Vital to fortify quake-risk buildings: Prof
Published on: Wednesday, October 07, 2015
Kota Kinabalu: It is vital for public safety to fortify buildings in areas vulnerable to earthquake, and measures taken must commensurate with the lifespan of the concrete building after a seismic audit or appraisal of the buildings followed by seismic retrofitting.The goal is to protect human life, ensuring that the structure will not collapse upon its occupants or passers-by, and that the structure can be safely exited.Earthquake engineering has developed a lot since the early days with various codes, and some of the more complex designs now use special earthquake protective elements, with principles like Tai Chi as seen in flexible rubber padding for base isolation and dampening or high ductility material with adequate setback space to absorb the seismic forces.
ADVERTISEMENT
"Buildings are important for the protection of people when earthquakes occur. Structural reliability can be optimised by controlling the seismic failure modes, which provides optimisation method for structural design."Professor Ma Jianxun of the China's Xi'an Jiaotong University said this, among other points, in his two lectures on key points of seismic design of masonry structure at a seminar organised by JCI at a leading hotel here. He explained that concrete structures have a durability of some 50 years, depending on the quality and material of their construction.For example, brick building structures can be reinforced with coatings of glass fibre and appropriate resin (epoxy or polyester).In lower floors these may be applied over entire exposed surfaces, while in upper floors this may be confined to narrow areas around window and door openings. This application provides tensile strength that stiffens the wall against bending away from the side with the application.
ADVERTISEMENT
The efficient protection of an entire building requires extensive analysis and engineering to determine the appropriate locations to be treated, if the lifespan of the building deems it is still worthwhile.Reinforced concrete columns typically contain large diameter vertical reinforcing bars (rebar) arranged in a ring, surrounded by lighter-gauge hoops of rebar.
ADVERTISEMENT
Upon analysis of failures due to earthquakes, it has been realised that the weakness was not in the vertical bars, but rather in inadequate strength and quantity of hoops.Once the integrity of the hoops is breached, the vertical rebar can flex outward, stressing the central column of concrete. The concrete then simply crumbles into small pieces, now unconstrained by the surrounding rebar. One simple retrofit is to surround the column with a jacket of steel plates formed and welded into a single cylinder.The space between the jacket and the column is then filled with concrete, a process called grouting. Where soil or structure conditions require such additional modification, additional pilings may be driven near the column base and concrete pads linking the pilings to the pylon are fabricated at or below ground level.The enumeration of the failure modes from inspection became one of the key problems of seismic reliability lectures presented within eight hours on Oct 5, according to the lecturers for the event, were too concise albeit informative, and, professionals, especially young engineers, would need at least a week to be able to grasp the essential aspects of the knowledge practicality and difference between the China Code GB50011 with a 60-year history and the European Code EC8 with its 30-year history by the European Commission.For China, its code ensures the three scenarios of no damage under low-level earthquakes, repairable damages under precautionary earthquakes and no collapse of buildings under high-level earthquake for recently constructed structures, compared to two scenarios under Euro Code 8 of limiting damage requirements and no collapse requirements.Prof Ma acknowledges that the thoughts of Chinese Professor Lin Tongyan in his "Structural Concepts and Architecture," a book which introduces the overall structure of concept planning methods, and the total structure system and sub-system inter-relationships and simplify the mechanical design methods "has transformed the thinking mode of the Western view on China's capabilities."Lin Tongyan first introduced the detail of irregular design in his book "the Concept and System of Structure". In that book he also set some specific parameter to describe how a structure will collapse because of that."For example, after a strong earthquake in Managua, Nicaragua in 1972, 80 per cent of the buildings collapsed," Prof Ma said.The Bank of America tower designed by Lin Tongyan is a typical example in civil engineering, which survived the Managua earthquake in 1972 by controlling the failure modes, changing the structural dynamic characteristics and reducing the seismic input.The present seismic design method strong columns and weak beams, major shear and minor flexure also embody a thought of controlling the failure modes for many structures which were designed without adequate detailing and reinforcement for seismic protection.Seismic retrofit or rehabilitation strategies have been developed in the past few decades following the introduction of new seismic provisions and the availability of advanced materials like fibre-reinforced polymers (FRP), fibre reinforced concrete and high strength steel).Retrofit strategies are different from retrofit techniques, where the former is the basic approach to achieve an overall retrofit performance objective, such as increasing strength, increasing deform-ability, reducing deformation demands while the latter is the technical methods to achieve that strategy like FRP jacketing.Stay up-to-date by following Daily Express’s Telegram channel.
Daily Express Malaysia
