Earthquakes Damage Mitigation Guidelines
ESD Target
Guideline Objectives
Main Issues Addressed
Issues Excluded
Background
Definitions
Underlying Assumptions
Aspect Identification
Assessment of Vulnerability
Mitigation Methodology
Mitigation Techniques
Environmental Targets
Compliance
Policy
References
ESD Target
Every building under State Government responsibility shall be designed
and managed with the expectation that, sometime during the life of the structure,
it will be the subject of an earthquake event.
Guideline Objectives
- identify design criteria and provide recommendations for earthquake resistance, for all specific building types and all building services
- identify the affects that soils and location have on earthquake design loads
- identify the consequences of design and detailing inadequacies in building vulnerability
- identify building structural and architectural details and requirements for earthquake resistance
- identify the potential failure mechanisms with regard to the various and alternative building services and framing systems available
- provide an awareness for planners, designers and managers of the potential hazards caused by earthquakes and the solutions available to reduce the vulnerability of buildings, structures or services should an earthquake occur.
Main Issues Addressed
— the nature of potential damage to buildings and services within the government's building porfolio
—the relationship between the Strategic Asset Management process and:
- Soil and Foundation Conditions
- Building Classification/Use
- Structural Systems
- Mechanical Services
- Electrical Services
- Hydraulic Services
- Architectural Features
- Access and Egress
Issues Excluded
— Compliance with the relevant codes and regulations
— Development of post-disaster strategies
— The methodology to overcome deficiencies in design for existing buildings
— Specific details to cater for earthquakes to avoid possible damage
— Buildings for which the Queensland State Government has no responsibility
— Infrastructure such as roads, dams, masts, aerials, bridges, etc.
— The methodology does not include provision for emergency services
Background - Earthquakes and how they arise
Earthquakes are caused by the differential movement of the tectonic plates which form the earth's crust. The differential movement of the plates, both at the plate's boundaries and within a plate, generates uneven stresses within the subsurface rock. When the stress becomes too great for the rock matrix to resist, rapid shearing and deformation takes place releasing the stored energy.
The energy released leads to a series of compression waves that pass through the crustal strata at varying speeds and magnitude depending on the properties of the strata encountered.
The waves are a complex mix of horizontal and vertical oscillations known as P, S and L waves. It is the S waves that generally cause damage to buildings, services and other infrastructure. The waves cause the ground to move in both horizontal and vertical directions (in extreme conditions by the order of many metres).
A stylized Seismograph Output
The soil type and profile on which any building sits influences the size of ground motion encountered. By example, the ground motion through a soft, silty sand is generally more damaging than the ground motion from the same earthquake intensity through a dense, gravelly soil.
Damage can also be associated with the presence of faults in rock formations, lineaments and at the interface of other geological features. Large lateral movements are often observed along pre-existing faults as the compression waves pass through the fault.
Australia is located within the central section of the Australian tectonic plate. Hence all of the seismic activity of any significance experienced within Australia has been derived from 'intraplate' earthquakes. These quakes are limited to the top 50 kilometres of the crust, are random in their location, and are generally smaller in magnitude than those associated with quakes arising at plate boundaries.
The hazard rating for an area is determined from past events, whether by electronic data monitoring or from peoples' recollections.
Queensland's hazard areas are generally confined to the land and continental shelf to the east of the Great Dividing Range.
The Maryborough - Gladstone region is considered an area of medium hazard rating, with the remainder of the coastal strip being medium to low. Western Queensland is generally considered to have a low hazard rating, although this is partly a result of the lack of data for the area.
Definitions
Relative Risk Factor
The "Relative Risk Factor" has been developed for this guideline to assist planners and designers in the selection of the most suitable site for a building. The factor is subjective and dependant on the type or component of the building or structure being assessed.
Damage
Four levels of damage to buildings were defined after the Newcastle earthquake. Damage notices using the different levels were placed on buildings and colour coded accordingly.
Damage can be defined as either minor or major, with sub-definitions of each.
Minor
TYPE A
Little or no damage, building is satisfactory for continued habitation (hairline cracks may be visible).
TYPE B
Some damage. Building is satisfactory for continued habitation but repairs are required
Major
TYPE C
Sufficient damage to building to be hazardous to occupants although building is repairable.
TYPE D
Building is hazardous to public and cannot be repair to original condition. Building is to be demolished.
Gravitational Acceleration (g)
Acceleration due to gravity; taken as 9.81 m/s2.
Irregular Structure/Building
A building that in plan or elevation varies in width from one section of the building to another by more than 15%. Typically this would be an "L" or "U" shaped building or large area podium floor plan with a slender tower over.
Soft Storeys
A section of a building that varies in stiffness by more than 30% to the floor above or below. These are typically open areas, under-cover carparks, or with a large open foyer or vestibule, with a rigid framed building above.
Soil types
The following soil profiles are defined in AS1170 Part 4 - 1993 and are used to determine forces on the foundations of structures. Each of the soil types has been given a type letter to enable easier use within these guidelines.
General structures:
Type A - Low strength rock or better
Type B1 - Extremely low strength rock or better
Type B2 - Not more than 30m of medium dense coarse sand and gravel, firm or stiff clays or controlled fill
Type C - More than 30m of medium dense coarse sand and gravel, firm or stiff clays or controlled fill
Type D - A soil profile of 20m or more with 6m to 12m of very soft to soft clays, very loose to loose sands, silt and/or uncontrolled fill
Type E - More than 12m of very soft to soft clay, very loose to loose sands, silt and/or uncontrolled fill
Domestic Structures:
Normal - Other than Soft
Soft - Any soil profile with more than 5m of soft clay, loose sand, silt and/or uncontrolled fill.
Underlying Assumptions
The ground motions specified in AS1170 Part 4 - 1993 are for the 'design earthquake' based on an estimated 90% probability of these ground motions not being exceeded in a 50-year period.
Aspect Identification
Typical building elements that are damaged during earthquakes:
- internal fittings and furniture movement;
- tall cupboards falling over;
- light fittings, air conditioning and ceiling units dislodging and coming loose;
- objects in high cupboards falling out causing damage and potential injury;
- wall linings which do not have capacity for horizontal or vertical movements;
- water damage due to broken pipes;
- loss of power due to broken power cables;
- brick walls with insufficient strength cracking and collapsing;
- unsupported masonry parapets falling over due to insufficient anchorage or bracing;
- windows cracking due to building movement;
- loss of communications network;
- precast panels and other architectural features falling from the building facades having insufficient or ineffective fixings;
- tiltup wall panels losing support due to insufficient or ineffective fixings;
- water pipes breaking at expansion joints and equipment connection points;
- water storage tanks (especially those on roofs) rupturing and or moving and breaking pipework;
- mechanical equipment moving off bases and causing disconnection;
- electrical equipment moving off bases and causing disconnection;
- power backup battery facilities falling off shelves causing loss of backup power;
- loss of support to suspended slabs from masonry walls where reinforcement has not continued through to the slab, particularly vulnerable in unreinforced masonry buildings;
- rotation of retaining walls due to increased vertical and horizontal earth pressures;
- differential movement between foundations and floor slabs due to ground movements;
- insufficient support to air conditioning equipment;
- differential movement between various soil types supporting foundations;
- irregular shaped buildings have different modes of vibration for the different sections of the building causing concentration of stresses and excessive loads at discontinuities;
- "Soft storeys" failure due to lack of support to withstand horizontal loading;
- load bearing walls with no continuity to upper or lower floor framing systems;
- failure of vibration isolation support;
- inadequate foundation system for earthquake loads;
- suspended slabs on unreinforced masonry walls losing support due to the lateral displacement of the wall under;
- columns cracking;
- punching of columns through suspended slabs;
- broken pipework;
- loss of service functions.
Assessment of Vulnerability
One method for rapidly assessing the potential vulnerability of buildings is through the use of relative risk factors. By assigning a numeric value to key, influential criteria governing the magnitude of any quake disaster, it is possible to target finite resources in a systematic and logical fashion.
Three elements are critical to any calculation of relative risk:
- the increased design load requirement (by the earthquake);
- the level of functionality for post-disaster performance;
- the number of occupants generally using the building.
Relative risk factors can be assigned using the following matrix:
| Relative Risk |
Soil Profile |
Ground |
Post-disaster |
No. of |
|---|---|---|---|---|
| 1 |
Type A |
0.3 - 0.4 |
Residential (singles) |
< 5 |
| 2 |
Type B |
0.4 - 0.6 |
Residential (family) |
5 to 10 |
| 3 |
Type C |
0.6 - 0.8 |
Non Essential eg. Commercial |
11 to 20 |
| 4 |
Type D |
0.8 - 1.0 |
Desirable eg. |
21 to 50 |
| 5 |
Type E |
> 1.0 |
Essential eg. Hospital |
> 50 |
By assigning the relative risk values and summing the totals for each building it becomes clear where available resources can be assigned.
| Building |
X |
Y |
Z |
|---|---|---|---|
| Locality |
4 |
2 |
1 |
| Soil Profile |
1 |
5 |
4 |
| Post-disaster Function |
3 |
5 |
1 |
| No. of occupants |
2 |
3 |
1 |
| Total |
10 |
15 |
7 |
Vulnerability could also include the ability of services to function following a quake. Accordingly an additional classification could be added which reflects the number of essential services located within a building, eg. backup power, emergency water storage, fire systems, sewerage control, communications equipment and computer systems. For example. Relative risk factors for the number of essential services (or any other factor pertinent to the time) could be assigned as follows:
| No. of Services |
Relative Risk Factor |
|---|---|
| 1 |
1 |
| 3 |
2 |
| 6 |
3 |
| 9 |
4 |
Mitigation Methodology
Assessment of Existing Buildings
A determination of which elements of an existing building will be susceptible to earthquake damage must be made. Where necessary a management plan can be developed for the building such that its use and/or its structural components can be modified so as to minimise potential injury or loss of life.
A management plan would include the recording of the framing system, facade system and also whether the building contains any vulnerable elements, such as unreinforced masonry, soft storeys, irregular structure shapes and any mechanical and electrical systems that may be required for post-disaster functionality of the building.
Flow chart to aid assessment of an existing building.
Planning and Design of New Buildings
Numerous elements have to be considered during both the planning and design of a new building. Those involved in the planning phase must take a broad perspective, taking note of how the building will relate in form and function to the wider socio-administrative environment. By example, one element to consider would be how the build would be used post-disaster.
Flow chart to aid in planning for a new building.
Design involves the selection of the appropriate facade systems, structural framing and foundation system, anchorage of mechanical and electrical components, provision for sufficient flexure in service pipes and ducts, and restraint of large moveable items.
Also, design should provide both the occupants with the ability to exit the building quickly in an emergency, as well as the opportunity for emergency service personnel to enter the building post-disaster.
All buildings will "move" to some extent during an earthquake. Some structures may suffer a permanent "set," leading to problems such as jammed doors and windows, cracked walls or differential settlement of foundations.
Buildings designed to AS1170 Part 4 - 1993 should provide good to adequate performance during and after an earthquake.
Flow chart to aid in the design of a new building.
Management of Existing Buildings
Building Management, Operational and Emergency Plans should be regularly reviewed and updated to anticipate issues arising from an earthquake event.
Priority should be given to strategies for minimising loss of life and injury. Clear and concise evacuation plans and strategies will assist in bringing order to what will be a chaotic environment.
An inventory of equipment useful in the post-disaster phase should be included in the building's management plan. The roll-out of Emergency Schedules and Procedures for checking the structure for weakened or damaged components will also be a post-disaster priority.
The management plan would include at least the following:
- Building Description
- Use of Building
- Building Elements
- Service Equipment
- Occupant Register.
Flow chart to aid creation of suitable management plans.
Maintenance of Existing Buildings
The building's existing maintenance plan should be reviewed so as to incorporate systematic checks on fabric integrity. Where possible these checks should include the inspection of elements like:
- brick ties to ensure they are not damaged or broken due to rust, etc;
- anchor bolts to service equipment have not corroded, loosened or missing;
- watering systems or landscaping have not caused a change in the water table or moisture content of the soil, etc.
These checks, tailored to the individual building, should ensure that the structure continues to function in accordance with its original design specification. The maintenance regime must remain a logical supplement to the building's overall management strategy.
The development of these procedures must be flexible and fluid. The maintenance process should include the continual upgrade of the following procedures:
- Building Description
- Occupancy Register
- Equipment Register
Flow chart for the maintenance of existing buildings.
Post Disaster and Disposal
After an earthquake, a rapid inspection of all buildings must be carried out. The inspection should classify each structure as being either "safe" "for occupancy" or "for operation", "is unsafe and requires repair " or is "unsafe and building requires demolition". Such assessment must be carried out by experienced building inspectors or structural engineers.
Contingency plans must ensure that all persons who occupied the building during the event have been accounted for. Emergency service personnel may require immediate access to retrieve injured persons; the need to co-ordinate such search exercises must be included in the plan. If the building has not been provided with post-earthquake safe operation, emergency service personnel may also be at risk while retrieving those injured.
As a consequence of an earthquake, the assessment of the building will include the requirements of emergency services for the:
- safe passage of rescuers;
- stability of the structure;
- rescue of trapped persons;
- access for emergency services (both personnel and vehicles);
- egress for occupants.
Emergency Services organisations should be contacted to assist in the development of disaster strategies and plans for individual buildings.
Flow diagram for post earthquake procedures.
Mitigation Techniques
Damage mitigation techniques must be deployed throughout the lifetime of a building. Within the Strategic Asset Management cycle this means consider damage mitigation practices at each stage of the cycle. Responsibility for ensuring the necessary consideration is given to damage mitigation lies predominantly with planners, designers and asset managers.
The following matrix provides a brief outline of the kinds of damage mitigation issues that may arise during the Strategic Asset Management cycle.
By example, for those at the 'design' stage who are considering 'electrical' aspects of a building - click the box containing "2.5"
| NA |
||||||
|---|---|---|---|---|---|---|
| NA |
||||||
| NA |
||||||
Environmental Targets
Australian earthquake loading standards for specific building types have been in force since 1993.
The Foreword to the Australian Standard AS1170 Part 4 - 1993, Earthquake Loads states:
"The purpose of designing structures for earthquake loads is to -
(a) minimize the risk of loss of life from structure collapse or damage in the event of an earthquake:
(b) improve the expected performance of structures; and
(c) improve the capability of structures that are essential to post-earthquake recovery to function during and after an earthquake, and to minimize the risk of damage to hazardous facilities."
The design of structures to this target will not necessarily prevent structural and non-structural damage in the event of an earthquake. The provisions provide the minimum criteria considered to be prudent for the protection of life by minimizing the likelihood of structural collapse.
Buildings constructed prior to the code should be reviewed and a risk assessment documented, particularly where buildings are designed for large occupancy, institutional or post-disaster uses. Retro-fitting usually has a high financial and resource cost; a cost benefit analysis to determine the level of retrofit must be documented.
Compliance
All buildings and structures are required to be designed in accordance with the following Australian Standards and the relevant standards pertinent to the building components being designed or constructed.
The following codes are both minimum and applicable to design for earthquakes in Australia to attain the potential for minimisation of failure due to earthquakes.
- AS 1170.1 Part 1 (1989) SAA Loading Code - Dead and live loads and load combinations
- AS 1170.4 Part 4 (1993) Earthquake Loads
- Building Code of Australia
Post quake, Standard AS 2601 (1991) The demolition of structures, is pertinent.
Policy
These Guidelines are to be used in the planning, design, management, operation and maintenance stages of a new building, and also in the management and maintenance of existing buildings.
This guideline provides only a background to the requirements necessary for the planning, design management, operation and maintenance of any building or structure. Before undertaking and specific structural or administrative change seek advice from relevant professionals with appropriate expertise and experience in earthquake engineering planning, design, emergency operation and management.
Applied Technology Council, 1989.
Procedures for the Post Earthquake Safety Evaluation of Buildings
Applied Technology Council ATC-20,California.
A variety of studies and photographs which indicate typical damage areas and
indicates where damage can occur and where to look for it in areas which failure
is not always visible from the outside
ESC, 1993.
The Practice of earthquake hazard assessment.
International Association of Seismology and Physics of the Earths Interior and European Seismological Commission.
An outline of the different methods used by the various countries in the earthquake hazard assessment for their areas
Federal Emergency Management Agency, 1996.
Guidelines for the Seismic Rehabilitation of Buildings.
Federal Emergency Management Agency (Report No. FEMA 273), Washington DC.
Guidelines outlining methods of repairing buildings after an event. Includes determination of loads, soil condition criteria, hazard levels, framing systems and models and analysis of various building systems
Federal Emergency Management Agency, 1988.
Rapid Visual Screening of Buildings for Potential Seismic Hazards: Supporting Documentation.
Federal Emergency Management Agency (Report No. FEMA 155), Washington DC.
Contains sketches and photographs which identify the various building types and framing systems as well as identifying potential hazard components of a building and the failure mechanisms
Federal Emergency Management Agency, 1989.
Seismic Evaluation of Existing Buildings: Supporting Documentation.
Federal Emergency Management Agency (Report No. FEMA 175), Washington DC
Contains typical forms used for evaluating seismic resistance of buildings including the responses
Federal Emergency Management Agency, 1988.
Rapid Visual Screening of Buildings for Potential Seismic Hazards: A Handbook.
Federal Emergency Management Agency , ATC-21, Washington DC.
Outlines a number of procedures for rapid visual screening of buildings for potential hazard and has developed a series of Q & A checklists to assist
Hughes P.R., Rynn J.M.W., 1993.
Limitations Of The Cornell-Mcguire Earthquake Risk Method: An Engineering Viewpoint For Australia.
National Earthquake Conference, Central United States Earthquake Consortium.
A discussion on the limitations of the typical method of determining earthquake risk as used by other countries for Australia
IEAust, 1990.
Newcastle Earthquake Study.
The Institution of Engineers Australia.
Document prepared by the Institution of Engineers discussing issues such as construction, design, insurance, previous seismicity, safety assessment, post disaster functions, risk management and heritage issues that were raised due to the Newcastle Earthquake
Newcastle City Council, 1989.
Newcastle Earthquake Response Record.
Newcastle City Council, Newcastle.
Reports by the various emergency departments into the procedures undertaken after the event and the problems that occurred
NCC and CERA, 1991.
Proceedings Papers "What We Have Learnt From the Newcastle Earthquake" Lessons in Building Design, Regulation Disaster Management, Earth Science and the Legal and Insurance Implications.
The University of Queensland, Australia.
A series of papers and notes on the Newcastle Earthquake ranging from design issues, emergency procedures, insurance aspects, construction issues, latent defects
Pedersen I.S., Hughes P.R., 1993
Engineering Implications for Continental Earthquakes: Inferences from the 1989 Newcastle Earthquake.
National Earthquake Conference, Central United States Earthquake Consortium
Paper discussion on the geology, history of the area, seismicity, extent of damage and design requirement in the Newcastle area after the Newcastle Earthquake
Rynn J.M.W., Hughes P.R., Brennan E., Pedersen I.S., Stuart H.J., 1993.
Final Report Of Urbanised Areas Of Australia Phase 2 1992-1993 Program "Earthquake Zonation For Southeast Queensland".
Centre for Earthquake Research in Australia.
Report which outlines the development of the earthquake zonation in Australia, in particular South East Queensland
Rynn J.M.W., 1993.
Methodology for Earthquake Zonation of Continental Regions-Example for the Sydney Region, Australia.
National Earthquake Conference, Central United States Earthquake Consortium.
Paper discussion on the method of determining the earthquake zones in Australia, in particular Sydney
Swiss Reinsurance, 1990.
Newcastle: The Writing on the Wall.
Swiss Reinsurance Company, Zurich Switzerland.
Reinsurance report on damage caused by the Newcastle earthquake.
The assistance of Hughes Consulting Services Pty Ltd, Indooroopilly, Brisbane is acknowledged
