As-built drawings are a very vital piece of information that every project must record. As-built drawings are also called record drawings, blue prints and sometimes referred as red-line drawings. These drawings reflect all changes made in the original specifications and working drawings during the construction process, and show the exact dimensions, geometry, location, and material properties of all elements of the work completed under the contract. Think of these drawings as a record of the final constructed product.
As-built drawings are important for at least two primary purposes. First, they are a record from which future system changes and/or additions can be designed. Secondly, in the engineering process of conducting a structural assessment a good knowledge of the existing structural elements is essential. Future rehabilitation projects will be more efficient, economical, and less disruptive if the as-built documents are accurate. Therefore, engineers must rely on the information provided by the as-built drawings. When developing as-built drawings, we are usually faced with the following two scenarios:
1- Structures with No Available Construction Drawings:
Obviously, the most difficult situation is when no construction drawings are available. In this case, neither the overall configuration of the structure or the material properties may be known. Thus, developing as-built drawings will be necessary.
Figure-1: NDT operator performing a GPR scan on a concrete slab.
A field investigation and a topographic survey shall be conducted to determine first the general layout of the structure, and then the exact configuration of elements that have significant strength (or stiffness), whether traditionally classified as structural or nonstructural. If members are covered, then limited removal of finishes will be necessary. Massive or critical reinforced concrete elements may require coring to determine the nature and engineering properties of the material such as measuring compressive strength, or finding the w/c ratio. The number of required cores could be reduced considerably when used in conjunction with non-destructive tests (NDT) like Rebound Hammer and Ultra Pulse Velocity (UPV). More advanced and less destructive methods, like the Ground Penetrating Radar (GPR), are currently available for determining concrete cover, rebars number, location and layout, post-tensioning location and level, and thicknesses of elements. With the new technologies, a well trained and certified NDT is key for any project, as constant engineering judgment as to the progression of destructive and non-destructive investigation must be exercised.
2- Structures with Available Construction Drawings:
The overall dimensional accuracy of the layout and the configuration of structural elements should be verified on the site. Given a reasonably complete picture of the configuration and detail of the structure from construction drawings, material properties, however, may vary from those specified on the drawings. Therefore, the material properties must still be verified in the field by extracting a representative number of concrete cores, and performing a series of NDTs, such as Rebound Hammer and Ultrasonic Pulse Velocity (UPV). Likewise, it is highly advisable to perform steel verification and random chipping for several locations in the structure (preferably critical elements) to verify layout/distribution of rebars as well as their actual diameter.
Figure-2: GPR 2D-profile showing layout of rebars (left pic shows profiles and right pic layout)
- The Balance Small Business. Juan Rodriguez. “Expert Tips When Recording As-Built Drawings”.
https://www.thebalancesmb.com/expert-tips-when-recording-as-built-drawings-844876 [viewed on August 26, 2018]
- Concrete Construction, Dan Bigman. “The Potential of GPR for Concrete Construction”. https://www.concreteconstruction.net/business/technology/the-potential-of-gpr-for-concrete-construction_o
[viewed on September 17, 2018]
- Figure 1, and 2: concreteconstruction.net