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Paper Title: A Brief Discussion on the Quality Issues of Masonry Structures Author: He Runfeng Abstract: Based on the quality problems encountered in masonry structures during engineering practice, this paper explains the causes of various cracks in such structures under different conditions. Keywords: masonry, quality issues, cracks. A masonry structure is a structure in which walls and columns made of blocks and mortar serve as the main load-bearing elements of a building. As is well known, building houses with masonry structures adheres to the principle of \"using local conditions and materials available in the area.\" Compared to reinforced concrete structures, it can save cement and steel, reducing costs. Therefore, for decades, masonry structures have played an irreplaceable role in the development and construction of New China. With the widespread use of masonry structures, many quality issues have also been identified. The common quality issues in masonry work fall into the following four categories: First, insufficient masonry strength. 1. The designed cross-section is too small, resulting in inadequate load-bearing capacity ； 2. The installation of water, electricity, heating, and plumbing equipment requires openings and grooves, which reduces the wall’s cross-sectional area significantly ； 3. The quality of the materials is substandard; for example, the strength grades of the bricks and mortar used in masonry do not meet the design requirements, and cement and admixtures that do not conform to standards are used ； 4. The construction quality is poor; the fullness of the mortar is severely inadequate, and the bricks were not soaked before construction, resulting in insufficient strength of the mortar joints. II. Misalignment and deformation of masonry structures 1. An excessive height-to-thickness ratio of masonry walls leads to instability and deformation during use ； 2. Construction quality issues, such as vertical deviation in the walls, increased deformation under stress after use, or even displacement ； 3. Improper construction sequence, such as building the vertical and horizontal walls at different times without proper jointing, leads to out-of-plane deformation and instability of the newly constructed wall ； 4. Improper construction techniques, such as the use of lime-sand bricks, lead to instability during masonry. III. Local damage or collapse 1. Walls may develop corners missing, holes, or even collapse partially due to collisions or impacts during construction or use ； 2. The walls were subjected to saponification corrosion during use, resulting in severe damage to some of them ； 3. Freezing methods were used for construction in winter, and no appropriate measures were taken during the thawing period, resulting in the collapse of the masonry walls. IV. Cracks in masonry: Cracks in masonry are the most common phenomenon associated with quality issues. Problems such as insufficient strength of the masonry, deformation and instability, as well as potential local collapses, can also be analyzed and identified through the pattern of the cracks that appear. The types and causes of cracks in masonry are summarized as follows: 1. Temperature deformation: (1) Due to sunlight exposure and temperature changes, different materials and various structural elements deform differently, and there are also strong constraints present. Cracks that occur due to the inconsistent deformation of the roof and the brick wall, resulting from exposure to sunlight and temperature changes as well as the different linear expansion coefficients of the two materials, are typically found at the ends of the top-floor brick walls in flat-roof brick-concrete structures. (2) The temperature or the difference between the ambient temperature and the target temperature is too large. If the length of the building is too great and no expansion joints are provided, vertical cracks that run throughout the entire height of the building will form, usually at the middle of the longitudinal walls. (3) The thermal deformation of brick walls is constrained by the foundation. If heating is not provided during the construction period in northern regions, the contraction of brick walls is constrained by the foundation, resulting in diagonal or vertical cracks in the masonry below the window sills. (4) The concrete shrinkage in masonry is significant (due to temperature and drying shrinkage). Such as the diagonal cracks that appear on the wall surfaces at both ends of longer cast-in-place canopies. 2. Uneven settlement of the foundation: (1) Large difference in foundation settlement. In brick-concrete structures with significant height differences, figure-eight cracks occur when the settlement of the foundation in the middle is greater than that at the ends ； When the settlement at both ends of the foundation is greater than that in the middle, inverted V-shaped cracks appear ； When the foundation changes suddenly and one end settles significantly, vertical cracks occur. (2) Local foundation collapse. For example, masonry structures located in air-raid shelters or above ancient wells develop cracks due to local ground subsidence. (3) Foundation frost heave. In northern regions, if the depth of the building foundations is insufficient and the foundation soil is prone to frost heave, it can cause cracks in the masonry. (4) Foundation flooding. Uneven settlement may occur after filling the foundation or local flooding of collapsible loam foundations, causing cracks in the longitudinal walls. (5) Drop in groundwater level. In soft soil foundations with high groundwater levels, artificial lowering of the groundwater level can cause additional settlement, leading to cracking in masonry structures. (6) Impact of adjacent buildings. 3. Cracks occur in existing buildings due to additional settlement caused by the construction of tall new buildings nearby, leading to extra stress on those existing structures. 3. Excessive structural loads or too small cross-sections of the masonry; (1) Insufficient compressive, bending, shear, and tensile strength. Vertical cracks in bricks under compressive stress at the center ； Vertical or diagonal cracks occur due to insufficient bending strength of the brick-built flat arch ； Horizontal cracks occur due to insufficient shear strength of the retaining wall ； Cracks along the mortar joints in the walls of the brick water tank. (2) Insufficient local compressive strength. Such as diagonal or vertical cracks under the girder or beam pad. 4. Improper design and construction: (1) Improper placement of settlement joints. If the settlement joint is not located at the point where the settlement difference is greatest ； The settlement joints are too narrow; when high-rise buildings settle and deform, the lower buildings also sink, causing the masonry to crack under compression. (2) The overall integrity of the building structure is poor. Such as cracks caused by the unreinforced concrete ring beams of the brick walls in stairwells in mixed-structure buildings not being closed. (3) Leave holes in the wall. Leaving a chimney hole at the junction of the interior and exterior walls of a residence can affect the connection between them. It cracked due to temperature changes after use. (4) Mixed use of different structures without appropriate measures. Cracks in the wall can occur when the deflection of reinforced concrete wall beams is too large. (5) Improper connection between old and new buildings. When an existing building is expanded, the foundations are separated while the old and new brick walls are combined into one, resulting in cracks in the wall at the junction. (6) The wall structure with large window openings is improperly designed. Such as vertical cracks that are wider at the top and narrower at the bottom beneath large window sills. 5. Poor material quality (1) Unstable mortar volume. If the safety standards of cement are not met, the use of pyrite slag with an excessive sulfur content in place of sand can cause cracking in the mortar. (2) The volume of bricks is unstable. If walls are built with gray sand bricks that have just been manufactured, uneven shrinkage can easily cause cracks. 6. Poor construction quality (1) Unreasonable masonry method, with missing structural rebar. If the interior and exterior walls are not constructed at the same time, without leaving step-like joints or without using reinforcing bars to connect them, vertical cracks running along the entire length may appear at the junction between the interior and exterior walls. (2) Broken bricks are used in the masonry, with many gaps and overlaps in the walls. For example, the exterior wall of a single-story factory building may develop cracks due to the concentrated use of broken bricks. (3) Improper placement of holes or grooves. For example, if a scaffold opening is left in the wall between windows that are 500 mm wide in an office building, it can cause cracks to appear in the masonry. 7. Earthquakes and Engineering Vibration (1) Earthquakes. Such as the diagonal or intersecting cracks that occur in multi-story brick-concrete structure dormitories under strong earthquakes. (2) No lower chord hip roof truss. If the top ridge beam lacks a lower rafters system, horizontal thrust is generated during earthquakes, causing vertical horizontal cracks in the top walls; V-shaped cracks appear at the corners of the top walls during earthquakes. (3) Uneven subsidence. If the floor slab has ring beams, during an earthquake, the side that subsides more significantly will develop diagonal cracks in the wall between windows. (4) Mechanical vibration. Such as cracks caused by blasting near a certain project. In summary, poorly designed structures, inferior materials, substandard construction, as well as cracks caused by earthquakes and mechanical vibrations are relatively easy to observe and identify. The most common causes of cracks in masonry are temperature-induced deformation and uneven settlement of the foundation; however, cracks can also arise from excessive loads or overly small cross-sections, and in such cases their severity is often high. The above are the types and causes of masonry cracks as summarized by me through relevant materials and engineering practice. For reference only by professionals and enthusiasts; any shortcomings or inaccuracies are welcome to be pointed out.