Temporary Works Design - A Quality Management Perspective

--ConSIG CWG 23:24, 18 Oct 2020 (BST)

[edit] Introduction

‘Temporary works’ is a widely used expression in the construction industry. It may be useful to consider a respected definition to begin. BS 5975:2019 – Code of practice for temporary works procedures and the permissible stress design of falsework [1], article [IP address hidden], says:

‘Temporary works can be described as providing an “engineered solution” that is used to support or protect either:

• An existing structure or the permanent works during construction; or
• To support an item of plant or equipment; or
• The vertical sides or side-slopes of an excavation during construction operations on site; or to provide access.

It is used to control stability, strength, deflection, fatigue, geotechnical effects and hydraulic effects within defined limits.’

Temporary works can also include structures in a temporary condition, and loads applied to a structure that differ from the original design load.

The construction of most types of permanent works will require the use of some form of temporary works. Examples where temporary works are required include:

• Earthworks;
• Structures;
• Equipment/plant foundations;
• Demolition;
• Providing measures to control health and safety and environmental impacts on site; and
• To facilitate testing.

This article focuses on the design aspects of temporary works.

Some good practice seen recently on a major project considered the fulfilment of temporary works as a three-part process at top level:

It specifically has the purpose of providing a method for assuring that the design of temporary works is developed, validated and can be effectively implemented.

This process has been used as the framework for this article.

[edit] Establishing the management system

It is evident that requirements for temporary works must be effectively managed. The approach adopted can be part of an ISO 9001 Quality management system [2] for an entire organisation, although this is not mandated by BS 5975 [1]. Nevertheless, the latter sets out key elements of temporary works that must be addressed by procedure including:

1. Appointments to leadership roles – organisation and on site
2. Appointments to leadership roles – design
3. Competence
4. Control of risk
5. Temporary Works Register

Besides the Contractor’s procedure, it is good practice for design organisations to have their own procedure to manage their involvement in temporary works covering competence, risk mitigation and communication with other parties.

Note 1: the Contractor would also include temporary works requirements in its quality plan.

[edit] Appointments to leadership roles – organisation and on site

The Designated Individual (DI) is a ‘senior person’ appointed to manage the organisation’s procedures for temporary works and thereby address the organisational leadership principle.

The Temporary Works Coordinator (TWC) is a person appointed with overall responsibility for managing temporary works on a site (site leadership principle). The TWC is appointed by the Principal Contractor (PC). A TWC can be appointed by another contractor to manage their own temporary works but they would ultimately be responsible to the PC’s TWC.

The TWC can delegate certain day-to-day activities, such as site inspection to a nominated Temporary Works Supervisor (TWS). All TWC and TWS appointments are recorded and identified in a register maintained by the DI, eg in an organogram.

[edit] Appointments to leadership roles – design

In the UK, the Principal Designer (PD) is required by Regulation 11 of the Construction Design & Management (CDM) Regulations 2015 [3] to plan, manage and monitor the pre-construction phase and coordinate matters relating to health and safety. They do not take liability for design. Sometimes the client takes on the PD role, but this is not the intent of CDM Regs.

In their design, the Permanent Works Designer (PWD) makes provision for such temporary works required and considers the methods of construction that may be used.

Similarly, the Temporary Works Designer (TWD) is responsible for the design of temporary works and their constructability.

The Temporary Works Design Checker (TWDC) is provided with the design brief, design statement or approval in principle (AIP) and the necessary drawings and other documents to facilitate the design check. They are confirming that the design satisfies the Design Brief and is adequate and correct.

They will check the entire structural system relevant to the stability of the works at each stage of construction.

The CAT 3 Design Checker - a CAT 3 design check is required on a wide range of temporary works projects. An independent party is engaged to perform a review of the final temporary works drawings and specifications with the purpose of assuring that the proposed design is a suitable concept, adequate and correct. They will not have access to the TWD’s calculations and must produce their own to verify the temporary works design.

Note 2: The role titles shown in bold in paras 1a) & 1b) above are drawn from those identified in BS 5975 [1].

[edit] Competence

It is necessary for individuals to be competent to perform the designated roles above. This requires a mix of qualifications, skills, experience and training, eg a TWD would be expected to have completed safety in design training. These people should be subject to performance review and follow a structured programme of Continuing Professional Development (CPD) to ensure their capabilities remain current.

Their knowledge must be relevant to the role as well as to the complexity of the work. Accordingly, the depth of knowledge required in different disciplines varies from general awareness training through to job-specific technical courses (eg railways work, demolition or tunnelling).

A key aspect of competence for designers is their understanding of the construction process. This can present a challenge for people who do not have enough site experience.

The company temporary works procedure should say how designers and design checkers are selected, assessed, approved and allocated. Those performing the key roles of checking and approval in design should be identified in an authority matrix, alongside the disciplines in which they have expertise. Checkers and approvers of documents, drawings, calculations and models should only be selected from the authority matrix.

[edit] Control of risk

A standard approach to risk assessment in ISO 31000:2018 - Risk Management - Guidelines [4] looks at eliminating or, at least, mitigating risk.

A risk management process

BS 5975 [1] identifies that risks associated with temporary works can arise from:

• Their design;
• Their construction and use; and
• The consequences of their failure.

Design risk is associated with the complexity of the design. The more challenging the design, the higher the level of risk. It is mitigated through Design Risk Assessment (see section 2b) and the selection of the Category of Design Check (see section 2c).

Risks relating to construction, use and removal of temporary works include the proposed method of construction of the temporary works and permanent works, standard of workmanship, suitability of materials, experience of the team in that application and manner of use. These are termed ‘Execution Risks’.

Risks associated with the ‘Consequence of Failure’ of the temporary works come from their location and what might be affected by the failure, eg adjacent assets.

‘Execution’ and ‘Consequence of Failure’ risks combine to form an ‘Implementation Risk’.

Each item of temporary works should be classified with their ‘Implementation Risk’ level: ‘Very Low’, ‘Low’, ‘Medium’ or ‘High’. Procedures to address the risks can then be tailored according to significance.

Finally, a ‘Level of Control’ is decided in the risk assessment which sets the organisation’s proposals for managing the risks. This can include who is authorised to sign permits, the content of the inspection and test plan and method statement, and the requirement for senior management or peer review.

[edit] Temporary Works Register

In order to assess this information, the Temporary Works Register is used on site as a tool for management control. The PC’s TWC is responsible for ensuring that there is an up-to-date register covering those aspects needed for control of the temporary works. There is no set template for this register. The register will normally include the check category (see 2c below) and risk classes (see 1d above). Risks relating to temporary works may be entered into a project Health & Safety Risk Register, eg to monitor the risk treatment actions arising and their current status. Status can be represented using Red, Amber or Green (RAG) colouring to further denote significance.

The Designer will use a Design Risk Assessment to identify hazards and their mitigation, eg those relating to CDM Regulations in the UK [3] or relevant laws in other jurisdictions. On the drawings, residual risks that would not be apparent to a competent contractor are shown, eg using hazard warning triangles or SHE boxes. An example of this would be where there is an interface between the temporary works and the build of the permanent construction, where the former needs to happen first. The TWC may then enter these safety risks into the project Health & Safety Register with residual risks being addressed in the Method Statement.

On more complex projects, the register may be contained in a database and, on others, it may be a spreadsheet; both of which should have access controlled to prevent unauthorised changes.

[edit] Design

In terms of quality, temporary works must be to the same standards as the permanent works. Consider that a permanent structure may never actually be loaded to its design capacity, eg an office building is mostly open space and is unlikely to get anywhere near to its design floor loading. Temporary works are nearly always loaded up to the design value.

Good communication is an important element in the successful design of temporary works, particularly in coordination between TWD and TWC. There is a duty for the TWD, indeed all designers, to cooperate with other designers and, indeed, anyone involved on the site and any adjacent sites – CDM Regulations, Code of Practice L153, Regulation 8 (4) [5] refers.

Increasingly BIM is being used, eg for scoping temporary works, adding another skillset to competencies needed in the design team.

Major elements of temporary works design would be:

1. Design Brief / Design Statement
2. Design Risk Assessment
3. Temporary Works Categories
4. An effective system of checking
5. Design Check Certificate
6. Design Change Control
7. Design Review

[edit] Design Brief / Design Statement

Except for very low risk temporary works, a Design Brief should be prepared by the site team and issued by the TWC to the TWD. The two must agree the brief prior to commencement of design, eg the TWD should confirm the risk classification proposed by the TWC.

A Design Statement is required for more complex projects, eg requiring CAT 3 Check or in some cases where any temporary works are proposed to be left in place. The Design Statement sets out the basis for design, which might include a theoretical model of the structure, how it might be analysed, and values of certain design parameters.

[edit] Design Risk Assessment

From the beginning, the buildability of the design is an important consideration together with its safety during construction, operation and maintenance. In the UK, CDM Regulations [3] must be observed for managing health, safety and welfare. Risks pertaining to the design, its construction and the maintenance and use of a structure must be understood.

First and foremost, a TWD should be taking a decision to minimise the use of temporary works as much as possible in order to eliminate or reduce the risks they present.

For those that remain, a Design Risk Assessment is used to manage the risks associated with the design of temporary works. The objective being to achieve a level of risk that is reduced ‘as far as reasonably practicable’. In addition, refer to the sections on Control of Risk and Temporary Works Register (see 1d and 1e).

The striking of temporary works (take down) when no longer required also needs to be considered in the design to ensure it can be done efficiently and safely. This is an area where sequencing of construction and/or removal could be necessary.

Those design risks that cannot be eliminated or mitigated must be passed on to the PC as ‘Residual risks’, together with the supporting information that describes them. This includes ‘Hold Points’ required by the TWD. ‘Hold Points’ are stages in the construction where design criteria must be satisfied and permission obtained to proceed.

The Design Risk Assessment is made available to the PC if requested, eg as part of the Design Package. The Contractor is most interested in the residual risks which should be clearly shown on the design output, e.g. drawings. This is what is referred to by the operative in the field.

[edit] Categories of Design Check in Temporary Works

As a key mitigation measure, the category (CAT) of design check selected is determined by the complexity of the design and the design risk presented. There are four categories:

BS 5975:2019 [1], article 13.7, gives further detail.

Note 3: In Categories 2 and 3, design checking is done without reference to the TWD’s calculations instead the Checker produces their own to verify the design.

[edit] An effective system of checking

BS 5975 [1,] article [IP address hidden], recommends using an effective system of checking, both for the design and its implementation. Where appropriate, the procedure should cover the management of the approval (by clients and/or third parties) of design and design checking processes.

The TWC confirms the level of checking required with the TWDC, referring to the table in section 2c).

Where CAT 3 checking is required, a common misconception is that the CAT 3 Design Checker does the checking for the design team. It does not. The Designer should be presenting a fully formed design solution for validation by the CAT 3 Design Checker.

As identified in section 1c) above, checkers and approvers of documents, drawings, calculations and models should only be selected from the authority matrix.

Interfaces need to be considered in the planning for design checking such as:

• Where there is more than one element of design, it needs to be ensured that each are compatible; and
• When designing temporary works on an existing site, interfaces with other structures must be understood, eg for bridge refurbishment.

[edit] Design Check Certificate

On successful completion of checking and approval, the TWD and TWDC sign the Design Check Certificate to confirm the accuracy of the design and that it meets the Design Brief.

BS 5975 [1], article 13.7.5, states the certificate should state the category of check and identify the drawings/sketches, specification and any design methodology.

It is normally required for at least CAT 2 and 3 Checks and is included in the Design Package submitted to the TWC.

[edit] Design Change Control

All changes must be referred to the TWD and recorded. Larger changes call for a re-design and a new Design Brief. Where there is such a significant design change, the revisions to drawings / specifications must be re-checked by the TWDC.

[edit] Design Review

The need for a Design Review is identified in the Design Brief issued by the TWC.

A Design Review is carried out when the TWC receives the design from the TWD, prior to distribution to colleagues for construction.

For control of risk reasons, the TWC will arrange a Design Review to consider:

• Compliance with the Design Brief, Approval in Principle (AIP) requirements, and suitability of the design;
• Effectiveness of the interfaces, eg with the permanent works, with other temporary works, between designers within the scheme, and between trades and subcontractors;
• Mitigation of risks associated with the design solution, eg where the complexity of the temporary works is significant and/or there are numerous third parties and/or stakeholders involved;
• The need for access and exclusion zones; and
• Hold points required, to be transferred to the Inspection & Test Plan (ITP).

The design review findings and conclusions will be recorded. The conclusions will be incorporated into the design output and/or the ITP or Method Statement. Residual risks will be addressed in the latter.

[edit] Implementation

1. Designer’s involvement
2. Some quality-related steps on site
3. Lessons learned activity

[edit] Designer’s involvement

The setting out of temporary works is not within the scope of this article which is focused on their design. What will be covered is the interface the Designer has with the Contractor during their implementation.

A design output is that Designers must provide the Contractor with information relating to temporary works in the Design Package. This should include information on construction method or sequence and any information that may impact on future maintenance or demolition.

The site team should construct the temporary works in accordance with the certified design. The TWC or TWS should then issue a ‘Permit to Proceed’ confirming the temporary works have been erected in accordance with the certified design and any agreed revisions.

Design clash: BS 5975 [1], article [IP address hidden], says that where the method of construction of the permanent works differs from that which has been proposed by the Permanent Works Designer, the temporary works design should include an assessment of the permanent works for the various stages of construction, modification or demolition to determine adequacy of strength and/or stability.

Design change emanating from site: if, on inspection, installed temporary works are found by the TWC to vary from its Approved For Construction (AFC) status (ie from the approved documents and drawings), then the implications, eg safety, need to be understood and design change control initiated, to involve the TWD and TWDC, so as to recover the situation (see section 2f above).

Note 4: if the constructed TW is deemed to have deviated from the AFC design then works must stop and be made safe until a redesign is completed.

When it is decided that temporary works become permanent, they must be incorporated as such in the permanent works design, eg using design change control, and subject to review and checking again.

[edit] Some quality-related steps on site

Whilst this is an article written from the design point-of-view, in this section it may be useful for Designers to understand some key aspects of quality management and, by association, safety that pertain for the Contractor at the implementation stage.

i) Work Instruction:

• A ‘Methods of working summary’, or similar title, is developed by the Contracts team and used to prepare detailed working Method Statements.
• Document and Drawing Control on site is managed as part of the Work Package File.

ii) The procedure for bringing temporary works into service involves:

• The review of the Risk Assessment and Method Statement (RAMS) and Inspection and Test Plans (ITP), after which the TWC signs off as approved.
• The observance of Safety Critical Hold Points during construction whereby permission to progress to the next stage in the implementation sequence is obtained, eg ‘Permit to Proceed’.
• Permission to load the temporary works where the TWC undertakes a final inspection before issuing a 'Permit to Load' to release the hold point.
• Managing the handover of temporary works to another user or multiple users.

iii) Inspection

• Weekly inspections are carried out by TWC or TWS. Nominated experts such as a registered scaffold inspector or, for lifting equipment, an Appointed Person can be brought in.
• Some elements are subject to statutory inspection, eg scaffold and excavations.
• Otherwise, visual inspections of scaffolding, eg sign-off that the appropriate scaffold tagging system (SCAFFTAG) is in place to control access. This must be done once per week.
• Global stability checks where potential single point of failures exist such as in conveyor systems, hoardings, etc.
• Periodic inspections by TWC and/or TWS.
• Primarily, inspections are looking for departure from the as-constructed condition.

iv) Specific temporary works such as demolition.

• The demolition process is defined by the production of an 'Acceptable Methodology' and creates records including:
  • Demolition RAMS signed-off;
  • Demolition Readiness Review Checklist;
  • Design Certificate (where contractually required); and
  • ‘Permit to Demolish’.

v) ‘Permit to Proceed’, eg ‘to Strike falsework’, is issued where load is to be transferred from the temporary works to the permanent works, eg to authorise take down of temporary works.

[edit] Lessons learned activity

Communication between PC and TWD should have a mechanism for lessons learned in the implementation of temporary works on site to be fed back to the TWD to allow for improvement in future designs, on the current project or future ones.

The Temporary Works forum website www.twforum.org.uk [6] is a source of best practice information for all involved in temporary works, including clients.

[edit] Conclusion

The fulfilment of temporary works can be considered as a three-part process at top level:

Operating to a recognised management system is important, eg to ensure design and construction people can understand each other’s inputs and outputs to the project. Developing and maintaining the competency (in relevant disciplines) of the people nominated for the specified roles, such as Temporary Works Designer (TWD) and Design Checker (TWDC), is key.

A framework for good communications between those parties is vital, eg between Temporary Works Coordinator (TWC) on site and TWD.

Design risk assessment, from concept, through outline design, detailed design, implementation of temporary works, to their striking (take down) or inclusion in the permanent works, is necessary and should comply with national legislation such as CDM Regulations [3, 5] in the UK.

Also part of the management system is an effective system of checking from design through to implementation. Categories of risk exist to help the TWD decide the appropriate level of checking and other management controls required for the type and severity of risk presented by the project. ISO 31000 [4] provides a process approach to risk mitigation.

BS 5975 [1] provides a necessary standard for temporary works design and implementation given the complexity of the subject, particularly on larger projects. Best practice information is also available from the Temporary Works forum [6].

[edit] References

[1] BS 5975:2019 – Code of practice for temporary works procedures and the permissible stress design of falsework.

[2] ISO 9001:2015 – Quality Management Systems – Requirements.

[3] UK’s Construction Design and Management (CDM) Regulations 2015.

[4] ISO 31000:2018 – Risk Management – Guidelines.

[5] CDM Regulations, Code of Practice L153, Part 3 Health and safety duties and roles, Regulation 8 General duties, article (4).

[6] Temporary Works forum website www.twforum.org.uk

Reviewer(s): Keith Hamlyn and Jim Richings

Rev 1 (16/9/2020): Original article written by Kevin Rogers and reviewed by Keith Hamlyn and Jim Richings on behalf of the Chartered Quality Institute, Construction Special Interest Group (ConSIG). Article peer reviewed by the ConSIG Competency Working Group and accepted for publication by the ConSIG Steering Committee.

[edit] Related articles on Designing Buildings Wiki

• Crane support..
• Facade retention.
• Falsework.
• Formwork.
• Quality.
• Scaffold.
• Shoring.
• Temporary works.
• Trench support.
• Tunnelling.