Determination of energy-based base
shear for ideal collapse mechanism
Journal Name:
- Dicle Üniversitesi Mühendislik Fakültesi Mühendislik Dergisi
Key Words:
Keywords (Original Language):
| Author Name | University of Author | Faculty of Author |
|---|---|---|
Abstract (2. Language):
Depending upon different geophysical and structural
factors, earthquakes cause several damages to
buildings. The duration and the magnitude of the
ground motion, soil type or fault properties may
affect the structural damage. However, the most
important parameter for the damage is to build
structures poorly engineered. Even though there
may exist moderate, heavy or major damages on
structures under seismic effects, the crucial aspect
for structural engineering is to prevent the total
collapse. Therefore, when new structures are
designed the yield mechanism of structures under
seismic effects should be considered in detail.
A nonlinear static procedure to estimate base shears
of reinforced concrete frame structures is presented
in the study considering global collapse state and
energy concepts. Since global failure mechanism,
where plastic hinges occur at beam ends and column
bases, is a preferable collapse mode for structures
under seismic effects to prevent the total collapse,
this type of failure mechanism is targeted at the
beginning of derivation of equations. Given the preselected
failure mechanism, the energy-balance
equality is written for frames.
Earthquake resistant structural design procedures in
current seismic design codes are traditionally
strength-based and direct displacement-based. The
strength and displacement capacity of structural
members are not desired to be less than seismic
demands of earthquakes in these procedures.
However, energy-based structural design which
considers the earthquake as an energy input to
structures may be a more rational approach.
In energy-balance equality written for frames, the
seismic input energy and plastic energy is modified
with a factor. Input energy is modified due to
structural damping and the energy which
contributes to structural damage is considered in the
equality. The plastic energy is decreased with a
factor, too, to consider the reduced hysteretic
properties. The reduction factors are obtained from
literature which are expressed by former
researchers. Four different factors are considered
and sixteen different base shear forces are obtained
for RC frames by taking combinations of these
factors.
Plastic target drift needs to be estimated while the
energy balance equality is set up. It can be obtained
from the difference of maximum drift between the
yield drift for the structure. For the probability level
of exceedance 10% in fifty years period, the
maximum story drift ratio is suggested as 2% for the
design earthquake within the study. This is the
performance criteria of the considered procedure.
Selecting a suitable post-yield stiffness ratio is an
important issue for performance-based structural
design. The appropriate post-yield stiffness ratios
for structural members are selected for calculation
of energy-based base shears. From literature and
experimental studies, the post-yield stiffness ratio is
assumed as 0.10 for RC members.
Seven real earthquake records, which are scaled in
time domain according to the Z2 type soil class, are
chosen to perform nonlinear time history analyses of
four- and seven-story RC frames. The maximum
base shear forces are compared with the results of
the energy-based method.
It can be seen from the study that the energy-based
base shears are directly proportional with the input
energy modification factor and inversely
proportional with the plastic energy modification
factor. Proportions of plastic and input energy
modification factors are obtained very close to
proportions of base shear forces, which are
calculated by using these modification factors.
Design base shear forces in current seismic codes
are generally calculated for a constant displacement
ductility of structures. Therefore, hysteretic
behaviors of structural members and hysteretic
damping are not included directly in these type of
calculations. However, in this study, the design base
shear forces for structures are obtained from energy
balance concept and nonlinear properties of
structural members are considered more detailed.
Bookmark/Search this post with
Abstract (Original Language):
Bu çalışmada, klasik iş-enerji bağıntısı ve yapı için önceden hedeflenen ideal bir göçme mekanizmasının
esas alınması ile deprem etkileri altında doğrusal elastik ötesi davranış gösteren betonarme çerçeve türü
yapılar için genel enerji denkleminden hareketle taban kesme kuvveti hesaplanmaktadır. Yapısal sönümden
dolayı, depremle birlikte yapı sistemlerine giren enerji bir katsayı ile modifiye edilmekte ve enerji denge
denklemi değiştirilmiş şekli ile yazılmaktadır. Enerji denkleminde yer alan plastik enerji, yapısal elemanların
çevrimsel davranışlarının daha gerçekçi bir şekilde hesaba katılmasının gerekliliğinden, belirlenen bir
katsayı ile azaltılmaktadır. Plastik ve giren enerjiler için azaltma faktörleri literatürdeki farklı çalışmaların
esas alınması ile belirlenmektedir. Yapı için belirlenen taban plastik dönmesi için yatay dış yükler tarafından
yapılan dış iş, Türk Deprem Yönetmeliği’ndeki eşdeğer statik yatay yük dağılımının dikkate alınması ile
hesaplanmaktadır. Plastik enerji ifadesi ile dış iş ifadelerinin eşitlenmesi sonucunda enerji esaslı taban
kesme kuvvetlerini veren denklemler, farklı azaltma faktörleri için türetilmektedir. Enerji esaslı tasarım
taban kesme kuvveti değerleri dört ve yedi katlı betonarme çerçeve yapılar için hesaplanmaktadır. Aynı
çerçeveler için Z2 yerel zemin sınıfına ait elastik tasarım ivme spektrumuna uyumlu olacak şekilde
ölçeklenen deprem ivme kayıtları ile gerçekleştirilen zaman tanım alanında doğrusal olmayan analizlerden
elde edilen en büyük taban kesme kuvvetlerinin ortalaması enerji esaslı taban kesme kuvvetleri ile
karşılaştırılmakta ve sonuçlar yorumlanmaktadır.
FULL TEXT (PDF):
- 3