to significant increases in shear wall designs compared to previous code cycles. Conclusion As in previous code cycles, architects and their consultants should remain aware of the significant changes to the governing building codes. Adapting to the mass timber additions, staying updated on local amendments, and ensuring effective communication with clients and engineers can prepare for successful project execution. Chris Bratt is an associate at BHB Structural. He is a licensed professional engineer and has been practicing structural engineering for 12 years. He can be reached at chris.bratt@bhbengineers.com. 29
RkJQdWJsaXNoZXIy MTg3NDExNQ==