Keywords: rigid connection, saddle-like connection, Khorjini, semi-rigid, semi-rigid connection.

The retrofitting process of steel or masonry structures could result in either the improvement of existing frames or the introduction of additional steel frames. Due to the dire importance of frame connections in retrofitting, the existence of certain obstacles posed by the limitations of existing ceilings in placing connection elements on the top of the frame must be considered. While all types of standard rigid, semi-rigid or simple connections need upper elements to maintain lateral stability of the connections [1], in the case of existing ceilings this requirement cannot be fulfilled due to the obstacle.

In order to provide stability it is required to place an upper angle in simple connections and a plate on top of the upper flange in rigid connections. Then special plates are designed to be placed on the lower side of the upper flange in order to overcome this obstacle. On the other hand, the use of simple frames is restricted, due to limitations of bracing. Therefore, frames with rigid connections must be utilized which would also require the employment of upper plates. In 2005, Foroughi [2] proposed a saddle-like type of connection with no plate or angle on top of the flange concerning the existing obstacles.

These plates are placed between the beams and welded underneath the upper flanges on the side of the column. Recently, the authors have conducted some research on different types of such connections [3]. The models were analyzed using finite element methods considering geometric and material nonlinearity. In order to corroborate the modeling, a sample was analyzed and the results were compared to a similar laboratory test model [4,5] which results to acceptable comparability. The proposed models were analyzed and in conclusion all four models showed favorable behaviour. The cyclic moment-rotation curve in all four models was stable and continues to a distortion point and it was capable of considerable energy absorption. Peripheral angle support was utilized in two of the models and peripheral plates were employed in the other two. The results show that the models with peripheral angle support behave as rigid connections with low ductility and reach the point of failure after 31 moment cycles. Shear rupture of the horizontal flange of the support angle was the mode of failure point, while the models with peripheral plates support behave as a rigid connection with desirable ductility after undergoing 43 cycles, the connection was stable and the failure mode was the yielding of beam at the vicinity of connection.

1

AISC, "Steel Construction Manual, Allowable Stress Design", 30th Edition, American Institute of Steel Construction, 2005.

2

M. Foroughi, "Report of Rehabilitation of Fallahzade Home", Yazd, Iran, 2005.

3

M. Shojaeefard, M. Foroughi, M.A. Barkhordari, "Study of Performance of Rigid Khorjini Connection with Upper Plate Replace Below of Top Flanges", MSc Thesis, Yazd University, Yazd, Iran, 2008.

4

A. Mazroui, S.R. Mirqaderi, E. Behnamfar, M. Dehqani Ronani, "Study of Design Code and technical properties of Khorjini Connections and proposing instructions", BHRC, Tehran, Iran.

5

M. Foroughi, M.A. Barkhordari, A. Niknam, "Analysis of Khorjini Connections in frames using nonlinear techniques", Iran University of Science and Technology, Tehran, 2006.

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