Page 422 - Forensic Structural Engineering Handbook

CONCRETE STRUCTURES 12.13

dimensions of the structure should be measured. Nondestructive means can be used to
determine the size and location of reinforcement.
When questions arise about the in-place strength of an existing structure, strength evalua-
tion is most often done following procedures in chapter 20 of ACI 318. As recommended there,
the strength evaluation should start with calculations based on as-built conditions. To the extent
feasible, analyses should be based on measured dimensions and material properties.
When sampling concrete, it is desirable, when conditions permit, to obtain three cores
for each 10,000 square feet of area and for each type of concrete in the structure. Similarly,
if a particular portion of the structure is suspected to have deficient concrete, three cores
should be obtained from the suspect concrete, if possible.
If deterioration of concrete is suspected, then samples must be obtained. Samples
approximately the size of a fist generally will be adequate if cores cannot be obtained.
In cases where litigation may follow, all samples should be tracked with chain-of-
custody records. These records should track who has possession and all activities associ-
ated with the sample from the time the sample is obtained through the end of any litigation.
A sample chain-of-custody sheet is shown in Fig. 12.9.
Where it is not practical to obtain core samples, nondestructive procedures described in
this section may be used. If access to the structure is not possible, values given in Table 12.2
can be used to estimate concrete strengths.
If it is not possible to obtain enough information to do a reliable analytical evaluation
of strength, an in-place load test can be used to determine the structure’s strength. Most
building codes require that a load test be done if a potential strength deficiency cannot be

CHAIN OF CUSTODY RECORD

Building Knowledge. Delivering Results.
5400 Old Orchard Road, Skokie, IL 60077-1030
(847) 965-7500 FAX: (847) 965-6541
Project name: CTL Group Date: Sheet of:
Project
No.: Sampled by:
Sample No.:

Sample description:
Photo or Sketch

Transmitted Transmitted Time Date Activity
by to

FIGURE 12.9 Sample chain of custody form. (Courtesy of CTLGroup.)