how to measure the differential settlement

[SantoZoo]

Hi Sir,

I want to know about the cracks found on wall and beam.

If the cracks are found on wall, we might think that it caused by differential settlement.
Then if there is any tools or instruments that can check and measure this settlement?
It's for existing building.

If I'm not wrong, when on the construction process, usually we create a red mark on column to indicate the level of its column.
And it can be used to keep the elevation in a plain as its designation.
If some columns settle let say 30mm, we can check and know that the red mark has moved 30mm.
But if the existing building that has a finishing or some aesthetic ornament, those red marks has gone.
Then how to check it?

Please your kindly advice about this.
Thank you.


Best Regards
Yusak Santoso

 

[FixedEarth]

We need an initial elevation readings when the building was new to make any sense of what has settled. Without that information, start from scratch - hire a geotechnical firm.

http://www.soilstructure.com/

 

[cvg]

finished floor elevation should have been set by a surveyor and should be indicated on the plans. from that, all other elevations can be calculated. Assuming the building was constructed properly according to the required finished floor elevation, a surveyor could come back at any later time and set a benchmark near the building that can be used to check the elevations and verify the amount of settlement.

if it is just differential settlement you need to check, than assuming the walls and floors were constructed plumb and level, than use a plumb bob and level to re-check them and you can easily verify differential settlement.

 

[oldestguy]

OK, measuring differential settlement. I use two methods. In a finished structure with interior walls, doors, etc. Take a garden hose and attach a clear plastic hose on each end, about 2 feet long. Fill the hose with water and check that the elevation is the same in each, meaning no air bubbles. Now have one helper at a "bench mark" with a survey rod or other measuring tool and you take another end with some measuring tool, such as a level rod. When a reading is done at one location the difference in elevation is the difference between the two measuring stick readings. With this you are not limited by walls, but have to hear each other for recording purposes. Much easier than transit and level rod.

The fittings you need usually can be found at the hardware store.

The construction rotating light method sometimes is too rough for precise elevation difference work.

Wall cracks can be monitored by drawing a line across the crack and mark two points 2 inches apart. Subsequent readings are the distance between these marks and the off set of the line at the crack. Easy done and can be inconspicuous.

 

[Ron]

Cracks in a wall can have a variety of causes....settlement is only one of them and settlement is less common than shrinkage as a cause of cracking.

Differential settlement can be difficult to measure, except when it is significant. As an example, you really need good initial elevation measurements as a baseline. If you do not have that, differential settlement can only be surmised from observations such as changes in level as described by oldestguy.

Depending on the structural framing system, even small amounts of differential settlement can cause cracking. As an example, a difference of about 1/4" in 20 feet, will crack masonry.

 

[oldestguy]

An interesting situation can occur this time of the year in northern areas. Some roof truss systems can expand and contract, top versus bottom cords, due to differing outside and inside temperatures. The result will be noticed inside at the junction of walls and ceilings. The cracks will change in width depending on time of day and cloud cover.

 

[PSlem]

To check from this time forward you can use

http://www.durhamgeo.com/testing/concrete/nondes-crackmon.htm