LUMBER USED IN CIVIL ENGINEERING CONSTRUCTION PROJECTS

Design values for lumber are contained in grading rules established by the National Lumber Grades Authority (Canadian), Northeastern Lumber Manufacturers Association, Northern Softwood Lumber Bureau, Redwood Inspection Service, Southern Pine Inspection Bureau, West Coast Lumber Inspection Bureau, and Western Wood Products Association.

The rules and the design values in them have been approved by the Board of Review of the American Lumber Standards Committee. They also have been certified for conformance with U.S. Department of Commerce Voluntary Product Standard PS 20-94 (American Softwood Lumber Standard).

In addition, design values for visually graded lumber may be established in accordance with ASTM D1990, ‘‘Standard Practice for Establishing Allowable Properties for Visually-Graded Dimensional Lumber from In-Grade Tests of Full- Size Specimens.’’

Design values for visually graded timbers, decking, and some species and grades of dimension lumber are based on provisions of ‘‘Establishing Structural Grades and Related Allowable Properties for Visually Graded Lumber,’’ ASTM D245.

ASTM D245 also specifies adjustments to be made in the strength properties of small clear specimens of wood, as determined in accordance with ‘‘Establishing Clear Wood Strength Values,’’ ASTM D2555, to obtain design values applicable to normal conditions of service.

The adjustments account for the effects of knots, slope of grain, splits, checks, size, duration of load, moisture content, and other influencing factors. Lumber structures designed with working stresses derived from D245 procedures and standard design criteria have a long history of satisfactory performance.

Design values for machine stress-rated (MSR) lumber and machine-evaluated lumber (MEL) are based on nondestructive tests of individual wood pieces. Certain visual-grade requirements also apply to such lumber.

The stress rating system used for MSR lumber and MEL is checked regularly by the responsible grading agency for conformance with established certification and quality-control procedures.

CIVIL CONSTRUCTION PROJECT RISK AND MITIGATION

Samuel Johnson famously wrote that ‘to build is to be robbed’. Facing the same challenges, but with the benefit of hindsight, Pope Pius II praised his architect for ‘lying about the costs’ following budget overruns on the building of Pienza Cathedral, which threatened at the time to bankrupt the Vatican.

Both of these experiences suggest that clients have been and continue to be exposed to a significant degree of cost risk when undertaking construction projects. Invariably, they also pick up much of the financial consequences of decisions, omissions and mistakes made by others working on their behalf.

Decisions made at the outset of a project: investing in land, selecting one project opportunity in favour of others; confirming a brief; or establishing project governance could all potentially have a substantial impact on project outcomes, and as a result carry significant risk. Unfortunately, many of these early decisions have to bemade without the benefit of a considered design response and may, as a result, be sub-optimal.

Whilst it is important that advice given to clients early in a project should give the team some ‘wiggle room’ to develop a preferred solution, it is also important to work within project disciplines once these are established. Effective teamwork during the design development process between the designer and cost consultant can help to mitigate many of these potential risks.

Design stages

As a client’s brief and concept designs are developed, a greater degree of fixity in terms of the design solution and predicted costs can be provided by the project team. This process is discussed in more detail in the section focused on cost planning.

However, as the design develops and cost certainty increases, so does the cost of changing the design, and the client and project team’s resistance to change.

Risk and risk transfer

As a project progresses to the appointment of contractors, the client’s overall financial commitment becomes better defined. More risk can also be transferred to third parties if the client so wishes.

Whilst under most procurement routes the client is required to accept risks associated with design performance, they will generally seek to transfer commercial and construction risks to the contractor through some form of a fixed price, lump sum contract.

Quite clearly, if the design information upon which the client obtains a contractual commitment is not complete, is ambiguous or is not fully coordinated then, not only will the client retain outstanding design risk, but will also find that the basis of his commercial risk transfer to the contractor is weakened.

Evidence from Construction Key Performance Indicators, published by the DTI, indicates the scale of this potential problem, showing that fewer than 80% of projects are completed with #10% of their original tender sum. Moreover, only around 50% of projects are completed within #5% of the tender sum.

Whilst some of this cost variation may reflect client changes, or problems on site, it is likely that some of these increases will have resulted from the consequences of continuing design development. In order to mitigate the client’s risk, it is incumbent upon the team to ensure that the design is completed to the appropriate level of detail and fixity required by the procurement route. To do otherwise risks rendering some of the effort expended in design development and cost-planning abortive.