Final answer:
Structural movement and most cracking problems are caused by D. All of the above: A. Change in materials due to temperature and humidity changes, B. Deflection under load, and C. Seismic forces. These factors can lead to deformation and cracks in structures like railways, roadways, and buildings, and are critical considerations in engineering and construction for ensuring structural integrity.
Step-by-step explanation:
Structural movement and most cracking problems are caused by D. All of the above: A. Change in materials due to temperature and humidity changes, B. Deflection under load, and C. Seismic forces. Each of these factors can independently or collaboratively influence the structural integrity of buildings and other constructions.
For example, thermal stress is associated with changes in materials due to temperature changes. This can cause structures like railroad tracks and roadways to buckle if they do not have the necessary expansion joints, and can lead to the creation of cracks in plaster walls of buildings as they expand and contract with varying temperatures. Additionally, power lines demonstrate thermal effects as they sag more in the summer and can snap in extreme cold if not properly designed to accommodate such changes. Another example is the use of different materials in composite fillings in dentistry to avoid thermal stress effects that can cause pain or cracks when exposed to temperature changes, due to differences in thermal expansion between materials.
Another factor, deflection under load, contributes to the movement and cracking in structural systems. When loads exceed the designed strength of a component or system, deflection can occur leading to possible damage or failure.
Finally, seismic forces can cause significant movement and cracking problems in structures. This is due to the dynamic loading that buildings and other structures must withstand during an earthquake, emphasizing the need for adequate seismic design and construction practices.