D4.A.5 Beam Design
Beams are designed for flexure, shear and torsion. For all these forces, all active beam loadings are scanned to create moment and shear envelopes, and locate critical sections. The total number of sections considered is thirteen (start, end, and 11 intermediate), unless that number is redefined with the NSECTION parameter.
D4.A.5.1 Design for Flexure
Design for flexure is performed per the rules of Chapter 10 of CSA Standard A23.3-94. Maximum sagging (creating tensile stress at the bottom face of the beam) and hogging (creating tensile stress at the top face) moments are calculated for all active load cases at each of the thirteen sections. Each of these sections are designed to resist the critical sagging and hogging moments. Currently, design of singly reinforced sections only is permitted. If the section dimensions are inadequate as a singly reinforced section, such a message will be printed in the output. Flexural design of beams is performed in two passes. In the first pass, effective depths of the sections are determined with the assumption of single layer of assumed reinforcement and reinforcement requirements are calculated. After the preliminary design, reinforcing bars are chosen from the internal database in single or multiple layers. The entire flexure design is performed again in a second pass taking into account the changed effective depths of sections calculated on the basis of reinforcement provided after the preliminary design. Final provision of flexural reinforcements are made then. Efforts have been made to meet the guideline for the curtailment of reinforcements as per CSA Standard A23.3-94. Although exact curtailment lengths are not mentioned explicitly in the design output (which finally will be more or less guided by the detailer taking into account other practical considerations), the user has the choice of printing reinforcements provided by STAAD at 13 equally spaced sections from which the final detailed drawing can be prepared.
The following annotations apply to the output for Beam Design.
- LEVEL
- Serial number of bar level which may contain one or more bar group.
- HEIGHT
- Height of bar level from the bottom of beam.
- BAR INFOrmation
- Reinforcement bar information specifying number of bars and size.
- FROM
- Distance from the start of the beam to the start of the rebar.
- TO
- Distance from the start of the beam to the end of the rebar.
- ANCHOR(STA,END)
- States whether anchorage, either a hook or continuation, is needed at start (STA) or at the end (END) of the bar.
D4.A.5.2 Design for Shear and Torsion
Design for shear and torsion is performed per the rules of Chapter 11 of CSA Standard A23.3-94. Shear reinforcement is calculated to resist both shear forces and torsional moments. Shear design is performed at the start and end sections. The location along the member span for design is chosen as the effective depth + SFACE at the start, and effective depth + EFACE at the end. The load case which gives rise to the highest stirrup area for shear & torsion is chosen as the critical one. The calculations are performed assuming 2-legged stirrups will be provided. The additional longitudinal steel area required for torsion is reported.
The stirrups are assumed to be U-shaped for beams with no torsion, and closed hoops for beams subjected to torsion.