No. 52 Parupuak Tabing school

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

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.

Performance of Hospitals: Yos Sudarso

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 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.

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.

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.

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.

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.

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.

Performance of Hospitals: M. Djamil

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.

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.

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 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.

STMIK Indonesia Building

STMIK Indonesia provides classes and training in computer related occupations such as information technology and computerized accounting. STMIK is housed in a 4 story building in Padang that was constructed in 1998.

The primary structural system consists of concrete moment frames with brick masonry infill. The interior non-structural partitions consist of brick masonry infill with small concrete “practical” columns at the window and door openings. The floors are formed with concrete slabs and we understand from discussions with people at the building that the foundation includes concrete piles.

Outside of a few hairline cracks there was no noticeable damage to the primary concrete frames. However, the brick masonry infill on the bottom two floors was extensively damaged, forcing the closure of the building.

On the upper two floors, however, the brick infill walls remained mostly intact with only a few minor shear cracks. This evidence, combined with the lack of damage to the concrete moment frames, suggests that the infill walls provided lateral support for the building until they were too damaged to do so.

There was some minor settlement at the foundation around the front entry. We were told that the building is supported by a pile foundation but that the entry slabs are not tied into the pile system, which may explain the settlement issues. It did not appear that the settlement posed a hazard to the building.

The main issue with this building is how the brick infill acted as a structural element even though it was likely not designed to do so. While the main structure was relatively undamaged the damage to the “non-structural” walls caused the building to be shut down.

Performance of Hospitals: Bunda Medical Centre

BMC consists of two 5 story towers with a single story connector building in between. The building structure appears to be either confined masonry or concrete frame with masonry infill. It is difficult to tell after the fact but there is evidence that the buildings are confined masonry.

Both towers suffered extensive damage in the earthquake, though neither is in danger of collapse. The hospital staff has evacuated both buildings and has erected a tent in the parking lot to provide clinical services. One of the nurses told us that everyone, including patients, were able to safely evacuate the buildings after the earthquake such that there were no fatalities.

There are extensive shear cracks in the brick walls at the lower levels of both towers, and one of the wall panels at the second floor suffered blow-out. There is also evidence of yielding in two of the concrete columns at the rear corners of the main tower. At the southwest corner of the patient tower the brick walls were blown out at two floors, and at the opposite corner the brick moved out from the slab but not far enough to fall down to the ground. There are no columns at these corners to confine the brick, which may have allowed the brick to fall out.

The single story connector building was being renovated at the time of the earthquake with masonry infill construction and there was no noticeable damage.

Both towers sustained shear cracking in the brick walls in the 2007 earthquakes. The cracks appear to have been filled with plaster or mortar. Some of these cracks reopened during this earthquake.