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While there are nearly 100 varieties of spirea, they all fall into two main types: Bridal wreath spireas or shrubby spireas. We would not be able to identify a specific variety for you. There are so many bridal wreath varieties to choose from! Visit your local nurseries or garden centers for a look at some of these shrubs!
https://www.gardeningknowhow.com/ornamental/shrubs/spirea/growing-spirea-shrubs.htm

Aside from pulling each one out, roots and all, you can try cutting them and immediately spraying with an herbicide, such as Round Up.

You will have to stay vigilant, as they will quickly come back. This treatment may be necessary several times before the problem is eradicated.

They, generally, have what is considered a long lifespan. This can last well over 50 years.

Without seeing the damage, and just by description, I would have to guess that one of two things could be happening:

It could be that the pad is putting too much weight on the root system, or the roots are being constricted by other means.

It could be a severe fungal infection.

A fungal infection will have a few cures, and a fungicide is a good start. This article will help: https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm

This article will offer more information on the care of the plant: https://www.gardeningknowhow.com/ornamental/shrubs/spirea/growing-spirea-shrubs.htm

Usually, since Spirea are low feeders and won't require much supplemental nutrients, a tip pruning can help rejuvenate an old shrubs. You may still try and give it a half strength dose of all purpose granular fertilizer during the years that the shrub is not productive.

These articles will help you with their care:

https://www.gardeningknowhow.com/ornamental/shrubs/spirea/growing-spirea-shrubs.htm

https://www.gardeningknowhow.com/ornamental/shrubs/spirea/cutting-back-spirea-shrubs.htm

Generally, you will prune them just after flowering. You may want to prune them as they each mature, but it isn't completely necessary. They tolerate pruning, very well!

Here is an article that will help:

https://www.gardeningknowhow.com/ornamental/shrubs/spirea/pruning-spirea-shrubs.htm

My guess without seeing the issue at hand is that they need to be fertilized or have succumbed to an infection. Cutting back any growth that is completely dead will be a good place to start.

For now, here is an article for their general care: https://www.gardeningknowhow.com/ornamental/shrubs/spirea/growing-spirea-shrubs.htm