Bolted Joints between Steel Beams and Reinforced Concrete Columns
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Abstract
The steel beams to RC columns joint are usually done by welding the beam to a steel core within the column.
This solution is well covered in one of the Journal of Structural Engineering papers “Guidelines for Design of
Joints between Steel Beams and Reinforced Concrete Columns”. The same methodology is assumed in the
Romanian code “Cod de proiectare pentru structuri de beton armat cu armatura rigida” NP033-99. However,
in case that a contractor avoids using on-site welding due to various difficulties, and a continuous steel beam
through the reinforced concrete column is still required, a bolted connection between the beam and the inner
steel core should be considered. This paper presents an extension of these guidelines to a bolted connection
type. A nonlinear finite element analysis with proper definition of contact relationships between components is
performed in order to assess the role of each principal contributor (i.e. steel panel, inner concrete and outer
concrete regions).
Introduction
Shear strength in RCS (reinforced concrete steel) connections is provided by three mechanisms: steel web
panel, inner diagonal concrete strut and outer diagonal concrete strut.
1. Steel web panel. In RCS connections the behaviour of the steel web panel is similar to that in steel
frames.
2. Inner concrete. The inner diagonal concrete strut is activated through bearing of the concrete on the
steel beam flanges and face bearing plates welded between the beam flanges at the column faces.
3. Outer concrete region. The horizontal concrete struts are mobilized through extended face bearing plates
(FBP) or steel column, above and below the steel beam – these struts may be separated into twocomponents: one parallel to the beam and one perpendicular. Those perpendiculars are selfequilibrating and those parallel to the beam are sent further to the outer compression field. (seeFigure 8 of ref [1])
Joint Forces
The joint should be design for the interaction of forces transferred to the joint by adjacent members, including
bending shear and axial load.
The design forces as per ref. [1] do not include the effects of axial forces in the concrete column, and since
axial forces in the beams are usually small, these are also excluded from calculations. It is considered
conservative to neglect the effects of axial compressive loads normally encountered in design. Moreover, it is
predictable that the strength of the concrete joint mechanisms will be greater in joints where beam frame into
four, rather than two sides of the column, due to additional confinement.
Effective Joint Width
The joint shear strength is calculated based on an effective width of the concrete joint, which is the sum of the
inner and outer panel widths. The concrete in the inner panel is mobilized through bearing against the FBP
between the beam flanges. The participation of concrete outside of the beam flanges is dependent on
mobilization of the horizontal compression struts that form through direct bearing of the extended FBP on
the concrete above and below the joint.
Analysis Results
This section presents the analysis results from the finite element analysis of the connection. The stress
diagrams presented in the following Figures provides information in Mp/m2
• Figure 6 presents the crack distribution along with the compressive stress field in the inner joint
region. The thickness of the inner joint region (an implicitly the thickness of its finite plane-stress
elements) was considered equal to the beam flange width – 350mm. The maximum principal
compressive stress in the strut is roughly 20MPa. Two compressive diagonal struts were developed –
due to presence of the flange steel-column. The maximum bearing stress is already attained – but is
very localized and since the model disregarded the steel band plates this not represents a concern
(maximum strain is 4⋅10-3 which is acceptable in case of strong confinement provided by the steel
band plates above and below the steel beam).
Conclusions
The success of a connection design in terms of deformation and strength is directly related to the overall
behavior of the building. Apparently, for a regular concrete building this goal may be attain more easily, but for
a composite structure this may be challenging. The success of connection design (in terms of stiffness and
strength) directly affects the response of the building and implicitly the possibility to meet the target drift ratio,
therefore special care have to be provided to particular connection types, especially if they have not been
tested enough.