Several members make up a building frame. A few prominent members are struts, ties, beams, columns, and walls that make up the building’s frame. It’s essential to understand how stress affects these, especially in a commercial building.
Struts are present in the frame to withstand compressive stress. This stress comes from the force of each level of the structure going down to the foundations. There will always be a reaction to that force, which creates present longitudinal stress, and struts are positioned in the frame to withstand this by strengthening other structural members and making the structure overall more rigid.
Compressive Stress Can Change the Shape of the Structural Members
When a strut is under constant compression, this can affect a member in many ways, depending on its properties. Also, as all parts of a frame are interlinked, this can cause other structural problems.
Compressive stress can change the shape of structural members and in struts, if it reaches a level of stress that is too much for the member, usually called buckling. Buckling can affect a member so that it will make it unstable and deform in shape, which happens when the stress from the load causes the member to move laterally and shorten.
A similar member that also is built to hold compressive stress is a column. Columns are a lot less slender than struts, and their purpose is to transmit the weight of the above structures down to the foundation. These provide support for the whole structure.
These compressive stresses can affect columns the same way as struts. However, columns are a lot thicker and can bear higher compressive stress resulting in the member taking a lot more to buckle, as they are thicker and expected to support a higher load than struts.
Beams are Generally Made of Steel and are Designed so They Can Withstand Stress
Ties are structural members designed to withstand tensile stress – making it an opposite to a strut. These generally connect the bottom of the rafters on the opposite sides of a roof structure. These will need to be made of a non-ductile material and a robust tensile strength to withstand the stress that will be constant. If ties don’t have these properties, the roof will sag as a result. Tensile stress affects structural members such as ties in a way that it can cause a deformity such as a bend. This, in simpler terms, would be the member being stretched, resulting in a dip.
However, most of the time, in a structure, it isn’t noticeable to the eye, and there will always be tensile stress present in a tie – this stress only starts to noticeably affect a member in that way if the tensile stress exceeds the tensile strength. This constant force on the object will eventually weaken the tie and deform its properties if the member’s properties haven’t been appropriately calculated to withstand these forces.
Another essential member that is affected by stresses in a structure would be the beam. When loads are applied to beams, this creates tension. Beams in structures are expected to carry loads that create forces perpendicular to the beam, as it is a longitudinal member supporting structures above.
Beams are generally made of steel, and they are designed so that they can withstand stress and prevent that stress from affecting the integrity of the member. However, if the loads have been miscalculated and the force distributed over the beam area is too high, it can be subjected to bending moments. This causes the beam to bend – not always visible.
The Role of Stresses in Failure
Structural failure is when a structure loses its structural integrity, which is an object’s ability to remain intact under a load. A structure or a member in a structure will have a certain amount of strength depending on its properties, which is how much stress it can withstand caused by loads and the forces resultant from those loads. When that member or whole structure meets its maximum amount of stress it can withhold, the object can begin to deform, which is a strain.
Too much strain, and the object will eventually fail. As stated before, structural members in a structure are all interlinked, yet sometimes stress can cause a localized failure rather than a total structural failure. When designing a structure, engineers prevent further loss by selecting materials that have a high safety factor for the load they are expecting to carry.
Stress-Based Failure is Mainly Caused Due to Yield and Fracture
This means that the structural members can carry a lot more than is usually expected from the building’s current use. All materials used in construction are tested to see their properties, so they can be deemed suitable for the task they are being assigned. Failure will happen in an object or structure when the stress state of that object is equal to that of the tested material that caused it to fail.
Stress-based failure is mainly caused due to yield and fracture. The material can be classified as either ductile or brittle, and ductile objects fail due to yield and those that are brittle to fracture. Upon assessment, the engineers can establish a stress-strain curve, which shows the relationship between the stress that the material is suspected to experience and the result’s strain. In other words, the object either surpasses its yield point in ductile materials or the ultimate tensile strength in brittle materials.
Typical ductile materials used in constructions would be steel and many types of alloys. These have very a very linear stress-strain curve up to a defined yield point – which means that the amount of stress and resultant strain coincides up the point where the object yields – and then fails. Brittle materials, such as concrete, will not have a yield point and will fail if the object experiences an elastic deformity.