1.What are the causes of decay and damage in old buildings?
Water:
Roof is the most important part of a historic building. Once water manages to get through the roof, the building's rate of decay will increase exponentially. Water not only c auses wood to rot but also creates c reates environments that are attractive to insects and other building-destroying creatures such as squirrels, mice and rats. If water gets into the foundation and the basement, it can destabilize the base of the building. Dampness can also penetrate through the walls and can deteriorate the building, furniture and its contents as well. Dampness can be caused by leaking gutters, inadequate plumbing, condensation due to inadequate ventilation, etc.
Rot:
Rot problems are closely related to wat er problems. There is something called "dry rot" that can compromise the strength of joists and r afters, but the most common form of rot is caused by the presence of water. Rotten rafters will eventually cause the roof to sag and then collapse if they are not repaired. The same thing can happen to floors if their joists become sodden and rotten.
Insects:
Termites are the kings of destroyers de stroyers when it comes to unwelcome insects in historic buildings. A large nest of termites can actually ac tually eat enough of the rafters, joists and beams to cause the building to collapse if they are left unchecked. Carpenter ants will cause similar damage, although they are not as fast or as voracious as termites. Other insects such as c ockroaches, ants, beetles, hornets and wasps are also equally dangerous.
Fungal decay:
Fungal stain or mould usually occurs when there is a presence of water or high moisture co ntent 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 g oods including down pipes and gutters; and at washing areas.
Peeling of paint:
Peeling paint usually occurs on building facades, mainly on plastered walls, columns and other areas which are exposed to excessive rain and dampness. Some buildings located near the sea may face a much greater risk once the signs of peeling paint are visible on t he exterior walls. This is because the amount of constant wind, rain and sun received c an easily turn the surfaces of the paint to be chalky and wrinkled or blistered.
Cracking of walls:
Cracks in wall, either vertical or diagonal, are common symptoms of structural instability. Diagonal cracks, which often being widest at the foundations and may terminate at the c orner of a building, often occur when shallow foundations are laid on shrinkable sub-soil that is drier than normal which leads in unsettled foundations or when there is a physical uplifting action of main roots of a large tree close to the walls.
Cracks due to unsettling foundations
Erosion of mortar joints:
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.
2.Factors reducing strength in brick work:
Type of bricks used: Various classes of bricks of varying qualities (1 st class, 2nd class, 3rd class, etc.) are available in the market and it is of utmost importance to select the appropriate brick depending on the purpose is it about to serve.
Binding mortar and its proportion: Mortars like Portland cement mortar or lime mortar can be used for brick work. The appropriate cement/lime-water ratio needs to be followed neglecting which the strength of the brick m asonry cannot be achieved.
Method of laying bricks and workmanship: Various methods can be adopted for brick laying and bonding (English, Flemish etc.) Flemish bonding of bricks is generally considered to be stronger than English bonding. Irrespective of the method adopted, care has to be taken to avoid formation of vertical joints at the time of laying of bricks which can weaken the masonry wall considerably.
Usage of defective bricks
Improper curing of the brick work at the time of construction.
3. Problems of timber roofing and their repair methods:
Timber failure may be attributed to
insect infestation, fungal attack, or shakes and splits caused during the drying out of unseasoned timber.
The three most common repair types would usually deal with:
beam end repairs, due to timber being embedded or in contact with damp masonry
losses of cross sectional area due to fungal or insect attack
longitudinal cracks appearing due to changes in moisture content of the timber.
Repair solutions: When carrying out a repair using timber it is important to select material of the same species, preferably from a reputable source and, most importantly, with a moisture content which matches to within one per cent that of the timber being repaired. If this condition is not met , the different drying rates of t he timber may cause problems with the re pair joint. Repair can take the following forms:
like-for-like repairs using timber from an appropriate source
'honest' repair, where steel strapping or plates are used
Like for like rapairs:
In like-for-like repairs , scarf re pairs allow the maximum amount of original timber to be retaine d. Scarfe joints are commonly used where the ends of timbers have decayed, for example in a damp exterior wall. This approach, enables the decayed timber to be cut out and replaced with sound material, depends on careful joint detailing for its structural integrity. Scarf joints are usually fixed using stainless steel bolts or screws with traditional wedges or adhesives used between each timber surface.
Honest repair:
This method includes Reinforcing timber with metalwork or by using steel plates Eg: a typical connection detail between a purlin and a principal beam was weakened due to the insect infestation of the mortice and tenon joints at the intersection. A mild steel plate was fixed to the top of the purlin and supported over the principal beam. This plate provided addition support to the purlins below via stirrup cradles welded to t he side of the mild steel upper plate. All that was visible below were the cradles supporting the purlin.
4. Joints in concrete structure:
Although concrete expands and contracts with changes in moisture and temperature the gener al overall tendency is to shrink and, therefore, crack. Irregular cracks are unsightly and difficult to maintain. Joints are simply pre-planned cracks. Concert cracks cannot be prevented entirely, but they can be controlled and minimized by properly designed joints. joints must be carefully designed and properly constructed if uncontrolled cracking of concrete flatwork is to be avoided. a. Control (contraction) joint – These joints are constructed to create planes of weakness so that cracks will occur at the desired location. b.Isolation (expansion) joints – They separate or isolate slabs from other parts of the structure such as walls, footings, or columns, and driveways and patios from sidewalks, garage slabs, stairs, light poles and other obstructions. They permit movement of t he slab and help minimize cracking caused when such movements are restr ained. c. Construction joints – These are joints that are placed at the end of a day’s work. In slabs t hey may be designed to permit movement and/or to transfer load. Often in reinforced concrete a conscious effort is made to clean the joint and bond the next day’s work.
5. LIST OUT THE GENERAL CAUSES OF FAILURES IN A BUILDING ALONG WITH NEAT SKETCHES.
Building components tend to fail depending upon materials, design, method of construction, environmental conditions and the use to which building is put. The causes of building collapse can be classified under: • Bad Design • Faulty Construction • Foundation Failure • Extraordinary Loads • Unexpected Failure Modes • Combination of Causes
Bad design can be due to errors of computation,, erroneous theories, reliance on inaccurate data, ignorance of the effects of repeated or impulsive stresses, and improper choice of m aterials or misunderstanding of their properties. The engineer is responsible for these failures, which are created at the drawing board. Faulty construction has been the most important cause of structural failure. This includes the use of salty sand to make concrete, the substitution of inferior steel for that specified, bad we lds, and other practices. Even an excellently designed and constructed structure will not stand on a bad foundation. Although the structure will carry its loads, the earth beneath it may not. The Leaning Tower of Pisa is a famous example of bad foundations. The displacements due to bad foundations may alter the stress distribution significantly. These are often natural, such as repeated heavy snowfalls, or the shaking of an earthquake, or the winds of a hurricane. A building that is intended to st and for some years should be designed to withstand these challenges. Unexpected failure modes are the most complex reasons for building failure. Any new type of structure is subject to unexpected failure, until its properties are well understood. Hence, they remain unexpected and fall under the unexpected failure modes. A building could collapse due to more than one of the above reasons hence a Combination of causes. 6. Write short notes on: 1) Sinking or sagging of balconies:
Balconies without rooftops that experience frequent exposure t o rainfall, snow and other types of moisture leads to sinking balconies. If a balcony does not have sufficient water protection, leaks can develop, moisture can sink in and the balcony can quickly become ruined. Since balcony water protection is so important, there are several materials that are manufactured to help provide additional balcony protection.
2) Strutting:
These are used in many ways and locations in a conventionally framed roof. Their function is always to support roof members, generally below purlins, where there are no conveniently located load-bearing walls. Strutting beams only support roof loads. The strutting beam transfers the roof load directly to load bearing walls. It must never rest on, or transfer load to, a ceiling joist.
3) Cracks above openings:
Causes: (a) Removal of windows or doors with inadequate propping, (b) Inadequate bearings, (c) Loads applied directly over the opening, (d) No lintels.
Cracks in drywall are usually caused by structural movement, such as settling in new homes. Many cracks occur on a seam, but they are also found in the m iddle of sheets over doorways or windows. In older homes, cracks above doorways or windows can be a sign of poor workmanship, increased building loads, or a more serious structural defect. Vertical cracks are typically caused by a seam being placed at the corner of an opening for a door or window. Diagonal cracks are usually attributed to settlement, increased loads, or structural issues Most cracks go completely through the panel, so just repairing the surface is not enough. The first step is to remove any loose material with a putty knife or utility knife. and cut a V-groove along the crack creating about 1/2 in. wide opening t hat goes almost completely through the panel to t he paper on the back. Fill this gap with joint compound and cover it with mesh or paper tape. Apply two or three coats of joint compound and feather each coat into the surrounding area. It would be a good idea to lightly apply sand after each coat. Always allow the joint compound dry between coats. Poor workmanship causes cracking when seams must land above an opening. It is general practice to keep the seam at least 7 in. away from the corner of an opening. Using drywall adhesive when attaching drywall will also help strengthen the seam. If the crack is at an angle, then it is not a seam cracking it is the drywall itself.
4) Leakage from toilets:
Types of leakage:
Checking for a bad wax seal - A bad wax seal can be easily identified by the following method. Place about ten drops of food coloring into the toilet bowl and mix the water around. Flush the toilet and add another ten drops of the same color food coloring and wait. If you se e the food coloring leaking around the base of your toilet bowl, you know that your wax seal has gone bad and you need to replace the toilet wax seal.
Checking for a bad toilet tank seal - To check for a bad toilet tank seal, place ten drops of food coloring into the toilet bowl tank and let the water sit for a few hours. If the colored water is running down the back of the commode and pooling at the base of your toilet, then your toilet tank seal is bad and will need to be repaired. Repairing the problem consists of replacing the seals that prevent water from leaking from the base of the toilet tank.
Checking for sweating toilet - Toilet tanks sweat when the humid air causes condensation to form on the cold toilet bowl tank. There are no seals to replace nor any leaks to repairs with a sweating toilet tank. There is only one way to prevent a sweating toilet tank and that is to insulate the toilet tank itself.
Repairing: To be certain that the leak is a toilet leak, add some drops of liquid food coloring into the toilet tank and wait about ten or fifteen minutes. If any of the food coloring is in the toilet bowl, you have a certified leaking toilet t ank. The most common cause for the toilet tank leaking is a faulty toilet bowl flapper. The flapper is what holds fresh water in the toilet tank until the toilet is flushed. Replacing the toilet flapper is a common repair. To replace a toilet flapper, just unhook the chain at the flush lever, carefully pull the flapper out of the bracket it is locked into and replace with a new flapper of the correct size. Another common reason for toilet leaks is that there is too much tension on the toilet lever chain. If you look in the toilet tank, you will see a chain attached to the toilet lever. If this chain is too tight, which in turn will hold the flapper away from its seal, then you can loosen the chain until the flapper seats on its seal properly. 5) Terrace water proofing:
In India, Terrace Waterproofing has always been done with very traditional materials. Typically systems like brickbat Coba, Lime terracing or the “Mud Fuska” technique are still very much in vogue. These
systems have been offering waterproofing with some insulation against heat. Some of the problems that these systems have are:
Heavy loading on the slab
Cracks on the surface, especially in c ase of brick bat coba
Expertise levels of application required for lime terracing/mud fuska not as good as in the olden days
Offer more insulation rather than a leak proof or a water-tight system
As they age breaking them and r e-doing the same system is risky for the slab; cracks caused in the slab increase the problem of leakage
Issues in carrying out water proofing: 1. Slope not proper-Slope must be provided for water drainage 2. Inadequate rain water pipes-Provide drain water pipes as re quired
3. Parapet wall not in good condition-Repair parapet masonry/plaster using mortar added with w/p compounds/polymer bonding agents 4. Internal cracks, honeycombs (finished with ordinary mortar), porosity, etc. which cannot be seen by eye-pack using inject grout at the place of leakage from top to bottom 5. Mechanical installations like cooling towers, AC units, etc., on the terrace-Foundations must be examined and repaired if required There are many different types of products on the market to address the above issues that can be broken broadly into two groups: acrylic products and bituminous based products: > Acrylic products: Are paint based and usually used in co njunction with a membrane/cloth. The product is easy to apply and relatively cheap. However, ac rylic products do not withstand ponding water (any area where water lies), their flexibility only lasts around two to three years and then they tend to crack, and if applied to steel, these products can trap water causing the steel t o rust. > Bituminous products are based in bitumen and have been used throughout history as waterproofing agents. Bitumen by itself is pliable at high tempe ratures and rigid at low temperatures. When hot, the polymer bitumen mix is inconsistent and it is the re inforcement that provides the required mechanical resistance. Therefore the most stabilising effect is given by reinforcements that contain glass-fibre. It gets applied using the torch-on method that is broken up into three parts: rolled/painted bitumen on primer, heat is used to use the polyester matting and lastly silver aluminium bitumen-based paint that is UV-reflective is applied. 7) Maintenance and repair of old buildings:
> Roofs: Roofs can be difficult and dangerous to access and so are often neglected but regular maintenance of a roof is essential to keep the whole building in good order Identifying problems: •Problems with the roof structure: defects in original construction; overloading of structure; timber
decay due to insect or fungal attack •Problems from previous repairs •Decay of the cladding materials •Poor original design e.g. lead sheeting •Poor ventilation
Repairing a historic roof: •Retain the roof’s structural integrity and historic significance •Minimise disturbance of the roof •Use traditional materials, techniques and carpentry details •Record the roof before starting and replicate original details except where they have failed .
Rain water disposal maintenance:
•Check that gutters, hoppers, downpipes and gullies are running freely. Need to be cleared at least twice annually •Check that gutters are falling the right way and don’t sag between brackets •Look for any leaking joints in gutters and downpipes •Check soakaways are working properly
8) Cracking of concrete floor slabs:
As concrete loses moisture, it shrinks in dimension. If concrete were left as it is placed, it would crack in random patterns. To avoid random cracking we cr eate joints at regularly spaced intervals, thus weakening the slab in a grid patter n. These joints, called control (or contraction) joints force t he cracking to occur in straight lines beneath the joints which are usually saw cut. Thus, a control joint is actually a designed crack. In the design and construction process there are literally hundreds of mistakes that can be m ade. The following are the most common that we encounter SHALLOW JOINTS The joints were not cut deep enough to induce the crack, leaving the slab to crack randomly. SLAB THICKNESS If the slab thickness varies, the slab contraction will encounter restraint, causing the slab to crack. JOINT SPACING Joints were spaced too far apart and the concrete cracked between the joints, rather than at the joints. DELAYED JOINTING The shrinkage stresses in the slab exceeded the strength of the concrete before the joints were cut. INADEQUATE BASE The base under the slab must be smooth and evenly, densely compacted. Uneven bases create re straint, causing the slab to crack.
ADDITIONAL CAUSES OF CRACKING > Concrete mix was too weak (too much water, etc.). > Slab was subjected to wind or sun, causing rapid drying and early stress build-up. > Steel reinforcing was improperly positioned. > Floor was designed for light loads, but operations imposed are heavy loads. > Slab was not properly cured to prolong water retention. The basic principles of crack repair are as follows: DON'T MAKE CONDITION WORSE If the crack is of hairline width, it is usually better to leave it alone. For additional protection against deterioration apply an epoxy coating over crack. CUT OUT ONLY WHEN NECESSARY If the crack snapped cleanly, with no islands, and if the edges of the crack have not spalled, merely fill the crack with a proper epoxy (semi-rigid). CUT OUT AS NARROW AS POSSIBLE Don't use a cutting tool (router, etc.) that will create a 1/2" wide repair of a 1/8" wide crack. CUT OUT DEEP ENOUGH When cutting out cracks, always go at least 1/2" deep to provide enough "bite" for the epoxy along the joint walls. DON'T WELD THE CRACK Most cracks in slabs-on-grade do not present structural problems. Welding the slab together at the crack may merely result in another crack occurring adjacent to the first. Use a semi-rigid epoxy for most crack repairs, especially for the first two years. DON'T FEATHER-EDGE REPAIRS To feather means to taper to -0- thickness. Instead, create a vertical edge of at least 1/2" deep on all crack repairs.
9) Pressure Grouting:
Cementitious Pressure Grouting is a technique where a series of 2" holes are drilled through the existing concrete slab and a grout tube is inserted into each hold. Cementitious "slabjack" grout is pumped under pressure through each hole. The grout displaces, compacts and solidifies, thus forming grout columns and or filling void areas, as applicable to each individual job. Pressure grouting stabilizes the existing concrete slab; however, lifting of the slab, if any, is contingent upon integrity of the concrete. Pressure grouting for stabilization is widely used under pool decks and lanai areas and driveways. The interior of a residence may also be stabilized in this manner. Pressure grouting is effective alone or in conjunction with helical piering system applications. Urethane Grouting for the purpose of soil stabilization is achieved by installing lengths of galvanized pipe into the soils at specified intervals and injecting urethane soil stabilization grout into the soils. As pumping takes place the pipes are raised, creating a stabilized soil curtain and or pile cap. These stabilized soils create a load bearing substrate.
