Earthquakes and other seismic activity caused by construction, human-made, or natural causes, can undoubtedly cause often-catastrophic damage to our built environment. With the goal of taking all precautions necessary to protect people, buildings, and infrastructure, seismic monitoring is taking a front seat for particular structures, especially in certain parts of the world.
California, Washington, and Oregon, as well as the Philippines, Japan, New Zealand and other parts of the world, are known to be prone to earthquakes. In fact, more than 50 percent of the world is earthquake prone. Are our countries, states, and regions prepared for post-quake building assessments to ensure safety?
Building codes for seismic monitoring
Looking to California as the example, seismic monitoring in building codes were recommended for many years, but not compulsory until 2007. The codes apply to structures built after July 1965 that are more than six stories tall and have an aggregate square footage of 60,000 square feet or more, or exceed 10 stories in height regardless of floor area. These structures, in California, are required to be equipped with no less than three approved recording accelerographs. The code also outlines the minimum instrumentation required, which includes accelerometers placed in the basement, midpoint, and top of a building, either on the top floor or the roof.
Any vendor that meets the instrumentation specifications is eligible for approval by California authorities. With this approval, a vendor can provide seismic monitoring equipment to meet code. REF TEK®, a Trimble brand, is one such approved vendor in California, and is one of only two approved companies to provide seismic monitoring instrumentation to the California Strong Motion Instrumentation Program (CSMIP), which oversees seismic monitoring for state and some other structures, such as hospitals and other buildings critical to the well-being of the state.
High-rise buildings, more than 10 stories, have additional recommendations specific to the number of stories in a building. The primary objective of high-rise building monitoring is to improve the safety and reliability of building systems by providing data to improve computer modeling and enable damage detection for post‐event condition assessment.
The minimum number of channels recommended for floors above ground is proportional to building height as per the following table from An Alternative Procedure for Seismic Analysis and Design of Tall Buildings Located in The Los Angeles Region, Los Angeles Tall Buildings Structural Design Council, 2008.
REF TEK is also qualified to meet these high-rise seismic monitoring building codes, which demand a more complex system beyond the three points of measurement required in most structures. Architects and structural engineers should follow the guidance of the Los Angeles Tall Buildings Structural Council and other authorities in California, which put forth the number of channels that need to be installed. A channel represents a set of data that reports whether a structure is sound after a shake event. For example, for a building with six to 10 stories, 12 channels are recommended. Or, a building of more than 50 stories needs more than 30 channels.
Monitoring the safety of buildings
Once a building is completed and meets the seismic monitoring building code requirements, the owner must prove the equipment is functioning properly. This reporting is conducted every 12 months and may be requested by state building authorities following a shake event. Following a strong shake event, a structural engineer can immediately use the recorded parameters for a complete building damage assessment.
It can be extraordinarily time-intensive and costly to conduct this reporting, as well as to replace any damaged or outdated equipment. Typically, the equipment is installed near completion of construction when an electrical engineer can set up the necessary cables and conduits for the instrumentation, which is placed behind walls and above ceilings. While this equipment is critical, it is entirely unseen. Alternatively, replacing damaged equipment or updating equipment for which replacement parts are no longer available comes at a great expense.
For many years, and still today in much of the world, seismic monitoring building codes are published as recommendations. Where the codes are mandatory, officials do not always check to see if they are being enforced.
Approximately seven years ago, the Los Angeles Department of Building Safety and the San Francisco Department of Building Inspections implemented a more rigorous process for verifying code compliance. If a building is non-compliant, the building owner will be fined. This fee goes up every six months until the building owner or management contacts an approved instrumentation provider, like REF TEK, to request the instrumentation needed to meet code.
A commitment to safety
When architects draw up plans for any building, in any country – whether seismic monitoring building codes are in place or not – they may choose to include seismic monitoring instrumentation within their plans. If designs do include instrumentation, a building cannot receive its certificate of occupancy if it is constructed without the specified instrumentation.
Another measure of safety for buildings in seismically-active areas is within the building materials themselves. In locations with little seismic activity, it can be expected that structures are designed and constructed with materials that can withstand a small amount of shaking.
However, for buildings in highly-seismic areas, like California and the Philippines, it is not only the building codes expected to help monitor the health of a structure after a shake event, but the building’s instrumentation as well.
The cloud and compliance
As an example, one of the REF TEK monitoring solution’s main features is the Shake Event Report that is immediately generated by the software after a shake event, containing all key building parameters related to the seismic activity such as peak acceleration, peak velocity, peak displacement, modified Mercalli intensity, spectral acceleration and mean period. The report also contains the ShakeMap generated by the United States Geological Survey (USGS). With notification automatically sent to the user, access to this data merely moments after a shake event allows the user to provide the information immediately to a structural engineer who can quickly verify whether or not the incident potentially damaged the integrity of the building.
Another critical report type that comes standard relays the functional condition of installed hardware. To generate this report, the software sends a calibration test pulse to the hardware and the response signal is then analyzed. This Hardware Compliance Report tells the user whether the equipment is in good working condition. The primary advantage of this report is that a user can prove the hardware is operational at any time to meet local building code reporting requirements. And, all of this is possible without the need to visit the site, saving both time and money.
Monitoring a structure's health
There are many systems used to monitor the health of any given structure, yet seismic monitoring is one of the most important for safe post-occupancy after a seismic event.
Whether it is checking a building as it is being constructed or after it is completed, this strategy should be required in more parts of the world. Looking at the potential damage to people, buildings, and infrastructure, a complete seismic monitoring system, including hardware and cloud-based software can help provide peace of mind and a greater sense of security both now and in the future.