Design Of Connections as Per Is 800:2007 and Interactive Design Of Semi_Rigid Steel Frames

Abstract

Globally, Structural steel design is based on “Limit State Design Method”. Philosophy of limit state design method (LSM) represents significant advancement over traditional design philosophies for steel structures. Limit state design method has presented a new era of safe and economic construction for steel structures. New standard IS 800:2007 for design of steel structures has provided an opportunity for modern design philosophy, design specifications and provisions as per Limit State Method of Design in our country. In design of steel structures, steel connections are important elements for controlling behaviour of structure. It is essential that to understand behaviour of steel frame, connectors are required to develop full or a little higher strength compared to members being joined in order to achieve a safe and an economical design.

Various types of shear and moment resisting connections have been designed along with their design approach, steps and with detailing using IS 800:2007 provisions. Examples have been worked out to understand concepts presented for design using bolts and weld in connections. Specifications, design steps and design provision have been summarized for connections using codal provisions of different countries. Examples of connection have been solved. Comparisons of design strength of different components have been presented using Indian, British and American Standards.

To distinguish behaviour of steel structures using different types of connections, steel structure have been analysed by considering ideally pinned or rigid end conditions at end of beams. Shear connections are designed for shear force evaluated from analysis. These connections have been provided in place of pinned end conditions where only shear force is to be resisted by joints. Moment connections have been designed and provided for rigid end conditions where shear force and bending moments both are to be resisted. Actually, these connections have not been providing ideally pinned or ideally rigid end conditions. Behaviour of connections is in between two ideal conditions described as above. Connections in actual conditions provide variable stiffness and behave as a semi rigid connections. Stiffness in connections has been dependent on various size parameters of the connections.

It is important to understand behaviour of connections for safe and economical design of steel structures. A method of analysis and design has been employed for steel frames with semi-rigid connections using IS 800:2007 Provisions in major project. Analysis takes into consideration of non linear behaviour of beam to column connections.

Frye and Morris polynomial model has been used for modeling of semi-rigid connections as suggested in IS 800: 2007. Secant stiffness has been calculated for connections using Frey and Morris polynomial modeling equation. The secant stiffness values have been incorporated in analysis using STAAD Pro.2006 instead of assumed ideally rigid/pinned end conditions in frame. Design procedure of members has been conducted using the Indian standard provisions. Design process has been repeated for selected member cross-sections to obtain optimum weight for members. Design methodology for a frame with different types of connections has been presented to demonstrate efficiency of this method.

Comparison of design parameters has been made for different types of semi-rigid connections. Design parameters like end span bending moment, mid span bending moment, shear force, axial force, weight of column and beams, total weight of frames, time period and top storey displacements of frames have been taken in to consideration for comparison. It has been observed from parametric study that design with higher economy has been realized with semi-rigid connections by a variation of connection stiffness that balances span moments and to end moments in a beam. Change in stiffness of connections has been resulting in to variation in magnitude of sway for frame.