How the bolted connection calculator works
This free bolted connection calculator checks a group of high-strength bolts in shear by AISC 360-22 §J3 and the instantaneous center of rotation method of the AISC Steel Construction Manual, Part 7. Choose the bolt size and grade, the hole type and whether the joint is bearing-type or slip-critical, then set the bolt pattern, the eccentricity and angle of the load, and the connected plate. Enter shear and tension by load case and the calculator checks every ASCE 7-22 combination in LRFD or ASD.
What it checks
- Bolt shear strength φFnvAb for Group A (A325), Group B (A490) and A307 bolts with threads included or excluded, in single or double shear
- Bearing and tearout at each bolt hole, 1.2lctFu ≤ 2.4dtFu, with the clear distance from the hole size of Table J3.3
- Eccentric shear by the instantaneous center method with the Crawford and Kulak load-deformation curve, solved in two dimensions so any load angle works, plus the elastic method for comparison
- Slip resistance for Class A and Class B surfaces, including the reduction for applied tension
- Combined tension and shear in bearing-type bolts by Eq. J3-3
- Block shear and shear yielding and rupture of the connected plate, and minimum spacing and edge distances
Method
The bolt group strength is C times the strength of one bolt, where the coefficient C comes from the instantaneous center of rotation. The calculator finds the center by Newton iteration so that the bolt forces balance the applied load in both directions and in moment, the same method used to build Tables 7-6 to 7-13 in the AISC Manual. For a concentric load, the strength is the sum of the individual bolt strengths, so edge bolts with lower tearout strength are counted correctly.
Assumptions and limitations
- Rectangular bolt patterns of up to 12 rows and 4 columns in one connected ply. Check the other connected parts separately.
- Prying action, filler plates, welds and the strength of the supporting member are not included.
- For eccentric loads, every bolt is assigned the lowest single-bolt strength, as in the AISC Manual tables.
Frequently asked questions
What is the coefficient C for an eccentric bolt group?
C is the effective number of bolts. Multiply it by the strength of one bolt to get the group strength. It equals the number of bolts for a concentric load and drops as the eccentricity grows. The calculator reports both the instantaneous center and the elastic values.
What is the shear strength of a 3/4 in. A325 bolt?
With threads included in a single shear plane, Fnv = 54 ksi and Ab = 0.442 in², so φrn = 0.75 × 54 × 0.442 = 17.9 kips (LRFD). Bearing or tearout at the hole may control, depending on the plate thickness and edge distance.
When are slip-critical bolts required?
Use slip-critical joints when slip would harm the structure: oversized or slotted holes parallel to the load, fatigue loading, joints with reversing loads and some seismic connections. They must also meet the bearing-type strength checks.
Does it include prying action?
No. Tension is shared equally by the bolts. For hanger and tee-stub connections, check prying with AISC Manual Part 9.
Related calculators
For educational and preliminary design purposes only. Always verify results with a licensed PE.