Home / civil engineering / Analysis strength designmethods are also presented. Included is an approximate method for beams. One-way slabs that gives reasonably conservative values for typical concrete framing systems

Analysis strength designmethods are also presented. Included is an approximate method for beams. One-way slabs that gives reasonably conservative values for typical concrete framing systems

The Strength Design Method analysis of ACI 318-05 is presented first.

Analysis methods are also presented. Included is an approximate method for beams. One-way slabs that gives reasonably conservative values for typical concrete framing systems

The information presented here is based on the requirements in the 2005 edition of ACI 318 Building Code. Requirements for Structural Concrete. Section numbers referenced herein are taken from that standard.
The Strength Design Method analysis requires that the design strength of a member should equal or exceed the required strength calculated by the code-specified factored load combinations.
The nominal strength of a member or cross-section is calculated using assumptions and strength equations of the Strength Design Method, before application of any strength reduction factors
A clear understanding of the code-prescribed strength requirements is essential before any design can proceed. These requirements are found in Chapter 9.

In general, the Design Strength of a member must be greater than or equal to the Required Strength of the member.
The Design Strength is equal to the strength reduction factor times the nominal strength of the member.
The Required Strength is equal to the load factor times the service load effects. Each of these items are discussed next.

Strength reduction factors, or phi-factors, account for understrength of a member due to variations in material strengths and dimension, inaccuracies in the design equations, the degree of ductility and required reliability of the loaded member, and the importance of the member in the structure. Phi-factors are given in ACI 9.3.
The nominal strength of a member or cross-section is calculated using assumptions and strength equations of the Strength Design Method, before application of any strength reduction factors

WP 20160113 016 169x300 - Analysis strength designmethods are also presented. Included is an approximate method for beams. One-way slabs that gives reasonably conservative values for typical concrete framing systems

Load factors are used to increase the service loads. Factored loads are the service loads specified in the general building code multiplied by the appropriate load factors

Various load types are listed here. Not all loads are applicable in every case.

Other loads, such as those due to flood, must also be included when applicable

Load combinations are specified in ACI 9.2. Therefore The factor assigned to each load is influenced by the degree of accuracy to which the load effect can be calculated and the variation that might be expected in the load during the life of the structure. Load factors also account for variability in the structural analysis used to compute bending moments and shear forces.

Load combinations given in ACI 9.2 are summarized here.

In assigning factors to combinations of loading. Some consideration is given to the probability of simultaneous occurrence of the loads. ACI 9.2 should be consulted for additional requirements. For the load combinations that need to be considered, based on the applicable load effects.
The required strength is obtained by multiplying the service load effects by the appropriate load factors.
Nominal strengths are defined in the code for, among other things, flexure, axial strength, shear, and torsion.

 

The design strength analysis is obtained by multiplying the nominal strength by the appropriate phi-factor.
All structural members and sections must be proportioned.  So that the general strength requirements are satisfied.
Analysis methods for reinforced concrete members is presented next, with emphasis on an approximate method for beams and one-way slabs.

In fact Chapter 8 in ACI 318-05 contains the general requirements for the analysis of any concrete structure. The first step in the frame analysis is the determination of service gravity loads and lateral loads, such as wind and seismic

 

The general building code. which the project is to be designed and constructed is to be used to determine the service loads, lateral loads, and all other applicable loads on the structure. ASCE 7, Minimum Design Loads for Buildings and Other Structures, is referenced in the latest edition of the International Building Code.  Which has been adopted in many jurisdictions throughout the U.S. For a specific project, however, the governing local building code should be consulted for any variances from the IBC or ASCE 7.
since Methods of analysis for reinforced concrete structures are presented in ACI 8.3. Factored loads are service loads multiplied by appropriate load factors.  Which are given in ACI 9.2, as discussed previously. For the strength design analysis method, an elastic analysis is used to obtain bending moments, shear forces, and other reactions. The assumptions that are specified in ACI 8.6 through 8.9 may be used in such an analysis. These assumptions are discussed next.

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