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The AAU-ETD digital repository system captures, stores, indexes, preserves, and distributes digital research material.Sun, 19 May 2019 15:10:01 GMT2019-05-19T15:10:01ZComparison of the Approximate and Exact Second Order Elastic Analysis Methods in Relation with Eurocode 8’s interstorey drift sensitivity Coefficient (θ) limit
http://localhost:80/xmlui/handle/123456789/18272
Comparison of the Approximate and Exact Second Order Elastic Analysis Methods in Relation with Eurocode 8’s interstorey drift sensitivity Coefficient (θ) limit
Seblework, Hailu
Stability of structures is a major issue that must be checked at the first stage of the design. It is
the ability of a structure to keep its equilibrium position after being disturbed by external actions.
One of the parameters used to check the stability of structures in code of practices is a second
order effect. The Eurocode families, Eurocode-2 and Eurocode-8 set the criteria for neglecting
second order effect by considering different parameters into account. In the EC8 approach to the
second order effect, inerstory drift sensitivity coefficient θ is the most important quantity
governing the analysis. The code allows to neglect the second order effect if θ is less than 0.1
and to use an amplification factor (1/1- θ) if θ does not exceed 0.2. It restricts the value of θ not
to exceed 0.3.
The second order effect is the phenomenon of additional force and moments produced by the
vertical load acting on the laterally deformed structure. Second order elastic analysis can be
evaluated in one of the two methods, approximate and “exact” second order elastic analysis
method. The accuracy limit of approximate second order elastic analysis method is illustrated by
comparing the results of the two methods in relation to the limit of interstory drift sensitivity
coefficient θ.
The procedure is done in two cases using simple elastic portal frames. In case I axial load is
applied only on the weak column of the frame, and in case II the load is applied on both strong
and weak columns. In both cases five portal frames with a different relative stiffness value of
columns are used to study the effect of the relative stiffness of columns on the bracing action of
strong column. These frames clearly show cases where the validity of the basic assumption
behind the approximate methods becomes uncertain.
The results of the investigation reveal that, the approximate method gives relatively good results
up to the value of θ=0.3 in the case of supported sway column. After this point, the P-δ effect,
which is neglected by the approximate method, becomes very high and the supported sway
column deflects in an elastic failure mode which is very different from the basic assumption of
approximate method. As a result, the approximate method becomes less accurate for θ values
greater than 0.3 compared to the “exact” one.
Thu, 01 Nov 2018 00:00:00 GMThttp://localhost:80/xmlui/handle/123456789/182722018-11-01T00:00:00ZEffectiveness of Swimmer Bars as Shear Reinforcement in Rectangular Reinforced Concrete Beam Under High Cyclic Loading
http://localhost:80/xmlui/handle/123456789/18271
Effectiveness of Swimmer Bars as Shear Reinforcement in Rectangular Reinforced Concrete Beam Under High Cyclic Loading
Molaligne, Nibret
Reinforced Concrete beams are important structural elements that transmit the loads from slabs and bridge decks, to structural column piers. The design of those beams must be safe against internal actions i.e. bending moments, shear forces and torsions so that they will perform effectively during their service life.
In building construction, stirrups are most commonly used as shear reinforcement. Stirrups may be vertical, inclined or bent up bars; but the cost and safety of shear reinforcement in reinforced concrete beams lead to the study of other alternatives. Swimmer bar system is a new type of shear reinforcement. It is a small inclined bar with its both ends bent horizontally for a short distance and spliced to both top and bottom flexural steel reinforcements.
Previous works on Swimmer bars revealed that the effect due to static load on beams reinforced with Swimmer bars has more shear carrying capacity than vertical stirrups and can be placed at larger spacing. The beam consisting of swimmer bars showed much more stiffness than beam with conventional bars. This research focuses on the potency of using swimmer bars instead of normal shear reinforcements with the same amount of reinforcement area under single sided high cyclic loading. In addition to the experimental test, a validated Finite Element Model (FEM), created in ABAQUS V6.13-1 is used to investigate the effect of rectangular spliced swimmer shear reinforcement bars.
Based on the experimental investigation and finite element analysis of this research, the ultimate load capacity of the beam is increased by 3.75% and the respective deflection is less in rectangular spliced swimmer bar beam as compared to normal stirrup beam. As a result, rectangular spliced swimmer bar improved the shear load carrying capacity in the reinforced concrete beams. Besides, compared to the normal stirrups, fewer and smaller cracks were observed when using spliced swimmer bars.
Fri, 01 Mar 2019 00:00:00 GMThttp://localhost:80/xmlui/handle/123456789/182712019-03-01T00:00:00ZA Study of Relationship between Seismic Provision and Progressive Collapse Resistance
http://localhost:80/xmlui/handle/123456789/18270
A Study of Relationship between Seismic Provision and Progressive Collapse Resistance
Mikiyas, Dasa
Progressive collapse is known to be the cause of most catastrophic structural failures around the world. Recent acts of terrorism including the destruction of the World Trade Center demand for methods to improve behavior of structures under these abnormal events. Design of structures against progressive collapse has not been an integral part of structural design. However, some codes such the GSA and UFC guideline have detail requirements to reduce the likelihood of progressive collapse. Effect of seismic provision in progressive collapse resistance was not mentioned in this guidelines.
Hence, one of this thesis aim was to investigating the relationship between seismic provision and progressive collapse resistance of RC framed structures. To achieve this, a six-story regular RC framed models were designed according to ES EN 1998:1-2015. Ground accelerations of 0.15g with low, medium and high ductility classes were used. Moreover, a deficient structure with insufficient development length and lap splice at connection was also considered. Progressive collapse analysis was carried out on the four structures by considering four different column loss scenarios. Nonlinear static (pushdown) analysis were adopted in all 16 cases of progressive collapse assessment based on GSA 2013 guidelines.
It was concluded that the progressive collapse resistance of a structure is influenced heavily by the design ductility. Buildings designed for lower ductility have higher yield loads but undergo lower deformations before collapse. On the other hand, buildings designed for higher ductility yield at lower loads but they undergo greater deformations and absorbs more energy to resist collapse. However, based on the progressive collapse analysis low ductility design is the one that perform good in progressive collapse with maximum load factor when compared with medium and high ductility design.
The other aim of this thesis was to study the development of CAA and CA analytical model for beam column sub-assemblage, and to investigate application of CAA into alternative path design. It was found that the analytical model was quite similar with experimental result and it shows that reinforced concrete beams can be modeled as rigid rectangular blocks between the hinge locations to determine CAA and CA capacity. In addition, with adequate boundary restraints and shear strength, CAA found to be applicable into the design against progressive collapse.
Sat, 01 Dec 2018 00:00:00 GMThttp://localhost:80/xmlui/handle/123456789/182702018-12-01T00:00:00ZEvaluation of Behavior Factor Provision of ES EN for RC Ductile Regular and Plan Irregular Building Structures using Nonlinear Analysis
http://localhost:80/xmlui/handle/123456789/18269
Evaluation of Behavior Factor Provision of ES EN for RC Ductile Regular and Plan Irregular Building Structures using Nonlinear Analysis
Getahun, Asres
Most recent seismic codes include response modification factors (R in US practice) or
behavior factors (q in European practice) in the definition of equivalent lateral force method
of analysis used for the design of earthquake resistant buildings. Seismic design makes use
of energy absorption and dissipation to reduce the design forces in order to achieve economy.
The behavior factor (q) or response modification factors (R) plays a central role in seismic
design process, since it is used to reduce the linear elastic design spectrum to account for the
energy dissipation capacity of the structure. In this study the evaluation of behavior factor for
regular and irregular ductile reinforced concrete structures using nonlinear analysis is
investigated. The evaluation is done by designing regular and irregular structures for different
ductility classes with the provision of our seismic code and by checking their performance
through non-linear analysis using CSI ETABS. In this paper parametric studies have been
conducted and the effects of different parameters (seismic location, ground type, number of
stories, ductility class and 3D modelling effects) on behavior factor are presented in detail.
Moreover, the evaluation of behavior factor using different models under favorable and
unfavorable conditions along with performance comparison of structures designed for
different ductility classes were done and the results are discussed and presented in this study.
Furthermore, the evaluation of behavior factor for 3D plan irregular reinforced concrete
structure under unfavorable conditions is done using non-linear dynamic analysis and the
findings are presented as well.
Thu, 01 Nov 2018 00:00:00 GMThttp://localhost:80/xmlui/handle/123456789/182692018-11-01T00:00:00Z