Many contracts for construction, maintenance or repair are awarded as Indefinite-Delivery-Indefinite Quantity (IDIQ) or Multiple-Award-Task-Order-Contracts (MATOC).
An agency will issue an RFP and award contracts for a certain number of years, to multiple contractors. During the life of the contract they will issue Task-Orders, which will be competed amongst those contract awardees.
For example, this recent Multiple Award Construction Contract for Mechanical, Electrical, and Plumbing includes HVAC, boilers, electrical, water/ sewer, communications and general construction.