Structural design processes

Design involves the integration of a range of process - see process mapping.

The simple model of:

          Input ----->  process  -----> outcomes

prompts the observation that deep focus on the quality of the inputs and quality of the processes is critical for achieving successful outcomes.  Designers therefore need to work hard to ensure that the inputs and processes that they use are the most appropriate that can be devised in the context.

This principle applies to all context where complex uncertainty is to be addressed.

Models of the 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 1 Stages in the creation of a structure

Figure 2 Design process stages

A basic model

Figure 2 shows a model of the design process. The 'system model' is information about the stucture being designed and about its context.

The process is not normally linear. 'Review and revise' is at the heart of the process. Iterations may be needed and revisions are made based on continuous review activity,

At the Inception, requirements for the performance of the stucture and for the design process are established and information about, for example, the site is identified.

At Conception, investigations are carried leading to a decisoin about the general form of the structre to be adopted.

At Production, the chosen form of structure is developed to produce drawings and specifications to be passed on to the construction stage. Other outcomes include documents that justify the decisions taken.

Process mapping

The Institution of Structural Egineers publishes a Structural Plan of Work that sets out an overall process for structural engineers working on the design of a building.

The stages in the IStructE Plan of Work are shown in Figure 1.

Figure 1 Stages in the IStructE Plan of Work

A process map for structural design based on the IStructE Plan of Work is shown in Table 1.

Table 1 Simplified process map for structural design

The work starts at the top left of the map with the definition of requirements and moves across the stages and down the sub-processes to achieve the basic project outcomes (e.g. in the case of structural design the basic outcome is in the form of drawings and specifications that define what the structure will be). Other outcomes are required that, for example, justify the choices made or show how risk was controlled. The row order of the sub-processes may not be significant.

The map is a simplified diagram of a real system plan. It does not show iterations that are common, especially at the concept stage

Risk

A structural collapse can have serious consequences and all structural engineering activities 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.

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." Hundreds 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.

Project Programme

The work of the project is controlled by a programme where tasks are defined and allocated and timelines are established.

Items in such a programme include:

• Task descriptions
• Task schedules.
• Manpower schedules
• Reviews

Core actions in preparing a project programe include:

• Break down the work into tasks.
• Estimate the time it will take to complete each task.
• Define the precedence of the tasks, i.e. decide which tasks can be carried out in parallel and which need to be handled consecutively.
• Identify any lead times needed for starting the tasks - e.g. where one needs to wait for information to be delivered.
• Identify critical tasks, i.e. those which if not done on time will cause delay in the overall completion
• Draw up a schedule for the work, typically using a bar chart which shows when each task should start and finish.  Leave some slack in the system to allow for unforeseen circumstances.
• Record progress and update the task times as the work proceeds.

Task Assignment

When assigning a task, take account of (a) the competence of the person who is to carry out the task and (b) the need to train people to do the task.

Reviews

Regular review meetings should be included in the schedule to address

• Progress in relation to the plan
• Progress in relation to meeting the requirements

Design Programme

A simpler form of the Plan of Work for design is shown in Table 1..

Table 1 Simplified process map for a structural design