Yapıların plastik enerji dengesine göre sismik tasarımı

Yapı sistemlerinin doğrusal olmayan analizi ve tasarımında enerji kavramına dayalı hesaplamalar, yer değiştirme esaslı yöntemlere bir alternatif olarak gelişmektedir. Enerjiye dayalı yapı tasarımı aynı zamanda yer değiştirme kavramını da içermekte ve diğer analizlere kıyasla daha rasyonel bir yöntem olarak anılmaktadır. Çalışmada kullanılan yöntemde, deprem etkisi yapıya bir enerji girişi olarak ele alınmakta ve yapı sistemi için genel enerji denge denklemi yazılmaktadır. Plastik mafsalların kiriş uçlarında ve kolon alt uçlarında oluştuğu ideal göçme mekanizması esas alınmaktadır. Yapı için bir göreli kat ötelemesi oranının hedeflenmesi ile tasarım yatay kuvvetlerinin sistem üzerinde yaptığı dış işin genel enerji dengesinden elde edilen plastik enerji ile eşitlenmesi sonucunda taban kesme kuvveti ifadesi türetilmektedir. Enerji esaslı taban kesme kuvvetinin seçilen 3 ve 5 katlı çelik çerçeve yapıların kat seviyelerine eşdeğer statik yük olarak etkitilmesinin ardından, belirli bir yönetmeliğe göre önceden boyutlandırılmış yapı taşıyıcı sisteminin plastik tasarımı belirlenen yeni taban kesme kuvvetine göre tekrarlanmaktadır. İteratif bir yaklaşım sunan tasarım yönteminde, bir önceki iterasyonun kesit boyutları elde edilene dek tasarım devam etmektedir. Tasarım sonucunda belirlenen taşıyıcı sistemin, enerji esaslı taban kesme kuvveti ile doğrusal olmayan artımsal itme analizinden belirlenen göreli kat ötelemesi oranları ile tasarımda hedeflenen göreli kat ötelemesi oranı karşılaştırılmaktadır. Esas alınan ideal göçme mekanizması durumunun oluşup-oluşmadığı kontrol edilmektedir. Sonuçlar ölçekli gerçek deprem ivme kayıtları ile gerçekleştirilen zaman tanım alanında doğrusal olmayan dinamik analizlerin verdiği sonuçlarla karşılaştırılıp, yorumlanmaktadır.

Anahtar Kelimeler:

Enerjiye dayalı tasarım, Enerji denge denklemi, Enerji esaslı taban kesme kuvveti, Plastik tasarım, Doğrusal olmayan statik ve dinamik analiz

Seismic design of structures based on plastic energy balance

Energy-based approaches are developed as an alternative to displacement-based methods in nonlinear analysis and design of structures. The structural design methodology based on energy concepts incorporates the displacement concept simultaneously and it may be mentioned more rational by comparison with the other existing methods. Earthquake is considered as an energy input to the structure within the study and then the general energy-balance equation is written for the structure system. Ideal collapse mechanism, where plastic hinges are assumed to be located on beam ends and column bases, is considered. An admissible interstory drift ratio is targeted for the design and base shear force expression is derived by equating the plastic energy from general energy-balance with the external work done by the design lateral forces. The new energy-based base shear force is distributed to story levels of 3- and 5-story steel structures as equivalent static lateral forces and then plastic design of structural system, which is predesigned that comply with a seismic code at the beginning of the methodology, is implemented. The structural design method involves an iterative technique and it is continued until the same sections of the former iteration are obtained. The interstory drift ratios obtained from pushover analysis using the inverted triangular distribution of energy-based base shear force are compared with the target drift of the design. The accepted ideal collapse mechanism is checked whether it occurs or not. The results are interpreted and compared to the results of nonlinear time history analyses performed by using the time histories of real earthquakes scaled in time domain.

Keywords:

Energy-based design, Energy-balance equation, Energy-based base shear force, Plastic design, Nonlinear static and dynamic analysis,

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