1 Woodframe Buildings Prepared for United States Geological Survey Pasadena CA and California Geological Survey Sacramento CA Under contract to SPA Risk LLC Denver CO By William Graf URS Corporation Los Angeles CA May 2008 The ShakeOut Scenario: U.S. Geological Survey Open File Report California Geological Survey Preliminary Report 25 version 1.0 U.S. Geological Survey Circular 1324 California Geological Survey Special Report 207 version 1.0 Note: over the course of the ShakeOut Scenario, the project name evolved. Where a study mentions the SoSAFE Scenario or San Andreas Fault Scenario, it refers to what is now named the ShakeOut Scenario.
2 William Graf, 12/19/07 Draft Damage to Wood-Framed Buildings OVERVIEW AND SUMMARY OF MAIN POINTS This chapter presents an overview of the behavior of wood-framed construction in earthquakes, and outlines the expected behavior of wood buildings in the San Andreas M7.8 earthquake scenario. Recommendations for post-earthquake inspection are given, measures to reduce earthquake damage to wood-framed structures are described, and areas for future research are outlined. Wood-framed buildings are the most common form of construction in Southern California. Wood-framed construction is used for single-family dwellings, for apartments, as well as for retail and office buildings, and structures for education and government. Past earthquakes have taught us much about the seismic response of wood-framed buildings. Wood buildings are light in weight and strong, and modern wood-framed buildings have performed well and provided a high level of life-safety in earthquakes. However, collapses of wood-framed buildings in the 1989 Loma Prieta Earthquake and the 1994 Northridge Earthquake focused the attention of the engineering community on a number of key weaknesses in wood frames. For example, apartment buildings with tuck-under parking can experience heavy damage and even collapse under intense shaking, and materials like stucco and gypsum wall-board provide poor resistance to cyclical earthquake motions. These dramatic failures have also spurred research including both testing and the development of sophisticated analytical models. Figure 1. Dwelling in Oakland with Failed Cripple Wall, 1989 Loma Prieta Earthquake Earthquakes such as the M7.8 San Andreas scenario will subject many thousands of wood-framed buildings to loads well beyond their elastic range, yet the nonlinear, inelastic behavior of wood-framed buildings is extremely difficult to model. The seismic behavior of wood-framed buildings is complex, but comprehensive tools for nonlinear static and
3 nonlinear dynamic analysis of realistic wood buildings are lacking. Before cracking of gypsum drywall and stucco finishes, typical wood-framed structures are very stiff. After these finishes crack, wood buildings rapidly degrade in stiffness, with dramatic shifts their dynamic properties. The strength of wood depends on the direction of its grain, defects in wood members such as splits and knots, and moisture content. Wood is subject to damage by fungus, water and fire. Modes of failure in wood structures include nail bending and slip, sliding and overturning of wall piers, shear failures in wall sheathing, various connection failures, and crushing of boundary members. Good earthquake performance of wood-framed buildings depends upon careful attention to component detailing (i.e., for members, walls, diaphragms and connections) and a good grasp of overall system behavior. Heavy, rigid elements such as masonry fireplaces and chimneys or masonry veneers require careful reinforcement and good connections to prevent damage to the light, flexible wood-framed structure under strong ground shaking. Figure 2. Apartment with Soft/Weak Story Collapsed in 1994 Northridge Earthquake Seismic building codes require explicit design by a Professional Engineer (Civil or Structural) for the earthquake force-resisting system for all buildings, but regular wood dwellings up to three stories in height may be built using prescriptive conventional lightframe construction rules (e.g., 1997 Uniform Building Code Section 2320, or 2006 International Building Code Section 2308). These buildings are deemed to comply with earthquake provisions without formal design. Larger structures and buildings not meeting the restrictions for conventional light-frame construction must be engineered. Until engineered design is required for dwellings, dwellings built under conventional light framing rules must be regarded as more vulnerable than engineered construction. The San Andreas M7.8 scenario will produce intense ground shaking of long duration over a wide region. Since the 1964 Great Alaskan Earthquake, we have not seen wood framed buildings exposed to intense ground shaking lasting minutes. Because materials like gypsum wallboard (drywall) and stucco crack and lose both strength and stiffness with cycles of loading beyond their elastic strength, older wood-framed buildings that rely on these materials to resist earthquake motions may experience more damage than expected. More recent wood-framed buildings, especially engineered wood-frames using plywood shear
4 walls, should perform well, even under the conditions produced by the San Andreas event considered. Wood-framed dwellings, town-homes and apartments provide the principal form of housing in Southern California, so damage to wood-framed housing will increase demands for shelter for the populations affected by large earthquakes like the one under consideration here. According to the 2000 Census, in Riverside, single-family dwellings account for about 70% of the housing units, while apartments and town-homes account for about 26%, and the balance from mobile homes. In San Bernardino, 61% of the housing units are single-family dwellings, and 24% of the units are in apartments and town-homes. Both counties saw substantial residential construction in the 1960 s, 70 s, 80 s at a time when wood-frames relied heavily upon gypsum wallboard and stucco as sheathing for shear walls, leaving them more vulnerable than older structures that sheathed wall in gypsum lath and plaster, or newer structures using plywood. Past earthquakes have demonstrated the value of a number of loss reduction measures, including: Bolting older homes (pre-1940) to their foundations and adding plywood sheathing to weak cripple walls where these exist. Connecting gravity posts to concrete foundation pads and floor beams in older homes and apartments with crawl spaces (see Figure 3). Strengthening older apartments with a soft/weak first story caused by tuck-under parking. In most cases, these retrofit measures may be shown to be cost-effective [Porter et al., Earthquake Spectra, 2006]. The first step in implementing such measures is to conduct surveys to identify the buildings with the specific weaknesses. Older buildings with crawl spaces and apartment buildings with tuck-under parking may be readily identified by visual surveys. The sections below provide greater detail for each of the points summarized above. Figure 3. Post Beneath Apartment not Secured to Foundation Pad or Floor Beam
5 DAMAGE TO WOOD BUILDINGS IN PAST EARTHQUAKES Perhaps the first systematic observations of earthquake damage wood-frames were made following the 1886 Charleston, South Carolina Earthquake (M7.3). The resistance of woodframed construction to damage in the 1906 San Francisco Earthquake was overshadowed by the devastating losses to wood buildings in the fire that followed. High levels of damage to dwellings in the 1925 Santa Barbara and 1933 Long Beach Earthquakes prompted the development of seismic design codes and a requirement to bolt wood-framed walls to reinforced concrete or masonry foundations. Collapses of wood-framed buildings in the 1989 Loma Prieta and 1994 Northridge Earthquakes focused the attention of the engineering community on a number of key weaknesses in wood frames for example, soft / weak story conditions created by tuck-under parking, and the seismic vulnerability of stucco and gypsum wall-board construction. A more detailed chronology of earthquake damage to wood frames is attached. SEISMIC RESPONSE OF WOOD-FRAMED BUILDINGS Wood-framed buildings are by far the most prevalent type of construction used for homes and apartment buildings, especially in Southern California. Wood-framed construction is also used for retail, office, school and government occupancies. Wood construction provides high strength with relatively low weight, and the high strength-to-weight ratio makes wood a good choice for earthquake-resistant construction. By understanding how wood structures resist earthquake ground motions, we can understand failures. Earthquakes generate complex, time-varying ground motions in three dimensions. Vertical ground motions generate forces that add or subtract to gravity, and safety margins inherent in the gravity load-carrying system helps prevent damage. When the ground moves horizontally, it accelerates the building, generating forces in each element of the building in proportion to its mass. The lateral force induced by earthquake ground motions is termed shear. The roof and floors act as deep beams ( diaphragms ) to collect these forces and deliver them to the wood-framed walls, where the wall sheathing typically gypsum board, stucco or plywood acts in shear to transfer the forces to the foundation. Overall, the building acts as a stiff box-like structure. The strength of the building depends upon the strength of the sheathing and connections, acting in a continuous load path. Roof and floor diaphragms must connect properly to walls, and the base of the walls need a strong positive connection to the foundation. Connections use nails, lag screws, bolts and specialized hardware. The resisting walls are called shear walls. Sheathing must be nailed to the framing, and forces must be transferred from the edge of one sheet to the next. Where forces are high, this requires closely spaced nailing to a wood member ( blocking ) along all edges of the sheathing. The structure must resist the horizontal forces and the overturning moments produced by the forces. Where overturning moments can produce uplift of tend of the wall, the uplift is resisted by special brackets or straps called hold-downs. Earthquake damage occurs when the demands generated by earthquake ground motions exceed the capacity of the structure. Earthquake demands depend not only upon the ground motion, but the dynamic interaction of the ground motion and the structural response. The building s dynamic characteristics depend upon its seismic mass (i.e., the weight of the structure above the foundation), stiffness and strength, as well as its capacity to absorb and dissipate energy
6 through damping (like the shock absorber on a car) and damage. As damage occurs, the dynamic characteristics of wood framed buildings change dramatically. Before cracking of gypsum drywall and stucco finishes, typical wood-framed structures are very stiff. After these finishes crack, wood buildings rapidly degrade in stiffness, causing dramatic shifts in the building s fundamental period of vibration the time required to complete one cycle of oscillation. A typical undamaged 1-story dwelling may have a fundamental period of vibration of 0.15 seconds or 0.2 seconds, but after heavy damage, its period may lengthen to 0.5 seconds or more. This shift in period greatly affects the part of the earthquake ground motion to which the building responds. For the San Andreas M7.8 scenario, in the area of strong shaking close to the fault, initial high levels of strong shaking may tune in to stiff, undamaged structures, causing cracking, nail slip and other damage that degrades the stiffness and strength. The damaged structure would now have a longer period that may tend to tune in and amplify the subsequent intense, rolling ground motions that may last for a minute or more, with the result that the building may experience much more damage than would occur in a smaller magnitude earthquake of similar initial intensity. The capacity or resistance of any particular wood-framed building depends upon the strength and ductility (toughness) of the elements of its structural system. Figure 4. Shattered Chimney 1992 Big Bear Earthquake The strength of a wood member like a 2x4 depends on the direction of its grain, defects in wood members such as splits and knots, and moisture content. Wood is subject to damage by
7 fungus, water and fire. Modes of failure in wood structures include nail bending and slip, sliding and overturning of wall piers, shear failures in wall sheathing, various connection failures, and crushing of boundary members. Good earthquake performance of wood-framed buildings depends upon careful attention to component detailing (i.e., for members, walls, diaphragms and connections) and a good grasp of overall system behavior. Heavy, rigid elements such as masonry fireplaces and chimneys (see Figure 4) or masonry veneers require careful reinforcement and good connections to prevent damage to the light, flexible woodframed structure under strong ground shaking. EVOLUTION OF WOOD-FRAME CONSTRUCTION The vulnerability of the wood-frame structures varies with the year and location of construction. With the exception of the City of Los Angeles, most of the affected building jurisdictions utilize the seismic provisions of the Uniform Building Code. The evolution of wood-frame construction under the UBC code is illustrated in the attached timeline. Seismic building codes have progressively incorporated many of the lessons learned from these earthquakes, and design and construction practice have evolved significantly through time although some changes resulted in increased damageability [cf: B. Schmid et al.]. In particular, low-rise wood-framed construction came to rely upon stucco and gypsum wallboard for high shear resistance in the 1960 s, 70 s and 80 s until allowable shear values were cut in half in the 1988 Uniform Building Code. More recent engineered wood-framed construction utilizes plywood or oriented strand board sheathing for the shear walls, with hold-down systems to prevent shear wall overturning, with steel straps to serve as collectors and prevent damage around openings in walls and floors. Figure 5 illustrates the evolution of wood-framed construction. Figure 5. Seismic Evolution of Wood-Framed Construction Following the Northridge earthquake, a number of significant changes were made in the Uniform Building Code and other local codes, with the intent of reducing the damage observed in wood frames in the Northridge earthquake. For example, the earthquake shear forces permitted in stucco and gypsum board wall sheathing were further reduced, and these materials were not permitted for use in resisting earthquake shear forces in the lower stories of multistory construction. The code revisions promoted an increased reliance on plywoodsheathed shear panels, and the height-to-length proportions were limited to avoid problems
8 observed with narrow panels. Hence, post-northridge wood-framed construction may perform better than the models derived from Northridge earthquake damage statistics. Unfortunately, the majority of wood-framed buildings in the San Bernardino, Riverside, Imperial and Ventura Counties were constructed in the period of highest vulnerability, from about (see the chart above). High levels of damage are expected to the wood framed buildings constructed in this period, with significant impacts on all the regional response and recovery resources. Figure 6. Year of construction for housing units in the 5 most affected counties. CONVENTIONAL LIGHT-FRAME CONSTRUCTION Given the complexity of wood as a structural system and the high level of detailing required to prevent component and system failures observed in past earthquakes, it seems surprising that current building codes do not require formal design of all wood buildings by a Professional Engineer. Seismic building codes require explicit design for the earthquake force-resisting system for other buildings, but since 1970 regular wood structures (including most dwellings) up to three stories in height may be built using prescriptive conventional light-frame construction rules (e.g., 1997 Uniform Building Code Section 2320, or 2006 International Building Code Section 2308). In this case, no formal earthquake structural design by an Architect, Professional Engineer (Civil) or Structural Engineer is required. Therefore, the actual lateral force-resisting capacity of wood-framed dwelling vary substantially much more than the capacity of structures designed by formal capacity calculations. These buildings are deemed to comply with earthquake provisions without formal design. Larger structures, irregular buildings and buildings not meeting the restrictions for conventional light-frame construction must be engineered. Conventional light-frame construction rules also omit important seismic detailing requirements, such as plywood sheathing, 3x sill plates, and connection hardware such as shear clips, collectors, and straps around floor and wall openings. Since most dwellings may be designed under conventional
9 light-frame construction rules, dwellings must be viewed as potentially more damageable than engineered wood-frame construction. SEISMIC WEAKNESSES OF WOOD FRAMES The weaknesses of wood-framed construction and rehabilitation techniques relevant to these weaknesses are detailed in Chapters 5 through 7 of FEMA 547. The major weaknesses involve: Older Buildings Weak and brittle shear wall sheathing materials permitted under previous codes (e.g., gypsum wall board and stucco); Unbraced cripple walls and lack of foundation anchorage in older buildings; Limited shear strength in straight sheathing, diagonal sheathing and spaced-sheathing diaphragms; Unreinforced brick and stone masonry chimneys further described below); and, Fragile or poorly attached masonry veneers. Multi-story Construction Soft- and weak-story conditions created by tuck-under parking designs, unless mitigated by steel moment frames or other special measures. Unknown performance of recent 4- and 5-story wood-framed apartment construction. These buildings are taller than those subjected to strong ground motion past earthquakes, and questions remain concerning the effectiveness of the hold-down systems used for the tall, narrow shear walls that often occur in these buildings. Foundation Damage Hillside homes these are susceptible to landslide, and are subject to torsion when not properly braced. Foundation problems from cut-and-fill lots; sloped or stepped foundations; and, liquefaction, landslide, lateral spreading. We discuss some of these weaknesses further below. SEISMIC DAMAGE TO CHIMNEYS Chimneys are a common feature of residential wood-framed construction, and damage to chimneys has been noted in every large historical earthquake. Older chimneys are particularly prone to earthquake damage (see Figure 4), in part due to changes that have occurred over time in the design and construction provisions of building codes, as well as inspection and enforcement practices.
10 PRIMARY ENGINEERING CONSIDERATIONS Dynamic interaction occurs between the chimney and the dwelling structure. A masonry chimney will act as a propped vertical cantilever under lateral seismic forces. The cross section of the cantilever changes from large base (fireplace) to the flue. In newer construction, the chimney is typically supported on a thickened portion of the foundation slab-on-grade, with some degree of rotational fixity at the base. A steel strap tie to the roof (and floor) diaphragm serves as lateral restraint. An engineering model may consider the chimney mass, strength and stiffness, the foundation support stiffness, the lateral (roof) support strength and stiffness, and the wood-framed structure s period. Post-earthquake data collection efforts should consider: Intensity of ground shaking The type of chimney unreinforced stone masonry unreinforced brick masonry reinforced brick or stone masonry light framed chimney Chimney connection to roof (and floor) diaphragms tied well not tied or poorly tied Type of dwelling 1-story multi-story relative seismic mass of the chimney compared to the wood-framed structure CHIMNEY DAMAGE IN THE 1994 NORTHRIDGE EARTHQUAKE URS performed detailed engineering inspections of more than 200 residences in 1994, following the Northridge earthquake. The surveys noted the type of chimney, date of construction, and damage state. 191 of the dwellings out of 225 had chimneys. URS noted: Older (pre-1940) chimneys occurred in areas mostly outside of the San Fernando Valley, and were subject to lower ground motions. Nevertheless, high damage and collapse occurred in some cases for peak ground acceleration (PGA) from 0.2g to 0.5g. Above 0.45g, all of these chimneys had some damage, but some chimneys were only cracked at 0.4g to 0.5g. Newer (post-1940) masonry and concrete chimneys fared better than older masonry and concrete chimneys, with collapses occurring from 0.25g up to 1.25g (the highest mean ground motion predicted at the inspected sites). New, framed chimneys were notably better in seismic performance, with only minor damage for ground motions up to 0.75g. OBSERVED CHIMNEY FAILURE MODES The chimney shatters above the roof line (this is the most common failure mode, especially for unreinforced chimneys). As a result: 1) the chimney falls away from dwelling, creating a falling hazard to anyone outside, or
11 2) the chimney falls on the roof of the structure, with possible damage to the roof. The chimney separates from the structure, and often collapses. This may result failure of the roof tie strap or inadequate bolting of the strap, as observed for light framed chimneys (in the 1992 Big Bear Earthquake) as well as masonry chimneys (in the 1989 Loma Prieta Earthquake). Masonry chimneys crack. The fireplace is damaged (typically as masonry cracking, or with separation of the masonry from the walls and ceiling). The roof is damaged and leaks (with possible water damage occurring later). Additional damage occurs to the wood-framed structure from chimney inertial forces CRIPPLE WALLS Cripple walls are another common feature in older wood-frame residential construction, pre-dating slab-on-grade construction. Cripple walls are a short wall occurring between the concrete or masonry foundation and a framed first floor (see Figure 7). They allow a crawl space useful for routing utilities into the building. Seismic weaknesses occur when the bottom plate of the cripple wall is not bolted to the foundation, where the sheathing of he cripple wall is weak (e.g., with straight sheathing), and where posts supporting interior walls and columns are not seismically secured to foundations and floor beams (see Figure 3). Figure 7. Excerpt from City of Los Angeles Recommended Rehabilitation Details: "Earthquake Hazard Reduction in Existing Wood Frame Residential Buildings with Weak Cripple Walls and Unbolted Sill Plates"
12 The seismic deficiencies associated with cripple wall construction are well known and documented in nearly all large historical earthquakes affecting wood-framed construction, yet to date no building jurisdictions have enacted mandatory rehabilitation ordinances. The City of Berkeley has a voluntary ordinance with tax incentives. Other jurisdictions like the City of Los Angeles Department of Building & Safety (LADBS) promote seismic rehabilitation of weak cripple walls by providing pre-approve retrofit details (see the excerpt in Figure 7. See also the discussion in FEMA 547. Figure 8. Apartment Building with tuck-under parking in the San Fernando Valley, damaged in the 1994 Northridge Earthquake, temporarily braced to prevent collapse. TUCK-UNDER PARKING In wood-frame construction, the roof and floors collect and redistribute the earthquake forces to "shear walls" that act as stiff panels and deliver the forces to the building foundations. Typical wood-frame buildings act like a box, with the tops and bottoms corresponding to roofs, floors and foundation, and the shear walls acting like the sides of the box. Like a box, this provides stiff and strong configuration to resist earthquake and wind loads. During the 1960s and early 1970s, tens of thousands of wood-framed, multi-unit residential buildings were constructed with tuck-under parking. However, such designs introduce large open area on the ground level where walls along the garage fronts are discontinued, leaving only slender columns to carry the gravity loads. The designs interrupt the "load path," like cutting out one of the side of the box at its base. As a result, the structural system is weaker, and prone to large distortions and twisting motions, multiplying damage. These buildings were generally constructed prior to the 1980 s. UBC revisions in 1976 and 1988 increased seismic load requirements and design with tuck-under parking has been discouraged (though not entirely eliminated). Newer apartment construction with a tuck-
13 under condition may have steel moment frames along the open face, or other structural systems to prevent a soft/weak story condition. To date, no building jurisdictions have enacted mandatory rehabilitation ordinances for tuck-under parking. Some cities have begun programs to inventory weak-story buildings. See also the discussion in of tuck-under parking and associated rehabilitation techniques in FEMA 547. SURFACE FAULT RUPTURE Note that some single-family homes are exempted from the restrictions of the Alquist- Priolo Act, and may be built across faults deemed active by the State. A single-family wood-frame or steel-frame dwelling not exceeding two stories when that dwelling is not part of a development of four or more dwellings. ANALYSIS AND DESIGN OF WOOD FRAMES The nonlinear, inelastic behavior of wood-framed buildings is extremely difficult to model. Wood as a material is light and strong, but its strength depends on the direction of wood grain, defects in wood members, and moisture content. Wood is subject to damage by fungus, water and fire. Modes of failure include nail bending and slip, sliding and overturning of wall piers, shear failures in wall sheathing, various connection failures, and crushing of boundary members. The roof and floor diaphragms of a wood building have rigidities that are similar to the rigidities of the wall elements that interconnect them. Whereas in the computer-based seismic analysis of steel or concrete buildings, we can assume that the roof and floors act as rigid diaphragms, such simplifying assumptions are not justified for most wood-framed buildings. Given this complexity, most engineers rely upon elastic models and simplifying assumptions. For example, roof and floor diaphragms are assumed to be flexible, so that loads may be distributed in proportion to tributary floor area. Design fees for Structural Engineers designing typical wood-framed buildings are low, and sophisticated tools for nonlinear static and nonlinear dynamic analysis of complete wood buildings are lacking. Good seismic performance of wood-framed construction relies heavily on good detailing of members and connections. Damage often occurs where seismic loads are transferred from diaphragm to shear wall, or from shear wall to foundation. Window and door openings often leave only narrow piers between them to resist seismic loads, with the result that these piers are subject to high shear and overturning forces. Modern wood-frames rely on sophisticated hold-down systems to resist overturning and shear transfer hardware (by Simpson Strong-Tie and others) to deliver the required performance. SURFACE FAULT RUPTURE Note that some single-family residences are exempted from the restrictions of the Alquist-Priolo Act, and so may be built across faults deemed active by the State. The Act exempts any single-family wood-frame or steel-frame dwelling not exceeding two stories when that dwelling is not part of a development of four or more dwellings.
14 WOOD-FRAME DAMAGE RELATIONSHIPS Figure 9 shows typical damage relationships for wood-frame construction, as published by J.H. Wiggins (1986), ATC-13, NIBS HAZUS software, and Wesson et al [Earthquake Spectra, 2004]. DAMAGE VARIABILITY From statistics of residential damage in past earthquakes [from studies by K. Steinbrugge, as well as the Northridge study by Wesson et al, etc.], it is clear that variations of ground shaking and variation in wood-frame building vulnerability produce high variability in the observed damage. Figure 10 plots the coefficient of variation of the Damage Factor (DF) as a function of mean Damage Factor for wood-framed construction, as found in large damage surveys by various researchers. The Damage Factor is defined as repair cost divided by the replacement value of the structure. Coefficient of variation is defined as the standard of deviation (sigma) divided by the mean. The plot shows that for 10% damage (DF=10%), the standard deviation of damage is about 15%, so mean damage ± one standard deviation would range from near zero to about 25 or 30 percent. For dwellings subjected to ground motions with peak horizontal accelerations of about 0.75g, damage states may range from no damage to rare cases of complete damage. Figure 10. Uncertainty in Wood-Frame Earthquake Damage COMMUNITIES IN HARM S WAY Based on the ground motion intensity shown in the simulations for the M7.8 San Andreas scenario, the geologic conditions, and age of the built environment, the following
15 communities are expected to experience significant damage to wood-framed construction. This list represents an initial guess, and is by no means rigorous or complete. Table 1. Communities with expected heavy or moderate damage to wood-frame construction in M7.8 San Andreas scenario Residential Communities with Expected Heavy Damage Bombay Beach Mecca Thermal Coachella Indio Bermuda Dunes Indian Wells Thousand Palms North Rancho Mirage Desert Hot Springs) North Palm Springs Yucaipa Redlands Highland Muscoy San Bernardino South Hesperia Wrightwood Palmdale Devore Valyermo Lakeview Residential Communities with Expected Moderate Damage Palm Springs Sun City Palm Desert Cathedral City Rancho Mirage Banning Beaumont Cherry Valley Calimesa Morongo Valley Rialto Colton Loma Linda Grand Terrace Highgrove Crestline Hesperia Lancaster Acton POST EARTHQUAKE INSPECTION Following earthquakes like the San Andreas scenario in question, local building jurisdictions and others will need to conduct inspections and safety postings. ATC-20 (www.atcouncil.org) describes a typical procedure for such inspections. Table 2, taken from the HAZUS MR-3 Technical Manual, presents descriptions of damage states for wood-framed construction. Additional considerations: Finishes to wood-framed construction (e.g., stucco and drywall) are often more susceptible to damage than other structural elements such as plywood shear walls. For this reason, they serve as good indicators of overall damage. See CUREE Publications No. EDA-02 through EDA-07. Damage to wood-framed construction varies dramatically from one site to another.
16 Even neighboring structures may show dramatically different damage levels. There are many reasons for this, but this variability should be expected. Thorough inspections should be done in areas strongly shaken, since brief surveys can easily miss instances of highly damage. In the southern part of Riverside County and Imperial County, initial damage reconnaissance may need to be done from the air due to the many small communities, widely scattered. Communications will be limited perhaps to cellular phones, radio, CB, and satellite phones. Outside access by roads may be limited in the vicinity of Salton Sea and in other areas subject to liquefaction, landslide and surface fault rupture We note that a high percentage of the residents in Riverside, San Bernardino, and Imperial County are employed in the construction industries. As such, they may be able to effect their own repairs in many cases. OPPORTUNITIES TO REDUCE THE DAMAGE Local building jurisdictions can take steps to prevent the earthquake damage that can occur to weak forms of wood-framed construction. The following steps may be considered: Require seismic evaluation of apartments with tuck-under parking constructed prior to 1980, using the procedures in ASCE or equivalent. Require seismic retrofit to remedy all soft/weak story conditions found. Require seismic evaluation of residences with cripple walls constructed prior to 1950, using the procedures in ASCE or equivalent. Require seismic retrofit to remedy all soft/weak story conditions, unanchored foundations, or unsecured posts found. Reinforce the quality chain require good design, thorough plan check and inspection, etc. Insist on engineered design for all new wood-frames, rather than permitting construction under conventional light-frame rules. Require inspection of older homes at time of sale or refinancing, with disclosure of known seismic weaknesses. Require the addition of plywood sheathing for roofs with spaced sheathing at the time of re-roofing.
17 REFERENCES Algermissen, S.T., Steinbrugge, K.V., Lagorio, H.L., "Estimation of Earthquake Losses to Buildings," USGS Open File Report ASCE/SEI 31-03, "Seismic Evaluation of Existing Buildings." Post-earthquake damage reconnaissance in the 1886 Charleston, South Carolina Earthquake Dutton, C.E., 1889, The Charleston earthquake of August 31, 1886, in U.S. Geological Survey Ninth Annual Report , p Taber, S., 1913, The South Carolina earthquake of January 1, 1913, Bulletin of the Seismological Society of America, v. 3, p Standard of Care in Structural Engineering Wood Frame Multiple Housing, by J.M. Steinbrugge, V.R. Bush and J.R. Johnson, Proceedings of SEAOC Annual Meeting, NIBS, HAZUS MR-3 Manual, 2007 Rojahn, C., ATC-13: "Earthquake Damage Evaluation Data for California," Applied Technology Council, Redwood City, CA. Rojahn, C., Poland, C., and Scawthorn, C., ATC-38: Database on the performance of structures near strong-motion recordings: 1994 Northridge. California earthquake" Applied Technology Council, Redwood City, CA.. Wiggins, J.H., and C.E. Taylor, NTS Engineering, "Damageability of Low-rise Construction: Data Bases; Categorization Techniques; Rating Procedures; Proposed Survey Procedures, Volume II", Report No Steinbrugge, K. V., 1982, Earthquakes, Volcanoes, and Tsunamis: An Anatomy of Hazards, Skandia American Group. FEMA 547, Techniques for the Seismic Rehabilitation of Existing Buildings, 2006 CUREE-Caltech Wood-frame Project, various publications. Wesson, Robert L., David M. Perkins, Edgar V. Leyendecker, Richard J. Roth, Jr., and Mark D. Petersen, Losses to Single-Family Housing from Ground Motions in the 1994 Northridge, California, Earthquake, Earthquake Spectra, Vol. 20, No. 3. Schmid, B.L., Nielsen, R.J., and Linderman, R.R., Narrow Plywood Shear Panels, Earthquake Spectra, EERI, August, Uniform Building Code (UBC), International Conference of Building Officials (ICBO), Whittier, California, various editions. International Code Council, International Building Code (IBC), 2000, 2003, 2006
Chapter 3 DESIGN AND CONSTRUCTION FEATURES IMPORTANT TO SEISMIC PERFORMANCE To satisfy the performance goals of the NEHRP Recommended Seismic Provisions, a number of characteristics are important to the
Retrofitting Post & Pier Houses 71 6 RETROFITTING POST & PIER HOUSES by James E. Russell, P.E. 72 Retrofitting Post & Pier Houses Retrofitting Post & Pier Houses 73 RETROFITTING POST AND PIER HOUSES This
Project Structural Conditions Survey and Seismic Vulnerability Assessment For SFCC Civic Center Campus 750 Eddy Street San Francisco, California 94109 Prepared For San Francisco Community College District
T H E G R EA T C A L IF O R N IA S H A K E O U T O C TO B E R 21, 201 0 S H A K E O U T. O R G 7 S T E P S T O E A R T H Q U A K E S A F E T Y S T E P 4. I D E N T I F Y Y O U R B U I L D I N G ' S P O
Expected Performance Rating System In researching seismic rating systems to determine how to best classify the facilities within the Portland Public School system, we searched out what was used by other
SEISMIC CODE EVALUATION MEXICO Evaluation conducted by Jorge Gutiérrez NAME OF DOCUMENT: Normas Técnicas Complementarias para Diseño por Sismo ( Complementary Technical Norms for Earthquake Resistant Design
Foundations 65 5 FOUNDATIONS by Richard Chylinski, FAIA and Timothy P. McCormick, P.E. 66 Foundations Foundations 67 FOUNDATIONS Let's assume that the retrofit has been done correctly from the roofline
Critical Facility Round Table October 16, 2003 San Francisco Seismic Risk for Data Centers David Bonneville Senior Principal Degenkolb Engineers San Francisco, California Presentation Outline Seismic Risk
What is Seismic Retrofitting? SEISMIC RETROFITTING A Seismic Retrofit provides existing structures with more resistance to seismic activity due to earthquakes. In buildings, this process typically includes
GAP.2.0.9 A Publication of Global Asset Protection Services LLC EARTHQUAKE DESIGN OF BUILDINGS INTRODUCTION Buildings in many areas of the world are susceptible to damage from moderate to severe earthquakes.
Dollars, deaths, and downtime: understand your building's seismic risk and how to evaluate it SEAOSC Strengthening Our Cities Summit 5 Nov 2015, Los Angeles, CA Keith Porter, PE PhD University of Colorado
Retrofitting in the Central US: A Federal Perspective 2012 National Earthquake Conference Michael Mahoney FEMA, Building Science Branch National Earthquake Hazards Reduction Program (NEHRP) NEHRP was formed
Volume, Special Issue, ICSTSD Behaviour of Steel Bracing as a Global Retrofitting Technique Miss S. S. Nibhorkar M. E (Structure) Scholar, Civil Engineering Department, G. H. Raisoni College of Engineering
KAREN CLARK & COMPANY KCC Event Brief: 2014 La Habra Earthquake June 2014 2 COPLEY PLACE BOSTON, MA 02116 T: 617.423.2800 F: 617.423.2808 Overview On Friday, March 28, 2014 at 9:09pm, a magnitude 5.1 earthquake
Structural Effective Beginning with the April 2011 The structural engineering exam is a breadth and exam examination offered in two components on successive days. The 8-hour Vertical Forces (Gravity/Other)
David Bell PJHM Architects, Inc. Young Nam Daniel Traub Thornton Tomasetti how to evaluate buildings and determine retrofit costs HOW TO EVALUATE BUILDINGS AND DETERMINE RETROFIT COSTS Presented by: David
3 Chapter Earthquake Damage: Types, Process, Categories Earthquakes leave behind a trail of damage and destruction. People s lives are affected by the loss of loved ones, destruction of property, economic
Repair of Earthquake-Damaged Masonry Fireplace Chimneys SOUTH NAPA EARTHQUAKE RECOVERY ADVISORY Purpose and Intended Audience The August 24, 2014 South Napa Earthquake has again served as a reminder that
San Diego Area Chapter International Code Council Carlsbad, Chula Vista, Coronado, Del Mar, El Cajon, El Centro, Encinitas, Escondido, Imperial Beach, La Mesa, Lemon Grove, National City, Oceanside, Poway,
City of San Diego s Efforts to Promote Seismic Safety Building Safety, Policy & Emergency Response 2011 EERI Annual Meeting San Diego February 10, 2011 I. Local Seismic Codes, Standards, Policies Outline
CITY OF BEAVERTON Community Development Department Building Division 12725 SW Millikan Way / PO Box 4755, Beaverton, OR 97076 Phone: (503) 526-2493 Fax: (503) 526-2550 General Information (503) 526-2222
SEISMIC RETROFITTING OF STRUCTURES RANJITH DISSANAYAKE DEPT. OF CIVIL ENGINEERING, FACULTY OF ENGINEERING, UNIVERSITY OF PERADENIYA, SRI LANKA ABSTRACT Many existing reinforced concrete structures in present
U.S. Technical Guide LP SolidStart LSL & LVL Wall Framing Technical Guide 1730F b -1.35E and 2360F b -1.55E LSL 2250F b -1.5E and 2900F b -2.0E LVL Please verify availability with the LP SolidStart Engineered
Paper No. 682 PERFORMANCE BASED SEISMIC EVALUATION AND RETROFITTING OF UNSYMMETRICAL MEDIUM RISE BUILDINGS- A CASE STUDY Jimmy Chandra, Pennung Warnitchai, Deepak Rayamajhi, Naveed Anwar and Shuaib Ahmad
Perforated Shearwall Design Method 1 Philip Line, P.E., Bradford K. Douglas, P.E., American Forest & Paper Association, USA Abstract Wood frame shearwalls are traditionally designed using full-height shearwall
Five reasons buildings fail in an earthquake and how to avoid them by Jeff White, AIA Published in Healthcare Design magazine There s a saying among seismologists: Earthquakes don t kill people. Buildings
Rehabilitation of a 1985 Steel Moment- Frame Building Gregg Haskell, a) M.EERI A 1985 steel moment frame is seismically upgraded using passive energy dissipation, without adding stiffness to the system.
Add Strength and Water Resistance When Repairing Your Walls Any home repair or remodeling work you do presents an opportunity to make your home fare better in the next storm. Whether you are just replacing
of the National Institute of Building Sciences Homebuilders Guide to Earthquake-Resistant Design and Construction FEMA 232 June 2006 Prepared by the Building Seismic Safety Council for the Federal Emergency
ASCE 41 Seismic Rehabilitation of Existing Buildings Presentation Topics: 1. How to define a Rehabilitation Objective per ASCE 41. 2. Data Collection and Testing. 3. Analysis Requirements. 4. Modeling.
CHAPTER 5 Elevating Your House Introduction One of the most common retrofitting methods is elevating a house to a required or desired Flood Protection Elevation (FPE). When a house is properly elevated,
SECTION 7 Engineered Buildings Field Investigation Types of Data to Be Collected and Recorded A field investigator looking at engineered buildings is expected to assess the type of damage to buildings.
SEISMIC DESIGN Various building codes consider the following categories for the analysis and design for earthquake loading: 1. Seismic Performance Category (SPC), varies from A to E, depending on how the
Chapter 5 DESIGN REQUIREMENTS 5.1 Seismic Design Categories The NEHRP Recommended Seismic Provisions recognizes that, independent of the quality of their design and construction, not all buildings pose
13 th World Conference on Earthquake Engineering Vancouver, B.C., Canada August 1-6, 2004 Paper No. 3292 DESIGN DRIFT REQUIREMENTS FOR LONG-PERIOD STRUCTURES Gary R. Searer 1 and Sigmund A. Freeman 2 SUMMARY
Patio Covers / Carports Building Guides for Homeowners Why Do I need a Permit? D I D Y O U K N O W? As owner-builder you are the responsible party of record on such a permit. If your work is being performed
Seismic Retrofit of Existing Buildings: Innovative Alternatives Moe Cheung and Simon Foo Public Works & Government Services Canada Hull, Quebec, Canada Jacques Granadino Public Works & Government Services
HURRICANE MITIGATION RETROFITS FOR EXISTING SITE-BUILT SINGLE FAMILY RESIDENTIAL STRUCTURES 101 Retrofits Required. Pursuant to Section 553.844 553.884, Florida Statutes, strengthening of existing site-built,
Chapter 3 FOUNDATIONS AND FOUNDATION WALLS This chapter discusses foundations and foundation walls constructed using the two most common foundation materials concrete and masonry. Although the IRC permits
Historic Boynton Beach High School Existing Building Assessment City of Boynton Beach February 10, 2011 SECTION 3 ONM & J STRUCTURAL ANALYSIS STRUCTURAL ENGINEERS SPECIAL INSPECTORS STRUCTURAL CONDITION
Perforated Shearwall Design Jeffrey Stone, Ph.D., Philip Line, P.E., Brian Weeks, P.E., American Forest & Paper Association Introduction In the segmented approach to wood frame shearwall design, shearwall
EARTHQUAKE MAGNITUDE Earliest measure of earthquake size Dimensionless number measured various ways, including M L local magnitude m b body wave magnitude M s surface wave magnitude M w moment magnitude
Guidelines for Promotion of Earthquake-resistance School Building July 2003 Department of Facilities Planning and Administration, Ministry of Education, Culture, Sports, Science and Technology JAPAN Preface
Cover Introduction In regard to precast concrete systems, the addition of two new categories of Seismic Force Resisting Systems (SFRS) in IBC 2006 has created some confusion about whether to specify intermediate
13 th World Conference on Earthquake Engineering Vancouver, B.C., Canada August 1-6, 2004 Paper No. 2136 AN ANALYSIS OF FIRE SPRINKLER SYSTEM FAILURES DURING THE NORTHRIDGE EARTHQUAKE AND COMPARISON WITH
COST ADVANTAGES OF BUCKLING RESTRAINED BRACED FRAME BUILDINGS May 27, 2009 INTRODUCTION Through the development of hypothetical model buildings, this study investigates the potential material savings and
Pacific Earthquake Engineering Research Center Framing Earthquake Retrofitting Decisions: The Case of Hillside Homes in Los Angeles Detlof von Winterfeldt University of Southern California Nels Roselund
ENGINEERING-BASED EARTHQUAKE RISK MANAGEMENT MRP Engineering Newsletter February 2012 The world recently experienced several major earthquakes, which caused severe local impacts and major worldwide repercussions.
Research & development Earthquake tragedy and application of seismic isolation, energy dissipation and other seismic control systems to protect structures in China 90% of the Chinese territory is seismic.
Retrofitting By Means Of Post Tensioning Khaled Nahlawi 1 Abstract An analytical program was prepared to retrofit the Holy Cross Church in Santa Cruz, California. An inelastic analysis was perfonned on
December 2013 For Immediate Release EARTHQUAKE PROBABLE MAXIMUM LOSS AND SEISMIC RISK ASSESSMENT ABSTRACT by Structural Engineering Group Marx Okubo Associates, Inc. Melissa Clark, PE, Associate, Denver
Chapter 9 CONCRETE STRUCTURE DESIGN REQUIREMENTS 9.1 GENERAL 9.1.1 Scope. The quality and testing of concrete and steel (reinforcing and anchoring) materials and the design and construction of concrete
Earthquake Risk Reduction Presentations Session 1 Slide 1 Earthquake Risk Reduction 1- Concepts & Terminology Welcome to the World Bank Institute s (WBI) Distance Learning (DL) course on Earthquake Risk
4.3.5 - Breakaway Walls Elevation of a structure on a properly designed foundation reduces the potential for water damage from flooding. When the space below the lowest elevated floor is maintained free
COMMONLY USED RESIDENTIAL BUILDING CODES INTERNATIONAL RESIDENTIAL CODE (2009) form revised 5/10 FOUNDATION 1. DESIGN OF FORMWORK. Section 1906.1 IBC 2009, Section R404.1.2.3.6 IRC 2009, ACI 318 Section
CHALLENGE JOURNAL OF STRUCTURAL MECHANICS 1 (4) (2015) 161 167 Seismic performance evaluation of an existing school building in Turkey Hüseyin Bilgin * Department of Civil Engineering, Epoka University,
Structural Seismic Retrofits For Hawaii Single Family Residences With Post and Pier Foundations Volume I Results of Study, Structural Analysis and Retrofit Strategies Prepared for FEMA Hazard Mitigation
EVALUATION OF SEISMIC RESPONSE - FACULTY OF LAND RECLAMATION AND ENVIRONMENTAL ENGINEERING -BUCHAREST Abstract Camelia SLAVE University of Agronomic Sciences and Veterinary Medicine of Bucharest, 59 Marasti
August 3, 2012 Existing Building Code 2012 versus the Rhode Island State By: Structural Engineers Association of Rhode Island, Building Code Committee Introduction At the request of the Building Code Standards
CITY OF SAN JOSE BUILDING DIVISION POLICY Policy on Water Heater Installations Policy No. UPC 510-1-94 Effective: September 1, 1995 Revised: February 10, 1996 All new and replacement water heaters installed
T H E W I N D Protecting Your Home From Hurricane Wind Damage During a hurricane, homes may be damaged or destroyed by high winds and high waves. Debris can break windows and doors, allowing high winds
CONVEGNO SISMA ED ELEMENTI NON STRUTTURALI Approcci, Stati Limite e Verifiche Prestazionali Bologna 24 ottobre 2014 PROGETTO DI ELEMENTI NON STRUTTURALI SOGGETTI AD AZIONI SISMICHE G. Michele Calvi IUSS
Bolting: Attachment Of The Mudsill To The Foundation If the mudsill of a house (the pink area in the illustration at right) is not bolted, the lateral loads (back and forth motions) of an earthquake can
EARTHQUAKE HOME RETROFIT HANDBOOK HOW TO COMPLETE THE HOME ASSESSMENT CHECKLIST Chapter 2 of 3 August 2002 Disclaimer The information in the Earthquake Home Retrofit Handbook is based on current earthquake
TECHNICAL NOTE On Cold-Formed Steel Construction 1201 15th Street, NW, Suite 320 W ashington, DC 20005 (202) 785-2022 $5.00 Design of Diagonal Strap Bracing Lateral Force Resisting Systems for the 2006
780 CMR: MASSACHUSETTS AMENDMENTS TO THE INTERNATIONAL EXISTING BUILDING CODE 2009 CHAPTER 34: EXISTING STRUCTURES 3401.1 Replace as follows: 3401.1 Scope. Chapter 34 of the International Building Code
4 EFFECTS OF SURFACE FAULT RUPTURE ON INFRASTRUCTURE 4.1 Introduction The preliminary reconnaissance efforts performed by GEER on August 24, 2014 (the day of the M6 South Napa earthquake) noted significant
Chapter 9 STRUCTURAL CONCEPT FOR LIGHT GAUGE STEEL FRAME SYSTEM 9.1 BACKGROUND Steel is widely used in the construction of multi-storey buildings. However, steel construction is seldom used and is traditionally
Property Inspection 83A Ascot Avenue North New Brighton Christchurch STRUCTURAL REPORT March 2013 This document has been prepared for the benefit of Clint Marston. No liability is accepted by this company
FROM THE FOUNDATION Truss Fabrication with Light Gage Steel Framing By Richard H. Kapp, P.E. Note: Italicized portions contributed by Brad Beczkalo. See article, p. 15. L ight gage steel trusses have been
NIST GCR 0-97-9 Applicability of Nonlinear Multiple-Degree-of-Freedom Modeling for Design NEHRP Consultants Joint Venture A Partnership of the Applied Technology Council and the Consortium of Universities
CONTENTS Current Status of Seismic Retrofitting Technology Damages of Past Earthquakes Seismic Diagnosis Method Building Control Section Urban Building Division Bureau of Urban Development, TMG Seismic
SEISMIC CAPACITY OF EXISTING RC SCHOOL BUILDINGS IN OTA CITY, TOKYO, JAPAN Toshio OHBA, Shigeru TAKADA, Yoshiaki NAKANO, Hideo KIMURA 4, Yoshimasa OWADA 5 And Tsuneo OKADA 6 SUMMARY The 995 Hyogoken-nambu
2012 Michigan Rehabilitation Code for Existing Buildings First Printing: June 2014 ISBN: 978-1-60983-208-7 COPYRIGHT 2014 by INTERNATIONAL CODE COUNCIL, INC. ALL RIGHTS RESERVED. This 2012 Michigan Rehabilitation
KPA The Joint Venture of EBA Engineering, Inc. and Kennedy Porter & Associates, Inc. 4813 Seton Drive, Baltimore, MD 21215 Phone: (410-358-7171) Fax: (410)358-7213 Building Condition Assessment: Baltimore,
A. GENERAL INFORMATION 1. Street Address of Property: City: State: Zip: 2. Property Owner s Name: 3. Date of inspection: 4. Inspector s Name: B. BUILDING SITE INSPECTION 5. Utility Service Safety: IMPORTANT
OSHA GUIDANCE DOCUMENT FALL PROTECTION IN RESIDENTIAL CONSTRUCTION OSHA GUIDANCE DOCUMENT FALL PROTECTION IN RESIDENTIAL CONSTRUCTION Table of Contents Executive Summary... 1 Introduction... 1 Installing
Buildings 2012, 2, 173-202; doi:10.3390/buildings2030173 Article OPEN ACCESS buildings ISSN 2075-5309 www.mdpi.com/journal/buildings/ Comparison of Energy Dissipation, Stiffness, and Damage of Structural
Article 5: Building Regulations Division 37: Additional Building Regulations for Archaic Materials and Methods of Construction (Added Additional Building Regulations for Archaic Materials and Methods of
FALL 2013 C C Reinforced Concrete Design CIVL 4135 ii 1 Chapter 1. Introduction 1.1. Reading Assignment Chapter 1 Sections 1.1 through 1.8 of text. 1.2. Introduction In the design and analysis of reinforced
Journal of Japan Association for Earthquake Engineering, Vol.4, No.3 (Special Issue), 2004 SEISMIC DESIGN OF HIGHWAY BRIDGES Kazuhiko KAWASHIMA 1 and Shigeki UNJOH 2 1 Member of JAEE, Professor, Department
ELECTRICAL SUBSTATION EQUIPMENT DAMAGE DATABASE FOR UPDATING FRAGILITY ESTIMATES Thalia ANAGNOS 1 And Dennis K OSTROM 2 SUMMARY A database has been created that contains data related to damaged and undamaged