Keywords: beam-to-column joints, finite element method, Eurocode 3, COSMOS/M.

Nowadays it is recognized that connections and members of steel frameworks have a semi rigid and nonlinear behaviour. One of the main concerns is how to incorporate the connection characteristics into an analysis, since it is generally carried out under the assumption that joints are either fully rigid or ideally pinned. Modern design codes (AISC-ASD [3], AISC-LRFD [2]) and the European prestandard (Eurocode 3 [4]) introduce the concept that the actual joints behave in an intermediate way between these two extreme cases. This assumes that the connections can transfer some moment and also have the rotational capacity that contributes to the overall structure internal actions. At present, research work is to develop methods for predicting the joint rotational response, that can be described by means of the in-plan moment-rotation curve in order to include semi-rigid joint effects in frame design. The moment-rotation curve of the connection can be obtained by means of experimental tests and theoretical, analytical and numerical (finite element) models.

Obviously, experimental tests are the most reliable and direct method in understanding the joint behaviour. However, it is impossible to test all of the connections that would be used in steel frames and this approach is devoted to underpin the validity of all subsequent theoretical and numerical work developed to predict the joint behaviour.

Theoretical and analytical models apply the basic concepts of mechanical and strength of materials to simplified models. These models are important because they often lead to the development of relatively simple design models that can be used routinely. Early attempts to develop a design methodology for the end plate connections were based on the tee-stub analogy and the yield line theory [1,5,6].

Finally, numerical modeling provides a means of carrying out wide ranging parametric studies to complement existing experimental results. Rigorous numerical modeling must take into account effects of material nonlinearity, bolt pretensioning, variability of contact between plates, etc. The finite element tecnique seems, in principle, to be the most suitable tool to investigate the response of a joint due to modern commercial finite element packages have the capability to model all these phenomena.

In this paper, beam-to-column bolted extended end plate connections, widely used because of the economy and simplicity of fabrication and assembly, are investigated for predicting their rotational behaviour (moment-rotation curve) that can be used in the frame analysis. In order to predict the rotational behaviour of this type of connection, a three-dimensional finite element model has been developed by the COSMOS/MRcode. The proposed model takes into consideration the interaction between the various components that are comprised in the connection. Thus, the modeling domain includes the beam, end plate, bolts and nuts and the column. The main novelty presented consists of accounting for the flexibility of the column components in the analysis. The column is modeled using solid elements. Other authors employ shell elements or use a rigid surface representing the column flange. Besides, the analysis incorporates the effects of material nonlinearity, for the plates and bolts, using the elastic-perfecty plastic stress-strain relationship. The results obtained from the finite element analysis are evaluated and verified by comparing the numerically predicted results with those of the corresponding tests carried out. The numerical results are also compared with a simplified theoretical model based on yield line analysis and the stub-tee analogy. The 3D finite element model presented in this paper can be used to generalize the rotational behaviour of end plate connections through more extensive parametric studies in order to take into consideration the connection flexibility and its effect on the performance of steel frames. So, extension of the methodology now presented may involve an improvement in analysis and design procedures of the proposed type of connection according to modern design codes.

1

H. Agerskov, "Analysis of bolted connections subject to prying", Journal of Structural Division, ASCE, 103: 2145-2163, 1977.

2

AISC, "Load and Resistance Factor Design Specification for Structural Steel Buildings (LRFD)", American Institute of Steel Construction, 1986.

3

AISC, "Allowable Stress Design Specification for Structural Steel Buildings (ASD)", American Institute of Steel Construction, 1989.

4

CEN, "Eurocode 3: Design of Steel Structures". European Committee for Standardization/TC250/SC3, 1986.

5

B. Kato, W. Mcguire, "Analysis of T-stub flange-to-column connections", Journal of Structural Division, ASCE, 99: 865-888, 1973.

6

A.P. Mann, L.J. Morris, "Limit design of extended endplate connections", Journal of Structural Division, ASCE, 105: 511-526, 1979.

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