Working stress method assumes that the structural material behaves in a linearly elastic manner.

Explanation:
The working stress method is a design approach used in civil engineering to ensure the safety and stability of structures. This method assumes that the material used for construction behaves in a linearly elastic manner, meaning that it follows Hooke's Law. According to Hooke's Law, the stress in a material is directly proportional to the strain, as long as the material remains within its elastic limit.

In the working stress method, the design of a structure is based on the concept of working stress or permissible stress. The permissible stress is a fraction of the ultimate strength of the material, and it is determined based on various factors such as the type of material, the type of loading, and the safety factor. The working stress is calculated by dividing the permissible stress by the appropriate factor of safety.

The assumption of linearly elastic behavior is important in the working stress method because it allows engineers to determine the maximum stress that the material can withstand without permanent deformation or failure. By designing the structure based on this maximum stress, the working stress method ensures that the structure remains within its elastic range and does not experience excessive deformation or failure.

However, it is important to note that the assumption of linearly elastic behavior may not always hold true in practical situations. Real-world materials often exhibit non-linear behavior, especially under high loads or extreme conditions. In such cases, more advanced methods such as the limit state method or the ultimate load method may be more appropriate for designing structures.

In conclusion, the working stress method assumes that the structural material behaves in a linearly elastic manner. This assumption allows engineers to design structures based on the concept of working stress, ensuring the safety and stability of the construction.