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The damaging impact of earthquakes to life and property prompts for new technologies to be incorporated into design and construction of buildings. These include using rubber polymers for structural reinforcement, says Angelica Buan in this article.
The major quakes that jolted Japan in 2011, and this year in Nepal as well as the Malaysian state of Sabah, tested the integrity of structures against seismic forces and sparked a lesson or two on preparedness and thoughtful structural planning.
With the tremblors, the extent of damage in the aftermath would leave anyone wondering if there was anything that could have been done to, at the very least, mitigate the impact.
In the case of Nepal, experts said that while the timing of the earthquake, which is endemic to the country owing to its geology, was predictable, yet most, if not all, of the residential, commercial and corporate structures were not quake-proof.
According to Professor GR Reddy, Head of the Structural and Seismic Engineering section, Reactor Safety Division, Bhabha Atomic Research Centre (BARC) in Mumbai, India, factors resulting in failure of structures could be due to increase in seismic demand; gaps in structure design; and reduced structural capacity with time. He also said that design concepts (in villages and towns), have been “based on thumb rules and not technical basis”.
In Malaysia, after the tremblor in seismic-active Sabah, designs of buildings and other structures have been revisited to check how they could withstand seismic impacts. Reports quoting Universiti Teknologi Malaysia’s Prof Dr Azlan Adnan, said that the country, for the time being, has no quake-proof design provision for buildings, adding that although seismic technology, such as base isolators and dampers, is also available in the country, the issue of cost is a hurdle to implementation.
Malaysia’s rubber seismic technology
The country, one of the world’s largest natural rubber (NR) producer, has been developing rubber seismic technology through the Malaysian Rubber Board (MRB). The agency has a facility capable for testing rubber bearings on compressive strength, shear stiffness, and damping value; it also has a research centre in the UK.
MRB has also helped the Philippines’s Department of Agriculture (DA) in developing NR seismic bearings. The Philippines lies on an earthquake prone zone within the Pacific Ring of Fire. The DA’s Bureau of Agricultural Research, together with the Philippine Rubber Industry Association (PRIA), collaborated with MRB in 2011 on R&D for local application of seismic bearings.
According to MRB, deployment of rubber seismic bearings can save up to 20% of construction cost as that eliminates extra materials for reinforcements. Plus, rubber bearings produced in Malaysia are usually given 50-year warranty.
Technology take from Japan
Advanced technologies in seismic retrofitting and designs are now being developed to dissipate or offer resistance to vibratory impact of earthquakes.
Japan, a leader in seismic technology, has buildings that survived the 8.9 Richter scale earthquake in 2011. The country sits on a seismic zone of at least four lithospheric plates.
Apart from a stringently adopted building code, deepfoundation structures sit on shock absorbers to dampen seismic energy; or on an isolated base that “sways” independently from the rest of the structure during ground motion.
Japan utilises the levitation and seismic isolation technologies. With the levitation technology, an airlift system employing airbags that are triggered by seismic activity would “lift” homes up from the ground to protect them from damage, until the tremblors stop.
The developer of this technology by inventor, Shoichi Sakamoto, was Japanese firm, Air Danshin Systems; it was launched in 2012. It is designed with mechanisms to be installed around the building and a sensor that reacts within 1 second of an earthquake. This activates a compressor, forcing air from a storage tank to fill the chamber and lifts the entire structure up to 1.18 in. A valve controls the air and keeps the building steady as it floats. When the earthquake stops, the building is lowered back onto the reinforced base. Emergency batteries are provided to ensure operation even during power outages.
Similar to this concept is California-based Air Pax’s newly patented hoverboard technology. Known as the Magnetic Field Architecture (MFA) Structural Isolation, it is utilised in combination with existing early warning systems like University of California (UC) Berkeley’s ShakeAlert early-warning software.
Air Pax said, on its website, that the three-part foundation system acts by decoupling an object or building from the earth to provide protection against earthquakes, floods and rises in sea levels.
Meanwhile, seismic isolation, which is also widely used for earthquake-proofing, enables structures to resist displacements during ground motion.
Good old rubber carries the bearing load
The base isolation technique is not new. The concept, used in monuments in Pasargadae (now in the Southeast of modern day Iran), goes back to 6th century BC, according to research on earthquake smart technology by Emma Keaney of Liverpool John Moores University.
The two-foundation concept consisted of the lower solid base made of stone, and was cemented together using lime and ashes/sand plaster; while the second foundation, laid out of wide slabs of polished stones, was fastened together with metal bars and clips to form a large plate, enabling it to slide during an earthquake.
According to Keaney, the first recorded isolation system (after the first official isolation system was registered and received a patent in the 1800s), was the lead rubber bearing (LRB) system; while a high damping rubber (HDR) system was developed in the 1980s, and first used in the US.
Then, the HDR paled in elasticity as it was prone to deformity after an earthquake and unable to return to its original state.
Nonetheless, rubber has been a widely used material for this purpose.
Sheela Thomas, Indian Rubber Board Chairperson and Secretary-General of the Association of Natural Rubber Producing Countries (ANRPC), told RJA in an interview: “Rubber has long been recognised as a useful engineering material for vibration isolation and relieving from stress and strain of major buildings and other constructions. Rubber–metal laminated bearings have been used in bridges since the 1950s to protect them from damaging stresses and strains as a result of bridge expansion and contraction (in response to ambient temperatures). This technique has also proven effective in isolating buildings from seismic and other forces of vibrations. Later rubber bearings with suitable modifications were used to isolate buildings from earthquakes. Such bearings have already been developed and are in use for seismic isolation in several developed countries, especially Japan and the US.”
Base isolation takes the brunt
For base isolation, Thomas said that the commonly used material is a rubber bearing, preferably made out of NR.
“Research and development work on NR bearings for isolating seismic vibrations was started in 1976 at the Earthquake Engineering Research Centre (EERC), now Pacific Engineering Research Centre, of the UC Berkeley. The work was undertaken as a joint effort of the EERC and the Malaysian Rubber Producers Research Association (MRPRA), UK (now known as the Tun Abdul Razak Research Centre). The technology that goes into the making of rubber bearings ensures that these are unaffected by time and are resistant to environmental degradation.”
Thomas also went on to explain that the bearings are made by vulcanisation-bonding of compounded rubber to thin steel reinforcing plates. “Rubber bearings have been very successfully used for tall buildings since the 1980s. Research is still going on for further improvements and innovations,” she explained,
Meanwhile, in another research, Dr SK Thakkar, ex-Professor Railway Chair and Professor of Earthquake Engineering, Indian Institute of Technology, said that bridge bearings are also subjected to deficiencies, associated with “inadequate seat width and to accommodate displacements in earthquakes”. He suggested that possible retrofit solutions would include, “replacing steel bearings by elastomeric bearings; by base isolation bearings, by bearing seat extension; or by provision of stoppers and devices to prevent jumping of the girders.”
This implies that, with the critical function of bearings in the integrity of mega-structures like bridges, rubber material provides the seismic-energy dissipation performance that is required.
“Experience and research show that use of rubber-based bearings in bridges and buildings will certainly save lives even if the structures are damaged during an earthquake.
Use of seismic/vibration isolators should be made mandatory for all sensitive and important installations such as nuclear and other power stations, hospitals, schools, high rise buildings, and defence establishments, especially in seismically active regions,” Thomas told RJA, in conclusion.