How can I straighten and strengthen this joint?
I can remove the screws holding them together if needed, but that's pretty much all I can do.
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Sign up to join this communityThat railing is probably fastened to posts on both to the left and right of your picture.
I have to say that whoever installed that railing in the first place with a splice like that mid span between supporting posts did not do a quality job. A splice should normally always be over a supporting post of be part of a double or triple beam made up of pieces of lumber with all splices offsetted a good distance from each other.
That should've never been mitered there. All miters should be on top of a support post...
If you're looking for a quick and inexpensive fix, cut a piece of pressure treated 2x4 about 24" long and attach it to the underside of your 2x4.
Another option is a couple of galvanized straps screwed to the underside of the miter, both opposing edges, or on all 4 sides if need be.
Last option, replace that piece of 2x4. Cut at center of supports on left and right and reattach your new 2x4.