4/4/2014 Semi-rigid behaviour of connections in precast concrete structures - ResearchGate

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Article

Semi-rigid behaviour of connections in precast concrete

structures

Source: OAI SIMILAR PUBLICATIONS

Consistent Practical Design of Concrete Structures

Bente Skovseth Nyhus

EVALUATION OF SHEAR STRENGTH OF HIGH STRENGTH

CONCRETE CORBELS USING STRUT AND TIE MODEL (STM)

Saeed Ahmad, Attaullah Shah

Guidelines for flexural resistance of FRP reinforced

concrete slabs and beams in fire

Emidio Nigro, Giuseppe Cefarelli, Antonio Bilotta, Gaetano Manfredi,

Edoardo Cosenza

Halil Görgün

ABSTRACT Multi-storey precast concrete skeletal structures are assembled from

individual prefabricated components which are erected on-site using various types of

connections. In the current design of these structures, beam-to-column connections are

assumed to be pin jointed. This current research work focuses on the flexural behaviour

of the beam-to-column connections and their effect on the behaviour of the global precast

concrete frame.

The experimental work has involved the determination of moment-rotation relationships

for semi-rigid precast concrete connections both in full scale connection tests and

smaller isolated joint tests. This has been done using the so called "component method"

in which the deformation of various parts of the connection and their interfaces are

summated, and compared with results from full scale sub-frame connection tests. The

effects of stress redistribution, shear interaction etc. are taken of by linear transformation

in the results from the full scale tests, enabling parametric equations to be formulated

empirically in order to describe the semi-rigid behaviour. Eight full scale column-beam-

slab assemblages were tested to determine the (hogging) moment-rotation behaviour of

double (balanced loading) and single sided in-plane connections. Two of the most

common types of connection were used, the welded plate and the billet type. Proprietary

hollow core slabs were tied to the beams by tensile reinforcing bars, which also provide

the in-plane continuity across the joint. The strength of the connections in the double

sided tests was at least 0.84 times the predicted moment of resistance of the composite

beam and slab. The strength of the single sided connections was limited by the strength

of the connection itself, and was approximately half of that for the double sided

connection, even though the connection was identical. The secant stiffness of the

connections ranged from 0.7 to 3.9 times the flexural stiffness of the attached beam.

When the connections were tested without the floor slabs and tie steel, the reduced

strength and stiffness were approximately a third and half respectively. This remarkable

contribution of the floor strength and stiffness to the flexural capacity of the joint is currently

neglected in the design process for precast concrete frames. Measurements of the extent

of damaged zones near to the connection in full scale tests showed that, unlike steel

connections, semi-rigid behaviour in precast concrete does not occur at a single nodal

position. In general the double sided connections were found to be more suited to a

semi-rigid design approach than the single sided ones.

Analytical studies were carried out to determine empirical design equations for column

effective length factors β in unbraced and partially braced precast concrete frames. The

main variables were the relative flexural stiffness α of the frame members, and the relative

linear rotational stiffness Ks of the connection to that of an encastre beam.

The variation of β factors with Ks and α are presented graphically and in the form of

design equations similar to those currently used in BS 8 110. The change in the response

of a structure is greatest when 0< Ks <1.5 where β is found to be more sensitive to

changes in Ks than α. When Ks >2 the changes in the behaviour are so small that they

may be ignored within the usual levels of accuracy associated with stability analysis. This

is an important finding because the experiments have found Ks to be generally less than

2 for typical sizes of beam. The results enable designers to determine β factors for

situations currently not catered for in design codes of practice, in particular the upper

storey of a partially braced frame. A design method is proposed to extend the concrete

column design approach in BS 8110 and EC2, whereby the strength and semi-rigid

stiffness of the connection enables column bending moments to be distributed to the

connected beams. However, the suitability of each type of connection towards a semi-rigid

design approach must be related to the stiffness and strength of the frame for which it is a

part. [less]

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4/4/2014 Semi-rigid behaviour of connections in precast concrete structures - ResearchGate

http://www.researchgate.net/publication/44003591_Semi-rigid_behaviour_of_connections_in_precast_concrete_structures 2/2

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