LBA LIA (English Learning Center)

October 20, 2009 by  
Filed under Uncategorized

LBA LIA was an afterschool English language learning center, built sometime after 2000, located in the city of Padang.  The building was a 4-story reinforced concrete frame building with brick infill.  After the September 30, 2009 earthquake, the first and second story of the building collapsed, resulting in 4 total fatalities.  Based on local accounts, 11 were trapped in the collapsed building after the earthquake but 7 of them were able to be saved. 

The typical beams and columns sizes used in the building are very small for supporting such heavy 4-story building.  The typical interior columns were 16”x18” and the typical interior beams were 14”x18”.  Notice that the partitions are brick walls, adding a lot more mass to the building.  The reinforcement used throughout the building are smooth rebars.  The concrete columns seem to lack adequate confinement for ductile detailing (Fig 6).  “Short hooked anchors” (Fig 7) are also very common throughout the building.  Notice that the short anchorage length does not satisfy the 12db requirement per ACI.

Front view of the collapsed building
Front view of the collapsed building
Side view of the collapsed building

Side view of the collapsed building

Back view of the collapsed building

Back view of the collapsed building

Third story columns shear failure at the stairs

Third story columns shear failure at the stairs

The beams and columns sizes are very minimal for such a heavy 4-story building

The beams and columns sizes are very minimal for such a heavy 4-story building

Damaged joint exposing lack of confinement from the minimal ties

Damaged joint exposing lack of confinement from the minimal ties

The hooked anchor commonly found in damaged buildings, which do not provide adequate anchorage length

The hooked anchor commonly found in damaged buildings, which do not provide adequate anchorage length

Pariaman City Hall

October 18, 2009 by  
Filed under Structural Observations

Located 45 km north of Padang, the city of Pariaman is located about 40 km from the epicenter of the Sept. 30 earthquake.   Constructed in 2007, the three-story city government building (Figure 1) experienced significant damage from the earthquake, necessitating all of the offices to be vacated and moved to temporary tents (Figure 2).  The exterior cladding, consisting of glass, infill brick partitions, and stucco/plaster finishes, suffered extensive damage (Figures 3-5).  Closer inspection from exposed portions of the structure revealed that the reinforced concrete (RC) moment frame to be largely intact and undamaged.  A walk-through of the building revealed extensive damage to interior partitions, which consisted of a combination of brick infill walls and gypsum board partitions.  Damage was most extensive at the 3rd floor, where major portions of the hung ceiling had collapsed.  The damage at the 3rd  floor was exacerbated by the lack of a rigid diaphragm at the roof level.  As shown in Figure 7, the roof consisted of a steel-framed gable roof that was supported atop RC columns that extended up from the 3rd floor.  While supported by perimeter beams at the roof, the RC columns were cantilevering in the out-of-plane direction, which combined with the flexibility of the steel roof, permitted racking of the roof diaphragm that triggered the extensive damage to the ceiling and 3rd floor partitions.    At the time of our visit, workers were on site removing files, furniture and salvageable doors and hardware.  This building provides an example where the earthquake deformation demands of the RC frame were within the damage threshold limits for the structure but greatly exceeded those of the non-structural architectural finishes.

Seismic Performance of Dutch Colonial Buildings

October 18, 2009 by  
Filed under Structural Observations

Seismic Performance of Dutch Colonial Buildings

October 17, 2009 by Sugeng Wijanto

INTRODUCTION

As we are aware a lot of the existing old buildings constitute relics of the Dutch colonial period that are 100 – 300 years old, were found particularly in the big cities in Indonesia such as Padang. A large number of these buildings represent constructions of 1 to 3 floors (low-rise buildings), constitute unreinforced masonry buildings with a floor slab construction that may consist of wood, clay-bricks piled in the shape of a curve which spans between two steel I-beams, or reinforced concrete. Normally building’s foundation  may constitute of a construction of clay-bricks, stone pad and timber logs. The roof frame may consist of a wood or steel structure and covered with roof tiles. The old URM buildings usually were built with masonry wall in consistent thickness for the height of the building and placed crosswise to make a “box-type” structural system. This system is meant to provide more stiffness in both direction and to give resistance for torsional effect.

Now and then the alteration of function of these buildings and repairing the building cosmetically only from the architectural viewpoint, while no structural review has ever been undertaken in renovation would cause a change of gravitation load.

CHARACTERISTIC OF CLAY-BRICK MATERIAL

The characteristic of unreinforced masonry constructions are found in old buildings consist of clay-brick piles which are attached to each other by simple mortar (lime mortar). There are various types of clay-brick piling which can be determined  from its thickness, i.e. 1 to 2 wythe clay-brick (modern building only half wythe clay-brick)

 

The average dimension of the old masonry unit is around length 250 mm x width 120 mm x thickness 55 mm. Based on the author’s experience conducting the compressive strength test using existing Dutch masonry units which were taken from old building built in 1907 (Semarang, Central Java) are quite variable and average compressive strength, fm, was found 6.5 MPa.

DAMAGE FEATURES

According to the data that we have recently taken from Padang earthquake, the performance of URM buildings could be damaged and worse could generate a total collapse. The masonry material has characteristics as heavy specific gravity, low ductility and also low tensile strength.

Typical damage features on URM buildings at Arau Street in Padang (see Figure 1 to 3):

  1. Diagonal cracks on the walls
  2. Failure on corners of the walls and the openings like doors and windows.
  3. Fallen roof parapet.
  4. The top framework was usually sliding off from its base
  5. Connection damage between foundation and walls, walls and walls and walls and top framework.

Based on recently earthquake experiences, repairation of old or historical buildings it would be commendable to have a Regional Regulation or standard from the Department of Public Works issued which necessitates a review of the structure’s analysis before undertaking renovation. Without the existence of a tight regulation, we will lost a lot of historical buildings in the future earthquake.

 

 

(a) Before Padang Earthquake

 

(b) After Padang Earthquake

Figure 1: URM building severe damaged

 

Before Padang Earthquake

 

After Padang Earthquake

Figure 2 : URM building totally collapsed

 

 

 

 

Figure 3 : URM building severe damaged

No. 52 Parupuak Tabing school

October 18, 2009 by  
Filed under Structural Observations

The No. 52 Parupuak Tabing school is an elementary school in North Padang that has 170 students. There are three buildings on this small campus arranged in a C-shape, all single story rectangular buildings, two classroom buildings and a small office building. The structure of each building is the same: confined masonry walls with gabled wood framed roofs. All three buildings are separated from each other by several feet.

The larger of the two classroom buildings that is at the spine of the “C” was constructed in 1984 and suffered substantial damage in the earthquake. The building was in the process of being renovated and all of the interior transverse cross walls had been removed with the intent that they would soon be replaced. As a result the ring beams on the longitudinal sides of the building that originally spanned approximately 13 feet now spanned 6 times that length, and thus the beams sustained permanent deflection along with the brick walls below. However, the brick remained in the wall. This is consistent with the out-of-plane behavior seen in other parts of West Sumatra after the 2007 earthquakes. The connection of the roof trusses to the ring beams remained intact such that the roof rode along with the ring beams. Also, the brick gable walls at the north and south ends of the building also failed, another behavior commonly seen in the West Sumatra earthquakes and other recent earthquakes in Indonesia.

The smaller of the two classroom buildings on the south side of the “C” was originally constructed in 1986 with a classroom added in 2005. This building also sustained damage, though it was of a different nature than the larger building. The confined masonry walls remained intact but there were numerous places where the foundation footings and floor slabs settled, as much as 4 inches at the west end. The only solid walls are on the west end and it appears that the lateral forces concentrated in these walls, as the largest settlement was at the ends of these walls. There were also vertical shear cracks between the walls and the confining concrete columns.

The office building on the north side of the “C” had damage similar to the classroom building at the south end. There was evidence of settlement in the foundation and vertical shear cracks between the concrete columns and the brick walls.

The school was constructed adjacent to a drainage ditch and there is a swampy area next to the smaller classroom building. This suggests that liquefaction played a role in the settlement. There was also sand on the floor in the classroom building, which school officials reported has having bubbled up through the cracks. These same officials told us that they could see waves in the ground during the earthquake.

The school is currently closed and the students are being taught at an adjacent mosque. The small classroom building is currently being used as a temporary sleeping place for local soldiers.

SMK Negeri 9 School

October 18, 2009 by  
Filed under Structural Observations

The SMK Negeri 9 school is located in downtown Padang across the street from the damaged Ambacang Hotel. The school serves high school students in 3 main buildings on the campus. The largest of the three buildings, a 3-story structure built in 1996, suffered major damage in the earthquake. We were told by school personnel that 2 people died and 5 others were injured. The other two classroom buildings as well as the school mosque were relatively undamaged and continue to hold classes. Classes displaced by the collapsed building were being held inside a tent in the school’s front court, and workers were in the process of building a temporary wood building to house more classes.

The collapsed school building structure consisted of concrete moment frames with brick infill walls both around the perimeter and inside of the building. The primary failure was the collapse of the third floor slab at the north end of the building. This slab came down onto the second floor slab below and also brought down the wood framed roof. School personnel told us that the collapse occurred approximately 5 minutes after the start of the shaking.

The column bays at the third floor comprised mostly of solid walls while the bays below were mostly windows with short infill walls below. This may have contributed to the failure of the slab since there was extensive hinging in the columns at the third floor level, thus potentially forming a soft story mechanism at that level. There was also evidence of captive column hinging at the first floor as well, whereas the second floor structure fell more or less intact.

Like many other concrete framed buildings that failed in Padang, the columns were reinforced with smooth longitudinal bars and thin ties with only 90 degree hooks and a relatively wide spacing. This along with the apparent soft story condition at the third floor and the captive columns at the first floor appears to have contributed to the collapse. What is not apparent is what caused only the north end of the building to fail. There did not appear to be any significant difference in the structure between the north and south ends.

There were a number of interior brick infilled partitions that fell, including the partition at the second floor directly adjacent to the slab break. This partition appeared to have fallen out of plane as one rather than in pieces. The north stairwell was part of the section that collapsed. The south stairwell remained standing but sustained heavy damage including the loss of the walls surrounding the stairwell and pullout of the stair from the second floor slab.

Masjid Nurul Iman

October 17, 2009 by  
Filed under Structural Observations

Masjid Nurul Iman is a large 2 story mosque located near the center of Padang City.  The structure was evaluated in the spring of this year as part of a research project by students at Stanford University studying potential tsunami evacuation structures in Padang.  Therefore, pre-earthquake photos and partial existing structural drawings were available for review.

Masjid Nurul Iman

MNI is one of the largest mosques in Padang, and has tall 6 meter story heights.  The foundation consists of a concrete slab on grade with grade beams and concrete piles.  The primary lateral force resisting system consists of reinforced concrete moment frames, and unreinforced brick masonry infill walls at the first story.  The second floor consists of a concrete slab, and the roof is a combination of concrete beams and steel truss dome framing.  The following photos were taken before the September 30th earthquake.

Masjid Nurul Iman
2nd Level Prayer Room

Dome Ceiling

2nd Floor Prayer Room

The building appeared to have performed well during the September 30th earthquake.  There was no visible damage to the main structural system, including the concrete beams and columns, as well as the full-height exterior brick infill walls.  At the first story, there were a few interior brick partition walls which collapsed.  These partial height walls did not extend to the bottom of the second floor, and were attached to the second floor with small concrete columns which could not resist the out-of-plane load induced by the brick wall and appeared to fail in bending.

First story collapsed brick partitions
First story collapsed brick partitions

Damage at the second story included the out-of-plane partial collapse of some brick balcony walls, the partial collapse of some small full height brick partition walls, and the collapse of about 1/3 of the gypsum board ceiling surrounding the dome.  It is possible that the relatively flexible roof dome diaphragm moved out of phase with the robust concrete structure below, and the differential movement caused the gypsum board ceiling to collapse.

Collapsed ceiling

Collapsed ceiling
Collapsed ceiling

The Stanford University student group evaluated the expected performance of Masjid Nurul Iman using the nonlinear static procedure (pushover analysis) outlined in ASCE 41.  The analysis was based on a deterministic tsunamigenic earthquake hazard with an estimated PGA of 0.25g (Site Class D).  The resulting pushover curve predicted a transient roof drift of 0.5% and permanent roof drift of 0.1%, which meets the performance requirements for Immediate Occupancy for concrete frame structures.  Strong motion data is not currently available for the September 30th earthquake, although USGS data estimated the event at MMI intensity VIII.

The mosque has been open since the earthquake, although the prayer area was moved from second floor to the first because of the risk of additional portions of the gypsum board ceiling collapsing.

Padang Fire Department and Early Search and Rescue Operations

October 17, 2009 by  
Filed under Social Science Observations

In the hours immediately following the earthquake, the Padang City Fire Department was the primary agency responsible for first response operations.  The Fire Department had practiced a preparedness drill in February, 2009 that improved performance in the 9/30 and 10/1 earthquakes. The training for preparedness included all city agencies and proved quite effective.  The City of Padang now has a new form of preparedness planning under the BPPD (City Planning Department). The Fire Department is the lead agency for emergency response operations under this plan. The principal officers use “handy-talkies” (radio devices) for communications within the department and among city personnel. Immediately after the earthquake, the principal government officers met at the radio station to establish the Emergency Operations Center (EOC), and then moved the EOC to the Mayor’s residence.

 Within five to ten minutes after the earthquake, 36 fire spots broke out in different areas of the city. The Padang Fire Department has one official station for a city of 900,000 residents, with 9 fire trucks and 36 trained personnel.  Further, one of the 9 trucks was damaged, as the roof of the garage at the fire station collapsed on the truck, rendering it unusable and leaving only 8 trucks for immediate service.  Given the rapid spread of the fire and no ladder trucks, the Department had to prioritize its operations.  The department responded to fires in residential areas first, given its priority for life safety.  They let fires in the commercial areas burn. After 48 hours, fire departments from neighboring municipalities in West Sumatra arrived to assist the Padang City crews, according to the previously established regional emergency plan.

 Fire personnel are also trained in urban search and rescue (USAR) techniques, and organized a team to rescue a woman who was pinned under debris.  External assistance came first from the TNI, at 3:00 a.m. on 10/1. At 6:00 a.m. on 10/1, the BNPD team came from Jakarta. Fire personnel were assisted in USAR operations by paramedics from the Indonesian Red Cross.

 Response to fires was hindered by debris from collapsed buildings in the streets.  The trucks had to take whatever routes were open.  During the first 48 hours, only Fire Department, Red Cross, and TNI personnel were engaged in response operations.  According to standard operating procedures, the Police should open the roads, but in this event, they were not available.  Coordination among agencies was provided primarily by instructions from the mayor.

 International Search and Rescue teams arrived on the second and third days.  The first team arrived from Australia, followed by teams from Switzerland, Japan, Korea, 21 international teams total. The teams arrived too late to provide much assistance. 

 Communications to support search and rescue operations primarily relied on “handi-talkies” within the Fire Department and cell phones with other agencies.  One cell phone network, ‘Flexi,” was operational. Fire stations, mosques, and the radio station have back-up generators, so they were able to communicate via radio, and the mayor was able to broadcast messages to the people via radio.

 In the immediate hours after the earthquake, gasoline was not available. The price increased by 350% at the stations.  The media exaggerated the inflation in the price of gasoline, but it was substantial. Fire personnel recommend a review of the current evacuation plan that would include the use of ‘smart’ signboards that could tell people where to go and update the situation reports in a rapidly changing disaster environment.

Performance of Hospitals: Yos Sudarso

October 15, 2009 by  
Filed under Structural Observations

Yos Sudarso Hospital is a multi-building 30,000 square meter hospital campus operated by the Catholic Archdiocese in Padang. This hospital has 145 beds and provides the full range of medical services including surgery, radiology, and even dental care. There are 7 main buildings on the hospital campus, almost of which are 3-story structures built with concrete moment frames with clay brick infill walls, concrete slab floors, and wood framed pitched roofs. The original building, which houses the hospital emergency department among other services, was constructed in 1971. The newest building, which houses the hospital’s intensive care units, was completed in 2003. There is also a single story wood framed lunch room built in 1993. All of the buildings are connected by either wood framed covered walkways or concrete framed connector buildings.

The Original 1971 Vintage Hospital Building

The Original 1971 Vintage Hospital Building

The primary earthquake damage occurred in the 3 story concrete framed building that connected the front building to the next building over. The columns supporting this building failed at the second floor, causing the floors above to come down. Remarkably, outside of a few cracks in the columns and slab the area below the second floor was undamaged and was still being used as a corridor by both patients and staff.

Collapsed Connector Building - 2nd Floor

Collapsed Connector Building - 2nd Floor

Hinged Column at Connector Building

Hinged Column at Connector Building

PA121077

Collapsed Corridor Building @ 3rd Floor

The original 1971 building also sustained damage, primarily at the second floor adjacent to the collapsed corridor where all of the concrete columns developed plastic hinges. A permanent 6” lateral drift was created at the third floor and roof. There was also damage to the roof overhangs and shear cracking in the brick infill. Interestingly, there is a gap between the concrete frame at the roof level and the roof framing as the concrete is below the roof trusses and the joists sit on top of the trusses. Despite the lack of a positive lateral load path there was no noticeable damage to either the main roof framing or the truss to concrete connections.

Column Hinging at the Second Floor Columns

Column Hinging at the Second Floor Columns

Newly Created Seismic Joint

Newly Created Seismic Joint

The other building that sustained extensive damage is the nurses housing building, a concrete frame/brick infill 3-story structure constructed in 1988. Many of the columns developed hinges directly below the second floor slab and many of the brick infill walls, both interior and exterior, sustained major damage and partial collapse. The two floors above had only minimal damage.

Nurses' Housing North Wall

Nurses' Housing North Wall

PA120031

Damage to the remaining buildings was mostly confined to shear cracks in the brick infill and cracking at the joints between the buildings. The joints were typically not constructed with any separations, so during the earthquake the buildings pounded against each other, causing the concrete to crack and spall at the battered joints.

Newly Created Seismic Joint

Newly Created Seismic Joint

The lack of separation between the buildings may have played a role in the partial collapse of the connector building. Another factor may have been the presence of several large water tanks on the roof of the connector building, which appear to have been installed long after the original construction.

Water Tanks on the Connector Building Roof

Water Tanks on the Connector Building Roof

Non-structural damage was extensive in the 1971 building that sustained the 6” of movement. Windows were shattered, cabinets were toppled, and many of the infill walls were damaged. The other building next to the collapsed corridor sustained similar damage but not to the same degree. Non-structural damage to the other buildings was minimal. The mechanical systems did not suffer major damage except for a major water line that ran through the collapsed corridor and was severed. Some of the radiology equipment moved in the earthquake but the hospital staff told us that none of them toppled over.

Hospital operations have been impacted by the earthquake. The emergency room is closed and emergency care is instead being provided within tents set up in the parking lot. There are also patients being treated in the undamaged lunch room building. The nurses who resided in the damaged nursing housing building have moved out and may not return. The hospital administrator told us that the total hospital capacity was down to 40% of what they could accommodate prior to the earthquake.

Emergency Services in the Parking Lot

Emergency Services in the Parking Lot

Performance of Hospitals: M. Djamil

October 14, 2009 by  
Filed under Structural Observations

The M. Djamil Hospital serves as Padang’s public hospital and is the largest medical facility in the area.There are 13 separate buildings on the campus and two of them, the outpatient services building and the building that include the laboratories, sustained substantial structural damage. Despite this, M. Djamil has remained open to patients following the earthquake. The hospital also sustained minor damage in the 2007 earthquakes.

The significant earthquake damage was to the 3 story building that housed the hospital’s administration offices and outpatient services. The outpatient building is comprised of a 3 story core section shaped like a cross and 2 story L-shaped wings at each corner, and was constructed in 1982.  The entire three story cross section, as well as one of the 2 story L-shaped sections, suffered a collapse of the second floor, which dropped up to 8′-6″.

The outpatient building was constructed with reinforced concrete moment frames with brick infill panels used for both the exterior walls and the interior partitions. This is a common type of construction in Padang, and unfortunately it is also a common building to have collapsed in this earthquake.

The collapsed hospital wing

The collapsed hospital wing

The collapsed first floor, as seen from the atrium

The collapsed first floor, as seen from the atrium

There was catastrophic hinging of the columns at the second floor, which was the primary cause of collapse of the building. In addition to a vertical drop there also appears to have been a lateral shift. At the north end of the cross section there is now a 9′-6″ gap between the 3 story wing and the 2 story wing where prior to the earthquake there was no gap. The hinging appears to be due to the use of smooth reinforcing bars in the column as well as inadequate stirrups that were not tightly spaced, not properly hooked at the corners, and not large enough to confine the core concrete. We have found many other concrete column failures in Padang that have had similar details. The horizonal and vertical irregularities of the building may have also played a role, though it is hard to tell since much of the evidence is buried under 10 feet of rubble. While a number of people were reportedly trapped under the collapsed floor we were told that there were no casualties.

An example of column hinging

An example of column hinging

The atrium at the center of the cross section suffered additional damage due to short columns supporting a heavy concrete roof. The roof was supported by beams spanning between one of four short columns at the atrium perimeter and a large column at the center. When the short columns failed the beams began to act as cantilever elements, causing substantial damage to the beams and to the center column. Fortunately enough of the beams and center column held to prevent the roof from falling.

The atrium center column and one of the failed beams

The atrium center column and one of the failed beams

One of the short columns at the roof, this one on the north end

One of the short columns at the roof, this one on the north end

The short column on the east side, the most heavily damaged of the four

The short column on the east side, the most heavily damaged of the four

The other portion of the hospital to sustained damage was the three story building directly adjacent to the outpatient building and housed the hospital’s labs. This building is also a 4 story reinforced concrete frame building with brick infill panels, and was constructed in 1994. There was a partial collapse of the roof mezzanine and a number of brick infill panels that had significant shear cracks. This damage forced the closure of the lab space. While the two buildings are connected by a two story bridge it does not appear that the collapse of the outpatient building caused the failures in the lab building. The connector bridge did not have any noticable structural damage.

The good news is that these two sections appear to be the only portions of the hospital campus to sustain significant damage. Other areas of the hospital, including the buildings that house the emergency department and the central plant, sustained little to no damage and are still open for patients.

Jembatan Siti Nurbaya (large concrete bridge south of the city)

October 13, 2009 by  
Filed under Uncategorized

The construction on Jembatan Siti Nurbaya began in 1994, was stopped due to a bad economy, and eventually completed in 1999. Jembatan Siti Nurbaya is the most substantial bridge over the Batang Arau, located at the South of the city center spanning roughly 70m. The bridge is approximately 10m wide and is a standard concrete box girder. The bridge itself faired very well in the September 30th earthquake with no apparent damage. The approaches, which consist of soil confined by concrete retaining walls, held up during the earthquake but sustained damage. The sidewalk on the South West approach separated and settled from the concrete retaining wall approximately 12”, as a result of an earthquake in 2007. This same location settled an additional 18” in the recent earthquake. In addition to the measurable separation, the south approach suffered damage in that the entire approach dropped relative to the bridge and the pavement split in two clear cracks forming deep longitudinal voids. Additionally, the North approach currently has about a two-inch crack spanning the entire width of the bridge just a few feet from the bridge-approach connection.

This bridge could serve as a key component for tsunami evacuation for two reasons: the bridge sits approximately 26 feet above the road below therefore the bridge is approximately 30 ft above sea level, which could potentially act as an evacuation site; the second use of the bridge is to facilitate numerous pedestrians, motorbikes and even cars, over the bridge to grant access to higher ground.

Photos to follow.

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