What is the earthquake resistance of ceilings? Thorough explanation of the basics of specific ceilings

Do you know the definition of "specific ceiling?"

The Great East Japan Earthquake, which is still fresh in our minds, caused a series of major damages due to falling ceilings in buildings. In response, the Ministry of Land, Infrastructure, Transport and Tourism has established new safety standards for ceilings. Ceilings with a structure subject to this standard – that is, specified ceilings – are now subject to this standard. In this article, we will explain the details of the specified ceilings in an easy-to-understand manner and introduce how to deal with them and how to solve the problem.

What is a specific ceiling?

Ceilings defined below are referred to as specific ceilings.

Definition of specific ceiling

A ceiling is a “ceiling that could cause serious harm if it were to fall down” and a specified ceiling is one that meets all of the following criteria

• Suspended ceilings (straight ceilings do not qualify as specified ceilings)
• Ceiling height: over 6m
• Area: over 200 m2
• Mass: Over 2kg/m2
• Installed in places where people use on a daily basis

This ceiling is often applicable to large facilities such as gymnasiums and airports.

Background of the Specified Ceiling

In the wake of the Great East Japan Earthquake of 2011, which caused significant damage from falling suspended ceilings, the government confirmed the need to review the earthquake resistance of suspended ceilings. In 2013, the Ministry of Land, Infrastructure, Transport and Tourism (MLIT) issued the “MLIT Notification No. 771 of 2013” and other technical standard notifications related to measures against falling ceilings as a summary of this review, which came into effect in 2014. The content of Notification No. 771 of 2013 by the Ministry of Land, Infrastructure, Transport and Tourism and Article 39 of the Building Standard Law Enforcement Order partially revised by the Notification are as follows.

Ministry of Land, Infrastructure, Transport and Tourism Notification No. 771 of 2013

Paragraph 3 is added to the existing “Article 39 of the Building Standards Law Enforcement Order” and the following items are established and revised for “specified ceilings” designated by the Minister.

• Measures to prevent fallout should be taken in accordance with the technical standards established by the Minister based on the provisions of Article 39, Paragraph 3 of the Building Standard Law Enforcement Ordinance.
• Revision of standards for structural calculations such as time history response calculations, etc., including the addition of calculations for preventing ceilings from falling out, etc.

Order for Enforcement of the Building Standards Act Article 39

1. (2) Roofing materials, interior materials, exterior materials, wall cladding, and other similar building elements, as well as advertising towers, decorative towers, and other items attached to the exterior of buildings, shall be kept from falling off due to wind pressure, earthquakes, and other vibrations and impacts.
2. Roofing materials, exterior materials, and walls facing the outdoors shall be constructed using structural methods specified by the Minister of Land, Infrastructure, Transport and Tourism as structurally safe.
3. (2) Specified ceilings (ceilings specified by the Minister of Land, Infrastructure, Transport and Tourism as those that are likely to cause serious harm due to falling out. The same shall apply hereinafter) (2) The structure of a specified ceiling (meaning a ceiling specified by the Minister of Land, Infrastructure, Transport and Tourism as a ceiling that may cause serious danger due to falling out.
4. (2) Specified ceilings that are particularly susceptible to corrosion, decay, or other deterioration shall be made of materials that are resistant to corrosion, decay, or other deterioration, or materials that have been subjected to effective rust-proofing, preservation, or other measures to prevent deterioration.

For a more detailed look, please refer to the documents issued by the Ministry of Land, Infrastructure, Transport and Tourism. Ministry of Land, Infrastructure, Transport and Tourism Notification No. 771.

What must be done if it falls under the specified ceiling?

If the ceiling of an existing building falls under the specified ceiling category, or if the ceiling of a new building being planned falls under the specified ceiling category, the specified measures must be taken. The measures are to “verify that the newly established standards are met and to externally prove the safety of the ceiling. The measures differ for existing buildings and new buildings, and especially for new buildings, there are three verification methods.

*Reference: Ministry of Land, Infrastructure, Transport and Tourism data

For existing buildings

The following “measures to prevent falling even if the ceiling is damaged = fall prevention measures” must be taken.

• Installation of nets
• Suspend the ceiling with wire, etc.

For new buildings

It is necessary to demonstrate safety by verifying that the ceiling will not be damaged by a medium earthquake (seismic intensity of 5 or lower to 5 or higher). Specifically, one of three verification methods, known as “routes,” is applied. The three “routes” are described in detail below.

Verification method 1: Specification route

As the name suggests, this method reduces the risk of falling by meeting certain standards in structural specifications. The safety of the ceiling is verified by conforming to specifications that take into account earthquake resistance and other factors. For more details, please refer to the following diagram provided by the Ministry of Land, Infrastructure, Transport and Tourism.

Verification method 2: Calculation route

This method verifies the earthquake resistance, etc. of ceilings by means of calculations specified in the public notice, when it is structurally difficult to apply the specification route. For detailed calculation methods, please refer to the ” Ministry of Land, Infrastructure, Transport and Tourism Notification No. 771.

Verification method 3: Ministerial approval route

Ceilings with complex structures, for example, may not conform to the specification route or calculation route. In such cases, the “ministerial approval route” is a method of verifying the safety and earthquake resistance of the ceiling through individual experiments and numerical calculations. There have been few cases so far, and the first case of ministerial certification made the news. News of the first case: Nikkei Newspaper, ” Suntory Hall Obtains First Ministerial Certification for Specified Ceiling.

The "Membrane Ceiling" Solution

If the specified ceiling is left in place, the new standard will not only increase the cost of compliance, but also raise concerns about seismic resistance and safety. In Japan, which is known as an earthquake-prone country, there is no such thing as too many safety measures. Membrane ceilings are a highly safe ceiling structure that does not fall under the category of specified ceilings, even in large spaces. Membrane ceilings are light, soft, and strong, and do not require hanging materials.

Light: Little damage from falling

The mass of the membrane material is only about 600 g/m². Compared to conventional ceiling materials, it is lightweight, minimizing damage to people and objects in the room in the event of a fall.

Soft: Resistant to deformation and collision, hard to shake or fall off

The thin and soft membrane material makes the ceiling structure capable of following deformation even in the event of large shaking, thus reducing the risk of falling to the floor. In addition, the high flexibility of the material can greatly enhance the interior design.

Strong: Catching falling objects

Although an extremely thin material only 1 mm thick, it is strong enough to catch falling objects.
Membrane ceilings with high earthquake resistance and safety are attracting attention, especially for large buildings with large areas and high ceilings, such as gymnasiums.

For more information on membrane ceilings, see ” What is a Membrane Ceiling?