Most popular FAQs
We are often asked when it is best to use ADC and when AdSec? After all, they both design reinforced concrete.
This is of course true, but ADC and AdSec approach the problem of concrete design from opposite directions: ADC takes the loads and gives you the rebar while AdSec takes the rebar and gives you the loads. Which is best depends on your situation.
Let’s first look at ADC, which is broken down into two aspects: AdBeam and AdCol.
AdBeam designs multi-span concrete beams, solid slabs and ribbed slabs. You define the number of spans, the supports and other geometries. ADC will then calculate the bending moments and shear forces, taking into account patch loading and redistribution, to give you the most efficient reinforcement arrangements.
AdCol is similar in approach to AdBeam, but instead designs a single lift of a concrete column. Here you supply the section, axial and moment loads; ADC will first give you the bars that meet the detailing rules and then tell you which sections carry the load including which is the most efficient.
As part of the results, you can choose to print out the Axial v. Moment (N/M) and Biaxial Moments for given Axial (M/M) charts.
AdSec takes a different approach to ADC: you give the reinforcement and AdSec will tell you how strong it is and if it is strong enough. It is thus much more powerful, flexible, and hence demanding than ADC. You could say that it is advanced analysis for advanced engineers.
As an example, while AdCol only lets you try circular and rectangular sections and AdBeam rectangular, T, taper, I and taper T, AdSec lets you analyse all of these concrete shapes plus many more, including steel sections, bridge beams and even sections you define yourself. Similarly, while ADC only has reinforced concrete, AdSec also has steel and FRP materials such as carbon fibre. In addition, while ADC only has set locations for the rebar, AdSec allows you to put it anywhere within the section, assisted by templates and Excel links. You can also prestress the rebar or create new materials.
What does AdSec give you? Firstly, like ADC, AdSec can output charts of axial load against moment (known as N/M charts). You can find examples of these in BS 8110 part 3. AdSec also plots major moment against minor moment (or Myy/Mzz charts) for various multiple axial loads. These tell you what moments you can put on a section in each direction for a given axial load
AdSec can also draw the change of section stiffness (EI) as it cracks under moment combined with varying axial loads. This can be very useful if you want to accurately predict concrete deflections. Alternatively, it can give you the curvature of the member as the moment increases.
Under serviceability loads, AdSec can calculate the crack widths around the section and highlight which bar is responsible for controlling the largest one.
Under ultimate loads AdSec can tell you if the section is adequate or not, plus it can tell you the maximum axial capacity for your specified moment and the maximum moment for your given axial load. You can also look in detail at the stresses and strains in the concrete and reinforcement.
Composite and Compound sections
AdSec can also create compound and composite sections. For example, you can define a concrete beam, load it up with its self-weight and the wet weight of the concrete slab, then analyse the compound beam/slab section under service loads. Another typical use is to take a steel column and either wrap it in concrete or fill the inside, enabling you to check the capacities of composite columns ore even mega-columns. You can also take an existing concrete beam or column and see how much extra capacity you can get from applying carbon-fibre plates to the outside.
What does this mean in practice? Let’s take a piling designer as an example. When you use ADC AdCol to design piles, you input the loads for each pile and are given the reinforcement in return. You might then rationalise the rebar choices or arrange beforehand that ADC only gave you a limited choice. If, on the other hand, you use AdSec, then you would define a number of standard piles in advance, work out their capacities, plot the N/M charts, etc, and then allocate the designs to the piles accordingly.
Similarly, if you are designing a concrete building, then ADC is excellent for standard beams and columns, but if you need something more advanced like composite columns or elliptical sections, then you need AdSec.
If, on the other hand, you are designing a bridge, then AdSec is the one for you.
In summary: ADC for quick and simple, and AdSec for advanced!
Enable prestressing by selecting the prestress advanced feature preference (‘Tools | Preferences | Advanced’) Then individual bars can be prestressed with force or strain in the general reinforcement table. The prestress can then be modified using the prestress factor for individual analysis cases.
AdSec uses analysis cases similar to those in GSA. So a ULS analysis case can be defined as 1.4L1 + 1.6L2 where load cases 1 and 2 are dead and imposed loads respectively.
With AdSec it is possible to analyse the effects of adding more structure onto existing sections that are already loaded.
For example, if we were modelling a reinforced concrete beam that is un-propped before the slab is cast on top. To do this we would need a beam section that stops at the slab soffit, a slab section that represents the effective width, and a compound section that has the two appropriately adjacent.
To conduct the staged analysis:
- Create a load for the Beam, say a Section Force applying the bending moment
- Create a SLS load case that applies that load to the Beam
- Run the SLS analysis for the Beam section
- Go to Tools > Extract Strain Plane… and chose the appropriate strain plane. This will create a new load that is a Component Strain on the Beam section
- Set the Compound section as active
- Create a new Section Force, etc. that represents the additional load
- Create a SLS or ULS load case that analyses the compound section for the extracted strain plane and the new load from #7
This method also works, for example, for strengthening existing in situ beams, columns, and slabs with steel or carbon fibre plates.
Sometimes AdSec finds it difficult to converge on some of the N/M chart points hence part of the chart becomes flat. it is because the defined solver parameters are insufficient to get a converged solution.
Slightly altering the solver parameters (either Maximum number of iterations or perturbation factor or both) will generate a perfect N/M chart. You can change these parameters at the N/M chart generation wizard>Analysis Control.
Occasionally AdSec may report that there is no solution found. This may be because there is no possible solution, or it may be that the iterative solver has not yet reached it.
You can change the search parameters in the SLS or ULS analysis wizard > Analysis Control.
Increase the maximum number of iterations. You may also find that adjusting the perturbation factor can help as well.
AdSec will also struggle to converge under pure axial load as there are an infinite number of possible strain planes that can satisfy that condition. The trick is to add a negligible moment into the load case, or even the code-based eccentricity, to ensure that AdSec has just the one solution to find.
In order to model non-linear cross sectional thermal gradients, break the section into a suitable number of strips/sections which are then compounded to make the overall section. You can then apply component strains to each in accordance with the thermal changes. This can be combined with the overall effects of axial forces and moments generated on the member by the end conditions; these will have to be derived independently. Ensure that each reinforcement bar/line/group exists wholly within a single section.
To achieve an almost regular section you can specify a standard section in the section wizard, convert it into a perimeter section (using the ‘Options | Expand Section’ command) and then adjust the perimeter section in the section wizard. In this circumstance any template reinforcement is converted to general reinforcement ensuring that the reinforcement definition remains complete.
The section wizard can be used to specify component sections; these can be used to build up compound sections.