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METHODS OF EVALUATION AND ELIMINATION OF DAMAGE AND CRACKING IN CONSTRUCTIONS OPERATED BUILDINGS AND STRUCTURES

Timely identification and elimination of defects and damage of building structures is an urgent problem because the appearance and development of cracks proves their poor condition and may worsen the conditions of operation of the building as a whole. Determining the causes of the emergence and nature of development of cracks helps to choose the right methods of their elimination, and to ensure reliable operation of the structures.
In compliance with Snip 2.03.01-84 “concrete and reinforced concrete structures” width of the disclosure of the cracks in the reinforced concrete structures is normalized on the basis of the reinforcement type and operating conditions. For example, structures in an enclosed area, the maximum allowable value is 0.4 mm for tanks and constructions in the ground and outdoors- -0.2 0.1 mm.
Standards containing general technical requirements, rules of acceptance of precast concrete and concrete products of factory manufacturing indicated the need to identify and measure the width of the disclosure of the cracks in factory monitoring.
During acceptance commissioning of buildings and structures in designs can be identified by eye visible cracks shrink, sediment and temperature patterns, which must be measured in accordance with the instructions on tool control for acceptance into operation the completed construction and residential buildings repaired.
In some cases, there is a need to monitor the draught of a building or structure and the development of cracks in some areas, that gives an opportunity to take appropriate action in a timely manner.

Types of cracks and their evaluation methods

When measuring the width of cracks should apply uniform disclosure of techniques that enable to get comparable results, evaluate the quality of rented buildings and structures and determine the nature of the cracks.
Depending on the causes of cracks are allocated sedimentary, shrink, temperature, corrosion and forceful nature.
Sedimentary cracks occur in structures because of differential settlement of Foundation buildings and structures caused by deficiencies in the design and survey works, exploitation, as well as natural processes. The nature of their development, manifested in its initial appearance in the Foundation, basement and subsequent distribution of the height of the building. Mostly cracks are located in field weakening sections, junctions of walls and ceilings, the pairing of external and internal walls because of material with different elastic properties.
This type of crack can cause damage to the communications engineering input, reducing the overall rigidity of the buildings and structures, and in some cases cause an emergency.
Shrinkage cracks are formed as a result of a violation of technology manufacturing structures at the factory and construction site. The nature of their development is the emergence of structures on the surface of the shallow random grid of cracks with small opening width; The ribbed panels they can pass on the border of the rib and shelves.
Shrinkage crack affect the condition of the fittings are the cause of weathered outer layer panel.
Temperature cracks occur due to thermal expansion or compression elements and parts designs with no expansion joints. Characters of the development is to change the width of the disclosure in accordance with the daily and seasonal fluctuations of temperature of external air: with increasing temperature, the crack down is closed. Direction of development of cracks is determined by tense structures.
Corrosive cracks appear when the accumulation of products of corrosion of reinforcing bars in concrete body and therefore tensile stresses. They usually develop only to the depth of the protective layer.
Power crack formed in the handling process of design, due to flawed design decisions, factory defects, damaged during transportation and installation, as well as non-compliance with operating rules.
The nature of the fracture depends on the deformation associated with longitudinal bending, gap, compression, stretching, and the influence of shear forces. In the ground bearing slabs in bearing walls crack may occur, crushing and spalling, usually in the most intense sections of structures in the columns of load-bearing walls, piers, tunnels, workers ferried plugs and plates of overlappings.
When you see the cracks in load-bearing structures of buildings should arrange for them monitoring using beacons and mark the place of measurement. In addition, they delineate the drawings of designs: the point of placing beacons mark and indicate the date of measurement and installation of beacons. At every crack constitute disclosure schedule.
There are qualitative and quantitative methods for evaluating rackrytija cracks. Qualitative methods allow to detect cracks, evaluate the tendency of their development without instrumental measurement characteristics. Quantitative methods enable to measure the width of the disclosure or the increment of cracks. They come in contact and remote and are applied as for one-time measurement and systematic observations.
The most common qualitative methods include the use of beacons: If you increase the width of the crack Lighthouse collapses.
Beacons are made of cement mortar, plaster, liquid glass, paper or of fotouprugogo material, which under the influence of deformations manifest polarizing effect. By number and colour bands are judged on the development intensity of deformations in the construction with a crack.
Luminescent crack detection method is to cover the surface of the ljuminescirujushhim composition followed by removal and inspection of the surface in the ultraviolet region of the spectrum. Remaining in the cracks of the composition gives an opportunity to see the tiniest cracks. It is used mainly for controlling the permeability of sealed tanks.
Chemical and acoustic methods are used for detection of end-to-end cracks. The chemical method is based on the effects of ammonia on photosensitive paper. The essence of the method consists in the following: surface design is photosensitive paper, with the reverse side establishes a ferrule that is blown by gaseous ammonia. According to the degree of colouring paper can judge the intensity of air filtration. Acoustic method enables through prostukivanija or velocity of ultrasonic pulses to determine the continuity of design. For these purposes use flaw detector.
Contact measuring instruments include bars (GOST 17435-72; GOST 427-75), a lighthouse with divisions, template-crack gauge, magnifying glass with the millimetric divisions, Microsoft. The following table shows the features of measuring the width of the disclosure of the cracks.
Lighthouse of plates, one of which has a Division-the simplest contact tool measurement.
Template-crack gauge is a set of calibrated lines drawn on a transparent plate. Combining the appropriate line with the crack, you can define its width. Is a portable device PIN.
For remote measurements of the width of the disclosure of the cracks used telescopes equipped with a microscope-mic, for example based on plane-parallel plates; optical devices with high precision measuring of small angles parallakticheskie (nozzle Belicina, okuljarnym instruments a mic on the Visual tube, microscope with tangential screw); Photogrammetric equipment Kit.
A means of measuring the width of the disclosure of the cracks
The name of the
Measuring range, mm
Measuring accuracy, mm
Measuring conditions
Measuring range (GOST 17435-72)
From 1.0
0.5
When you install the beacons on sedimentary crack.
Magnifier Brinell
0.1 -20
0.1
In factory and field conditions
Microscope WORLD-2
-6.0 0.15
0.05
In factory and field conditions
Time zone indicator type
0.01 -10.0
0.01
When lengthy observation of cracks
Strain gauge lever type TR
0.001
0.001
When laboratory tests
Template-crack gauge
0.05 -2.0
0.1
When express factory control and natural conditions
Opto-mechanical device based on theodolite (GOST 10529-79)
0.05 -5.0
0.02 -0.5 depending on the distance to the object (from 1.5 to 50 m)
For remote measuring of cracks on the facades of tall buildings and structures
The principle of operation of the optical and mechanical device, is that the disclosure of the cracks in width measurement, range 0-5 mm with plate ploskoparallel’noj plate is carried out, which in the form of nozzles mounted on the ocular part of the telescope. To measure the cracks with the disclosure of more than 5 mm telescope is equipped with a device for the measurement of angles, such as the parallakticheskih nozzle Belicina.

Mechanical methods of measurement of the width of the disclosure of the cracks based on the application of the indicators type of watch and mechanical deformation strain gauges, strain gauges, for example Gugenbergera (the latter are mainly used in the laboratory).

In situ monitor disclosure width of cracks using exercise time deformation indicator type (messury) with 0.01 mm divisions. It can be installed permanently (indoors) or used as a portable with a base of 10, 15 and 20 cm.
Precise quantification to increase the width of cracks or detect periodic deformation cracks and joints of panels (for example, under the influence of changes in air temperature) allows you to give way, namely, the systematic measurement of distances between the special indicator portable rappers (bars with balls, established on each side of the crack (interface).
When observations for joints of panels anchors mounted in three levels within the same floor.
For zadelki anchors in concrete vysverlivajutsja apertures in diameter of 12 mm and a depth of about 30 mm; the installation is carried out on a cement-Sandy solution. Inside the premises for this purpose you can use Alabaster.
During measurements on exterior surfaces to exclude their own thermal deformations of the indicator must be amended by using the antitemperaturnogo reference.
The frequency of the measurements depends on the nature of the damage.
Measure the width of the disclosure of the cracks can and non-standard means, have undergone metrological certification in accordance with GOST 8.326.78.
Calibration, alignment and operation of measuring instruments in accordance with the annexed thereto documents manual (GOST 2.601-68).
The survey designs, damaged cracked, sometimes there is a need to measure the length and depth of cracks, as well as recording their locations.
Crack length measured on using kurvimetra KU (GOST 300-69) with an accuracy of 0.5 cm, rulers or roulette, depth probes, as well as by assessing the velocity of ultrasonic pulses from a source to a receiver installed on the surface of the construction near the edges of the cracks.
Appropriate is to prepare a sketch of the design with the designation of cracks or photographing the site where previously reinforced plate indicating the date, place, time, temperature of external and internal air or other characteristics relevant to the assessment of the State of design.
Maximum allowable crack width depends on the type of construction, a static diagram of its work, material properties, geometry and the destination object.
This value must be specified in the project and normative documents on products of factory manufacturing, construction and installation works and maintenance of buildings and structures. When you see the cracks with characteristics in excess of predel’nye values, it is necessary to take urgent measures to ensure the safety of the operation of the facility, to produce a technical survey in order to identify the causes of the cracks and repair as necessary.

Methods of removing cracks and reinforcement of operated buildings

Reasons causing the need to eliminate cracks: loss of strength of the material of construction: accelerating corrosion fixings and fittings; hydration of the material of construction through a crack and, as a consequence, the deterioration of the thermal qualities of the structure, reducing its longevity as a result of freezing and thawing; deterioration of decorative designs.
Reasons causing the need to reinforce building structures: adaptation and use them under increased strain in the reconstruction and modernization of the buildings, the device additional insulation, etc.; reduction of strength and deformativnyh qualities of designs in the process.
Restoration and increase of strength and ensuring durability of designs can be achieved by:
-restore the solidity of the material injection mortars;
-increase of the working section of the structure;
-changes the original static schemes of work and stress-deformed condition of construction elements and buildings as a whole;
-unloading device designs.
The choice of method of repairing structures, damaged cracked, is carried out on the basis of analysis of technical surveys of buildings based on causes of damage extent reduce the performance of the construction and its residual service life.
One of the most promising methods to restore the initial strength and solidity of constructions is the injection of polimerastvorov into the cracks.
Method injection is that cracked damaged masonry or concrete structure through special pipes under pressure up to 0.6 Mpa pump cement-polymer or polymer solutions based on polijepoksidov.
To reinforce the masonry with opening width of cracks 5 mm and more, we recommend the following solutions:
-cement-polymer made from cement, polyvinyl acetate (LaTeX) and water in a ratio (1.0:0.15:0.6) laced with small or finely sand in quantities of 25-30% by weight of cement;
-sand-cement (cement: sand: 0.25 1.0) with the ratio in/c equal to 0.5 -0.6;
-cement (bespeschanye cement: sand-1:0) when the ratio v/TS equal to 0.5 -0.6.
If the width of the disclosure of the cracks of less than 5 mm, the effective will be:
-Epoxy compositions comprising (weight): epoxy resin ED-20 (ED-16)-100, MGF modifier-9-30, PAP hardener-15, sand-50, as well as solutions:
-polymer-cement (cement: polymer: water-1.0:0.15:0.6);
-sand-cement (cement: sand: 0.25 1.0) laced with finely sand in quantities of 25% by weight of cement Vries ratio in/c equal to 0.7 -0.8;
-cement (bespeschanye cement: water: 0.7 1.0). As an astringent for cement mortar Portland cement used activity not below 40 MPA (fineness of not less than 2400 cm2/g, the normal density of cement test within 22-25%); with lesser shlakoportlandtsement, viscosity dissolved in injecting slurries, as well as putstsolanovyj portlandtsement.
The composition of solutions include small (size of module (MK) within 1-1, 5) or tonkomolotyj (to cement fineness) sand.
Cement injections add following plasticizers:
-sodium nitrite in the amount of 5% by weight of cement;
-polymer in the form divinilstirol’nogo or PVA GLUE polivinilatsetatnoj emulsii LaTeX СКС-65GP-b with p/TS, equal to 0.05;
-Super p-3 in quantities of 1-2% by weight of cement;
-gidrofobizirujushhuju integrated organic-C-CODE in the amount of -0.3 0.2% by weight of cement in conjunction with sodium nitrite;
-the limy dough in quantities of 15% by weight of cement for designs operating in dry conditions.
Polimertsementnye injectable formulations are prepared using as polymer PVA or SKS-65GP-b with p/TS, equal to 0.15 -02.
Injection ready solutions in design is done using rastvoronacoca. When small amounts of works, we recommend that you use manual, e.g. C-402, performance 0.18 m3/h. Example of pneumatic blower can serve as installation c-562, used in the construction industry for applying liquid fillers.
Injection method got widespread abroad. Thus, the use of low polijepoksidov quick curing allows the firm to “Balm B.B.” produce sealing cracks with 0.06 mm opening width a depth of up to 2 m. Special packing glands, inhibit the release of polymer on the surface, that gives you the opportunity to opt out of drilling construction surface mounting pipe.
Before injection onto the cracked surface is imposed a temporary seal, which throughout the devastated surface leave the input holes. If the crack runs through the entire concrete block, in order to avoid leakage of polyepoxy compacted also back plane. Dosing pumps direct resin and hardener to the mixing head, where the composition through the gland is forced into the crack until it appears in the adjacent hole. After this first hole is condensed and pressure continues through the next hole.
To renounce the use of pipes with in’ecirovanii polymer solutions allows the developed method injection through the washer, which can be reused after annealing or mechanical cleaning.
Metal disc with threaded hole is glued on the surface so that the centres of the holes match crack. The solution is injected via the perestavljavshi socket.
Method injection mortars allows you to fully restore the damaged structure, but its deformativnos’ may be slightly higher. Apart from the obvious advantages of this method has drawbacks that limit its scope, namely: If the load and the impact that caused the cracks, recur during further operation restored structures, damage will arise again. In this regard, the appropriate method when a crack caused by loose draught buildings, concrete shrinkage, fire, earthquake. In other cases, it can be used after creating an additional safety margin design. Furthermore, for the production of works required highly skilled staff.
The traditional and most common methods of repair and reinforcement of brick buildings reinforced device; mortar, concrete and metal enclosed zones.
Intense metal belt carry out from round steel diameter 20-36 mm. The maximum length for most of his hand (15-18 m 3) should not exceed 1.5 length short. The deformed part of the building, taken from the waist, attached to working on a length equal to not less than 1.5 length of deformed parts. Belts are installed in the ceiling plane. To prevent crushing the masonry (the corners of the building are fixed parts of no. 12-16. Tension rods npoizvoditsja couplings: on each straight belt installed base and tensioning sleeve. Installation and tensioning of belts start with lower floors.

Device method applied in zones of tension mainly defects and damage the grounds, stabilizes the uneven rainfall without laborious work on connection requirements or strengthening of foundations and interference in the normal operation of the building.

With significant damage masonry cracks and the need to strengthen the support site overlay on a wall can be used in the manufacture of belts from wireframes. The two reinforcement skeleton are the outer and inner edges, walls and connected by anchors.
Longitudinal and transverse rods are made of reinforcement A-I Ø 16. The tension of the belts is done by screwing the nut anchors evenly from corners and intersections of the walls to the middle.
Wide application of metal clips while repairing damaged walls cracked, due to the ease of their manufacture and installation. High efficiency (increasing the bearing capacity of the pier at 2-2, 5 times and the versatility of the technology installation, independent of the type of damage, are used to apply the standard metal frame design magazines.
Disadvantages of the method should include the high labour input (space and restoring the plaster layer) and metal, pabot. In addition, metal ferrule worsens thermal properties of external enclosures. Piers height up to 2 m and a width of up to 1.6 m strengthen the tie straps (clamps) from Strip steel-35×5-60×12 with step of not less than 500 mm and longitudinal parts (uprights)-L50x5. When aspect ratio usilivaemogo Pier more 1.0:2.5 requires additional transverse link bolt, skip through the masonry, the diameter of which shall be equal to twice the cross-section of the connecting laths. When renovating buildings damaged brick walls vertical and inclined cracks (warp deformation, buckling walls offset floors) can apply Staples-coupler made of segments of the channel (# 16-20).   Anchors serve as bolts with a diameter of 20-22 mm or Ruffs, mounted at a distance of not less than 1.5 wall thickness from cracks in increments of no more than 2 m. Beams are installed in 2; After the installation of the structures it is closed up solution and thoroughly compacted.
Place tearing off the exterior brick walls from the Interior are repaired using metal frames or reinforced concrete dowels which walls also indent.
Reinforcement technology of large-panel buildings unlike brick are not tested and has a number of features:
-no hidden and ignored stocks strength that requires consideration of the actual work of building elements when you modify the schema and konstruktivnej load increase of own design of amplification;
-the use of innovative materials and technologies;
-presence of defects and damages not occurring in the practice of exploiting stone buildings;

-excess physical deterioration of the buildings, makes the need to not only recover, but to improve the durability of certain structural elements;

-lack of experience massive overhauls of large-panel buildings.
In the first years of operation of large-panel buildings (built before 1964 г.) was marked by intensive corrosion of steel ties and fixings.
In order to prevent premature destruction of the site bearing on run exterior walls in houses designed by the method of installation of prefabricated concrete or metal console racks, partly imbedded load from runs through compressing metal wedges. As the destruction of the node are redistributed these loads on the rack.
It should be noted, however, that this method is not widely used due to the high labour intensity and the large amount of work done by hand and, moreover, its application is connected with the necessity of occupants.
Advantage of this method is the use of industrial designs, as well as relieving the designs (the latter during installation).

Device console racks is only implemented in practice, the method of relieving the exterior wall panels and transfer the load onto the base. Developed design solutions for mounting riser that discharges designs from pristennyh racks outside the building that allows to mechanize work and improve the performance of joints of exterior wall panels.

Razrabotanytehnologii strengthening walls panels ammunition, shirts and narashhivanijami.
To strengthen the walls of cellular concrete is recommended reinforced plaster and concrete cages that prevent increased cracking. Due to the shrinkage of mortar and concrete clips tightly rolled Panel and work together with them.
Metal reinforced plaster and concrete shirts represent unlocked with one hand (mostly on the outside) magazines and used to reinforce the Central compressed patands elements. This gives the possibility not to destroy a quarter of partition walls.
Fitting shirts are fixed to panels anchors installed in prosverlivaemye on 2/3 of the thickness of the panels holes, as well as the fixture panels via korotyshi.
Strengthening of a reinforced plaster and concrete narashhivanijami is implemented by increasing the working section of the element, as well as the transfer of part of the load from the weight of floors in the building (the build-up from the inside), and the mass of the outer walls through building-on the base (at the device additional reinforced concrete walls based on widening the existing Foundation).
Amature unilateral help is attached to the Panel similarly fixture shirts, bilateral-using metallic links installed in the drilled hole in the usilivaemogo element and connecting between a fitting two layers.

To strengthen the end wall, damaged through cracks as a result of the compression panels Center recommended installation of monolithic reinforced concrete walls from outside and inside the building. Such constructs designed to end walls with shrink and sedimentary cracked.

Individual panels through cracks can be strengthened through bilateral building concrete walls with a thickness of 80 mm each, connected by anchors from a wire in diameter of 8 mm, inserted in the drilled hole in the Panel.
A comprehensive overhaul of the buildings unit building can be used as a generic method. Build-up of load-bearing walls is made at any time of year: it is capable to perceive the loads from mass, improves temperature-humidity mode wall panels. However, in case of impossibility of organization of work is hampered by the occupants and ushireniju operation Foundation.
Build-up on the outside protects the wall constructions of climate impacts and thereby increases their durability. Build-up across the expanse of friendly walls increases the spatial rigidity of the building and improves the degree of sealing joints of panels. This should take into account the efforts from temperature deformations panels and shrinkage of the concrete building.
The most effective building material is dispersive-reinforced concrete with high strength. Promising to perform help can become a method of shotcrete.
For the restoration of buildings damaged during earthquakes, and to improve their method of seismic devices polimerrastvornyh shponok.
Reinforced Polimerrastvornaja feather (PASH) represents the indent, carved in concrete adjacent reinforced concrete elements depending on the existing efforts of one or more terminals a-III and filled with epoxy polimerrastvorom. PASH made of epoxy polimjorrastvora with high strength and adhesion to concrete and reinforcement, ensure transfer of effort stretching and shearing and, in addition, that have low material. However, they device requires highly skilled performers.

North Building-climatic zone to 80-95% damage bearing constructions connected on the destruction of pile foundations under the influence of thermal deformations caused by effort and destruction of meralotnoj reinforced concrete grillage.

Effective method-pile with steel tip previously tense stator.
Ferrule consists of four longitudinal Struts as ravnobokih corners and transverse naprjagaemyh elements-studs.

Once unloaded piles and open to the required depth recorded in the project position rack pulled together among themselves “Voltage Controlled heeled stiletto (100-150 Mpa) is created using ottarirovannyh wrenches in three phases starting from the Center and moving clips to both its ends.

Problems of strengthening and eliminating excessive deflections and cracking in the stretched zone plates floors in buildings of the first period of industrial House engaged specialists from different institutions. As a result of repair techniques were developed, the most important of which are:
-increased without changing the static patterns (nabetonki, extra valves);
device design of riser that discharges (pulling up plates of overlappings to metal beams);
-strengthening with changing static schemes of work and stress-strain State of (0,1 proof stress of prestressing device horizontal tightening, conversion of split slabs in continuous).
The simplest javljaetsjametod strengthening plates of overlappings by increasing the height of cross-section through a device on concrete thickness 20-30 mm. If this can be done in additional reinforcement. Method applies when the carrier is able to absorb the additional load.
Widespread in practice, major repairs of buildings received device method riser that discharges designs from metal beams, stacked along the working span plates and bound to them by using the bolts head which is M22 flush.
If necessary, increase the rigidity of the riser that discharges the construction across the passage may establish additional beams.

This method is characterized by a high metal (metal consumption per slab floors are 60-80 kg); through the use of metal beams decreases floor height in light (10-15 cm).

Lower compared with the above method determines the efficiency of metal device naprjagaemyh puffs, available on the bottom of the hole floor slabs. The tension is created by the tension nuts anchoring devices fixed to the ceiling, or tightening the two neighbouring puffs band. Also suggested that similar structures for enhancing solid slabs.
The use of massive anchoring devices on the bottom face plate requires applying the plaster layer with a thickness of at least 50-60 mm or podshivnogo plasterboard ceiling. Developed and tested in practice, the method of strengthening plates of overlappings with the help of naprjagaemyh shprengel’nyh puffs, not increasing the thickness of the panels. They are made of reinforced steel A-I Ø 10 and placed along the working passage within the level floor slabs. Originally produced a partial disassembly of the floor construction from transverse walls and then punched out hole inclined holes in the slab floor. At the bottom of its facets arranged furrow connecting centers of inclined holes.

Sprengel is made (bent at the place) so that its length is the horizontal part (distance between curved branches) was equal to the distance between the holes on the bottom of the floor slabs in the subsequent heat Sprengel.

Sprengel start plate overlap as heat it jelektrotermicheskim way (welding transformer), and then the nuts on the ends of branches to otognutyh Sprengel are tightened.
Device is included in the work after it has cooled. The horizontal part of the Sprengel, laid in the furrow, zachekanivaetsja solution. The variant of the device of a plaster or podshivnogo plasterboard ceiling with a thickness of up to 15 mm without the device at the bottom of the furrow; floor slabs.
There is also shprengel’nyh installation method puffs without preheating; they can be used for amplification and other structures cracked buildings damaged.

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