It is Friday afternoon on a five-storey commercial fit-out. The plumbing subcontractor emails a marked-up beam elevation: three 100 mm sanitary sleeves punched through beam B-3, a 300 mm wide by 600 mm deep interior beam, somewhere around the third point of the span. Formwork closes Monday. The site engineer forwards it with one line: "For approval, sir."
From the reviewer's chair the first question is not whether the sleeves are a good idea. It is sharper: which of my objections can I actually enforce, and which are only my preference? That is what separates a stamped rejection from "noted, proceed with conditions," and it is what decides whether the argument on Monday morning goes anywhere. Get it wrong and you either wave through a hole that hurts the beam, or you hold up a pour on a preference you cannot defend — and a coring mobilization after the fact runs ₱15,000 to ₱30,000 before anybody talks about repair.
Most of the geometry is settled by one figure: ACI 314R-11, Fig. 6.8.2.2, "Location of conduits and pipes passing horizontally through girders, beams, and joists," from the Guide to Simplified Design for Reinforced Concrete Buildings. Useful, widely photocopied, and routinely quoted as if it were code.
Without reproducing the drawing, the rules it encodes are these, for a beam of clear span l and overall depth h.
Note how narrow that window really is: l÷3 - l÷4 = l÷12, so the permissible zone is always one-twelfth of the clear span. On a 6 m clear span that is 500 mm. On a 4 m clear span it is 4000 ÷ 12 = 333 mm, which will not hold two 100 mm sleeves at the required spacing.
Carry the logic, not just the picture; the logic is what lets you argue a borderline case. On a uniformly loaded simply supported beam, shear at distance x from the support is proportional to (l÷2 - x). At x = l÷4 that is l÷4, one-half of the end shear; at x = l÷3 it is l÷6, one-third. The window opens only after shear has fallen by half, leaving the first quarter-span — where the web works hardest carrying diagonal compression across the member — untouched. Moment runs the other way: midspan moment is wl²÷8, while at x = l÷3 it is w(l÷3)(2l÷3)÷2 = wl²÷9, and wl²÷9 divided by wl²÷8 gives 8÷9 = 0.889. Across the middle third the moment never drops below about 89 percent of peak, so the guide keeps that stretch clear.
The vertical band works the same way through the depth: bottom third for the flexural tension steel and its cover, top third for the compression block, middle third nearest the neutral axis, where a hole costs the section least. In one line: horizontal position is a shear decision, vertical position is a flexure decision.
Ask a room of engineers where a hole does least harm and you get two camps, and both are wrong. One says midspan, "because shear is zero there." The other says hard against the column, "because moment is zero there." The correct answer is a narrow band between the two, and neither instinct lands on it.
The figure is also drawn for a simply supported member. Real frame beams carry peak negative moment and peak shear at the same end, with tension steel on top, so a continuous beam deserves a second look rather than a copy-paste.
Then there is l itself: clear span, not grid dimension. On a 6.4 m grid with 400 mm columns, using 6.4 m instead of 6.0 m shifts the near boundary by 100 mm (1500 to 1600) and the far one by 133 mm (2000 to 2133) — enough to push a sleeve out of a window only 500 mm wide. And the most damaging error of all is quoting the whole figure as if it were binding. It is not.
ACI 314R-11 is a guide. The "R" means report, and the document is non-mandatory by construction. Nobody is obliged to place a sleeve between l÷4 and l÷3, or to keep it inside a mid-depth band of h÷3.
ACI 318 does carry mandatory language on conduits and pipes embedded in concrete. The provisions that bear on this check — not an exhaustive list — include:
One scope qualifier decides the Monday argument. ACI 318 attaches the size and spacing limits to conduits and pipes embedded within a slab, wall or beam — other than those merely passing through — and allows them to be superseded where the conduit and pipe drawings are approved by the structural designer. Read literally, a sanitary sleeve crossing a beam transversely is the archetype of a pipe “merely passing through,” so the clause that binds it is the one requiring an embedment not to impair the strength of the construction significantly. Most reviewers apply the one-third and three-diameter limits to transverse sleeves anyway, and it is conservative to do so — but the contractor’s engineer can and does make this argument, so know it before you are standing in front of it.
NSCP 2015, Chapter 4, Structural Concrete, carries equivalent embedment provisions here. Quote the requirement in words on your review comment, and never quote a section number you have not opened in the edition sitting on your desk. Renumbering between ACI 318 editions has already put wrong clause references into local transmittals, and a wrong number is worse than no number.
The reviewer's one-line summary: the clause that binds every penetration is the requirement that an embedment must not impair the strength of the construction significantly — that one always applies, and it puts the burden on the proponent to show the section still works. Diameter ≤ h÷3 and spacing ≥ 3 diameters carry mandatory force for pipes embedded within the member, and are the conservative yardstick most reviewers apply to transverse sleeves too. The l÷4-to-l÷3 window and the mid-depth band are guide recommendations — strong ones, but you enforce them as written only if the project specification adopts them.
Which points to the cheapest move available to a designer: write the window into the documents. One line on the general structural notes, requiring sleeves through beams to fall within the permissible zones of ACI 314R-11, Fig. 6.8.2.2, converts guidance into a contract requirement you can hold a subcontractor to.
Half a column at each end: 400 ÷ 2 = 200 mm.
l = 6400 - 200 - 200 = 6000 mm.
h ÷ 3 = 600 ÷ 3 = 200 mm. Proposed 100 mm ≤ 200 mm. Passes.
Band depth = h ÷ 3 = 600 ÷ 3 = 200 mm.
Mid-depth = 600 ÷ 2 = 300 mm above soffit.
Half the band = 200 ÷ 2 = 100 mm.
Lower boundary = 300 - 100 = 200 mm above soffit. Upper boundary = 300 + 100 = 400 mm above soffit.
A 100 mm sleeve on the centreline occupies 300 - 50 = 250 mm up to 300 + 50 = 350 mm. Slack below: 250 - 200 = 50 mm. Slack above: 400 - 350 = 50 mm. Passes.
Concrete left solid = 250 below plus 600 - 350 = 250 above, so 250 + 250 = 500 mm, and 500 ÷ 600 = 0.833, or 83.3 percent of the depth.
This beam is monolithic with a 125 mm slab, so the stem below the slab is 600 - 125 = 475 mm deep. The top of the band sits 475 - 400 = 75 mm below the underside of the slab. The whole band is inside the stem, which is what you want.
Now see what happens if MEP measures the visible stem instead. Taking h = 475 mm gives a maximum diameter of 475 ÷ 3 = 158.3 mm, a band depth of 158.3 mm, a mid-depth of 475 ÷ 2 = 237.5 mm, and half a band of 158.3 ÷ 2 = 79.2 mm — so the band runs 237.5 - 79.2 = 158.3 mm to 237.5 + 79.2 = 316.7 mm above the soffit. The same 100 mm sleeve at 300 mm now has its crown at 350 mm, which is 350 - 316.7 = 33.3 mm outside. Two readings of the same beam, two different verdicts. Define h once, on the drawing.
l ÷ 4 = 6000 ÷ 4 = 1500 mm. l ÷ 3 = 6000 ÷ 3 = 2000 mm.
Window width = 2000 - 1500 = 500 mm, which checks against l ÷ 12 = 6000 ÷ 12 = 500 mm.
Far-end window, measured from the same left face: 6000 - 2000 = 4000 mm to 6000 - 1500 = 4500 mm.
Layout check: 1500 + 500 + 2000 + 500 + 1500 = 6000 mm, and the blocked central band is 4000 - 2000 = 2000 mm = 6000 ÷ 3, the middle third exactly.
3 × diameter = 3 × 100 = 300 mm. Proposed 250 mm < 300 mm. Fails by 300 - 250 = 50 mm. This is the mandatory one.
At 250 mm spacing the three centres land at 1750 - 250 = 1500 mm, 1750 mm, and 1750 + 250 = 2000 mm.
Outer edge of the first sleeve = 1500 - 50 = 1450 mm, which is 1500 - 1450 = 50 mm outside the window. Outer edge of the last = 2000 + 50 = 2050 mm, which is 2050 - 2000 = 50 mm outside. Fails at both ends.
Now try three at the compliant 300 mm spacing. The footprint of n sleeves of diameter d is (n - 1) gaps of 3d plus half a diameter beyond each outer centre, so footprint = (n - 1)(3d) + d = (3n - 2)d. For n = 3 and d = 100: (3 × 3 - 2) × 100 = 7 × 100 = 700 mm against a 500 mm window. Since 700 > 500, three sleeves cannot share one window at all, however they are centred.
This is the first thing the subcontractor will propose, so answer it before he asks. Three sleeves need 7d ≤ 500, that is d ≤ 500 ÷ 7 = 71.4 mm.
At 75 mm: 7 × 75 = 525 mm, which exceeds 500 mm by 525 - 500 = 25 mm. Still fails.
At 50 mm: 7 × 50 = 350 mm, and 500 - 350 = 150 mm to spare. Fits.
So stepping down one size does nothing; only a drop to 50 mm works, and a 50 mm sanitary line is not an option. Two sleeves, by contrast, need (3 × 2 - 2)d = 4d ≤ 500, so d ≤ 500 ÷ 4 = 125 mm — the 100 mm sleeves fit in pairs with 500 - 400 = 100 mm to spare. Split the group; do not shrink it.
Two sleeves in the near window at 300 mm centres, group centred at (1500 + 2000) ÷ 2 = 1750 mm. Half the spacing = 300 ÷ 2 = 150 mm.
Centres at 1750 - 150 = 1600 mm and 1750 + 150 = 1900 mm. Edges at 1600 - 50 = 1550 mm and 1900 + 50 = 1950 mm.
Clearance: 1550 - 1500 = 50 mm and 2000 - 1950 = 50 mm. Footprint = 4 × 100 = 400 mm ≤ 500 mm. Passes.
The third sleeve moves to the far window: centre at (4000 + 4500) ÷ 2 = 4250 mm from the left face, edges at 4250 - 50 = 4200 mm and 4250 + 50 = 4300 mm, both inside 4000 mm to 4500 mm with 4200 - 4000 = 200 mm to spare each side. Passes.
All three stay at 300 mm above the soffit, unchanged. The third line simply crosses the beam 4250 − 2000 = 2250 mm further along than proposed — a routing change absorbed in a morning if it is raised now instead of after the pour.
The review comment writes itself. Diameter accepted; spacing revised to 300 mm per the mandatory embedment limit; group split two-and-one across the permissible zones; sleeves centred 300 mm above soffit measured from the form; no stirrup cut or displaced.
This check is five divisions and four comparisons: trivial once, tedious across forty beams, and easy to fumble at 4:40 on a Friday. So are span-to-depth checks, development lengths and the rest of the arithmetic that surrounds them, which is why RHCES keeps a library of 155 free engineering web tools that run in the browser.
Not on ACI 314R-11 alone, since that document is a non-mandatory guide. What a checker can hold you to is the mandatory requirement that an embedment must not significantly impair the strength of the construction, which puts the burden on you to show the section still works at that location under the governing shear. If your project specification or general structural notes adopt the figure, the window becomes a contract requirement and the rejection needs no argument at all. That is exactly why it belongs in the notes.
Not on site authority. The guide's zone addresses pipes placed before concreting, with reinforcement detailed around them; it says nothing about cutting hardened concrete. Coring needs written approval from the engineer of record, a cover meter or GPR scan to locate bars and stirrups before the drill touches concrete, and an absolute prohibition on cutting flexural tension steel. A core inside the window and the mid-depth band has the best chance of acceptance. Cut reinforcement is a design change, not a site adjustment, and the realistic outcomes are a smaller pipe, a rerouted line, or a designed opening with trimmer bars.
The one-third-of-thickness diameter limit and the three-diameter spacing come from ACI 318 embedment provisions covering slabs, walls, and beams alike, so measure against the thickness of the element the pipe is actually embedded in. The l÷4-to-l÷3 window and the mid-depth band belong to the girder, beam, and joist figure in ACI 314R-11; no equivalent window is offered there for slabs, so a slab penetration outside the ordinary sleeve sizes goes to the engineer of record for a designed opening.