UNIT V---METHODICAL APPROACH TO REPAIRS bc 5 th sem breif notes
UNIT V---METHODICAL APPROACH TO REPAIRS
CRACKS OVER OPENINGS :
The cracks over the windows had developed over many years due to rusting lintels.
Lintels are made of steel and support the brick over a window openings.
Rusting lintels are the number one reason cracks occur above window frames.
This generally is not a structural issue, but can develop into a structural issue if left unrepaired.
REPAIR :
The only true way to tell if a crack is active is to install a crack monitor.
The proper way to install a crack monitor is to epoxy the monitor to both sides of the crack and leave on the wall or foundation for as long as possible.
SINKING BALCONIES :
Loose railings on decks and walkways are one of the areas that we need to be aware of.
Wood railing, iron railings, stucco, or even concrete have to be checked regularly to be safe.
The bolt holding the iron railing pulls away from the building. There is no wood framing behind the siding at that point, therefore it has no structural strength.
More important, is the fact that the railing is pulling away from the building. Usually this is a sign of the front edge of the deck or balcony is sinking
DECAY OF FLOORING
TIMBER :
Building materials are decayed by the effects of adverse environmental conditions and the extent of damage depends on both the materials and the conditions.
Among the most vulnerable materials are timber, paint, textiles and paper.
However, timber provides specialized ecological niches and many organisms have evolved to use it as a food
The most common and destructive to timber are dry rot, wet rot, common furniture beetle, and death watch beetle.
Orthodox remedial treatments often entail the loss of irreplaceable decorative finishes, floors and ceilings
Furthermore, treatment of the infestations with chemicals is not only expensive, inconvenient, hazardous to the operatives and occupants but also environmentally unacceptable and usually unnecessary.
Environmental control and preventative maintenance provide an alternative, less destructive solution, and remain the most widely used methods for preventing biological decay.
Jack Arch Roof
Jack arch Roof construction can be done in brick or concrete. The arch of the Jack arch roof is either made of brick or of concrete. The arch is supported on the lower flange of mild steel joists (RSJs). The rolled steel joists are supported at their ends on the walls or on the longitudinal girders. They are spaced at a distance of 1m to 1.5m centre to centre.
The two main causes of Jack-arch roof leakage are:
1. Poor quality of cement
2. Inappropriate grade of sand
Repair of the roof
The Jack Arch roof leakage problem has to be fixed and should be so done so as to avoid future recurring water leakage problem. This can be achieved by waterproofing the roof.
Here are the four simple steps to repairing and waterproofing the Jack Arch Roof:
Step one: The old cement mortar and tiles are to be removed so that the new cement mortar settles and becomes firm over the rough roof surface.
Step two: After scraping of the cement mortar, fresh cement mortar is laid and left to dry.
Step three: After the drying of cement mortar, waterproofing is done to avoid any kind of further leakage. Waterproofing material is mixed in a drum of water and splashed over the cement mortar layer. We must make sure that every corner of the roof is to be covered with this waterproofing material.
Step four: After the process of waterproofing, tiling is done with the help of a suitable adhesive.
MADRAS ROOF TERRACE :
Wooden beams, normally teak wood in those days, would be first placed upon opposite walls across the width of the room, 18 to 24 inches apart. In case room spans are wider, steel sections would be first placed dividing the room into shorter spans, along which teak beams run. High density and high strength clay bricks, made to special thin size measuring 1”x3”x6”, are used in Madras terracing.
Properly mixed and matured lime mortar is used for bonding the flat tiles that are placed at an angle of 45 degrees to the wall, or diagonally across the room width.
These terrace tiles, placed on the edge, ensured tensile strength.
The roof is cured for a minimum of one week to achieve early setting. Thereafter, a three-inch thick layer of broken bricks or brick bats would be laid where nearly half the volume would be made up of lime mortar, three parts brick, one part gravel and one part sand. This layer provided the compressive strength and load bearing capacity to the roof.
This layer needs to be well compacted, cured and levelled.
The final layer would depend upon the slab being an intermediate one or the final roof.
If intermediate, a floor finish like red oxide or lime mortar would be applied and if final, there would be courses of flat weather-proof tiles topped by thick mortar to slope.
SINKING FOUNDATION:
A sinking foundation is one issue that can occur if the foundation is laid improperly or on unstable soil. Sinking foundations are problems that need to be addressed and examined as soon as they are noticed to prevent further damage and repair costs to the rest of the house.How to spot a sinking foundation:
The house gradually slants to one side
Windows or doors become jammed or mis-aligned
Cracks in the basement,slab and walls of the living area
Water puddles that form around the base of your home may also indicate foundation problems
Sinking foundation repair:
The first step in fixing a sinking foundation is to have your home examined by a professional.
There are several different techniques used to fix a sinking foundation, and each is more appropriate in certain situations-
High-pressure grouting works by injecting grout into unstable soil to improve its integrity, and in some cases, to lift the structure of the house up, as well.
The introduction of load-bearing piers can be used to lift and stabilize a sinking foundation; they are an economical and permanent solution to foundation problems in many instances.
Helical piers can be used in some situations where other piers cannot. These, too, provide an economical and permanent solution to sinking foundations, and are especially useful where fill material or a high water table is present.
STRUTTING:
Strutting constitutes a construction technique used to reinforce buildings. Basically, a strut consists of a support system used to bolster beams in floors and ceilings.
Various types of strutting exist, some using wood and some using galvanized steel.
Struts help prevent long joists, or wooden beams running from wall-to-wall in ceilings and floors, from buckling or warping.
Two types of wooden struts exist, herringbone struts and solid strutting. Requirements of size and material apply to both.
Joist Size Requirements
Joists only require timber strutting if they meet or exceed certain size requirements.
Depending upon the source, any joist longer than 2, 2.4 or 2.5 meters, requires strutting.
Joists measuring between 2 and 4.5 meters, require one strut, placed in the middle of the boards, for support.
Joists longer than 4.5 meters require two rows of strutting, each placed a third of the joist length away from a wall.
For instance, a 9-meter joist requires one strut, 3 meters in from each wall.
Strut Size Requirements
Timber struts must meet certain size requirements to prove effective on construction projects.
To possess the strength required, solid timber struts should be at least 38 millimeters, or approximately 1.5 inches, wide and possess a depth of at least 75 percent that of the joists in question.
Herringbone struts require timber measuring 38 by 38 millimeters for proper construction, unless the distance between joists measures more than three times the three times the depth of the joist, in which case thicker wood is required to give herringbone struts the necessary strength.
Herringbone strutting
The purpose of herringbone strutting to floor joists found in older dwellings or the solid nogging method used in newer buildings is to distribute the weight across more than one joist, and also to help prevent the joists from twisting.
Solid strutting
Uses Short members (boards) which are fixed vertically
between floor joists to stiffen the joists.
PROPPING :
In moderately firm ground, after a depth of 3 or 4 feet has been excavated, a few rough planks or "poling hoards" P P are placed at intervals varying with the nature of the soil against the sides of the trench, and kept up by jamming or wedging in between them struts (S) of rough scantling from 4 to 6 inches square.
In looser ground it is necessary to place the poling boards closer together, and so support them by 3-inch planks W W called "walings." The struts must be made thick, in proportion to the width of the trench and the pressure upon them, and their distance apart will depend upon the strength of the walings and the nature of the soiL.
UNDERPINNING:
Underpinning may be necessary for a variety of reasons:
The original foundation is simply not strong or stable enough.
The usage of the structure has changed.
The properties of the soil supporting the foundation may have changed (possibly through subsidence) or were mischaracterized during design.
The construction of nearby structures necessitates the excavation of soil supporting existing foundations.
It is more economical, due to land price or otherwise, to work on the present structure's foundation than to build a new one.
Mass concrete underpinning
This underpinning method strengthens an existing structure's foundation by digging boxes by hand underneath and sequentially pouring concrete in a strategic order.
The final result is basically a foundation built underneath the existing foundation.
This underpinning method is generally applied when the existing foundation is at a shallow depth, however, the method still works very well even at fifty feet deep.
The method has not changed since its inception with its use of utilitarian tools such as shovels and post hole diggers.
Heavy machinery is not used in this method due to the tight nature of the boxes being dug.
There are several advantages to using this method of underpinning including the simplicity of the engineering, the low cost of labor to produce the result, and the continuity of the structure's uses during construction.
Mass Concrete Underpinning
Beam and base underpinning
The beam and base method of underpinning is a more technically advanced adaptation of traditional mass concrete underpinning.
A reinforced concrete beam is constructed below, above or in replacement of the existing footing.
The beam then transfers the load of the building to mass concrete bases, which are constructed at designed strategic locations.
Base sizes and depths are dependent upon the prevailing ground conditions. Beam design is dependent upon the configuration of the building and the applied loads.
Anti-heave precautions are often incorporated in schemes where potential expansion of clay soils may occur.
Mini-pile underpinning
Mini-piles have the greatest value where ground conditions are very variable, where access is restrictive, where environmental pollution aspects are significant, and where structural movements in service must be minimal.
Mini-piled underpinning is generally used when the loads from the foundations need to be transferred to stable soils at considerable depths - usually in excess of 5.0 metres.
Mini-piles may either be augured or driven steel cased, and are normally between 150mm and 300mm in diameter.
Mini Pile Underpinning
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