ACI 357R-84 Guide for the Design and Construction of Fixed Offshore Concrete Structures

ACI 357R-84 Guide for the Design and Construction of Fixed Offshore Concrete Structures.
When the design is governed by earthquake, then other transient environmental loads are usually not assumed to act simultaneously. In certain special circumstances, when the design is not controlled by a single environmental load, it may be necessary to consider the simultaneous occurrence of environmental events. However, the overall probability of survival is not required to be any greater than that associated with a single event. While it is assumed that the critical design loadings will be identified from the load combinations in Eq. (4-l), (4-2), and (4-3), the designer should be aware that there may be other simultaneously occurring load combinations that can cause critical load effects. This may be particularly evident during construction and installation phases. 4.4.1.2 Strength Reduction Factors: The selection of strength reduction factors $ for concrete members should be based on ACI 318. The +-factors not only account for vari- ability in stress-strain characteristics of concrete and rein- forcement, but also reflect variations in the behavior of differ- ent types of concrete members, and variations in quality and construction tolerances. Alternatively, the expected strength of concrete members can be determined by using idealized stress-strain curves such as shown in Fig. 4.4.1 and 4.4.2 for concrete and rein- forcing steel, respectively, in conjunction with material fac- tors Y m . For prestressing steel, actual diagrams as supplied by the manufacturer should be used together with a material fac- tor Y m = 1.15.
While the material factors are directly applied to the stress- strain curves to limit the maximum stress, it should be recog- nized that the intent of using materials factors is similar to using ACI 318 strength reduction factors, in that the use of these factors will achieve the desired reliability. Under no circumstances should + factors and y, factors be used simultaneously. 4.4.2 Serviceability requirements- The structure may be checked elastically (working stress method) or by the use of stress-strain diagrams (Fig. 4.4.1 and 4.4.2) with material factors, y, = 1.0 to verify its serviceability. It is important that cracking in structural members be limited so that the du- rability of the concrete is not impaired. Control of cracking based on limiting reinforcing stresses is recommended. Table 4.1 is intended to serve as a guide for limiting such stresses. Allowable stresses contained in Table 4.1 apply to rein- forcing steel oriented within 10 deg of a principal stress direc- tion. Allowable stresses should be reduced if the angular de- viation between reinforcing steel and principal stress is more than 10 deg. Guidelines for reducing allowable stresses are contained in Chapter 19 of ACI 318. For thin-walled, hollow structural cross sections the max- imum permissible membrane strain across the walls should not cause cracking under any combination of D, L, T, and E using a load factor, yr. = 1.0. E shall be the probable value of environmental event or combination of events corresponding to the recurrence interval selected (usually 100 years).ACI 357R pdf download.