BS 8110 – Part 3: Design charts for singly reinforced beams, doubly reinforced beams and rectangular columns

Full Description

BS 8110 Part 3 is the part of the British Standard for structural concrete that contains design charts for singly reinforced beams, doubly reinforced beams and rectangular columns. Engineers and students use these charts as a quick aid when checking reinforced concrete sections at the ultimate limit state.

What is BS 8110 Part 3?

BS 8110 is the British Standard code of practice for the structural use of concrete. Part 1 covers design and construction, Part 2 covers special circumstances, and Part 3 provides design charts. The Part 3 charts are based on the assumptions in BS 8110-1, using the parabolic-rectangular stress block throughout. They cannot give the complete detailed design of a member, but they help when analyzing the cross section of a beam or column at the ultimate limit state.

When to use it

• To size the tension reinforcement in a singly reinforced beam
• To check whether a beam needs compression steel and size it as a doubly reinforced section
• To check a rectangular column section for combined axial load and bending
• To make a fast hand check of computer output or a consultant’s design
• When studying reinforced concrete design to BS 8110
• When reviewing older structures that were designed to BS 8110

What’s included

This download contains BS 8110 Part 3: design charts for singly reinforced beams, doubly reinforced beams and rectangular columns. The charts are a design aid for analyzing member cross sections at the ultimate limit state and are intended to be used together with the design rules in BS 8110 Part 1.

How to use the design charts

1. Find the design moment and, for columns, the design axial load from your analysis.
2. Note the section size, effective depth, concrete grade and reinforcement grade.
3. Work out the non-dimensional values the chart uses for your section.
4. Pick the chart that matches the member type and material grades.
5. Read off the required reinforcement ratio and convert it to an area of steel.
6. Choose bar sizes, then complete the other checks in Part 1, such as shear, deflection, cracking and detailing.

Tips

• Use the charts as a check, not as the whole design. Detailing rules still apply.
• Interpolate carefully between curves and round reinforcement up, not down.
• Confirm which code your project specification requires before you start design work.

Related templates and guides

• Manual for the Design of Reinforced Concrete Building Structures
• Rebar Takeoff – quantify the reinforcement once the design is set.
• Reinforcement Checklist – inspect rebar on site before the pour.
• Rebar – glossary definition
• Browse all codes and standards

Frequently asked questions

What is BS 8110?

BS 8110 is the British Standard for the structural use of concrete. It sets out how to design and build reinforced and prestressed concrete structures. It has three parts: Part 1 for routine design and construction, Part 2 for special circumstances, and Part 3 for design charts for beams and columns.

Is BS 8110 still used?

In the UK, BS 8110 was withdrawn and replaced by Eurocode 2 (BS EN 1992). It is still referenced on some projects and in some countries, used in teaching, and needed when assessing older buildings. Always check which design code your project specification and local authority require.

What is the difference between a singly and a doubly reinforced beam?

A singly reinforced beam has main reinforcement only in the tension zone. A doubly reinforced beam also has reinforcement in the compression zone. Compression steel is added when the beam depth is limited and the design moment is more than a singly reinforced section can carry.

Can BS 8110 Part 3 charts be used for complete design?

No. The standard states that the charts cannot be used to obtain the complete detailed design of a member. They are an aid for analyzing the cross section at the ultimate limit state. Shear, deflection, cracking, anchorage and detailing still need to be checked using BS 8110 Part 1.

What is the parabolic-rectangular stress block?

It is the idealized shape of the compressive stress in concrete at failure: stress rises along a parabolic curve and then stays constant up to the ultimate strain. BS 8110 Part 3 charts use this stress block throughout, which is why their results can differ slightly from hand calculations using the simplified rectangular block.