Bolted Moment Connection

The purpose of this paper is to develop an understanding of how bolt preloads are distributed within a joint as each bolt is tightened in turn by the use of a calibrated torque wrench. It discusses how the order that the joints nuts/bolts are tightened can affect the final bolt preload. It also investigates the effect on incrementally increasing the bolt preload through a series of applications of the controlled torque tightening sequence.
Classical analysis methods are used to develop a method of analysis that can be applied to most preloaded bolted joints. It is assumed that the static friction coefficient is approximately 15% less than the dynamic friction.
It is found that the bolt preload distribution across the joint can range from slightly above the target preload to significantly less than the target preload. The bolts with a preload greater than the target preload are found to be those tightened towards the end of the tightening sequence, usually located close to the outer edges of the joint’s bolt array. The bolts with a preload less than the target preload are those tightened early in the tightening sequence, located centrally within the joints bolt array.
The methods presented can be used to optimise bolted joint design and assembly procedures. Optimising the design of preloaded bolted joints leads to more efficient use of the joints.

The purpose of this technical note is to develop an understanding of the influence of asymmetrical geometry within preloaded bolted joints. Classical analysis methods are applied to the analysis of preloaded bolted joints that use asymmetrical bolt group patterns. Both a detailed analysis of asymmetrical joints, using classical beam theory, and a less detailed design analysis are considered. The detailed analysis method is extended, using Rotscher's pressure cone, and is suitable to produce calculated bolt loads that can be used in a fatigue analysis. The design analysis provides a quick method of establishing the structural integrity of the asymmetrical joint. The detailed analysis method can be applied to the structure being connected by the bolted joint and the welds connecting the structure to the joint flanges. The design method is also appropriate for application to sprung suspension systems. The methods presented are suitable for use in automated procedures of calculation, such as spread sheets, MathCAD ©, SMathSutdio ©, etc.

The purpose of this paper is to present a paradigm, or guide, to the analysis of preloaded bolted joints made using multiple bolts. Classical analysis methods are applied to the interaction of the joint elements subjected to combinations of both in-plane and out-of-plane loads and moments. The distribution of the external loads and moments within the preloaded joint is determined in relationship to individual bolts. An analysis of loads and stresses in individual bolts and dowels along with flange bending and thread shear in tapped or threaded holes is developed. The article brings together a number of concepts and links them into a practical design analysis process that is applicable for many cases of preloaded bolted joints and are adequate to demonstrate the structural integrity of each element of the joint. Interpretation of results, within the context of design standards, is provided. In some cases finite element methods may be more appropriate, and the methods discussed can be used in the validation process.

Classical analysis methods are applied to show how flexural deflections due to shear strain in the flange pack produce bending moments and tensile loads on bolts within preloaded bolted joints. It was found that in joints made with long bolts these loads can be significant. The loads can cause yielding of the bolt, reducing bolt preload. The methods presented are adequate to demonstrate the structural integrity of joints made with long bolts or with a small footprint.

This paper will present a general design method for single or multi-bolt connections of beams with arbitrary thin-walled cross sections, suitable for application in computer programs. The design method is based on the classical strain iteration algorithm for cross sections, which is described in [6]. In this method, the ultimate capacity of bolted connections will be obtained using an iterative numerical determination of the elastic-plastic stress distribution in the connection elements. The numerical method will be derived in two steps – the numerical determination of the stress distribution in the connection for a given combination of internal forces and – the determination of the ultimate capacity of the connection. Furthermore analytical design formulas for a multi-bolt tube connection will be derived. Finally results of numerical and analytical calculations will be compared with corresponding test results.