Load Tests of Concrete Structures: Methods, Magnitude, Protocols, and Acceptance Criteria

Description

Significant revisions were made in Chapter 9 of ACI 318-02to the load factors to be used for determining required strength. The load factor for dead load was reduced from 1.4to 1.2, and the load factor for live load was reduced from 1.7to 1.6; other changes were also made as given in equations for required strength in Chapter 9. The strength-reduction factors (φ-factors) were also modified.

The φ-factor for shear and torsion was reduced from 0.85 to 0.75, while the φ-factor for compression-controlled members was reduced from 0.70to 0.65 unless spiral reinforcement is provided. The φ-factor for tension-controlled members (most flexural members)was not reduced, and remains 0.9.The load factors and load combinations of ACI 318-05match those of ASCE 7-02 (American Society of Civil Engi-neers 2002). The changes were made to unify the load factors used to design concrete structures with those generally usedto design structures constructed of other materials, such as structural steel.

The changes also facilitated the design of concrete structures that included members of materials otherthan concrete.Chapter 20 (Strength Evaluation of Existing Structures) of318-02 and 318-05 was not changed from the previous codewith regard to load test procedures. Section 20.3.2 (LoadIntensity) of ACI 318-02 was not changed from the 1999edition; that is, the total test load (including dead loadalready in place) was still defined to be not less than0.85(1.4D + 1.7L), with live load permitted to be reduced inaccordance with the applicable building code.