Movements in masonry structures are deformations generated by a variety of factors. The types and reasons of masonry structure movement are examined. There are a variety of elements that cause or cause deformations in masonry constructions, such as temperature fluctuations and changes in moisture content. These movements must be taken into account in order to avoid damaging masonry structures. Significant pressures may be generated as a result of masonry members being restricted by interconnection with masonry elements that move differently. Because masonry is a brittle material, movement limitation causes it to fracture and develop cracks, which allow water to permeate and potentially harm the building materials.
Because remedial treatments are inconvenient and expensive most of the time, it’s critical to consider masonry building movement during the design stage.
Types and Causes of Movements in Masonry Buildings
Variations in moisture Temperature variations cause deformation as a result of applied loads. Movements that lay the foundation Materials’ chemical reactions
Movements in Masonry Buildings due to Moisture variations
Changes in moisture content cause dimensional changes in masonry materials, which is true of all forms of construction materials except metal. These dimensional changes may be permanent, or in other words, irreversible. For example, clay bricks experience long-term moisture expansion that reaches its maximum value after the unit has cooled. Not only does the moisture expansion rate of clay brick decrease over time, but it also varies greatly depending on the type of clay and the degree of firing.
The British Standard provides guidelines on movement caused by moisture changes, stating that the normal expected movement range in fired clay units is typically less than 0.02 percent.The absorption of moisture from the atmosphere caused long-term expansion. Both external and internal walls absorb moisture, although the former does it far more quickly. At all stages of their lives, all types of masonry materials show reversible shrinkage or expansion with altering moisture content. Table 1 shows typical moisture movement values for masonry, concrete, and steel.
Temperature Changes Cause Movements in Masonry Structures Thermal movement is determined by the material’s coefficient of expansion and the temperature range to which masonry pieces will be exposed. Temperature ranges are difficult to assess because they are based on other material qualities such as thermal capacity and reflectivity, however coefficients of thermal expansion are offered. The material’s modulus of elasticity, temperature fluctuations, and coefficient of thermal expansion all influence the intensity of these stresses. In a real-life construction, the distribution of stress along the restrained edges of the masonry wall is not uniform, hence crack development is likely. However, complete restraint in masonry edges is impossible, which is why heat changes may occur.
Deformations due to Applied Loads
Creep, shrinkage, and elastic motions are all examples of deformations caused by applied load.When a masonry element, such as a pier, is subjected to axial compressive loads, its height is somewhat reduced, and it may return to its original position if the stress is removed. In this situation, the pier has an elastic behaviour. The pier behaviour would be plastic if modest permanent deformation occurred after the vertical compressive load was removed, and this process is known as creep.Because clay brickwork does not creep under typical loads, it should not show significant signs of creep. With reinforced components, when estimation of initial elastic deformation and deformations due to permanent loading is required, taking creep into account is increasingly important in the design of masonry structures.
Deformations due to Foundation Movements
Movements caused by foundations are the most common cause of cracking in masonry walls. Due to the frequent drop and increase in moisture content of the soil beneath the masonry structure, masonry buildings erected on clay soil are more likely to experience foundation movements. In some regions, building masonry faults are caused by soil settlement on infilled sites and mining operations. If these issues are predicted, it is critical to take precautionary steps with regard to foundation design. For example, the most basic method is to ensure that the foundation level is one metre below the surface.
Furthermore, more effective and elaborate procedures are required to handle these concerns and prevent foundation problems in mining subsidence and poor soils.
Movements in Masonry Buildings due to Chemical Reactions in Materials
In most cases, masonry materials are not subjected to chemical attacks, but sulphate attack on mortar, concrete blocks, wall ties, and other steel components used in masonry buildings might cause issues. The expansion of mortar or concrete due to sulphate assault could cause masonry to disintegrate. Soluble salts can come from clay bricks or ground water, and if the masonry is constantly moist, the attack will develop. Movement caused by chemical reactions can be successfully addressed by carefully selecting cement ingredients, such as using sulphate resistant cement below the damp proof course level when the problem is caused by subsurface water.
Temperature and moisture fluctuations in the constituent materials, as well as surrounding factors such as reinforced concrete beams, slabs, and roofs, are typically linked to movement in masonry walls of buildings. These changes also put stress on the walls, which can cause significant damage and, as a result, harm the building’s performance and durability. The goal of this research is to look at what influences temperature and moisture transport in walls. Masonry units (concrete blocks and clay bricks) are well recognised for expanding when wet and shrinking when dry. So, to assess the dimensions and weight fluctuations of masonry unit specimens (with or without a mortar joint) due to moisture and temperature changes, experimental procedures were established.
Thermal Cracking
Although masonry can deform elastically over time to allow tiny quantities of movement, major changes typically result in cracks. Cracks might form in the mortar joints or in the masonry units themselves. Differential foundation settlement, drying shrinkage, expansion and contraction due to ambient thermal and moisture variations, improper support over openings, the effects of freeze-thaw cycles, the corrosion of iron and steel wall reinforcement, differential movement between building materials, salt expansion, and the bulging or leaning of walls are all causes of cracking. Warm weather causes above-ground brick walls to expand (especially if facing south or west) and cool weather causes them to contract. This causes strains in the walls, which, depending on the situation, might result in a variety of cracking patterns.
Aside from problems induced by differential settlement or earthquakes, structural problems are most typically encountered over openings and (less commonly) under roof eaves or in areas of structural overloading. The masonry units will show cracks through the units rather than along the weaker mortar joist in these cases. Cracking or displacement of masonry around openings due to deflection or collapse of the lintels or arches that bridge the apertures, or displacement due to overstressed masonry units are common displacement issues. As the wood sags or decays, cracks will appear in older masonry walls with wood lintels. Lintels made of iron and steel deflect or corrode over time, causing cracking. In most cases, resolving such issues entails replacing defective components and rebuilding the surrounding region.
Cracking or outward displacement of a pitched roof’s eaves caused by failure of (or absence of) horizontal roof connections, causing the roof to spread outward. The brick wall may split horizontally immediately below the eaves due to the roof’s lateral thrust, or it may migrate outward with the roof. It’s also possible that the roof is leaking. When this happens, thoroughly inspect the roof structure to see whether there has been a failure owing to improper ceiling rafter placement or a lack of rafter ties. If this is the case, more horizontal ties or tension members will need to be added, and the roof will need to be pulled back into place if possible. The masonry that has been damaged can then be repaired.The weight is also a factor.
The most common types of cracks are organised in the following 7 groups Plastic Settlement. Plastic Shrinkage. Early Thermal Contraction. Long-term Drying Shrinkage. Crazing. Corrosion of Reinforcement. Alkali-aggregate Reaction.
The simplest explanation is that structural cracks indicate there has been movement in the foundation
The crack is not touching the main wall.
Also Check
Acoustic Properties of Building Materials for Noise Control