I could not find any official economic impact assessment, and there are no released official assessments according to a non-government assessment I found.
However, national security investigations were performed prior to the steel and aluminum tariffs, and an investigation into Chinese trade practices was performed prior to the China-related tariffs. These investigations are used as justification for the tariffs, though they are not focused on the impacts of tariffs.
This report is an impact assessment prepared by the consulting firm Trade Partnership Worldwide, LLC, for the Consumer Technology Association and National Retail Federation. The report covers the impact on the US economy of several China-related tariff scenarios, such as China matching US tariffs or US tariffs being raised from $50 to $100 billion. This report includes the following line, indicating that comprehensive government reports, if made, have not been released:
Administration officials have not released any research that quantifies impacts of the proposed
U.S. tariffs, coupled with proposed Chinese retaliation on the U.S. economy and U.S. jobs in any
detail: e.g., the overall impact on GDP, exports (bilateral and in total), imports and jobs.
CTA and NRF represent about $17 million in lobbying efforts, and it can be assumed that other large trade groups ordered similar assessments. Because of this, even if the administration did not perform their own economic assessments lawmakers are being influence indirectly by lobbyist's assessments.
As for government assessments, the US Department of Commerce performed investigations into potential security issues with importing steel and aluminum. However, these investigations were focused on security issues of current import amounts, rather than economic impacts of tariffs on those imports.
As for China related tariffs, this executive investigation into Chinese trade practices, particularly those relating to technology and intellectual property, is the justification for tariffs on Chinese products. Much like the steel/aluminum investigation, this investigation is simply focused on the current trade relationship with China, rather than the economic impacts of tariffs aimed at changing that relationship.