Calculation Software for Mechanical, Structural, Hobbyist Designers

Free! Bolt Stress Calculator


"Success is a by-product of consistently applying the fundementals"

Digitool creates user friendly, intuitive calculation software for design engineers, whilst making use of technology to improve accessibility. The software can be used anywhere in the world and on any device, be it a smart mobile phone, tablet or desktop computer providing there is an internet connection. No installation or licence is required and the software is up and running within seconds.

We offer web based calculation software for mechanical, structural and hobbyist designers. To date we have released a bolted joint calculator, which facilitates the design of tension, moment and torsion resisting joints. Combined loading is also supported along with arbitrary bolt positions and joint configurations. The software is based on calculation methods presented in the text book "Shigley's Mechanical Engineering Design" and in the German Industry Standard VDI 2230. Both texts assume that a bolted joint behaves like a set of springs in series and parallel. When a bolted joint is preloaded, the joint plates are compressed and the bolt is stretched. When an external working load is applied to the bolted joint, the load translated to the bolt is a function of the relative stiffness of the bolt and plate. Therefore, if compression exists in the joint plates, only a fraction of the external working load is transferred to the bolt. This theory is explained in more detail in the reference section of this website.

When designers analyse structures using finite element analysis (FEA) software, it is common practice to assume bolted joints are fully bonded. The forces and moments which are translated to these joints are extrapolated from the analysis and a side study is performed which usually takes the form of hand calculations. It is done this way to reduce the FEA model complexity and processing time. If the bolted joint was to be modelled with a high degree of fidelity, which is necessary for meaningful results, then there is a requirement to establish a set of non-linear contact conditions, which are laborious to define and slow to process. With the Digitool bolted joint software these joints can be analysed quickly and efficiently as a side study thus reducing the complexity of the modelling process and time overhead.

The next planned release is a welded joint design tool, which will also support combined loads and user defined weld runs. The software will enable the designer to efficiently size the leg length of the weld which may contribute to reduced welding costs and distortion. It is common practice in industry to assume that full penetration welds give the same strength as the parent metal and subsequently can be analysed as a fully bonded connection. However, the ability of a partial penetration or fillet weld to resist direct loads and moments depends on their effective throat length. A separate calculation can be performed using the extrapolated forces and moments from an FEA study to avoid the need for a complex and time-consuming analysis.

Designed to supplement commercial FEA software

Reduce processing time by separating out more rudimentary calculations such as bolted and welded connections.

Visual Stress Plots

Visual indications highlighting components with the highest stress levels


Designed using responsive web technology so the software will look as good on a mobile phone as it does on your desktop.

Reduces the need for repetitive hand calculations

Eliminates potential errors in creating hand calculations. Just check the inputs not the workings.