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TWs Design Procedure

We delve into the essential roles and responsibilities of key personnel in the realm of temporary works design and execution. These roles are pivotal in ensuring the smooth and safe functioning of temporary works, which are crucial in construction projects. Each role, from the Lead Engineer to the Supervisor, plays a unique part in this intricate process, balancing design, safety, and practicality. The design and management of temporary works are complex tasks requiring specialized knowledge and coordination. This section outlines the specific responsibilities and expectations for each role, emphasizing their contribution to the overall success of the project.

Eduardo Sendín

Principal Engineer & Founder

These roles are like cogs in a well-oiled machine, each essential and interconnected. It's their skill in managing temporary works that ensures our projects are not only structurally sound but also safe and efficient.

Table of Content.

1. Design Process

Design Process Chart

2. Key Personnel Roles & Responsibilities

  • Temporary Works Designer Lead Engineer (TWDLE)
    Overview: Senior designer overseeing temporary works design and coordination.
  • Temporary Works Principal Engineer (TWPE)
    Overview: Manages pre-construction planning and health and safety coordination.
  • Temporary Works Designer (TWD)
    Overview: Responsible for the design and constructability of temporary works.
  • Temporary Works Design Checker (TWDC)
    Overview: Reviews and verifies temporary works designs.
  • Temporary Works Coordinator (TWC)
    Overview: Manages and coordinates all temporary works on-site.
  • Temporary Works Supervisor (TWS)
    Overview: Assists in supervising and ensuring compliance of temporary works.

3. Risk Management

ES calculations standardize risk assessment and management, emphasizing design complexity, risk mitigation, and buildability in temporary works.

4. Design Check Category

ES calculations standardize risk assessment and management, emphasizing design complexity, risk mitigation, and buildability in temporary works.

1. Design Process

2. Key Personnel Roles & Responsibilities

1.1 Temporary Works Designer Lead Engineer (TWDLE)

  • The TW Designer Lead Engineer (TWDLE) is a senior designer appointed to manage the ESC’s procedures for temporary works and thereby address the organizational leadership principle.

    The TWDLE shall manage the design interfaces of the temporary works designers (TWD) or checkers (TWDC), whether ESC is carrying out the checker role. The lead designer might not necessarily be the Principal Engineer, also a Senior Engineer or Associate Engineer can perform this role.

    The lead designer should ensure that:

    1. There is a distribution of design task amongst appropriate designer, especially where the design of temporary works is an integral part of the permanent works methodology.
    2. The communication of design data between organizations is controlled and any iterations are completed to the required levels.
    3. Design contributions from all designers are compatible with each other.
    4. They have a holistic understanding of the whole design.
    5. The design output is complete and clearly communicated.
    6. The Permanent Works Designer and Temporary Works Coordinator are informed about significant residual risk associated with the design.

    On completion of the design, the Design Lead Engineer shall issue a design certificate or design check certificate. Where the category of design check is not specified by the contractors’ procedures or the client, the TWDLE, in consultation with the TWC, should advice the minimum category of design check.

1.2 Temporary Works Principal Engineer (TWPE)

  • The Temporary Works Principal Engineer (TWPE) shall plan, manage, and monitor the pre-construction phase and coordinate matters relating to health and safety.

    The Temporary Works Principal Engineer should ensure that:

    1. There is a coherent construction method which identifies all key temporary conditions and temporary works.
    2. The finally agreed construction method, sequence and temporary works are not deleterious to the permanent works design.
    3. Designers follow the recommendations, codes of practice and relevant standards.
    4. They share information with TWDLE and, ultimately, with permanent structure designer, and the PC’s TWC and TWC, that might influence the design of permanent works or the selection of construction methods.
    5. Designers take account of the construction phase plan.
    6. They provide appropriate information relating to temporary works that would be required for the health and safety file; this should include information on construction method or sequence including associated temporary woks which might impact on future maintenance or deconstruction.

1.3 Temporary Works Designer (TWD)

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

    The Temporary Works Designer shall confirm that the design details and outline methodologies are accurately translated into the design outputs, and that the design follows appropriate engineering principles. This includes any assumed construction methods, sequences, temporary works requirements, and loads to be either imposed on or supported by the permanent works.

    TWD should confirm that the design output adequately describes the design in a design certificate or other suitable form of record.

1.4 Temporary Works Design Checker (TWDC)

  • The Temporary Works Design Checker (TWDC) is responsible for the review of the design of temporary works and their constructability.

    The Temporary Works Design Checker (TWDC) shall confirm that the design details and outline methodologies are accurately translated into the design outputs, and that the design follows appropriate engineering principles. This includes any assumed construction methods, sequences, temporary works requirements, and loads to be either imposed on or supported by the permanent works.

    TWDC should confirm that the design output adequately describes the design in a design check certificate or other suitable form of record.

1.5 Temporary Works Coordinator (TWC)

  • 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 shall be recorded and identified in a register maintained by the Contractor Designated Individual, for example in an organogram.

1.6 Temporary Works Supervisor (TWS)

  • The Temporary Works Supervisor (TWS), where appointed, should be responsible to the PC’s TWC or TWC as appropriate. The TWS should assist the PC’s TWC or TWC, as appropriate, in the supervision and checking of the temporary works.

3. Risk Management

2.1 Risk Management Approach

  • The TW Designer Lead Engineer (TWDLE) is a senior designer appointed to manage the ESC’s procedures for temporary works and thereby address the organizational leadership principle.

    The TWDLE shall manage the design interfaces of the temporary works designers (TWD) or checkers (TWDC), whether ESC is carrying out the checker role. The lead designer might not necessarily be the Principal Engineer, also a Senior Engineer or Associate Engineer can perform this role.

    The lead designer should ensure that:

    1. There is a distribution of design task amongst appropriate designer, especially where the design of temporary works is an integral part of the permanent works methodology.
    2. The communication of design data between organizations is controlled and any iterations are completed to the required levels.
    3. Design contributions from all designers are compatible with each other.
    4. They have a holistic understanding of the whole design.
    5. The design output is complete and clearly communicated.
    6. The Permanent Works Designer and Temporary Works Coordinator are informed about significant residual risk associated with the design.

    On completion of the design, the Design Lead Engineer shall issue a design certificate or design check certificate. Where the category of design check is not specified by the contractors’ procedures or the client, the TWDLE, in consultation with the TWC, should advice the minimum category of design check.

4. Design Check Category

Category. Scope Comment Independence Checker Examples

0

Restricted to standard solutions only, to ensure the site conditions do not conflict with the scope or limitations of the chosen standard solution. These may include standards trench boxes.

This applies to the use of standard solutions and not the original design, which requires both structural calculation and checking to Category 1, 2 or 3, as appropriate.

Because this is a site issue, the check may be carried out by another member of the site or design team.

  • Kicker shutters, local and small scale shaping of the ground, small, single lift short duration access scaffolds controlled by ‘Scaftag’ or similar
  • Shallow trenches, pits and excavated batters, not exceeding 1.2m depth with no significant overburden or groundwater.
  • Low-rise formwork at ground/excavation level, max 2.4m double sided, 0.9m single sided 
  • Non-design scaffolds to TG20:13xxi tables
  • Site hoarding and fencing less than 2m high
  • Other low risk items generally less than 1.2m high or 1.2m deep

1

For simple designs. These may include: formwork, falsework, needling and propping to brickwork openings in single storey constructions.

Such designs would be undertaken using simple methods of analysis and be in accordance with the relevant standards, supplier’s technical literature or other reference publications.

The check may be carried out by another member of the design team.

  • Use of standard components to catalogue design
  • Pits and trenches to CIRIA 97 Trenching Practice XXII
  • Excavated slopes not exceeding 30deg incline or 2m height in free draining soil
  • Designed scaffolds and loading platforms to TG20:13xxi tables
  • Double sided formwork with access platforms at ground/excavation level
  • Single sided formwork to 2.4m
  • Routine formworks/falseworks at not more than 6m height, slabs not exceeding 500mm thick, beams not exceeding 1m width, 1.5m depth
  • Mobile crane outrigger foundations in good ground crane to 50T
  • Piling gates, simple and medium designs
  • Permanent falsework e.g. metal decking
  • Site hoarding and fencing greater than 2m high
  • Concrete pumps outriggers with good access /good ground conditions

2

On more complex or involved designs. Designs for excavations including excavation support using sheet piles, for foundations, for structural steelwork connections, for reinforced concrete. Designs where stability is obtained by restraint at the top of the temporary works (e.g. top-restrained falsework).

Category 2 checks would include designs where a considerable degree of interpretation of loading or soils’ information is required before the design of the foundation or excavation support or slope is carried out.

The check should be carried out by an individual not involved in the design and not consulted by the designer.

  • Departures from catalogue design for standard components
  • Formwork and falsework at height greater 6m or for heavy suspended slabs and beams
  • Falseworks requiring the use of bridging and similar heavy equipment
  • Inclined formwork
  • Special designed scaffolds
  • Large, complex or unusual system formwork or falsework
  • Cofferdams and sheet piled walls, contiguous piled temporary walls
  • Excavation frames
  • Underpinning sequences (routine)
  • Slope stability and battered excavation; surcharging weak ground
  • Demolition methods and temporary conditions - generally

3

For complex or innovative designs, which result in complex sequences of moving and/or construction of either the temporary works or permanent works. It also includes basement excavations and tunnels.

These designs include unusual designs or where significant departures from standards, novel methods of analysis or considerable exercise of engineering judgment are involved.

The check should be carried out by another organization and should include an overall check to assure co-ordination of the whole design.

  • Temporary works combining inter-acting multiple designs
  • Unusual concepts
  • Bridge erection schemes and bridge temporary bracing
  • Bridge demolition
  • Structurally complex partial demolition or modification of existing structures
  • Excavations and cofferdams in tidal conditions
  • Excavations and cofferdams in poor ground (fill to deeper than 5m, water bearing fills)
  • Large basement excavation and propping schemes
  • Underpinning in poor soils, with surcharge and/or where the ‘pins’ act as retaining walls
  • Pile and crane mats on poor ground (soft clays, water bearing soils, loose materials)
  • Complex or suspended tower crane bases
  • Components used as part of a crane or other mechanical equipment
  • Hydraulic pressure pipework testing
  • Pneumatic pressure pipework testing
  • Abnormal stress cases in the permanent works resulting from temporary conditions
  • Any scheme reliant on the ‘observational method’ or sensors and monitoring
  • Assessment of structures likely to be affected by settlement or vibration caused by the method of work

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