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Post-installed anchors do not universally replace cast-in anchors, but they can remove a major sequencing constraint when a project cannot wait for anchor cages, concrete pours or long design cycles. EJOT’s account of the £121 million Herring Bridge project in Great Yarmouth shows the point: the team used bespoke M36 LIEBIG Ultraplus mechanical undercut anchors, in 1.45 m and 1.09 m lengths, to install bridge-operating machinery after the concrete work had progressed. EJOT says this allowed equipment to be installed “when ready” rather than “when scripted”. That is a manufacturer case study, not an independent comparative trial, and its mixed-length arrangement was project-specific. The practical lesson is to compare the exact anchor, approval, concrete condition, loads, geometry, installation controls and programme—not to assume that either installation method is always superior.
What is the difference between cast-in and post-installed anchors?
Cast-in anchors are positioned before concrete is poured, then become embedded as the concrete hardens. Post-installed anchors are installed after the concrete has cured, usually by drilling a hole and fitting a mechanical or bonded anchor. The distinction is primarily about when the connection is created, but that timing affects design coordination, construction sequence, inspection and the ability to change locations later.
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A cast-in system can be efficient when the anchor layout is known early and the reinforcement, formwork and baseplate tolerances are under control. Its weakness is commitment: a late design change or a misplaced anchor can create costly remedial work. Post-installation shifts the drilling operation later, when the as-built concrete and equipment locations are visible. That flexibility is valuable for retrofit work, phased construction, congested sites and machinery that cannot be finalised at the start of the pour.
Neither label tells you the connection’s capacity by itself. Performance depends on the specific product and approval, concrete strength and cracking state, embedment, member thickness, edge and spacing distances, load direction and magnitude, drilling method, hole cleaning, installation torque or setting procedure, and inspection.
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| Decision factor | Cast-in anchor | Post-installed anchor |
|---|---|---|
| Installation point | Before the concrete pour | After concrete has hardened, commonly by drilling |
| Programme effect | Requires early design and coordination | Can defer final fastening locations and equipment installation |
| Change tolerance | Low once concrete is placed | Greater flexibility, subject to reinforcement scans, edge distances and approval limits |
| Critical controls | Positioning, formwork restraint and pour quality | Hole diameter and depth, drilling method, cleaning, setting, torque and inspection |
| Design basis | Project specification and anchor system details | Product-specific evaluation or ETA plus the governing design code |
A peer-reviewed overview of anchor behaviour provides useful general background on this cast-in/post-installed distinction, but it does not validate any particular EJOT product or the Herring Bridge design. See the peer-reviewed discussion of anchor performance.
How did post-installation help the Herring Bridge project?
EJOT’s Herring Bridge case study describes a project in Great Yarmouth valued at £121 million. The bridge’s operating mechanism required substantial baseplates and high-capacity connections. The project team considered post-installed anchors so cofferdam construction could progress without waiting for the extended design time that the case study associates with cast-in placement.
EJOT says it manufactured bespoke M36 LIEBIG Ultraplus mechanical undercut anchors in two lengths: 1.45 m and 1.09 m. Both lengths were used on the same baseplates. These dimensions describe that project’s anchors; they are not general performance ratings or a recommendation for other baseplates.
The case study reports that an initial concept used more anchors at shallower embedment. The team concluded that the concrete capacity would not support the projected forces under that arrangement, so it developed a mixed-length solution. EJOT UK anchoring specialist Paul Papworth explained the design rationale this way:
“Whilst the ETA does not legislate for such a permutation, i.e. the use of different lengths of anchor in the same baseplate, the ACI (American Concrete Institute) Building Code does because it takes into account the additional area of resistance in the concrete which can be created by the approach.”
That statement is important for two reasons. First, an ETA or evaluation document may not cover every configuration a project engineer wants to use. Second, another design framework may provide a route for checking a configuration, but only when the engineer demonstrates that its assumptions, resistance models and detailing rules apply. The Herring Bridge arrangement should therefore be read as a project-specific approval strategy, not as blanket permission to mix anchor lengths.
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EJOT says the post-installed approach reduced design and construction time and delivered associated cost benefits. It also says machinery could be installed “when ready” rather than “when scripted”. The case study does not provide an independent, quantified comparison of hours or pounds saved, so those benefits should be treated as reported project outcomes rather than universal results.
How does the LIEBIG Ultraplus mechanism differ from a standard expansion anchor?
EJOT describes LIEBIG Ultraplus as a heavy-duty mechanical undercut anchor. Its explanation is that the anchor’s undercut transfers compression between the anchor and the surrounding concrete surface, creating a stress-transfer pattern that EJOT says resembles its cast-in comparison. EJOT contrasts that behaviour with standard undercut anchors in which partial expansion forces at the bottom of the anchor create compression.
This is a manufacturer’s technical description of one product family. It does not establish that post-installed anchors generally match cast-in anchors, nor does it remove the need to check concrete breakout, steel strength, pull-out, pry-out, shear, combined loading and serviceability effects. The relevant product diameter, embedment and installation method must be taken from current technical documentation.
EJOT’s Anchoring Technology catalogue explains the company’s product terminology and installation principles. Use the catalogue alongside the product’s current approval and the project engineer’s calculations; a catalogue description is not, by itself, a design approval.
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A post-installed option is worth evaluating when the benefit of late installation outweighs the added drilling, inspection and design controls. Typical triggers include:
- Late or evolving equipment information: machinery, baseplates or service penetrations are not frozen when the concrete pour is scheduled.
- Phased construction: the structure must advance while the fastening design or supplied equipment is still being finalised.
- Access to hardened concrete: the team can safely scan, drill, clean and inspect the connection zone.
- Retrofit or strengthening: the existing member has no practical cast-in provision.
- High-capacity detailing: a product-specific undercut system can satisfy the required tension, shear and combined-load checks within the available member thickness and edge distances.
Conversely, cast-in anchors may remain preferable where reinforcement congestion makes drilling risky, where the connection is repetitive and fully coordinated before the pour, or where the project cannot tolerate drilling noise, dust, water management and hold-point inspections. A post-installed solution is not automatically faster: drilling and verification can become the programme’s critical path if access is poor or the hole-quality requirements are demanding.
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What must the engineer check before specifying post-installed anchors?
The following checklist turns the general comparison into a project decision. The design team should document each item rather than relying on a headline capacity or a familiar anchor name.
- Approval and code scope. Identify the exact manufacturer, model, diameter, embedment range and installation condition covered by the ETA, ICC-ES report or other recognised evaluation. Confirm the governing concrete design standard and whether the approval covers cracked concrete, seismic actions, fire exposure or sustained tension where relevant.
- Concrete condition. Establish compressive strength, age, cracking state, member thickness and reinforcement layout. Scan before drilling and confirm that the proposed hole will not cut reinforcement or services.
- Actions. Separate tension, shear, bending and prying effects, then check combined loading. Include installation and operating loads, fatigue or vibration where machinery is involved, accidental actions and any temporary construction cases.
- Geometry. Verify effective embedment, edge distance, anchor spacing, baseplate thickness, hole clearance and the available concrete volume. A nominally high-capacity anchor can lose resistance when installed close to an edge or another anchor.
- Installation procedure. Specify drilling equipment, bit type, hole diameter and depth, cleaning sequence, anchor setting, torque or expansion operation, temperature limits and weather protection. Define who is competent to perform each step.
- Inspection and records. Set hold points for reinforcement scanning, hole-depth checks, cleaning verification, torque records, proof checks where required and photographic or digital records. Treat non-conforming holes according to an engineer-approved repair procedure.
- Baseplate and grout details. Check hole access through the plate, washer and nut arrangement, levelling, grout strength, slot tolerances and load transfer between the equipment and concrete. Anchor calculations cannot compensate for a flexible or poorly supported baseplate.
- Sequence and maintenance. Confirm when drilling can occur, how dust and water will be controlled, how the connection will be protected during commissioning and whether future retightening or inspection is possible.
What does the Herring Bridge mixed-length decision prove—and what does it not prove?
It demonstrates that a project team can develop a bespoke post-installed arrangement for demanding machinery when conventional cast-in sequencing is inconvenient. It also shows why the design route may involve more than one code: the case study says the mixed-length combination was outside the anchor’s ETA, while the team used a combination of design codes, including the American Concrete Institute Building Code, to secure approval.
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1Scan for outdated or missing drivers - takes under a minute2Repair Windows errors before they cause bigger problems3Fix the driver behind crashes, sound loss and screen glitchesIt does not prove that any two anchor lengths may be mixed on a baseplate, that every undercut anchor behaves like a cast-in anchor, or that post-installation will always cost less. The dimensions, loading, concrete geometry, drilling quality and engineering checks from that project cannot be transferred to another bridge, plant room or façade support without a new design.
BAM Farrans’ Lynsey McNeilly said in the case study that the project’s results showed a post-install approach could be advantageous even where cast-in was viable. That is a participant’s statement published by EJOT, not independent test evidence. Use it as context for the project decision, not as a general performance claim.
How should you read approvals and evaluation reports?
Start with the product identity and the exact configuration. An approval normally states the anchor family, sizes, effective embedments, concrete strengths, cracked or uncracked concrete conditions, installation method and design equations or limitations. Check the issue date and validity before using it in a submittal.
For example, ICC-ES ESR-4870 is a separate evaluation for EJOT WAe-VI and WAe-EI wedge anchors. It describes evaluated use in specified cracked and uncracked concrete conditions and identifies those anchors as an alternative to cast-in-place anchors under the cited code editions. It is not an approval for LIEBIG Ultraplus and does not validate the Herring Bridge mixed-length arrangement. The report was reissued in March 2025 and stated that it was subject to renewal in March 2026; its current renewal status should be confirmed with ICC Evaluation Service or the manufacturer before relying on it for a November 2026 project.
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Where a proposed arrangement falls outside the approval, the engineer may need a project-specific design using the governing code, supplemental testing, a formal deviation review or an alternative anchor. “The product is approved” is not the same as “this installation is approved.”
What are the main failure modes and how can a project control them?
Post-installed connections can fail through steel rupture, concrete cone breakout, pull-out, splitting, pry-out, edge breakout or excessive displacement. Installation defects add another layer: an oversized or shallow hole, incomplete cleaning, incorrect torque, damage to threads, drilling into reinforcement or a gap under the baseplate can reduce capacity.
Controls should be practical and auditable. Scan and mark reinforcement before drilling; use calibrated equipment; keep a hole log; require installers to record depth, cleaning and setting; and stop work when the concrete is weaker, thinner or more cracked than the design assumed. If a hole is abandoned or damaged, do not simply move the anchor closer to an edge or drill again without an engineer’s revised layout. For machinery, include commissioning vibration and alignment checks, not only installation torque.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How do schedule and cost trade-offs work in practice?
The economic case is project-specific. Post-installation can avoid redesigning formwork, waiting for a final anchor cage or delaying machinery delivery. It can also add engineering time, scanning, specialist drilling, dust extraction, access equipment, inspection and remedial provisions. EJOT reports schedule and cost benefits at Herring Bridge but publishes no independent quantified comparison, so a business case should use the project’s own programme and rates.
A useful comparison has two parallel schedules: the earliest date for a cast-in anchor to be designed, fabricated, fixed, poured and surveyed, and the earliest date for a post-installed anchor to be designed, scanned, drilled, inspected and loaded. Price both the normal sequence and realistic recovery work for misplaced anchors, reinforcement clashes, failed inspections or delayed equipment.
What should a specification and installation plan contain?
State the product and approval by exact designation, not merely “heavy-duty anchor”. Include diameter, effective embedment, hole diameter and depth, concrete strength and cracking assumptions, edge and spacing limits, design code, corrosion or environmental category, installation tools, cleaning method, torque or setting requirements, inspection records and acceptance criteria.
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Drawings should show anchor coordinates, tolerances, baseplate holes, reinforcement exclusion zones and any different lengths or embedments. If lengths are mixed, identify the engineering justification and the document that authorises it. The method statement should define competent installers, hold points and the response to non-conforming holes. Require the final as-built record before the equipment is commissioned.
So, are post-installed anchors displacing cast-in anchors?
No universal displacement is supported by the available evidence. The stronger conclusion is narrower: advances in products such as EJOT’s LIEBIG Ultraplus give engineers another route when programme, access or late design information make cast-in placement awkward. The Herring Bridge account is a persuasive example of that route being engineered for a demanding application, but it remains a manufacturer case study with project-specific dimensions and approvals.
Choose cast-in when early coordination, repetition and controlled formwork make it the lower-risk sequence. Choose post-installed when hardened-concrete access and disciplined installation can deliver a documented, approved connection while preserving programme flexibility. In both cases, the anchor is only one part of the load path; the concrete member, baseplate, grout, reinforcement and installation quality must be designed together.
Frequently Asked Questions
Can a post-installed anchor be used in cracked concrete?
Only if the exact anchor and installation configuration is approved for cracked concrete and the design code permits the intended loading. Cracking state, concrete strength, embedment and edge distances must match the evaluation report; a product name alone is not sufficient.
What does M36 mean on an anchor specification?
M36 identifies a metric nominal thread diameter of about 36 mm. It does not state the anchor’s effective embedment, steel grade, allowable load or suitability for a particular concrete member; those values come from the product documentation and design.
How can a contractor verify that a drilled hole is acceptable?
Use the project method statement and the manufacturer’s installation instructions: verify location and depth, clean the hole in the specified sequence, check the anchor setting and torque with suitable equipment, and record the result. Any hole that is shallow, oversized, contaminated or obstructed should be assessed under an engineer-approved non-conformance procedure.
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Does an ICC-ES report cover every anchor made by the same manufacturer?
No. An ICC-ES report is tied to the products, sizes, materials, installation conditions and code scope named in that report. ESR-4870 concerns WAe-VI and WAe-EI wedge anchors, so it should not be treated as approval for LIEBIG Ultraplus or for a different anchor arrangement.
