1. Overestimation of Design Loads
Overestimation occurs when the designer sets live loads in the building that exceed its actual function and the requirements of the code, aiming to increase safety factors and to mitigate project risks. This inevitably leads to:
Increase in the quantity of steel.
Increase in the quantity of concrete.
Increased likelihood of foundation settlement due to increased building weight.
Increased impact of shrinkage stresses due to temperature changes.
2. Overestimation of Required Concrete Strength
In residential buildings that do not exceed 3 or 4 stories, it is important to use concrete with adequate strength without overestimation in the design strength. It is crucial to avoid overestimating the required concrete strength as high design strength may not be achievable due to the varying capabilities of some concrete plants in different locations, and the varying skills of contractors. Sometimes, poor supervision increases the likelihood of errors. Therefore, it is essential to request design concrete strength that aligns with the capabilities of the plants and contractors to avoid these errors.
3. Overestimation in Reinforcement Steel
In residential buildings that do not exceed 3-4 stories and where column spacing ranges from 3-5 meters, it is difficult to use large diameter steel bars such as 25 or 32 mm, which should only be used for necessary and justified cases. Typically, the diameter should not exceed 20 mm unless there are valid design reasons. In standard balanced designs, the expected diameters are as follows:
Diameter 16 or 18 mm for beams and columns.
Diameter 12 or 14 mm for ribs.
Diameter 14 or 16 mm for foundations and ties.
4. Overestimation in Concrete Dimensions, Especially Slabs
Sometimes, slab thickness is overestimated, where the required thickness for part of the slab is generalized for the entire slab. In reality, if loads and weights are not overestimated and the weight of the hollow blocks is considered, slab thickness should not exceed 28-32 cm. If the thickness is 37 or 42 cm, the designer should explain the reasons, which are often due to large spans between columns.
5. Ignoring the Importance of the Soil Report
Some designs ignore the soil report or assume strong or weak soil without verification, leading to incorrect design and causing problems in execution.
6. Ignoring the Execution Method
Some designs are excessively varied, containing all diameters of steel and various sizes of columns, and the slab having more than three types of thickness in the same floor, such as 20 cm, 32 cm, and 37 cm. Such designs cause complexity, increased cost, confusion, and errors on-site during execution.
7. Overestimation in Specifications
When cylindrical concrete strength is requested instead of cubic, the strength needs to be 15% higher. This can be confusing for concrete plants and, more importantly, might be overlooked by the supervisor or contractor, resulting in a loss of 15% strength due to this oversight. Additionally, insisting on a specific type of steel can be confusing, as all steel approved by the Standards Authority is acceptable, provided its compliance and related tests are verified.
8. Failure to Provide a Calculation Note
The calculation note is one of the most important documents that explain how the building was designed, the assumed loads, and the application of specifications, soil report, and code. It verifies the stresses resulting from loads as well as the dimensions of structural elements and steel diameters according to engineering standards.
9. Lack of Coordination Between Structural and Architectural Engineers
Lack of coordination between the architectural and structural engineers is a significant flaw in the design office. One of the direct results is the structural engineer placing columns on beams, causing errors in beam design and a significant increase in steel quantities and beam section dimensions. It also leads to errors in slab and beam heights and conflicts in HVAC and aluminum plans.
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