Single-Sided Embedded Bolt vs Through-Tie
> In brief > - The two approaches need different wall build-ups. > - The anchor carries what the through-tie would have carried. > - A like-for-like comparison needs the same certificate basis.
A normal tie works because it is in tension between two faces: the rod pulls, the anchor plates push back on the formwork, and the two cancel. Take one face away and that balance has to be rebuilt somewhere else — in the concrete already cast, in a bracket, or in the ground. This is the situation on a diaphragm wall against an excavation face, a core wall against an existing structure, or a tank where the second face will never be accessible.
Our own production and test data are available on request — see how our factory works and contact the engineering team for the documents behind any figure quoted here.
Single-sided embedded bolt is a fastener cast into a previous pour or footing, anchoring new formwork to it. Through-tie refers to a rod that passes through both faces of the formwork, carrying the load in tension. Pull-out load means the force required to extract the embedded bolt from the hardened concrete. Edge distance is the spacing from the bolt to the free edge of the concrete, critical for preventing breakout. Embedment depth refers to the length of the bolt embedded in the concrete, essential for its pull-out capacity.
The two routes.
A single-sided embedded bolt is cast into a previous pour or into a footing, and the new formwork is anchored to it. The bolt carries the pull-out load into the hardened concrete. Nothing passes through the new wall.
A through-tie needs both faces. Where the far face exists but is already built, a through-tie can sometimes be replaced by a bolt anchored into the old concrete, or by a tie welded to an embedded plate. Where the far face is soil or rock, an anchor has to go into the ground instead.
| Criterion | Single-sided embedded bolt | Through-tie |
|---|---|---|
| Faces required | One | Two |
| Load path | Pull-out into hardened concrete or ground | Tension between two formwork faces |
| Hardware recovered | Partly — the outer bar and nuts | Yes — the whole rod |
| Depends on previous pour strength | Yes | No |
| Typical exposure | Diaphragm walls, cores, tank walls, additions | Standard walls and slabs with two accessible faces |
| Main failure mode | Pull-out or edge breakout | Rod yield or anchor plate punching |
Why single-sided work is harder to get right.
The load does not disappear; it has to be carried by something that was cast earlier. Three things decide whether the detail holds:
- EMBEDMENT DEPTH AND EDGE DISTANCE — a bolt near an edge can break out a cone of concrete instead of developing its full pull-out capacity. Spacing to the free edge and to the next bolt matters as much as depth.
- STRENGTH OF THE HOST CONCRETE AT THE TIME OF LOADING — if the previous pour has not reached the specified strength, the bolt is being asked to load concrete that is not ready. Curing records matter here, not the calendar.
- ALIGNMENT — an embedded bolt cast out of position cannot be moved. Templates and a check before the pour are the only reliable control.
Standard basis: EN 13670 — Execution of concrete structures
Sequencing rules that prevent most failures.
- Set the bolts with a template rigid enough to hold position during the pour and vibration.
- Check the position after the pour and before the formwork is erected; record it.
- Confirm the host concrete strength from cube or cylinder results before loading the bolts.
- Tighten to a defined torque, not "until it feels right" — an under-torqued bolt lets the panel move, an over-torqued one can strip the thread or crack the concrete locally.
- Load the bolts progressively as the pour rises; the pressure is not uniform and neither should the tightening be.
Where a through-tie is still the better answer.
If both faces are accessible, a through-tie is usually cheaper and more forgiving: the load path is simple, the hardware is reusable, and the capacity is easy to verify with a pull test. Single-sided anchorage is chosen because access forces it, not because it is better. On retaining walls against soil where the excavation face is later backfilled, it is worth checking whether a temporary through-tie with a sleeve is possible before committing to embedded bolts.
Pull-out testing.
For embedded bolts, a pull-out test on the actual installation is the only direct verification. Test a sample of bolts to the specified load before the pour, keep the records with the pour card, and replace any bolt that has been tested beyond its working load. A bolt that has been proof-loaded is a bolt that has been used.
Standard basis: ISO 898-1
What to specify when ordering.
- Bolt diameter, grade and thread standard, matched to the nuts and plates used with it.
- Embedment depth and the minimum concrete strength required at loading.
- Edge distance and spacing assumed in the design — these must appear on the setting-out drawing, not only in the calculation.
- Whether the bolts are supplied with templates, and whether the template is reusable.
- Surface treatment: bolts that stay in the ground or in a wet environment need protection appropriate to the exposure, and the coating must not reduce thread fit.
For walls that must retain water, the water-stop decision is separate from the anchorage decision — see cast iron water stop nut vs welded plate.
References and standards.
- EN 13670 — Execution of concrete structures
- ACI 347 — Guide to formwork for concrete
- OSHA 1926.703 — Concrete equipment and formwork
- OSHA concrete safety and health topics
- EN 14399-1 — High-strength structural bolting assemblies
- ISO 16047 — Hexagon head bolts and hex nuts
About us: This article compares single-sided embedded bolts and through-ties, checked against our production and test data. Our factory produces a wide range of formwork fasteners. Our contact page provides access to the engineering team for detailed inquiries, and the about page documents how our factory works. This article was reviewed by the Qianheng Formwork Engineering team.