I’d like to point out that a Professional Engineer’s standard of care typically includes a site visit to assess field conditions and get an overall understanding of the structure. This can obviously not be accomplished through the internet. The information provided here is meant for planning purposes only (general sizing and budgeting) and is based on the information provided by you. All loading cases considered are for vertical loads only, no lateral analysis has been completed. The information should be verified by a professional engineer who can visit the site to ensure that potentially important information has not been overlooked or omitted.
For Door #1, 18' beam with 3' of brick load and supporting roof rafters:
You can use a W8x24 (50 ksi) steel beam for your 18’ clear span beam. The beam is 6.5” wide and 7.875” deep. It weighs 24 pounds per foot of beam length.
For Door #2, 18' beam with 3' of brick load only:
You can use a W6x16 (50 ksi) steel beam for your 18’ clear span beam. The beam is 4” wide and 6.25” deep. It weighs 16 pounds per foot of beam length.
You will need to have a local engineer detail your connections, size your column supports, and determine foundation requirements.
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