Strengthening of load-bearing elements

Summary

The culture of emergency must be replaced with a culture of prevention. And this should happen not only in view of cost-savings, not only in economic terms. Prevention must be intended mainly as a social and cultural attitude that gives its fruits in a short, medium and long-term perspective. Not investing in prevention means to transfer irresponsibly the social and economic costs of disaster on the shoulders of future generations.

Strengthening vertical elements

A basic requirement for vertical elements is that they do not lose load capacity at extreme (maximum) loads, which could lead to partial or complete structural failure. The formation of “soft” sections /joints/ in compressed columns is totally unacceptable.
The vertical bearing elements – columns and shear walls, transmit vertical and horizontal loads from the structure to the foundations of the building.

Apparent signs of weak areas in the columns will be found by conducting diagonal cracks. If such are found, then best practice is to consult with an expert. Exposed and corroded steel reinforcement in columns or shear walls also threatens the security of the building, and special attention should be paid. Their cosmetic cover, mostly with plaster, is extremely undesirable! In practice, frame structures are encountered, the vertical elements of which are out of the structure and do not take up vertical forces. Owners, often ignore the condition of these elements by ignoring the fact that they depend on the behavior of the building in the event of a seismic impact.

In practice, a wide variety of methods are used to amplify vertical elements depending on the needed effect – increasing vertical or horizontal load bearing capacity, ductility and others.
A typical approach would be to determine the reinforcement of columns with a skeleton of steel profiles, as well as the additional casing with a reinforced concrete.

More advanced and cost-effective systems are based on composite systems, and they have a number of advantages over conventional ones. Choosing an appropriate system is a complex task depending on a number of factors specific to each project.

Additional reinforcement of reinforced concrete horizontal elements

The most common case of cracks forming in the slabs is occures immediately after their deformation due to unacceptable slack. The reason for cracking in this case may be the lack of necessary formwork support to carry the minimumamount of required strength of the concrete.Could as well be its lower strength performance or perhaps incorrectly placed or wrongly constructed steel reinforcement. All of these scenarios are common in old house built dating back to the middle of the last century. Typically, these types of cracks do not increase their size during the lifetime of the structure. If the floor slack is greater than the allowable, measures should be taken to bring it into a design state that guarantees safety exploitation in the future. There are innovative, elegant reinforcing systems that allow straightening corrections in already built reinforced concrete slabs within 24 ÷ 48 hours without the presence of “wet” processes. Cracking of the slab can also occur as a result of the concrete curing after application. These cracks must be closed by a cement plaster to protect reinforcement and concrete from external influences. This is especially true for rooms with high humidity or aggressive agents in their environment, where dense filling of the cracks is absolutely necessary as soon as they occur.

Inaccessible slacks are also observed in beam elements. In addition to the above-mentioned causes, the corrosion at the lower section of the beam significantly reduces its vertical load bending and shears capacity.

Reinforcement of wooden and metal elements

Wooden beams, columns, capitals and others can be seen both in the oldest houses and in modern architectural solutions in new buildings. Their aesthetic value is high and their preservation in the original during restoration is becoming a challenge. A classic method of repairing wooden load-bearing elements in our construction practice is to combine them with metallic elements that take up all or part of the load. A major disadvantage of this solution is the addition of visible metal elements that do not always fit into the overall appearance. Foreign research studies show the potential for symbiosis between one of the oldest building materials – wood and modern composite materials – glass, carbon, and others. Unlike classic approaches, the use of composite systems allows minimal intervention on original wood elements. Extremely high mechanical performance reduces their size, making them undetected when added to the original design.

Strengthening of beamwork

According to Bulgarian National Statistical Institute there are 973 652 semi-solid buildings with brick walls and floor slabs built on beamwork. Most of them need major overhaul of the wooden beams and their connections to the brick walls of the building. The main objectives of such a repair are to observe the aesthetic appearance of the beamwork, to replace or reinforce the affected beams and, above all, to increase the seismic resistance of the building. Wooden floor is the weakest place in taking seismic impacts. In their original form, they do not have enough stiffness to properly redistribute horizontal loads on the vertical load-bearing elements. This leads to overloading the columns and is a prerequisite for serious consequences for the building and its occupants. Luckily, there are a number of foreign norms that address this problem and offer tried and tested solutions that are applicable to our building practice.

усилване гредоред

Foundations strengthening

The foundations are the lowest positioned building elements in a building. Their function is the transmission of loads from the top of the structure onto the soil – the earth’s foundation. Nowadays most of them are made of reinforced concrete, but in older buildings there are concrete, rubble concrete, masonry with natural stones or clay bricks, wood, metal and others. Depending on the depth of foundation, they are shallow or deeply laid. Shallow foundations can be made in depths of as little as 1m, while deep foundations can be made at depths of 20 – 65m. Shallow foundations are used for small, light buildings, while deep ones are for large, heavy buildings. According to their geometrical features, the shallow piles are individual footings, strip footings, raft foundations or combination. The deep foundations are in the form of piles, diaphragm walls and borehole foundations. The most common reason for cracks appearing on the walls of buildings is the uneven sinking of the foundations. The reasons for it can be varied in relation to the natural and manmade processes in the soil around and under the building. In addition to cosmetic defects, the sinking of the foundations leads to increasing the stresses in the elements of the building which reduces bearing capacity. Determining the agents and expedience on their removal is subject to a thorough techno-economic analysis. In any case the first step is consultation with an expert in the field and postponing this step can lead to more expensive repairs and extremely unwanted consequences.

Reinforcement of masonry structures

A common occurrence in old houses is the complete renovation – inside and out. The main goal of the owner is to use the already constructed supporting structure of the building. In a number of cases, even at initial inspection, defects in buildings were observed, such as highly developed cracks in bearing brick walls, uneven sinking of foundations and others. These defects are a clear sign of partial or total depletion of earthquake resistance, which actually threatens the lives of the inhabitants. Reconstructions should be carefully considered with regards to the age of the masonry, the planned changes that would involve new openings in the walls, the obsolete ways of construction and the calculation of the buildings at past times. Regarding to the state of the existing construction, measures may be necessary to strengthen it, in particular, to increase the seismic stability.

An entire reconstruction and repair is an expensive and complex task to conduct from scratch ,which would be meaningless if not carried out in a proper way If done negligently ina few years it would have to be repaired due to later defects and shortcomings in the old structure of the house. Consultation with an expert at the preparation of the project stage is a necessary part of the repair in order to guaranteeing the safety, long life and profitability of the entire construction project.

 

Injection of joints and cracks in buildings and swimming pools

Resins and mortar injection are applied as an alternative to well-known foils, membrane plasters and other waterproofing. The injected waterproofing solutions are particularly effective in the local appearance of moisture or leakage in wall or floor elements and especially in the connection between them. Its main advantages are the water tightness created throughout the section, the corrosion protection of the reinforcement, the rapid execution without the need for chiseling, the deformability after bonding, the long service life of the injected polyurethane resins (as the life of the building), while the polyurethane does not damage the environment and the individual. More about solving the problem of moisture in the underground parts of the building can be found here.

New door and  window openings

In recent years, people’s lives have changed at an exceptional rate. Massive new appliances, different furniture schemes, modern architectural solutions are entering. All this must fit into our old houses built in a past era. The small windows in the old houses, the lack of a direct connection between the premises or the yard decrease the ergonomics of our home. Luckily a reconstruction involving new opening of light spaces for a door or window is quite possible in most cases(even in cases where the hole/gap is in a brick or reinforced concrete wall of the building). This, of course, can only be executed with an approved design by a civil engineer with experience in reconstruction repairs and well acquainted with the different types of work necessary for the reinforcement of the concrete and the masonry structures.

 

 

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