A structural investigation is a planned process used to establish how an existing building, structure or structural element was constructed, what condition it is in and whether the available information is sufficient for a proposed engineering decision.
The investigation may combine record review, visual inspection, dimensional surveys, concrete scanning, local opening-up works, material sampling, laboratory testing, monitoring and structural analysis. The scope depends on the question that needs to be answered.
Structural investigations are commonly required before refurbishment, change of use, demolition, temporary works, installation of heavy plant, formation of new openings, façade replacement, building-safety remediation or assessment of visible deterioration.
Construction engineer scanning the floor while a colleague holds a tablet on an active building site
The key point is this: a structural investigation should be designed around a specific engineering question. Testing without a defined objective can produce large amounts of data without resolving the decision the structural engineer, contractor or building owner actually needs to make.

What Is a Structural Investigation?

A structural investigation gathers evidence about an existing structure so that a competent engineer can assess its construction, condition, capacity or suitability for proposed work.
The investigation may be limited to one local detail, such as confirming reinforcement around a proposed opening, or it may cover an entire building where the structural system is poorly documented.
Typical subjects include:
  • Concrete slabs, beams, columns and walls.
  • Steel frames and connections.
  • Masonry walls, piers and arches.
  • Timber floors, roofs and framing.
  • Foundations and ground-bearing elements.
  • Façade support systems.
  • Balconies, barriers and balustrades.
  • Temporary works interfaces.
  • Post-tensioned structures.
  • Existing anchors, fixings and cast-in components.
The investigation itself provides evidence. The structural engineer uses that evidence with calculations, design assumptions and professional judgement to reach an engineering conclusion.

Structural Investigation Versus Structural Survey

The terms structural investigation and structural survey are sometimes used interchangeably, but they can describe different levels of work.
Term Typical Meaning Possible Output
Visual structural survey Inspection of visible elements, defects and structural arrangements. Condition observations, photographs and recommendations.
Non-destructive investigation Use of scanning, measurement or testing without significant opening-up. Reinforcement maps, thickness estimates and condition-related data.
Intrusive structural investigation Controlled opening-up, sampling or exposure of concealed construction. Verified dimensions, materials, connections and physical condition.
Structural assessment Engineering review of evidence against loading, design and performance requirements. Calculations, conclusions and design recommendations.
A visual survey may identify that further investigation is required, but it may not provide enough evidence to confirm concealed reinforcement, connection details, material strength or foundation construction.

Why Are Structural Investigations Required?

Existing structures are often assessed using incomplete, outdated or inconsistent information. Drawings may be missing, construction may differ from the design or later alterations may not have been recorded.
An investigation may be required to support:
  • Office, residential or commercial refurbishment.
  • Change of use or increased loading.
  • Installation of heavy plant or equipment.
  • Formation of new slab, wall or roof openings.
  • Removal of structural or potentially structural elements.
  • Façade replacement or remediation.
  • Demolition planning and sequencing.
  • Temporary works design.
  • Investigation of cracking, movement or deterioration.
  • Assessment following impact, fire, flooding or accidental damage.
  • Verification of existing anchors or connections.
  • Building-safety and compliance work.
The investigation reduces uncertainty. It does not eliminate every unknown, but it allows assumptions to be replaced with measured and observed evidence where this is practical.

Why Existing Drawings May Not Be Enough

Record drawings can be valuable, but they should not automatically be treated as a complete as-built record.
Possible differences include:
  • Reinforcement moved during construction.
  • Bar sizes or spacing changed.
  • Services were diverted.
  • Openings were formed or infilled later.
  • Columns, walls or beams were altered.
  • Repair materials concealed the original construction.
  • Temporary details became permanent.
  • Later fit-outs introduced additional loads.
  • Drawings show design intent rather than final construction.
The investigation should use drawings to guide the survey while checking critical details against actual site conditions.
Related STRUCTinspect Guidance
STRUCTinspect has discussed the importance of verified site evidence for refurbishment in Structural Investigation for Office Retrofit: Beyond the Energy Model. Energy, architectural and services strategies depend on understanding the actual structure and concealed interfaces.

What Questions Can a Structural Investigation Answer?

Engineering Question Possible Investigation Evidence What Still Requires Engineering Review?
How thick is the slab? Scanning, cores, drilled measurements or exposed edges. Whether the thickness is sufficient for the proposed loading.
What reinforcement is present? GPR, cover meter and local breakouts. Structural capacity, anchorage and adequacy.
What material was used? Cores, samples, visual exposure and laboratory testing. How the measured properties affect design or repair.
How is the connection formed? Opening-up, endoscopy, scanning and measurement. Connection resistance and required strengthening.
Why is the structure cracking? Crack mapping, monitoring, opening-up, material and movement data. Cause, significance and remedial strategy.
Can a new opening be formed? Reinforcement, tendon, thickness and support information. Opening design, trimming and temporary works.

Typical Stages of a Structural Investigation

1. Define the Engineering Question

The investigation should begin with a clear statement of what must be determined.
Examples include:
  • Confirm the reinforcement around a proposed slab opening.
  • Establish whether an existing floor can support new plant.
  • Identify how a façade bracket is fixed to the structure.
  • Determine the construction of an undocumented wall.
  • Investigate the cause and extent of concrete cracking.
  • Confirm slab thickness and material strength.
  • Identify whether a wall is loadbearing.
A defined question allows the engineer to select methods that produce relevant evidence.

2. Review Existing Information

The desk study may review:
  • Structural drawings.
  • Architectural drawings.
  • Specifications.
  • Reinforcement schedules.
  • Post-tensioning layouts.
  • Previous investigation reports.
  • Repair records.
  • Alteration drawings.
  • Historic photographs.
  • Operation and maintenance information.
The review identifies known information, contradictions and gaps that require site verification.

3. Complete an Initial Site Inspection

An initial inspection helps confirm access, visible construction, defects and practical constraints before intrusive work is planned.
The inspection may record:
  • Structural grid and element arrangement.
  • Visible cracking, movement or deterioration.
  • Finishes concealing the structure.
  • Access restrictions.
  • Existing services.
  • Occupied or sensitive areas.
  • Work-at-height requirements.
  • Locations suitable for scanning or opening-up.

4. Prepare the Investigation Specification

The specification should define the locations, quantities, methods, dimensions and required outputs.
It should also identify who is responsible for interpreting the results and approving any change to the scope.

5. Complete Non-Destructive Surveys

Non-destructive methods can map concealed features and help select the most informative intrusive locations.

6. Complete Targeted Intrusive Work

Opening-up, sampling or direct exposure is then used where physical confirmation is required.

7. Test Samples and Review Results

Laboratory and site data should be checked against the original question. Unexpected findings may require additional investigation.

8. Complete Engineering Assessment

The structural engineer combines the investigation results with calculations, loading information and design requirements.

9. Issue the Investigation Report

The final report should record the scope, evidence, limitations and recommended next steps.

Non-Destructive Structural Investigation Methods

Non-destructive testing can gather information without significantly damaging the element. The appropriate method depends on the material and investigation objective.
Method Possible Information Main Limitation
Ground-penetrating radar Reinforcement, tendons, services, interfaces and possible thickness. Deep features may be masked by shallow reinforcement.
Electromagnetic cover meter Shallow reinforcement position and estimated cover. Congested steel can distort readings.
Ultrasonic testing Material continuity, thickness and possible internal anomalies. Interpretation depends on material properties and geometry.
Rebound hammer testing Surface-hardness-related comparison across concrete areas. Does not directly establish compressive strength without correlation.
Half-cell potential survey Evidence relating to corrosion probability in reinforcement. Does not directly measure section loss.
Crack monitoring Change in crack width or movement over time. Monitoring alone may not identify the cause.
Dimensional survey Element dimensions, alignment, levels and deflection. Does not confirm concealed construction or material properties.

Concrete Scanning Within Structural Investigations

Concrete scanning is frequently used early in an investigation to understand reinforcement patterns and select locations for cores, drilling or breakouts.
It may help identify:
  • Reinforcement direction and approximate spacing.
  • Estimated concrete cover.
  • Possible reinforcement layers.
  • Post-tensioning tendons or ducts.
  • Embedded services.
  • Possible element thickness.
  • Cast-in plates or channels.
  • Areas of reinforcement congestion.
For a detailed explanation of scanner outputs and limitations, read What Can a Concrete Scanner Detect?.
Scanning reduces unnecessary damage by helping the engineer target intrusive work. It does not normally confirm reinforcement grade, exact bar size, anchorage, corrosion condition or concrete strength.

Visual Inspection and Defect Mapping

A visual inspection is usually one of the first investigation activities. It establishes the visible condition of the structure and helps direct later testing.
The inspection may record:
  • Crack location, orientation and width.
  • Spalling and delamination.
  • Corrosion staining.
  • Water ingress and dampness.
  • Movement at joints.
  • Distortion or deflection.
  • Previous repairs.
  • Exposed reinforcement.
  • Impact or fire damage.
  • Construction changes and undocumented openings.
The survey should distinguish between observation and diagnosis. A diagonal crack may be measured and mapped visually, but its structural cause requires engineering assessment and possibly further investigation.

Dimensional and Level Surveys

Structural dimensions can differ from drawings or vary across the building. Survey measurements may confirm:
  • Slab, wall and beam dimensions.
  • Column sizes.
  • Floor levels.
  • Deflection profiles.
  • Verticality.
  • Opening positions.
  • Connection geometry.
  • Façade support locations.
Where the engineer needs dimensions for calculations, the survey method and measurement reference should be recorded clearly.

What Is an Intrusive Structural Investigation?

An intrusive structural investigation physically exposes, drills, cuts or samples part of the structure to verify concealed information.
Common intrusive methods include:
  • Concrete reinforcement breakouts.
  • Concrete cores.
  • Masonry opening-up.
  • Inspection holes through finishes.
  • Endoscope or borescope openings.
  • Exposure of steel connections.
  • Removal of local fire protection.
  • Timber inspection openings.
  • Foundation trial pits.
  • Local excavation around buried elements.
Intrusive work provides direct evidence but creates greater site risk, disruption and reinstatement requirements. It should therefore be targeted carefully.

Why Non-Destructive Testing Often Comes First

Non-destructive surveys can identify the most informative locations for opening-up. This reduces the chance of forming unnecessary or poorly positioned openings.
For example:
  • Scanning can locate a reinforcement bar before a controlled breakout.
  • GPR can help choose a concrete core position away from significant steel.
  • A cover survey can identify low-cover zones for durability checks.
  • Crack mapping can identify representative monitoring locations.
  • Thermal or moisture surveys can target opening-up around suspected water paths.
The investigation should balance the need for direct confirmation against damage, cost, programme and occupancy constraints.

Concrete Reinforcement Breakouts

A reinforcement breakout removes a controlled area of concrete to expose the embedded steel.
It may confirm:
  • Bar diameter.
  • Bar spacing and direction.
  • Concrete cover.
  • Links or stirrups.
  • Reinforcement layers.
  • Local lap or anchorage details.
  • Corrosion or section loss.
  • Bond and surrounding concrete condition.
Scanning should normally be completed before breakout so the opening targets the required bar without cutting or damaging it.
The breakout size, depth and repair method should be agreed before work begins.

Concrete Core Sampling

Concrete cores provide physical samples that can support assessment of:
  • Compressive strength.
  • Concrete thickness.
  • Layered construction.
  • Density.
  • Carbonation.
  • Chloride content.
  • Petrographic condition.
  • Cracking or internal defects.
Core positions should be selected jointly from structural and testing considerations. The core should be representative of the required concrete while avoiding important reinforcement, tendons and services.
The core diameter, orientation, length and laboratory requirements should be specified before extraction.

Steelwork Opening-Up

Existing steel connections may be concealed behind ceilings, cladding, fire protection or finishes.
Opening-up may be used to confirm:
  • Member size and section type.
  • Plate dimensions.
  • Bolt number and arrangement.
  • Weld type and extent.
  • Bearing details.
  • Connection geometry.
  • Corrosion or damage.
  • Fire-protection thickness and type.
Removal of fire protection or coatings may create additional safety and reinstatement requirements. Hazardous-material information may also be necessary before disturbing existing finishes.

Masonry Opening-Up

Masonry investigations may need to establish:
  • Wall thickness.
  • Solid or cavity construction.
  • Brick, block or stone arrangement.
  • Bond pattern.
  • Presence of wall ties.
  • Lintel construction.
  • Embedded steelwork.
  • Condition of mortar and units.
  • Whether the wall bears on the structure below.
A local opening may not represent the entire wall. Several locations may be required where construction varies or alterations are suspected.

Foundation Investigations

Foundation investigations may include trial pits, local excavation, scanning, cores and ground testing.
The scope may seek to confirm:
  • Foundation type.
  • Plan dimensions.
  • Depth below ground level.
  • Concrete condition.
  • Reinforcement.
  • Bearing strata.
  • Relationship with adjacent foundations.
  • Underground services.
Excavation near foundations can affect stability and should be planned with appropriate temporary works, service information and engineering control.

Material Testing Within Structural Investigations

Material testing provides evidence about the properties or condition of the structural materials.
Material Possible Tests Possible Evidence
Concrete Core strength, carbonation, chloride, petrography, density and pull-off testing. Strength, composition, deterioration and repair-substrate condition.
Steel Material identification, hardness, thickness and weld examination. Section properties, material characteristics and connection condition.
Masonry Unit testing, mortar testing, flat-jack testing and sampling. Material strength, stress and construction characteristics.
Timber Moisture, resistance drilling, probing and species or grade assessment. Decay, section loss and material condition.
The testing method should be selected by the engineer or materials specialist against the required design or condition information.

Concrete Strength Investigation

Concrete strength may be investigated using a combination of non-destructive comparison methods and physical core testing.
A rebound hammer can help compare surface hardness across locations, but it does not directly replace compressive testing of cores.
Core results are influenced by:
  • Core diameter and length.
  • Orientation.
  • Moisture condition.
  • Presence of reinforcement.
  • Damage during extraction.
  • Concrete age and condition.
  • Test preparation and laboratory procedure.
The structural engineer should specify the sampling plan and interpret the results for the existing structure.

Durability Investigations

A durability investigation assesses mechanisms that may affect the remaining service life or condition of reinforced concrete.
The investigation may combine:
  • Visual defect mapping.
  • Concrete cover measurement.
  • Carbonation testing.
  • Chloride sampling.
  • Half-cell potential surveys.
  • Concrete resistivity testing.
  • Local reinforcement exposure.
  • Delamination surveys.
  • Moisture and water-path investigation.
One result should not be interpreted in isolation. Low cover may increase vulnerability, but it does not by itself prove corrosion. Corrosion staining may indicate deterioration, but the extent and cause still require investigation.

Structural Load Testing

Where calculations and construction information cannot provide sufficient confidence, controlled structural load testing may sometimes be considered.
A load test should have:
  • A defined engineering objective.
  • A specified test load.
  • Agreed acceptance criteria.
  • A designed reaction and loading arrangement.
  • Deflection or displacement monitoring.
  • Exclusion zones and emergency controls.
  • Engineer-approved RAMS.
  • A clear reporting and interpretation route.
Load testing should not be improvised as a substitute for missing design information. It is a specialist investigation activity requiring engineering control.

How Is a Structural Investigation Scope Planned?

The scope should be proportionate to the decision and the consequences of uncertainty.
The planning process should consider:
  • The proposed alteration or loading.
  • The structural system.
  • Available drawings and their reliability.
  • Known defects or incidents.
  • Access to concealed elements.
  • Occupancy and disruption constraints.
  • Hazardous materials.
  • Services and post-tensioning.
  • Temporary works requirements.
  • Testing and laboratory lead times.
  • Repair and reinstatement requirements.

The Investigation Brief Should Be Specific

A good investigation brief should identify:
  • Each structural element to be investigated.
  • The location and number of test points.
  • The required dimensions of openings or samples.
  • The features to be confirmed.
  • The required testing methods.
  • Required photographs and drawings.
  • Laboratory testing requirements.
  • Reinstatement responsibility.
  • The required report format.
  • The engineer responsible for interpretation.
Phrases such as “investigate the slab” or “check the wall” are normally too broad to price, plan or execute reliably.

How Are Investigation Locations Selected?

Locations should be selected because they provide relevant evidence, not only because they are easy to access.
The selection may target:
  • Representative structural bays.
  • Areas of highest loading.
  • Support and connection zones.
  • Locations of visible distress.
  • Different construction phases.
  • Areas where drawings are uncertain.
  • Proposed openings or alterations.
  • Locations where finishes can be reinstated reasonably.
Testing only the most convenient locations may produce unrepresentative confidence.

How Many Investigation Locations Are Required?

There is no universal number. The quantity depends on the size and variability of the structure, the available records and the consequence of the decision.
More locations may be needed where:
  • The building has several construction phases.
  • Structural arrangements vary.
  • Previous alterations are suspected.
  • Results differ from drawings.
  • Defects are widespread.
  • The proposed change has high structural consequence.
  • Initial findings show significant variability.
The engineer may adopt a staged approach, using initial results to decide whether additional work is required.

Staged Structural Investigations

A staged investigation controls cost and disruption while allowing the scope to respond to evidence.
Stage Typical Work Decision Supported
Stage 1 Desk study and visual inspection. Identify gaps and priority investigation areas.
Stage 2 Non-destructive surveys and dimensional checks. Map concealed construction and target intrusive work.
Stage 3 Opening-up, cores and material samples. Physically verify critical details and properties.
Stage 4 Additional targeted testing or monitoring. Resolve unexpected findings or remaining uncertainty.

Practical Site Requirements

Structural investigations often take place in occupied, live construction or constrained environments. Access and logistics can determine whether the technical scope is achievable.
The project should confirm:
  • Site access and induction requirements.
  • Working hours.
  • Permit requirements.
  • Power and water availability.
  • Work-at-height access.
  • Scaffold, MEWP or platform provision.
  • Protection of occupied areas.
  • Dust, noise and vibration restrictions.
  • Waste removal.
  • Fire alarm or service isolation.
  • Reinstatement standards.

Service and Post-Tensioning Risks

Intrusive work should not begin until embedded-service and post-tensioning risks have been reviewed.
Controls may include:
  • Review of service drawings.
  • Concrete scanning.
  • Electrical service detection.
  • Isolation of relevant systems.
  • Post-tensioning drawings.
  • Permit-to-drill procedures.
  • Maximum-depth controls.
  • Stop-work instructions.
Scanning reduces risk but does not guarantee the detection of every small, deep or masked feature.

Temporary Works and Structural Stability

Some investigation activities can affect structural stability. Examples include:
  • Excavating beside foundations.
  • Removing loadbearing finishes or encasement.
  • Opening masonry near bearings.
  • Exposing steel connections.
  • Forming large concrete breakouts.
  • Removing façade support components.
  • Loading floors with test equipment or reaction plant.
The engineer should determine whether propping, sequencing or temporary works are required before the investigation begins.

Investigation RAMS

The RAMS should translate the technical scope into a safe and controlled site method.
It should address:
  • Exact work locations.
  • Equipment and access.
  • Services and post-tensioning.
  • Maximum drilling or breakout depths.
  • Dust, noise and water control.
  • Falling-object risks.
  • Exclusion zones.
  • Temporary works.
  • Stop conditions.
  • Sample identification.
  • Reinstatement.
  • Emergency arrangements.
STRUCTinspect has covered the relationship between technical methodology and practical controls in What a Structural Testing RAMS Must Contain Before Loading Starts. The same principle applies to structural investigations: the written method should reflect the actual equipment, access, structural risks and decision points.

Sample Identification and Chain of Custody

Samples should be traceable from the structure to the laboratory result.
The record may include:
  • Unique sample reference.
  • Project and element.
  • Exact location.
  • Orientation.
  • Depth.
  • Date and time of extraction.
  • Photographs.
  • Sample condition.
  • Requested laboratory tests.
  • Packaging and transport details.
Poor sample identification can make valid laboratory data unusable because the result cannot be related confidently to the structure.

Reinstatement of Investigation Openings

The scope should define whether openings are:
  • Left open temporarily for inspection.
  • Made safe only.
  • Reinstated immediately.
  • Repaired by another contractor.
  • Completed using a specified repair system.
The repair method should consider:
  • Substrate preparation.
  • Reinforcement protection.
  • Bonding requirements.
  • Repair material.
  • Fire and acoustic performance.
  • Waterproofing.
  • Surface finish.
  • Curing and protection.
A cosmetic patch may not be sufficient where structural concrete, fire protection, waterproofing or durability performance must be restored.

Unexpected Findings During Investigation

Investigations frequently identify conditions that differ from drawings or assumptions.
Examples include:
  • Different slab thickness.
  • Missing or additional reinforcement.
  • Unexpected post-tensioning.
  • Unrecorded services.
  • Voids or layered construction.
  • Corrosion or damaged steel.
  • Previous alterations.
  • Different foundation type.
  • Unexpected hazardous materials.
The methodology should include a stop-and-review process. Operatives should not extend the opening or improvise additional testing without appropriate approval.

What Should a Structural Investigation Report Include?

  • Project name, address and report reference.
  • Client and instructing party.
  • Investigation objectives.
  • Documents and drawings reviewed.
  • Scope and investigation locations.
  • Methods and equipment.
  • Access and surface conditions.
  • Visual observations.
  • Measured dimensions.
  • Scanning and non-destructive findings.
  • Opening-up and intrusive findings.
  • Sample and laboratory results.
  • Photographs and marked-up drawings.
  • Differences from record information.
  • Unresolved or uncertain areas.
  • Limitations.
  • Recommendations for further work.
The report should preserve enough location information for each result to be related to the correct element later.

Measured Results Versus Engineering Interpretation

The report should distinguish between:
Evidence Type Example Responsibility
Observed A 0.4 mm diagonal crack was measured at the beam end. Survey or investigation team records the evidence.
Measured The exposed reinforcement measured approximately 20 mm in diameter. Testing team reports the result and method.
Interpreted The radar response is consistent with a tendon duct. Competent operator explains the evidence and uncertainty.
Assessed The beam requires strengthening for the proposed loading. Responsible structural engineer completes the assessment.
This separation prevents testing results from being mistaken for design approval.

Photographs and Drawings

Photographs should include both context and detail.
Useful records include:
  • General location views.
  • Investigation position before work.
  • Scanning and surface markings.
  • Opening dimensions.
  • Exposed construction.
  • Measured bars, plates or connections.
  • Sample locations.
  • Defects and deterioration.
  • Completed reinstatement.
Marked-up plans should identify levels, grids, structural elements and unique investigation references.

Limitations of Structural Investigations

An investigation samples selected areas. It cannot normally expose or test every part of the structure.
Relevant limitations may include:
  • Restricted access.
  • Occupied areas.
  • Finishes that could not be removed.
  • Services preventing opening-up.
  • One-sided access to structural elements.
  • Limited sample quantities.
  • Variability between construction phases.
  • Reinforcement congestion.
  • Unverified record information.
  • Areas left untested.
  • Temporary site conditions.
  • Testing methods that provide indirect estimates.
The report should identify project-specific limitations rather than relying only on broad disclaimer wording.

Can Investigation Results Be Applied to Untested Areas?

Results should not automatically be assumed to represent the whole structure.
The ability to extrapolate depends on:
  • Consistency of construction.
  • Reliability of drawings.
  • Number and distribution of investigation locations.
  • Variation in measured results.
  • Different construction phases.
  • Previous alterations.
  • Material and exposure conditions.
The structural engineer should decide whether the evidence is representative or whether further locations are required.

What Structural Investigations Cannot Prove Alone

A structural investigation does not automatically provide:
  • Complete knowledge of every concealed detail.
  • A guarantee of structural adequacy.
  • Approval for an alteration.
  • Confirmation that untested areas are identical.
  • A permanent prediction of future condition.
  • A design where only testing was instructed.
  • Removal of the need for temporary works.
  • Removal of construction and permit controls.
The investigation supplies evidence to the responsible engineer and project team.

Common Structural Investigation Mistakes

Mistake Why It Is a Problem Better Approach
No defined engineering question. Testing may generate data without resolving the decision. Define the required information before selecting methods.
Relying only on record drawings. The as-built structure may differ from design information. Verify critical details on site.
Selecting only convenient locations. Results may not represent critical or variable zones. Target representative and high-risk locations.
Using scanning where physical confirmation is required. Bar size, condition or connection details may remain uncertain. Use targeted opening-up after non-destructive mapping.
Opening-up without scanning for services or tendons. The work may damage concealed systems. Use appropriate detection and permit controls first.
No reinstatement plan. Openings may remain unsafe or improperly repaired. Define making-safe and repair responsibilities in advance.
Applying local results to the whole building. Construction may vary between areas and phases. Assess representativeness and state limitations.

Structural Investigation Brief Checklist

  • Engineering question: state exactly what the investigation must establish.
  • Proposed works: describe the alteration, load, repair or assessment being considered.
  • Structure: identify the building, level, grid and elements.
  • Existing information: provide drawings, reports and alteration records.
  • Investigation locations: mark each required position.
  • Methods: specify visual, scanning, opening-up, sampling and testing requirements.
  • Dimensions: state required breakout, core or access-hole sizes.
  • Material tests: identify laboratory requirements.
  • Services: provide drawings and isolation information.
  • Post-tensioning: identify known or suspected tendon systems.
  • Access: confirm scaffold, MEWP, ceiling removal or excavation requirements.
  • Temporary works: identify propping or stability controls.
  • Occupied areas: define noise, dust and working-hour restrictions.
  • Reinstatement: state the required repair standard and responsibility.
  • Reporting: define photographs, drawings, data and report format.
  • Interpretation: identify the structural engineer responsible for assessment.

Evidence-Based Summary

A structural investigation is a planned process used to gather evidence about the construction, condition and performance of an existing structure.
It may combine document review, visual inspection, dimensional surveys, non-destructive testing, intrusive opening-up, sampling and laboratory testing.
The scope should be developed around a defined engineering question rather than a generic request for testing.
Non-destructive methods can map the wider structure and help target the most informative intrusive locations.
Intrusive investigation provides direct confirmation but requires service checks, structural control, access planning and reinstatement.
Investigation results apply primarily to the tested locations and should not automatically be extrapolated across untested areas.
The responsible structural engineer uses the investigation evidence to complete calculations, assess significance and determine whether further work, repair or strengthening is required.

FAQ: Structural Investigations

What is a structural investigation?
A structural investigation gathers evidence about an existing structure using surveys, measurements, scanning, opening-up, sampling and testing so that an engineer can assess it.
When is a structural investigation required?
It may be required before refurbishment, change of use, increased loading, new openings, demolition, temporary works, façade remediation or investigation of defects and damage.
Is a structural investigation the same as a structural survey?
A structural survey may be primarily visual, while a detailed investigation can include non-destructive testing, opening-up, sampling and laboratory analysis.
Who specifies a structural investigation?
The responsible structural engineer or designer should normally define the information, locations, methods and quantities needed for the engineering assessment.
Can scanning replace structural opening-up?
Not always. Scanning can locate and map concealed features, but exact bar size, connection details, material condition and construction build-up may require physical exposure.
What is an intrusive structural investigation?
It involves physically opening, drilling, cutting, sampling or excavating part of the structure to verify concealed information directly.
What tests can be included?
Possible methods include concrete scanning, cover surveys, cores, rebound hammer testing, carbonation testing, chloride sampling, load testing, crack monitoring and connection opening-up.
How many investigation locations are needed?
The quantity depends on the structure, variability, available information and consequence of the proposed decision. A staged investigation may be appropriate.
Can results from one location be applied everywhere?
Not automatically. The engineer should assess whether the tested position is representative of other areas and whether construction is consistent.
Do investigation openings need to be repaired?
Normally, the project should define how openings will be made safe or reinstated, including structural, fire, acoustic, waterproofing and finish requirements.
Does an investigation confirm structural capacity?
The investigation provides evidence. Structural capacity is determined by the responsible engineer using the results, loading information and calculations.
What should happen if unexpected construction is found?
The work should stop at the agreed safe point, the finding should be recorded and the engineer should review whether the scope or method needs to change.
What should a structural investigation report include?
It should include objectives, reviewed information, locations, methods, measurements, test results, photographs, drawings, differences from records, limitations and recommendations.

Source Context and Editorial Note

This article is a STRUCTinspect technical explainer covering the planning, delivery and reporting of structural investigations for existing buildings and construction projects.
It provides general information rather than a project-specific investigation specification. Survey methods, test quantities, sampling locations, temporary works, laboratory testing and acceptance requirements should be selected for the particular structure and engineering objective.
This article does not provide structural engineering, temporary works, materials, health and safety, contractual or construction advice. Investigation findings should be reviewed by the appropriate structural engineer, designer, materials specialist, contractor or competent professional responsible for the assessment and proposed works.