Mustafa FENER, Pınar YILMAZ, Kamil KAYABALI, Özgür AKTÜRK, Farhad HABIBZADEH

Zemin sıvılaşmasının enerji yaklaşımıyla değerlendirilmesi

Depremler sırasında yapılarda oluşan hasar (kısmen veya tamamen) birkaç on yıl boyuncakapsamlı araştırmalara konu olan zemin sıvılaşmasından kaynaklanabilir. Kumlu tabakanınsıvılaşmaya duyarlılığı, zeminin sıvılaşma direncinin (kapasite) bir deprem tarafından uygulananyük (talep) ile kıyaslanmasıyla ölçülür. Bu kapsamda gerilme temelli sıvılaşma değerlendirmesi enpopüler yöntemdir. Bu yöntemin başlıca belirsizliği anakayadaki maksimum yatay yer ivmesinin(amax) hesaplanmasıdır. Zemin seviyesinde de bir amax belirlemek için yer tepki analizi veyabasitleştirilmiş bir varsayım gereklidir. Gerilme temelli yaklaşıma dayalı olarak geliştirilen birimdeformasyon temelli yaklaşımda da benzer kısıtlamalar bulunmaktadır. Kumlu zeminin birimhacim başına düşen sıvılaşma enerjisi kapasitesini belirlemek için burulmalı kesme halkası gibilaboratuvar teknikleri bulunmaktadır. Benzer şekilde, deprem kaydının enerjisi basit fi zik ilkelerikullanılarak hesaplanabilir. Herhangi bir deprem kaydının talebi hesaplanırken hız-zaman kaydı vezeminin birim kütlesi kullanılır. Bu araştırmanın amacı zemin sıvılaşmasının değerlendirilmesi içinenerjiye dayalı yöntemin kullanılabilirliğini göstermektir. Ek olarak, gerilme ve birim deformasyontemelli yaklaşımların eksiklikleri genel hatlarıyla verilmiş ve enerji tabanlı yaklaşımın avantajlarıtartışılmıştır.

Assessment of souil liquefaction using the energy approach

Damage to structures during earthquakes may be fully or partly caused by soil liquefaction, which has been the subject of extensive research for several decades. Liquefaction susceptibility of a sandy deposit is performed by comparing the resistance of a soil to liquefaction (i.e., capacity) to the load imparted by an earthquake (i.e., demand). In this regard, the stress-based method of liquefaction assessment is by far the most popular. It involves uncertainties mostly related to the computation of the maximum horizontal ground acceleration (amax) at bedrock. A site response analysis or a simplifi ed assumption is necessary to determine the amax on the ground level as well. Developing from the stress-based approach, the strain-based approach has also similar constraints. There exist laboratory techniques such as torsional shear to determine the capacity of a sandy soil in terms of liquefaction energy per unit volume. Likewise, the energy of a strong motion record can be set by employing simple physics principles. For this, a velocity time history and the unit mass of the soil are employed to compute the demand of any strong motion record. The scope of this investigation is to illustrate the usability of the energy-based method for the evaluation of soil liquefaction. The defi ciencies of the stress- and strain-based approaches are outlined and the advantages of the energy-based approach are discussed.

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