Statically indeterminate
Reinforced concrete buildings are most of the times statically indeterminate structures. This means that the internal forces and reactions in the structure cannot be determined solely by applying the equations of static equilibrium. The behavior of these structures requires additional analysis methods, such as the use of compatibility and equilibrium equations, along with the consideration of material properties and structural behavior.

Explanation:

Definition of statically determinate and indeterminate structures:
- A statically determinate structure is one in which the reactions and internal forces can be determined by using the equations of static equilibrium alone. This type of structure does not have any redundant members or supports.
- On the other hand, a statically indeterminate structure is one in which the reactions and internal forces cannot be determined by static equilibrium equations alone. This type of structure has one or more redundant members or supports.

Characteristics of reinforced concrete buildings:
Reinforced concrete buildings are commonly used in the construction industry due to their strength, durability, and versatility. These structures consist of a combination of concrete and steel reinforcement, which work together to resist applied loads and ensure the stability of the building.

Reasons why reinforced concrete buildings are statically indeterminate:
1. Redundancy in structural elements:
Reinforced concrete buildings often have redundant members, such as beams, columns, and slabs. These additional members provide structural redundancy, which means that the structure can still support the loads even if one or more members fail. The presence of redundancy makes the structure statically indeterminate.

2. Composite action:
Reinforced concrete buildings rely on the composite action between concrete and steel reinforcement to resist applied loads. The interaction between these two materials creates internal forces that cannot be determined solely by static equilibrium equations.

3. Nonlinear behavior:
Concrete and steel exhibit nonlinear behavior under loading. The stiffness and strength of these materials change as the applied loads increase. This nonlinearity further complicates the analysis of reinforced concrete structures and makes them statically indeterminate.

4. Distribution of loads:
The distribution of loads in a reinforced concrete building is not always uniform. Different parts of the structure may experience varying levels of loading, which affects the internal forces and reactions. This variability adds to the complexity of analyzing the structure using static equilibrium equations alone.

Conclusion:
Reinforced concrete buildings are most of the times statically indeterminate structures due to the presence of redundant members, composite action between concrete and steel, nonlinear behavior of materials, and the non-uniform distribution of loads. Analyzing these structures requires the application of advanced analysis methods to determine the internal forces and reactions accurately.