Delivery System 1/5

By Eng. Ahmed Said  updated September 2022

1:            Design-Bid-Build delivery system (DBB).

Also known as the general contracting project delivery method, in this system, one phase is finished before starting the next. The most traditional systems used in the world, where the project is designed entirely before the start of work and then the use of a general contractor bears the responsibility of building the project in full using a contract with the specific owner and passes through three stages:

1.     Design stage.

It uses the services of a designer who designs the project within the requirements of the owner and within the estimated budget in advance.

2.     Bidding or Tender stage.

Where construction services are purchased from a contractor based on the design.

3.     Build or construction stage.

During this, the project is constructed and built within the scope of the specific work and design documents and contract.

Figure 1 Design-Bid-Build Delivery System

Cost Estimation

These previous phases may go through a series of cost estimates that accompany the development of design processes that contribute significantly to the project cost management scenario and the price of the contracted contractor when the design is completed within the owner's budget.

The absence of construction input into the project design may limit the effectiveness and constructability of the design.[9]

These preliminary estimates of the project and prior to contracting with the contractor are used by the designer as a basis for estimating design and licensing fees.

This sequence inevitably leads to sealed bids and fixed business prices.

 

Figure 2 DBB Relationships

Figure 3 DBB with PM/CM

 

Multiple-Prime Contracting

The employer can be entrusted to several contractors based on his experience after the division of the project works into integrated work packages and then management of the project in order to ensure continuous coordination between the contractors.

The designer is also responsible for limited supervision of the work and answers the contractor's questions regarding the design. The owner may use a construction management consultant to monitor implementation quality and measure progress.

Scope of application and use

This method is suitable for projects with a limited budget and is sensitive to cost increases and is not sensitive to the schedule where the owner controls the design and modifications during implementation within budget limits constrained by an agreed increase.

Next is the strength, weakness, and applications of the Design-Bid-Build system:

Figure 4 Strengths, Weaknesses, and Applications of Design-Bid-Build (DBB) System.

Advantages

·       A familiar method, especially in government contracts.

·       The system does not need effort or experience in managing the processes and stages of design and delivery where it is done by parties other than the owner.

·       The designer and the contractor are responsible for the operations before the owner.

·       The scope of work is more specific to both construction and design.

·       Competitiveness among contractors is the ruling and the lowest price is accepted.

·       Provide opportunities for general contractors to acquire and develop

 

Disadvantages

·       Multiple stages and their separation mean a longer period and a timetable for implementation is unrealistic for non-interference of parties in the design.

·       The final price cannot be determined before receiving contractors' bids.

·       Redesign may be required if the bid price exceeds the owner's budget.

·       Choosing the lowest price does not guarantee the quality of contractors and subcontractors.

·       Cost estimates change during design and implementation because the design inputs are not clear to the contractor.

·       Lack of building inputs in the design of the project may limit the effectiveness and ease of design.

·       Increase orders for change and claims.

·       Multiprotocol interference in implementation affects cost and design.

·       The probability of conflict is higher due to the extension of project time, cost, and frequent interference from project parties.

·       Cannot be relied upon for projects that are sensitive to time and cost.

 Contract system for DBB:

For vertical projects such as buildings and services projects, the contract system is a sealed price for work items or a lump sum item price.

Roads, bridges, and other horizontal projects are usually the price of the unit and the performance is measured therefore the owner pays the money for the quantities executed.

This is done through direct bidding or by inviting specialized contractors and conducting competition between them. The owner may use the pre-qualification method for contractors by applying a set of criteria to determine the efficiency of the contractors and their abilities and thus allow the competitors to compete and then choose the lowest price.

This guarantees the owner and the contractor's ability to execute the project.

In public and government competitions, laws impose a package of financial and procedural restrictions that make it more complex and affect the choice of the best. In the private sector, the employer can choose the best among the competitors and then negotiate the price to get the best value for money.

Therefore, as a natural result of the absence of building inputs during design, and vice versa, the absence of design input during competition makes the cost estimate more sensitive and the reserve coefficient higher therefore the added value for the contingency is higher.

The cost estimator is subject to several pressures that affect the cost calculation, which takes into consideration the nature of competition and the absence of design inputs.