One member, two failure modes, two crews
A steel column is a single piece of stock that fails in two entirely unrelated ways depending on which end you are looking at. Along its length it buckles — it goes sideways under load long before the steel yields, and everything that governs that behaviour lives in geometry: the shape of the section, the distance between points where something holds it, and how truly plumb it was when you released the crane. At its foot it crushes — the load funnels down through a plate into concrete an order of magnitude weaker than the steel above it, and everything that governs that behaviour lives in area, flatness and contact.
That split runs straight through the schedule. The buckling end belongs to the erection crew with the theodolite and the guy cables. The bearing end belongs to whoever poured the pier and whoever mixes the grout, often a different contractor in a different week. A great many column problems are handoff problems between those two, and they surface as a load path that looks fine on paper and turns into a hairline crack in the pier six months later.
Reading the shop drawing, separate the information the same way. Section designation, unbraced length, cap detail and splice location are slenderness data — they tell you what the member needs from you while it is standing free. Baseplate dimensions, anchor pattern, grout thickness and plate thickness are bearing data — they tell you what the foundation needs from the plate. Column weight and pick point sit awkwardly between the two: they belong to rigging, but they also decide whether four anchor rods can hold a temporary load nobody calculated.
Sequence follows the same logic. Bearing gets set first because it cannot be adjusted afterwards, then slenderness gets managed continuously from the moment the column leaves the ground until the last brace is welded and the deck is on. Anyone who reverses that order — steel up fast, base fixed later — has committed to shimming and grouting under a loaded member, which is a repair rather than an installation.
The top end: what actually holds a column up
Buckling capacity has almost nothing to do with the strength of the steel and almost everything to do with unbraced length. Double the free length of a column and its buckling capacity falls sharply — the relationship is not linear and it does not forgive. That matters on site in a way it does not in an office: the engineer designed a column braced at every floor, and during erection there are no floors. The temporary condition is routinely the worst load case the member will ever see, and it is the one nobody hands you a drawing for.
Section shape carries the same story. A wide-flange column is strong about one axis and weak about the other; the weak axis picks the direction of failure, and it is the axis your temporary bracing has to cover. Square HSS is close to equal both ways, which is why it appears at exposed columns and long unbraced runs. Rectangular HSS reintroduces a weak axis and reintroduces the problem. Before rigging anything, know which way the section is soft and orient guys accordingly — two cables at ninety degrees, not two cables pulling the same axis because that happens to be where the anchors are.
Splices are unbraced-length events. A column shipped in two lifts is two slender members until the splice is complete and the connection developed, and a bolted splice left snug-tight is not the restraint a fully tensioned one provides. Do not release a crane on a splice that has not been made to the drawing, and do not let a bolt-up crew leave a tier half done because the shift ended.
Plumbing tolerance is not cosmetic. AISC 303, the Code of Standard Practice for Steel Buildings and Bridges, sets erection tolerances for column plumbness as a ratio of height with absolute limits, and the ratio exists because out-of-plumb creates eccentricity — the load no longer runs down the centroid, it runs down a lever arm. A column leaning within tolerance carries a small extra moment the designer accounted for. One leaning outside it carries a moment nobody did, and that moment lands in the baseplate below as uneven pressure. The two ends are linked: a slenderness error at the top becomes a bearing error at the base.
Weight enters here for two reasons. Rigging, obviously — pick point, sling angle, crane chart. Less obviously, temporary anchorage: four anchor rods sized for the finished structure are, during erection, resisting the overturning of a free-standing cantilever with real dead weight at the top. Wind on an unbraced tier is a genuine load and it has dropped steel. Knowing the true weight per foot of the sections you are standing lets you check the temporary case instead of assuming it.
Weight per foot is the number that decides your pick, your sling angle and whether four anchor rods can hold a free-standing tier in wind, so pull it in the laydown yard rather than after the column is in the air.
The tube's outer width.
The tube's outer height.
The tube's nominal wall thickness.
Weight per unit length
12.76 lb/ft
- Cross-sectional area
- 3.75 in²
They open the calculator with your figures already in it
HSS (Square/Rectangular Tube) Weight Calculator: 12.76 lb/ft — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Add the equipment this sizes
This result is a specification — 12.76 lb/ft — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
What this calculation does not cover
- The 7,850 kg/m³ (490 pcf) built into this is carbon steel and nothing else. The same outline in austenitic stainless is nearer 8,000 kg/m³ (499 pcf) and in aluminium about 2,700, so an aluminium section reads close to three times heavier here than it weighs. That gap matters most where the figure is feeding a lift plan, a temporary works check or a freight cost rather than a steel schedule.
- Weight is not a substitution rule. Two sections at the same mass per unit length can behave nothing alike — a deep thin-walled tube and a small thick-walled one of equal mass have very different second moments of area, section moduli and radii of gyration, and it is those, not the mass, that set deflection and buckling. Swapping in a section because it weighs about the same changes how the frame moves.
Bracing the free-standing condition
Temporary supports get treated as a formality and they are the reason erection stays legal. OSHA 29 CFR 1926 Subpart R, the steel erection standard, requires columns to be anchored to resist a specified minimum eccentric load applied at the top of the column shaft, and it sets a minimum number of anchor rods per column. Those provisions exist because unbraced columns have failed under nothing more than their own weight and a gust. Where a design shows fewer rods than the standard requires, that is a question to raise before the pour, not a field improvisation after it.
Guy cables want two things: an angle shallow enough to develop real horizontal restraint, and an anchorage that will not walk. Cables tied off to a slab edge, to rebar dowels, or to another unbraced column are decoration. Anchor to mass, tension both directions of the weak axis, and check tension after the first night — cables relax, temperature moves steel, and a guy that was tight at four in the afternoon is slack at seven the next morning.
Long HSS columns benefit from an intermediate restraint even where nothing in the permanent structure lands there, because halving the free length transforms the buckling condition. If the erection sequence leaves a column standing three storeys with no floor framing, a mid-height brace back to an adjacent bay takes an afternoon and removes the single most dangerous condition on the job.
Watch the weather window while surveying. Plumbing steel in gusty conditions produces readings that change while you take them; steel with full sun on one face and shade on the other reads differently at dawn than at noon. Surveyors who work the same time of day get repeatable numbers. Those who chase the instrument through an afternoon are chasing thermal movement, not error.
The bottom end: spreading load into concrete
Everything at the base comes down to one exchange: steel that will happily take tens of thousands of pounds per square inch handing off to concrete that will take a small fraction of that. The plate exists purely to spread the column load over enough area that the concrete beneath is not overstressed, and it has two variables — plan area and thickness. Area sets the average pressure. Thickness controls whether the plate stays flat enough to deliver that pressure across the whole footprint or dishes and dumps the load into a ring under the column shaft.
A thin plate under a heavy column is worse than a small plate, because the pressure distribution is no longer what anybody assumed. Corners lift, the concrete directly beneath the section crushes, and the failure shows as spalling around the pier edge rather than anything visible in the steel. When a submittal proposes a thinner plate than the drawing, that is a design change and it goes back through the engineer of record.
Concrete strength governs allowable pressure, and it is the value most often taken on faith. The pier may have been poured to a specified strength months earlier by another trade, cured through a cold snap, and never cylinder-tested at the age you are loading it. Confined bearing on a pier larger than the plate can be permitted to carry more than an unconfined edge condition under provisions in ACI 318, Building Code Requirements for Structural Concrete — but confinement requires concrete on all sides, and a plate set flush to the edge of an undersized pier has none of it. Measure the pier before you set. An edge distance shortfall is discovered cheaply with a tape and expensively with a crack.
Uplift and moment change the picture again. A base designed for pure compression assumes a uniform pressure block; introduce a moment from a braced frame or a wind-loaded canopy and part of the plate goes into tension, the anchor rods pick up that tension, and compression concentrates on the far edge at a much higher pressure than the average. Fixed bases with moment are a different detail entirely, and they are not interchangeable with pinned bases on site because the anchor pattern looks similar.
Standing at the pier with plate dimensions, column load and concrete strength in front of you, this is the check that says whether what is about to be set will overstress the concrete — while the answer can still be changed and before grout makes it permanent.
The total factored axial (compressive) load the column transfers to the baseplate.
The baseplate's footprint area in contact with the concrete.
The specified compressive strength of the supporting concrete.
The ratio of the supporting concrete area (A2) to the loaded baseplate area (A1).
Actual bearing pressure
453 psi
The bearing pressure under this plate is below the design bearing strength, with phi = 0.65 applied to the ACI nominal shown with it — ACI 318 gives it. The load compared here has to be a factored one, not a service load. Being under one limit is not a design. Nothing else is checked here — not the other limit states, not the connections, not the member the load arrives from.
- Nominal bearing strength Bn/A1
- 6,164.1 psi
- Design bearing strength phi*Bn/A1 (phi = 0.65)
- 4,006.67 psi
They open the calculator with your figures already in it
Steel Column Baseplate Concrete Bearing Pressure Calculator: 453 psi — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Add the equipment this sizes
This result is a specification — 453 psi — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
What this calculation does not cover
- The pressure reported is the axial load spread evenly over the whole plate, which is only true for a concentric load with no base moment. Once a column moment gives the resultant an eccentricity greater than one sixth of the plate length, the plate bears on part of its area only and the peak pressure at the compression edge rises well above the uniform figure shown here.
- The A2/A1 ratio is taken as typed and is never checked against real geometry. ACI permits the square-root term only where A2 is geometrically similar to and concentric with the loaded area, lies wholly within the support, and can be reached on a load spread no flatter than two horizontal to one vertical, so a shallow pier or a column set near a pier edge has a smaller usable A2 than its plan dimensions suggest.
- The comparison is made in LRFD terms: a factored load against a design strength with phi = 0.65. An allowable stress design check instead compares an unfactored service load against the nominal strength divided by AISC 360 J8's omega of 2.31, which this page does not calculate, so entering a service load against the phi-reduced strength shown here overstates the margin by roughly the load factor.
- The stress is checked against the concrete only, but where the plate is set on grout or shims it is the material at the plate face that governs first. Grout weaker than f'c, an incompletely filled pocket, or setting shims carrying load before the grout cures all reduce the contact area that the uniform pressure assumes.
- Bearing is a local crushing check on the concrete directly beneath the plate. It says nothing about the soil pressure under the footing, punching or one-way shear through the pier or footing, or the bursting reinforcement needed where the concentrated load spreads out, and a pier can satisfy this check while failing any of those.
Anchor rods: the one thing you cannot move
Anchor rods are set in wet concrete by people who will not be there when the steel arrives, and they are the most common cause of a stopped erection. ASTM F1554, the standard specification for anchor bolts in 36, 55 and 105 ksi yield grades, is the designation you will see called out; the grade drives capacity, and colour coding on the rod ends is how it gets verified in the field. Substituting a grade because the yard had it on the shelf is not a substitution anyone on site can make.
Layout accuracy is protected by templates, not by tape measures. A rigid template bolted to the formwork, checked on the diagonal and left in place through the pour, is the difference between a smooth set and a day with a torch. Rods tied to rebar cages migrate during concrete placement — vibration walks them, and a rod that started plumb finishes leaning. Check the pattern after the pour while the pour crew is still on site.
Oversized holes in the baseplate exist to absorb layout error and they have a limit. AISC 303 gives standard hole sizes and the corresponding plate washer requirements; those washers are structural, not incidental, because an oversized hole without one lets the nut pull through the plate. Field-cutting a hole larger to catch a misplaced rod destroys edge distance in the plate and must go to the engineer.
Projection is the second failure mode. Too short and there is not enough thread to develop the nut above plate and grout; too long and the rod fouls the column, the fireproofing or the finish. Where rods are galvanized to ASTM A123, the coating thickness means nuts must be tapped oversize and matched to the rods — mixing coated and uncoated hardware seizes threads halfway down and leaves a nut that will neither turn nor come off.
Correcting a mislocated rod is a repair with defined methods — chemically anchored replacements, plate extension, in some cases a redesigned pattern — and every one of them needs the engineer of record. Cutting rods off and welding new ones to the stubs is not a method. Where welding to an anchor rod is contemplated at all, weldability of the grade governs, and several F1554 grades are not intended for welding without supplementary requirements specified at the time of order.
Count the pattern against the template dimension while the pour crew is still standing there, because a rod short or a rod out of line is otherwise discovered by a crane rather than by a tape.
The baseplate's overall length (long side).
The baseplate's overall width (short side).
The maximum allowable spacing between anchor bolts around the perimeter.
How far the centre of a corner rod is held back from the plate edge.
Total anchor bolts
10 anchor bolts
- Bolts per long side
- 4
- Bolts per short side
- 3
- Pitch along each long side
- 0.56 ft
- Pitch across each short side
- 0.5 ft
They open the calculator with your figures already in it
Baseplate Anchor Bolt Pattern Layout Calculator: 10 anchor bolts — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
What this calculation does not cover
- The pattern assumed here is a uniform run of rods along all four plate edges. Many column bases instead put rods only outside the flanges in two rows, and a rod that this layout places behind the column section, a stiffener or a shear lug may have no room for a socket or spanner. The calculator does not check wrench access or clashes with the column profile.
- The only rule applied is the maximum spacing you enter, but anchor rod groups are normally governed by the opposite limit. Rods placed too close together have overlapping concrete breakout cones, which cuts the tension capacity of the group well below the sum of the individual rods, and distance to the concrete edge controls the same failure. Enter a small maximum spacing and this page will return a dense pattern with nothing checking that the rods are far enough apart, or far enough from the concrete edge, to develop their capacity; those minima come from the anchor design, typically ACI 318 Chapter 17.
- The edge distance is taken as given and is never checked. It is the figure that has to satisfy the plate — an oversized hole, a washer covering it, and a socket that can reach the nut — and separately the concrete, where distance to a pier face is what stops a breakout cone forming. Those are different numbers from different codes, and the larger of them governs; this page divides by whichever one you type.
- The two pitches are even divisions of each side, so they sit at or below the maximum rather than on it, and the long and short sides will usually differ from each other. Neither is a gauge line across the plate: the rods on the two long sides face each other at the plate width less twice the edge distance, and that cross dimension, along with which rod is the datum, still has to be put on the drawing by hand.
- Nothing about the rods themselves comes out of this calculation: no diameter, embedment depth, projection above the grout line, thread length, baseplate hole size or washer type. The number is also a pattern count rather than a purchase quantity, so it carries no spares for bent or misplaced rods, no template rods, and no levelling or double nuts.
Shims, leveling nuts and the grout that finishes it
Between the underside of the plate and the top of the concrete there is a gap, and how that gap gets filled decides whether the bearing calculation means anything. Two methods dominate: steel shim packs and leveling nuts. Shim packs are stacks of plate placed directly under the baseplate, adjusted until the column is level, and left permanently. Leveling nuts sit on the anchor rods below the plate and let elevation be dialled in by turning a nut. Both are valid; mixing them carelessly is not.
Shim packs must sit where the load is — under the column shaft footprint, not out at the plate corners — and must be wide enough not to punch into the concrete. Stacking a dozen thin shims to bridge a low pour gives a springy pack that shifts under load and is difficult to grout around. Where the gap is large, the answer is proper shim stock or a levelling course, not more shims.
Leveling nuts make the anchor rods carry the full column weight in bending until the grout cures, which is a real load case for slender rods under heavy columns. Where they are used, keep the gap small, get grout in promptly, and do not leave a heavy column standing on four rods for weeks.
Grout is a structural component. Non-shrink grout conforming to ASTM C1107, the specification for packaged dry hydraulic-cement grout, is what drawings normally call for, and non-shrink is the entire point: an ordinary sand-cement mix shrinks away from the plate and leaves a void exactly where pressure is highest. Placement matters as much as product — grout goes in from one side and flows across so air escapes ahead of it, never poured from two sides to trap a bubble under the middle of the plate. A vent hole in a large plate is cheap insurance.
Curing conditions govern the result. Grout placed onto a frozen pier, or into a form in direct summer sun with no protection, does not reach its strength; hot and cold weather placement requirements, along with the specified strength itself, vary by jurisdiction and by project specification, and the local building code adopting ACI 318 is what settles it. After cure, sound the perimeter — a hollow ring under a hammer means a void, and a void under a baseplate is an uncontrolled reduction in bearing area that no calculation covered.
Everything between the shaft and the pier
- Column shaft — the slender end of the member, whose weight per foot sets the rigging and decides what the anchor rods hold while the tier stands free HSS (Square/Rectangular Tube) Weight Calculator
- Baseplate — spreads a column load into concrete an order of magnitude weaker; plan area sets average pressure and thickness decides whether that pressure reaches the corners at all Steel Column Baseplate Concrete Bearing Pressure Calculator
- Shim pack — stacked under the column footprint rather than out at the plate corners, wide enough not to punch the concrete, and left permanently in place
- Non-shrink grout bed — a structural component, not a filler; placed from one side so air escapes ahead of the flow, and mixed by the bag against a pocket volume somebody has to know Baseplate Anchor Bolt Count & Grout Pocket Volume Calculator
- Concrete pier — confinement on all four sides of the plate is what earns the higher allowable bearing, so an edge distance shortfall here cancels an assumption made in the office Column Pier Size from Baseplate Edge Distance Calculator
Grout is mixed on the day and thrown away by the bag, so having the pocket volume in hand is what keeps a placement from being finished with a second, weaker batch.
The total factored uplift (tension) load the baseplate connection must resist.
The lowest governing rated tensile capacity for a single anchor, per ACI 318 Chapter 17.
The baseplate's plan (footprint) area.
The thickness of the leveling grout pocket beneath the baseplate.
Anchor bolts needed
4 anchors
Use the lowest governing rated tensile capacity for your specific anchor (steel strength, concrete breakout, or pullout per ACI 318 Chapter 17) — not an assumed value. AISC Design Guide 1 covers full baseplate/anchor rod design.
- Grout pocket volume
- 3.62 gal
They open the calculator with your figures already in it
Baseplate Anchor Bolt Count & Grout Pocket Volume Calculator: 4 anchors — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
What this calculation does not cover
- Dividing one total by one anchor's capacity assumes every rod pulls the same. A column base carrying moment does not work that way: the axial load and the moment together decide the tension, and it lands almost entirely on the rods to one side of the plate, so a group sized on a shared total can be two rods short where it counts and two rods idle where it does not.
- Says nothing about setting the rods. Anchor rods are cast before the column exists, located off a template, and the tolerance they have to land within is tight — a group placed out of position is the commonest problem on a steel job, and the remedy (oversized plate washers, a replacement plate, field welding) is an engineering decision rather than a site one, because it changes the load path the count assumed.
- The grout figure is a pocket volume, not an order. Bagged non-shrink grout is sold against a yield quoted at a stated consistency, and a flowable mix yields differently from a plastic one, so the volume converts to bags only through that product's own table — and the pocket has to be filled from one side with a head behind it, because a void left under a plate is exactly the bearing area the column was sized on.
Tolerance, inspection and the handoff
The two ends demand different verification. At the base you check flatness, elevation, full contact and anchor condition. At the top you check plumb, splice completion and bracing. Neither gets signed until the other is done, because they interact: a base set high or low throws the elevation of every beam framing into that column, and a column plumbed against an out-of-level base was plumbed against a moving reference.
Concrete tolerances and steel tolerances are written by different bodies and they do not match. ACI 117, the specification for tolerances for concrete construction and materials, governs where the pier surface lands; AISC 303 governs where the steel lands. The gap between them is absorbed by the grout space, which is why specified grout thickness is a design decision rather than a leftover dimension. Trimming it to save material removes the adjustment range the erector was counting on.
Welded base details, used instead of or alongside bolted connections, fall under AWS D1.1, the structural welding code for steel, and carry their own inspection requirements including qualified procedures and qualified welders. A field weld at a column base in a moment frame is not a tack weld task and should never be treated as one.
Document what you set. Anchor rod as-built positions, shim pack locations and thicknesses, grout batch and placement date, and final plumb readings are the record that answers questions two years later when a floor is reported out of level. Crews that photograph the base before grouting have evidence; crews that do not have opinions.
Close out by walking the same split the job opened with. Along the length: is every point the design assumed would brace this column actually built and connected, or is the member still leaning on temporary steel somebody is about to strike? At the foot: is the plate in full contact, is the grout sound, are the nuts at the specified condition, are the rods protected from corrosion where the detail requires it? A column that passes both questions is finished. One that passes only the second is still an erection, not a structure.
Before the crane picks
The short list that keeps both ends of the member honest — run it at the pier, not from the office.
- Pier dimensions and edge distance — Tape the pier before setting; confined bearing needs concrete on all sides of the plate, and an undersized pier removes that benefit entirely.
- Anchor rod grade, pattern and projection — Verify the F1554 grade marking, check the pattern against the template dimension, and confirm thread projection clears plate, washer and nut.
- Baseplate thickness against the drawing — A thinner plate than specified changes the pressure distribution, not just the takeoff; any substitution goes back to the engineer of record.
- Shim stock sized for the gap — Shims belong under the column footprint, wide enough not to punch the concrete; a tall stack of thin shims signals a bad pour rather than a fix.
- Non-shrink grout and a placement plan — ASTM C1107 material, one-side placement so air escapes ahead of the flow, and weather protection suited to the day.
- Temporary bracing and guy anchorage — Two directions covering the weak axis, anchored to mass rather than to another unbraced column, and re-tensioned the following morning.
Opens the calculators above on one screen with the dimensions from this article already filled in. Quantities only — this site publishes no price list, because local prices vary too much to publish honestly.