Destructive bend test, three beam types

Engineering test poster

An engineering poster is read the way a test report is read: rig, standard, tolerances, then the table of what broke and how. This A0 landscape example puts eight of twelve beam specimens in a failure load table, one load against deflection curve per beam type, and the plate and screw tolerances in the methods block.

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The whole board

The poster at full size, exactly as it prints. Every number, citation and caption on it was written for this example, so the layout is being judged on real content.

Screwed steel flitch plates raise the failure load of 240 mm timber beams by 48 percent

O. Baptiste ¹, H. Sato ¹, G. Ferreira ²

1 Structures Laboratory, Corriedale Institute of Technology · 2 Corriedale Timber Products

Abstract

Twelve 240 by 90 mm laminated timber beams were loaded to failure in four point bending over 3.6 m: four timber only, four with a glued 6 mm steel flitch plate, four with the same plate screwed at 150 mm pitch. Mean failure loads: 28.4, 36.9 and 42.1 kN. Screwed plates carried 48 percent more than timber alone, and two of four glued beams failed early by bond slip, the finding that decides how these beams are built.

METHODS

Specimens. 240 x 90 mm laminated timber, 3.6 m span, four per type: timber only, glued flitch, screwed flitch.

Rig. Four point bend with load points at the third points, 250 kN actuator, two LVDTs at midspan for deflection.

Rate. Displacement control at 2 mm per minute, loaded monotonically to failure; load and deflection logged at 10 Hz.

Standard. Test arrangement and specimen conditioning followed the national timber structures bending test standard cited below.

Tolerances. Plate thickness 6.0 mm plus or minus 0.1 mm; screw pitch 150 mm plus or minus 2 mm; span set to plus or minus 5 mm.

FAILURE LOAD AND MODE

Specimen	Type	Failure load kN	Mode
T1	Timber only	27.8	Tension
T2	Timber only	29.1	Tension
G1	Glued flitch	35.6	Bond slip
G2	Glued flitch	38.0	Tension
S1	Screwed flitch	41.2	Tension
S2	Screwed flitch	43.5	Screw yield
S3	Screwed flitch	42.0	Tension
S4	Screwed flitch	41.7	Tension
Caption (optional)

Why flitch plates

A flitch beam sandwiches a steel plate inside a timber section so a renovation can carry new load without a deeper beam, and the steel works only while it stays composite with the timber. How the plate is fixed is therefore the whole question. Glue gives the stiffest connection on paper and the least forgiving one in practice: a glue line cannot be inspected after assembly, cures badly in cold or dusty site conditions, and when it lets go it lets go at once. Screws are slower to install and leave visible heads, but every one of them can be checked, and a screwed connection sheds load gradually rather than suddenly. Published capacity tables for flitch beams in this size range assume full composite action and say nothing about which fixing method delivers it at failure. These twelve beams were tested to answer exactly that: whether glue or screws hold the plate to failure, what each fixing costs in ultimate load, and which failure mode a designer should expect to govern. Eight of the twelve specimens are printed in the table; the other four are in the results text, and every mean on this board can be recomputed from them.

REFERENCES

1.Baptiste O, Sato H. Four point bending of composite timber steel sections: rig design and measurement. Structures Testing Journal 2024;19(2):101-116.

2.Ferreira G, Baptiste O. Flitch beam behaviour under sustained and short term load. Timber Engineering Notes 2025;8(1):40-56.

3.Sato H, Marchetti V. Reporting destructive test series: a checklist for structures laboratories. Laboratory Practice in Engineering 2023;5(3):177-190.

Glued flitch

Screwed flitch

Timber only

Figure 1. Load against midspan deflection, one representative beam per type. Glued and screwed share a slope; screwed fails highest at 42 kN.

Source: Trial dataset, 2026.

Results

Mean failure loads were 28.4 kN for timber only (27.8, 29.1, 28.0, 28.7), 36.9 kN for glued flitch (35.6, 38.0, 37.2, 36.8) and 42.1 kN for screwed flitch (41.2, 43.5, 42.0, 41.7). Screwed plates carried 48 percent more than timber alone (42.1 / 28.4 = 1.48) and glued plates 30 percent more. Two of the four glued beams failed by bond slip below the glued mean, at 35.6 and 37.2 kN. Initial stiffness was within 6 percent between glued and screwed beams, so the fixing showed itself only at failure. Eleven of twelve failures started on the tension face; the twelfth was screw yield at 43.5 kN, the highest load recorded in the series. The four specimens not shown in the table are T3 at 28.0 kN and T4 at 28.7 kN, both tension, and G3 at 37.2 kN by bond slip with G4 at 36.8 kN in tension. Deflection at failure averaged 34 mm for timber, 30 mm glued and 41 mm screwed, so the strongest group also gave the most warning.

+48%

failure load, screwed flitch against timber only

42.1 against 28.4 kN mean, n = 4 beams per type

Discussion

The number that matters most is not a mean. Two of four glued beams failing by bond slip means the glued connection, not the steel or the timber, set their capacity, and a site assembled glue line has every disadvantage the laboratory one did not. The screwed group was also the most consistent, with a range of 2.3 kN against 2.4 for glued and 1.3 for timber, and its one non tension failure was ductile screw yield at the top of the series. Stiffness being near identical between the two fixing methods removes the usual argument for glue. Four specimens per type is a small series from a single timber batch, so these means carry no design status; they support a fixing recommendation, not a capacity table.

Screwed plates: 42.1 kN mean failure load

Glued plates: 2 of 4 failed by bond slip

Timber only: 28.4 kN mean

Recommend screwed plates for site assembly

Block by block

What each block on the board is for, in the order a reader walks it.

Title band and authors: The title is the design recommendation with its number: screwed steel flitch plates raise the failure load of 240 mm timber beams by 48 percent. The timber supplier appears as a second affiliation, which is where a test series like this usually gets its specimens.
Abstract: Four sentences carry the series: twelve beams, three types, 3.6 metre span, mean failure loads of 28.4, 36.9 and 42.1 kN, and the sentence that matters most, two of four glued beams failed early by bond slip. The abstract flags the mode, not just the means.
Methods: rig, rate, standard, tolerances: Five protocol entries: specimens, the four point rig with its 250 kN actuator and two midspan LVDTs, the 2 mm per minute displacement rate, the national bending test standard followed, and tolerances, plate thickness 6.0 plus or minus 0.1 mm, screw pitch 150 plus or minus 2 mm.
Failure load and mode by specimen (table): The eight row table lists specimen, type, failure load in kN and failure mode, from T1 at 27.8 kN in tension to S2 at 43.5 kN by screw yield. The other four specimens are printed in the results text, so all twelve are on the board and every mean can be recomputed.
Introduction: why flitch plates: The intro block sits beside the table and frames the choice the series was built to settle: glue gives the stiffest connection on paper and the least forgiving one on site, because a glue line cannot be inspected after assembly, while every screw can be checked. The published capacity tables assume composite action either fixing may not deliver at failure.
Load against deflection (Figure 1): One representative curve per beam type, not twelve overlapping lines: timber to 28 kN at 34 mm, glued to 37 kN, screwed to 42 kN at 41 mm. Three lines keep the shape difference readable at a metre, and glued and screwed sharing a slope makes the stiffness point without prose.
Results and the key number: The results text prints all four values behind each mean and the arithmetic of the headline: 42.1 over 28.4 is 1.48, the plus 48 percent in the stat block. It also reports what the table only hints at, that the two bond slip failures were the two lowest glued results.
Discussion, conclusion points and references: The discussion argues the mode matters more than the mean: a fixing that fails by bond slip in half its specimens sets the design recommendation regardless of averages, and four specimens per type supports a fixing choice, not a capacity table. The three references are invented for this fictional study, because the reference block is required on this layout; replace them with your sources.
How to adapt this board: Put your specimens in the table one row each with their failure mode, and if you tested more than eight, keep the extremes and the odd modes in the table and move the rest to results. Chart one representative curve per type, cite your test standard in methods, and print tolerances, because that is what a test engineer scans for first.

What makes this board work

The table is the evidence

Eight rows carry specimen, type, load and mode, and the screwed mean of 42.1 kN is the arithmetic of rows S1 to S4. A reader can rebuild every mean on the board from the table plus four values in the results text.

One curve per type

Figure 1 shows three load deflection lines, not twelve, so the shared slope of glued and screwed beams and the higher screwed failure load read from across an exhibition hall.

Tolerances printed

Plate thickness 6.0 plus or minus 0.1 mm and screw pitch 150 plus or minus 2 mm sit in the methods block. Tolerances are the first thing a test reviewer looks for and the first thing most posters omit.

Questions people ask

What goes on an engineering poster?

The rig, the standard followed, the tolerances, a table of results by specimen, one chart, and a recommendation sized to the evidence. This board ends at a fixing recommendation rather than a capacity claim because twelve beams from one timber batch support the first and not the second.

Can the table hold all twelve specimens?

The table slot on this layout holds eight rows plus a header, so this board prints eight specimens and puts the remaining four in the results text with their loads and modes. Choose the table rows to carry the story: here that means both bond slip failures and the screw yield specimen.

Which chart suits load against deflection?

A line chart with one series per specimen type. The figure slot on this layout accepts all ten chart kinds, and line is the one that shows stiffness as slope and ductility as length of run. Twelve individual curves would be honest but unreadable; one representative curve per type is the poster convention.

Should I show a photo of the rig?

No poster layout has a fillable image slot, so the rig lives in a methods entry: four point bend, load at third points, 250 kN actuator, two LVDTs at midspan. That one sentence answers what a photo would, and rig photographs with dimensions belong behind the QR code.

Can I cite a standard on the board?

Yes, twice: name the test standard in the methods protocol where the procedure is described, and put the full citation in the reference list. This board does both, and it also states the loading rate and specimen conditioning so a reader can judge conformity rather than take it on faith.

Is landscape right for engineering results?

Landscape suits a board organised around a wide table, which is the natural shape of a specimen by specimen test series; this example is on the A0 landscape canvas at 2340 by 1656. A portrait board suits a single dominant figure better than a table led layout.

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Sources

Written and checked by the OneCraft team. Last checked 2 September 2026.