EMERGENCY GUIDELINE FOR CLASSIFICATION OF RISK LEVELS OF EARTHQUAKE DAMAGED REINFORCED CONCRETE BUILDINGS

As a part of Coordinated Technical Project on the Development of Repair and Strengthening Techniques for Buildings and Structures Damaged by Earthquakes, initiated in 1981 by Ministry of Constructiont Guidelines for Post-Earthquake Inspection and Evaluation of Earthquake Damage in Reinforced Concrete Buildings were developed. This paper describes the Guideline for Emergency Inspection and Evaluation for Hazard Risk of Damaged Buildings toward Aftershocks, which is intended for technical ~ffic7rs of a municipal government to evaluate a risk of damaged buildings immediately after earthquake hazards and to determine safe public buildings for use as places for evacuation and medical treatment. Damages of structural members, possible falling and overturning objects are to be investigated by external observation of a building. Editor's Note: This paper was presented at the Third Meeting on the Evaluatioh of Structures for Seismic Hazard, Tokyo, May 17, 1985.

Inspectiofi and Evaluation (drafted by K.
Takiguchi) is used to estimate the damage approximately a week after the earthquake.The Guideline for Second'""Levtn :i:fi §pectidh and :tvaluation (drafted l9Y 1'1.Okubo} examines ttte repairing al'Hi tettofitting needs of a severely damaged building and assists the planning of a repair job, This paper d@ §c:rilies the etiriergency guideline, ,in which damages of structu:tai members, possible falling of Objects, and possible overturning of objects are taken into account.

OBJECT AND SCOPE
A main earthquake is norffially followed by many after-shocks of coopa:table or smaller intensities, which might itt:tthe:t develop the damage of a bu:ilding.Therefore, immediately after a da.firag:iflg eartthgttake, n is urgent to determine the risk of severely damaged buildings.If a building is shown to be dangerous, the public S-bould be kept away from the building and the 'iise of such a building must be prohibited, If tnere exists any concern abo-ut the safety of a building, the public efhoold be warned against the use of the building, At the same time, it is important to identify safe buildings which can be used as a shelter for evacuation or a place for medical treatment.This decision must be made immediately by local governments of the affected area probably without the assistance of professional and knowlegeable structural engineers.This guideline is used for reinforced concrete frame-type and boxed-type structures in the area suffered from a strong earthquake to investigate possible hazards towards human lives inside as well as outside a damaged building, taking into account the risk of collapsing of the building by possible after-shocks and falling and overturning of interior and exterior finishings and mechanical equipments.Based on the results of investigation, the building may be prohibited from entering or warned against regular use.The guideline examines all public buildings in the affected area for possible usage as shelters for evacuation and places for medical treatment.

METHOD OF INVESTIGATION
The investigation should be carried out within one or two days after an earthquake.A person in charge of the investigation may not be a structural engineer, but an ordinary building or civil engineer of the local government.The investigation may be completed in half an hour for a building, following a manual.No instrument may be required during this investigation.
It is not possible, in a limited time, to investigate all buildings in an affected area and evaluate a risk against human hazards by possible after-shocks.Hence, a private building is investigated only when its occupant reports a severe damage.on the other hands, all public buildings, eligible for use as a shelter and a place for medical treatment, should be investigated.The practical wisdom should be exercised in determining the degree of risk.The risk may be reduced if a balcony exists under the falling object.

Heavy overturning objects can jeopardize passers-by.
Therefore, the emergency staircases, machine equipments, vending machines, fuel containers, masonry fences, book cases, lockers, tables, desks, display shelves, doors, and others should be examined for a possible overturning.Again, the criteria for possible overturning and accompanying risk may vary from an object to another depending on the geometry, weight, fixity, and damage of the object.The practical wisdom should be exercised in determining the risk.

Risk levels of a building and structural members may be classified from A to C, where risk level
A can be tolerable, whereas risk level c is dangerous.The risk levels are briefly described below; a) Risk Level C: 1) A corner of a building settles more than 1.0 m due to the failure of sub-structure, such as piles, foundation, or soil.
2) A building tilts more than 2 degrees due to the failure of the sub-structure.b) Risk Level B: 1) A corner of a building settles more than 0.2 m due to the failure of sub-structure.
2) A building tilts more than 1 degrees due to the failure of sub-structure.
3) More than 10 per cent of external columns of a frame construction (or external walls of box-type construction) suffer damage greater than or equal to Damage Level 4. 4) More than 1 percent of external columns of a frame construction (or external walls of a box-type construction) suffer damage greater than or equal to Damage Level 5.

c) Risk Level A:
A damage state not included in either damage states C or B.
The failure of sub-structure such as foundation, piles, and soil may cause the settlement and tilting of an entire structure, sometimes without accompanying structural damage, as shown in Fig. 1.Such tilting or settlement of an entire building caused by failure of the sub-structure is called "overall tilting" or "overall settlement".The structure may also be tilted by the failure of structural members such as columns, walls, and beams, as shown in Fig. 2. The latter is called "partial inclination" and may be classified into two cases; i.e., the sloping of slabs due to the collapse of columns, and inclination of columns due to a large lateral deflection.In these cases, severe damage can be observed in either columns or walls.Therefore, the damage in the vertical structural members may be examined to define the damage rate instead of measuring an inclination angle of columns, walls, or slabs.
Sometimes, a large lateral deflection may accompany severe damage in girders, but the.damage in girders is normally difficult to observe hidden by ceilings.At the same time, the angle of inclination is difficult to measure with the eye.Therefore, the damage in girders is not included herein.If a large sidesway deflection is observed clearly attributable to the damage in girders, the damage may be estimated as "overall tilting" of the building.
The measurement of inclination and settlement is made with the eye.When the angle of inclination becomes approximately 1 to 2 degrees, the lateral deflection becomes 1/60 to 1/30 of the story height.In other words, the lateral deflection becomes 6 to 12 cm for a normal story height of approximately 3.5m.When the overall angle of inclination exceeds 2 degrees (Fig. 3), or the settlement at a corner exceeds 1.0 m (Fig. 4), anyone can judge the building to be dangerous from external appearances.
The decision of risk should be based on the remaining resistance of a building.However, instead of structural analysis, a simple method is used; i.e., if structural members suffer damage less than damage level 3, then the structure is assumed to maintain the original resistance.It is beneficial for the public safety to overestimate the risk and keep the public away from a damaged building because the investigation has to be completed in a limited time and by an inexperienced officer.In case of a large earthquake, the criteria for a safe building may be loosened to increase the usable number of shelters for evacuation and places for medical treatment.If more than 10 percent of columns in a frame building or walls in a box-type building suffer damages hard to imagine the original shape (damage level 5), and the floors above and the roof are observed to sink, the lateral resistance against aftershocks may be judged insufficient.Such columns and walls are doubtful to expect a resistance even against gravitational loads.In this case, the structure can be determined to be dangerous (Fig. 5).The occupant can normally judge the building to be dangerous using their own practical wisdom.
In order to examine the safety of a building, the survey of structural damage is not sufficient.Exterior and interior finishings, curtain walls and wthdow glasses may be broken and fall to the ground.Therefore, the area of possible falling objects is dangerous.The overturning objects should also be examined.The risk levels of possible falling and overturning objects are not defined herein, but rather the evaluation is relied on the practical wisdom of investigators because the criteria for possible overturning and accompanying risk may vary from an object to another depending on the geometry, weight, fixity, and damage of the object.Further study is necessary to establish the criteria.

DETERMINATION OF RISK
On the basis of observation about damages of structural members, possible falling objects, and possible overturning objects, the risk of a building is determined as (1) danger, (2) caution, and (3) safe.The classification of safe is applied only to public buildings because the public buildings need be assured for safety when they are used for evacuation and medical treatment.
Those buildings classified neither as danger nor as caution are not necessarily safe, but non-public buildings are to be investigated only when they are heavily damaged and when some assistance is requested for the risk evaluation.A building should be identified as "completed" after investigation.
A building or a part of a building is classified to (a) danger, (b) caution, or (c) safe by the following criteria: a) Danger: (1) the entire structure if more than one C-rank or two Brank risk level items exist in structural damages, (2) the area of heavily damaged columns (or walls) of damage level 4 or 5 to the nearest healthy (damage level 3 or less) columns (or walls) and that above the designated area if columns (or walls) suffer damage of level 5, A building where risk level B items exist in the survey of structural damages, possible falling and overturning objects.A public building with no structural damage greater than damage level 3 and free from any risk level B nor C items in possible falling and overturning objects.The damage to interior columns in a frame type construction (or interior walls in a boxtype construction) should be evaluated in a manner identical to those of exterior structural members.The availability of city water, city gas, electricity, and sanitary facilities, usability of staircases, the safety of entrances, the storage of dangerous materials should be examined before the final decision is made.

ACTIONS
The purpose of the emergency guideline is to determine whether an area is safe or dangerous, and not to recommend to remove dangerous falling objects nor to suggest any reinforcement to the damage.Such actions should be taken after the emergency decisions have been made for entire buildings of the affected area.The following actions should be taken; a) Danger: _ (1) When an entire building has been ~ classified to "danger", the building and area one-half of the height away from the building shall be posted "No entrance".However, a reinforced concrete building within the designated area may be exempted as long as its entrance does not fall into the prohibited area.

EXAMPLE OF MORE THAN 10% OF FIRST STORY COLUMNS DAMAGED BEYOND
A RECOGNISABLE STATE (1978 Miyagiken-Oki Earthquake) (2) The area of a part of a building classified to danger shall be posted "No " entrance" only in that area.
(3) When falling objects are classified to "danger", the area within the radius equal to the height of the falling objects shall be posted "No entrance".
(4) When overturning objects are classified to "danger", the area within the radius equal to the height of the overturning objects shall be posted "No entrance".
The area posted "No entrance" should be prohibited to enter except for those who investigate damages and those specially permitted by the local government.

b) caution:
Those buildings classified to "caution" shall be posted "Warning against entrance".
The area posted "Warning against entrance" is not recommended to enter.In other words, those associated with the building may go into the building with caution only when it is necessary.The public is not allowed to go into the building.For example, in a commercial building, the employees may go into the building, but the facilities should not be used for business.

c) Safe:
Those public building classified to "safe" shall be posted "safe".Public buildings shall not be evacuation nor treatment.

REMOVAL OF BAN
not classified to "safe" used as a shelter for as a place for medical If a structural engineer of the local government or that approved by the local government investigates the damage of a building in details, and judges the building to be safe, the decision of risk about the structure, possible falling or overturning objects may be removed.The emergency guideline is not perfect, but rather a guiding rule.Therefore, if a person with sufficient knowledge about the performance of the reinforced concrete gives a decision different from the guideline after a detailed investigation, the revised decision should be respected with the approval of the local government.If a dangerous item is removed or strengthened, the ban to enter the area may be removed with the approval of the local government.

APPENDIX: CLASSIFICATION OF DAMAGE LEVELS OF STRUCTURAL MEMBERS
In estimating the damage rate, the columns and walls in the most severely damaged storey should be investigated for the existance and extent of (1) cracking of concrete, (2)   crushing of concrete can be found at the top and bottom of a column, and reinforcing bars may be partially exposed.In the middle part of a column, inclined cracks open approximately 1 to 5mm.Normally these cracks can be easily recognised.Spalling of concrete at the top and bottom of a column occurs only outside of the reinforcing cage.The bending of vertical reinforcing bars is not found.The resistance of a column will not be reduced at this stage of damage.
(2) Damage Level 4 (Fig. A4): crushing of concrete exists, and the reinforcing bars may be seen partially or wholly.The width of cracks may exceed 5mm.Vertical reinforcing bars may be bent, concrete over more than one half column width may spall out along inclined cracks in the middle of a column exposing vertical reinforcing bars.Exposed horizontal reinforcing bars may be pulled outward or fractured.A column or wall at this stage of damage has reached the maximum resistance and degradtion of resistance has started.In case of an additional deflection incurred by a large after-shock, the member may not be able to support the floors above.
(3) Damage Level 5 (Fig. A5): The reinforcing bars are bent and the concrete inside the reinforcing cage is crushed.The height of a member can be seen to be clearly shortened.Floor slab and roof supported by such a member can sink and slope.Vertical reinforcing bars are bent along the inclined cracks in the middle part of a column or wall.The column or wall cannot support the floors above and lateral resistance is significantly reduced.
More than 10 percent of external columns of a frame construction (or external walls of a box-type construction) suffer damage greater than or equal to Damage Level 5.

FIGURE 2 -
FIGURE 2 -EXAMPLES OF PARTIAL INCLINATION

FIGURE 3 -
FIGURE 3 -EXAMPLE OF OVERALL INCLINATION OF MORE THAN TWO DEGREES (Ref. 1, 1964 Niigata Earthquake)

Fig( 1 )
Damage Level 3 (Fig.A3): FIGURE Al -TYPICAL CRACK PATTERNS (Ref, Al) crishing and spalling of concrete, and (3) bending and fracture of reinforcing bars.The wall in a box-type structure is a wall of more than 45cm width.The width of the walls is measured with the eye.The