Shrinking beam?

[Magnus83]

Hello!
The glued laminated timber beam used for the conversion of the load-bearing lightweight concrete wall with a support of 25 cm (steel plate 2+3 mm) on the existing wall is fully adequate according to the engineer. The ceiling structure is also made of lightweight concrete elements.

When the remaining renovation was finally completed and it was time for the ceiling moldings, I noticed a gap had appeared between the beam and the ceiling structure, primarily corresponding to the support part, about 2 mm between the beam and the ceiling structure. (I did not examine the entire beam length, but since the ceiling elements are joined at the level of the beam, the majority should have contact with the beam).

Now to the question itself - what has caused this gap? Is it simply drying/shrinkage of the beam? (Discovered during the winter months, so I assume it was driest then). There are no visible signs of any direct "settling damage" at the support.
And since the affected ceiling elements partially rest on the original wall, I assume the gap can be explained by potential wood shrinkage. Could this have been prevented when the work was done?

I addressed the discovery with a couple of wedges from each side before the moldings were installed, so it should not have any direct impact - or what do you knowledgeable people think?

 

[Düsseldorff]

Hmm maybe but doubtful about that. Glulam swells and shrinks in response to moisture, like wood in general. For glulam, it's usually estimated at about 0.2 percent along the fibers and 0.1 percent across the fibers for every percent change in moisture content.

 

[Magnus83]

Hmm maybe but doubtful. Glulam expands and contracts with humidity, like wood in general. For glulam, it's usually estimated to be about 0.2 percent along the fibers and 0.1 percent across the fibers for each percent change in moisture content.

Hmm, if it can't be related to the beam and no visible settling is seen (I think the underlying wall section should bulge a bit) what could then be behind the gap?

 

[Düsseldorff]

Have we ruled out measurement errors?

 

[Magnus83]

Have we ruled out measurement error?

Not quite sure what you mean, but contact was initially present, yet when discovered a square with 1mm could be inserted into the space...

 

[Düsseldorff]

Not quite sure what you mean, but contact existed initially, but upon inspection, a square of 1mm could be inserted into the space...

Ok, I find it hard to believe that the beam would have dried that much. Or hard to see, it simply hasn't. It must be something else that has moved.

 

[Thomas_Blekinge]

Hmm maybe, but I'm doubtful about that. Glulam swells and shrinks with moisture, like wood in general. For glulam, it's usually estimated at about 0.2 percent along the fibers and 0.1 percent across the fibers for every percent change in moisture content.

Are you sure about the figures? Regular wood swells significantly more across the grain.

 

[Düsseldorff]

Are you sure about the figures? Regular wood swells significantly more across the grain direction.

You're right, I mixed up the figures and also missed a zero. It should be 0.2 percent across. And 0.01 percent along. Sorry for that.

 

[Magnus83]

You are right, I mixed up the numbers and also missed a zero. It should be 0.2 percent across. And 0.01 percent lengthwise. Sorry about that.

Ok, found this: In heated Swedish residences in central Sweden, the moisture content in wood is on average 7.5% throughout the year and is highest in summer (7–12%) and lowest in winter (2–6%).
That is a max of about 10% units.

10*0.002*270(beams)= 5.4 mm
Then 2 mm doesn't sound completely unlikely anymore, or am I thinking wrong?

 

[Magnus83]

Ok, found this: In heated Swedish homes in central Sweden, the moisture content in timber throughout the year averages 7.5%, and it is highest in summer (7–12%) and lowest in winter (2–6%).
That is, a maximum of about 10% units.

10*0.002*270(beam)= 5.4 mm
So 2 mm doesn't sound completely unlikely anymore, or am I thinking wrong?

Am I right to think that shrinkage could still be the cause, or should I continue to look for signs of settling - any tips on how to address this if so?

 

[Düsseldorff]

Ok, found this: In heated Swedish homes in Central Sweden, the moisture content in wood is on average 7.5% throughout the year, and it is highest in the summer (7–12%) and lowest in the winter (2–6%).
Thus, a maximum of about 10% units.

10*0.002*270(beam)= 5.4 mm
Then 2 mm doesn't seem completely unlikely anymore, or am I thinking wrong?

Sorry, didn't see that you replied.

Don't we usually count on a 2-6% moisture content in the winter? Lowest 7 in the winter and highest 12 in the summer in glulam.

 

[Magnus83]

Sorry saw that you didn't reply.

You don't usually consider 2-6% moisture content in the winter, right? Lowest 7 in the winter and highest 12 in the summer for glulam.

You end up with about 2-3 mm as potential shrinkage as I understand it, 5% units difference...

 

[Düsseldorff]

You end up with 2-3 mm as potential shrinkage as I understand it 5% unit difference...

And that corresponds to the gap, right? Then I probably had the wrong initial reaction. The gap might be explained by drying.

 

[Magnus83]

And that corresponds to the gap, right? Then I probably had the wrong spontaneous reaction. The gap may be explained by drying.

Yes exactly, that's roughly what the gap is... I'm mostly looking to either buy that the gap t is due to drying or if I need to look for any other reason, visual inspection gives me no clues...