The 2011 earthquake in Japan resulted in thousands of lives being lost and about ¥25 trillion worth of property damage, plus the loss assessment is far from over. Experts say that earthquakes per se are not dangerous but other concurring incidences as well as damage to infrastructure are. Now that mega earthquakes are resounding across the globe, especially in highly seismic-prone areas, one question stands out: How safe is infrastructure? This topic was covered extensively at the recent IRTEC in Malaysia with Prof James M. Kelly awarded this year’s Mahathir Science Award for his work on rubber bearings.
Modern engineering throughout the decades has undoubtedly reduced the number of casualties during earthquakes. Rubber has been regarded as an invaluable engineering component to reinforce structures, considering also that it has inherent damping capability.
As early as the 1950s, rubber laminated bearings were used in bridges to safeguard them from strains of expansion and contraction – a technique that was also applied to buildings to isolate them from seismic forces. Rubber bearings made from natural rubber (NR) have been used for base isolation.
Evolving further, R&D joint efforts have been conducted on NR bearings. This has involved the former Earthquake Engineering Research Centre or EERC (presently known as Pacific Engineering Research Centre) of the University of California at Berkeley, led by Prof James M. Kelly (who was awarded this year’s Mahathir Science Award for this technology), and the Malaysian Rubber Producers Research Association (MRPRA) in the UK that have been researching NR bearings since 1976.
Based on their studies, rubber bearings are proven “resistant to environmental degradation and unaffected by time.” They are also easy to manufacture: the bearings are made by vulcanisation-bonding of compounded rubber to thin steel reinforcing plates.
These rubber bearings have been used for up to eight-storey high buildings whilst continuous research takes place to further improve their capability.
A more efficient technique
According to Dr Kamarudin Ab Malek, CEO of the UK-based Tun Abdul Razak Research Centre (TARRC), during his presentation at the International Rubber Technology and Economic Congress (IRTEC) held October 10-11 in Malaysia, conventional structures tend to amplify forces and affect larger inter-storey drift compared to a base-isolated structure, which results in a nil amplification of forces and inter-storey drift.
The first rubber base-isolated building was the four-storey Foothill Communities Law and Justice Centre in Rancho Cucamonga San Bernardino County built in 1985. With a full basement and sub-basement isolation system, consisting of 98 rubber bearings reinforced with steel plates, the building was designed to withstand an 8.9 magnitude earthquake.
Dr Kamarudin also explained that rubber bearings may not totally eradicate the seismic forces, illustrating a comparison between the eight floors of the University of Southern California (USC) Teaching Hospital in Los Angeles, which used rubber bearings, and the Los Angeles County (LAC) General Hospital built on conventional structural systems in the aftermath of the 6.7 magnitude Northridge earthquake in 1994.
However, the bearings could mitigate seismic impact. At USC, accelerations were reduced by 70% at the base, thus requiring no repairs and remaining operational post-earthquake. Meanwhile, the LAC General Hospital, at 225% amplified forced, suffered US$400 million damage.
Whilst in the past, rubber bearings with dampers have been used as isolators, improved options of High Damping Rubber Bearings (HDRBs) are offered now. In Japan, HRDBs are used in structures such as the six-storey West Japan Postal Computer Centre in Kobe that has 120 bearings installed and which withstood damages during the 6.9 magnitude Kobe earthquake in 1995. These bearings are also installed in other buildings such as the Tohoku Electric Power Company in Sendai, Miyako; and the Nagoya, Nishinomiya and Totsukawa bridges.
Thereafter, the application of this technology increased; more apartments and condominiums are beginning to use the rubber isolators and existing bridges are being retrofitted with HRDBs.
Globally, thousands of structures are installed with the rubber bearings.
The building of the state phone company SIP in Ancona, Italy, was the first base-isolated building in Europe.
In earthquake-prone Iran, the HRDB technology was used for the first time after the 6.6 magnitude Bam earthquake in 1993 crippled the southeastern historical city. The project, a 10,000-unit residential development in Parand, consisting of 150 eight to 12-storey high blocks, was undertaken by Fame Square, a subsidiary of the Malaysian developer Amona Group. The completed project has more than 8,000 rubber bearings installed. The Malaysian Rubber Board (MRB) has been involved in the design, testing and bearings manufacture of the said project.
Some Southeast Asian countries, such as the Philippines, are mulling the use of the seismic rubber bearings for their infrastructure and retrofitting the existing ones.
The second Penang Bridge
The anti-seismic performance of HRDBs is utilised in the construction of Malaysian state Penang’s second bridge, a 24-km long bridge, purported to be the longest in all of Southeast Asia, extending from the Penang island to the mainland. “This is the first commercial use of the rubber bearings in Malaysia,” said Dr Kamarudin.
The bridge, which is longer than the first Penang Bridge that spans 13.5 km, commenced construction in 2008 and will be completed in 2013. It has more than 2,700 HRDBs installed and boasts a lifespan of 120 years; it can also withstand up to 180 tonnage load.
Dr Kamarudin said that the RM4.5 Billion project has significant savings in construction cost since seismic bearings are used to brace it against the destruction of the strongest magnitude earthquake over a 2,500 year return period.
Manufacturing these bearings is the Malaysian engineering and construction specialist, Doshin Rubber. Amongst other accomplished projects using HRDBs, the company, a subsidiary of the Kossan Group, has manufactured the High Rubber Damping Pads (HRDP) for use in the Parand, Iran, project. It also made the specialised 900 mm x 400 mm x 300 mm thick Laminated Rubber (Neoprene) bearing pads for the base of the Petronas Philharmonic Hall in the Kuala Lumpur Commercial Centre (KLCC) to cancel external noise and vibrations.
In his presentation, Or Tan Teng, CEO of Doshin, said, “At our facility we are able to produce laminated bearing pads and seismic bearings. The facility has 1,500 tonne/month mixing capacity with fully computerised and automatic dosing mixers.” He also said that the company has a performance testing facility for products for all projects.(RJA)