How to Read Support Reactions in STAAD.Pro

STAAD.Pro will print support reactions whether or not anyone can use them. A useful table needs units, global directions, the case or combination name, and a map from node number to the column mark on the drawing. Without those, civil receives FX, FY, FZ for node 118 and has to guess which way the building faces.

This article is the STAAD-specific companion to understanding column reactions in PEB design. If your PEB frames were sized in MBS, you may still be reading STAAD because a consultant asked for a check model. Do not issue both tables for the same revision. If MBS is the issue master, process that extract — StruTools MBS Reactions is built for that printout — and keep STAAD as a check you can explain.

Nothing here writes load-combination formulas. Which combinations appear is a design-basis decision, covered as process in load cases and combinations. The reading job is to report what this model actually produced, then review output before anyone draws footings.

Where STAAD.Pro reports support reactions

Reactions appear in post-processing tables and in printed output for the load cases you asked for. If you did not request the combination civil needs, it will not be there. If you requested everything, the table will include experimental cases you forgot to delete. Filter on purpose. The model checking pass should already have confirmed that supports sit on the intended joints.

Graphical arrows in the viewer are a sanity check, not an issue document. They hide units and they rotate with the view. Issue numbers from a table, with a sketch.

Global directions, local confusion

STAAD support reactions are typically in the global axis system. That is a gift if you documented which global axis is vertical and which way +X runs on the plan. It is a trap if the model’s vertical is Y and civil expects Z as vertical, or if the building was rotated relative to architectural north. Write the mapping once on the reaction sheet.

Sign convention

A positive global force on the support is the force of the structure on the support, or the opposite, depending on how you read the documentation for your version. Pick the interpretation, put arrows on a sketch, and stick to it. Do not flip signs “because the footing looks better.”

Moments at pinned supports

If the support is a pin, moments should be zero (or numerical noise). Non-zero moments mean the support is not the pin you drew, or you are reading a different node.

Cases, combinations and envelopes

A single load case is not a foundation design. Combinations are. Envelopes of combinations are maxima and minima that may not occur together. If you print an envelope, say so. If civil’s foundation model needs coincident FX, FY, FZ, MZ for one combination, print that combination. Do not hand-assemble a mega-row from different cases.

From node numbers to marks civil can find

Build a map: STAAD support node → column mark → grid intersection. Put the mark on the table. If two nodes share a base (a dirty duplicate), fix geometry first; do not add the reactions and hope. This mapping is the same discipline PEB teams use on column reaction packages.

• Every supported node appears once.
• Marks match the drawing you will issue with this table.
• Corner, braced-bay and crane columns are identifiable.
• Units on every page.
• Analysis filename and date in the header.
• Checker has compared one typical and one special support to the on-screen table.

When STAAD reactions disagree with MBS or with “engineering judgement”

Disagreement is a clue. Different fixity, different secondaries, different combinations, different units, or a duplicate node. Work the list. Averaging STAAD and MBS is not a method. If STAAD is only a check, document the comparison and still issue one master table, as argued in the PEB software guide.

If you use Excel to rearrange STAAD output, freeze the mapping row. Last job’s “FX is along the building” may not be true after a rotated model. Treat the workbook as a controlled extract, in the same spirit as MBS Reactions.

Producing a STAAD reaction table for issue

The printout is raw material. The issued table is a document.

1. Confirm supports, units and combinations in the frozen model.
2. Print or export reactions for the cases civil actually needs.
3. Map nodes to marks and grids.
4. Add axis sketch, units, envelope statement and filename.
5. Spot-check pinned moments, a gravity-only vertical sum where appropriate, and a windward uplift candidate.
6. Issue with the matching base plan revision.
7. Supersede previous tables in the same folder.
8. If geometry changes, repeat; do not edit numbers by hand in Excel.

Engineering tips

• If vertical reactions under gravity-only look smaller than the known steel plus cladding weight, look for missing loads or unit errors before looking at wind.
• Watch supports that report huge moments on a “pinned” job.
• Do not email a screenshot of the GUI table; it has no revision block.
• Keep service and strength on separate sheets if your civil team wants both.
• When a support is a spring, say so; the reaction is not a rigid-base reaction.
• Name experimental combinations so they cannot be selected in a tired export.

Misreadings that look like software bugs

Reading local member end forces as support reactions

End forces are in member axes and include the member’s own convention. Supports are at joints in global axes. Different objects.

Summing envelope maxima across a line of columns to “check equilibrium”

Those maxima are from different cases. Equilibrium is checked per case, not per envelope stew.

Dropping tension because the spreadsheet format was “compression only”

Uplift is information. Hiding it does not hold the building down.

Using STAAD node numbers on a civil drawing without a map

The contractor will not survey node 42. Give a mark.

STAAD support-reaction reading checklist

If you cannot tick these, you are not ready to issue.

• Supports sit on the intended joints.
• Global axis mapping is sketched.
• Units written.
• Combinations named from the design basis.
• Envelope versus coincident is stated.
• Node-to-mark map complete.
• Pinned supports show no meaningful moments.
• Uplift visible where expected.
• No experimental cases in the issued set.
• Filename and revision on the table.
• Matches the base plan being issued.

Frequently asked questions

Are STAAD.Pro support reactions in global or local axes?

Support reactions are normally reported in the global axis system. Member end forces are a different output. Confirm in the documentation for your version if you have custom print settings, and always put a sketch on the issued table.

Why is the moment not zero at a pinned base?

The support may not actually be pinned, you may be reading a nearby node, or you may be looking at an envelope that includes a fixed-base case. Check the support specification first.

Can I issue STAAD reactions for a PEB that was sized in MBS?

Only if the STAAD model is a true equivalent and you have chosen it as the issue master. Otherwise issue MBS reactions and keep STAAD as a documented check. See PEB column reactions.

What if civil wants reactions in service load combinations I did not run?

Add the combinations the design basis allows, rerun, and issue a new table. Do not factor strength results by a guessed ratio in Excel.

A reaction is only as clear as its axes and its name

Reading STAAD.Pro support reactions is a documentation problem as much as a post-processing problem. Global directions, units, combination identity, envelopes and node-to-mark maps turn a printout into something foundations can use. Without them, the numbers are trivia.

Use this with PEB column reactions and analysis output review. StruTools does not replace civil design or the project’s combination rules. When MBS is the PEB engine, MBS Reactions may be the cleaner extract path — still with the same annotation discipline.