Keywords: Monolithic structures, prefabricated structures, panels, formwork, column, supporting beam, frame part

MONOLITHIC WALL AND COLUMN STRUCTURES

Monolithic structures are carried out directly on the site by placing a ductile construction material (concrete) into a prefabricated formwork in which the necessary reinforcement is deposited.

Monolithic concrete and reinforced concrete walls

Concrete wall structural system is roughly 10 times more bearable compared to brick masonry system. For monolithic load-bearing walls, heavy concrete (1800-2400 kg/m³) and medium-heavy (1200-1600 kg/m³, eg ceramsite concrete, slag-cement concrete) are used. The concrete has a high compressive strength and transmits tensile stress if it is reinforced. Plain concrete is used only for compressive structures. Reinforced concrete can be used for structures stressed by tension and bending. Heavy concrete walls are usually designed with a thickness of 150 to 200 mm and must always be accompanied with thermal insulation.

Monolithic concrete load-bearing walls are used mainly for civil buildings, for buildings of diverse shapes and complicated floor plans, receding and overhanging structures, high-rise buildings and buildings with high architectural demands.

The concrete mixture is poured into the prepared formwork. Formwork gives the structure a shape and divides it into individual work units. Formwork must allow easy storage of the reinforcement and the concrete mix. Different materials such as wood, steel, plywood or paper are used for formwork. Traditional wooden individual wooden formwork is laborious and uneconomical. Currently, the large-area formwork systems are used. Partial formwork of horizontal plywood or metal or plastic panels with reinforced frame enables multiple uses. The forming system which consists of large panels has different design variants. There is also paper formwork for columns of circular and irregular shapes. The perfectly rigid connection of the concrete walls with the ceiling structure can be achieved by using tunnel formwork, which allows concreting of ceilings and walls at the same time. On high-rise buildings, a sliding or drawn formwork is used, which is formed by formwork panels attached to the lifting frame. Concreting of the walls into the sliding formwork is continuous, the formwork continuously moves vertically at a speed of 100 to 150 mm/hour. Sliding formwork is mainly used in the construction of chimneys, and forces, reinforcement cores. Built-in lost formwork remains a permanent part of the building where it performs the function of surface coating, thermal or sound insulation and fire protection. The construction can also be improved from the thermal insulation by inserting polystyrene boards into a lost formwork. In addition to the cladding boards, reinforced concrete blocks may be used, where the closed cavities with the insulated thermal insulation are cast with concrete dressing. Sheeting cement-bonded bricks with insulated thermal insulation boards as lost formwork.

Surface coating of monolithic walls is made by plastering or facing. The perimeter walls of heavy concrete should be thermally insulated.

Monolithic reinforced concrete column structure

Monolithic reinforced concrete column systems are solid structures made of columns, beams or heads and ceiling structure. The monolithic connection of the vertical and horizontal elements gives the skeleton sufficient stiffness even for high-rise buildings. The advantages of the monolithic skeleton are mainly the integrity of the structure, strength, stiffness and resistance to the effects of extraordinary loads or in the undermined and seismically unstable area.

Columns of monolithic skeletons have squares, rectangles, circles, or composed cross-sections (eg shape I or T). Columns are mainly stressed. However, the monolithic connection with horizontal structures also brings bending stress to them, so they have to be reinforced. The minimum size of monolithic columns is 200 mm. Columns 300 x 400 to 400 x 500 m are usually used in conventional rectangular skeleton structural system. Elements sizes must always be verified by static assessment.

Supporting beams and ceilings beams are also dimensioned based on static calculation. The supporting beam height is approximately 1/8 to 1/12 axis distance of the columns.

Monolithic reinforced concrete skeletons are made as frame, head or slab structures:

• Frame skeleton system: The load-bearing frames can be arranged in the transverse direction, in the longitudinal direction or in the two-way direction (space frames). Supporting beams can be cantilevered in front of pillars.
• Flat slab with column head skeleton system: Flat slab with column head skeleton system is a special case design with two-way arrangements supporting beams. The supporting beams are reduced to heavily reinforced stripes running in the ceilings above the head of the columns. These hidden beams carry a bidirectionally reinforced ceiling slab. Ceiling heads may be rectangular, polygonal or circular. This system is used for objects loaded with large payloads. The disadvantage is complicated formwork.
• Flat slab skeleton system. The slab monolithic skeleton has a ceiling structure directly supported by columns. The slab has a flat ceiling. A flat head is formed around the column. Columns are usually located in a square module network. Ceiling slab should be circumferentially cantilevered that large bending moments are not brought into the outer columns. Skeletons with slab ceilings are used for objects with lower payloads. Their advantage is a flat view, the possibility of free partitioning of the partitions and easy execution.

Column structure systems are also stressed by volume changes due to temperature effects. Expansion joints can be made in reinforced concrete skeletons in several ways:

• Duplication of columns is the most common and most common way of dilatation. The disadvantage of this modification is the interruption of the modular system, which is unfavorably reflected in the front of the building
• Duplication of supporting beams can be done in duplicate. One of the beams is mounted on a column bracket or on the rebate of a neighbouring beam having a higher height.
• The ceiling panel can be created by an inserted field.

PREFABRICATED WALL AND COLUMN STRUCTURES

Prefabricated structures consist of prefabricated full-area or rod-shaped parts, which are bonded to the structure eg by welding, concrete dressing, in the historic stone pillars of 2500 years BC using coupling pins of hard (eg cedar) wood. Prefabricated parts of vertical structures can be made of ceramic, heavy or lightweight concrete or steel. The rigid connection of reinforced concrete columns with supporting beam (welds + concrete dressing) formed frames that are the basis of prefabricated skeletons.

Prefabricated concrete reinforced concrete walls

The load-bearing walls of the prefabricated elements began to be widely used in the 1950s. The first prefabricated panels were made in the form of blocks and blocopanels, later in the form of panels:

Blocks are wall element panels, their height is ½ to 1/3 of floor height, thickness 300 to 400 mm. Blocks were made of crushed concrete, slag-cement, porous concrete, and they are placed in a mortar bed. Block constructions were referred to as a semi-assembled system. They are currently used only exceptionally in the reconstruction and adaptation of apartment buildings.

Blocopanels are wall element of floor height and a width of 1200 to 1500 mm. The thickness of the blockopanels is given by mechanical and thermal-technical properties (250 - 400 mm). They were made from the same materials as blocks. In the wall constructions, they were joined by welding reinforcement and grouting of joints.

Panels are large-area panels whose dimensions are limited by the characteristics of the material used and the lifting device's load. Wall panels typically have an area of 10 to 20 square meters. The height corresponds to the height of the floors. Their usual 150 mm thickness meets acoustic and fire protection requirements. Wall panels are made of concrete, reinforced concrete, lightweight concrete, ceramic blocks or as a layered element (sandwich construction).

Depending on the layout of the load-bearing walls, we recognize transverse, longitudinal and bi-directional systems. Depending on the function, we are able to distinguish the interior load-bearing wall panels and the peripheral load-bearing wall panels. Internal load-bearing panels are produced in thicknesses of 150 - 200 mm and in a length of multiple 300. Wall panels may be full or with holes. Concrete panels must have a structural reinforcement that is particularly relevant for transport and assembly. The interlocking is provided by the contact reinforcement in the form of steel pins, loops or steel joint plates. In addition to the static function, the perimeter wall panel must fulfil the thermal insulation function in particular. Both of these functions can be fulfilled by the single-layer panel. However, it is preferable to manufacture a two-layer or three-layer sandwich panel. Single-layer panels are made of lightweight concrete and hollow ceramic inserts. The two-layer panels have a concrete or reinforced concrete support layer and an outer layer of lightweight concrete or ceramic materials. The three-layer panels consist of a reinforced concrete or reinforced concrete board with a thickness of 100 - 150 mm and a thermal insulating core (polystyrene, mineral wool). The stiffening panels form an internal reinforcing wall, which provides stability prefabricated buildings. The stiffening walls are not loaded with ceilings, but they are stressed by carrying the effects of horizontal forces. Their thickness varies from 80 to 100 mm.

Prefabricated reinforced concrete column structure

Prefabricated reinforced concrete skeletons have evolved from monolithic structures. The first assembled skeletons appeared in the 1930s. During the development, more than 30 systems of prefabricated skeleton systems were built. Many of these systems have been unified and replaced by a unified system - an open set-up system of assembled frame skeletons characterized by the unified principle of supporting beams and columns that are still in use.

Frame assembled skeleton is made up of supporting beam mounted on columns. Frames are formed by dividing the monolithic frame off its joints, at the sites of the smallest bending moments. In columns, it is usually a half to a third of their height. For beams is in a quarter to a fifth of the span. The H-frames are formed in such a division and retaining the rigid joints. The frames П are created by dividing the columns in the heel. Console columns and split beams are formed by separating the beam from the columns on which the brackets remain. Columns with continuous beams are formed by dividing monolithic skeletons in the joint. Supporting beams are interconnected either directly above the columns, or extend over the columns and contact the field. The basic connections include the intersection of two columns, the intersection of two beams and the contact of the beam and the column.