Lintels in ICF Walls

[coatsandrew]

I'm designing a 2-story structure with exterior ICF bearing walls. The ICF manufacturer (with Contractor ties) is requesting we keep all lintels within coursing of their 16 7/8" high ICF wall blocks. I have a few spans over 1st floor windows that have floor beams from the 2nd floor bearing directly in the mid-span of the lintel and about 24" above the bottom of lintel. My question is, since the entire wall is going to be one concrete mass, is the lintel depth only the distance from the bottom of the lintel to the top of the stirrups within the lintel, or can I consider all of the concrete above the window head? This would be approximately 6 ft since the concrete mass would be from top of window head on 1st floor to bottom of window sill on 2nd floor. I could also only consider the bottom 2 ft of the mass to be part of the beam/lintel to be slightly conservative.

 

[ishvaaag]

In my view and no code providing otherwise you can design it as built, with some compression concrete collaboration above and even with the whole height of concrete (if solid, solidary, and well reinforced). The key to the issue is to ensure no crack will form so minimum reinforcement in the concrete is paramount, as deep beam considerations (or vertical plane plate) if you are dimensioning structurally so.

 

[concretemasonry]

You should contact the supplier of the ICF units for suggestions, since if they are one of the few better ones (not those that also make foam trays for the Walmart meat department).

They generally have great technical information, structural engineers AND experience with ICF construction on multi-story construction.

I suspect the ICF supplier is listening to their customer (who requests to do it one/his way), but may have seen the same situation on taller buildings. It is not a unique situation. Cutting the forms is no major cost problem (just a saw or a hot wire), but the design assumptions are up to the designer.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[JAE]

This isn't an answer to get from an ICF supplier in my opinion.

The ICF is simply a form. The wall (the concrete wall that results) is simply that - a concrete wall. Whether it got there by custom forms or by ICF forms has no bearing on its structural behavior.

Design the "lintel" as a deep concrete beam if you want - or if you put in discrete stirrups and depend on the stirrups for shear capacity, design it as a beam within a wall.

However, it will most likely behave as a deep beam.

 

[dik]

I treat lintels as fully fixed usually with top and bot rfg. and use an 'S' shaped hairpin for stirrup rfg. You can also used hooked rfg around the lintel rfg and 'hang' the opening from the mass of conc above, if applicable. Did my first ICF 3 storey 'walk-up' about 40 years ago... and it's still standing... floors of 8" HC precast planks...

Dik

 

[concretemasonry]

What stage is the project in - design or construction?

It is a cost and constructability request from a contractor. The structural design and assumptions are a total responsibility of the structural engineer. If the contractor has made a proposal it seems it will be prudent to check out the knowledge and experience the form supplier has (if appreciable) since some exceptions can present positive options.

A supplier in a specialized system MAY have a great deal of domestic and international experience with similar situations and that should take little time to make a decision on the accountability of the suppliers technical knowledge and experience credentials.

I have met a number of ICF professional engineers that can run circles around a typical professional structural engineer in a specialized or different type of construction. - That was when I was in a semi-adversary situation with them.

There is a wide range of technical knowledge and experience in the ICF industry.

If this is just in the design stage and not awarded, it is up to the designer to make the design/detail or assumptions based on what he knows. Some contractors with an inside track to the owner do try to take advantage and try to affect the ultimate design.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[JAE]

concretemasonry - using ICF forms to create concrete wall systems is not a "specialized or different type of construction". It is simply cast-in-place concrete construction.

We work with a major ICF supplier as their structural consultant and they certainly aren't high end structural engineers. They wouldn't want to be as their business is formwork, not design.