Keywords: finite element, nonlinear, web angles, seated connections, rigidity, weld, moment-rotation curves.

In conventional design of simply supported steel beams, the most common types of connections are either web framing angles or seated connections. The design codes require that the beam reactions must be adequately carried by connection while sufficient inelastic rotational capacity should exist in the connections to prevent transferring the moment from beam to column; therefore careful detailing is necessary to obtain a pinned joint. In both web angle and seated connections cases, the shop connections are usually welded while the field connections are preferably bolted. Such method which provide both economy and quality of the connection has been widely accepted by fabricators and design engineers. Consequently less attention was paid to the study of the behaviour of the fully welded pinned connections. Despite the difficulties associated with field welding, especially in terms of the weld quality and inspection, fully welded connections are widely being used because of their design simplicity, economic advantages and decrease in shop handling and fabrication operations.

However based on the current design code no combination of seated connections with the web angles is recommended, but an evaluation of such a connection is also necessary for two reasons. First of all, this type of connection may be fabricated as a result of inadequate design or constructions procedures. Secondly, the combination of the web angle and seated connection can be regarded as a semi rigid joint which can be included in the lateral load carrying system, hence understanding of its behaviour can be useful when an existing steel structure with simple frames and insufficient lateral strength is being retrofitted.

In the current paper a numerical approach based on the nonlinear finite element method was adopted to study the behaviour of several types of welded connections. The commonly used top and seat angle connection was chosen as a basis for modelling and other components such as web angles and stiffeners of various shape and positions were included in the subsequent modelling. The stress distribution patterns and yield stress concentration zones were also compared for various combinations. Results show that the rigidity of the connections increases as web angles are added to the joints. However the changes in the degrees of rigidity are less apparent because the overall stiffness of the connection increases as a result of the changes in sizes and configurations of the contributing elements. The effects of parameters such as size and position of the web angles, the top and seat elements along with the dimensions of the connecting welds were also studied.

Finally, conclusions were made to be used as a guide in the design of semi rigid connections.

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