# Design Requirements of Concrete Based on ACI 318-19 Reading time: 1 minute

There are several requirements established in ACI 318-19 (Building Code Requirements for Concrete and Commentary) that concrete materials need to meet; otherwise, it would not be suitable for the construction of a structure.

These requirements vary from one structure to another one. They include minimum permissible concrete compressive strength for a particular structure, modulus of rupture, etc.

## Design Requirements of Concrete Based on ACI 318-19

### 1. Compressive Strength

The compressive strength of concrete is specified based on the following criteria.

1. Based on table 1.
2. Based on the strength requirements of a structure under consideration.
3. Based on the durability requirements of the structure. Sometimes, the durability requirements enforce the use of high concrete compressive strength.

Table 1 Minimum Design Concrete Compressive Strength for Different Concrete Structures

### 2. Modulus of elasticity

The modulus of elasticity of concrete used to compute deflections, a period of vibration, and drift of structures. It is calculated using equations that are provided by ACI 318-19 Code or testing. There are differences between values obtained from equations and those achieved from testing.

However, the theoretical values from equations are suitable for the majority of structures. Significant differences between equation values and test results are noticed for high strength concrete, lightweight concrete, and concrete mixtures with a low quantity of coarse aggregate such as self-consolidation concrete mixture.

Modulus of elasticity of concrete is computed using the following expressions:

For values of Wc between 1440 and 2560 Kg/m^3:

For Normal-weight concrete:

Where:

Ec: modulus of elasticity

Wc: weight of concrete

Fc’: concrete compressive strength

Finally, modulus of elasticity of concrete evaluated through tests in certain conditions, such as verification of the achievement of specified elastic modulus or when its value used in proportioning of concrete mixture.

### 3. Modulus of rupture

The modulus of rupture is computed using the following formula:

Where:

Lamda: modification factor which is determined based on table 2 or table 3:

Table 2 Values of ? for Lightweight Concrete Based on Equilibrium Density

Table 3 Values of ? for Lightweight Concrete Based on the Composition of Aggregates