About Steel Connection Design Calculator
The steel connection design calculator evaluates bolted and welded connections for shear, bearing, tension, weld, and plate failure modes per EN 1993-1-8 and AISC 360. It is used by structural engineers to design fin plate, end plate, base plate, and bracing gusset connections and to identify the governing limit state.
Enter the design shear, axial, and moment, select the bolt group, weld, and plate configuration, and the tool returns the utilization for each check, the overall governing mode, and a pass/fail verdict that updates as you type.
How It Works
- Compute bolt shear, bearing, and tension resistances from the bolt grade, diameter, plate thickness, and edge/end distances per EC3 Table 3.4 or AISC J3.
- For eccentric loading, distribute the shear and moment over the bolt group using the elastic method to find the most heavily loaded bolt.
- Compute the fillet weld design resistance per unit length from the effective throat and either the EC3 correlation factor or the AISC directional method.
- Check the connection plate for gross/net section, block shear, and bending, then report the governing utilization across all modes with a pass/fail verdict.
Worked Example
An M20 grade 8.8 bolt (tensile area As = 245 mm2, fub = 800 MPa) with threads in the shear plane per EC3 gives a shear resistance Fv,Rd = 0.6 * 800 * 245 / (1.25 * 1000) = 94.1 kN per plane. A 6 mm fillet weld in S275 (fu = 430, beta_w = 0.85) has a throat a = 0.707 * 6 = 4.24 mm and capacity Fw,Rd = (430 / sqrt(3)) * 4.24 / (0.85 * 1.25 * 1000) = 0.99 kN/mm.
Formulas
- Bolt shear resistance (EC3)
Fv_Rd = alpha_v * fub * A / gammaM2- Bolt bearing resistance (EC3)
Fb_Rd = k1 * alpha_b * fu * d * t / gammaM2- Fillet weld resistance (EC3, simplified)
Fw_Rd = (fu / sqrt(3)) * a / (beta_w * gammaM2)- Combined shear-tension (EC3)
V / Fv_Rd + T / (1.4 * Ft_Rd) <= 1.0
Standards & References
- EN 1993-1-8 (Eurocode 3)
- AISC 360
Frequently Asked Questions
Which connection types can I design?
The calculator covers fin plate, flexible and extended end plate, flush end plate, base plate, and bracing gusset connections, checking bolts, welds, and plates for each.
How is an eccentric bolt group analyzed?
The tool uses the elastic method: direct shear is shared equally among the bolts while the moment produces a force on each bolt proportional to its distance from the group centroid. The bolt with the largest resultant governs the design.
Does threads-in-shear-plane affect the result?
Yes. With threads in the shear plane EC3 uses the reduced tensile stress area As; with threads excluded it uses the gross area Ab. AISC similarly switches between Fnv = 0.563*fub (threads included) and 0.75*fub (excluded).
What is the governing mode shown in the results?
It is the check with the highest utilization across all bolt, weld, and plate limit states, so you can see immediately whether the connection is controlled by bolt shear, bearing, weld capacity, block shear, or net section.