Wood Column Design Step by Step - Tall Wall with Wind + Axial (NDS 2024 Worked Example)

Introduction

0:00A column in a tall exterior wall is the most under checked member in light commercial framing. It looks like a post, so it gets checked like a post: axial load over allowable stress, done. But it is holding up a twenty two foot wall that the wind is pushing on, and NDS 2024, section 3.9.2 says the compression and the bending amplify each other. We are going to take one column all the way through, by allowable stress design, and then enter the same design in the software and confirm it matches, number for number.

0:32Here is the whole point of this example in two numbers. Check the axial load alone, NDS 3.7, and the worst gravity case comes in at zero point two eight three. Twenty eight percent of capacity: a comfortable looking post. Run the combined check instead, section 3.9.2, equation 3.9 dash 3, and the same column on the same day comes in at zero point eight four two. Three times the axial ratio.

0:57And it is worse than a missed margin. Drop one size, to an eight by eight, and the axial number still reads a reassuring zero point three five four while the real ratio is one point five one zero. That is a failure, fifty one percent past the limit, that an axial only check never sees at all. One note before we start. Every number in this example was produced by the same calculation chain that runs StructSuite's Wood and Steel Column module, and the agreement between the two is locked by an automated regression test. At the end of this video we will enter the design in the app and watch it reproduce every one of these results.

The structure - what we are designing

1:35Here is the structure. A heated shop and storage building with a twenty two foot clear wall height. The proportions of a gym, a sanctuary, an apparatus bay or an equipment barn. The long walls are framed with eight by ten Douglas Fir-Larch timber columns at eight feet on center, running full height from the sill to the roof girder line. Horizontal girts span the eight feet between columns and carry the wall panel, and the roof girders land on the columns.

2:01Both panels are drawn to the same scale, nine pixels to the foot. On top, the elevation along the wall, with the eight foot tributary strip of the column we are designing shaded in green. Underneath, a section through that column. Snow, three thousand pounds, and dead, three thousand two hundred pounds, come down the axis. The red comb across the height is the wind: two hundred and twenty seven pounds per foot, which is twenty eight point four pounds per square foot acting over eight feet of wall. The dashed blue curve is the deflected shape, one point zero three inches at midheight, drawn exaggerated. Pinned top and bottom, K sub e equals one point zero, both loads concentric on the axis. Keep this picture — almost every number that follows is measured off it.

2:43So each column does two jobs at once. It carries the roof girder reaction down, and it spans twenty two feet vertically as a beam against wind pressure on its eight foot strip of wall. That is what makes it a beam column rather than a post, and it is why one check is not enough.

The one idea - what makes a column a beam-column

2:59Before any arithmetic, the one idea the whole example rests on. Take the wind away and this is a slender post: find its slenderness, get the column stability factor out of equation 3.7 dash 1, compare f sub c to F prime sub c. Put the wind back and two things change, both in the wrong direction. First, a moment appears — twenty two feet of wall pushing on one column line is eight thousand two hundred and forty pound feet at midheight, bending stress the axial check has no slot for. Second, the axial load makes that moment worse: the column is already bowed out of plane by the wind, so the compression rides that bow and adds curvature. That is the P delta effect, and NDS 2024 handles it in closed form with the one minus f sub

3:42c over F sub c E one term in the denominator of equation 3.9 dash 3 — an amplifier that grows as the compression approaches the buckling stress in the plane of bending. Which brings up the fact that decides this design, and the one most likely to be got wrong on a rectangular column. It has two slenderness ratios, and they do two different jobs. The larger one sets the column stability factor, and therefore the axial capacity. The one in the plane of bending sets F sub c E one, and therefore the moment amplifier. On this column they differ by twenty seven percent, which means F sub c E one is five hundred p s i while the buckling stress behind the stability factor is only three hundred and twelve. Use one number for both and the interaction check is wrong.

4:30Left panel: the weak axis, in the plane of the wall. No lateral load there — pure buckling across the seven and a half inch width. Two sixty four over seven point five is thirty five point two, the larger ratio, and F sub c E on that axis is three hundred and twelve p s i. Right panel: the strong axis, out of the wall, the plane the wind bends it in, across the nine and a half inch depth. Two sixty four over nine point five is twenty seven point eight, and that is the ratio behind F sub c E one, five hundred p s i. And the bottom panel is the section in plan, drawn to scale: the wind comes at the seven and a half inch face, and the nine and a half inch depth is the one

5:06doing the bending work. Four rows of girts frame into both faces of every column, so the obvious objection is that the column is plainly held at those points. It is not. Girts that span column to column are relative bracing: they hold the columns a fixed distance apart, but they do not hold any one of them still. In the buckling mode that actually threatens this wall — every column bowing the same way at the same moment — the girts neither stretch nor shorten, so they never pick up a pound of load.

5:36They become bracing only when the line they form runs to something that does not move: a braced bay, an end shear wall, a connection into the roof diaphragm. Only then does NDS Appendix A point eleven ask whether the girts and their connections carry the accumulated brace force, roughly two percent of the column compression, without slipping. A girt sized to hold wall panel against wind, screwed through a lap, has usually been asked neither question. So the honest model is a column unbraced over its full twenty two feet about both axes.

Inputs - where each parameter comes from

6:07Now the inputs — every one of them. Every input is either a code prescribed value with its section cited on the row, or a takeoff from the framing plan. Nothing is a guess. The height, twenty two feet, pinned top and bottom, so K sub e is one point zero — Appendix G Table G one, mode d: the base is a bearing and anchor connection, the top is a girder seat, and neither is a moment connection. The member, an eight by ten Douglas Fir-Larch timber, grade number two, Posts and Timbers: seven and a half by nine and a half dressed, seventy one point two five square inches, a section modulus of one hundred twelve point eight, a moment of inertia of five hundred thirty five point nine. Five by five and larger is a timber, so the design values come from Supplement Table 4 D, not 4

6:50A — and the size class is Posts and Timbers because the nominal width does not exceed the thickness by more than two inches. Then the loads: three thousand two hundred pounds of dead, three thousand of snow, and two hundred twenty seven pounds per foot of wind on the strong axis. Dry service, under one hundred degrees, not incised. And the sill is Hem-Fir number two — because bearing is checked on the sill's compression perpendicular value, four hundred and five p s i, not on the column's six hundred twenty five.

7:20The dead load takeoff. Roof — panel, purlins, insulation, ceiling — twenty pounds per square foot over a ninety six square foot tributary, eight feet by twelve, is one thousand nine hundred and twenty pounds. Wall — girts, panel, insulation, liner — seven pounds per square foot over one hundred seventy six square feet, eight feet by twenty two, is one thousand two hundred and thirty two. Total three thousand one hundred fifty two, entered rounded to the nearest hundred: three thousand two hundred pounds. And below the line, the column's own weight, seventeen point three pounds per foot over twenty two feet, three hundred eighty one pounds — added by the module, not entered by you.

7:57And the snow. ASCE 7-22, section 7.3, with a strength level ground snow load of fifty pounds per square foot, an exposure factor of zero point nine for Exposure C with a fully exposed roof, a thermal factor of one and an importance factor of one. Zero point seven times zero point nine times fifty is thirty one point five pounds per square foot, and the roof is low slope, so the sloped roof snow load is the same number. Over ninety six square feet that is three thousand and twenty four pounds, entered as three thousand.

Step 1 - Wind on the wall: from basic wind speed to plf

8:28Step one. Turning a wind speed on a map into pounds per foot on this column. First, which chapter. A wall column that carries only its own strip of wall and delivers it to the roof diaphragm and the foundation is a component, not part of the main wind force resisting system. So it is designed by ASCE 7-22, Chapter 30 — components and cladding — not Chapter 27. That matters, because components and cladding pressures are higher: the same wall run on MWFRS coefficients would give a noticeably smaller line load.

9:02The velocity pressure. Zero point zero zero two five six, times the velocity pressure exposure coefficient — zero point nine three, at a mean roof height of twenty four feet in Exposure C, from Table 26.10 dash 1 — times a topographic factor of one for flat ground, times a directionality factor of zero point eight five, times a ground elevation factor of one, times the basic wind speed squared. One hundred and fifteen miles an hour, Risk Category two. That comes to twenty six point eight pounds per square foot.

9:33Next, the effective wind area — and note it is not simply the tributary area. ASCE 7-22, section 26.2 defines it as the span times the greater of the spacing and one third of the span. Twenty two feet times the greater of eight and seven point three three is one hundred and seventy six square feet. That area is what you take into Figure 30.3 dash 1, wall Zone four, and log interpolate between minus one point one at ten square feet and minus zero point eight at five hundred: the external pressure coefficient is minus zero point eight eight. The internal pressure coefficient is plus or minus zero point one eight for an enclosed building.

10:13The design pressure is the velocity pressure times the external coefficient minus the internal one: twenty six point eight times minus zero point eight eight minus zero point one eight, which is minus twenty eight point four pounds per square foot. Suction governs — the pressure case is plus twenty five point seven — and the section 30.2.2 floor of sixteen pounds per square foot is comfortably cleared. Multiply by the eight foot wall bay this column line carries and the line load is two hundred and twenty seven pounds per foot.

10:42Two things about that number are easy to get wrong. First, it is a strength level load: ASCE 7-22 pressures come from the ultimate wind speed map, so two hundred and twenty seven pounds per foot is the load that gets multiplied by zero point six in the allowable stress design combinations. Enter the full two hundred and twenty seven and let the combination provider apply the zero point six — entering one hundred and thirty six because it is ASD double counts the factor. Second, suction governs, and it does not matter which way it points: the section is symmetric, so the design is set by the larger magnitude, and the module generates the plus and minus pairs and reports both.

Step 2 - Load combinations, each with its own CD

11:23Step two. The load combinations — nine of them — and the detail that makes picking a worst case by eye unreliable. Nine allowable stress design combinations come out of section 2.4.1, and three details matter more than the arithmetic. Wind enters at zero point six W, ASD's conversion from the strength level map. Snow enters at zero point seven S, because ASCE 7-22 moved to strength level ground snow — so the module writes D plus zero point seven S, not D plus S. And the load duration factor is per combination, from NDS Table 2.3.2: zero point nine for dead only, one point one five for the two month snow cases, one point six for anything containing wind. Capacity and demand both move from row to row, which is exactly why a worst load case picked by eye is unreliable.

12:14Here they are, with the plus or minus wind pairs collapsed onto one row each. One a, dead alone: three thousand five hundred eighty one pounds at zero point nine. Three a, dead plus zero point seven snow: five thousand six hundred eighty one pounds at one point one five, the largest axial load in the whole set. Four a: five thousand one hundred fifty six. Five a, dead plus or minus zero point six W: the same three thousand five hundred eighty one of axial, a duration factor of one point six, and a lateral factor of zero point six that turns two hundred twenty seven pounds per foot into one hundred thirty six point two.

12:46Six a, the mixed case, at a lateral factor of zero point four five — one hundred two point two pounds per foot — on five thousand one hundred fifty six pounds of axial. And seven a, zero point six D plus or minus zero point six W: the full lateral load riding on only two thousand one hundred forty nine pounds. Dead here includes the three hundred eighty one pounds of self weight. And note that three a, with the largest axial load in the set, is not the one that designs this column.

Step 3 - Slenderness

13:16Step three. Slenderness — the two ratios we met earlier, worked out. Back to the section, because the only two numbers this step needs are on it: the twenty two foot height, and the fact that nothing braces the column between its ends. The effective length is the effective length factor times the actual length: one point zero times twenty two feet, two hundred and sixty four inches. And it is the same both ways, because the column is unbraced over its full height about both axes. What differs between the two axes is not the length. It is the dimension you divide it by.

13:51So: the weak axis, y y, in the plane of the wall, divides two hundred sixty four by the seven and a half inch width and gets thirty five point two. That is the larger ratio, it governs, and it is the one that sets the column stability factor through F sub c E equals zero point eight two two times E prime sub min over the ratio squared — three hundred eleven point eight p s i.

14:10The strong axis, x x, out of the wall, divides two hundred sixty four by the nine and a half inch depth and gets twenty seven point eight. That is the plane of bending, and it sets F sub c E one in equation 3.9 dash 3: five hundred point three p s i. Two consequences. First, thirty five point two is under the code limit of fifty, so this column is permitted. StructSuite blocks Step five outright above fifty rather than printing a ratio for a column the code does not permit — and at this height an eight by eight would also be at thirty five point two, but a six by ten would be at forty eight point zero, uncomfortably close to that wall. Second, the ratio between the two buckling stresses: thirty five point two over twenty seven point eight, squared,

14:55is one point six zero. F sub c E one is sixty percent higher than the F sub c E behind the stability factor, purely because the column is deeper in the direction the wind bends it. That is the whole reason a rectangular section is the right shape for this job.

Step 4 - Reference values: Table 4D, and which half of it

15:11Step four. The reference design values — and a table split that has teeth. An eight by ten is seven and a half inches by nine and a half dressed. Both dimensions are five inches nominal or greater, so this is a timber, and timbers read NDS 2024 Supplement Table 4 D — never Table 4 A, which covers two to four inch dimension lumber. And Table 4 D then splits again, into Posts and Timbers and Beams and Stringers.

15:37Here is what those three readings give you, for the same species and the same grade. Bending: nine hundred p s i on Table 4 A, seven hundred and fifty on 4 D Posts and Timbers, eight hundred and seventy five on Beams and Stringers. Compression parallel to grain: one thousand three hundred fifty, seven hundred, and six hundred. Minimum modulus: five hundred eighty thousand on 4 A, four hundred seventy thousand on both halves of 4 D.

16:00An eight by ten is Posts and Timbers; an eight by twelve is Beams and Stringers. Going one size up changes which row of the table you are reading, not just the section properties — and it changes the compression value in the unhelpful direction. StructSuite ties the two selections together: the table you pick drives which Table 1 B size classes are selectable, and within 4 D the grade list is filtered to the class the chosen section belongs to, so a Posts and Timbers section can never quietly design on Beams and Stringers values.

16:32So the values this design actually uses. Bending, seven hundred and fifty p s i. Compression parallel to grain, seven hundred. Shear, one hundred and seventy. Compression perpendicular to grain, six hundred and twenty five — that is the column's own value, and we will come back to why it is not the one the bearing check uses. Modulus of elasticity, one point three million. And the minimum modulus for stability, four hundred and seventy thousand.

17:00And the adjustment factors. Dry service and normal temperature leave the wet service, temperature and incising factors all at one point zero. The size factor is one point zero on both the compression and bending values: Table 4 D tabulates timbers directly, and the twelve over d to the one ninth size factor only appears above twelve inches of depth. The beam stability factor is one point zero, because the compression edge in the plane of bending is held by the girts and the wall panel along its full length, section 3.3.3.3. And the repetitive member factor does not apply at all: 4.3.9 grants it only to dimension lumber two to four inches thick. The module does not merely leave it at one here; it does not offer the control, because there is no reading of Table 4 D under which this section

17:43could earn it.

Step 5 - Column stability CP

17:48Step five. The column stability factor — and a result that surprises people the first time they see it. F sub c E depends only on stiffness and slenderness, so it is one number for the whole design: zero point eight two two times four hundred seventy thousand, over thirty five point two squared, is three hundred eleven point eight p s i. F sub c star, on the other hand, carries the load duration factor — so the stability factor itself is different in every combination family.

18:17Dead only, at a duration factor of zero point nine: F sub c star is six hundred and thirty, the ratio is zero point four nine five, the stability factor is zero point four three zero, and the usable compression value is two hundred seventy point nine. Dead plus snow, at one point one five: eight hundred and five, zero point three eight seven, zero point three five zero, two hundred eighty one point five. And anything with wind, at one point six: eleven hundred twenty, zero point two seven eight, zero point two six zero, two hundred ninety one point three.

18:50Read those three rows again. Going from the snow case to the wind case raises F sub c star by thirty nine percent — and raises the usable F prime sub c by three point five percent, from two hundred eighty one point five to two hundred ninety one point three. Buckling does not care how long the load lasts, and equation 3.7 dash 1 knows it: as the duration factor pushes F sub c star up, the stability factor falls almost in step. If you have ever wondered why a tall post refuses to get better when you switch to a wind combination, this table is the answer.

19:23And it is worth knowing what bracing the weak axis would buy, before you detail it. Turn on Braced between the ends in Step one, put a designed brace at midheight so the weak axis length is eleven feet, and the stability factor at one point six rises from zero point two six zero to zero point three nine five — a fifty two percent increase in axial capacity. The governing design ratio moves from zero point eight four two to zero point eight two five. Two per cent. This column is bending governed, and only depth in the bending plane changes that. And note what a designed brace has to mean before you may enter it:

19:55blocking at the column faces is not a brace by itself, the line it forms has to reach an anchor. Blocking plus an anchored line is bracing, and you enter eleven feet. Blocking alone is carpentry, and you leave the toggle off.

Step 6 - Axial compression alone - the check that misleads

20:10Step six. The axial check on its own — the one that gets this column wrong. The worst axial stress is under dead plus zero point seven snow. Five thousand six hundred eighty one pounds over seventy one point two five square inches is seventy nine point seven pounds per square inch, against an allowable of two hundred eighty one point five — the snow row's stability factor of zero point three five zero at a duration factor of one point one five.

20:36Zero point two eight three. Every other row is lower. An axial only design stops here, records zero point two eight, and specifies an eight by ten with what looks like a three and a half times margin. Keep watching.

Step 7 - Combined bending + axial - this governs

20:50Step seven. The combined check — and this is the one that designs the column. The section again, because every number in this step comes off it: the twenty two foot height, the two hundred twenty seven pounds per foot of wind, and the pinned ends that decide what that wind does. For each wind combination the module takes the strong axis moment from the statics of the end condition you picked in Step one, converts it to bending stress, and runs the interaction. This column is pinned pinned, so that is w h squared over eight at midheight. The governing case is dead plus zero point six W, where the wind is scaled to one hundred thirty six point two pounds per foot. One thirty six point two times twenty two squared over eight is eight thousand two hundred and forty pound

21:30feet at midheight, and one thirty six point two times twenty two over two is one thousand four hundred and ninety eight pounds of shear at each end. The bending stress is the moment over the section modulus: eight thousand two hundred forty times twelve, over one hundred twelve point eight, is eight hundred seventy six point six pounds per square inch. The axial stress on this row is three thousand five hundred eighty one over seventy one point two five — only fifty point three. The adjusted bending value is the tabulated seven hundred and fifty times the duration factor of one point six, and nothing else, because every other factor is one: twelve hundred p s i.

22:08The adjusted compression value is two hundred ninety one point three. And F sub c E one — the strong axis value, in the plane of bending — is zero point eight two two times four hundred seventy thousand over twenty seven point eight squared, five hundred point three. Before the interaction, one gate. Equation 3.9 dash 3 is only meaningful while the axial stress stays below F sub c E one: as it approaches, the amplifier's denominator goes to zero and the amplified bending demand grows without bound, and at or above it the member has already failed by buckling in the plane of bending. Fifty point three against five hundred point three — far away, so the check is permitted. StructSuite reports a row that fails this gate as not permitted rather than printing a fictitious number, and

22:52that means resize, not re round. And the interaction itself. The axial ratio, fifty point three over two hundred ninety one point three, squared, is zero point zero three zero. The bending term is eight hundred seventy six point six, over twelve hundred times one minus fifty point three over five hundred point three — that denominator is one thousand seventy nine point four — which is zero point eight one two. Add them: zero point eight four two, under one point zero. And this is the governing demand over capacity ratio of the whole design.

23:27Read the anatomy of that number. The axial term, in amber, contributes zero point zero three zero — almost nothing, because it enters squared. The bending term, in blue, is zero point eight one two, essentially the entire design ratio, and it leaves zero point one five eight of margin to the one point zero limit. Now look at the second bar. Without the P delta amplifier the bending ratio would be zero point seven three one. Dividing by one minus fifty point three over five hundred point three — dividing by zero point nine zero zero — pushes it to zero point eight one two. Fifty pounds per square inch of compression, only seventeen percent of this column's own axial capacity, adds eleven percent to the bending demand.

24:11The other wind rows land where the shape of the equation says they should. The mixed case, dead plus three quarters of zero point six W plus three quarters of zero point seven snow, has more axial and less moment, and comes in at zero point seven zero two. The uplift style case, zero point six dead plus zero point six W, keeps the full moment on the smallest axial load, and comes in at zero point seven eight eight. And notice the governing row carries only sixty three percent of the largest axial load in the whole set.

24:41And one warning that belongs with every beam column. Table G one is usually read as an effective length table, but the same restraints decide what a lateral load does to the member, and only two of the six modes give w h squared over eight. A fixed free cantilever, at two point one, carries w h squared over two at the base — four times this column's moment from the identical wind. Pinned fixed with sway, at two point four, the same, at the top. Fixed fixed with sway gives w h squared over three; fixed fixed with no sway, over twelve. The module reads the moment from whichever mode you picked and names the formula it used, so the pick that sets your slenderness also sets your bending.

25:18A freestanding porch or deck post is the case to watch — it is the one people habitually enter with a pinned pinned moment in mind. Zero point eight four two, and it passes — but it is three times the axial ratio we recorded two steps ago, on the same column, under the same code, on the same day.

Step 8 - Shear, and the diagrams

25:37Step eight. Shear — which the module draws but does not check on columns — and the diagrams. The module draws the shear diagram but does not run a shear check on columns, so here is the hand check. The end shear is one thousand four hundred ninety eight pounds; one point five times that over seventy one point two five square inches is thirty one point five pounds per square inch, against an allowable of one hundred seventy times one point six, two hundred seventy two. A ratio of zero point one one six. It is never close on a wall column, which is exactly why it is worth confirming once rather than assuming forever.

26:13And these are the four diagrams the module draws for the governing combination. Axial, growing from three thousand two hundred pounds at the top to three thousand five hundred eighty one at the base — the self weight adds three hundred eighty one on the way down. Shear, linear from minus fourteen ninety eight at the top, through zero at midheight, to plus fourteen ninety eight at the base. Moment, parabolic, peaking at eight thousand two hundred forty pound feet at midheight, which is the eight hundred seventy seven pounds per square inch we just used. And deflection, peaking at one point zero three inches, L over two hundred fifty six — shown, but not judged. Step nine is where we judge it.

Step 9 - Deflection

26:50Step nine. Deflection — a check the strength calculation does not make, and the one that can overtake it on a tall wall. StructSuite version one says so on the page, in as many words: lateral load deflection serviceability, the IBC Table 1604.3 limits, is not evaluated — strength checks only. The diagram is there so the number is in front of you; the limit is yours to apply. So let us apply it. The modulus is one point three million and the moment of inertia is five hundred thirty five point nine, and the midheight deflection of a uniformly loaded simple span is five w L to the fourth over three hundred eighty four E prime I.

27:30Three loads, three answers. The full components and cladding wind, two hundred twenty seven pounds per foot, gives one point seven one seven inches — L over one hundred fifty four, and that is reference only. The ASD wind, zero point six W, one hundred thirty six point two pounds per foot, gives one point zero three zero inches, L over two hundred fifty six — that is the number to use if the column supports glass edges, under IBC 2024 section 2403.3. And zero point four two W, ninety five point three pounds per foot, gives zero point seven two one inches, L over three hundred sixty six — which is the load footnote f of Table 1604.3 permits for deflection.

28:13And the limits themselves, at a length of two hundred sixty four inches. L over one hundred twenty, for exterior walls with flexible finishes — a metal panel, which is this building — is two point two zero zero inches against zero point seven two one used: a ratio of zero point three two eight. L over two hundred forty, for brittle finishes such as a gypsum liner, is one point one zero zero inches: zero point six five six. And L over one hundred seventy five with a hard three quarter inch cap, for framing supporting glass edges, is zero point seven five zero inches — against the full one point zero three zero, a ratio of one point three seven three. That one fails.

28:53Same column, same wind, three answers. Footnote f of IBC Table 1604.3 permits the wind load to be taken as zero point four two times the components and cladding load for deflection — that is where zero point seven two one inches comes from, and against a wall limit it is comfortable. Put a glass edge on this column and section 2403.3 applies its own limit, at the full design load, with a hard three quarter inch cap:

29:16the same eight by ten fails it by thirty seven percent. And the strength check does not move an inch between those three cases. Know which limit your wall actually has before you size the column, because on tall walls stiffness overtakes strength quickly.

Step 10 - Bearing on the sill

29:32Step ten. Bearing — the last check, and the one where the species that matters is not the column's. Compression perpendicular to grain belongs to the member being crushed — the Hem-Fir number two sill, at four hundred and five pounds per square inch out of Table 4 A, not the Douglas Fir column at six hundred and twenty five. Name the sill in Step five of the module and the check uses the right member. Five thousand six hundred eighty one pounds over seven and a half by nine and a half inches is seventy nine point seven pounds per square inch, against four hundred and five: a ratio of zero point one nine seven.

30:08Two details on that line. The bearing area factor is one point zero, not the one point zero five the formula would give: NDS 3.10.4 grants it only where the bearing length is less than six inches, and this column is seven and a half inches wide. The factor quietly disappears once the post gets big, which is the opposite of what most people assume. And the load duration factor never applies to compression perpendicular to grain — Table 2.3.2, footnote one — so the wind's one point six buys nothing here. Which is why the largest gravity combination, dead plus zero point seven snow, is the one that matters for bearing, even though a wind row governs everything else.

Six mistakes that show up on tall wall columns

30:48Before the summary: six mistakes that show up on tall wall columns. Every alternative here was run through the same engine, so the cost of each one is a real number, not a warning. One: checking the axial load and stopping. Zero point two eight three against a real zero point eight four two. The mistake is invisible because zero point two eight looks safe, and the load that causes it never appears in an axial load list. Any column that is also a wind column, a guardrail post or a braced bay end post needs the 3.9.2 check.

31:18Two: reading Table 4 A for a timber. Enter this eight by ten under the dimension lumber Douglas Fir-Larch species instead of Douglas Fir-Larch Timbers and it designs on nine hundred and one thousand three hundred fifty instead of seven fifty and seven hundred. The interaction then reports zero point six eight one — nineteen percent unconservative on a member already at eighty four percent. StructSuite gates the size list against the table you picked; a hand calculation has no such gate. Three: dropping one size to save a bit. The eight by eight — same species, same grade, two inches shallower — comes in at one point five one zero, fifty one percent past the limit, while its axial ratio still reads a reassuring zero point three five four.

31:57And a grade jump does not rescue it: the same eight by eight in number one still lands at zero point nine zero three. Four: reaching for depth without watching width. A six by ten has the same nine and a half inch bending depth and looks like a cheaper way to get there. It is not. The weak axis ratio jumps to forty eight point zero, within a whisker of the limit of fifty, F sub c E collapses to one hundred sixty eight pounds per square inch, the axial ratio alone climbs to zero point six seven five, and the interaction lands at one point one five six — a fail. On a tall column the narrow face is a real constraint, not a detailing afterthought.

32:35Five: claiming end fixity you have not detailed. Switching from one point zero to zero point eight on the strength of the base is bolted down moves the answer from zero point eight four two to zero point seven nine four. A six percent gain, for a claim that a base plate with two anchors cannot support. Six: stretching the same column taller. Height is brutal on a beam column, because it hits the moment through h squared, the amplifier through F sub c E one, and the stability factor, all at once. The same eight by ten: eighteen feet, zero point five three eight; twenty two feet, zero point eight four two; twenty six feet, one point two four eight, a fail; twenty eight feet, one point four nine nine. A four foot increase past this design turns a passing column into

33:15a twenty five percent overstress. Re run, never extrapolate.

Summary of results - 8x10 DF-L No. 2, 22 ft, W = 227 plf

33:20And the summary. Every check on one page. Combined bending plus axial, equation 3.9 dash 3, under dead plus zero point six W: zero point eight four two — it governs, and it passes. The uplift side case, zero point seven eight eight. The mixed case, zero point seven zero two. Axial alone, under dead plus zero point seven snow: zero point two eight three. Shear, zero point one one six, checked here rather than by the module. Bearing on the sill, zero point one nine seven. And wall deflection against L over two hundred forty, zero point six five six, again checked here. The column works, and it is a wind row carrying only sixty three percent of the largest axial load in the set that decides it. For completeness: dead alone is an axial ratio of zero point one eight six, and four a

34:06is zero point two five seven.

Now in StructSuite - entering the same column in the app

34:11Now let's enter this exact column in StructSuite's Wood and Steel Column module, starting from a completely blank project, and watch it reproduce every number we just found by hand.

App Step 1 - Geometry and end conditions

34:22Step one, Geometry and End Conditions. Blank. The first control in the step is the design material: Wood, to NDS 2024 by allowable stress design, or Steel, to AISC 360-22, by LRFD. The same module runs both, with Chapter E for axial capacity and Chapter F for flexure, combined per section H one with the Appendix eight B one moment amplifier — so you can enter this geometry once and compare an eight by ten timber against an HSS six by six on screen. We are staying on wood.

34:56Column height, unbraced length: twenty two feet. And the effective length factor, chosen by picking a buckling mode off NDS Table G one — the module draws all six, with the theoretical value and the recommended design value under each. We pick the fourth: pinned pinned, no sway, recommended K sub e of one point zero. This is not only a slenderness choice. As we saw, it is also what decides the moment the wind produces — and the step above it says so, naming the w h squared over eight formula that this pick carries.

35:30One toggle worth pausing on, precisely because we leave it off. Braced between the ends takes an unbraced length per axis, and zero means braced continuously — sheathing on a stud is the usual case. Leaving it off is what makes both axes read the full twenty two feet, which is the model this column honestly has. The description in the app says the same thing the guide did: sheathing, blocking or girts that are designed as bracing shorten the unbraced length in the plane they brace.

35:56Step one complete: twenty two feet, pinned pinned, unbraced both ways.

App Step 2 - Load definition

36:01Step two, Load Definition — the axial loads, and the lateral load that makes this a beam column. Blank, with two empty load rows and the ASCE 7-22 type list on each: D for dead, L for live, L r for roof live, S for snow, R for rain, W for wind, E for earthquake. This column only ever sees D and S on the axial side. Include column self weight is checked by default, and its own row sits underneath, grayed, saying From Step three. The moment we pick an eight by ten it fills in: seventeen point three pounds per foot times twenty two feet, three hundred eighty one pounds, added to D. That is the three hundred eighty one pounds the hand calculation carried in every row without ever typing it.

36:44The first row: type D, three thousand two hundred pounds — the roof and wall takeoff, rounded to the nearest hundred, exactly as the guide entered it. The second row starts as live load; we change the type to S for snow, and enter three thousand pounds. That one dropdown is what makes the combination provider write D plus zero point seven S instead of D plus L — and the zero point seven is the module's, not ours.

37:08And here is the control the whole example turns on: Lateral load on the column, bending about the strong axis. Wind on an exposed post or wall column, seismic on a cantilevered element, a guard load at the top of a deck post. The description states the rule explicitly — the moment follows from the end condition picked in Step one, and it names the formula that pick produces — and then the lateral case is checked together with the axial load in Step five, per NDS 2024 section 3.9.2.

37:38Its type is W, wind — and the type is not decoration: it is what carries the zero point six factor in ASD, the same way an E would carry zero point seven. The app says so on the row. Distribution: uniform over the full height, which is what a wall panel delivering wind to a column line actually does. The other option is concentrated at a height — a guard load on a deck post, say — and the module warns you if you place it above the top of the column.

38:07Two hundred and twenty seven pounds per foot. The full strength level load, exactly as the guide insisted: the module applies the zero point six itself, in every combination that contains W. Step two complete: three thousand two hundred pounds of dead, three thousand of snow, self weight on, and two hundred twenty seven pounds per foot of wind across the height.

App Step 3 - Material and section

38:29Step three, Material and Section — and this is where the Table 4 A versus Table 4 D trap lives. Five product categories for a column, grouped by the standard they come from: Sawn Lumber and Glulam under the NDS Supplement, then LVL, LSL and PSL among the engineered wood products. I-Joists are absent, and deliberately — the dataset publishes no compression parallel to grain value for them, so they cannot be designed as columns here.

38:58Sawn Lumber, which is already the default. And now the choice that matters. Three design value tables: 4 A for visually graded dimension lumber two to four inches thick, 4 B for Southern Pine dimension lumber, and 4 D for visually graded timbers, five by five and larger. Our eight by ten is a timber, so 4 D. Watch what this radio does to the section list further down — it is not just a filter on this table.

39:25Table 4 D itself, exactly as printed in the Supplement, with the three most common species pinned to the top and the rest behind a Show more row. Open Douglas Fir-Larch, Douglas Fir, Western Larch. And notice that the grade names carry their size classification: number two Posts and Timbers is a different row from number two Beams and Stringers, with different values — seven hundred and fifty against eight hundred and seventy five in bending, seven hundred against six hundred in compression. We pick number two Posts and Timbers, and the row lights up with the values the hand calculation used: bending seven fifty, tension four seventy five, shear one seventy, compression perpendicular six twenty five, compression parallel seven hundred, modulus one point three million, and minimum modulus four hundred seventy thousand.

40:13Sub step three, section size, is the whole of Supplement Table 1 B. And here is what the 4 D radio did: the Dimension Lumber group is grayed out, with a note saying dimension lumber sizes are available when Table 4 A, 4 B or 4 C is selected, and the Boards group carries its own note pointing at 4 A or 4 B. The selected design value table strictly drives which size classes you may pick — so the pairing that gives you zero point six eight one instead of zero point eight four two is not reachable by accident. Open Timbers, five by five and larger, Post and Timber.

40:46Eight by ten. Standard dressed size seven and a half by nine and a half, area seventy one point two five, section modulus one hundred twelve point eight, moment of inertia five hundred thirty five point nine — read straight off Table 1 B, exactly the numbers the hand calculation used. The weight columns on the right are where that seventeen point three pounds per foot of self weight comes from.

41:08Step three complete: Douglas Fir-Larch Timbers, number two Posts and Timbers, eight by ten.

App Step 4 - Design parameters

41:14Step four collects every NDS adjustment factor in one place, each tagged either calculated by the program or provided by you. Wet service and temperature both default to dry and under one hundred degrees — one point zero each — which is what this heated, enclosed building has. The size factor is calculated and comes out at one point zero, for exactly the reason the guide gave: Table 4 D tabulates timbers directly.

41:38And notice what is not here. There is no repetitive member control, because the section is a timber and NDS 4.3.9 could never grant it — the module does not show a factor it would have to refuse. The load duration factor is tagged calculated, and the note says why: it is load combination specific. Expand it and the module lists every combination with its own factor — zero point nine on the dead only row, one point one five on the snow rows, one point six on every row containing wind, straight out of Table 2.3.2.

42:12And the column stability factor, with the full substitution printed. Effective length, one point zero zero times twenty two, both ways. Slenderness twenty seven point eight on the strong axis, thirty five point two on the weak — and the larger is under the fifty limit of 3.7.1.4. E prime minimum, four hundred seventy thousand. F sub c star at the governing duration factor. F sub c E equals zero point eight two two times four hundred seventy thousand over thirty five point two squared, three hundred twelve p s i.

42:39c equals zero point eight for sawn lumber. And equation 3.7 dash 1 solved out to a stability factor of zero point two six zero. Every line we worked by hand, on screen, with this column's own numbers in it. And the step's own footnote states the thing worth remembering: the value shown is computed at the governing combination's duration factor, and each combination in Step five recomputes the stability factor and the allowable at its own.

App Step 5 - Design verification

43:10Step five, Design Verification. This is where we check the app's answer against every number we found by hand — and where we see all nine combinations it evaluated, not just the one that governs. Nine rows, plus bearing. Each carries its own axial load, its own f and F prime, an axial demand over capacity column, a Combined M plus P column — which only appears because a lateral load is present — and a result. And read across the wind rows: the axial column never exceeds a quarter, while the combined column climbs to zero point eight four two. Two different questions, two different answers, on the same row.

43:47Before the details, the bearing input the guide made a point of. Plate or sill material bearing under the column — because compression perpendicular to grain belongs to the member being crushed, not the post. Left alone it uses the column species and says so; we name the sill instead: Hem-Fir. Grade number two. That swaps the bearing check from the Douglas Fir column's six hundred twenty five pounds per square inch to the sill's four hundred and five — which is what turns a comfortable looking number into the honest zero point one nine seven.

44:18Clicking any row opens the full derivation for that combination. Dead alone first: three thousand five hundred eighty one pounds, with the axial demand broken out into the three hundred eighty one pounds of self weight plus the three thousand two hundred we entered. Duration factor zero point nine, stability factor zero point four three zero, allowable two hundred seventy point nine, and an axial ratio of zero point one eight six — the number the guide gave for completeness.

44:46Dead plus zero point seven snow — the largest axial load in the set, five thousand six hundred eighty one pounds. Duration factor one point one five, stability factor zero point three five zero, allowable two hundred eighty one point five, ratio zero point two eight three. That is the worst the axial check ever gets on this column, and it matches the hand calculation exactly. Dead plus three quarters of zero point seven snow: five thousand one hundred fifty six pounds, axial ratio zero point two five seven. Written the way the code writes it, three quarters times zero point seven — never collapsed to zero point five two five, so the provenance of the factor stays visible.

45:27And the governing row: dead plus zero point six W. Below the axial block sits a second block — Combined bending plus axial, NDS 3.9.2, detailed calculation — and it is the hand calculation, line for line. The moment from the pinned pinned statics, eight thousand two hundred forty pound feet. The bending stress, eight hundred seventy six point six. F sub c E one on the bending plane, five hundred point three. The buckling gate, checked and passed. And equation 3.9 dash 3 solved out: zero point zero three zero plus zero point eight one two equals zero point eight four two.

46:01The same combination with the wind reversed. The module generates both signs and evaluates both — and because the section is symmetric, the answer is the same zero point eight four two. That is a result worth seeing rather than assuming. Combination six a: dead plus three quarters of zero point six W plus three quarters of zero point seven snow. More axial, less moment — five thousand one hundred fifty six pounds against a lateral factor of zero point four five — and the interaction comes in at zero point seven zero two.

46:33And its mirror, with the wind the other way. Combination seven a: zero point six dead plus zero point six W. The full moment on the smallest axial load in the set, two thousand one hundred forty nine pounds — and it lands at zero point seven eight eight, the second worst row in the design. That is the row an engineer who only looks at axial load would dismiss first.

46:57And its mirror. Finally the bearing row. Full end bearing area, b times d. The derivation states that the load duration factor does not apply, names the Hem-Fir sill as the source of the four hundred and five, and reports zero point one nine seven. It also tells you the bearing length it used — the shorter column face, seven and a half inches — which is exactly why the bearing area factor is one point zero and not one point zero five.

App Step 6 - Visualization

47:27Step six, Visualization — the diagrams, for every load case and every combination the app knows about, not just the governing one. The sidebar lists the individual load cases first — dead, snow and wind — then all nine combinations, and it already tags which one governs and which check it governs: combined M plus P, on dead plus zero point six W. Under the list, a colour keyed legend of the applied loads for whichever case is shown.

47:54Dead load by itself: three thousand five hundred eighty one pounds down the axis, including self weight, and no lateral load at all. Snow by itself: three thousand pounds, unfactored. Note this is the raw case, not the zero point seven S of the combination. And wind by itself — the full two hundred and twenty seven pounds per foot, with no axial load at all, which is the clearest look you will get at the pure bending the wall delivers.

48:20Now the combinations. Dead alone: axial only, the base reaction drawn in purple, and flat V, M and deflection panels — nothing is pushing sideways. Dead plus zero point seven snow: five thousand six hundred eighty one pounds, the largest axial in the set, and still no lateral load. This is the picture behind the zero point two eight three, and it is a picture with nothing interesting in it — which is the point.

48:45And dead plus zero point six W, the governing case. Compare this directly to the hand drawn figure from earlier in the video: axial from three thousand two hundred at the top to three thousand five hundred eighty one at the base, shear from minus fourteen ninety eight to plus fourteen ninety eight crossing zero at midheight, the parabolic moment peaking at eight thousand two hundred forty pound feet, and the deflection at one point zero three inches.

49:07Same four panels, same order, same numbers — drawn by the app from the same closed forms the checks used. The mirrored wind direction: the diagrams flip and the magnitudes do not. The mixed case, six a, at a lateral factor of zero point four five — visibly a smaller moment on a larger axial load, exactly as the zero point seven zero two ratio said. And seven a, zero point six dead plus zero point six W: the moment is back to full size while the axial column has shrunk. Twelve views in this sidebar, three load cases and nine combinations, every one of them one click away — and every governing tag matching what we found by working through this column by hand at the start of the video.

Hand calculation vs. StructSuite - every number matches

49:53One last comparison, side by side, before we close. The governing combined check, zero point eight four two both ways. The uplift side case, zero point seven eight eight. The mixed case, zero point seven zero two. The axial check, zero point two eight three. Dead alone, zero point one eight six. Bearing on the named Hem-Fir sill, zero point one nine seven. The column stability factor at a duration factor of one point six, zero point two six zero. And both slenderness ratios, thirty five point two on the weak axis and twenty seven point eight in the plane of bending. Every governing number in this design, worked two completely different ways, agrees.

50:32That is the whole point of building this video the way we built it. Every figure, every table, every formula came straight from the written guide — nothing here was summarized or invented for the camera. Every field you watched us enter in the app is a number this video derived first, by hand, from the code. And the check that decides this column — three times the axial ratio, on a row carrying barely half the peak axial load — is the one an axial only design never runs at all. Read the article, or watch this video. Either way, you get the same column, and now you have watched it check out twice.