description of thesis

8/13/2019 Description of Thesis

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INSA Rennes pg. 1 PISEY KEO

RESISTANCE OF STEEL-CONCRETE

HYBRID ELEMENTS UNDERCOMBINED FLEXION-COMPRESSION

LOADING

For decades, in building as well as in bridge construction, the composite steel-concrete

structure has been used worldwide because of not only its mechanical efficiency but also the

economy in material and time consumption for construction. Concrete is a construction

materials which is strong in compression. However, while it is in tension, the cement holdingthe aggregate in place can be cracked. Beside this, steel is the strong one in tension but it is

instable while in compression. In composite steel-concrete structure, there is advantage such

that concrete has the roles not only to resists in compression but also to prevent local

buckling of the steel. The two materials work together by transferring shear force at the

interface between them. There are three types of shear transfer: by friction, by bond and by

shear connector. The behavior of composite member depends largely on the interface

resistance. While its rigidity is very high, the full interaction is obtained. Nevertheless, there

is a limitary of the stiffness and the interlayer slip is occurred at the interface i.e. the relative

displacement between layers. That is the well-known phenomena in composite material.

Twenty-first centuries is the challenge in

building high. With the development of

technology, the hybrid structure is more and

more used for high rise buildings. Mostly they

are built using reinforced concrete as the core

wall and structural steel as the outer embracing

frame. The reinforced concrete core wall

provides the rigidity to resist deflection caused

by lateral load, while the steel frame is used to

avoid blocking of valuable exterior view. It can

be seen in some high-rise buildings,International Finance Center Tower 2 at Hong

Kong for example, that composite columns

with several encased steel profiles are used for

structural external steel frame. Each steel

profiles are connected by bolted or welded to

each other to ensure together workability.

However, there is lack of information on the

behavior of this type of composite column.Figure 1. Hybrid Column at Hong Kong

International Finance Center Tower 2


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THESIS DESCRIPTION

The topic of thesis is in the areas of research in the medium term of Structural Engineering

Research Group of INSA Rennes. It has developed for over thirty years, pre-normative

research type in the field of composite steel and concrete structures. One outcome of this

work was the significant participation of researchers from INSA in drafting the newEuropean standards Eurocodes, particularly Eurocodes 4 and 8, dealing with the design of

composite steel and concrete structures, and seismic design respectively.

However, although the Eurocodes represent the progress of previous regulations, they are

only one step moved, and they must be constantly adapted to changing scientific knowledge,

and the evolution of practice and civil engineering technologies.

Thus, in the field of reinforced concrete structures such as, especially in high-rise buildings, it

is more often using columns or concrete walls containing multiple embedded profiles,

because the loads are such that classical reinforcement is not sufficient.

Those composite elements belong to structures defined as hybrid, which means that they

are neither reinforced concrete structures in the sense of Eurocode 2 or ACI318, nor

composite steel concrete structures in the sense of Eurocode 4 or AISC 2010. Gaps in

knowledge are common to all types of hybrid elements, as they are mostly related to the

problem of force transmission between concrete and embedded steel profiles, a situation in

which it is not known how to combine the resistances provided by bond, by stud connectors

and/or by plate bearings, and how to reinforce the concrete in the transition zones between

classical reinforced concrete and composite in order to avoid damaging effects due to curved

stress flows.

Other elements of the same type exist:

- Connections of flat slabs to columns by shear keys comprised of metalprofiles;

- Steel elements embedded in concrete in general, and particularly steelreinforcement around openings in the central cores, reinforcements of concrete

column with a steel profile on one level, reinforcements in walls in areas of

discontinuity, etc...

There is little or no information on the design of concrete-steel connecting these elements,

including the ends of the elements, but also on the length of the elements (including

quantification of the effects of friction and nesting).

To address these aspects, a research project called SMARTCOCO was mounted at European

level. It brings together the University of Lige, Imperial College London, INSA Rennes,

ArcelorMittal and a Belgian company BESIX. It aims to establish a design guide of hybrid

elements.

The thesis presented here will serve primarily to lay the theoretical foundations for scientific

experimental results of the project. It will be focused specifically on the problem of the

instability of hybrids column. It will aim to formulate a final design method, taking into

account the effects of coupling phenomena on the stiffness of the columns. This research will

therefore a strong connection with research SMARTCOCO and integrate experimental andtheoretical results on the design of local and global connections.


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THESIS PROGRAM

The main objective is to define a general approach to design hybrid columns. The program

will focus on different stages:

1. Bibliographic studyThe literature review will review the elastic and inelastic behavior of composite beam, the

finite element formulation of composite beam, the instability design methods in concrete,

steel and mixed, and will report the state of the art of hybrid columns presented in the

literature.

2. Detailed modelingFinite element formulation will be established to make static analyzes by considering on

geometric and material nonlinearity. The model takes into account both nonlinear material

behavior and interface problems between the materials. To do this, it will rely on theexperience of the team structure of INSA Rennes in this type of modeling and programming,

and the preparatory work done in master courses.

The analytical study will firstly focus on the elastic behavior of the hybrid column. Then, it

will step into finite element formulation based on displacement, force and mixed method on

the nonlinearity of material first and nonlinearity of geometry next.

This numerical modeling will study the behavior of column with varying heights, and will

highlight the effect of the behavior of interfaces on the overall behavior of the column. Steel

and concrete connection can be made in different ways; and there will be parametric studies

for stiffness characteristics and variable strength.

3. Calibration of numerical models sectional typeThe procedure to be used to achieve the design of mega-column using various sectional

computing tools such as software GALA, CCD, or CINELU will be defined. It will take

account of defined sections and equivalent inertia of embedded profiles, and also consider on

the effect of the interface.

4. Development of a design procedure manualInspired by computational methods instability existing standards (methods of nominal

curvature and rigidity of nominal Eurocode 2, method based on an amplification factor in

Eurocode 4), the formula for design manual will be developed.

5. Evaluation of the effect of longitudinal connection mode


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The previous numerical studies will be developed in conjunction with the experimental

program. It will be in a final phase of integrating the experimental results in terms of

stiffness and strength of the concrete-steel connection, in order to derive a design

method and a way of taking into account the flexibility introduced by the connection.

Figure 1. Hybrid Column at Hong Kong

International Finance Center Tower 2

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