Seán FitzSimons investigates hard and soft logic links in construction projects and makes the case for avoiding the use of soft‐logic without any consideration for resources. Whether preparing a programme, administering a contract or reviewing the administration of a contract, it is important to understand the differences between hard and soft logic. Hard logic refers to relationships between activities that cannot be altered, while soft logic refers to relationships between activities that are largely a matter of preference. When a series of activities are linked with soft logic, it is important to bear in mind that a delay to one of those activities will not necessarily delay the subsequent activities, which may be undertaken at the same time as the issue on an adjacent section is resolved. Soft logic is a principle that is generally well understood on linear projects that are often either dominated by soft logic or contain very few activities. Perhaps, understandably, the presence of soft logic is often not as well catered for on other project types, which may appear upon first glance to be dominated by hard logic.

Multi‐storey buildings initially dominated by hard logic

Multi-storey buildings, for instance, are initially dominated by hard logic. The construction of foundations is required prior to the construction of concrete cores. The cores are required to progress the floor construction and so on. However, once the shell is under way and the building obtains a degree of water tightness (or air tightness in warmer climates), typically the critical path shifts from the building envelope to the internal works. At this stage, the M&E works are free to progress on several floors but it may not be strictly necessary to work through the floors in sequence. Progressing the works on the fifth floor of a building ahead of those on the fourth floor, although it may not be the preferred sequence, is entirely possible, and would not necessarily cause any delay to the project. Take, for example, a five‐storey building where a number of floors are released for M&E works at the same time. The programme extract below depicts M&E activities in the building. First fix M&E works are linked through successive floors with finish‐to‐start links. These links indicate the intention for one team to work their way up the building one floor at a time. Since the floors are, in theory, interchangeable, the logic links can be considered to be soft logic links. Second fix works on any given floor are shown to be dependent on the completion of the first fix works on that floor (a hard logic link) and the second fix works on the earlier floor (a soft logic link).

Problems arise if works are progressed out of sequence

At first glance, the sequence and programming exercise appears reasonable. Indeed, if the works progressed as planned, the programme and any subsequent updates would accurately describe progress and the critical sequence. However, problems arise if the works are progressed out of sequence. Imagine the scenario whereby, due to an issue with the design on the first floor, it was desirable to commence the M&E first fix on the second floor. One might assume that, with a number of work fronts available, this would not pose too many difficulties and that the first floor could be completed subsequently. However, the programme logic set out above struggles to cope with this scenario. As illustrated below, although the work on the first floor has simply been swapped for that on the second floor, when the programme is updated using ‘retained logic’, after one week’s progress on the first fix M&E on the second floor, the programme indicates a one‐week delay. The problem is not simply that the programme has been updated with ‘retained logic’. If the programme is updated using ‘progress override’, the end result is the same but a new problem has been introduced, in the form of the ‘stacking’ of activities.

Accurate critical path and forecast completion date

It can be seen from the above illustrations that where soft logic is used, as soon as the sequence changes from the planned sequence, the programme struggles to produce an accurate critical path and forecast completion date. Considering these discrepancies are introduced on a programme with only six activities and after only one week’s worth of progress, one can begin to imagine the difficulties that might be experienced on a project with many thousands of activities which is due to take a number of years. Unfortunately, there is no ‘easy fix’ to this issue. The soft logic linking the activities through the floors assumes that the physical works on each floor have a direct link to one another, when, in reality, they are only associated with one another by virtue of the fact that they are likely to use the same resources. As a result, if a programme that responds appropriately to progress updates is something that is desirable or necessary, it is necessary to invest the time to ensure the programme considers the amount of works to be carried out and the resources available to perform the work. The illustration below shows how the programme reacts when updated to take account of the quantity or work to be done and the maximum number of resources available to undertake the work. In this illustration, even though all the soft logic links have been removed, the programme produces the correct result, i.e., after one week’s worth of work, the planned critical path (concurrent critical paths in this case) and the planned completion date are maintained.

Issue of resourcing made it all the way to a Technology and Construction Court decision recently

Interestingly, the issue of resourcing made it all the way to a Technology and Construction Court decision recently, where Justice Stuart‐Smith criticised one of the appointed programming experts for failing “to consider whether it was feasible to resource such numbers of activities simultaneously”.1 Supported, in part, by this point, Justice Stuart‐Smith concluded that the evidence of the expert in question was “so artificial as to be effectively valueless”. One might equally consider a programme that does not provide an accurate description of the critical path or provide a realistic planned completion date to be effectively useless. Rather than build programmes that are so easily rendered useless, it is therefore preferable that project managers understand where their intended sequence is based on soft logic. Where soft logic links are a crucial part of the programme make‐up, it is imperative to ensure that the programme considers the scope of work and the resources available to undertake the work. If this is done effectively, one might hope that an accurate description of the critical path can be published at appropriate intervals in progress reports, rather than years later in a court judgment. Reference 1.[2013] EWHC 2916 (TCC) Author: Seán FitzSimons, an associate director with Clandillon Civil Consulting, is a chartered civil engineer with 13 years’ experience in the planning, design, construction and administration of major construction works. He has worked both as a design manager and as part of the contractor’s management team on a number of prestigious projects, including the N17/N18 Gort to Tuam scheme; the N9/N10 Knocktopher to Powerstown; and the M3 Clonee to Kells.