Minsheng Industrial Group
425 Hong Feng Road
Pudong New Area
Shanghai 201206
Tel: 86-21-5030-1126
Fax: 86-21-5030-2916
Beijing
Room 1507, Kuntai
International Mansion,
No.12 B Chaowai Street,
Beijing 100020
Tel: 86-10-59251256
Fax: 86-10-59251259
FII China Email: info@bcfii.cn
The evaluation of building performance has identified problems with some wood-frame buildings even though, overall, wood-frame buildings have been found to be safe in earthquakes. These deficiencies are described in brief to provide an understanding of failure modes and how they can be avoided.
Weak First Storey: Experience in past earthquakes has shown that weak and soft first storeys will make buildings susceptible to the effects of earthquakes. Providing adequately braced or sheathed walls is essential to ensure conventionally built wood-frame buildings can resist earthquakes. Large openings in the walls such as windows, doors and garage doors can leave too little wall area to provide adequate resistance to the lateral forces imposed by earthquakes. Unless these walls are adequately reinforced, lack of wall capacity leads to large distortions and eventual collapse. California experience has shown that apartments built with first storey garages are particularly vulnerable to earthquakes and building codes have recognized that buildings with soft storeys have to be carefully designed an detailed to resist earthquakes. Engineering solutions can be provided for new or existing structures that require additional wall reinforcement.
Connections to Foundations: Anchor bolts are used to prevent a structure from moving off its foundation. Some old houses were built without using anchor bolts to connect the wood structure to the foundation. Experience has shown that these structures can be retrofitted by adding connections between the wood framing and foundation.
Cripple Walls: Cripple walls, also known as keen walls or pony walls, are the short stud walls between the floors and foundations in some houses. Many older buildings that had unbraced cripple walls sustained structural damage during California earthquakes. Strengthening the walls using wood structural sheathing is an effective method of bracing cripple walls.
Chimneys: Unreinforced masonry chimneys are particularly susceptible to earthquake damage. Failure of the chimneys can cause damage to the roof and walls of the structure below. Also, damaged chimneys may be dangerous in aftershocks following the initial earthquake. Bracing chimneys or using chimneys from lighter materials can help prevent damage in future earthquakes.
Unrestrained Furnishings, Components and Appliances: Tall objects such as bookcases can topple, and sliding or rolling objects can become projectiles. Heavy, unbraced interior partition walls can fall over, and improperly attached canopies and curtain walls (for example, brick cladding) can fall on passers-by. Domestic gas water heaters, unless properly braced and secured, can easily tip over or displace, causing possible leakage of gas and the risk of explosion Bracing furnishings, components and appliances can be a cost effective way of reducing earthquake damage and costs.
Building codes are continuously evolving to address structural issues related to earthquake safety but they do not typically deal with furnishing and appliances nor do they address existing buildings. Increasingly homeowners in areas prone to earthquakes are assessing their houses or having their houses assessed by professionals. Homeowners can easily undertake many of the upgrades themselves. Government agencies provide upgrade information and much of it is available electronically. The Association of Bay Area Governments www.abag.ca.gov and the California Seismic Safety Commission at www.seismic.ca.gov both have useful information for homeowners and building professionals. In Canada, the Canada Mortgage and Housing Corporation has prepared a Residential Guide to Earthquake Resistance.