Masonry, generally comprising bricks or blocks laid in courses and interspersed with cementitious mortar, is at essence a composite ceramic material. Ceramic materials by their very nature are full of compressive strength, stiff, hard and low in electrical and thermal conductivity. These properties make them useful building materials, however ceramics are also very brittle, so that these people have a low tensile strength compared to other materials, including steel.
Not only is masonry weak in tension, but as a result of the regular construction methods there are also regions of weakness within masonry structures. This is because the bricks or blocks are laid in courses and bedded in mortar. The mortar forms joints relating to the individual clay or concrete units of masonry, both horizontally and vertically, from which you will find inherent structural weaknesses. It is at these points where wall panels, columns and piers are usually to fail due to lateral loading. The weakest joints in the masonry wall panel are in the horizontal "bed joints", with enhanced strength perpendicular towards the bed joints given by the shear connection between "keying" (overlapping) from the masonry units at alternate layers.
For slabs or walls constructed from isotropic materials (that is to say materials whose properties tend not to deviate established by orientation) and supported on four sides it's typical that the material will "span" the shortest distance. This means the majority with the forces will probably be accommodated with the slab or wall in the orientation relative to the shortest distance between supports. Masonry wall panels aren't different as they are isotropic in the sense of the stiffness, and, just like a reinforced concrete floor slab, a vertical masonry wall panel also requires support (on account of lateral load imparted upon it - that is generally due to wind pressures). A wall panel constructed included in a normal dwelling will therefore generally span vertically - involving the ground as well as a supported floor or roof.
The disadvantage from the wall panels spanning vertically is always that when afflicted by lateral wind pressures the resultant bending from the panel subjects the bed joints to tensile forces - in addition to being previously explained these are the weakest points in a masonry wall panel. Therefore, as a way to reinforce the wall panels which otherwise would span vertically, it can be necessary to setup buttressing "shear" walls. This ensures that at least a proportion with the panel spans horizontally, and that the stress around the wall panel is carried from the shear effects occurring as a result of keying of the masonry units within the vertical direction. These buttressing supports can be supplied by suitably designed masonry returns, or otherwise not steel frame structures.
In the UK, the Building Regulations Approved Document A for structures outlines the limiting dimensions for any buttressing masonry wall or pier. BS5628 part 1, (the code of practice to the structural use of unreinforced masonry) specifies that no lateral load-resisting wall panel really should have dimensions (defined by support positions) in excess of 50 times its effective thickness, which, for the cavity wall formed of two 100mm leaves of masonry is 6.65 m. The successor to BS5628, Eurocode 6, stipulates wall panel limiting dimensions in relation to span distances and thicknesses, even though it states the size is for the purpose of ensuring adequate serviceability (so that finishes do not deteriorate) as opposed to ultimate limits of allowable load before failure.
So how come ensuring fake stone wall panels are adequately supported against lateral loads matter? Well, you'll find two solutions to that question - one is of serviceability then one is of ultimate structural capacity before failure.
Clearly we usually do not want our wall to drop as a result of wind loading, so there is a clear incentive here to ensure how the wall panel is sufficiently strong that it will not collapse, but what about serviceability? What are we focused on? Surely if your wall doesn't fail as there are nothing to worry about?.. Well, the treatment depends on your attitude towards construction.
You probably haven't noticed before, but if you appear carefully at wall panels on the lot of older buildings you'll quite often see a "bowing" or curving of the wall panel vertically. This is an effect of the wall panel that's inadequately designed for serviceability. The wall panel bows with time because of inadequate lateral support caused by defects for example poor tying and inadequate load transfer at floor level, in conjunction with the progressive outcomes of creep on account of moisture absorption, frost attack and thermal expansion and contraction. A wall panel like this will not only arrive in structural surveys which reflect for the value of the property, but may also with time result within the collapse with the wall panel.
How can these problems be remedied or, even better, prevented?.. In order to know this we should instead know why they occur. There are a number of logic behind why these types of things occur. Often this really is because of inadequate restraint strapping in the wall to some floor or ceiling, on account of insufficient cavity tie provision or simply that this floor isn't able to in the role of a horizontal support by transferring lateral forces from your wall panel to shear walls in the property. The former issues might be resolved in some instances by tying retrospectively. The latter problem is where things be a little more complex.
In order how the floor can transfer lateral forces it's required to be sufficiently stiff which it behaves as a diaphragm - transferring the forces from your side wall panel returning to other masonry returns. In other words a floor panel must be stiff where there must also be all you need return walls within the building. This is where the dark art of engineering judgement over lateral stability will come into play. In the event that there are insufficient returns within the property it's possible that there is actually a large structural failure - therefore we must be cautious about these products.
If you are thinking about removing a substantial wall panel from a home to produce a big open space, or else you are constructing a masonry structure with hardly any masonry walls, be prepared to either alter your layout to ensure there exists sufficient masonry, or otherwise not be prepared for that installation of an lateral load- resisting steel frame. The choice of these options relies on the amount you are willing to pay in design fees, just because a masonry structure generally requires significantly less design input with a structural engineer than a steel structure.