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What ductility class structure do we really need?

posted Aug 10, 2019, 9:16 AM by jeffery jim   [ updated Aug 10, 2019, 9:38 AM ]

Back in 2015, the largest earthquake with magnitude of 6.0 Richter scale hit Kundasang, Ranau. This incident severely affect many of those residing at surrounding areas with multiple (almost or more than hundred shock waves) after killing many on its initial tremor early morning.

One of the most structure that have been investigated ever since by many professionals and academicians is the teachers flat/quarters at SMK Ranau. I did use this as a case study during one of my talk when training Sabah State JKR personnel. It is a classic case study.

After almost two or three years after my first article about this when i try to demystify the issue of the safety of the design for this structure by conducting finite element analysis, i found another conference proceeding paper which discusses similar subject but a little bit bemused and at the same time amused with their claim.

Nevertheless, i shall not discuss their finding since there are gaps between professionals and academicians when talking about dilapidation or the criteria or criterion of what defined as lapse serviceability state limit. The outcome from my calculation to their calculation differs, similarly with outcomes for diagnosis and prognosis. One particular claim that which need to be cleared here is the purported claim in this paper about the column joint crack. Desktop studies shows otherwise, where the crack is actually construction joint; perpendicular to the column direction.

Now, i am not interested with their finding on this but i am thankful that some of the data in regards to the t value or time step value which projected the excitation value. The highest value is 0.11m/s2 or 0.12g from this paper. The Seismic Hazard Map in Malaysian Annex indicate the value of around 0.17g.

From Soil of Sabah Map, SMK Ranau is situated in between Pinosuk and Brantian Soil. In this case it sits on a plateau with colluvium. Colluvium is a heterogeneous mix of sediment which increases the S multiplication factor increases from 1.3 to 1.8 for class C soil. Hence, it is appropriate to say the peak ground acceleration reacting on the structure have increased to 0.216g.

Despite of its soft story at the ground floor, the structure hardly lapse its designed ultimate limit state and one have to accept that the performance without increasing the ductility class to DCM or DCH will still be robust enough to restrain the structure by force instead of energy. Unlike recommendation made in Eurocode where 'ag' value of more than 0.1G requires special design, we can also accept that the DCL designed is robust enough to withstand magnitude 6.0 which is situated 6km away.

Therefore, we can generally accept that DCL based on Eurocode 2 or BS 8110 or BS 8103 can survived such magnitude although the damage limitation percentage may increased. It is also reasonable to increase the design from DCL to DCH or DCM to reduce the damage limitation percentage to a mere 10%.

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