D. CAN/CSA-A23.3-10 Beam Design Principles
The CAN/CSA-A23.3-10 Beam Design Brief is for single or multi-span, prismatic, rectangular solid, or tee shaped members. The member sections must be defined as PRISMATIC sections in the STAAD.Pro data file.
Refer to D. Suitable Member Properties for more details.
Beams are designed for flexure, torsion, and shear only. Each member is divided into equally spaced sections along its length and the design is performed at each of these locations. You can specify the number of segments to be considered (between 4 and 25) for each span. Sections are also taken at the face of supports and at locations of the maximum positive and negative bending moments.
Design for Flexure
The main (longitudinal) reinforcement is calculated for both sagging and hogging moments (i.e., positive and negative moment, respectively) on the basis of the section profile and parameters defined in the Design Brief. Compression reinforcement is provided where required.
The design of a beam is based on an envelope of the design forces, and thus, at each of the defined sections the program determines the required area of steel for both the maximum hogging moment and maximum sagging moment values from the analysis.
The beam is then divided into sub-beams, those that can use the same reinforcement cage and having
- Same overall beam size
- Same cover requirements
For each sub-beam, the sections that have the largest sagging and hogging moments are identified and the most efficient reinforcement pattern is calculated for the range of bars specified in the Design Brief. The program does not have a limit on the number of bars in any one layer as long as the spacing requirements specified in the code are satisfied. The program can handle a maximum of four layers of reinforcement, two each for the top and bottom layers.
The program then performs a check at each of the defined sections to determine the number of bars, if any, that can be cut off. The reinforcement bars will not be curtailed at these sections in the following cases:
- If the bars are required for compression, or
- If curtailing these bars would result in a failure of crack-width checks, or
- If curtailing these bars would result in a failure of the minimum reinforcement checks.
Design for Shear
The shear reinforcement is designed to resist the major axis shear force envelope, Fz , acting on the beam. The minor axis shear forces are not considered in the design.
The bar size for the shear links and the minimum number of shear legs to be provided are specified in the Design Brief. Therefore, the required spacing for minimum links can be defined. The program then checks each section to determine the shear force VEd and concrete shear capacity VRd,c . From this, the section is classified as either a minimum link or a high shear section. Adjacent sections of the same type are grouped into zones. For non minimum link zones, the shear links are designed for the maximum shear force within that zone.
The number of shear legs and the shear link size is specified in the Design Brief. Therefore the required spacing for minimum links can be defined. The program then checks each section to determine the shear stress, v, and concrete shear capacity, vc . From this, the section is classified as either minimum link or a high shear section. Adjacent sections of the same type are grouped into zones. For non minimum link zones, the shear links are designed for the maximum shear force within that zone.
If necessary, additional legs may be added to the shear links in order to restrain tension or compression reinforcement.
Minimum shear links required,V, for shear forces between these values
Code Clauses Implemented
The requirements of CAN/CSA-A23.3-10 utilized in the design module are as follows:
Service Limit States
Ultimate Limit States