Unit C1 1.3 Causes of damage to the structure of buildings Flashcards
Causes of Structural damage
weather: solar radiation, rain and wind.
Overloading of structures: Dead loads, live loads and dynamic loads.
Damage from moving plant.
Hot and corrosive atmospheres.
Vibration.
Alterations to structural members.
Subsidence: Overloading, water, excavations and mines and tunnels.
Deterioration of building materials.
Excavations.
Unauthorised modification.
Failure modes
Poor design that doesn’t consider:
likely forces or circumstances.
The specification of inappropriate building materials.
Causes of damage due to weather: Solar
Solar radiation causes materials to heat up and expand, causing dimensional change, when rain fall on a heated surface it can cause shock, especially to building membranes
Causes of damage due to weather: Rain
Rain is the greatest cause of weather damage to buildings,
humidity fluctuation causes dimensional change, leading to deformation, crazing and cracking,
driven by winds it can erode and dissolve soft materials, rising damp can cause flaking and cracking
freezing in pores causes stresses in bricks, stones and concrete,
moisture can promote the corrosion of metals,
snow and ice can increase the loading,
moisture driven by wind can accumulate in the pores causing expansion, slower surface drying can add stresses which can disintegrate the surface layer
Causes of damage due to weather: Wind
Causes direct physical damage to buildings,
creates dampness by driving moisture into the building,
creates excessive heat loss due to uncontrolled air transfer,
compression forces or suction forces can result in the over loading or even lifting of a building, this can be worse on a high or exposed building.
Causes of damage due to overloading: Dead loads
Dead loads: Building materials, columns, walls and floors bearing the load of dividing walls, partitions and their own weight.
Causes of damage due to overloading: Live loads
People, furniture, equipment and goods, these can change on a daily basis.
Causes of damage due to overloading: Dynamic loads
Loads that can change rapidly, winds, water and snow
Causes of damage due to: moving plant and construction
Repetitive strikes from moving plant (hgvs, forklifts) can weaken a structure, heavy steel guards should be erected.
Nearby construction can also damage structures, excavations can cause severe subsidence.
Causes of damage due to: Hot and corrosive atmospheres
Chemical: Sulphur dioxide, carbon dioxide, oxygen and ozone in the presence of moisture form certain acids that can attack, metals, concrete, cement and stone.
Atmospheric: Oxygen combines with metal creating rust, this usually expands the metal affecting adjacent materials.
Electrolytic: Reaction between two dissimilar metals, or a metal and a none metal.
Presence of moisture can cause galvanic action.
Causes of damage due to: Vibration
Traffic, machinery and certain processes.
Causes of vibration include:
Out of balance rotation,
friction between moving parts and,
impacts or percussion.
Causes weakness in the structural members and jointing systems, i.e welds, bolts and adhesives.
Causes of damage due to: Structural alterations
Any major structural work must involve an expert to assess the change in loads caused. Removal could have serious repercussions
Causes of damage due to: Subsidence: overloading
The introduction of additional structural parts or different materials or certain additional plant process
Causes of damage due to: Subsidence: Water content
Removing water will shrink the soil.
Adding water will make the soil heave.
Designed water removal could be from a pit or basement being constructed or, the planting or removal of trees.
Causes of damage due to: Subsidence: Mines and tunnels
Buildings are prone to subsidence when built over a mine or tunnel, when in disuse the roof collapses resulting in the ground level changing, can be seen at the surface as a gradual wave.
Causes of damage due to: Subsidence: Excavations
Excavations can remove part of the load bearing bulb of pressure, can also happen when tunnelling.
Signs include, sagging arches and beams, semi-random cracks and the fracture of pipe joints.
Deterioration of building materials
Timber
fails due to natural features, grains, knots, and insect attack.
Concrete
Incorrect mix-Type and nature of the steel reinforcement-spalling-wrong type of aggregate-reaction to a hostile environment.
Steel
Corrosion-brittle failure-fatigue-creep or stress
All the above can deteriorate due to:
the environment, vibration, standard of workmanship, lack of maintenance
Unauthorised modifications
Modifications to load bearing, beams, walls, and floors must be considered before making any significant modifications
Signs of structural damage
Sagging roof Bulging or cracked walls Flaking masonry Collapsed walls Corrosion on brickwork Dampness Dry or wet rot Gaps around window frames or doors Uneven floors
Failure modes which can lead to collapse 1
POOR DESIGN that fails to take into account the loading, likely forces and circumstances which may increase the loading or the specification of inappropriate materials
SUBSTANDARD CONSTRUCTION poor quality building methods or materials which won’t withstand the expected load
Failure modes which can lead to collapse 2
CUTTING ROOF BEAMS Which weakens the structure for the roof
PUNCTURING FLOORS which affects the load bearing capacity and overall contribution to the structure
REMOVAL OF INTERNAL WALLS which may be load bearing, supporting the floors and roof structure above
