This paper is the first in a series of papers that looks at the improved performance of structures through seismic retrofitting. This paper serves to introduce the topic of seismic retrofitting by focusing on the differences between mandatory and voluntary retrofitting and discusses some of the many reasons for performing seismic retrofits on existing structures.
Subsequent papers will build on these basics by examining and evaluating the differences between the types and degree of improvements’ values in terms of building performance and financial impacts.
Improvement of the lateral force-resisting system (“LFRS”) (a.k.a. Seismic Improvements) of a structure serves many different purposes. At its basic level, improving the LFRS is meant to improve the structure’s ability to protect the safety of its occupants and reduce the likelihood of building collapse. Improvement of the LFRS at the basic level will inherently improve the structure’s ability to sustain lesser damage, and thus potentially reduce the exposure to financial losses. At subsequent higher levels of improvement, the focus is to prevent partial or full building collapse and further increase the structure’s ability to remain operational after an event and minimize business interruption. The highest level of improvements of the LFRS are such that the structure will sustain essentially no structural damage from a seismic event.
Seismic retrofit of existing buildings is a means of improving a structure’s ability to resist seismically induced horizontal forces due to ground shaking. In many cases, seismic retrofitting is in response to mandates from an Authority Having Jurisdiction (“AHJ”). In other cases, seismic improvements are made on a voluntary basis at the desire of building Ownership. It is important to remember that not all seismic improvements are the same.
Mandatory seismic improvements can be triggered by one or more of the following conditions occurring at the structure’s location:
It is worth noting that while these events will trigger mandatory seismic improvements, AHJs and the building codes only focus on the most basic level of protecting the building occupants from death or injury; they do not focus on financial losses or disruption in building services after a seismic event. There are higher performance levels than those of life safety and collapse prevention that are sought through meeting the requirements of the building codes. Retention of service or immediate occupancy are examples of increased levels of performance that may be desired by Ownership or a tenant.
A voluntary seismic retrofit is one that is undertaken by a property owner on strictly a voluntary basis and can include partial or full measures to improve the LFRS of the structure. Property owners may have one or more motives to implement these improvements that can be attributed to some or multiple reasons outlined below:
Demonstrated in this paper are the many reasons for performing seismic retrofits on existing structures, both voluntary and mandatory. These measures can be readily (or with some difficulty) achieved depending on the structure type and occupancy conditions within the structure. They can also be costly or relatively inexpensive to achieve when considering the benefit gained by the improvements. These factors should be considered before embarking on a seismic retrofit plan or evaluating the seismic improvements made to an existing structure because not all seismic improvements are the same.
Jeff Dyer is a Senior Vice President in J.S. Held’s Forensic Architecture & Engineering Practice. He is experienced with all phases of design from preliminary conceptual and schematic design through construction documents, specifications, and administration. His experience also includes structural engineering and design for many facility types including automobile dealerships, business parks, churches, industrial facilities, institutional facilities, manufacturing facilities, office buildings, parking structures, recreational facilities, research & technological facilities, residential structures, retail shopping centers/malls, schools, warehouses, and water/wastewater facilities. Mr. Dyer has also offered Earthquake Disaster Preparedness consulting services to several of our clients.
Jeff can be reached at [email protected] or +1 949 417 2690.
Wade Sticht is the West Regional Lead in J.S. Held’s Forensic Architecture & Engineering Practice. He is a specialist in forensic structural and civil engineering investigations, construction defect evaluations, building envelope and moisture intrusion problems, and wind, hail, hurricane, and earthquake damage evaluations. He has performed several hundred investigations for insurance companies, attorneys, and property owners. As a licensed professional engineer, Mr. Sticht is experienced with wood, masonry, concrete, and steel design. Past design projects include single and multi-family residential, light commercial and low-rise steel framed buildings, precast concrete parking structures, retaining walls, and similar small structures.
Wade can be reached at [email protected] or +1 385 283 6865.
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