"which was designed to" is correct and usable in written English.
You can use it to refer to a plan or purpose of something, e.g. "The app was designed to make online ordering easier."
The bill seeks to entrench this mechanism, which was designed to keep land in Jewish hands.
Some witnesses criticized the size of the kiosk, which was designed to accommodate four rangers.
The ads imitate the editorial content which was designed to mimic components of advertising.
The NHS, which was designed to treat acute illnesses, now treats chronic diseases.
The tiger, they said, had been caged within the trailer, which was designed to carry cattle.
He was active in the Navy's development of the Polaris missile, which was designed to be launched from submarines.
But the law, which was designed to promote fresh food in French kitchens, is causing a revolt among chefs.
**Ultimately, Trump's win was enabled by America's antiquated electoral system, which was designed to prevent each vote from counting equally.
The company expanded considerably after 1964, when it moved to the new Lincoln Center, which was designed to Balanchine's specifications.
Unfortunately, there were not enough students on the course which was designed to introduce businessmen to Chinese commerce.
About 130,000 vehicles a day use the bridge, which was designed to carry about 100,000 vehicles.
