Final answer:
The correct answer is 'cooling'. It is crucial to cool structural steel during a fire to prevent collapse. Engineering designs consider thermal stresses and materials' expansion properties for structural integrity.
Step-by-step explanation:
The correct answer to the question is d) cooling. Cooling structural steel with fire streams is crucial in a fire situation because steel can weaken significantly under high temperatures, potentially leading to a structure's collapse. In the context of engineering, managing temperature effects is essential for structural integrity. For example, thermal expansion in materials is a common factor considered in design to prevent thermal stress. Highway designs, for instance, include gaps between blocks to allow for expansion and contraction. Concrete structures often use steel reinforcement rods, as steel and concrete have similar coefficients of linear expansion, so they expand and contract in unison, reducing thermal stress. Furthermore, these steel rods act as reinforcement to increase the strain values that a structure can withstand before reaching its breaking point, relating to both compressive and tensile forces.