First guidance on the sophisticated structural engineering method coming soon
Help is on the way for structural engineers driving toward improving the efficiency, reliability and resilience of buildings through performance-based wind design. And though it could take a decade or more for PBWD to become mainstream for practitioners, the authors of the first two PBWD documents, both debuting this year, are hailing them as milestones.
âPBWD provides the opportunity to engineer unique structural systems for buildings with atypical shapes or aerodynamic characteristics that do not fit the constraints of the prescriptive code-based wind-force resisting systems,â said Donald R. Scott, a senior principal at PCS Structural Solutions, at Structures Congress 2019. The conference, organized by the Structural Engineering Institute (SEI) of the American Society of Civil Engineers (ASCE) and held April 24-27 in Orlando, drew 1,058 registrants.
Scott is the principal investigator leading the team of 14 structural experts writing the Prestandard for Performance-Based Wind Design, the first document ever produced to aid in PBWD. Five peer reviewers are currently pouring over the final draft. The ASCE/SEI document, underwritten by a $150,000 grant from the Charles Pankow Foundation, will be available on the Pankow foundation and ASCE/SEI websites for free download by the end of July.
The publication is intended as a precursor to a PBWD standard that would eventually be incorporated into the model building codeâgiving designers a code-approved alternative to the prescriptive, or cookbook, provisions of the code.
Following quickly on the heels of the prestandard, the ASCE/SEI task committee on design and performance of tall buildings for wind is writing its own consensus document. Also a first of its kind, Design and Performance of Tall Buildings for Wind, written by eight experts, assembles best practices for the design of high-rises to achieve specified performance targets under wind demands. It represents a consensus among design firms, wind engineers and academia.
The publication describes aspects of wind design and performance that many codes do not specify, according to Preetam Biswas, an associate director of Skidmore, Owings & Merrill and chair of the task committee. The writers of the manual and the prestandard are coordinating their work, he said.
The draft of the manual is 95% complete and expected out in digital form by the end of the year. A print version should be available at Structures Congress 2020, April 5 to 8 in St. Louis.
Momentum is Building
Momentum is building for all types of performance-based design, which is a sophisticated engineering approach that relies on advanced analytic and design methods to enable engineers to reliably predict behavior of a structure when it is subjected to any defined loads, whether wind, seismic or fire.
The only way to get approval for a PBWD is to go through the alternate means and methods provision of the code. Few want to do this because building officials, unfamiliar with PBWD, are reluctant to approve the designs. In addition, a PBWD will require peer review. That translates to a longer and potentially murkier approvals process, which gives many building owners pause.
PBD in any form ârequires specialized expertise or knowledge,â said Ronald O. Hamburger, a senior principal at Simpson Gumpertz & Heger and the father of the 20-year-old performance-based seismic design (PBSD) approach for building retrofits. âIt is not for everyone,â he added.
Engineers agree that for PBWD to proliferate, there is much work to be done educating not only engineers but architects, developers, other stakeholders and especially code officials as to the potential advantagesâand risksâassociated with the approach. The guidelines are intended to help establish prudent means of practice and provide some protection, in terms of legal liability, for the predicted performance, said those involved.
Benefits of PBWD will be abundantly clear to many practitioners and owners, yet others may need to be convinced, chorused the authors of both documents. For starters, owners and designers need to be taught that the performance of designs produced by following the prescriptive requirements of the building code may not be sufficient, said Scott.
âMany project stakeholders believe that if their b