unit 1 bc,Failures breif notes
UNIT I---FAILURES
Substandard materials and design errors are identified as major causes of component failure.
The causes of building collapse can be classified as-
• Bad Design
• Faulty Construction
• Foundation Failure
• Extraordinary Loads
• Unexpected Failure Modes
• Combination of Causes
1.The common causes of bad design as well as design failure:
Internal factors/Human Errors
The internal factors for bad design does not mean only errors of computation, but a failure to take into account the loads the structure should be able to carry and improper choice of materials or misunderstanding of their properties.
External Factors
These are often natural, such as extraordinary loads, heavy rains, an earthquake, or the winds of a hurricane and a defective site with very unusual ground conditions like sinking holes, swampy land etc.
Inadequate Awareness
Many structural failures have been the consequence of poor technical research and knowledge
2.The common causes of construction failure are:
Inappropriate construction techniques
Use of inferior or sub-standard building materials is another reason of building failures. Overloading during the life span of building can critically weaken the structural reliability of the building.
Performance failures
Failure may occur due to inadequate supervision and control of site operations and quality control.
3.The common causes of materials failure are:
Most of the structural failures are associated with materials and are the consequence of human blunder involving a lack of knowledge about materials or the combination of contrary materials.
CAUSES OF PROBLEMS IN OLD BUILDINGS:
1.Fungal Stain / Harmful Growth:
• Fungal stain or mould usually occurs when there is a presence of water or high moisture content in masonry walls.
• It can easily flourish in environmental conditions of high humidity and lack of ventilation.
• Fungal stain can be seen on wall surfaces of a bathroom, kitchen, near rainwater goods including down pipes and gutters; and at washing areas.
2.Erosion of Mortar Joints:
• The main function of a mortar joint is to even out irregularities of individual blocks, whether they be of stones or bricks.
• At the same time it provides some adhesion between the blocks.
• Causes to the erosion of mortar joints include a presence of salt crystallization, scouring action of winds; and disintegrating effects of plant growing on a wall or water penetration leading to the concentrations of moisture and dampness.
3.Peeling Paint
• Peeling paint usually occurs on building facades, mainly on plastered walls, columns and other areas which are exposed to excessive rain and dampness.
• This is because the amount of constant wind, rain and sun received can easily turn the surfaces of the paint to be chalky and wrinkled or blistered.
• In many historic buildings, there are layers of paints being applied on plastered walls.
• Apart from lime wash, there are many types of paints used on wall surfaces including emulsion, oil-based, tar, bituminous and oil-bound water paint. All of these require different methods of removing depending on the nature and conditions of the paints.
4.Poor Installation of Air-Conditioning Units
• Depending on the building function, structures and the effects on building fabric, one should consider three main aspects before deciding to install the air-conditioning units in any historic buildings-
• Firstly, the cooler and drier air produced by the air-conditioning systems may possibly cause shrinkage of building materials.
• Secondly, there will be a possibility of condensation either on the surfaces or within the structure of the fabric. This allows the build-up of mould or fungal stains.
• Thirdly, there may be problems of installation which include difficulties in installing the units.
5.Defective Plastered Rendering
• In many historic buildings, defective plastered rendering occurs mostly on external walls, columns and ceiling.
• the defects are normally caused by biological attacks due to rain, evaporation, condensation, air pollution, dehydration and thermal stress.
• Other causes may come from mould or harmful growth, insects, animals and traffic vibration.
6.Cracking of Walls / Leaning Walls
• Cracks in wall, either vertical or diagonal, are common symptoms of structural instability.
• Diagonal cracks--- widest at the foundations and may end at the corner of a building -often occur when shallow foundations are laid on shrinkable sub-soil that is drier than normal or when there is a physical uplifting action of main roots of a large tree close to the walls.
7.Defective Rainwater Goods
• Common problems associated with the defective rainwater goods include sagging or missing eaves gutters, corroded or broken galvanized iron down pipes or leaking rainwater heads.
• Lack of proper fixings of the wall, particularly by means of projecting lead ears or lugs can cause instability to the down pipes
8.Decayed Floorboards
• Timber floorboards are widely used in many historic buildings
• The main causes to the deterioration are insect and termite attacks, careless lifting of weakened boards by occupants, electricians or plumbers; lack of natural seasoning and preservatives, and corroded nails.
9.Insect or Termite Attacks
• Timber has been widely used in many historic buildings. It can deteriorate easily if it is exposed to water penetration, high moisture content and loading beyond its capacity.
• Insect or termite attacks usually happen in a damp and digestible timber which can be found in elements such as wall plates, the feet of rafters and bearing ends of beams and trusses and in all timbers which are placed against or built into damp walling.
10.Roof Defects
• Common defects of roof tiles include the corrosion of nails fixing the tiles to battens and rafters, the decay of battens; cracking of tiles which may be caused by harmful growth or walk upon.
• The harmful growth is quite dangerous to the tiles because it may lift the tiles and create leaks.
11.Dampness Penetration Through Walls
• Dampness penetration through walls can be a serious matter, particularly to the buildings which are located close to water sources.
• It can cause not only deterioration to the building structures but damages to furnishings and contents as well.
• Water penetration occurs commonly through walls exposed to prevailing wet wind or rain.
• Dampness may also occur in walls because of other factors such as leaking gutters or down pipes, defective drains, burst plumbing and condensation due to inadequate ventilation.
• Dampness may also enter a building from the ground through cracks or mortar joints in the foundation walls.
12.Unstable Foundations
• Foundations are a part of a building which distributes loads from roofs, walls and floors on to the earth below.
• Most of the common problems occured in the foundations depend on the geology of the ground upon which a building stands and is surrounded by, structural failures; and presence and height of a water table.
• Unstable foundations may occur because of several reasons including --- shrinking clay soil(occurs when sub soil is drying and water table is low) ---penetration of dampness and water that may decay walls and foundations ---presence of large trees near the building --- the undertaking of extensive excavations or mining nearby ---landslides caused by heavy rain, heavy construction near a historic building --- traffic vibrations, deteriorating of building materials and the increased loads, particularly when there are changes in building function.
FACTORS THAT GOVERN BUILDING DEFECTS OR PROBLEMS:
There are 5 factors that govern building defects or problems.1.Climatic Conditions
Fungal stain, harmful growth, peeling paint, erosion of mortar joints and defective plastered rendering are a few examples associated with this factor.
2.Location of Building
• Buildings that are located near the sea or rivers tend to have common building defects. This is because the water coming from the ground causes dampness penetration and structural instability.
• For example, during the conservation work of the Sultan Abdul Samad Building in Kuala Lumpur, damp-proof courses had to be installed in order to prevent rising water coming from nearby Gombak River
3.Building Type and Change in Use
• Most historic buildings that maintain their original functions or uses appear to have less problem internally, even though there were symptoms of building defects found on the external fabric.
• Buildings that change their use and spaces should consider the effect of the new use on the existing structure. This is because historic buildings were built to only hold certain loads and sometimes may not withstand additional loads.
4.Maintenance of Building
• Historic buildings that neglect building maintenance may fall into several defects which may lead to structural failures.
• To secure the general structural stability and life of a building, it is important to regularly inspect not only the main structural elements including foundations, walls and roofs; but other common building problems.
5.Building Age
• All elements of historic buildings tend to deteriorate at a lesser or greater rate depending upon their location and function.
• Aging building materials, particularly timber should be checked once there are signs of fungal and termite attacks
Preliminary inspection/observation include 5 steps-
• Climate surroundings
• Location of structure
• Building type
• Age of the building
• Physical inspection
DAMAGE
Result of wrong loading.
Physical harm caused to something in such a way as to impair its value, usefulness, or normal function
DECAY
Deterioration over a long period.
Rot or decompose through the action of bacteria and fungi.
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