Reinforced Concrete Design / An integrated design: one structure, end to end
The load path, end to end
Every previous module answered a question about one member. This one follows the load from where it lands to where it stops.
Lesson review: expert verification remains open
This lesson has received a full-context editorial review and a check of its technical explanations. Selected arithmetic has been checked separately. This is not independent engineering sign-off.
Corrections checked in this pass
- Rebuilt the load take-down and dependent beam, column and pad results; removed unsupported overall pass claims.
Checks needed for project use
- A concrete-design reviewer must check the stated first-generation clauses, National Annex choices, detailing rules and factor sets. Numerical agreement alone does not establish code compliance.
- Column end moments, effective length, creep and governing combinations remain needed for N-M and stability. Check ground resistance, settlement and full detailing.
These are educational models and exercises. Check their assumptions before using the results. The full technical content and every diagram have not yet been independently verified.
Concrete and steel calculations retain their stated first-generation Eurocode teaching basis. Use the standards and amendments specified for your project; do not mix generations without an appropriate design basis.
Read the lesson register and outstanding review notesWhy this matters
Loads change as member sizes are revised. This example records a consistent baseline, then follows an optional beam-depth change through the column and footing. Keep the load basis visible so that later checks use the same structure.
By the end of this lesson you should be able to
- Convert area loads to line and point loads
- Count slab, beam downstand and column self-weight once
- Keep permanent and variable actions separate
- Carry two office floors and a roof without an imposed-load reduction
What you should already know
- Actions and combinations (Module 2)
- Slab behaviour and one-way spanning (Module 9)
- Beam and column design (Modules 8 and 10)
- Pad foundations (Module 11)
The building
One floor of a three-storey office building, in in-situ reinforced concrete. The frame is a regular grid:
- Columns on a 7.5 m by 5.0 m grid, storey height 3.5 m
- Beams span the 7.5 m direction, at 5.0 m centres
- A one-way slab spans the 5.0 m between beams
- C30/37 concrete, 500 MPa reinforcement throughout
- Allowable bearing pressure 200 kN/m²
That is the whole structure. Four members, and the load has exactly one way to reach the ground:
slab → beam → column → pad → ground
Each arrow is a change of units as well as a change of member. The slab carries an area load in kN/m². It delivers a line load in kN/m to the beam. The beam delivers a point load in kN to the column. The column delivers a point load to the pad, which spreads it back into a pressure in kN/m².
Getting those conversions right is most of a load take-down, and every one of them is equilibrium — there is no code in any of it.
Worked example
The load take-down, slab to ground
Given
- Regular internal grid 7.5 m ×5.0 m; two office floors and one roof;3.5 m storeys
- 200 mm slab;350 ×550 mm beams;400 mm square columns
- Office gk =7.5 kPa, qk =3.0 kPa; roof gk =6.5 kPa, qk =1.5 kPa
- Concrete 25 kN/m³; selected gravity factors 1.35G +1.5Q
Find
Obtain one consistent unreduced gravity-load take-down.
Assumptions
- Simply supported gravity idealisation; actual continuity, lateral actions and frame stability require a separate structural model
- No imposed-load reduction and no accompanying-action reduction: the sum is a conservative illustrative gravity envelope, not a complete project combination envelope
- Roof permanent load comprises the same 5.0 kPa slab plus 1.5 kPa finishes/services, without partitions
Practice
The slab carries gk = 7.5 kN/m² and the beams are at 5.0 m centres. The beam is 350 × 550 with a 200 mm slab. What is the total permanent line load on the beam, in kN/m?
Practice
With gk = 40.56 kN/m and qk = 15.0 kN/m, what is the design moment on the 7.5 m simply supported beam, in kNm?
Practice
For the baseline 550 mm beam, one internal office floor delivers 7.5 kPa over 37.5 m² plus 22.96875 kN of beam downstand weight. What permanent load reaches the column before its own self-weight, in kN?
Check yourself
Why must the permanent and variable loads be tracked separately all the way down the column, instead of being combined at each floor?
Check each conversion
Tributary widths must add up to the loaded floor width. Tributary areas must add up to the floor area. Downstream sums must include the member self-weight once.
For the pad, match the action combination to the supplied ground criterion. This example uses an allowable service pressure; a geotechnical ultimate resistance check uses the appropriate design actions and resistance instead.
Summary
- The example carries two office floors and a roof with no imposed-load reduction
- The beam take-down includes only its downstand self-weight
- Use required steel and the flanged concrete area in the T-beam span/depth calculation