Tolerances and workmanship for the construction of reinforced masonry wall is important to provide required strength and aesthetics appearances to structures.
Construction technology has been evolved and developed over years however; masonry constructions that have been practiced for many years are still man made art.
To achieve required structural integrity and planed aesthetic appearances of reinforced masonry structures, different tolerances are established and therefore should be considered during construction.
Figure-1: Reinforced Masonry Wall Construction
Almost all reinforced masonry construction materials are produced to specific tolerances similarly; approximately entire masonry members are constructed and built to determined tolerances.
Since, masonry is an exposed construction materials, that is why more strict tolerances might be imposed on masonry structures compare with those limitations that are imposed on other structural systems which are ordinarily protected inside after the construction is finished.
All tolerances pertained to the installation of masonry members are specified in Building Code Requirements and Specification for Masonry Structures (ACI 530.1-11) except for the tolerances which are determined in the contract document.
The purpose of providing placement and contraction tolerances by ACI 530.1-11, is to protect and safeguard the performance of the structure. However, the designated values in ACI 530.1-11 is more than enough for achieving normal aesthetic aspiration.
It is possible to impose more strict tolerances in the project records to manufacture an acceptable and more aesthetically appealing masonry structure.
It should be known that not only applying more rigid and tough construction tolerances could increase construction expenses but also make the work substantially difficult and considerably complicated.
In this article specified tolerances which are included in ACI 530.1-11 and are necessary for construction of reinforced masonry structure will be discussed.
Tolerances and Workmanship for Reinforced Masonry Construction
Following are the different types of tolerances for reinforced masonry construction:
- Mortar joint tolerances
- Plumb and alignment tolerances
- Location of reinforced masonry elements
- Tolerances for reinforcement Placement
Mortar Joint Tolerances for Reinforced Masonry Construction
Generally, modifications in the thickness of mortar joints are the primary focus from aesthetic point of view but it could be the cause for bad performance of reinforced masonry structures.
There are numbers of tolerances which are contained within ACI 530.1-11 by which compromising structural performance is prevented. By and large, the mortar bed joint thickness for nearly all reinforced masonry structures is 9.5 mm in which +/- 3.2 mm variations is allowed apart from the joint between first layer of masonry and top surface of the footing.
In this case, mortar joint thickness could be varied from 6.4 to 19 mm to make rooms for the variations of the top of the footing.
Regarding head joints, variations from +9.5 mm to -6.4 mm are permitted for instance the designated thickness of 9.5 mm can be varied from maximum of 19 mm to minimum thickness of 3.2 mm. All specifications are illustrated in Figure-2.
Figure-2: Mortar Thickness Joint Tolerances
Plumb and Alignment Tolerances for Reinforced Masonry Construction
Alignments and out of plumb tolerances are imposed by ACI 530.1-11 to decrease applied load eccentricity and consequently avoid declining the maximum load capacity of the element and ultimately this lead to better structural performance.
Reinforced masonry structural elements such as walls and columns are not permitted to be constructed higher than minimum 6.4 mm to maximum 13 mm from determined dimensions in both elevation and cross section.
Variations from plumb must be within ultimate value of +/-13 mm at the same time keep slope of smaller than 6.4 mm in 3048 mm.
The alignment of both walls and columns can be varied from story to another one by 13 mm for bearing columns and walls and 19 mm for non-bearing walls and columns. Figure-3 illustrates alignment and plumb tolerances.
Figure-3: Plumb and Alignment Tolerances for Reinforced Masonry Construction
Location of Reinforced Masonry Elements
As per ACI 530.1-11, for better connection and continuity of separate members, masonry elements are needed to be positioned within maximum distance of 19 mm from their planned location and must not be more than 13 mm in 6096 mm. These tolerances reduce unexpected eccentricity of axial loads.
Another tolerance requirement imposed by ACI 530.1-11 is to place building masonry elements within 6.4 mm per story height and must be less than maximum value of 19 mm. Figure 4 clarifies tolerances for location of reinforced masonry elements.
Figure-4: Tolerances for Location of Reinforced Masonry Elements
Tolerances for Reinforcement Placement
Reinforcement placement tolerance for flexural elements like reinforced masonry wall is +/-13 mm if effective depth, which is the distance from masonry compression face to the reinforcement centerline, is 203 mm or smaller.
The tolerance is +/-25 mm for effective depth larger than 203 mm and equal or less than 610 mm in addition to use +/-32 mm when effective depth is more than 610 mm.
Regarding Vertical reinforcement, it should be installed within +/-51 mm from its planned position.
Moreover, one might notice that, tolerances for horizontal reinforcement placement are tougher than vertical reinforcement because small shift from the determined location in the latter will not produce considerable effect on the out of plane performance of the structural element.
Figure-5: Tolerances for Reinforcement Placement