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Provisions of this chapter shall apply to strength evaluation of existing structures by analytical means or by load testing.
If there is doubt that a part or all of a structure meets the safety requirements of this Code and the structure is to remain in service, a strength evaluation shall be carried out as required by the licensed design professional or building official.
If the effect of a strength deficiency is well understood and it is practical to measure the dimensions and determine the material properties of the members required for analysis, an analytical evaluation of strength based on this information is permitted. Required data shall be determined in accordance with 27.3.
If the effect of a strength deficiency is not well understood or it is not practical to measure the dimensions and determine the material properties of the members required for analysis, a load test is required in accordance with 27.4.
If uncertainty about the strength of part or all of a structure involves deterioration, and if the observed response during the load test satisfies the acceptance criteria in 27.4.5, the structure or part of the structure is permitted to remain in service for a time period specified by the licensed design professional. If deemed necessary by the licensed design professional, periodic re-evaluations shall be conducted.
Dimensions of members shall be established at critical sections.
Locations and sizes of reinforcement shall be determined by measurement. It shall be permitted to base reinforcement locations on available drawings if field-verified at representative locations to confirm the information on the drawings.
If required, an estimated equivalent fc' shall be based on analysis of results of cylinder tests from the original construction or tests of cores removed from the part of the structure where strength is in question.
The method for obtaining and testing cores shall be in accordance with ASTM C42.
The properties of reinforcement are permitted to be based on tensile tests of representative samples of the material in the structure.
If dimensions, size, and location of reinforcement, and material properties are determined in accordance with 27.3.1, it is permitted to increase ϕ from the design values elsewhere in this Code; however, ϕ shall not exceed the limits in Table 27.3.2.1.

Table 27.3.2.1—Maximum permissible strength reduction factors

Strength Classification Transverse reinforcement Maximum permissible ϕ
Flexure, axial, or both Tension controlled All cases 1.0
Compression controlled Spirals[1] 0.9
Other 0.8
Shear, torsion, or both 0.8
Bearing 0.8

[1]Spirals shall satisfy 10.7.6.3, 20.2.2, and 25.7.3.

Load tests shall be conducted in a manner that provides for safety of life and the structure during the test.
Safety measures shall not interfere with the load test or affect the results.
The portion of the structure subject to the test load shall be at least 56 days old. If the owner of the structure, the contractor, the licensed design professional, and all other involved parties agree, it shall be permitted to perform the load test at an earlier age.
A precast member to be made composite with cast-in-place concrete shall be permitted to be tested in flexure as a precast member alone in accordance with (a) and (b):

(a) Test loads shall be applied only when calculations indicate the isolated precast member will not fail by compression or buckling.

(b) The test load, when applied to the precast member alone, shall induce the same total force in the tensile reinforcement as would be produced by loading the composite member with the test load in accordance with 27.4.2.

Test load arrangements shall be selected to maximize the deflection, load effects, and stresses in the critical regions of the members being evaluated.
The total test load Tt, including dead load already in place, shall be at least the greatest of (a), (b), and (c):
  (a) Tt = 1.15D + 1.5L + 0.4(Lr or S or R) (27.4.2.2a)
  (b) Tt = 1.15D + 0.9L + 1.5(Lr or S or R) (27.4.2.2b)
  (c) Tt = 1.3D (27.4.2.2c)
It is permitted to reduce L in 27.4.2.2 in accordance with the general building code.
The load factor on the live load L in 27.4.2.2(b) shall be permitted to be reduced to 0.45 except for parking structures, areas occupied as places of public assembly, or areas where L is greater than 100 lb/ft2.
Total test load Tt shall be applied in at least four approximately equal increments.
Uniform Tt shall be applied in a manner that ensures uniform distribution of the load transmitted to the structure or portion of the structure being tested. Arching of the test load shall be avoided.
After the final load increment is applied, Tt shall remain on the structure for at least 24 hours unless signs of distress, as noted in 27.4.5, are observed.
After all response measurements are recorded, the test load shall be removed as soon as practical.
Response measurements, such as deflection, strain, slip, and crack width, shall be made at locations where maximum response is expected. Additional measurements shall be made if required.
The initial value for all applicable response measurements shall be obtained not more than 1 hour before applying the first load increment.
A set of response measurements shall be recorded after each load increment is applied and after Tt has been applied on the structure for at least 24 hours.
A set of final response measurements shall be made 24 hours after Tt is removed.
The portion of the structure tested shall show no spalling or crushing of concrete, or other evidence of failure.
Members tested shall not exhibit cracks indicating imminent shear failure.
In regions of members without transverse reinforcement, structural cracks inclined to the longitudinal axis and having a horizontal projection greater than the depth of the member shall be evaluated. For variable-depth members, the depth shall be measured at the mid-length of the crack.
In regions of anchorage and lap splices of reinforcement, short inclined cracks or horizontal cracks along the line of reinforcement shall be evaluated.
Measured deflections shall satisfy (a) or (b):
  (a) (27.4.5.5a)
  (b) (27.4.5.5b)
If 27.4.5.5 is not satisfied, it shall be permitted to repeat the load test, provided that the second load test begins no earlier than 72 hours after removal of externally applied loads from the first load test.
Portions of the structure tested in the second load test shall be considered acceptable if:
(27.4.5.7)
If the structure under investigation does not satisfy conditions or criteria of 27.3 or 27.4.5, the structure shall be permitted for use at a lower load rating, based on the results of the load test or analysis, if approved by the building official.
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