16) Hospital, Muzaffarabad Collapsed 20*
* Test results taken from survived buildings
Comparison of damage level and Schmidt hammer test results
As can be found above, buildings with lower concrete strength generally have more serious damage. The good quality of concrete should be therefore achieved for a better seismic performance.
(2) Reinforcement detail and its quality
In some buildings in Islamabad and most buildings in Abottabad, Balakot, and Muzaffarabad, reinforcing bars in beams are not properly anchored within the beam-column joint core concrete. They are straightly developed and terminated at the surface of exterior columns. Lap splices of beam rebars provided in the interior beam-column joints are often too short to properly transfer forces acting on joints. Poorly detailed reinforcement may be easily pulled out of the core and/or may cause separation of shell concrete from the core, and the beams and columns do not form rigid connections. This would therefore lead to a premature failure like pin-connected frames rather than moment resisting frames, as is often found during field surveys, before the members attain their strength and ductility during shaking. This can be avoided through placing the beam reinforcement into the column reinforcement cage, and providing enough development length bent into joint core concrete to form plastic hinges at member ends.
Rebars are often found failed in a brittle manner, showing no necking at the fractured section. Ductile reinforcement is significantly essential for ductile behavior of structures.
(3) Shear Reinforcement and Concrete Confinement
The sizes of shear reinforcing bars are often too small (6mm to 8mm) and they are provided with a space generally wider than 25cm at mid-span of columns. Hooks are generally 90-degree even when the structural drawing specifies 135-degree. The shear reinforcement would easily open following the spalling of concrete cover. A well confined concrete core with closely spaced lateral reinforcement having 135-degree hooks is essential for higher ductility (lateral deformation capacity under shaking) and axial load carrying capacity.
(4) Nonstructural Damage to URM walls
Damaged block/brick infilled walls are observed in many buildings. Falling debris from failed wall are significantly hazardous and even life threatening to occupants. Such damage to nonstructural walls should be avoided through proper detailing.
The lack of lateral stiffness and deformability of the structural members appears to be the cause of collapse in many buildings. As is found in previous damaging earthquakes in the world, the better performance can be achieved through providing RC shear walls and/or RM (reinforced masonry) walls in both principal axes of a building. RC shear walls and RM walls would be good candidates to reduce nonstructural damage and to improve seismic performance of buildings.
(5) Beam-column Joints
No lateral reinforcement is generally placed within the beam-column joints in practice.
Concrete spilling at the joints is observed in some buildings, exposing the buckled longitudinal reinforcement. Properly confined beam-column joints are most essential for RC structures to perform successfully during earthquakes.
(6) Pounding
Closely neighboring buildings with narrow gaps at expansion joints sustain pounding damage. Expansion joints should be therefore designed and constructed properly considering deformations expected during shaking.
(7) Site Effects
In general, site effects and resulting amplified ground motions significantly affect structural responses. It should be noted that microtremor measurements at the building site and its vicinity would help us understand the relationship between site effects and observed damage.
(8) Strong Ground Motion Observations
Strong motion records are significantly valuable information to understand the relationship between observed damage and input ground motions during earthquakes. They are also informative to identify design seismic loads. Although some records are reportedly obtained during the event, a more densely installed strong motion network is recommended.
(9) Quantitative Post-earthquake Damage Inspection
Some seriously damaged buildings are still in continuous use before properly rehabilitated. One may find such examples in commercial buildings and shops in Muzaffarabad. To mitigate life-threatening hazard of damaged buildings due to aftershocks, quick inspection system and inspection engineers are most needed.
(10) Rehabilitation Strategies and Techniques
In some areas, damaged buildings are not properly repaired or strengthened. Problems found during the survey can be listed below:
* Damaged sections are not fully recovered to the original.
* Buckled rebars are not replaced nor additionally confined.
* Tilted buildings are not re-centered nor are no additional members provided to avoid further inclination. If the damaged buildings are not repaired properly, the seismic performance to be achieved by the rehabilitated structure is quite questionable. The development of a technical manual is most essential to provide good information to guide engineers and practitioners for appropriate rehabilitations.
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