Glulam Beam Design Step by Step - Cantilever Balcony Example (NDS 2024)

Introduction

0:00A simple span beam never asks the most interesting glulam question: what happens when the tension face flips? This example does. We will take one beam all the way through, by allowable stress design, to NDS 2024. Loads, analysis, every check, and then we will enter the same design in the software and confirm it matches, number for number. A glulam floor beam runs sixteen feet between supports inside the building, then cantilevers six feet past the exterior wall to carry a balcony. That means the beam does two different jobs. At midspan the bottom fiber is in tension, which is the ordinary case. But over the exterior support the moment reverses, and the top fiber goes into tension.

0:42And a glulam built from a bending optimized layup does not have the same strength both ways up. The positive bending value for the class we will pick is two thousand four hundred pounds per square inch; the negative value is only one thousand four hundred and fifty. So the face the cantilever loads is the weaker one, and as we will see, the negative moment ends up governing the whole design.

1:04One note before we start. Every number in this example was produced by the same calculation engine that runs StructSuite's Wood Beam 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

1:23Here is the structure. A pin at the left end, a roller at the exterior wall sixteen feet along, and the beam runs on another six feet to a free end. In amber, the interior floor load across the back span. In blue, the balcony load on the cantilever, which is heavier. And in pink, at the very tip, a moment — that is the guardrail. The guardrail itself and its horizontal force are drawn as a gray shadow, because that force never touches the beam directly. Only its moment does. Watch that pink arrow; it is the detail most people miss.

Inputs - where each parameter comes from

1:57Before any arithmetic, every input. Every input is either a code prescribed value, with its section cited on the row, or a framing decision you read off the plans. Nothing is a guess. The two that get missed most often are the balcony live load and the guardrail force — and both of those come from the code, not from judgment. So: the geometry, a sixteen foot back span pin to roller plus a six foot cantilever, with beams at six feet on center. The interior floor, fifteen pounds per square foot dead and forty live. The balcony, the same fifteen dead but sixty live, because IBC Table 1607.1 gives balconies one and a half times the area they serve. The guardrail, fifty pounds per linear foot at forty two inches, from IBC 1607.9. The material, twenty four F, one point eight E Douglas Fir glulam. Dry service, normal temperature. And deflection

2:47limits of L over 360 for live load and L over 240 for total.

Step 1 - Tributary width: how area loads become line loads

2:57Step one. Turning loads that are given per square foot into a line load along the beam. This is the framing plan. The floor and the balcony are framed with joists and sheathing spanning between parallel glulam beams, spaced six feet on center. The thin lines are the joists. Each beam carries the strip of floor that has no closer beam to run to — halfway to the neighbor on each side. Three feet plus three feet. So the tributary width is six feet, and it is the same inside the building and out on the balcony.

3:25The arithmetic is one multiplication. The interior floor dead load is fifteen pounds per square foot. Multiply by the six foot tributary width and the beam sees ninety pounds per linear foot. Every other load on this beam is found exactly the same way. Which gives us these. Interior dead, fifteen times six, ninety pounds per foot. Interior live, forty times six, two hundred and forty. On the balcony the dead load is the same ninety, but the live load is sixty pounds per square foot rather than forty, so it comes out at three hundred and sixty. The balcony is the heavier strip, and it is the one hanging off the end — that combination is what makes this beam interesting.

4:03And the beam adds its own weight, seventeen point three pounds per foot, which is sixty nine point one nine square inches of section at thirty six pounds per cubic foot. StructSuite adds that automatically. And this is exactly what you enter in StructSuite: a pounds per square foot value and a tributary width for each load, with its start and end positions. The app does the multiplication and records it in the report, so a plan checker can check your framing plan against one multiplication rather than guessing where a line load came from.

Step 2 - The guardrail end moment

4:35Step two. The guardrail — and this is the load most people leave out. IBC 1607.9 requires guard top rails to resist fifty pounds per linear foot, or a two hundred pound concentrated load — each applied in any direction, and not concurrently. The beam's tributary length of rail is its spacing, six feet. So the distributed case gives fifty times six, three hundred pounds; the concentrated case gives two hundred. Three hundred governs.

5:01The rail force acts forty two inches above the beam — three and a half feet — and it comes back to the beam tip as a concentrated moment. Three hundred pounds times three and a half feet is one thousand and fifty pound feet, applied at x equals twenty two feet, which is the free end. It is a live load, so it enters every combination that contains L.

5:21And "any direction" is a sign choice you have to make. An outward push and an inward pull give opposite moment signs at the tip. We ran both through the engine. The sign that adds to the hogging moment governs the flexure check — a demand over capacity ratio of zero point five one one, against zero point four zero the other way — so that is the design case. In the app this is a single concentrated moment entry at twenty two feet; flip its sign to check both directions.

Step 3 - Section and material: reading Tables 5A and 1C

5:49Step three. The section and the material, read out of two tables in the NDS Supplement. From NDS Supplement Table 5A, stress class twenty four F, one point eight E, Douglas Fir. These are the values exactly as tabulated. Positive bending, two thousand four hundred pounds per square inch. Negative bending, one thousand four hundred and fifty. Shear parallel to grain, two hundred and sixty five. Compression perpendicular to grain, six hundred and fifty. And the modulus of elasticity, one point eight million.

6:21Those two bending values are the heart of this example. The positive value applies when the bottom laminations are in tension, which is normal sagging. The negative value applies when the top is in tension — exactly what happens over our interior support. The manufacturer puts the premium tension rated laminations on the bottom of a twenty four F layup. The top face does not get them, so it earns only one thousand four hundred and fifty pounds per square inch.

6:48And you can see it in the cross section. Five and an eighth inches wide, thirteen and a half inches deep, nine laminations of an inch and a half each. The amber laminations at the bottom are the premium tension rated ones. Flip the bending — as this cantilever does over its support — and it is the ordinary laminations at the top that have to carry the tension. The geometry comes from Table 1C, for Western species. A five and an eighth by thirteen and a half glulam has an area of sixty nine point one nine square inches, a section modulus of one hundred and fifty five point seven cubic inches, and a moment of inertia of one thousand and fifty one inches to the fourth. We will use all three.

Step 4 - Analysis: reactions, shear and moment, with a sign reversal

7:30Step four. The analysis. Unfactored dead plus live, including the self weight: the interior span carries three hundred and forty seven point three pounds per foot, the balcony four hundred and sixty seven point three, and there is the one thousand and fifty pound foot rail moment at the tip. The reactions. At the pin, two thousand one hundred and eighty seven pounds. At the roller on the wall, six thousand one hundred and seventy three.

7:56The interior support carries almost three times what the end support does, because it picks up the whole balcony plus its share of the back span. And the statics close exactly: three forty seven point three times sixteen, plus four sixty seven point three times six, is five thousand five hundred and fifty seven plus two thousand eight hundred and four, eight thousand three hundred and sixty pounds — which is exactly the two reactions added together.

8:21Here are the shear and moment diagrams, and they show two things a simple span never does. Follow the shear first: it starts at plus two thousand one hundred and eighty seven at the pin, falls as the load accumulates, crosses zero at six point three feet, and reaches minus three thousand three hundred and seventy just inside the support. Then it jumps by the reaction to plus two thousand eight hundred and four and runs out along the cantilever. Now the moment. It rises to a peak of six thousand eight hundred and eighty seven at six point three feet — where the shear crossed zero — then falls, changes sign at twelve point six feet, and reaches minus nine thousand four hundred and sixty one at the support.

8:57And look at the tip: the moment diagram does not end at zero. It ends at minus one thousand and fifty pound feet, closed out by the guardrail moment we applied. So the governing internal forces for dead plus live are: a positive moment of six thousand eight hundred and eighty seven pound feet at six point three feet, a negative moment of nine thousand four hundred and sixty one at the interior support, and a shear of three thousand three hundred and seventy pounds just inside the support on the back span side. Note the hogging moment is thirty seven percent larger than the sagging moment. The cantilever runs this design.

Step 5 - Adjustment factors, and CD per combination

9:35Step five. The adjustment factors. For glulam, the Table 5A values are adjusted per NDS Chapter 5. Wet service, temperature and incising factors are all one point zero: the beam is dry, under a hundred degrees, and glulam is not incised. The beam stability factor is taken as one point zero on the assumption that the compression edge is braced — we will come back to that, because it matters.

9:58The volume factor is zero point nine eight four, which barely bites at this size. The flat use and repetitive member factors do not apply. And the load duration factor depends on the combination. And that last one is worth dwelling on. The load duration factor belongs to the combination, not to the member. The engine evaluates every allowable stress design combination with its own factor: the dead load alone combination sees capacities multiplied by zero point nine, while dead plus live sees them multiplied by one point zero. That is why a report shows different capacities for the same member under different combinations, and it is why dead plus live governs here.

10:39There is one combination that is opt-in. In seismic design category D through F, ASCE 7-22, section 12.4.4 requires horizontal cantilevers to also be designed for a supplemental net upward force of zero point one four D. The module shows that toggle in Step 2 whenever the beam has an end cantilever. Checking it adds the uplift combination — and although it carries only a dead load term, it is a seismic effect, so it runs at a load duration factor of one point six, not the permanent zero point nine. This example's site is not asserted to be in category D through F, so we leave the toggle off, and the combination list we just saw is complete.

11:21And a warning that belongs with every cantilever. Taking the beam stability factor as one point zero means each compression edge is laterally supported where it is in compression. In the back span that is the top edge, braced by the joists and the sheathing. But over the support and along the cantilever, it is the bottom edge that is in compression — and nothing is bracing that by default. Provide full depth blocking at the support and brace the cantilever's bottom edge, or enter the unbraced length and let the module compute the stability factor per NDS 3.3.3. Miss this in the field and the capacity you calculated does not exist.

Step 6 - Flexure: two checks, two strengths

11:58Step six. Flexure — and because the two faces have different reference strengths, this is two checks, not one. Both faces get the same adjustments; only the reference value differs. Start with the positive bending value, two thousand four hundred. Multiply by the volume factor, zero point nine eight four, and the load duration factor, one point zero. The adjusted value is two thousand three hundred and sixty one pounds per square inch. Multiply by the section modulus, one hundred and fifty five point seven cubic inches, divide by twelve to turn inch pounds into foot pounds, and the sagging capacity is thirty thousand six hundred and thirty three pound feet.

12:36Now the identical three factors, but starting from the negative bending value — one thousand four hundred and fifty, not two thousand four hundred. Same volume factor, same duration factor. The adjusted value is one thousand four hundred and twenty six, and the hogging capacity is eighteen thousand five hundred and seven pound feet. That is forty percent less than the same beam can carry the other way up. Put them side by side. Sagging: a demand of six thousand eight hundred and eighty seven against a capacity of thirty thousand six hundred and thirty three — a ratio of zero point two two five. Hogging: nine thousand four hundred and sixty one against eighteen thousand five hundred and seven — zero point five one one, and it governs.

13:20So flexure passes, at zero point five one one, and the governing check is the hogging one. Read those two rows again, because they are the whole lesson. The sagging check uses barely a quarter of the section. The hogging check, with a smaller moment than the section could carry in sagging, consumes sixty four percent — because the top face is forty percent weaker. A cantilevered glulam is designed by its weak face.

Step 7 - Shear

13:44Step seven. Shear. The adjusted shear value is two hundred and sixty five pounds per square inch — the shear reduction factor and the duration factor are both one. The capacity is two thirds of that times the area: two thirds times two hundred and sixty five times sixty nine point one nine, which is twelve thousand two hundred and twenty four pounds. The demand: one point five times the shear over the area — one point five times three thousand three hundred and seventy over sixty nine point one nine, which is seventy three pounds per square inch. And you can check that shear against the reactions we found earlier: two thousand one hundred and eighty seven minus three forty seven point three times sixteen is three thousand three hundred and seventy pounds. It closes.

14:29Three thousand three hundred and seventy against twelve thousand two hundred and twenty four is a ratio of zero point two seven six. Shear passes comfortably — it usually does on a beam this deep.

Step 8 - Deflection

14:42Step eight. Deflection — and there are three subtleties here that catch people out. First, the stiffness: a modulus of one point eight million and a moment of inertia of one thousand and fifty one. Second, per NDS 3.2.1 the deflection limit belongs to each span, so the sixteen foot back span and the six foot cantilever are checked separately, not as one member. And third, for a cantilever the limit length is twice the projection — two times six, twelve feet — per IBC Table 1604.3.

15:12And one more. The total load column is not dead plus live. IBC Table 1604.3, footnote d, limits it to the deflection due to the creep component of long term dead load deflection plus the short term live load deflection — and for wood that is dry at installation and used dry, that creep component is permitted to be estimated as the immediate dead load deflection from half the dead load. So the case actually checked is zero point five D plus L.

15:39And both cases are governed by the same span — the cantilever. Live load only reaches zero point two nine one inches against a limit of zero point four, a ratio of zero point seven three. The total load case reaches zero point two seven seven against zero point six, a ratio of zero point four six. Both pass, but the live load case is using nearly three quarters of its allowance — and that is the number that sized this beam.

16:04But deflection of which arrangement? ASCE 7-22, section 4.3.3 says the uniform live load applied only to a portion of a member has to be accounted for if it produces a more unfavourable load effect. For this beam that means three cases: both spans loaded, the back span alone, and the cantilever alone. And the reason it matters is not obvious — loading the room actually helps the balcony, because the back span's sag rotates the beam over the support in the direction that lifts the tip.

16:35Here are all three. With both spans loaded the tip moves sixty six thousandths of an inch — almost nothing, and that is the figure that makes a cantilever look comfortable. Empty the room, which is the ordinary case of someone standing on the balcony, and that help disappears: the tip drops to zero point two nine one inches. Four point four times as far, from the most everyday loading there is. This single arrangement is the reason the published beam is a five and an eighth by thirteen and a half and not the twelve it started as — on a twelve the same beam reaches zero point four one four against a zero point four limit and fails, while every strength check still passes comfortably.

Step 9 - Bearing

17:13Step nine. Bearing — the last check, and the one where the two supports behave differently. With a three inch bearing length, the bearing area factor depends on where the bearing sits. NDS 3.10.4 grants it only for bearings less than six inches in length and not nearer than three inches to the end of a member — because the reference compression perpendicular value already applies to bearings of any length at the ends of a member. So the end pin takes a factor of one point zero, giving six hundred and fifty pounds per square inch. The interior wall support takes three plus zero point three seven five, over three, which is one point one two five — giving seven hundred and thirty one. And note there is no load duration factor on bearing, per Table 2.3.2.

17:57So at the end pin, two thousand one hundred and eighty seven pounds over a three inch by five and an eighth inch bearing is one hundred and forty two pounds per square inch, against six hundred and fifty — a ratio of zero point two two. At the wall support, six thousand one hundred and seventy three pounds gives four hundred and two pounds per square inch against seven hundred and thirty one — zero point five five.

18:20The wall support works almost three times harder than the end support. So check the plate and the post underneath it for that same six thousand one hundred and seventy three pounds — the beam passing does not mean what it lands on does.

Two checks engineers skip on cantilevers

18:33Before we summarize, two checks that get skipped on cantilevers — and should not be. First, pattern loading and uplift. Live load does not have to occupy the whole floor. Re-run the model with the interior live load removed — balcony live and the rail moment only, dead load everywhere — and the end reaction collapses from two thousand one hundred and eighty seven pounds to two hundred and sixty seven. This beam is two hundred and sixty seven pounds away from lifting off its end support. A slightly longer cantilever, a heavier balcony finish, or a lighter interior floor, and you need a tie down at the pin. One extra run in StructSuite, deleting the interior live load item, shows it. And in seismic design category D through F the code makes it mandatory anyway — that is the zero point one four D

19:16combination we mentioned. Second, the stress class is not decoration. Take the same five and an eighth by thirteen and a half section in class sixteen F, one point three E, where the negative bending value is only nine hundred and twenty five pounds per square inch. The hogging capacity becomes eleven thousand eight hundred and six pound feet — against our nine thousand four hundred and sixty one pound foot demand. A ratio of zero point eight zero one, against zero point five one one for twenty four F. One class down costs fifty seven percent of the margin, and all of it on the hogging face. The cantilever's negative moment is precisely where cheaper stress classes run out, so pick the class for the weak face, not the strong one.

The arrangement question - why ASCE 7-22 4.3.3 changes this beam

20:00Before the summary, the question that decided this member. We met it in the deflection step; it is worth seeing on its own, because it is the single most skipped check on a continuous beam. Section 4.3.3 says the uniform live load applied only to a portion of a structure or member shall be accounted for if it produces a more unfavourable load effect. Section 4.3.3.1 names the arrangements to check: adjacent spans, or alternate spans. For two spans that is three arrangements; for three spans, four.

20:29Not every permutation — for a uniform load on a prismatic member, the arrangements the code names are the ones that can actually govern. The textbook result for a two span beam makes the point without any of our numbers. Load both spans and the span moment is zero point zero seven zero three w L squared. Load one span only and it rises to zero point zero nine five seven — thirty six percent higher.

20:52The support moment moves the other way, halving. And the loaded span deflects up to about twice as far. Fully loaded is simply not the worst case. And here it is on our beam. The hogging moment does not move at all — nine thousand four hundred and sixty one either way — so the governing flexure ratio is unchanged at zero point five one one. The sagging moment rises forty eight percent, to ten thousand one hundred and seventy pound feet, but it lands on the strong face of the glulam and never threatens anything. It is the last row that matters: the cantilever tip goes from sixty six thousandths of an inch to zero point two nine one. Four point four times. Strength was never the issue — the arrangement was.

Summary of results - 5.125 x 13.5 glulam, 24F-1.8E DF

21:35And the summary. Every check on one page. Flexure hogging, the governing one, at zero point five one one. Flexure sagging at zero point two two five. Shear at zero point two seven six. Deflection at zero point four six. Bearing at the wall at zero point five five. The beam works — the hogging check at the cantilever support is the highest of the strength checks, and the deflection of the unloaded back span is what set the depth.

Now in StructSuite - entering the same beam in the app

22:02Now let's enter this exact beam in StructSuite's Wood Beam module, starting from a completely blank project, and watch it reproduce every number we just found by hand.

App Step 1 - Geometry and configuration

22:12Step one, Geometry and Configuration. This is where the beam's spans and supports are laid out. Blank. Wood is already selected as the design material — the module also does steel beams to AISC 360-22, by LRFD, with W-shapes and HSS, if you ever need to compare a wood and a steel option for the same beam side by side. We are staying on wood, per NDS 2024, allowable stress design.

22:41Span 1 is the back span: sixteen feet, pin to what will become the roller. Add span. Watch what happens: the module inserts a new middle support and a new end support, and it resets both of them to their own defaults. That matters — if you had already set the old end support to something other than Pinned before adding the span, that choice is gone. Set supports after you add spans, not before.

23:04Span 2, the cantilever: six feet. Now the middle support, at the wall, becomes a roller. And the end of the cantilever becomes Free — nothing holds it up. That is what makes this a cantilever rather than a second simple span. The other options here are Pinned, which resists vertical load but lets the beam rotate, and Fixed, which resists rotation too — useful for a moment connection, not for a beam end sitting on a wall.

23:33And there is the schematic: pinned, sixteen feet, roller, six feet, free. One more control worth knowing about, even though we do not use it here: Sloped member, for a rafter or a pitched beam. Turn that on and the dead load and self weight convert by the sloped length factor to the horizontal projection, while live, roof live, snow and wind stay exactly as entered — because those act on the horizontal footprint regardless of the roof pitch. Our beam is horizontal, so it stays off.

App Step 2 - Load definition

23:59Step two, Load Definition. Every load we found by hand in Step 1 of the hand calculation gets entered here. Blank, the module offers seven ASCE 7-22 load types: D for dead, L for live, L-r for roof live, S for snow, R for rain, W for wind, and E for earthquake. This beam only ever sees D and L, but if you were sizing a roof beam you would reach for L-r or S the same way, and if a shear wall chord ran through a beam you might see E. Distribution offers uniform, a point load, a triangular or trapezoidal load, and a concentrated moment — that last one is what our guardrail becomes.

24:36Include member self-weight is checked by default, and it is grayed out until Step 3 has a section — the moment we pick five and an eighth by thirteen and a half glulam, this row fills itself in at seventeen point three pounds per foot, automatically added to D. That is one fewer number for you to compute by hand. The first load row. Type D, Distribution Uniform, and here is the choice that matters: Input as. Left as plf you type a line load directly.

25:03Switch it to psf times tributary width, and two new boxes appear — the area load and the tributary width — with a read-only plf-equivalent so you can see the multiplication happen. Fifteen, six. Ninety plf, same as the hand calculation. Then Full span is unchecked, which opens a start and an end position: zero to sixteen, the interior segment only. Same pattern for the interior live load: Type L, forty psf, six foot tributary, zero to sixteen feet.

25:33Add load, for the balcony dead: fifteen psf again — the dead load per square foot does not change between the floor and the balcony — six foot tributary, but now positioned sixteen to twenty two feet, the cantilever segment. Add load again for the balcony live: sixty psf this time, not forty — the one and a half times multiplier for balconies is something you apply when you choose the number, the app does not guess it for you — same six foot tributary, same sixteen to twenty two foot span.

26:02And Add load one more time for the guardrail. Type L, because it is a live load and has to enter every combination with L. Switch Distribution to Concentrated moment, and the fields change completely: no more psf or tributary width, just a moment value and a position. One thousand fifty pound feet, at twenty two feet — the free tip. One control worth pausing on. Right there in Step 2, above the load rows, sits a checkbox: horizontal cantilever in Seismic Design Category D through F, citing ASCE 7-22, section 12.4.4. The module only offers this because our beam has a free end — a simple span would never see it.

26:38Checking it would add a supplemental zero point one four D net upward combination at a load duration factor of one point six. Our site is not asserted to be in that seismic category, so we leave it unchecked, exactly as the hand calculation did — but it is worth knowing the app is watching your geometry and surfacing code sections you might otherwise forget to check for.

App Step 3 - Material and section

27:03Step three, Material and Section — where the beam becomes an actual, buildable piece of glulam. Six product categories. Sawn Lumber and Glulam under the NDS Supplement; then four engineered wood products — LVL, LSL, PSL, and I-Joist, the TJI and BCI family. If this were a simple residential floor beam you might reach for LVL instead; for a long cantilever with a reversing moment, glulam's ability to put different laminations on each face is exactly the tool this beam needs.

27:36Glulam. That reveals Table 5A for bending members, Table 5B for axial members, and a species choice — Douglas Fir, Southern Pine, or Western Species — which sets the volume factor calculation. Douglas Fir, our hand calculation's assumption, is already the default. And the whole Table 5A, exactly as printed in the NDS Supplement — every stress class from sixteen F, one point three E, up to thirty F, two point one E Southern Pine, with both bending values side by side so you can see, for every single class in this table, that the negative value always trails the positive one. We pick twenty four F, one point eight E — the row this example uses.

28:16Section size, Table 1C for Western species. Each glulam width — two and a half, three and an eighth, three and a half, five and an eighth, and on up to twelve and a quarter inches — expands to its own table of depths. We expand five and an eighth. And thirteen and a half inches deep. Area, section modulus, moment of inertia — sixty nine point one nine, one hundred fifty five point seven, one thousand and fifty one — read straight off this table, exactly the numbers the hand calculation used.

App Step 4 - Adjustment factors

28:44Step four collects every NDS adjustment factor in one place, tagged either calculated by the program or user defined by you. C M, wet service, and C t, temperature, both default to dry service and normal temperature — one point zero each — which is worth knowing even when it does not change anything: C M drops below one only above nineteen percent moisture content, and C t only matters above one hundred degrees Fahrenheit, so most buildings never touch either one. C f u, flat use, is calculated and stays at one because that factor only applies to the weak axis; our beam bends about its strong axis. C D, load duration, is calculated per combination — we will watch that change from row to row in a moment. And bearing length is optional; skip it and the app simply omits the bearing check.

29:32We enter three inches, matching the hand calculation, so the bearing check runs. One factor deserves real attention: C L, the beam stability factor. It defaults to one point zero on the assumption that the compression edge is continuously braced — and that is exactly what it is, an assumption the app is making on your behalf, not something it has verified from your framing plan. If the compression edge is not actually braced — remember, over this cantilever's support it is the bottom edge that goes into compression, not the top — you enter an unbraced length here instead, and the module computes C L properly, per NDS 3.3.3. Skipping this on a real cantilever is exactly the field mistake the hand calculation warned about earlier in this video.

App Step 6 - Design verification

30:18Step six, Design Verification. This is where we check the app's answer against every number we found by hand — and where we see every load combination it evaluated, not just the one that governs. Six rows. Four strength combinations for moment and shear — D alone, D plus L, D plus three quarters L, and zero point six D — and two separate deflection cases, because deflection is a serviceability check, not a strength one, and it runs under its own rules: L alone against L over 360, and zero point five D plus L, the total load case, against L over 240. Every ratio here is a demand over capacity, so anything at or under one point zero passes.

31:00Click the D-alone row and it opens the full derivation for that combination — the same Table 5A values, the same C V and C D, worked out under dead load by itself. D alone gives the smallest demand of the four strength rows, at zero point one four two for flexure — it never governs here, but the app runs it anyway, because a beam with almost no live load, like an interior corridor, could see dead-alone govern instead.

31:25D plus L — the one that matters. And here is the app's own derivation, word for word what we did by hand: F b positive prime equals F b x positive times C M times C t times the lesser of C L and C V times C fu times C D. Two thousand four hundred, times one, times one, times zero point nine eight four, times one, times one — two thousand three hundred sixty one p s i. Notice one detail the app states explicitly that the hand calculation folded in silently: C L and C V are not multiplied together, the lesser of the two applies — they both address the same failure mode, so using both would double count it. M n positive, thirty thousand six hundred thirty three. F b negative prime the same way, fourteen hundred

32:06fifty as the starting value, giving M n negative of eighteen thousand five hundred seven. D over C positive, zero point two two five; D over C negative, zero point five one one — the governing one. Exactly what we calculated. Scroll to the shear derivation for the same combination, and it adds something the hand calculation only touched on: it computes shear two ways. An analytic value straight from the support reaction, three thousand three hundred fifty two pounds, and a sampled value read off the finite-element shear diagram, three thousand three hundred twenty three — the larger of the two governs, because a coarse diagram sample could otherwise miss the true peak. It also notes, explicitly, that it is not taking the NDS 3.4.2.2 allowance to ignore uniform load within one beam depth of the support — that reduction exists in the code,

32:54the app simply does not apply it automatically, so if you want the benefit you take it yourself. D plus three quarters L: the same combination with live load knocked down to seventy five percent, one of the four ASCE strength combinations you check even when it never governs — for a beam with several different variable loads acting together, this is the row that sometimes wins instead of full D plus L.

33:23And zero point six D — the uplift-checking combination, dead load alone at sixty percent. Its whole purpose is to see whether a reduced dead load, paired with a wind or seismic term elsewhere in a full load path, could flip a reaction into tension. For this beam, by itself, it produces the smallest demand of all four rows and both reactions stay solidly positive — no uplift signal here. That is a different question from the pattern-loading uplift we found by hand a few minutes ago, where removing the interior live load — not scaling dead load — dropped the end reaction to two hundred fifty four pounds. The built-in combinations do not run that pattern for you; that check has to be set up by hand, exactly as the guide describes.

34:04The two deflection rows sit apart from strength, and clicking them opens their own derivation. L alone, live load only: E prime is one point eight million, unchanged since C M and C t are both one. Zero point zero nine four two inches, against a limit of L over 360 — but L here is the cantilever's own limit length, twice its projection, twelve feet, giving a limit of zero point four inches. D over C zero point two three six. Matches the hand calculation's point zero nine four.

34:33And zero point five D plus L, the total-load case — the app states the IBC footnote reasoning explicitly, the same reasoning the hand calculation walked through: this column estimates long-term creep as the immediate deflection from half the dead load, plus the full short-term live load, and it is not to be combined with the NDS 3.5.2 creep factor — one or the other, never both. Zero point one five two four inches, against the sixteen-foot back span's limit of L over 240, zero point eight inches. D over C zero point one nine. Matches.

35:06And scrolled further down the same D-plus-L detail: bearing. Two supports, two different C b values, exactly as the hand calculation found — the end pin at C b equals one point zero, giving one hundred forty two p s i against six hundred fifty, a ratio of zero point two one nine; the interior wall support at C b equals one point one two five, four hundred and two p s i against seven hundred thirty one, zero point five four nine. The app adds one thing worth remembering: the six hundred fifty p s i reference value it is using is the beam's own F c perpendicular — it has no idea what the plate, sill, or post underneath is made of. If that material is softer than the glulam, you tell the app by naming it here, or the bearing

35:48check is only checking the beam, not the connection.

App Step 7 - Visualization

35:53Step seven, Visualization — the diagrams, for every load case and every combination the app knows about, not just the governing one. The sidebar lists the same six combinations from Step 6, plus the two individual load cases, dead alone and live alone, and it already tags which ones govern: D plus L governs flexure, shear, and bearing; L alone governs deflection. Let's step through all eight. Dead load by itself. Ninety plf on the back span, ninety on the balcony, plus the beam's own weight — no live load, no rail moment, since the moment we applied is a live load and does not appear here.

36:29Live load by itself: two hundred forty plf on the back span, three hundred sixty on the balcony, and now the rail moment appears at the tip, because that is where it lives. D plus L — the beam model at the top, then shear, moment, and deflection stacked below it. Compare this directly to the hand-drawn figure from earlier in this video: same shear from plus two thousand one hundred seventy four to minus three thousand three hundred fifty two, same moment from plus six thousand eight hundred forty two to minus nine thousand four hundred twenty six, same sign reversal, same non-zero ending at the tip. The app also reports a deflection of point one nine one one inches here — that is the raw D-plus-L deflection at its single worst point along the whole beam, not the same number as either of the two code-limited checks we

37:14just saw in Step 6, which look at each span separately and use the code's own load cases. Three different, legitimate numbers answering three different questions — worth not confusing with each other. D plus three quarters L — visibly a scaled-down version of the D-plus-L diagram, live load knocked back to seventy five percent, exactly as the combination name says. Zero point six D: both reactions shrink — four hundred thirty five pounds and nine hundred fifty six — and both stay positive. No uplift signal in this combination, for this beam.

37:48And the two deflection-only views: live load alone against L over 360 — — and zero point five D plus L against L over 240. Eight views, six combinations plus two load cases, every one of them one click away, and every governing tag matching what we found by working through this beam by hand at the start of the video.

Hand calculation vs. StructSuite - every number matches

38:10One last comparison, side by side, before we close. Flexure hogging, zero point five one one both ways. Sagging, zero point two two five. Shear, zero point two seven six. Deflection live, zero point seven two seven both ways — the governing arrangement is the loaded balcony off an empty room. Total load deflection, zero point four six one. Bearing at the end pin, zero point two two by hand, zero point two one nine in the app. Bearing at the wall, zero point five five by hand, zero point five four nine in the app. Every governing number in this design, worked two completely different ways, agrees.

38:46That 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. And every field you watched us enter in the app is a number this video derived first, by hand, from the code. Read the article, or watch this video — either way, you get the same beam, and now you have watched it check out twice.