Job Aid: Understanding Substantial Structural Damage In .

6m ago
39 Views
0 Downloads
952.28 KB
10 Pages
Transcription

Public AssistanceApril 2017Understanding Substantial Structural Damage in the InternationalExisting Building CodeThis document will help you understand how the concept of Substantial Structural Damage (SSD) is used within theInternational Existing Building Code (IEBC ). FEMA’s Public Assistance Required Minimum Standards Policyfound in the Public Assistance Program and Policy Guide, Chapter 2 – Section VII.B.2,1 (Policy) requires thatprojects receiving FEMA assistance for repair or replacement incorporate the natural hazards-related provisions ofthe most recent edition of the International Code Council’s (ICC ) International Building Code (IBC ),International Residential Code (IRC ), and/or the IEBC. The policy applies to buildings that have sustained anylevel of damage (including, possibly, SSD or Substantial Damage), as well as projects involving new construction,such as improved projects2, alternate projects3, or projects eligible for replacement in accordance with 44 CFR, Part206.226(f). The relevant code provisions include not only the design criteria for repair or replacement construction,but also those provisions that determine whether repair to the pre-damage condition is sufficient, or whether repairmust be supplemented by improvement. One of those scope-determining provisions involves the concept of SSD.Which Building Codes Include SSD Provisions? The IBC is a code for new construction. The 2015 edition of the IBC no longer contains provisions for existingbuildings. Therefore, while the definition of SSD remains in IBC Chapter 2, the code does not cite it. Instead,IBC Section 101.4.7 refers the reader to the IEBC. Where the IEBC requires repairs that involve new members 4or where it requires improvement (retrofit) in addition to repair, IBC provisions sometimes apply to the newwork. IBC provisions also apply to new construction when FEMA policy allows replacement instead of repair. The IEBC is a code for regulating work on existing buildings. It contains provisions that assess damage, requirerepair, and sometimes trigger improvement. One condition that triggers improvement is Substantial StructuralDamage. A feature of the IEBC is that it allows many conditions to remain in existing buildings that would nolonger be allowed in similar new buildings. When improvement is required, the IEBC also sometimes allows lessstringent criteria than the IBC. The IEBC applies to all building types and occupancies that, in new construction,would be regulated by the IBC. It can also be used for residential buildings that, in new construction, would beregulated by the IRC. (The IEBC provides three methods, only two of which use the concept of SSD; see OtherThings to Know, below.) The IRC is primarily a code for new construction of one- and two-family dwellings and certain townhouses.Section R102.7.1 generally requires repair of damage, but the IRC does not use the concept of SSD to triggerimprovement relative to the pre-damage condition. (Appendix J contains alternative provisions similar to thoseof the IEBC, but it is rarely adopted.) Thus, the IRC and the IEBC are different in how they treat damage andhow they trigger improvements. (See Other Things to Know, below.)1FEMA Public Assistance Program and Policy Guide FP 104-009-2, April 2017.244 CFR § 206.203(d)(1)344 CFR § 206.203(d)(2)4New members refer to new structural members or new building elements.“FEMA’s mission is to support our citizens and first responders to ensure that as a nation we work together to build, sustain, and Improve ourcapability to prepare for, protect against, respond to, recover from, and mitigate all hazards.”

Federal Emergency Management AgencyPublic AssistanceApril 2017Since neither the IBC nor the IRC directly use the concept of SSD, this Job Aid considers application of the IEBConly. It applies to the repair provisions in either the IEBC’s Prescriptive method (Section 404) or the IEBC’s WorkArea method (Chapter 6). (See Other Things to Know, below, for more about the IEBC’s three methods.)How SSD Relates to RepairsThe IEBC, at minimum, requires any damage to be repaired by restoring it to the pre-damage condition (Sections404.1 or 601.1). In some cases, the code requires not only repair of the damage, but also improvement of the buildingbeyond its pre-damage condition. With respect to natural hazards, the IEBC “triggers” such improvements whendamage is classified as either Substantial Damage or Substantial Structural Damage. Substantial Damage (SD), defined in terms of repair cost, requires the entire structure to be retrofitted to meet therequirements for new flood-resistant construction (Section 404.5 or 606.2.4). The IEBC’s SD provisions applyonly in flood hazard areas. Substantial Structural Damage (SSD), defined in terms of capacity loss, requires evaluation and/or retrofit ofcertain structural elements other than the damaged elements, as explained further below.It is possible for a building to sustain both SD and SSD in the same event, in which case both sets of requirementswill apply. Even so, SSD is different from SD, despite the similar names. (See the Public Assistance Job Aid onUnderstanding Substantial Damage in the International Building Code, International Existing Building Code,or International Residential Code ts/130382) for more onSubstantial Damage.The IEBC defines SSD as follows:5SUBSTANTIAL STRUCTURAL DAMAGE. A condition where one or both of the following apply:1. The vertical elements of the lateral force-resisting system have suffered damage such that the lateral loadcarrying capacity of any story in any horizontal direction has been reduced by more than 33 percent from itspredamage condition.2. The capacity of any vertical component carrying gravity load, or any group of such components, that supportsmore than 30 percent of the total area of the structure’s floor(s) and roof(s) has been reduced more than 20percent from its predamage condition and the remaining capacity of such affected elements, with respect to alldead and live loads, is less than 75 percent of that required by this code for new buildings of similar structure,purpose and location.The cause of the damage is irrelevant to the definition. However, if SSD is present, the criteria for the triggeredretrofits, as well as some of the exceptions to the triggered scope, refer to specific types of loads or hazards.Each of the two types of SSD triggers its own scope of improvement, and each requires its own design criteria: SSD to the lateral system (Type 1 in the definition) requires the entire lateral system – even the parts that sustainedno damage – to be evaluated for certain wind and seismic loads and retrofitted as needed. One- and two-familydwellings are exempt from seismic work, as are buildings outside regions of high seismicity as long as the SSDwas not caused by earthquake. (Sections 404.2 or 606.2.2)5The definition reprinted here includes errata published by ICC on February 1, 2016.“FEMA’s mission is to support our citizens and first responders to ensure that as a nation we work together to build, sustain, and improve ourcapability to prepare for, protect against, respond to, recover from, and mitigate all hazards.”

Federal Emergency Management AgencyPublic AssistanceApril 2017 SSD to the gravity system (Type 2 in the definition) requires the damaged members, as well as those undamagedmembers supporting their loads, to be retrofitted to carry the dead and live loads (and snow, if the damage wascaused by snow) required for new construction. (Sections 404.3 or 606.2.3)In addition: SSD to the gravity system caused by wind or earthquake is to be treated like SSD to the lateral system (Sections404.3.1 or 606.2.3.1). This is because such damage indicates that the building’s lateral system was inadequate toprotect the gravity system from a critical loss of capacity. The definition of SSD requires an assessment of capacity loss to the “vertical” elements or components. Inthe case of SSD to the gravity system, these are the columns or bearing walls, but not the floor framing ordiaphragms. In the case of SSD to the lateral system, these are the walls or frames that characterize the system,but not the diaphragms or other load path components. Thus, one of the most common wind-induced structuraldamage modes – wind uplift of the roof deck or roof support structure – cannot be classified as SSD because theroof deck and framing are not considered vertical elements. While nonstructural damage can indicate structural damage, nonstructural damage does not count toward SSD.Even if SSD has occurred, nonstructural components are not required to be evaluated or retrofitted. Section 502.3 states that any work necessary to comply with the code’s repair provisions is considered part of therepair and is not intended to trigger further requirements as an alteration6 project. Though the provision is not asclear as it could be, this should be understood to mean that even a seismic, wind, or flood upgrade triggered bySD or SSD should not be classified or regulated as a voluntary alteration. (Technically, Section 502.3 applies onlyto the Work Area method, but the same idea, though unstated, should apply to the Prescriptive method as well.)Making the SSD DeterminationBecause SSD is defined in terms of capacity loss to structural elements, making the SSD determination requires anunderstanding of the building’s structural system, as well as the extent and meaning of the damage. Making the SSDdetermination requires two separate assessments, one for each type of SSD: For each story, in each direction, assess the reduction in lateral load-carrying capacity of the vertical structuralelements of the lateral force-resisting system. For each damaged gravity load-carrying vertical element, or group of elements, assess the reduction in gravityload-carrying capacity.Although the SSD definition includes specific values of capacity loss, the code provides no guidance for quantifyingthe loss and makes no requirements regarding the types of investigation or analysis that might be needed. Somedocuments have been developed to guide the assessment of damage,7 but even these are not comprehensive withrespect to structure types and damage sources. Therefore, different approaches and ample judgment are typicallyapplied. In the absence of an objective standard, the code official,8 retains the right to require or waive morethorough documentation, testing, analysis, or peer review depending on what the permit applicant is claiming.6An “alteration” per the 2015 IEBC is defined as any construction or renovation to an existing structure other than a repair or addition.7Examples include FEMA 306 which provides guidance on the evaluation of earthquake-damaged concrete and masonry walls and FEMA 352 whichoffers a methodology for assessing earthquake damage to welded steel moment frames.8The IEBC defines and uses the term “code official” in essentially the same way that the IBC defines and uses “building official.”“FEMA’s mission is to support our citizens and first responders to ensure that as a nation we work together to build, sustain, and improve ourcapability to prepare for, protect against, respond to, recover from, and mitigate all hazards.”

Federal Emergency Management AgencyPublic AssistanceApril 2017Where the damage is obviously minimal or obviously severe, a thorough knowledge of the structural system mightnot be necessary. Nevertheless, professionals making an SSD determination should understand that structural damagecan sometimes be hidden, and that even visible damage can be misleading if the structural system is unknown.By FEMA policy, a determination of whether SSD has occurred may be made by the code official, the recipient’s orsub-recipient’s registered design professional, or another qualified individual. FEMA may review the determinationto ensure consistency with the IEBC requirements. If needed, FEMA may hire a technical assistance contractor toassist in these determinations.Other Things to Know Substantial Structural Damage and Substantial Damage are two conditions in which the IEBC requires a buildingto be improved beyond its pre-damage condition. In addition, though separate from the IEBC, FEMA policy alsoallows improvement of a damaged building through replacement when the cost of repair would exceed 50 percentof the replacement cost. The IEBC allows the permit applicant to select one of three compliance methods. The IEBC sections cited inthis Job Aid come from the Prescriptive method (Section 404) and the Work Area method (Chapter 6). ThePerformance method is rarely used to regulate repairs, and its provisions are not well maintained or consistentlyinterpreted. FEMA interprets the IEBC as limiting the Performance method to relatively recent buildings, orbuildings in which the pre-damage structural system already complies with IBC requirements for new construction. With this interpretation, there would never be a need to improve the structure even if SSD did occur. However, some jurisdictions have interpreted the Performance method to allow exemptions even to non-conformingbuildings and never to require improvement even in the case of SSD. This interpretation is inconsistent withFEMA policy. As noted above, the IEBC can be applied to any structure type or occupancy, including one- and two-familydwellings. Some jurisdictions, however, allow the IRC, which does not include SSD provisions, to be used forexisting dwellings. FEMA may require the use of the IEBC in these cases.References2015 International Existing Building Code. International Code Council, 2014.2015 International Building Code. International Code Council, 2014.2015 International Residential Code. International Code Council, 2014.“FEMA’s mission is to support our citizens and first responders to ensure that as a nation we work together to build, sustain, and impro