VERTICAL LOAD-BEARING MASONRY STRUCTURES
Keywords: Masonry structures, brick masonry, stone masonry, block masonry, mixed masonry, brick bond, mortar
VERTICAL LOAD-BEARING STRUCTURES
The basic function of vertical load-bearing structures is to transfer all loads from horizontal structures to the foundations of the object and stiffened the object. Other features may be dividing, thermal, acoustic, fireproof or aesthetic. According to the ground plan position, the vertical structure includes inner load-bearing walls, stairwells walls, peripheral walls, reinforcing walls, columns, pillars and partitions.
The walls are structures where the height and length of the wall outweigh its thickness (usually a rectangular cross-section).
The columns are structures where the height prevails above floor plan dimensions (typically square, rectangular, circular).
The pillar is a structure where the height of the pillar prevails over floor plan dimensions (versus the column is more massive, usually square or rectangular cross-section).
LOAD-BEARING MASONRY STRUCTURES
The masonry structures are made of individual natural or artificial masonry elements connected by mortar or laid dry. The design of brick walls is based on static calculation, thermal-technical assessment and fire resistance assessment.
Masonry structure has relatively good resistance to compressive stress. The tensile load-bearing capacity of the masonry is practically negligible. The load-bearing capacity of the masonry is determined by the used wall elements, the mortar type and the masonry bonding.
According to the type of masonry element used, there are brick masonry, block masonry, stone masonry and mixed masonry.
BRICK MASONRY
Bricks are manufactured in various materials and dimensional formats with holes or without holes. The most commonly used were burnt bricks of and metric perforated bricks.
The mortar is a mixture of binders, fillers and water. The strength of the mortar is chosen according to the required load capacity of the masonry. Depending on the amount of binder and final strength, we divide mortars into:
- Lime mortars with a compressive strength of max. 1.0 MPa
- Limestone cement mortars with a compressive strength of 1.0 - 2.5 MPa
- Cement mortars with a compressive strength of 5.0 - 20.0 MPa
The final load-bearing capacity of the masonry does not only the properties of the used materials but also their mutual arrangement or bond. The classic brick bond is characterized by:
- A masonry pieces that are placed in horizontal layers
- Head joints should be shifted in two layers above each other
- Bed joints and head joins should be completely filled with mortar
According to the orientation of the bricks in the masonry, there are stretcher and header. The stretcher is a longitudinally oriented element applied in the face of the masonry by its length. The header is a transversely oriented element applied in the face of the masonry by its width.
The resulting load-bearing capacity of the masonry affects not only the mechanical parameters of the bonded materials but also masonry bonding. Classic masonry bonding includes stretcher bond, header bond and English bond. The cross bond, Dutch bond, or Polish (Gothic) bond are applied less. Stretcher bond is composed only of stretchers that are bonding by ½ bricks. Header bond is composed only of headers bonded by ¼ bricks. English bond (semi-cross bond) rotates stretcher bonds and header bonds. In each layer, the bricks overlap in the transverse direction by ½ bricks, in the longitudinal direction by ¼ bricks.
BLOCK MASONRY
Block masonry have evolved from brick masonry in response to stricter thermal technical requirements. The block masonry wall is implemented as brickwork. Thermally stricter requirements satisfy the blocks, which are lightened from the cavities or are lightened in mass. Blocks are made from lightweight concrete, diatomaceous earth, slag, fly ash, etc. The cavities are either continuous or closed. Blocks of closed-cell cavities are laid down. The blocks with closed cavities are laid down by cavities oriented downwards.
Ceramic blocks
Ceramic blocks of older types such as CD-INA, CD-IVA, CD-IZA have been replaced by a new generation of blocks, such as Porotherm, Kintherm or Supertherm, which are produced in dimensional series for single-layer load-bearing masonry. With the latest types, blocks are already filled with heat insulating material (EPS, mineral wool) from production. In addition to the basic elements, additional elements are available - half blocks, end blocks,
The mortar layer in the bed joint, or even in the head join, of 10 mm thick, reduces the thermal properties of the masonry. For this reason, the head joints are only partly filled. Two or three strips of mortar bed are realized in the bed joints. Alternatively, special lightened mortars, such as perlite, ceramics, etc., or heat insulating tapes may be used.
Lightweight concrete blocks
Lightweight concrete blocks are manufactured in different strength classes. The products have high precision and can be bonded dry in the head joints without the use of mortar or can be bonded by tongue and groove. Precision calibrated blocks can be glued (joint thickness 1 - 3 mm).
Lightweight concrete blocks are characterized by a low density (500-1000 kg/m3), which makes it possible to produce and use large-dimension blocks to accelerate the brickwork process. Porous concrete products are easily workable. The disadvantage is their water absorption. In their soaked condition, their thermal insulating properties and load-bearing capacity are reduced. Relatively low compressive strength limits the use of lightweight concrete blocks to low-floor structures.
STONE MASONRY
Natural stone masonry is currently not used widely. The disadvantage is mainly its density (2200 to 2400 kg/m3), difficult and costly workability, poor thermal insulation properties and airtightness. The advantage is resistance to weather and mechanical influences and aesthetic architectural effect.
For stone masonry, stone elements of different sizes and shapes are used. The random rubble is characterized by irregular shapes without stoneworking. Rubbles are roughly worked stone elements of the shape of an approximate parallelepiped. Ashlar is prism-shaped elements roughly machined used for facing masonry. Stone blocks feature regular shapes and stoneworking as needed.
Stone masonry is not usually plastered and joints are filled with cement mortar. The width of the head joint and bed joints is 15 - 40 mm. According to the arrangement of the layers and shapes of stones, stone masonry is divided into:
- Random rubble masonry is used for base structures and plinths. The strength of masonry from unprocessed stone is influenced by the quality of its bonding. The joint joints are not to be continuous, the width of the load joints is 15 - 40 mm.
- Squared rubble masonry is made of partially worked stones (squared rubble). Depending on the method of processing, we recognize the rough squared rubble and fine squared rubble. Rough squared rubble masonry may not have the same thickness of the layers and the joints may be oblique. Fine squared rubble masonry is done from fine squared rubble with a clean machined line and the head joints must be vertical.
- Polygonial rubble masonry is used for terrain and decorative purposes. \polygonialmasonry is most commonly used for decorative purposes. The masonry consists of selected stone, which has the shape of irregular four to octagonal. The linkage and bed joints are machined to a depth of about 80 mm and the visible face is left untreated.
- Ashlar masonry is made from machined stones of prescribed shapes and dimensions. Ashlar masonry is used for tiling of representative buildings, monuments, etc.
MIXED MASONRY
Mixed masonry is a combination of two or more building materials in one construction unit. Typically, this is a combination of bricks and stones, bricks and concrete, concrete and stone, blocks and concrete. The advantage of mixed masonry is the possibility of using the advantages of individual materials, such as the aesthetic effect of stone on the outer face of the building and high strength of concrete