Structural Inspection Perth / Diagnosing Structural Movement in Buildings
Brick cracks are mostly more than just a cosmetic problem; they could be an indication that your building foundation needs repair. Cracked bricks can be the result of foundation settling, which can create a lot of damage. It’s very important to find and repair the cause of the cracked bricks before they grow into a larger problem.
Cracks in the foundation are common in most buildings but they can be a sign of problems yet to come.
Cracks on the inside of the building are a serious sign of trouble and should be immediately evacuated and repaired. Inside cracks imply that the building has shifted enough to cause structural damage and is likely not safe to be inside. Most people call this settling and a small amount of it is normal as the ground around the building shifts but normal does not mean safe. Every crack can be a disaster waiting happen if not taken care of. Nearly every Building Inspector in Perth categorize visible cracks to "normal settlement cracks" In some cases, that's right; but in most cases, it is not
Example 1 Figure 1.1
If one imagines arrows right angles to the crack, as shown dashed in the diagramm in Figure 1.1, then one can see that the movement in either down to the left hand corner or up to the right hand side. The arrows points to where the movement is and this is usually pointing at the defect. In this case there is nothing that could possible cause movement up to the right. The solution is therefore reasonably obvious. In the absence of other evidence the movement is likely to be caused by the tree.
There are, however, always some cracks that cannot be diagnosed quickly by a simple visual inspection.
Example 2 Figure 1.2
It is quite common to see diagonal cracking above an opening in a brick wall, similar to that shown in the diagramm in Figure 1.2. The cracking forms a triangle running through the brick courses at around 45° from the support points at either side.
Once again, imagine arrows at right angles to the cracks as shown in the diagramm. In this case two of the imaginary arrows at right angles to the cracks intersect on the lintel. - good evidence. In fact if two arrows intersect at the same point it is almost certainly the position of the defect. The movement is deflection of the lintel (beam) supporting the masonry above the opening
Different Structural Cracks:
If a wall has an upwards overload adjacent to a downwards overload, it may crack vertically so that one side rises or sinks with respect to the other.
Vertical cracks are usually caused by settlement, compaction, or soil eroding under the footing. Overloading from above can occur when framing members fail forcing loads to areas that were not designed for them. Similar cracks can also be caused by overloads from below, such as frost or hydraulic expansion of the soil.
When up and down loads are applied so the forces are offset from one another, cracks are likely to occur at an angle. Cracks of this type may be found when
there is a major discontinuity in the soil or if a building is built on expansive clays.
When a wall is overloaded from the outside, soil pressure, or improper backfill, it may bow inward and crack horizontally (Figure 3). In a block wall, the crack is usually in a mortar joint and is wider on the inner face. An additional cause of horizontal cracking may be settlement of the foundation. If a foundation is laid on top of unstable soil, the wall which lacks the proper support could drop resulting in a horizontal crack without vertical displacement of the wall surface. Horizontal cracks, wide cracks (the thickness of your fingernail or greater) or a pattern of cracks starting on one side of a corner and picking up on the other side show the foundation is unable to bear the home’s weight.
Diagonal cracking is almost always structurally related. Diagonal cracking is defined in this example as a crack that tears through the material, not a step crack that follows the mortar joints. To understand the source or cause of a diagonal crack, draw an imaginary line perpendicular to the center of the crack, down. This should point to the source or reason for the cracking.
Example: Assume that a frame floor system is carrying enough weight to cause it to sag, and the subject wall is parallel to the joist system. The sag would typically be farthest from the bearing points (at mid-span), where there is likely to be diagonal cracking. Draw an imaginary line perpendicular to the crack, from the center of the crack, downwards toward the floor. This should point to mid-span of the floor joist.
In the above example, the cracking would typically occur 1'–4' from the corner of the settled wall, because the wall that is perpendicular to the settled wall is likely to be supported differently and resist movement. A wall that is on a foundation, beam or is perpendicular to the floor joists, will be supported better than a wall that is
parallel to the floor joists.
Settlement Cracks Compared With Shrinkage Cracks in Poured Concrete Slabs
Foundation settlement cracks are vertical, extending up through the structure. For a brick home, you may see cracks following the mortar joints in the brick wall. In most cases, the settlement crack itself has no structural significance. Rather, we are concerned that the house could continue to settle over time.
Most settlement cracks are the result of short-term settlement. Ongoing settlement is unlikely and uncommon. Unfortunately, it is very difficult to identify ongoing settlement from a one-time visit to the home. Since multiple visits to the home over a few years is not compatible with a real estate transaction, we have to use our experience to ‘read the cracks’ and take an educated guess as to whether ongoing settlement is likely.
- Settlement crack size: A larger settlement crack is more likely to be due to ongoing movement than a smaller settlement crack. While there are no hard and fast rules, a settlement crack or series of settlement cracks that have a sum total opening of less than 1/4 inch are probably not due to ongoing settlement.
- Direction of movement: A typical settlement crack is vertical, where the crack opens up. The bumps and crevices line up and fit together like the pieces of a puzzle. If the crack face has moved in any other directions, such as a shear crack, the quarter-inch rule described above does not apply. This can be a significant structural concern.
- Repaired and re-cracked: A settlement crack that has been repaired and has re-cracked (not just a hairline crack) also could indicate ongoing movement.
A newly poured, concrete foundation may contain small cracks because concrete shrinks as it cures. Fortunately, a shrinkage crack in a foundation wall is not structurally significant. Here’s how to recognize a shrinkage crack in a poured, concrete foundation:
- The crack will be small, less than 1/8th of an inch wide.
- The crack will be vertical.
- The crack will not extend up through the structure. The crack is in the foundation wall only.
- Shrinkage cracks usually occur in the middle third of the length of the foundation wall. If the crack is located towards the end of the length of the foundation wall, it’s probably not a shrinkage crack.