Structural drawing review

BulbTheBuilder · Jul 28, 2023

A friend of mine with no building knowledge asked me to review a structural drawing for him which kind of looks messy to me. The engineer used metric units and Eurocode to design which I am not typically familiar with. Regardless, concept of design is basic across all design codes and things in the drawing set don't make sense to me.

The structure is meant to be a concrete braced frame with isolated footing. The region has non-seismic activities and the wind speed for MRI 700 years is less than 40mph, somewhere in Africa and the code the "engineer" used is Eurocode. Now, I am not typically familiar with Eurocode as a result, I don't know if there governing clauses on why certain things were done. I asked my friend to reach out to the engineer for clarification on certain concerns and questions, but the engineer is claiming everything has been done per code. To make things easier, I requested for snapshot of pages of the code but he is adamant to produce any and I don't have a copy of the Eurocode myself.

I would appreciate anyone familiar with Eurocode to provide any feedback since most things shown the drawing don't seem right.

For isolated footing, why have all these 300mmx300mm (approximately 12"x12") ground beams. I see no reason or use of them unless they were meant for the edges of the slab as restraints.

And why add strip footing and 300mm (12" thick)CMU for a slab on grade? Is it something recommend in European code?

The slab is a slab-on-grade supported just on the soil which has a bearing capacity of 250kN/m² (`5220psf). The soil is more than adequate to hold the slab so why go extra mile to even add 12" solid CMUs?

The interesting part is the shear wall. The shear wall from the drawings is "disconnected" from the building and only has 1 beam connecting to it. All other side of the shear wall is then unbraced from ground to roof level (5 levels with 4m~12feet floor-to-floor) as they have a staircase around. Although, the wind speed isn't high I am not comfortable seeing such a general arrangement as the shear walls are basically useless in the scenario and the columns will need to be designed as unbraced frames rather than braced.

I have not completed my review on the drawings, but I am seeing a lot of questionable items I have decided not to proceed any further. I am tempted to tell me friend the "engineer" is probably a guy dumping things a software application like the Midas guy but I am being respectful and holding back any comments for now.

Lomarandil · Jul 28, 2023

I am also not directly familiar with Eurocode, but I've done a lot of developing world design and reviewed several plans like this designed by developing world engineers per EC.

Unfortunately, many engineers in the developing world (and even those in the west) don't have a great understanding of the interaction between building and foundation design. So it's very common to have systems like this that are either 1: heavily redundant or 2: actually detrimental and working against each other, either out of misunderstanding or to comply with the existing local construction practice.

The ground beams can provide convenient construction joint locations (there is a SOG joint detail, right? [wink]

) for sites where concrete batch size/delivery is challenging. If not specifically jointed, the restraint is detrimental to slab performance, and a thickened slab with 3:1 transitions would be better.

Otherwise, the ground beams are typically included to "tie everything together" (not necessarily needed in non-seismic zones, but often applied anyway) or to shorten ground floor column length.

It's common to see blockwork specified beneath wall lines, since compaction quality is often questionable. But I don't think this is particularly effective, especially in combination with the excavation needed for the individual footings. That money can usually be better spent elsewhere (and throw 10% back to extra passes of compaction). Certainly the idea of a ground beam and strip footing as separate elements is pretty silly.

Your shear wall observation is certainly a concern. There's probably some connection from the landing to column line E, but I'd pretty much discount the shear core and want the building to work just as moment frames.

Bulb said:
I am tempted to tell me friend the "engineer" is probably a guy dumping things a software application like the Midas guy

Yeah, the odds are pretty high.

1503-44 · Jul 28, 2023

Yeah, same here. Did structures in the US long time ago. Been outside doing other things for 40 years now. You do see different methodologies.

I wouldn't think the grade beams are inappropriate, if the walls are cmu, especially if load bearing, but even still, not that unusual.

It doesn't sound like a shear wall design. If it's braced, or moment frame, (both directions?), why have shear walls. So, grade beams presumably are for cmu support only. 300x300 are relatively small anyway. QC on in the ground concrete is often nonexistent, so concrete can be 2000 psi stuff. A bit extra is usually a good idea.

I don't have a problem with the ground beams used with footings, since the ground beams only carry the weight of the cmu walls, while the footings probably carry the weight of all stuff above. Ground beams might be used to take any shear loads off the footing piers and distribute the shear into ground. Then you just have vertical on the footings. I've done that myself.

Considering the light loads you mention, especially no seismic, I don't yet see any obvious problems.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

BulbTheBuilder · Jul 28, 2023

Lomarandii said:
The ground beams can provide convenient construction joint locations (there is a SOG joint detail, right? wink)

Currently, there are no SoG joint details. I have proposed they add construction joints.

Lomarandii said:
Otherwise, the ground beams are typically included to "tie everything together" (not necessarily needed in non-seismic zones, but often applied anyway) or to shorten ground floor column length.

From the third snapshot, you can see the ground beams are connected to the SoG. Can't we use the slab to reduce the unbraced length? There should be a cheaper option (monetary and labor-wise. I guess labor is cheaper)

Lomarandii said:
It's common to see blockwork specified beneath wall lines, since compaction quality is often questionable. But I don't think this is particularly effective, especially in combination with the excavation needed for the individual footings. That money can usually be better spent elsewhere (and throw 10% back to extra passes of compaction). Certainly the idea of a ground beam and strip footing as separate elements is pretty silly.

Honestly, if it's to satisfy local concept of building then I'm Ok but the cost involved is just ridiculous. Thanks for your input!

@1503-44
Walls are not load-bearing. They are there just for partitioning,

Apparently, the feedback I got on that is he wants the "shear walls" for the elevator. For such a shorter building, a 12" (300mm) thick wall for just an elevator is an over-kill. I suggested columns can be used at the area just for elevators.

That's a great comment but I doubt that's what is being done in this scenario

Lomarandil · Jul 28, 2023

Yeah, a lot of designers will default to CIP concrete shear walls around an elevator core.

While that's often a good solution, it isn't mandatory (for most cases) and can be problematic to accomplish depending on local concrete placement techniques.

It takes some extra attention to drift and elevator specifications to design a moment frame (and infill wall) elevator core, but it is possible.

BulbTheBuilder · Jul 28, 2023

Thanks a lot, Lomarandil! I guess I overlooked constructability of structures in such regions. I have a better understanding of how things are like now at other places.

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