3.1 Survey of Nonstructural Components
The nonstructural components listed in the tables and checklists provided in the appendices are at least initially within the scope of the construction of a building and its building permit. After occupancy of the building, these are items that are most commonly found in commercial, multiple-unit residential, or public buildings. A complex facility such as a hospital, research laboratory, or industrial plant will contain many additional types of specialized equipment that are not explicitly addressed in this guide.
The goal of a facility survey is to identify nonstructural components that may be vulnerable to earthquake damage. As noted earlier, it may be advisable to seek the help of a professional with expertise in this area. During the survey, the following three basic questions should be kept in mind as each nonstructural item is considered:
- Could anyone get hurt by this item in an earthquake? (Life Safety)
- Could a large property loss result? (Property Loss)
- Would interruptions and outages be a serious problem? (Functional Loss)
For some components, the answers to these three questions may not be immediately obvious, since failure of an item may result in both direct damage and indirect damage. It is important not only to view each item as a discrete object that could tip or fall and hurt someone directly, but also to consider the consequences of failure. Several examples will serve to illustrate the point:
- If a fire sprinkler line breaks, this may cause minor damage to the sprinkler itself but result in major damage to architectural finishes and contents of the building. Even if the building does not sustain any other damage, the occupants may not be able to use the facility until the fire safety system is repaired. The potential for direct and indirect property losses in this case are much greater than the repair cost for the sprinkler system.
- The battery rack used to start an emergency generator is generally located in a locked mechanical room and is unlikely to hurt anyone, even if the rack and batteries fall on the floor. In this case, even though the direct life safety threat is probably low, if the fallen batteries cannot start the emergency generator, building occupants may be injured attempting to evacuate the building in the dark, or the lives of hospital patients on life-support systems may be jeopardized. Thus the indirect losses are larger than the direct losses.
- Gas-fired residential water heaters have rarely injured anyone as they fall, but they have frequently caused postearthquake fires due to ruptured gas lines.
A word of caution is in order regarding the field survey. While it may be relatively straightforward to assess whether or not an item is positively restrained to resist earthquake forces, the effectiveness of the restraint must also be judged. In the case of bookshelves in an office area, there may be hardware anchoring the shelving to the wall, but unless the hardware is secured to a solid wall or directly to a stud in a partition wall that is also braced, the anchorage may be ineffective in a strong earthquake. The illustrated examples in Chapter 6 show many photos of unanchored, poorly anchored, and well anchored nonstructural components and provide seismic mitigation details for many common situations. As shown in the flowchart in Chapter 1 (Figure 1.2-1), the reader is advised to complete Chapter 4 and Chapter 5 (as applicable) and to review the illustrations and details in Chapter 6 before performing a facility survey and reviewing the questions in the checklist. If the checklist asks whether or not something is securely anchored, then the existing situation should be compared to the seismic mitigation details shown in Chapter 6 for that or a similar item. Also, the installation notes in Chapter 6.6 provide general guidance on recommended hardware and procedures.
The field survey may be performed by using the forms and checklists in Appendices C, D, and E.
Appendix C, the Nonstructural Inventory Form, shown in Figure 3.1.1-1 contains a blank nonstructural inventory form that can be used to record field observations. At the start of the survey, this form should be filled in, in order to identify the facility. This inventory form provides a place to record field observations made while walking through the facility and reviewing the questions in the checklist in Appendix D. When an item in the checklist is noncompliant, it should be entered as a line item in the inventory form. The form also contains space to add risk ratings from Appendix E according to the facility's seismic shaking intensity; this could be done during the field survey or could be added to the form later. The space provided for notes may be used to identify the type of problem observed, such as "unanchored" or "bolts undersized."
During the initial survey, it may be helpful to create a list containing a large number of items which may be shortened later, perhaps by dropping low-priority items. At the initial stage, it is better to be conservative and to overestimate vulnerabilities than to be too optimistic. In this version, Appendix C is provided as a sample of the inventory form prepared by the U.S. Bureau of Reclamation. The electronic file containing the sorting algorithm can be downloaded from the Bureau, FEMA 74, Prioritized Inventory (XLS 4MB).
Figure 3.1.1-1 Sample nonstructural inventory form from Appendix C.
Appendix D, Nonstructural Earthquake Hazards Checklists, shown in Figure 3.1.1-2 is a checklist with questions designed to help identify vulnerable nonstructural items and potential hazards associated with each item. The checklist should be carried during the field survey to help identify vulnerable items. The questions on the checklist are all stated in such a way that a "Noncompliantce (NC)" answer is indicative of a potential problem. Each nonstructural component with a potential problem should be listed as a line item on the nonstructural inventory form of Appendix C showing the location and quantity of the item with any relevant comments. If an example is available for this item in Chapter 6, it may be helpful to note the detail type and example number for future reference.
Figure 3.1.1-2 Sample checklist questions from Appendix D.
Appendix E, Nonstructural Seismic Risk Ratings, summarizes estimated seismic risk ratings stated as Low, Medium, and High for many common components based on their exposure to Low, Moderate or High levels of shaking intensity map in Figure 3.1.1-1. The risk ratings are based on the risk to Life Safety, Property Loss and Functional Loss for unanchored or unbraced items located at or near the base of a low-rise building of ordinary occupancy. The risk ratings are further explained in Section 3.2.2 and in the introduction to Appendix E. A sample of the risk ratings in Appendix E is shown below.
Figure 3.1.1-3 Sample risk ratings from Appendix E.
The survey method provided here was developed for use by non-engineers. Nonstructural survey methods for use by engineers are available both in Seismic Evaluation of Existing Buildings (ASCE/SEI 31-03) and in Chapter 11 of Seismic Rehabilitation of Existing Buildings (ASCE/SEI 41-06).
The evaluation methods described in these ASCE documents are more quantitative than those presented here and often require that engineering calculations be performed to determine the adequacy of the existing conditions.