Structural design process
Figure 1 shows how, when creating a structure, one starts with a set of requirements that define the performance of the structure. This is transformed by a design process into design output, i.e. into information about what the structure will be and justification for the design decisions.. A construction process then transforms the design output into the physical structure.
Figure 2 shows the stages in the Institution of Structural Engineers Plan of Work. This Plan of Work is for structural engineers working on the design of a building structure.
Figure 3 shows a model of the design process. The stages of the Plan of Work correspond to the stages in the design process as follows:
- Inception: Stages 0 and 1
- Conception: Stage 2
- Production: Stages 4 and 4.5
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Design activities
Main design activities include:
Resource allocation A budget for the design work needs to be established. This depends on:
- What the client is prepared to pay for
- Whether the design is innovative. Innovation increases the risk of unsatisfactory outcomes and requires more detailed attention to design process activiites.
- Whether the context is familiar to the members of the design team, Experience can allow some decisions to be made with less attention to detail.
- The degree to which the context is safety-critical. Most structures are safety-critical to some degree. The safety of the users of the structure should be treated as the responsibility of all involved in the design including the client. Safety criteria must be accepted as non-negotiable when making decisions. [Refer to case studies of failures: Tay Bridge, Edinburgh schools, Grenfell Tower Fire, Florida Bridge]
Plan Work to a plan for the design activities.
Review and revise The process is not normally linear. There may be backtracking. It is essential (a) to shedule regular meetings to review progress and to check outcomes against requirements and (b) to be constantly alert for unforseen circumstances, faults, erors.
Gather information - about the site, about the regulatory framework, etc.
Establish the structural design brief. Based on the client design brief and a list of design issues (see Figure 3), establish the Structural Design Brief. This is a list of all the requirements (objectives and constraints) that relate to the structural design and should include information about the processes to be used to ensure that satifactory outcomes. Guidance.
Option analysis Develop a set of options to a degree of detail sufficient to assess them against the requirements. Compare them against the requirements and decide on the form of the structure to be used.
Design proposal Prepare a validation report for the client
Refine the design Carry out technical assessment and further checks against all requirements.
Design verification Prepare a report that shows that the design will satisfy the requirements
Design output Produce drawings, specifications, etc.
Structural design issues
Figure 3 illustates some of the issues that may need to be considered in structural design.
Working with other disciplines
Adopt a holistic view (i.e. address all relevant issues) both in the structural context and in relation to the other disciplines that may be involved in the project, i.e. actively collaborate with contractors, architects, building services engineers, environmental specialists, etc.
Risk
A structural collapse can have serious consequences and all strauctural engineering ativitie should be treated as being, to some degree, safety critical.
It is important to pay special attention to the requirements of the client but such considerations should not over-ride duty of care to the publc. Of funds are not available to build a safe structure, the project should not be undertaken,
Naval architect, Stephen Payne, designer of the Queen Mary 2, said (at a talk given to the Institution of Engineers in Scotland) in 2020). "When designing a cruise liner, the regulations represent the starting point for my safety assessment. The Titanic met the then current regulations." Thousands of people might drown if a passenger liner was lost at sea. There are equivalent risks in structural design e.g. for a long span bridge or the roof of a sports stadium. Use of the principle that the starting point for design should be the regulations should be adopted in all strutural designs. This requires critical thinking by all participants.
Design reviews
That requirements are kept under review throughout the design process is a main critical thinking strategy.
At the start of the process It is especially important to focus on the requirements - to ensure that all requirements have been identified and are adequately addressed in the design. For examples of the use of requirements see Footbridge and Industrial bulding. The reasons for structural failures can often be led back to faults in the use of requirents - see, for example, the following case studies: Tay Rail Bridge Disaster, Ronan Point Collapse, Florida Bridge Failure, Hartford Civic Center Collapse. Processes for identifying requirements and for ensuring that they are addressed need to be used.
Review actiities include:
- Constant review activity Throughout the design process, there should be continual assessment of the inputs, the processes and the outputs - see Figure 4. This involves asking questions such as: Are important issues being missed? Should I seek advice about this? Has this been properly assessed? Such questions need to answered and action taken when appropriate.
- Design reviews The design programme should include a schedule of formal meetings of the design team to review (a) progress and (b) the satisfaction of requirements.
- Milestone reviews The two major reviews in the design plan are:
- At the end of the concept stage the state of the design is reviewed to ensure that what is proposed has the potential to satisfy the requirements i.e. that the design is valid. This results in a Design Proposal for agreement by the client..
- The final review verifies that the design will satisfy the requirements.