Structural engineering notes
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Practical structural engineering notes, worked out with real numbers from our own design sheets. They are written for Filipino engineers and builders, and each one shows the calculation step by step so you can check it yourself. This is general information, not a substitute for the engineer of record on your project.
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Adding Water to Concrete on Site: What Half a Pail Does to Strength
Why extra water makes concrete weaker, with real numbers for a 40 kg bag: 22 L gives about 29 MPa, 30 L only about 17 MPa. What to do instead.
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Why Column Ties Need 135-Degree Hooks (and Closer Spacing Near the Beams)
A 90-degree tie hook opens in an earthquake. A worked NSCP 2015 SMRF column shows the common detail is 4.5 times short on confinement, and how to fix it.
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A CHB Fence Is Not a Retaining Wall: The Numbers
Filling a lot 2 m high behind a hollow-block fence? A worked check gives a fence-type wall a factor of safety of 0.41 against overturning, and shows the fix.
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Isolated Footing Design to NSCP 2015: A Complete Worked Example
Step-by-step NSCP 2015 design of a 2.40 x 2.40 m isolated footing: soil pressure with moments, one-way shear, punching, flexure, development and dowels.
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Development Length and Lap Splices in NSCP 2015, Step by Step
How long must a 20 mm bar be embedded or lapped? An NSCP 2015 worked example: 462 mm detailed, 756 mm by the simple table, 600 mm Class B lap, 266 mm hook.
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Tie Wire Is Not Structural, but Slab Top Bars Still Need Ties and Spacers
Tie wire adds no strength, but with spacers it keeps slab top bars at their design height. An NSCP 2015 example shows the strength lost when they drop.
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Strap Footing for a Column on the Property Line: Why an Ordinary Tie Beam Is Not Enough
A column on the property line cannot have a centred footing. A worked NSCP 2015 sample shows why an ordinary tie beam falls short and what a strap needs.
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Why a C Purlin Should Not Be Laid Flat (and Why Sag Rods Still Matter)
A C purlin laid flat carries the roof on its weak axis. A worked NSCP 2015 check gives a ratio of 3.28 laid flat, and 0.70 upright with sag rods.
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Building Separation From the Property Line: How Much Gap Does NSCP 2015 Require?
A worked NSCP 2015 check of the seismic gap at the property line: for this sample 3-storey frame the roof ΔM is 132 mm, so a 50 mm gap is too small.
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More Steel, Less Design Strength: Net Tensile Strain and φ in NSCP 2015
Adding 33% more bottom steel to a 350 x 500 beam lowered its design strength from 368 to 360 kN·m. A worked NSCP 2015 check of net tensile strain and φ.
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Corner Columns and Biaxial Bending: Why Passing Each Axis Is Not Enough
A corner column bends about both axes at once. In an NSCP 2015 example each axis passes at 0.62, but the sheet's straight-line check sums them to 1.24.
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A Balcony Slab Is a Cantilever: Thickness and Top Bars to NSCP 2015
A 1.5 m balcony slab is a cantilever. An NSCP 2015 check shows why 100 mm is below the code minimum, why extra bars do not settle it, and how 150 mm meets it.
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Stair Reinforcement at the Kink: Cross the Bars, Do Not Run Them Around the Corner
Bottom bars bent around the inside corner under a stair landing push outward on the cover. A worked NSCP 2015 sample shows the force and the crossed-bar fix.
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Column Offset on an Isolated Footing: Why Size Alone Is Not Enough
The same 2.4 m footing passes with the column centred and fails with it 300 mm off-centre. A worked NSCP 2015 soil pressure check, and how to fix it.