International Journal of Engineering Science Invention Research & Development; Vol. II Issue XI May e-issn:

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1 ANALYTICAL & EXPERIMENTAL STUDY on STRUCTURAL STEEL CONNECTIONS USING COMPONENT BASED FINITE ELEMENT MODEL Kathirvelmurugan K R V #, Satheshkumar K * # Final year - M.E Structural Engineering ( Batch), * Assistant Professor Civil Engineering Jay Shriram Group of Institutions, Tirupur, Tamil Nadu. Affiliated to Anna University, Chennai, Tamil Nadu. 1 kathirvelmurugan1991@gmail.com, 2 sathescivil@gmail.com Abstract Steel structures are the emerging mode of construction due to its rapid construction speed and its response to seismic loads. Design of structural steel connections are the challenging part in the steel structure. Since a connection is having two or more structural members like rolled sections and plates which are connected using fasteners, design procedures are comparatively complex than RCC structures. In order to reduce the complexity in the design of connections, Finite Element Model (FEM) has introduced for the effective analysis of structural connection. As an advancement of FEM, this paper initiate a study on new technique called Component Based Finite Element Model (CBFEM) for the analysis of connections. This method will optimize the connection by reducing the structural defects and increase the moment carrying capacity. This paper gives an introduction to a software program based on CBFEM method to analysis and design of structural steel connection, and a comparative study is also carried out with conventional design procedure to verify and validate the applications in connection design and advantages of this method. Keywords Steel Structure, Structural connections, Finite Element Model, Analytical Model, Experimental Study. I. INTRODUCTION One of the key parts in structural analysis and design of the steel structure is calculation of structural joint or connections. The majority of the construction defect is caused by connection failure. In order to get the efficient structural steel connection various design methods and software are in practice now a day. This study is on one of the method of design which is using a new technique called Component Based Finite Element Model (CBFEM), through which we can get an efficient connection to carry the desired load and moments. II. NEED FOR THE STUDY In order to get the efficient connection, each and every component of the connection such as rolled sections, fasteners, plates etc need to be modeled separately based on their exact functions. This the scenario which brings the need for component based modeling. By the formation of model for each component in a connection, the program will interpret the ultimate strength of each component for serving its purpose. So the result will be efficient with optimum components to carry the desired load and moment. Kathirvelmurugan K R V and Satheshkumar K ijesird, Vol. II Issue XI May 2016/721 III. APPLICATION OF FEM IN STEEL STRUCTURE A variety applications of FEM are used in steel structure due is easy visualization of reactions due to applied load as well. Both the linear and nonlinear analysis on structural members are possible with the FEM, hence the design process will be easier. FEM software with intelligent technologies is used to visualize the maximum stress affected area, so that the design engineer can able to find the ultimate load carrying of any section. FEM is not only used for stress analysis, for the calculation of Maximum bending moment, shear force and deflection is also possible. So the design parameters are inputs and as the output we will get the optimum results on the preferred structural members. IV. COMPONENT BASED FINITE ELEMENT MODEL

2 CBFEM is based on disintegration of the whole joint into separated components steel sections, steel plates, welds, bolts, anchors etc. Each component has its own analysis model, so this method will form individual finite element model for each components of the connection. First step in creating of model is the preparation of geometry. The geometry of the connection is depending on which purpose the connection is going to be formed. After the geometry of the connection, each and every component can be derived. As all we know the initial stage of FEM is messing, the software will form messing for each and every component of the connection. The plates connected by welds are modeled separately. They are connected by weld component only, which is characterized by weld in plane and out of plane tensile stiffness and resistance. The bolts are modeled as two followers of interpolation links with its tensile and shear trainer stiffness and adequate resistance. Slender compressed plates are checked for local buckling. Possible post buckling behavior of sections is introduced by effective stress of each compressed plate. Procedure starts with decomposition of a joint to components, see Fig. 1, followed by their description in terms of normal/shear force deformation behaviour. After that, components are grouped to examine joint moment-rotational behavior and classification/ representation in a spring/shear model and application in global analyses. The components in Fig. 1 represent 1. Column web in shear 2. Column web in compression 3. Beam flange and web in compression 4. Column flange in bending 5. Bolts in tension 6. End plate in bending 7. Column web in tension Advantage of the component model is integration of current experimental and analytical knowledge of connections components behavior (bolts, welds and plates). This provides very accurate prediction of behavior in elastic and ultimate level of loading. Verification of the model is possible using simplified calculation. Fig. 1 Component model of symmetrical beam to column connection with end plates V. COMPOSITION OF CBFEM MODEL CBFEM is based on decomposition of the whole joint into separated components steel plates, welds, bolts and anchors, concrete block. Each component has its own analysis model: 1. 2D plate finite elements for steel plates of stubs of hot/cold formed cross section 2. Force interpolation constrains for welds 3. Nonlinear springs for bolts and anchors 4. Contact elements between plates in connections First step in creating of the model is preparation of its geometry. Structural engineer creates the structural joint by applying manufacturing operations using these components, see Fig. 2. Meshing of the components is automatically done by software. Fig. 2 Manufacturing operation for structural joint and Messing operation in software The plates connected by welds are modeled separately. They are connected by weld component only, which is characterized by weld in plane and out of plane tensile stiffness and resistance. The bolts are modeled as two fans of interpolation links with its tensile and shear tri-linear stiffness and Kathirvelmurugan K R V and Satheshkumar K ijesird, Vol. II Issue XI May 2016/722

3 adequate resistance. Slender compressed plates are checked for local buckling. Possible post buckling behavior of sections is introduced by effective stress of each compressed plate. VI. CASE STUDIES A. WELDED PORTAL FRAME EAVES MOMENT CONNECTION The CBFEM model of the portal frame eaves moment connection with parallel stiffeners was verified by the CM. Results show a good agreement between two models. After that, sensitivity study was performed. Beam IPE cross-section size is variable parameter shown on horizontal axis, see Fig. 3. Column HEB 260 was considered. The resistance shown on vertical axis represents force couple of bending moment in plane My and vertical shear force Vz for which the ultimate limit state was reached. It is assumed, that bending moment and shear force values are equal. Resistance of the connection was governed by two components, column panel in shear and beam flange in compression. Comparison of critical component for both CBFEM and CM models was made. The same component was critical in both models for all parameters. Results of both models are very similar; differences in resistance are up to 7% and only in uncommon cases, e.g. column HEB 260, beam IPE 500. beam web, parallel stiffeners and inclined stiffener in compressed part of column web. These models were verified against CM with good accuracy. However, reaching this results using CM to the joint with inclined stiffener is very time consuming and with limited optimization features. Fig. 4 Influence of the shear stiffener to eaves moment connection; from left 46,5 KNm; 61,3 knm; and 73,0 knm B. COLUMN BASE WITH BASE PLATE Nowadays, column base with base plate design with or without stiffeners. The example is calculated with loading in two perpendicular principal directions; in case of loading by bending moments in general plane the result is obtained by interaction. The accuracy of interaction is limited to linear behaviour and may result in 30 % overestimation. The CBFEM model was validated with good accuracy against experiments both from literature and carried out specifically for this purpose by authors. The verification of cases loaded by moment in major/minor axes performed against CM gives good results. The CBFEM model, directly performing calculation under general loading, allows engineers to optimize stiffeners and plate. Fig. 3 Sensitivity study, Column HEB 260, variable parameter is beam crosssection size Study of the moment connection in the corner of portal frame is visualised on Fig. 5. Design resistance and distribution of internal stresses are shown for three types of a joint - with unstiffened Fig. 5 Stress in concrete under unstiffened base plate 35 mm (left) and stiffened base plate 22 mm loaded by general moment (right) Kathirvelmurugan K R V and Satheshkumar K ijesird, Vol. II Issue XI May 2016/723

4 connection cannot be defined without analysis of a connection located next to it. Fig. 6 Base plate loaded by general moment. a) Deformed shape, b) stress in contact area C. ANALYSIS OF A COMPLEX STEEL JOINT Interaction of several connections in one joint is very hard to solve using conventional methods. Analytical needs to be created manually for every type of the joint. On the other hand, there are no limitations for typology and number of members used in CBFEM method. General effectiveness of the method is shown on an example of a frame joint. There are following members in the joint: connection on bolted end-plate with ribs, connection on shifted end-plate with stiffener, connection of skewed beam on short end-plate, rectangular hole in the web and several stiffeners. Fig. 8 Stresses and plastic zones in complex steel joint VII. APPLICATION OF CBFEM IN STEEL STRUCTURE Apart from the above case studies various type of steel connections can be applicable to get the optimized result using CBFEM, following are the some examples. Fig. 9 Plate-to-plate connection. A) Actual Connection Fig. 10 Anchoring connections. A) Actual Connection Fig. 7 Complex frame joint interaction of more connections. All these members can be solved separately, but the overall capacity of the joint is also defined by their interactions true capacity of a given Kathirvelmurugan K R V and Satheshkumar K ijesird, Vol. II Issue XI May 2016/724

5 Fig. 11 Base Plate Connection to Footing. A) Actual Connection VIII. Fig. 12 Bracket T- Joint. A) Actual Connection ADVANTAGES OF CBFEM OVER CONVENTIONAL METHOD Since CBFEM method adopting component meshing system and individual component analysis, this method has following advantages over the conventional design methods, 1. This method can able to made models for general configurations for different types of connection, where as the FEM can give only specific modal for each type of connection. So the design process will be faster in CBFEM method. 2. Using CBFEM method model for various steel sections like hot rolled sections, cold form sections, pre-engineered sections, builtup sections etc can be formed. But conventional FEM can give only for defined hot rolled sections. This property enables the structural engineer to adopt desired section for ease fabrication. 3. CBFEM has unlimited scope of connection members in one connection, since it considering each member as different component, whereas the conventional component models are lagged in this part. 4. Buckling analysis for flange and web of I- sections are possible with this CBFEM, but most of the conventional methods are failed to perform the same. 5. Since the CBFEM method analyzes each components of the connection, the connection will be comparatively lighter for same moment carrying capacity to the conventional method. This will considerably reduce the construction cost. 6. Connection designed using this method will be safer because of its all components analysis system, which reduces the risk factor of the connection. IX. CONCLUSIONS Commonly used conventional method is laborious for hand calculation and its application by design tools in practice is limited to certain types of connections and their loading. Use of computer based design of structural connections by CBFEM is limited to proper validation and verification procedures. Its validation using both published and undisclosed experiments with open and hollow section connections and column bases is under progress. Based on configurations verified by published results, CBFEM provides more variability in geometry and loading than simplified procedures in conventional design methods. ACKNOWLEDGMENT The authors thanking our beloved Chairman Thiru. K.M. Thangaraj, and Principal Dr. R. Maguteeswaran who provide excellent educational facilities and equipped platform. And also thanking Mr. R. Gopinath M.E. (Ph.D) HOD. and Mr. S. Karthick M.E. (Ph.D) Assistant Professor of Jay Shriram Group of Institutions, Tirupur Tamil Nadu for their technical inputs and co-ordination to do this research. Kathirvelmurugan K R V and Satheshkumar K ijesird, Vol. II Issue XI May 2016/725

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