A Remodeled Design Standard for Aging BuildingsJan 08 2016 · 0 comments · NISHKIAN DEAN, Renovation, Seismic ·0
Aging and historic structures bring a style of their own into the skyline as they mesh with the sleek lines and polished surfaces of modern construction. Old age, poor or nonexistent drawings, past renovations, and other unknown conditions mean bringing these structures up to current code represents a unique challenge. The design team should be aware of the most up to date code standards and how they can be utilized in the project jurisdiction. American Society of Civil Engineers (ASCE) 41-13 is one such code that deserves attention.
ASCE 41-13 is the combination of two past ASCE documents, ASCE 31-03 and ASCE 41-06. However these documents have origins in ATC 14, FEMA 178, FEMA 310 and FEMA 273. Both landmark documents represent a major shift in the evaluation of seismic risk of existing structures and how those risks can be mitigated though retrofit. The combination of these documents in ASCE 41-13 removed any inconsistencies the two documents had in their previous forms. Engineers familiar with the separate codes will recognize the three-tiered approach found in ASCE 31 while incorporating ASCE 41 for all technical procedures.
ASCE 41 uses two sets of performance objectives depending on whether the building is an existing structure or new construction: Basic Performance Objective for Existing Buildings (BPOE) and Basic Performance Objective for New Buildings (BPON), respectively. BPON is intended as a link between the ASCE 7 and ASCE 41. The BSE-1N Hazard level of ASCE 41 results in the same short term ground shaking design acceleration as ASCE 7-10. ASCE 41-13 allows for existing structures to be evaluated to a lower hazard level than those from ASCE 7-10. This lower risk is considered acceptable because the existing structure is presumed to have a shorter remaining life span. This reduction also prevents buildings recently built from being rendered deficient with minor changes to the design standard.
ASCE 41 can be utilized for both voluntary and triggered or mandated upgrades. If the retrofit is voluntary then ASCE 41-13 can be utilized on its own as meeting a performance criteria. Mandated retrofits, such as those required for a change in occupancy, require performance objectives set by the jurisdiction’s code. International Building Code (IBC) Section 3401.6 allows for the use of the International Existing Building Code (IEBC) and ASCE 41 can then be selected as an option in IEBC chapter 3.
With the implementation of these new performance objectives, owners are becoming more knowledgeable while adding value to existing structures with necessary seismic upgrades. ASCE 41-13 represents a milestone in the practice of evaluating seismic hazards and retrofits on existing structures.