How do structural engineers approach the design of large$-$scale infrastructure projects to ensure both safety and longevity? Consider factors such as material selection, load$-$bearing capacities, environmental impacts, and potential risks. Additionally, how do they incorporate principles of sustainability and resilience into their designs to mitigate the effects of natural disasters and climate change? Describe the iterative process of analysis, simulation, and refinement that engineers typically employ to optimize structural integrity while balancing economic constraints and societal needs.