An adjustable post support uses a threaded member or slotted connection to accommodate alignment during installation. The section drawing shows a threaded support and separate compression and uplift load cases. Explore how rod area, yield strength and a selected divisor affect a simple axial-yield comparison; the results are not a rating for the complete post connection.
Adjustable Post Hanger Interactive Calculator
Vary threaded-rod area, yield strength, safety factor, compression and uplift load to compare each load with an axial-yield allowance. This does not rate the complete hanger.
Equation Used
The calculator divides threaded-rod stress area A_t times yield strength F_y by the selected factor Omega. Both load cases are compared with that same axial-yield allowance. Compression can instead be limited by buckling; threads, plates, anchors, fasteners and the supporting material require separate checks.
- Only rod axial yield is calculated; another part of the connection may govern.
- Loads are treated as concentric axial compression or tension.
- The illustrative default stress area is 0.334 in^2; confirm the actual thread and material properties for a real rod.
- The default divisor is Omega = 2.0 for this illustration; it does not establish compliance with a design standard.
How the adjustment works
In the illustrated threaded support, a nut establishes the position of a plate along a rod. Other post bases use slots to accommodate position during installation. These are different forms of adjustment: a slotted anchor connection does not necessarily provide a screw-operated height adjustment.
Once installed, the connection must transfer its specified loads through the post, saddle or plate, rod, fasteners and supporting structure. Compression, uplift, shear and bending do not follow identical load paths and cannot share one assumed assembly rating.
Main parts
- Post saddle or bearing plate: connects to or supports the post.
- Threaded rod and nuts: provide the illustrated adjustment and axial load path.
- Washers and locking hardware: distribute bearing forces and secure the specified assembly.
- Base plate and anchors: transfer loads to the supporting structure.
- Supporting material: timber, steel, concrete or another substrate that also needs an appropriate connection design.
Adjustment travel, thread engagement, rod exposure, hardware and locking details must come from the chosen design. Do not infer permission to adjust a loaded structure from the presence of a threaded rod.
Where adjustment is useful
Adjustment can help align posts or supports when installation dimensions vary. Possible applications include timber framing, equipment supports and purpose-designed levelling assemblies. The required connection depends on the actual loads, bracing, foundation and environment.
For a specific example of a different adjustment arrangement, Simpson Strong-Tie’s ABU installation guide describes a slotted post base with a standoff. Its installation and ratings must be taken from the specific product documentation; the threaded-rod drawing and calculation here do not describe or rate that product.
A base with several bolts is not automatically a moment-resisting connection. Rotation restraint, uplift and lateral resistance require their own documented design. The APB manufacturer’s guidance, for example, explicitly limits use where posts lack top support.
The axial-yield comparison
The displayed equation is P_allow = A_t × F_y / Ω. Here A_t is the entered stress area, F_y is yield strength and Ω is the selected divisor. With area in in² and strength in psi, the result is lbf. With area in mm² and strength in MPa, it is N.
For either entered load, utilization = load / P_allow × 100%. Reserve capacity is the calculated allowance minus the larger of the separate compression and uplift loads. It is not capacity reserved in a certified product.
This expression addresses axial yielding only. It does not calculate compression buckling, combined bending, thread stripping, plate deformation, fastener failure, anchor failure or the strength of wood and concrete. In particular, a long exposed rod in compression can buckle before its material reaches yield strength.
A result below 100% means only that the entered load is below this calculated allowance. It does not select a rod, establish code compliance or approve the complete connection.
Worked example: two separate axial loads
Use illustrative inputs A_t = 0.334 in², F_y = 105,000 psi and Ω = 2.0. Compare a compression load of 9,500 lbf and a separate uplift load of 3,200 lbf. No particular building, rod product or foundation is being specified.
- Axial-yield allowance = 0.334 × 105,000 / 2 = 17,535 lbf.
- Compression utilization = 9,500 / 17,535 × 100 = 54.2%.
- Uplift utilization = 3,200 / 17,535 × 100 = 18.2%.
- Reserve against the larger entered case = 17,535 − 9,500 = 8,035 lbf.
Changing only stress area to 0.226 in² reduces this allowance to 11,865 lbf; changing it to 0.606 in² raises it to 31,815 lbf. Those comparisons show the equation’s linear dependence on area. They do not decide which rod or support is suitable.
For an 18,000 lbf load, the original allowance gives 102.7% utilization. This exceeds the selected allowance; it does not mean that material yield begins exactly at 100%, because the allowance already includes the divisor. All other connection and stability checks remain necessary.
Comparing support arrangements
| Arrangement | Adjustment principle | What needs checking |
|---|---|---|
| Threaded support | A nut or screw establishes position along a thread | Rod exposure, engagement, locking and all applicable load cases |
| Slotted post base | Slots allow installation positioning before fastening | Permitted slot movement, fasteners, anchors and published capacities |
| Fixed or fabricated saddle | Position established by its fabrication and mounting | Fit, bearing, welds or fasteners and the complete load path |
Load rating, adjustment range, corrosion protection, cost and service life are specific to a product and installation. No general capacity or lifetime follows from the support type alone.
Adjustable post-support questions
Can I adjust the support while the post is loaded?
Only when the specific support and an appropriate procedure permit it. A threaded adjustment feature is not evidence that the assembly is a lifting jack. Changes to a loaded structure need a suitable support and load-transfer plan; this calculator does not provide one.
Does a utilization below 100% mean the hanger is suitable?
No. It means the entered axial load is below A_t × F_y / Ω. Buckling, threads, plates, anchors, fasteners, bending and the supporting material are outside this calculation.
Does a four-bolt base automatically resist overturning moment?
No. Bolt count alone does not establish rotational restraint or stability. Use the documented capacities and conditions for the complete connection, including the post and foundation.
Which washers and locking parts should I install?
Use those specified for the chosen support, anchor and fastener system. Their dimensions and material affect bearing and locking; the axial-yield equation cannot select them.
Does gradual settlement identify rod creep?
No. Movement can arise in the support, fasteners, timber, bearing surfaces or foundation. Record the movement and have the load path assessed before adjusting or modifying a structural connection.
Does the calculator check wind or earthquake resistance?
No. The uplift input is a separate axial load comparison only. Lateral forces, load combinations, ductility, anchorage and the applicable design requirements need a complete structural assessment.
References & Further Reading
- Wikipedia contributors. Post (structural). Wikipedia
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