Earthquake Structural Damage PDF

EARTHQUAKE STRUCTURAL DAMAGE CETS461 Earthquake Engineering SOFT STORY A soft story, also known as a weak story, is defined as a story in a building that has substantially less resistance, or stiffness, than the stories above or below it. In essence, a soft story has inadequate she...

EARTHQUAKE STRUCTURAL DAMAGE CETS461 Earthquake Engineering SOFT STORY A soft story, also known as a weak story, is defined as a story in a building that has substantially less resistance, or stiffness, than the stories above or below it. In essence, a soft story has inadequate shear resistance or inadequate ductility (energy absorption capacity) to resist the earthquake- induced building stresses. CETS461 Earthquake Engineering SOFT STORY Although not always the case, the usual location of the soft story is at the ground floor of the building. This is because many buildings are designed to have an open first-floor area that is easily accessible to the public. Thus, the first floor may contain large open areas between columns, without adequate shear resistance. CETS461 Earthquake Engineering SOFT STORY The earthquake-induced building movement also causes the first floor to be subjected to the greatest stress, which compounds the problem of a soft story on the ground floor CETS461 Earthquake Engineering SOFT STORY In shaking a building, an earthquake ground motion will search for every structural weakness. These weaknesses are usually created by sharp changes in stiffness, strength and/or ductility, and the effects of these weaknesses are accentuated by poor distribution of reactive masses. CETS461 Earthquake Engineering SOFT STORY Severe structural damage suffered by several modern buildings during recent earthquakes illustrates the importance of avoiding sudden changes in lateral stiffness and strength. A typical example of the detrimental effects that these discontinuities can induce is seen in the case of buildings with a “soft story.” CETS461 Earthquake Engineering SOFT STORY Inspection of earthquake damage as well as the results of analytical studies have shown that structural systems with a soft story can lead to serious problems during severe earthquake ground shaking. Numerous examples illustrate such damage and therefore emphasize the need for avoiding the soft story by using an even distribution of flexibility, strength, and mass CETS461 Earthquake Engineering  CETS461 Earthquake Engineering Heavy damage in the weak story of a five-floor building in Adapazari (17 August 1999 Kocaeli earthquake, (M = 7.4) (Isik G., 2006). CETS461 Earthquake Engineering CETS461 Earthquake Engineering CETS461 Earthquake Engineering CETS461 Earthquake Engineering CETS461 Earthquake Engineering  CETS461 Earthquake Engineering 2 Examples of buildings subjected to soft-story collapse during the Nepal earthquake. CETS461 Earthquake Engineering CETS461 Earthquake Engineering SOFT STORY There are many existing buildings in regions of high seismic risk that, because of their structural systems and/or of the interaction with non- structural components, have soft stories with either inadequate shear resistance or inadequate ductility (energy absorption capacity) in the event of being subjected to severe earthquake ground shaking. Hence, they need to be retrofitted. Usually, the most economical way of retrofitting such a building is by adding proper shear walls or bracing to the soft stories. CETS461 Earthquake Engineering CETS461 Earthquake Engineering CETS461 Earthquake Engineering  CETS461 Earthquake Engineering Collapsed 1st floor of a residential house in Brgy Poblacion, Padada, Davao Del Sur.  CETS461 Earthquake Engineering A three-storey residential house in Buyagan, Benguet, which was under construction, collapsed due to the 7.0- magnitude July 2022 earthquake.  CETS461 Earthquake Engineering A three-storey residential house in Buyagan, Benguet, which was under construction, collapsed due to the 7.0- magnitude July 2022 earthquake.  CETS461 Earthquake Engineering A three-storey residential house in Buyagan, Benguet, which was under construction, collapsed due to the 7.0- magnitude July 2022 earthquake.  CETS461 Earthquake Engineering A three-storey residential house in Buyagan, Benguet, which was under construction, collapsed due to the 7.0- magnitude July 2022 earthquake.  CETS461 Earthquake Engineering A three-storey residential house in Buyagan, Benguet, which was under construction, collapsed due to the 7.0- magnitude July 2022 earthquake.  CETS461 Earthquake Engineering A three-storey residential house in Buyagan, Benguet, which was under construction, collapsed due to the 7.0- magnitude July 2022 earthquake. CETS461 Earthquake Engineering SOFT STORY While damage and collapse due to a soft story are most often observed in buildings, they can also be developed in other types of structures. For example, Figs. 4.12 and 4.13 show an elevated gas tank that was supported by reinforced concrete columns. The lower level containing the concrete columns behaved as a soft story in that the columns were unable to provide adequate shear resistance during the earthquake. CETS461 Earthquake Engineering CETS461 Earthquake Engineering  CETS461 Earthquake Engineering Figure 3(a) – Collapsed slender and weak framed staging of water tanks in Manfera village; Figure 3(b) - Severe damage occurred to elevated water tanks with frame staging which caused water tank pulled down in Bhachau (C Rai 2003). CETS461 Earthquake Engineering PANCAKING Pancaking occurs when the earthquake shaking causes a soft story to collapse, leading to total failure of the overlying floors. These floors crush and compress together such that the final collapsed condition of the building consists of one floor stacked on top of another, much like a stack of pancakes. CETS461 Earthquake Engineering PANCAKING Pancaking of reinforced concrete multistory buildings was common throughout the earthquake-stricken region of Turkey due to the Izmit earthquake on August 17, 1999. Examples of pancaking caused by this earthquake are shown in Figs. 4.14 to 4.16. CETS461 Earthquake Engineering CETS461 Earthquake Engineering CETS461 Earthquake Engineering CETS461 Earthquake Engineering PANCAKING Concerning the damage caused by the Izmit earthquake, Bruneau (1999) states: Pancaking is attributed to the presence of “soft” lower stories and insufficiently reinforced connections at the column-beam joints. Most of these buildings had a “soft” story—a story with most of its space unenclosed—and a shallow foundation and offered little or no lateral resistance to ground shaking. CETS461 Earthquake Engineering PANCAKING As many as 115,000 of these buildings—some engineered, some not—were unable to withstand the strong ground shaking and were either badly damaged or collapsed outright, entombing sleeping occupants beneath the rubble. Partial collapses involved the first two stories. The sobering fact is that Turkey still has an existing inventory of several hundred thousand of these highly vulnerable buildings. Some will need to undergo major seismic retrofits; others will be demolished. CETS461 Earthquake Engineering PANCAKING Another example of pancaking is shown in Fig. 4.17. The site is located in Mexico City, and the damage was caused by the Michoacan earthquake in Mexico on September 19, 1985. CETS461 Earthquake Engineering PANCAKING Note in Fig. 4.17 that there was pancaking of only the upper several floors of the parking garage. The restaurant building that abutted the parking garage provided additional lateral support, which enabled the lower three floors of the parking garage to resist the earthquake shaking. The upper floors of the parking garage did not have this additional lateral support and thus experienced pancaking during the earthquake.  CETS461 Earthquake Engineering Earthquake-induced pancake-type progressive collapse (Islamabad, 2005) CETS461 Earthquake Engineering  CETS461 Earthquake Engineering Surviving hımış house next to a row of collapsed reinforced concrete buildings, Adapazari, Turkey, 1999  CETS461 Earthquake Engineering Pancake-collapse of a three-storey building (formerly Southern Trade) in Padada, Davao del Sur  CETS461 Earthquake Engineering The collapsed Hyatt Terraces Baguio Hotel after the earthquake in Baguio  CETS461 Earthquake Engineering The Hyatt Terraces Hotel collapsed during the 1990 killer earthquake that devastated Luzon, leaving Baguio City with the most number of casualties and severe damages.// Photo from Inquirer.Net CETS461 Earthquake Engineering CETS461 Earthquake Engineering SHEAR WALLS Many different types of structural systems can be used to resist the inertia forces in a building that are induced by the earthquake ground motion. For example, the structural engineer could use braced frames, moment-resisting frames, and shear walls to resist the lateral earthquake- induced forces. CETS461 Earthquake Engineering SHEAR WALLS Shear walls are designed to hold adjacent columns or vertical support members in place and then transfer the lateral forces to the foundation. The forces resisted by shear walls are predominately shear forces, although a slender shear wall could also be subjected to significant bending. CETS461 Earthquake Engineering SHEAR WALLS Figure 4.18 shows the failure of a shear wall at the West Anchorage High School caused by the Prince William Sound earthquake in Alaska on March 27, 1964. Although the shear wall shown in Fig. 4.18 contains four small windows, often a shear wall is designed and constructed as a solid and continuous wall, without any window or door openings. CETS461 Earthquake Engineering SHEAR WALLS The X shaped cracks between the two lower windows in Fig. 4.18 are 45° diagonal tension cracks, which are typical and characteristic of earthquake-induced damage. These diagonal tension cracks are formed as the shear wall moves back and forth in response to the earthquake ground motion. CETS461 Earthquake Engineering CETS461 Earthquake Engineering SHEAR WALLS Common problems with shear walls are that they have inadequate strength to resist the lateral forces and that they are inadequately attached to the foundation. For example, having inadequate shear walls on a particular building level can create a soft story. A soft story could also be created if there is a discontinuity in the shear walls from one floor to the other, such as a floor where its shear walls are not aligned with the shear walls on the upper or lower floors. CETS461 Earthquake Engineering SHEAR WALLS Even when adequately designed and constructed, shear walls will not guarantee the survival of the building. For example, Fig. 4.19 shows a comparatively new building that was proclaimed as “earthquake-proof” because of the box-type construction consisting of numerous shear walls. Nevertheless, the structure was severely damaged because of earthquake-induced settlement of the building. CETS461 Earthquake Engineering SHEAR WALLS CETS461 Earthquake Engineering SHEAR WALLS Shear wall failure modes observed in recent earthquakes in (a) Chile (NIST 2014) and (b) New Zealand (Elwood et al. 2012) CETS461 Earthquake Engineering SHEAR WALLS Out-of-plane buckling of shear walls under seismic action (a) Christchurch earthquake (2011) (b) Experiment  CETS461 Earthquake Engineering SHEAR WALLS Observed damage to shear walls in Chile: a) Concrete crushing, b) Rebar buckling, and c) Lateral (out-of-plane) instability, Images: Wallace et al. (2012)  CETS461 Earthquake Engineering Collapse of the 16-story building in İskenderun, Building #1 (aka MCG Tower) (a), semi-collapsed situation between the two earthquakes (b), source of a and b: (Artıgerçek 2023), cut building and the base of the U-shaped RC wall (c), cut ground foor columns and shear wall (d)  CETS461 Earthquake Engineering Collapse of the 16-story building in İskenderun, Building #1 (aka MCG Tower) (a), semi-collapsed situation between the two earthquakes (b), source of a and b: (Artıgerçek 2023), cut building and the base of the U-shaped RC wall (c), cut ground foor columns and shear wall (d)  CETS461 Earthquake Engineering Collapse of the 16-story building in İskenderun, Building #1 (aka MCG Tower) (a), semi-collapsed situation between the two earthquakes (b), source of a and b: (Artıgerçek 2023), cut building and the base of the U-shaped RC wall (c), cut ground foor columns and shear wall (d) CETS461 Earthquake Engineering WOOD FRAME STRUCTURES There are exceptions to the general rule that wood-frame structures are resistant to collapse. For example, in the 1995 Kobe earthquake, the vast majority of deaths were due to the collapse of one- and two-story residential and commercial wood-frame structures. More than 200,000 houses, about 10 percent of all houses in the Hyogo prefecture, were damaged, including more than 80,000 collapsed houses, 70,000 severely damaged, and 7000 consumed by fire. CETS461 Earthquake Engineering WOOD FRAME STRUCTURES It is generally recognized that single-family wood-frame structures that include shear walls in their construction are very resistant to collapse from earthquake shaking. This is due to several factors, such as their flexibility, strength, and light dead loads, which produce low earthquake-induced inertia loads. These factors make the wood-frame construction much better at resisting shear forces and hence more resistant to collapse. CETS461 Earthquake Engineering WOOD FRAME STRUCTURES The collapse of the houses has been attributed to several factors, such as (EQE Summary Report, 1995): Age-related deterioration, such as wood rot, that weakened structural members. Post and beam construction that often included open first-floor areas (i.e., a soft first floor), with few interior partitions that were able to resist lateral earthquake loads. Weak connections between the walls and the foundation. CETS461 Earthquake Engineering WOOD FRAME STRUCTURES Inadequate foundations that often consisted of stones or concrete blocks. Poor soil conditions consisting of thick deposits of soft or liquefiable soil that settled during the earthquake. Because of the inadequate foundations, the wood-frame structures were unable to accommodate the settlement. CETS461 Earthquake Engineering WOOD FRAME STRUCTURES Inertia loads from heavy roofs that exceeded the lateral earthquake load-resisting capacity of the supporting walls. The heavy roofs were created by using thick mud or heavy tile and were used to resist the winds from typhoons. However, when the heavy roofs collapsed during the earthquake, they crushed the underlying structure. CETS461 Earthquake Engineering CETS461 Earthquake Engineering CETS461 Earthquake Engineering CETS461 Earthquake Engineering CETS461 Earthquake Engineering CETS461 Earthquake Engineering POUNDING DAMAGE Pounding damage can occur when two buildings are constructed close to each other and, as they rock back-and-forth during the earthquake, they collide into each other. Even when two buildings having dissimilar construction materials or different heights are constructed adjacent to each other, it does not necessarily mean that they will be subjected to pounding damage. CETS461 Earthquake Engineering POUNDING DAMAGE For example, as shown in Fig. 4.17, the restaurant that was constructed adjacent to the parking garage actually provided lateral support to the garage and prevented the three lower levels from collapsing. CETS461 Earthquake Engineering POUNDING DAMAGE In the common situation for pounding damage, a much taller building, which has a higher period and larger amplitude of vibration, is constructed against a squat and short building that has a lower period and smaller amplitude of vibration. Thus, during the earthquake, the buildings will vibrate at different frequencies and amplitudes, and they can collide with each other. CETS461 Earthquake Engineering POUNDING DAMAGE The effects of pounding can be especially severe if the floors of one building impact the other building at different elevations, so that, for example, the floor of one building hits a supporting column of an adjacent building. CETS461 Earthquake Engineering POUNDING DAMAGE Figure 4.20 shows an example of pounding damage to the Anchorage-Westward Hotel caused by the Prince William Sound earthquake in Alaska on March 27, 1964. Although not evident in the photograph, the structure shown on the right half of the photograph is a 14-story hotel. The structure visible on the left half of Fig. 4.20 is the hotel ballroom. CETS461 Earthquake Engineering POUNDING DAMAGE The pounding damage occurred at the junction of the 14-story hotel and the short and squat ballroom. Note in Fig. 4.20 that the main cracking emanates from the upper left corner of the street- level doorway. The doorway is a structural weak point, which has been exploited during the side-to- side shaking during the earthquake. CETS461 Earthquake Engineering POUNDING DAMAGE Another example of pounding damage and eventual collapse is shown in Fig. 4.21. The buildings were damaged during the Izmit earthquake in Turkey on August 17, 1999. As shown in Fig. 4.21, the pounding damage was accompanied by the collapse of the two buildings into each other.  CETS461 Earthquake Engineering Hammering of two adjacent buildings in Hassa, Hatay (a), inside look from the building on the right (b)  CETS461 Earthquake Engineering Building pounding (New Zealand, 2009)  CETS461 Earthquake Engineering a. Damage of buildings due to pounding during past earthquakes a damage of reinforced concrete buildings with floors at different elevations in the 1999 Athens earthquake (Photo Courtesy: A. Pomonis),  CETS461 Earthquake Engineering b. structural pounding damage at expansion joint of Secretariat building in Gangtok during 2011 Sikkim earthquake (Photo Courtesy: Alpa Sheth)  CETS461 Earthquake Engineering C. pounding between new and old building during 6 April 2009, L’Aquila earthquake  CETS461 Earthquake Engineering Pounding damage in adjacent buildings of different heights  CETS461 Earthquake Engineering Pounding damage in adjacent buildings of different heights  CETS461 Earthquake Engineering Damages caused by pounding during the M8.0 Wenchuan earthquake on May 12, 2008 CETS461 Earthquake Engineering POUNDING DAMAGE It is very difficult to model the pounding effects of two structures and hence design structures to resist such damage. As a practical matter, the best design approach to prevent pounding damage is to provide sufficient space between the structures to avoid the problem. CETS461 Earthquake Engineering POUNDING DAMAGE If two buildings must be constructed adjacent to each other, then one design feature should be to have the floors of both buildings at the same elevations, so that the floor of one building does not hit a supporting column of an adjacent building. CETS461 Earthquake Engineering IMPACT DAMAGE FROM COLLAPSE OF ADJACENT STRUCTURES Similar to pounding damage, the collapse of a building can affect adjacent structures. For example, Fig. 4.22 shows a building that has lost a corner column due to the collapse of an adjacent building during the Izmit Earthquake in Turkey on August 17, 1999. The buildings were under construction at the time of the earthquake. CETS461 Earthquake Engineering IMPACT DAMAGE FROM COLLAPSE OF ADJACENT STRUCTURES Note that the roof of the collapsed building now rests on the third story corner of the standing building. Since the geotechnical engineer and engineering geologist are usually required to discuss any “earthquake hazards” that could affect the planned construction, it may be appropriate for them to evaluate possible collapse of adjacent buildings founded on poor soil or susceptible to geologic hazards. CETS461 Earthquake Engineering CETS461 Earthquake Engineering ASYMMETRY Similar to pounding damage, buildings that are asymmetric, such as T- or L-shaped buildings, can experience damage as different parts of the building vibrate at different frequencies and amplitudes. This difference in movement of different parts of the building is due to the relative stiffness of each portion of the building. CETS461 Earthquake Engineering ASYMMETRY For example, for the T-shaped building, the two segments that make up the building are usually much stiffer in their long directions, then across the segments. Thus, damage tends to occur where the two segments of the T join together. CETS461 Earthquake Engineering ASYMMETRY For example, for the T-shaped building, the two segments that make up the building are usually much stiffer in their long directions, then across the segments. Thus, damage tends to occur where the two segments of the T join together. CETS461 Earthquake Engineering CETS461 Earthquake Engineering