This article is about ACI 318-19 Concrete design examples pdf, ACI 318 concrete cover requirements, concrete grade as per ACI 318. ACI 318-19 (Building Code Requirements for Concrete and Commentary) sets forth specific requirements that concrete materials must meet to ensure their suitability for structural construction.
These requirements vary depending on the type of structure being built. They encompass criteria such as the minimum allowable compressive strength of the concrete for a given structure and the modulus of rupture, among others.
Concrete Design Requirements Based on ACI 318-19
1. Compressive Strength
The compressive strength of concrete is determined through various criteria. These include referencing table 1, which provides specific guidelines for strength specifications. Additionally, the strength requirements of the structure being considered play a crucial role in determining the appropriate compressive strength of the concrete. Furthermore, the durability requirements of the structure may necessitate the use of high concrete compressive strength. This is because durability considerations can impose the need for stronger concrete to ensure the longevity and resilience of the structure.
Table 1 Minimum Design Concrete Compressive Strength for Different Concrete Structures
| Type of application | Minimum concrete compressive strength, MPa |
| General | 17 |
| Foundations for structures assigned to SDC A, B, or C | 17 |
| Foundations for Residential and Utility use and occupancy classification with stud bearing wall construction two stories or less assigned to SDC D, E, or F | 17 |
| Foundations for structures assigned to SDC D, E, or F other than Residential and Utility use and occupancy classification with stud bearing wall construction two stories or less | 21 |
| Special moment frames | 21 |
| Structural walls with Grade 420 or 550 reinforcement | 21 |
| Structural walls with Grade 690 reinforcement | 35 |
| Precast-non-prestressed driven piles Drilled shafts | 28 |
| Precast-prestressed driven piles | 35 |
| Note: Maximum compressive strength of lightweight concrete in structural walls, moment frames, and their foundations should not be higher than 35MPa, as per ACI 318-19. Disregard this condition if the strength and toughness of elements made with lightweight concrete are equal or greater than that of comparable members made with conventional concrete. Experimental evidence should demonstrate such a result. |
2. Modulus of elasticity
The modulus of elasticity of concrete is an important parameter used to determine deflections, vibration periods, and drift in structures. It is typically calculated using equations provided by the ACI 318-19 Code or through testing. While there may be variations between values obtained from equations and those obtained from testing, the theoretical values derived from equations are generally suitable for the majority of structures.
However, significant differences can be observed between equation values and test results, particularly in the case of high-strength concrete, lightweight concrete, and concrete mixtures with a low quantity of coarse aggregate, such as self-consolidating concrete mixtures.
To calculate the modulus of elasticity of concrete, specific expressions are used. For concrete density (Wc) values falling within the range of 1440 to 2560 kg/m^3, certain equations or formulas are employed.
In summary, the modulus of elasticity of concrete plays a crucial role in assessing structural behavior. While equations provide reasonable estimates for most structures, it is important to acknowledge the disparities that may arise, particularly when dealing with high-strength concrete, lightweight concrete, and concrete mixtures with low coarse aggregate content.
For Normal-weight concrete:
The modulus of elasticity of concrete (Ec) is determined through tests that assess specific conditions, such as verifying whether the specified elastic modulus has been attained or when its value is utilized in proportioning concrete mixtures. These tests evaluate the relationship between Ec, the weight of concrete (Wc), and the concrete compressive strength (Fc’).
Fig. 2: Modulus of Elasticity of Concrete
3. Modulus of Rupture
The modulus of rupture is determined through a specific mathematical calculation.
The modification factor, lambda, is determined based on the information provided in either Table 2 or Table 3.
Table 2 Values of ? for Lightweight Concrete Based on Equilibrium Density
| Wc, Kg/m^3 | Lamda |
| Equal or smaller than 1600 | 0.75 |
| Greater than 1600 but equal or lower than 2160 | 0.0075*Wc equal or lower than 1 |
| Greater than 2160 | 1 |
Table 3 Values of ? for Lightweight Concrete Based on the Composition of Aggregates
| Concrete | Composition of aggregates | Lamda |
| All-lightweight | Lightweight fine and coarse aggregates | 0.75 |
| Lightweight, fine blend | Lightweight coarse aggregate blended fine aggregate composed of lightweight aggregate and normal-weight aggregate. | 0.75 to 0.85 |
| Sand-lightweight | Normal weight aggregate, coarse aggregate is lightweight. | 0.85 |
| Sand-lightweight, coarse blend | Normal weight fine aggregate, and blended coarse aggregate composed of lightweight and normal-weight aggregate. | 0.85 to 1 |
