Chapter 20Design Assisted by Testing

20.2.1 Acceptance Test

This is intended as a non-destructive test for confirming structural performance. It should be recognized that

the loading applied to certain structures might cause permanent distortions. Such effects do not necessarily indicate structural failure in acceptance test. However, the possibility of their occurrence should be agreed to before testing.

The load for acceptance test, $F_{\mathrm{test,a}}$ shall be determined from:

$F_{\mathrm{test,a}} =$ (Self weight) + (1.15 $\times$ Remainder of the permanent load) + (1.25 $\times$ Variable load)

The assembly shall satisfy the following criteria:

a) It shall demonstrate substantially linear behaviour under test loading; and

b) On removal of the test load, the residual deflection shall not exceed 20 percent of the maximum-recorded deflection.

If the above criteria are not satisfied the test may be repeated one more time only, when the assembly shall satisfy the following criteria:

1. It shall demonstrate substantially linear behaviour on the second application of test loading, and

2. Corresponding recorded residual deflection in the second test shall not exceed 10 percent of the maximum deflection during the test.

20.2.2 Strength Test

Strength test is used to confirm the calculated resistance of a structure or component. Where a number of items are to be constructed to a common design, and one or more prototypes are tested to confirm their strength, the others may be accepted without any additional test, provided they are similar in all relevant respects to the prototype.

Before carrying out the strength test, the specimen should first be subjected to and satisfy the acceptance test. Since the resistance of the assembly under test depends on the material properties, the actual yield strength of all the steel materials in the assembly shall be determined from coupon {test piece as defined in the accepted standard [6-6(7)]} tests. The mean value of the yield strength, $f_{\mathrm{ym}}$, taken from such tests shall be determined with due regard to the importance of each element in the assembly. The strength test load $F_{\mathrm{test,s}}$ (including self weight) shall be determined from:

where

$f_{\mathrm{y}} =$ characteristic yield stress of the material as assumed in the design;

$F_{\mathrm{d}} =$ factored design load for the ultimate limit state; and

$\gamma_{mi} =$ partial safety factor for the type of failure, as prescribed in this standard.

At this load there shall be no failure by buckling or rupture of any part of the structure or component tested. On removal of the test load, the deflection should decrease by at least 20 percent of the maximum deflection at $F_{\mathrm{test,s}}$.

20.2.3 Test to Failure (Ultimate Strength Test)

The objective of a test to failure is to determine the design resistance from the ultimate resistance. In this situation it is still desirable to carry out the acceptance and strength tests, before test to failure.

Not less than three tests shall be carried out on nominally identical specimens. An estimate should be made of the anticipated ultimate resistance as a basis for such tests. During a test to failure, the loading shall first be applied in increments up to the strength test load. Subsequent load increments shall then be determined from consideration of the principal load deflection plot. The test load resistance, $F_{test,R}$ shall be determined as that load at which the specimen is unable to sustain any further increase in load. At this load, gross permanent distortion is likely to have occurred and in some cases such large gross deformation may define the test limit. If the deviation of any individual test result exceeds 10 percent of the mean value obtained for all the three tests, at least three more tests shall be carried out. When the deviation from the mean does not exceed 10 percent of the mean, the design resistance may be evaluated as given below:

a) When the failure is ductile, the design resistance, $F_{\mathrm{d}}$ may be determined from:

where

$F_{\text{test, Min}} =$ minimum test result from the tests to failure,

$f_{\mathrm{ym}} =$ average yield strength as obtained from the material tests, and

$f_{\mathrm{y}}$ = characteristic yield stress of the grade of steel.

b) In the case of a sudden (brittle) rupture type failure, the design resistance may be determined from:

where

$f_{u}$ = characteristic ultimate stress of the grade of steel used, and

$f_{\mathrm{um}} =$ average ultimate tensile strength of the material obtained from tests.

c) In the case of a sudden (brittle) buckling type failure, the design resistance shall be determined from:

d) In ductile buckling type failure in which the relevant slenderness $\lambda$ can be reliably assessed, the design resistance may be determined from:

PART 6 STRUCTURAL DESIGN — SECTION 6 STEEL

where

$\chi =$ reduction factor for the relevant buckling curve, and

20.2.4 Check Tests

Where a component or assembly is designed on the basis of strength tests or tests to failure and a production run is carried out of such items, an appropriate number of samples (not less than two) shall be selected from each production batch at random for check tests.

20.2.4.1 The samples shall be carefully examined to ensure that they are similar in all respects to the prototype tested, particular attention being given to the following:

a) Dimensions of components and connections,

b) Tolerance and workmanship, and

c) Quality of steel used, checked with reference to mill test certificates.

20.2.4.2 Where it is not possible to determine either the variations or the effect of variations from the prototype, an acceptance test shall be carried out as a check test.

20.2.4.3 In this check test, the deflections shall be measured at the same positions as in the acceptance test of the prototype. The maximum measured deflection shall not exceed 120 percent of the deflection recorded during the acceptance test on the prototype and the residual deflection should not be more than 105 percent of that recorded for the prototype.

20.5.1 Acceptance for Strength

The test structure, sub-structure, member or connection shall be deemed to comply with the requirements for strength if it is able to sustain the strength test load for at least 15 min.

It shall then be inspected to determine the nature and extent of any damage incurred during the test. The effects of the damage shall be considered and if necessary appropriate repairs to the damaged parts carried out.

20.5.2 Acceptance for Serviceability

The maximum deformation of the structure or member under the serviceability limit state test load shall be within the serviceability limit values appropriate to the structure.