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Useful information

Types of structures

Choosing the type of structure depends on:

  • the purpose of the building: this determines vertical and horizontal compartmenting, for optimum conditions of use and comfort;
  • the location of the building: this influences the type of foundation and the building's height;
  • the height of the building: this determines the type of structure (higher heights mean higher loads);
  • the materials used in construction;
  • the construction technology.

The main components of a building's support structure are the following:

The infrastructure, which connects the building with the ground, and consists of foundations, support pillars and footers, the floor on top of the basement.

The superstructure, built above the ground and consisting of vertical support elements (pillars, loadbearing walls), horizontal support elements (floors) and sloping support elements (stairways, ramps).

The solution for the structure is chosen in the design process and it must met all the requirements imposed for that particular building.

1. Loadbearing masonry structures

Loadbearing masonry structures are used in housing buildings with a maximum of five storeys. This limitation is imposed by the requirement of obtaining appropriate wall thicknesses while maintaining cost effectiveness, bearing in mind the physical properties of the masonry materials and the earthquake risk of the area.

The minimum thickness of masonry walls results from the requirements of strength and stability, but also from those of thermal and phonic insulation.

Loadbearing masonry structures are designed as three-dimensional systems consisting of loadbearing walls and bracing walls, placed as symmetrically as possible relative to the two main direction (lengthwise and crosswise), the result being a very stable box-sectioned structure. The loadbearing and bracing walls are placed both in accordance to functional requirements and to those of strength and stability for walls and floors, while maintaining technical simplicity and cost effectiveness.

For the building to respond best to earthquakes, it is recommended to use during design shapes that are as close to rectangles as possible.

In the case of irregular shapes (L, T or U) and of buildings with varying heights and rigidities, they must be separated, through seismic gaps, in rectangular sections.

The height of the building and the maximum number of floors for all types of structures are determined depending on the seismic characteristics of the location.

2. Loadbearing walls made of monolithic reinforced concrete

This type of structure is widely used in regions with frequent earthquakes, being used in general for buildings with a large number of floors. the main advantage of these support structures is that they have a high capacity of supporting both gravitational loads and horizontal loads (wind, earthquake).

This structure consists of a number of vertical diaphragms (loadbearing walls of monolithic reinforced concrete), which, together with the horizontal diaphragms (the floors), form a three-dimensional rigid system.

The floors are made of monolithic reinforced concrete (cast on site) or of prefabricated reinforced concrete, their choice being influenced also by the technological process used when executing the diaphragms. The use of diagrams of monolithic reinforced concrete has technical and economic advantages in the case of multi-storeyed buildings, in which the functional requirements allow an identical distribution of loadbearing walls on all floors and an even horizontal distribution. As a rule, they are used for collective housing, dormitories, hotels, hospitals and sanatoriums, office buildings etc.

3. Frame support structures

Frame structures consist, in principle, of a three-dimensional system composed of vertical bars (pillars) and horizontal bars (girders).

The frames follow two orthogonal directions, corresponding to the building's main axes.

The frames may be made of monolithic reinforced concrete, prefabricated concrete or metal.

The walls have the role of compartmenting, closing and insulating the building (soundproofing and thermal insulation).

The floors are supported by the girders.

Interior space may be organised differently from one floor to another.

Frame structures are designed on purpose for taking over and transmitting integrally all the vertical and horizontal loads the building is subjected to.

This particular structural system has the advantage of great flexibility in terms of compartmenting on each floor; however, the requirements for rebar are higher, and the non-bearing closing and compartmenting elements are difficult to connect with structural elements.

Frame structures consist, in principle, of a three-dimensional system composed of vertical bars (pillars) and horizontal bars (girders), rigidly connected in nodes. The system is developed, as a rule, following two orthogonal directions, corresponding to the building's main axes, and the grid for the distribution of pillars is regular, being conditioned by functional requirements, by those of strength and stability for the structure, by the way the floors are built, as well as by the execution technology.

The beams in the frames are support points for the elements of the floors; the latter are executed depending on technology, on the degree of seismic protection required for the location, on the distribution of utilities etc.

Reinforced concrete frame structures that are well designed as a whole and in detail behave very well in case of earthquake and are used in buildings with a maximum of 15 storeys. For higher buildings, the required rigidity is obtained by thickening the pillars, but this affects cost effectiveness.

4. Reinforced concrete frames and diaphragms (mixed structures)

Structural systems consisting of reinforced concrete frames and diaphragms, also called "dual type structures", are built by associating the abovementioned two structural systems, thus putting to good use the advantages of each system, and obtaining an even better behaviour in case of earthquakes.

The functional aspect – flexibility on organising interior space – is covered by the frame structure, while the strength and deformation during earthquakes id provided for by the diaphragms.

Depending on where the diaphragms are located in the building, dual structural systems have several types of construction:

  • structures with insulated diaphragms, located on the outside (on gables) and on the inside of the building (in the stairwell and between apartments);
  • structures that have all the diaphragms grouped together as a central core, including, as a rule, the spaces needed for vertical circulation, for plumbing and other utilities etc.;
  • structures with rigid cores, placed symmetrically at the ends of a bar-type building;
  • structures with full diaphragms, developed along the length of one opening or bay (the space between two beams), located in various places in the building, in relation to the architectural parti.