11.2 Investigation and Rehabilitation of Local Hospital

Transcription

1 11.2 Investigation and Rehabilitation of Local Hospital The hospital owned by Dr. Patel was investigated on the request of the owner of the hospital if there was any possibility of repairing the buildings of the hospital. Therefore, the team decided to measure natural period of the buildings and if there was any acoustic emission indicating the crack propagation in addition to the visual inspections and checking the technical drawings before drawing conclusions. Micro-tremor measurement systems for the earthquake investigation to India consist of basically two components: 1) Three Micro-tremor sensors (Tokyo Sokki - Figure 11.22(a)) 2) Monitoring, Logging and Processing Device (NEC Laptop Computer - Figure 11.22(b)) There are three mutually perpendicular micro-tremor sensors, which generate waves with a given frequency and records the reflected waves. The reflected waves are simultaneously monitored and logged by a lap-top computer and the measured data are processed using a soft-wear to obtain the natural frequency or periods of the structure or ground. The devices are operated through the electric power with 110V AC or 12V DC Battery. (a) Micro-tremor sensors (b) Monitoring, logging and processing device Figure Set-up for micro-tremor measurements Micro-tremor measurements were carried out on the ground, first floor and second floor of the hospital buildings. The measurements indicated that the natural period of the 88

2 buildings was 3-5 times that of non-damaged buildings of similar kind (Figure 11.20). This measurement result clearly implied that the buildings were severely damaged by the earthquake of January 26, Acoustic emission measuring system consists of three components: 1) Acoustic Emission Sensors and (NF Electronic Instruments with a frequency range of 100kHz-2Mhz) and Acoustic Emission Tester (NF Electronic Instruments 9501 AE Tester with a AE counting rate range of count/sec) 2) Data Logging and Monitoring Soft-wear: AEW2 (No:601021) developed by Human-data Company (Tokyo, Japan) 3) Data Recording Device: Dell Laptop computer (Latitude) The acoustic emission measurements were carried out at one of the buildings on the ground floor as shown in Figure The location was close to horizontally running crack in one of the bearing walls. The aim was to investigate whether further crack propagation occurring under static conditions. The frequency range of the sensors was designed such that they do not pick up the acoustic waves caused by the vehicle traffic or other human sources. The acoustic emission device can pick up the acoustic emissions caused by crack propagation. Under normal conditions, if the buildings are structurally safe, there should be no further crack propagation due to external loading such as the weight of the building or the load due to vehicles passing nearby the buildings. Figure shows a record of acoustic emission for a period of 500 seconds. During this period, 12 acoustic emissions occurred. This clearly demonstrated that the crack propagation had been still taking place under very small external loading due to the passage of the vehicles. This measurement result strongly implied that the building was structurally unsafe. Figure The acoustic emission measurement set-up at Dr. Patel s hospital 89

3 Figure The record of acoustic emissions measured at the location shown in Figure Two buildings of the hospital are of masonry type. Almost the all walls of buildings were fractured and the fracturing of the walls at the ground floor, which support the top floors, was quite severe. Both X-type fractures due to shearing and horizontal separation type fractures due to out-of plane loading in the walls were observed. The damaged state of buildings from the visual inspection according to damage charts prepared by the Japan Architectural Engineering Society and the Earthquake Research Department of Turkey can be assigned as severely damaged. The structural design drawings of the buildings shown by Dr. Patel were checked by the team. Since the buildings are of masonary type, the walls are the principal load bearing elements. Since the load bearing walls were severely fractured, it was concluded that the buildings are structurally unsafe. On the basis of micro-tremor and acoustic emission measurements, visual inspection and checking the design drawings of the buildings, it can be firmly stated that the buildings are severely damaged by the earthquake and they are structurally unsafe due to heavy fracturing in the load-bearing walls. To repair these buildings, all fractures must be filled by cement or resin injection to increase the shearing and bonding resistance of the walls. Furthermore, the walls must be jacketed using steel reinforcement and concrete. Peeling the fractures and applying cement paste on those 90

4 fractures will not be sufficient to make the buildings structurally safe, which seem to be the common practice of repairing the damaged buildings in the earthquake area right now. Such an example was seen in Sharma Resort Hotel as shown in Figure There are numerous examples in earthquake engineering, which demonstrated that how such repairs could be causing huge casualties, for example, as observed in the November 12, 1999 Duzce-Bolu earthquake in Turkey. The buildings damaged in Duzce during the August 17, 1999 Kocaeli earthquake and repaired with only pasting cement on the fractures were totally collapsed during the November 12, 1999 earthquake. Therefore, it is the opinions of the investigation committee that it would be wise to completely demolish the present damaged buildings and to built new ones according to the seismic design codes for the seismic zone V since the hospital buildings will house many small children. It should not be forgotten that the hospitals can not be allowed to collapse during earthquakes. Figure Wrongly repaired wall at Sharma Resort Hotel at Gandhidham It was reported later that this hospital building was demolished and new buildings would be built in near future on the following principles; A) Light weight construction, B) Membrane envelope and C) Floating foundation. In these principles, the floating foundation shown in Figure 22.26, is very effective to cut the transfer of ground motion to the superstructure and to enhance the earthquake resistance of the new buildings. 91

5 Figure The floating foundation for the newly planned hospital building 92